ASOMEA-IX
9th Workshop on Advanced Spectroscopy ofOrganic Materials for Electronic Applications

October 23 (Tuesday) – 26 (Friday), 2018
Schluchsee, Germany

Schluchsee 2018 – ASOMEA-IXASOMEA-IX
9th Workshop on Advanced Spectroscopy ofOrganic Materials for Electronic Applications
October 23 (Tuesday) – 26 (Friday), 2018
Schluchsee, Germany
The series of biannual ASOMEA-workshops began in 2001 as a meeting of Swedish andJapanese scientists working with spectroscopic techniques and theoretical modeling for a better
understanding of organic electronic materials and related interfaces. In 2016 the scope of theworkshop was widened to include the German community and the intention to focus on organic
materials at advanced stages, in situ/operando techniques, and time-resolved spectroscopy toname just a few.
The size and focus of the meeting will support a lively and intimate atmosphere with discussions
on the overall progress and development of spectroscopic methods in particular.

Scientific Topics

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
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Spectroscopy of Molecular Liquids, Solids and Interfaces
UV and X-ray Photoelectron Spectroscopies/Microscopies
X-ray Absorption and Emission Spectroscopies
Time-resolved/Multi-colored Spectroscopies
Ambient Pressure/Operando Spectroscopies
and more

Organizers

OfficeProf. Dr. Ulrich Höfer
SFB 1083, Philipps-Universität Marburg
D-35032 Marburg

Dr. Helen A. Pfuhl
SFB 1083, Philipps-Universität Marburg
D-35032 Marburg

Prof. Dr. Norbert Koch
SFB 951, Humboldt-Universität zu Berlin
D-12489 Berlin

Dr. Maurizio Roczen
SFB 951, Humboldt-Universität zu Berlin
D-12489 Berlin1International Program Committee
Satoshi Kera, Institute for Molecular Science, Japan
Joachim Schnadt, Lund University, Sweden
Stacey Sörensen, Lund University, Sweden
Petra Tegeder, Universität Heidelberg, Germany
Jun Yoshinobu, University of Tokyo, Japan

Meeting History
2016
2014
2011
2009
2007
2005
2003
2001

Okazaki, Japan
Lund, Sweden
Ishikawa, Japan
Krusenberg Herrgard, Uppsala, Sweden
Chiba, Japan
Vadstena, Sweden
Shonan Village, Tokyo, Japan
Orenas Castle, Glumslov, Sweden

Financial Support
Funded through the Deutsche Forschungsgemeinschaft (DFG) via Collaborative ResearchCenters SFB 1083 "Structure and Dynamics of Internal Interfaces" and SFB 951 "Hybrid
Inorganic/Organic Systems for Opto-Electronics" (HIOS).
Additional support provided by the "Japan Society for the Promotion of Science" (JSPS).

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Schluchsee 2018 – ASOMEA-IX

Scientific Program3

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Schluchsee 2018 – ASOMEA-IX

Timetable
Tuesday, 23.10.

Thursday, 25.10.

Friday, 26.10.

Breakfast

Breakfast

Session 1 (Höfer)
Kera
Broch
Cocchi

Session 5 (Tegeder)
Lyu
Blumstengel
Gottfried

Session 9 (Rensmo)
Tautz
Tegeder
T. Yamada

Coffee BreakCoffee BreakCoffee BreakSession 2 (Nakayama)
HaradaOzawa
Stadtmüller

Session 6 (Cocchi)
Draxl
Pucci
Jakob

Session 10 (Koch)
Rossi
Shibuta
Duhm

Wednesday, 24.10.

07:00-08:55

Breakfast

08:55-09:00

Welcome09:00-10:00

10:00-11:00

11:00-12:00

12:00-13:00

Closing

13:00-14:00

Lunch BreakLunch BreakLunch Break

14:00-15:00
Session 3 (Ozawa)
FahlmanRensmoAkaike15:00-16:00

Coffee BreakSession 7 (Shibuta)
Y. Yamada
Witte
YoshidaExcursion

16:00-17:00
Session 4 (Duhm)
Nakayama
Dürr
Peisert17:00-18:00

Poster Preparation
18:00-19:00

Coffee BreakSession 8 (Broch)
Yoshinobu
Casu
Ueno

Registration
Dinner

19:00-20:00
Conference Dinner

Reception & Dinner
20:00-21:00

Poster Session

21:00-21:30

5

Wednesday, 24.10.201808:55 – 09:00

Welcome Address

Session 1

Chair: Ulrich Höfer, Uni Marburg

09:00 – 09:35

Satoshi Kera, NIMS-IMS, Okazaki
Evolution of electron localization upon assembling the moleculeson the surface

09:35 – 10:10

Katharina Broch, Uni Tübingen
The impact of charge transfer states on the photophysics ofacenes

10:10 – 10:30

Caterina Cocchi, HU BerlinCollective behavior in the optical excitations of push-pull
chromophores and their J-aggregate
Coffee BreakSession 2

Chair: Yasuo Nakayama, Tokyo Univ. of Science

11:00 – 11:35

Yoshihisa Harada, Tokyo Univ.
RIXS for hydrogen bond of liquid water at interfaces

11:35 – 12:10

Kenichi Ozawa, Tokyo Inst. of Technol.
Transient photoexcited state at p/n heterojunction in organic
photovoltaics: A time-resolved soft X-ray photoelectron
spectroscopy study

12:10 – 12:30

Benjamin Stadtmüller, Uni Kaiserslautern
Photoemission tomography of fullerenes on surfaces
Lunch Break6

Schluchsee 2018 – ASOMEA-IX

Wednesday, 24.10.2018 (continued)
Session 3

Chair: Kenichi Ozawa, Tokyo Inst. of Technology

14:30 – 15:05

Mats Fahlman, Linköping Univ.
Ternary organic bulk heterojunction solar cells

15:05 – 15:40

Håkan Rensmo, Uppsala Univ.
Understanding hybrid solar cell interfaces using photoelectron
spectroscopy

15:40 – 16:00

Kouki Akaike, Tokyo Univ. of Science
Effects of molecular orientation of fullerene derivative on device
performance of bilayer solar cell
Coffee BreakSession 4

Chair: Steffen Duhm, Soochow Univ., Suzhou

16:30 – 17:05

Yasuo Nakayama, Tokyo Univ. of Science
Structural and electronic characterization of well-definedmolecular interfaces

17:05 – 17:40

Michael Dürr, Uni Gießen
Reaction dynamics of organic molecules on Si(001) – a route
towards controlled organic functionalization of silicon surfaces

17:40 – 18:00

Heiko Peisert, Uni Tübingen
Electronic structure and interface properties of FePc and
FePcF16 on metal substrates

18:00 – 18:15

Break for preparation of Poster Session
Dinner

19:30 – 21:30

Poster Session

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Thursday, 25.10.2018
Session 5

Chair: Petra Tegeder, Uni Heidelberg

09:00 – 09:35

Jiong Lyu, Nat. Univ. Singapore
Recent STM studies of single molecule and defect in gated 2D
material devices

09:35 – 10:10

Sylke Blumstengel, HU Berlin
Fingerprint of charge redistribution at hybrid inorganic/organicinterfaces revealed by differential reflectance spectroscopy

10:10 – 10:30

Michael Gottfried, Uni Marburg
Molecular Topology and Metal Organic Interactions
Coffee BreakSession 6

Chair: Caterina Cocchi, HU Berlin

11:00 – 11:35

Claudia Draxl, HU Berlin
Theoretical spectroscopy at hybrid interfaces

11:35 – 12:10

Annemarie Pucchi, Uni Heidelberg
Infrared analytics of functional layers for organic electronics

12:10 – 12:30

Peter Jakob, Uni Marburg
Electron-vibron coupling at molecule-metal interfaces
Lunch Break8

Schluchsee 2018 – ASOMEA-IX

Thursday, 25.10.2018 (continued)
Session 7

Chair: Christian Kumpf, FZ Jülich

15:00 – 15:35

Yoichi Yamada, Tsukuba Univ.
Exploring the structure-property relationships of the wellordered organic films

15:35 – 16:10

Gregor Witte, Uni Marburg
Optoelectronic properties of crystalline organic thin films andheterostructures

16:10 – 16:30

Hiroyuki Yoshida, Chiba Univ.
The evolution of intermolecular energy bands of occupied andunoccupied molecular states in organic thin film
Coffee BreakSession 8

Chair: Katharina Broch, Uni Tübingen

17:00 – 17:35

Jun Yoshinobu, Tokyo Univ.
Gas exposure effects on monolayer pentacene FET studied byusing non-invasive GaIn probes

17:35 – 17:55

Benedetta Casu, Uni Tübingen
Nanoscale studies of organic radicals: interface, and spinterface

17:55 – 18:10

Nobuo Ueno, Chiba Univ.
Introduction to JSPS and its international programs
Conference Dinner

9

Friday, 26.10.2018
Session 9

Chair: Håkan Rensmo, Uppsala Univ.

09:00 – 09:35

Stefan Tautz, FZ JülichDispersive states at molecule-metal interfaces

09:35 – 10:10

Petra Tegeder, Uni Heidelberg
Formation of occupied and unoccupied hybrid bands atinterfaces between metals and organic molecules

10:10 – 10:30

Takashi Yamada, Osaka Univ.
Unoccupied electronic states and excited dimer formation at theperylene/graphite interface
Coffee BreakSession 10

Chair: Norbert Koch, HU Berlin

11:00 – 11:35

Mariana Rossi, FHI Berlin
Critical interplay of atomic structure and level alignment inorganic/inorganic interfaces

11:35 – 12:10

Masahiro Shibuta, Keio Inst.
Spectroscopy and imaging of photocarriers in organic functionalfilms probed by two-photon photoemission

12:10 – 12:30

Steffen Duhm, Soochow Univ., Suzhou
Organic-inorganic energy-level alignment: From academic
interfaces to devices
Closing Remarks
Lunch Break10

Schluchsee 2018 – ASOMEA-IX

Oral Abstracts Wednesday

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Schluchsee 2018 – ASOMEA-IX

Wednesday 09:00

Evolution of electron localization uponassembling the molecules on the surface
Satoshi Kera
Department of Photo-Molecular Science, Institute for Molecular Science, JapanSOKENDAI(The Graduate University for Advanced Studies), Japan
Graduate School of Engineering, Chiba University, Japane-mail: kera@ims.ac.jp

Functional organic molecule (FOM) has recently attracted considerable attention both on
fundamental research and device applications because of peculiar properties not found ininorganics and small molecules. However the mechanisms and its origin of various device
characteristics are still under controversial. Scientific mysteries would be raised because people
have believed that electronic structure of FOM would be conserved as in an isolated molecule forsolid state due to weak van der Waals interaction. To reveal characteristics of FOM the key
investigation would be on precise experiments on the electronic structure at various interfaces,
including organic-organic and organic-inorganic (metal/semiconductor) contacts.
High-resolution angle-resolved photoelectron spectroscopy of organic monolayer and bilayer
films of perfluoropentacene (PFP) prepared on Ag(111) and graphite substrates are performed toreveal the impact of weak electronic interaction and strong electron-phonon coupling on themolecular orbital states. By comparing two weakly interacting interfaces, we confirm thelocalization of wave-function spread of each state at the physisorbed interface and shed light on
the character of an electron cloud in functional molecular materials. Recent results taken by the
momentum microscopy which allows to find a global view of an electron cloud in very short
experimental time will be shown to discuss.

13

Wednesday 09:35

The impact of charge-transfer stateson the photophysics of acenes
Katharina Broch
Institute of Applied Physics, Eberhard-Karls-Universität Tübingen, Germany
e-mail: katharina-anna.broch@uni-tuebingen.de

Charge transfer between a donor and an acceptor is a key parameter for device performance oforganic solar cells and constitutes the prototypical scenario for the study of charge-transfer
states. However, during the last decade, the formation of a charge-transfer state after opticalexcitation of neat thin films has gained increasing attention due to its strong impact on theirphotophysics [1]. Effects such as the sign and magnitude of the Davydov-splitting can only becorrectly calculated if a significant mixture of charge transfer and Frenkel exciton states aretaken into account [1]. Furthermore, charge-transfer states mediate complex photophysicalprocesses, such as the conversion of an excited singlet state into two triplet states onneighbouring molecules. Therefore, the understanding of the impact of these states onphotophysical processes is one way towards a tailoring of photophysical properties of organic
semiconductors.
The talk will focus on the photophysics of pentacene in blends with molecules of different
acceptor strength [2,3], studied using transient absorption spectroscopy and time-resolved
photoluminescence spectroscopy. In strongly-interacting blends, the photophysics of the chargetransfer state between the compounds and its dependence on the mixing ratio will be discussed[2]. In the second part of the talk, an alternative approach to tailoring intermolecular interactions
will be suggested by introducing spacer molecules in mixed thin films via coevaporation. Using
the Davydov-splitting as convenient metric, it will be demonstrated that the charge-transfer
character of the lowest electronic excitation can be modified in these blends. Finally, it will be
discussed how such a modification affects the time scales of photophysical phenomena [3].

Fig. 1 Davydov-splitting in pentacene:spacer molecule blends as a metric of charge-transfer character [3].
[1] D. Beljonne et al., Phys. Rev. Lett., 110, 226402 (2013).
[2] K. Broch et al., Phys. stat. sol. (RRL), 8, 1700064 (2017).
[3] K. Broch et al., Nat. Commun., 9, 954, (2018).

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Schluchsee 2018 – ASOMEA-IX

Wednesday 10:10

Collective behavior in the optical excitations ofpush-pull chromophores and their J-aggregate
Michele Guerrini1, Daniele Varsano2, Arrigo Calzolari2,
Caterina Cocchi3, Stefano Corni2,4
1 Dept. of Physics, Inform. & Mathematics, Univ. of Modena & Reggio Emilia, Italy
2 CNR-NANO, Istituto Nanoscienze, Centro S3, Modena, Italy
3 Physics Department & IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
4 Department of Chemical Sciences, University of Padova, Italye-mail: caterina.cocchi@physik.hu-berlin.deWithin a first-principles study based on density-functional theory and many-body perturbation
theory (GW approximation and Bethe-Salpeter equation), we investigate the optical excitationsof a J-aggregate formed by the C24H19F4N push-pull chromophore, which is known for its
enhanced nonlinear optical properties [1]. We focus on the so-called J-band, the sharp absorption
peak dominating the spectral onset of the aggregate, which is red-shifted by a few hundred meVcompared to the to the first bright excitation in isolated molecule. We demonstrate the collective
nature of the excitations forming the J-band by analyzing their character in terms of dipole
distribution and spatial extension. In this context, we discuss the role of molecular packing,which plays an important role in the optical properties of this J-aggregate [2]. Our results shedlight on the microscopic mechanisms leading to the formation of the characteristic absorption
peak in J-aggregates and offer new perspectives for understanding the nature of collective
excitations in molecular materials [3].

Fig. 1 Optical spectrum of molecule and J-aggregate computed from MBPT.
The red-shift of the J-band is highlighted and the exciton (transition) density of the first peakis shown for the aggregate (monomer) in the inset.

[1] C. Botta et al., J. Mater. Chem. C 2, 5275 (2014).
[2] M. Guerrini et al., submitted (2018).
[3] M. Guerrini et al., in preparation (2018).

15

Wednesday 11:00

RIXS for hydrogen bond of liquid water at interfaces
Y. Harada1,2,3, K. Yamazoe2, J. Miyawaki1,2,3, Y.-T. Cui2,3, Y. Higaki4,5,
Y. Inutsuka4, D. Murakami4,5, M. Tanaka4,5 and A. Takahara4,5
1
Department of Advanced Materials Science, The University of Tokyo, Japan
2
Institute for Solid State Physics, The University of Tokyo, Japan
3
Synchrotron Radiation Research Organization, The University of Tokyo, Japan
4
Graduate School of Engineering, Kyushu University, Japan
5
Institute for Materials Chemistry and Engineering, Kyushu University, Japane-mail: harada@issp.u-tokyo.ac.jp

X-ray absorption (XAS) and emission (XES) spectroscopy of liquid water are one of the cuttingedge techniques to determine the local hydrogen bond network of liquid water throughobservation of the valence electronic structure.[1-3] An XES study of liquid water at an interface
gives us a good opportunity to explore isolated or highly ordered water molecules than expectedin bulk liquid water. In this paper, XES studies on such “unique” water molecules are presented;
an isolated extreme is water in a less hydrogen bonded network of acetonitrile. The otherextreme is water encapsulated in a polymer.[4] Poly(2-(methacryloyloxy)ethyl
trimethylammonium chloride) (PMTAC) brushes,[5] which represent high-density polymer
chains, are well suited for investigating the interaction between water and polymers as well as
confinement of water by these polymer brushes. The apparent relationship between each
XAS/XES spectral profile and a specific hydrogen bond configuration characterized by its
strength and local symmetry is demonstrated through these extreme cases. The results indicatedthat the confined water has tetrahedrally coordinated hydrogen bonds with a uniform distortion
like high pressure ice, which should be naturally connected to control the antifouling andlubricating functions of polyelectrolyte brushes. Based on the knowledge of the interpretation of
XES spectra of liquid water we further studied water in the close vicinity of biocompatible
polymer Poly(2-methoxyethyl acrylate) (PMEA). [6] The result will be discussed in terms of therole of interfacial water.
[1]
[2]
[3]
[4]
[5]
[6]

T. Fransson et al., Chem. Rev. 116, 7551 (2016).
S. Myneni et al., J. Phys. Condens. Matter 14, L213 (2002).
T. Tokushima et al., Chem. Phys. Lett. 460, 387 (2008).
K. Yamazoe et al., Langmuir 33, 3954 (2017).
M. Kobayashi et al., Langmuir 28, 7212 (2012).
M.Tanaka et al., Biomaterials 21, 1471 (2000).

16

Wednesday 11:35

Schluchsee 2018 – ASOMEA-IX

Transient photoexcited state at p/n heterojunctionin organic photovoltaics: A time-resolved
soft X-ray photoelectron spectroscopy study
Kenichi Ozawa
Department of Chemistry, Tokyo Institute of Technology, Japane-mail: ozawa.k.ab@m.titech.ac.jp

A ubiquitous light-harvesting system paves the way to a zero-emission sustainable society.
Organic photovoltaics is a leading solution for such an system as an inexpensive renewableenergy source so that great efforts have been devoted to the enhancement of light-electricity
conversion efficiency. In the photovoltaics, the conversion efficiency is directly linked to exciton
quenching and an electron-hole recombination at the heterojunction in the p-type and n-typeorganic semiconductor layers. Thus, it is important to establish atomistic picture of thephotoexcited carrier behavior at the p/n junction. In our study, transient photoexcited states ofphthalocyanine (Pc), fullerene (C60) at a Pc/C60 heterojunction fabricated on TiO2 (Fig. 1) havebeen examined by time-resolved soft X-ray photoelectron spectroscopy (TRXPS) utilizing alaser-pump/synchrotron-radiation-probe technique, which was conducted at BL07LUS of
SPring-8.
One of great advantages of TRXPS is that time-evolution of excited states are traceable
individually for each component. In our case, for example, transient photoexcited states of C60
and Pc were determined separately by analyzing the chemical shift of C 1s core-level spectra(Fig. 1). Such information cannot be accessible by techniques such as transient UV-vis
absorption/emission spectroscopy and laser-pump/laser-probe photoelectron spectroscopy, bywhich dynamics of the excited carriers are directly examined. TRXPS is more suitable to study
carrier dynamics in the complex system like an organic solar cell that is composed of several
components. In the presentation, more details of the experimental result will be presented anddiscussed.

Fig. 1 A schematic drawing of the Pc/C60/TiO2 junction (left) and its energy diagram (center).
A C 1s XPS spectrum which is deconvoluted into the C60 and Pc components (right).

The TRXPS measurements were conducted under the approval of the Synchrotron Radiation Research Organization,
The University of Tokyo (Proposal Nos. 2016B7503, 2017A7533). Supports from Iwao Matsuda and Susumu
Yamamoto (Univ. Tokyo) are greatly appreciated.

17

Wednesday 12:10

Photoemission tomography of fullerenes on surfaces
Benjamin Stadtmüller1, Norman Haag1, Daniel Lüftner2, Christina Schott1, Johannes
Seidel1, Leah L. Kelly1, Giovanni Zamborlini3, Matteo Jugovac3,
Vitaliy Feyer3, Peter Puschnig2, Mirko Cinchetti4, Martin Aeschlimann1
1

Dept. of Physics & Res. Center OPTIMAS, Univ. Kaiserslautern, 67663 Kaiserslautern, Germ.
2
Institute of Physics, University of Graz, NAWI Graz, Universitätsplatz 5, 8010 Graz, Austria
3Peter Grünberg Institut (PGI-6), Forschungszentrum Jülich, 52425 Jülich, Germany
4
Experimentelle Physik VI, Technische Universität Dortmund, 44221 Dortmund, Germany

e-mail: bstadtmueller@physik.uni-kl.de

One of the great challenge for molecular-based electronics is the design of metal-organicinterfaces with dedicated functionalities. In this regard, the combination of angle resolved
photoemission spectroscopy (ARPES) with photoemission tomography (PT) has emerged as
powerful tool to study and understand the fundamental phenomena of these interfaces. The PT
approach allows one to assign spectroscopic ARPES features to the emitting molecular orbital
and to reveal modifications of the molecular wave functions caused by the interactions at theinterface. In this way, PT provides a unique view onto the interfacial electronic properties andthe interactions at the metal-organic interface. So far, however, PT has mainly been limited toplanar 2D molecules on surfaces.
Here, we will demonstrate that the PT framework can also be applied to three dimensional
molecules. As prototypical systems, we have chosen the fullerene molecules C60 and Sc3N@C80.
For a C60 film on Ag(111), the ARPES signal of the two highest occupied molecular orbitals(HOMOs) reveals a strong band dispersion while the lower lying orbitals appear as well-definedemission maxima in momentum space, see Fig. 1. The emission pattern of all molecular features
can be well described in the framework of
PT. Accordingly, we can assign the strongly
dispersing bands to the HOMO and HOMO-1
bands while the well-defined emission
maxima are due to σ-orbitals of C60. A
similarly good agreement between theexperiment and the PT simulation is found
for the fullerene Sc3N@C80.
In this way, our comprehensive investigationof thin films of fullerene molecules clearly
underlines the potential of photoemission
tomography to describe the momentum
revolved photoemission yield of three
dimensional molecules on surfaces.

Fig. 1 ARPES data and corresponding PT
simulation for a thin film (10ML) of C60 on
Ag(111) (EPh=35eV, TSample=50K).

18

Wednesday 14:30

Schluchsee 2018 – ASOMEA-IX

Ternary organic bulk heterojunction solar cells
Chuanfei Wang,1 Xianjie Liu,1 Liangqi Ouyang,1 Xiaofeng Xu,1Ergang Wang,2 Mats Fahlman1
1
Department of Physics, Chemistry and Biology, Linkoping University, Sweden
2
Dept. of Chemistry & Chemical Engineering, Chalmers Univ. of Technology, Sweden
e-mail: mats.fahlman@liu.se

One of the most important tasks during design and fabrication of organic electronic devices is todetermine the energy levels of the organic materials and understand the energy level alignment at
the interfaces. We use electronic structure measurements of neat polymer films and theirinterfaces combined with modeling to design ternary organic bulk heterojunction solar cells
featuring minimum voltage loss [1] and demonstrate for the first time that open circuit voltage
can be enhanced in ternary solar cells compared to the reference binary ones while alsoenhancing the power conversion efficiency [2]. The key design concept is to select interface
combinations that enhance dissociation of the donor and acceptor excitons and to suppress
bimolecular and trap-assistant recombination [1,2, 3].
Ultraviolet Photoelectron Spectroscopy (UPS), Inverse Photoemission Spectroscopy (IPES), andcyclic voltammetry (CV) typically are employed to obtain the oxidation/reduction energies of thedonor and acceptor materials used in organic photovoltaics (OPV). CV is particularly popular as
it is comparatively cheap and can obtain both oxidation and reduction energies, unlike UPS and
IPES. The values obtained differ between the techniques, but a linear relationship is typicallyfound, though the slope and intercept of this relation varies significantly between studies andtypes of organic materials [4-7]. We study a series of typical OPV materials and find a linear
relationship of slope 1 between CV oxidation potentials and UPS ionization potentials, but the
precision in the CV-derived IP values are not sufficient, however, to enable precise design ofenergy level alignment at heterojunctions [8].

[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]

C. Wang et al, Adv. Energy Mater., 6, 1700390 (2017).
C. Wang et al, Nano Energy, 37, 24 (2017).
Q. Bao et al, Adv. Funct. Mater. 24, 6309 (2014).
B.W. D'Andrade et al, Org. Electron. 6, 11 (2005).
P.I. Djurovich et al, Org. Electron. 10, 515 (2009).
J. Sworakowski et al, Org. Electron. 33, 300 (2016).
J. Sworakowski et al, Org. Electron. 48, 46 (2017).
C. Wang et al, Sol. RRL DOI: 10.1002/solr.201800122.

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Wednesday 15:05

Understanding hybrid solar cell interfaces
using photoelectron spectroscopyHåkan Rensmo
Molecular and Condensed Matter Physics, Department of Physics and Astronomy,
Uppsala University, Box 516, 751 20 Uppsala, Sweden
e-mail: hakan.rensmo@physics.uu.se

Partly building on the developments of dye-sensitized solar cells, the last couple of years havewitnessed a new development of hybrid perovskite materials used in optoelectronic applications
such as solar cells [1,2]. Starting with materials such as CH3NH3PbI3 there are now recordbreaking cells containing a large variety of cations and anions such as Cs+, Rb+, formamidinium
as well as Br-, I-. The efficiency of the conversion process in these systems is largely dependent
on the properties of the interfacial region including material organisation, character of the energy
levels as well as on energy matching between the different materials. Insight into such material
properties is therefore crucial in order to understand and optimize the function. Photoelectron
spectroscopy is an ideal tool for non-destructive chemical and electronic characterization of suchinterfaces and our group is in the forefront of developing such x-ray based spectroscopy
techniques and implementing them to investigations on energy materials. Specifically, thepresentation will show how to implement new opportunities in photoelectron spectroscopy forthe understanding of the interface structure and energy matching in solar cell materials and how
conditions (humidity, light and voltage) can effect the structure. [3-5]

[1]
[2]
[3]
[4]
[5]

S.D. Stranks, H.J. Snaith, Nat Nanotechnol 10, 391 (2015).
NREL Best Research-Cell Efficiencies. www.nrel.gov/pv/assets/images/efficiency_chart.jpg.
B. Philippe et al., Chem Mater. 27(5):1720, (2015).
U.B. Cappel et al., Phys Chem Chem Phys 18, 21921, (2016).
U.B. Cappel et al., Acs Appl Mater Inter. 9, 34970 (2017).

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Schluchsee 2018 – ASOMEA-IX

Wednesday 15:40

Effects of molecular orientation of fullerene derivativeon device performance of bilayer solar cell
Kouki Akaike1, Takumi Kumai1, Kyohei Nakano2,
Hiroyuki Yoshida3,4, Keisuke Tajima2, Kaname Kanai1
1Dept. of Physics, Fac. of Science & Technol., Tokyo University of Science, Japan
2
Center for Emergent Matter Science, RIKEN, Japan
3
Graduate School of Engineering, Chiba University, Japan
4
Molecular Chirality Research Center, Chiba University, Japane-mail: kouki.akaike@rs.tus.ac.jp

The orientation of the molecular semiconductors at the donor/acceptor interface is critical for the
carrier generation and recombination in organic photovoltaics (OPVs). To provide interface
design rule for efficient OPVs, the impact of the orientation of not only donor but also acceptor
on fundamental property and device performance has to be investigated. In this study, wedemonstrate the orientational change of [6,6]-pheny-C61-butyric acid methyl ester [PC61BM,
inset in Fig. 1(a)] upon crystallization, employing metastable atom electron spectroscopy(MAES) that can probe the outermost electron density. As shown in Fig. 1(a), The MAES
spectrum of amorphous (a-) PC61BM shows the enhanced signal in the region I, where the πorbitals of C60 backbone are contributed. In contrast, the spectrum of crystalline (c-) PC61BM
shows the enhanced photoemission in the region II, where the π-orbitals of the side chain
distribute. The results suggest the surface exposure of the side chain outside the c-PC61BM film,
which was speculated by Zhong et al [1]. Based on this finding, we fabricated the direct contactof the C60 backbone with standing molecules of sexithiophene (6T) and indirect contact throughthe side chain. Characterizing the bilayer OPVs reveals the higher open circuit voltage (VOC) forc-PC61BM/6T device [Fig. 1(b)] owing to the increased energy of the charge transfer states andreduced carrier recombination at the D/A interface.

Fig. 1 (a) MAES spectra of a- and c-PC61BM films. The energy ranges I and II correspond to the photoemission
from the π-orbitals of C60 backbone and side chains, respectively. (b) Current density-voltage curves of the bilayerOPVs comprising a- or c-PC61BM/standing 6T heterostructures.
[1] Y. Zhong et al., Adv. Energy Mater. 4, 1301332 (2014).

21

Wednesday 16:30

Structural and electronic characterizationof well-defined molecular interfaces
Yasuo Nakayama
Department of Pure and Applied Chemistry, Tokyo University of Science, Japane-mail: nkym@rs.tus.ac.jp

Functionalities of organic electronic devices arise from molecular interfaces in most cases.
Therefore, understanding of structural and electronic properties at the molecular contacts is
crucial for progress in science and technology in this field. Practical interfaces in the devices
themselves are unlikely to be ideal targets for pursuing molecular-scale phenomena at thecontacts due to their complex and heterogeneous natures. In contrast, a paradigm of the surface
science, that is examination into well-defined interfaces built on single crystal surfaces of one
material, may open a route for approaching clear understanding of the interfacial phenomena
driving the organic electronic devices, even though such ideal interfaces may be oversimplified
for directly modeling the devices themselves. In this contribution, recent advancement in
structural and electronic characterization of well-defined interfaces formed on organic
semiconductor single crystal surfaces (Fig. 1) achieved by surface science methodologies, suchas grazing incidence X-ray diffraction [1-4] and photoelectron spectroscopy [5,6], is discussed.

n-alkane

perfluoro-pentacene

C60

single crystal
rubrenesingle crystal
pentacene

Fig. 1 Schematic drawings of the topical well-defined molecular interfaces.

[1]
[2]
[3]
[4]
[5]
[6]

Y. Nakayama et al., ACS Appl. Mater. Interf. 8, 13499 (2016).
R. Tsuruta et al., J. Cryst. Growth, 468, 770 (2017).
Y. Nakayama et al., Adv. Mater. Interf. 5, 1800084 (2018).
Y. Nakayama et al., Hyomen-kagaku (J. Surf. Sci. Soc. Jpn.) 38, 324 (2017).
Y. Nakayama et al., Org. Electron. 14, 1825 (2013).
M. Yamamoto et al., e-J. Surf. Sci. Nanotechnol. 13, 59 (2015).

22

Wednesday 17:05

Schluchsee 2018 – ASOMEA-IX

Reaction dynamics of organic molecules on Si(001)– a route towards controlledorganic functionalization of silicon surfaces*
Michael Dürr
Institute of Applied Physics, Justus Liebig University Giessen, Germany
e-mail: michael.duerr@ap.physik.uni-giessen.de

The adsorption of organic molecules on silicon has been the subject of intense research due tothe potential applications of organic functionalization of silicon surfaces in semiconductor
technology. The high reactivity of the silicon dangling bonds towards almost all organic
functional groups, however, presents a major hindrance for the first basic reaction step of such afunctionalization, i.e., chemoselective attachment of bifunctional organic molecules on thepristine silicon surface. Due to this high reactivity, the final adsorption products typically consistof a mixture of molecules adsorbed via different functional groups. For the preparation of wellordered organic layers on silicon, it is thus important to learn how to control the reactions of thesingle functional groups.
Using various spectroscopic techniques, such as XPS, UPS, and nonlinear optics, in combination
with scanning tunneling microscopy and molecular beam techniques, we investigated in detailthe reaction mechanisms, kinetics, and dynamics of different functional groups on Si(001). We
make use of these results in order to control the respective reactions by either changing the
localized electronic surface states or the molecules’ very properties. Electronic excitation andhyperthermal energy distributions of the incoming molecules are investigated as further means ofcontrol.
Our main strategy for the controlled functionalization of Si(001) is then based on functionalized
cyclooctynes as cyclooctyne's strained triple bond is associated with a direct adsorption channelon the Si(001) surface, in contrast to almost all other organic molecules, which adsorb via
weakly bound intermediates [1]. As a consequence, cyclooctyne derivatives with different
functional side groups react on Si(001) selectively via the strained cyclooctyne triple bond whileleaving the side groups intact(Fig. 1). This second functional group is then used for the covalentattachment of further organic reagents on the road to well-defined molecular architectures on
Si(001).

Fig. 1: Bifunctional cyclooctynes react selectively via the strained triple bond of cyclooctyne.
* work performed within SFB 1083 and GRK 1782
[1] M. Reutzel et al., J. Phys. Chem. C 120, 26284 (2016).

23

Wednesday 17:40

Electronic structure and interface properties of
FePc and FePcF16 on metal substrates
Axel Belser, Fotini Petraki, Thomas Chassé, Heiko Peisert
Institute of Physical and Theoretical Chemistry, University of Tübingen, Germany
e-mail: heiko.peisert@uni-tuebingen.de

Normalized TEY (arb. units)

The interfacial electronic structure of iron phthalocyanine (FePc) and perfluorinated ironphthalocyanine (FePcF16) is investigated by photoexcited electron spectroscopies: Photoemission(XPS and UPS) and X-ray absorption spectroscopy (XAS or NEXAFS). The strength and natureof the interaction at the interface depend distinctly on the substrate. As example, a strong
interaction of the central metal atom of both phthalocyanines occurs on Ag(111), where theformed interface states close to the Fermi level are determined by the interaction between Fe 3d
states and substrate related states.[1, 2] On the other hand, also the macrocycle and the nitrogen
atom is involved in the interaction.
Valuable information about the electronic structure of the iron ion is obtained from XAS. A
drastic change of the XAS peak shape is observed for thicker FePcF16 films on both Ag(111) andCu(111), although the molecular orientation is very similar to coverages of few monolayers.
Since in both cases the film thickness is distinctly beyond the monolayer regime, interface
interactions can be ruled out as a possible origin of this behavior. Rather, the different XAS peak
shapes seem to indicate that the multiplicity depend on the detailed arrangement of the FePcF16
molecules.[3] The large flexibility of the ground state of Fe in FePcF16 could be of high interestfor spintronic applications.

Fe L3 edge @ grazing incidence

Fe L3 edge @ normal incidence

a)

b)

Fe L3

Fe L3
5.5 nm

5.5 nmA3

B2
3.0 nmA2

3.0 nmA1

1.2 nm

A0
706

708

c)

710

712

Photon energy (eV)

1.2 nm0.5 nmB1

0.5 nm714

706

708 710 712 714
Photon energy (eV)Fig. 1 FePcF16 on Cu(111): XAS spectra of Fe L edge at a) grazing and b) normal incidence.
The feature A0 can be understood by a hybridization of Fe and substrate related orbitals, whereas theincreasing complexity at higher coverages point to a change of the spin multiplicity. c) Illustration of thechange of the electronic structure of the Fe ion as a consequence of the different arrangement of the molecules.
[1] H. Peisert et al., J Electron Spectrosc, 204, 49-60 (2015).
[2] F. Petraki et al., J Phys Chem C, 116, 11110-11116 (2012).
[3] A. Belser et al., J. Phys. Chem. C, 122, 15390–15394 (2018).

24

Schluchsee 2018 – ASOMEA-IX

Oral Abstracts Thursday

25

26

Schluchsee 2018 – ASOMEA-IX

Thursday 09:00

Recent STM studies of single molecule and defectin gated 2D material devices
Jiong Lyu
Department of Chemistry, National University of Singapore, Singapore andCentre for Advanced 2D Materials, National University of Singapore, Singapore
e-mail: chmluj@nus.edu.sg

The ability to modify the electronic properties of 2D materials via charge-donating or chargeaccepting molecules creates new opportunities for fabricating hybrid devices at the nanoscale. In
this talk, I will first discuss about new experiments that involve the exploration of individual andself-assembled molecules adsorbed onto the surface of a back-gated graphene device. The backgated graphene device substrate is unique for single-molecule surface investigations in that it canbe electrostatically gated, thus changing and manipulating the charge-state of the supported
molecules. Understanding the charge transfer and the resulting electronic structure atmolecule/2D materials interface is essential for tuning the electronic and magnetic characteristics
of such hybrid devices. I will also talk about a recent demonstration of a giant Stark effect in
few-layer black phosphorus (BP) via electrostatic gating. Using LT-STM, we observed that amonotonic reduction of the bandgap of few layer BP occurs after the injected electronscompensate the existing defect-induced holes. We also employed LT-STM to probe the charge
state of shallow acceptors in black phosphorus together with an aim to understand the spatial
structures of bound hole states near individual acceptors. Our findings open up the new avenue
for the investigation into charge transport through single dopants in gated BP nanodevices.

Fig. 1 (a) A back-gated few-layer BP device (b-c) STM imaging and spectroscopy of a gated BP device (d-e) Edgetemplated synthesis of F4TCNQ molecular arrays on a gated graphene FET device.

[1]
[2]
[3]
[4]

S. Wickenburg et al., Nature Comm. 7, 13553 (2016).
Z.Z. Qiu et al., Nano Letters 17 (11), 6935 (2017).
Y.P. Liu et al., Nano Letters 17 (3), 1970 (2017).
Y.P. Liu et al., Nature Nanotechn. (2018).

27

Thursday 09:35

Fingerprint of charge redistribution at
hybrid inorganic/organic interfaces revealed
by differential reflectance spectroscopy
Tino Meisel1, Mino Sparenberg1, Sergey Sadofev1,
Emil List-Kratochvil2, Sylke Blumstengel2
1
Institut für Physik, Humboldt-Universität zu Berlin, Germany
2Inst. f. Physik, Inst. f. Chemie & IRIS Adlershof, Humboldt-Univ. zu Berlin, Germany
e-mail: sylke.blumstengel@physik.hu-berlin.deHybrid structures combining conjugated organic molecules and inorganic semiconductors allow
to merge the better of two worlds. To achieve optoelectronic functionality exceeding that of theindividual constituent, both the electronic and optical properties of the hybrid interface mustmeet certain requirements. Charge redistribution occurring upon deposition of conjugatedorganic molecules on semiconductor surfaces modulates the electrostatic potential at the hybridinterface. This effect has been exploited to tune the interfacial energy levels. It can be expectedthat charge redistribution also profoundly affects the optical properties of the hybrid interface.
This talk will show that differential reflectance (DR) spectroscopy allows tracking of thosechanges as a function of the molecular coverage starting from the submonolayer regime [1]. The
spectra are recorded in real time and in situ during the deposition of the molecules. At theexample of various ZnO/organic interfaces it will be shown that the electric field associated withthe modulation of the electrostatic potential causes a strong modification of the excitonic
absorption of the semiconductor surface. Modelling of the DR spectra considering a WannierMott exciton in an electric field yields the magnitude of the field strength. Consequently, thecharge-transfer induced modification of the electrostatic potential and the related changes in the
optical spectra are obtained simultaneously. The findings provide insight into the subtle interplay
between optical and electronic properties. The consequences on the effectiveness of excitonic
coupling across such hybrid interfaces will be discussed.
[1] T. Meisel et al., J. Phys. Chem. C 122, 12913 (2018).

28

Schluchsee 2018 – ASOMEA-IX

Thursday 10:10

Molecular Topology and Metal-Organic Interactions
Benedikt P. Klein1, Nadine van der Heijden2, Markus Franke3, Stefan R. Kachel1, François
C. Bocquet3, Martin Schmid1, Ralf Tonner1, Ingmar Swart2,
Christian Kumpf3, Reinhard J. Maurer4, J. Michael Gottfried1
1
Fachbereich Chemie, Philipps-Universität Marburg, Germany
2
Debye Institute for Nanomaterial Science, Utrecht University, The Netherlands
3Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, Germany
4
Department of Chemistry, University of Warwick, United Kingdom
e-mail: michael.gottfried@chemie.uni-marburg.de
Interfaces between -conjugated organic semiconductors and metal electrodes play a crucial rolein the performance of organic (opto)electronic devices. Rational strategies for the improvementof these devices therefore require a detailed understanding of the chemical, electronic andgeometric interface structure. In this contribution, we show that the interaction of aromatic
molecules with metals depends on the topology of their -electron systems. This is demonstrated
for the isomers azulene, which has a non-alternant -system with a 5-7 ring structure, andnaphthalene, which has an alternant -system with a 6-6 ring structure. We found that azuleneinteracts much more strongly with a Cu(111) surface, where its adsorption energy is 1.8 eV,compared to 1.0 eV for naphthalene. The different bond strengths are reflected in the adsorption
heights, which are 2.30 Å for azulene and 3.04 Å for naphthalene, as measured by NIXSW.
Related differences were observed in the electronic structure of the two interfaces. Substantial
transfer of negative charge from the metal to the molecule occurs only for azulene, but not fornaphthalene. The observed differences in the molecule/metal bond are related to the -electronic
structure. Azulene has a low-lying LUMO, which is close to the Fermi energy of copper and thus
hybridizes with its electronic states, as is shown by photoemission, NEXAFS, and STM data in
combination with DFT-based theoretical analysis. Similar trends were observed for other metal
surfaces such as Ag(111) and Pt(111). Our results indicate that the electronic properties ofmetal/organic interfaces can be adjusted through modifications of the -topology of the organic
semiconductor.

Fig. 1 Alternant (naphthalene) and non-alternant (azulene) -electron systems on a copper (111) surface. The
numbers indicate the respective experimental adsorption heights and adsorption energies.

29

Thursday 11:00

Theoretical spectroscopy at hybrid interfaces
Claudia Draxl
Humboldt-Universität zu Berlin andFritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany
e-mail: claudia.draxl@physik.hu-berlin.de

From a theory point of view, the ab initio description of organic materials and, in particular, theirinterfaces to inorganic counterparts remains an exciting though challenging issue. Only having
proper theoretical concepts and numerical tools in hand which consistently capture the featuresof molecular materials, from single molecules to hybrid interfaces, allows for getting insight into
the leading excitation processes. As many-body effects play a dominant role forefront
methodology, that is capable of reliably predicting the electronic structure and opticalexcitations, is a must.
Selected examples, among them pyridine and poly(para-phenylene) on ZnO will show how
many-body perturbation theory combined with density-functional theory can be used to explore,
control, and predict level alignment and band gaps as well as light-matter interaction at hybridinterfaces, and how simple models and lower-level theory can fail.

30

Schluchsee 2018 – ASOMEA-IX

Infrared analytics of functional layers
for organic electronics
1

Annemarie Pucci1,2
Dept. of Physics & Astronomy and Centre for Advanced Materials,
Ruprecht-Karls-Universität Heidelberg, Germany
2
InnovationLab Heidelberg, Germany
e-mail: pucci@kip.uni-heidelberg.de

Infrared (IR) spectroscopy is a powerful non-destructive tool with extreme chemical andstructural sensitivity. IR spectra reveal absorption lines from all those specific vibrations ofmolecules or optical phonons that can couple to the incident photons. IR spectroscopy is also
sensitive to low-energetic electronic excitations of plasmonic or polaronic nature innanostructures of finite size. Nowadays modern IR techniques provide the photometricsensitivity to detect intensity changes down to 10-4, so analytics of monolayers and interfaces ispossible if referencing is done carefully. The examples presented in the talk will be the opticalphonons and phonon polaritons of ultrathin oxide layers (used to modify electrode surfaces), theIR characterization of the conductivity of gold [1] and ITO layers [2], the IR polaron in doped
polymers (e.g. [3]), and the charge transfer between organic and inorganic materials as forexample CBP/MoO3 (e.g. [4]) and TAPP-Br (molecules produced by L. Gade's team, see [5]) on
the ordered Si(553)-1x2-Au surface [6].

[1]
[2]
[3]
[4]
[5]
[6]

J. Trollmann, A. Pucci, J. Phys. Chem. C 118, 15011 (2014).
A. Tamanai et al., Phys. Status Solidi A 214, 1600467 (2017).
L. Müller et al., Chem. Mater. 28, 4432 (2016).
S. Beck et al., J. Phys. Chem. C 119, 12545 (2015).
L. Hahn et al., Chem. Eur. J. 21, 17691(2015).
F. Hötzel et al., J. Phys. Chem. C 121, 8120 (2017).

Financial support by the German Science Foundation (DFG, collaborative research center SFB1246 and the research
unit FOR1700) and by the German Federal Ministry of Education and Research (BMBF, INTERPHASE project) is
gratefully acknowledged.

31

Thursday 12:10

Electron-vibron coupling at molecule-metal interfaces
P. Jakob, S. Thussing, C.R. Braatz, S. Flade
Department of Physics, Philipps-Universität Marburg, Germany
e-mail: peter.jakob@physik.uni-marburg.de

Dynamical charge transfer processes at interfaces in general proceed on the timescale of a few fs
or even below. Due to their high relevance in various technical devices and research areas related
to photovoltaic and optoelectronic excitations it is highly desirable to achieve a profoundunderstanding of such processes and to identify relevant parameters that control the timescaleand efficiency of this charge transfer.
Experimental studies on electron transfer between two weakly coupled electronic systems often
suffer from the fact that pump/probe excitation schemes or photoemission spectroscopy ingeneral involves electronically excited systems. Adoption of the derived dynamical properties tothe neutral ground state species (or the-like) must then remain ambiguous. In the present study
excitation of vibrational modes has been employed to study electron transfer dynamics forground-state configurations of molecular adsorbates. Even though this approach comprises a
non-ground state situation as well (vibrational excitation), deviation from thereof remains minor
as compared to electronic excitations associated with one or two-photon photoemission
spectroscopy.
By means of analyzing line shapes of vibrational modes subject to interfacial dynamical chargetransfer (IDCT) [1, 2] we are able to accurately and reliably characterize the electron transfer
dynamics between adsorbed molecules and a metal substrate. Thereby, the vibrational mode
frequency acts as an accurate internal clock to quantify the relevant time scale of these processes.
It is invoked that the non-adiabaticity of the electron-vibron coupling is correlated with thecoupling of a molecular orbital at F to substrate electronic levels and that the relevant timescales are reflected in the width of this molecular orbital which is directly linked to fluctuationsin the occupancy of this molecular orbital.

Fig. 1 Scheme describing interfacial dynamical charge transfer between NTCDA anda metal substrate, induced by the excitation of a totally symmetric molecular vibration.
[1] D.C. Langreth, Phys. Rev. Lett. 54, 126 (1985).
[2] C.R. Braatz et al., J. Chem. Phys. 136, 134706 (2012).

32

Thursday 15:00

Schluchsee 2018 – ASOMEA-IX

Exploring the structure-property relationships of
the well-ordered organic films
Yoichi Yamada
Faculty of Pure and Applied Sciences, Tsukuba Universität, Japane-mail: yamada@bk.tsukuba.ac.jp

Since organic materials show significant structure-property relationships, their macroscopic
properties should be discussed based on the measurements of well-ordered system. Much
progresses in this viewpoint has been made through the single crystalline systems, establishing
the understanding of the device properties based on the electron theory. Films, on the other hand,
have been still difficult target due to enhanced imperfections, despite their high importance.
We have been investigating the structure-property relationships of the organic film systems using
the well-defined systems, based on the molecular-scale structural determination by means of thescanning tunneling microscopy at room temperature. Here, we discuss the recent topics in two
well-ordered film systems, (i) Organic semiconductors with enhanced intermolecular force, and(ii) Ordered OLED films.
(i) In the case of the organic semiconductors with enhanced intermolecular interaction such as
picene, 6-phenacene and DNTT, phase transition of the monolayer, from face-on to bulk-like
configuration, was observed on flat metal surfaces such as Au(111) and Ag(111) (Fig.1[1]).
Upon the phase transition, the splitting of HOMO was seen, suggesting the formation of thedispersed HOMO band. The bulk-like, corrugated monolayer can also work as a template formultilayers, resulting in well aligned crystalline islands with huge domain sizes larger than 100μm.
(ii) Even the case of the complicated OLED molecules such as 4CzIPN which has attracted
much attention for exhibiting the thermally-activated delayed fluorescence (TADF), well orderedfilms were possible and their electronic and optical properties were determined [2]. Fig.2 shows
the ordered monolayer of 4CzIPN on the Ag(111) surface, showing a sparse packing.
Photoemission spectra of this sparse monolayer can be well fitted by the DFT calculations of
DOS of the monomer, suggesting the isolated nature of the molecules. The 4CzIPN films on theglass substrate showed well defined TADF with strong angular dependence reflecting significant
ordering in the film.

DNTT

picene[1] Y. Yamada et al., J. Phys. Chem. C 120, 21536 (2016).
[2] Y. Yamada et al., J. Phys. Chem. Lett. 9, 853 (2018).

33

Thursday 15:35

Optoelectronic properties ofcrystalline organic thin films and hetero-structures
Gregor Witte
Faculty of Physics, Philipps-Universität Marburg, Germany
e-mail: gregor.witte@physik.uni-marburg.de

Despite the recent success of optoelectronic organic devices, the fundamental understanding of
the involved photo-physical processes is still incomplete. This is mainly due to the complex
microstructure of blends utilized in customary devices that hampers precise microscopic
interface studies. Polycyclic aromatic molecules such as oligoacenes are versatile building
blocks which form crystalline films and can also be modified chemically, e.g. by fluorination
which turns the p-type pentacene (PEN) into the n-type perfluoropentacene (PFP). Although the
preparation of organic single crystals is frequently not possible, poly-crystalline films with large
crystalline domains, predetermined molecular orientation and even of specific polymorphs canbe prepared by tuning the growth kinetics and employing template effects. Using spatiallyresolved micro-spectroscopy allows to characterize in detail the optical properties of the various
crystalline phases [1]. For the case of PEN films the exciton energies of the various polymorphs
reveal small but characteristic temperature dependent shifts that reflect a notable strain at theinterface due to the different thermal expansion coefficient of the organic films and the inorganic
support [2]. For the case of PFP, heteroepitaxial crystalline films can be grown onto alkali halide
substrates which render polarization and directional resolved optical measurements on individual
crystalline molecular domains possible. Based on time- and polarization-resolved pump-probe
experiments, this allows studying correlations between molecular packing motifs and singletexciton fission processes [3]. Furthermore, structural and optical properties of molecular
acceptor/donor hetero-systems are discussed at the examples of PEN/PFP. Using the concept oftemplated film growth, this affords the realization of hetero-stacks with well-defined molecularinterfaces either in standing or lying molecular orientation [4] and thus allow to explore theenergetics and dynamics of charge transfer excitons at structurally well-defined interfaces [5].

[1]
[2]
[3]
[4]
[5]

T. Rangel et al., PNAS 115, 284 (2018).
L. von Helden et al., Appl. Phys. Lett. 110, 141904 (2017).
K. Kolata et al., ACS Nano 8, 7377 (2014).
T. Breuer, G. Witte, ACS Appl. Mater. & Interfaces 7, 20485 (2015).
A. Rinn et al., ACS Appl. Mater. & Interfaces 9, 42020 (2017).

34

Schluchsee 2018 – ASOMEA-IX

Thursday 16:10

The evolution of intermolecular energy bands of occupied andunoccupied molecular states in organic thin films
Yuki Kashimoto1, Keiichirou Yonezawa2, Matthias Meissner2,3,
Marco Gruenewald3, Takahiro Ueba2, Satoshi Kera1,2, Roman Forker3,
Torsten Fritz3, Hiroyuki Yoshida1,4
1
Grad. School of Eng., Chiba Univ., Japan; 2 Inst. for Molecular Sci., Japan;
3Inst. f. Festkörperphysik, Friedrich-Schiller-Univ. Jena, Germany;4
Molecular Chirality Research Center, Chiba University, Japane-mail: hyoshida@chiba-u.jp
The hole and electron transports in organic semiconductors occur through the intermolecular
overlap of the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecularorbitals (LUMOs), respectively. The orbital overlap results in the splitting of energy levels which
evolve into the energy band structure in an infinite system. A measure of the overlap is thetransfer integral t. So far, only the splitting in molecular physical dimers [1] and the HOMO
band dispersion [2] were observed because preparing physical oligomers beyond the dimers is
not easy with organic molecules. Further, no such observations were reported for the LUMO due
to the lack of suitable techniques.
In this work, physical oligomers with a controlled number of constituent molecules were realizedby tin-phthalocyanine (SnPc) films on graphite grown layer-by-layer in one-dimensional
columns. The observation of the splitting of the LUMO became feasible by our new technique,low energy inverse photoelectron spectroscopies (LEIPS) [3,4]. The observed spectral line
shapes for both HOMO and LUMO from dimer to pentamer are well-reproduced by thecalculated energy splittings based on the Hückel approximation. We determined the transfer
integrals for the HOMO as (100 ± 10) meV and for the LUMO as (128 ± 10) meV [5].

Fig. 1 HOMO and LUMO splittings of SnPc physical oligomers.

[1]
[2]
[3]
[4]
[5]

S. Kera et al., Phys. Rev. B 75, 121305 (2007).
N. Ueno, S. Kera, Prog. Surf. Sci. 83, 490 (2008).
H. Yoshida, Chem. Phys. Lett. 539-540, 180 (2012).
H. Yoshida, J. Electron Spectrosc. Relat. Phenom. 204, 116 (2015).
Y. Kashimoto et al., J. Phys. Chem. C 122, 12090 (2018) (ACS Editors’ Choice).

35

Thursday 17:00

Gas exposure effects on monolayer pentacene FET studied
by using non-invasive GaIn probes
S. Yoshimoto, R. Miyahara, K. Mukai and J. Yoshinobu
The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Japane-mail: yoshinobu@issp.u-tokyo.ac.jp

The interactions of gaseous molecules with organic field effect transistors (OFETs) play a crucialrole in the electronic transport property. Chemical interactions including oxidization are a serious
issue for degradation of long-term stability of organic devices. Physical adsorption can also
modify electronic states of OFETs. Gaseous molecules may diffuse into OFET film throughdefect sites such as grain boundaries, resulting in a change in the film structure and/or theformation of a gap state.
Recently, we have developed the non-invasive liquid-metal GaIn four-probe measurement
method for the FET properties of organic monolayer and thin films [1, 2]. In OFET devices,
probe-organic contact resistance affects device characteristics even in four-probe measurement
because a change in contact resistance at the source probe induces a change in channel potential,
resulting in different local carrier density. To overcome this problem, we introduced a feedback
circuit between a source probe and a channel voltage probe to keep the channel potential
constant [3].
In this presentation, we report that the electrical transport property of monolayer pentacene ishighly sensitive to a small amount of exposure to O2, N2 and Ar gases using independentlydriven four GaIn probes [2]. Liquid metal GaIn probes have been used as non-invasive
conductivity electrodes for monolayer OFET films in a vacuum chamber. We carried out the
fabrication of monolayer pentacene and the four-probe measurement without exposure toatmospheric air. Four GaIn probes were used in situ to measure conductivity in the channel
separately from the overall characteristics including contact resistance at the electrode probes[3].
The results show that oxygen exposure of 1 L (10−6 Torr s) reduces mobility to 8% of theoriginal value in the monolayer film, and the reduction is irreversible, i.e., mobility does notrecover its original value after the evacuation. Furthermore, chemically inert gases of nitrogenand argon also reduce the mobility. Therefore, physisorption of gaseous molecules must be
involved in this exposure effects. Taking these findings together with the results of photoelectron
spectroscopy and atomic force microscopy measurements [2], we propose that the reduction is
attributed to the physisorption of atoms/molecules at grain boundaries formed by the coalescenceof monolayer islands.

[1] S. Yoshimoto et al., Appl. Phys. Lett. 111, 073301 (2017).
[2] S. Yoshimoto et al., Organic Electronics 54, 34 (2018).
[3] S. Yoshimoto et al., Rev. Sci. Instrum. 82, 093902 (2011).

36

Thursday 17:35

Schluchsee 2018 – ASOMEA-IX

Nanoscale studies of organic radicals:interface, and spinterface
M. Benedetta Casu
Institute of Physical and Theoretical Chemistry, University of Tübingen, Germany
e-mail: benedetta.casu@uni-tuebingen.de

Our technological development was made possible also due to the discovery and synthesis of
new materials with characteristics at the nanoscale that are designed for specific purposes. This“on purpose” approach, joined to the development of preparation and growth methods, has led touse thin films rather than bulk materials in devices. For several decades thin films, surfaces andinterfaces have been intensively investigated. Indeed, device performances rely on the optimized
match of thin films of different nature, such as organic/inorganic semiconductors and metals forcontacts.
Surprisingly, in comparison, little attention has been devoted to the deposition of organic radicals
on a substrate. This might be due to the fact these materials are considered not stable enough forevaporation. In this work, we demonstrate that it is possible to evaporate and deposit organic
radicals onto well-defined surfaces under controlled conditions, without degradation.
Using soft X-ray spectroscopies, performed also at synchrotrons, we investigate thin film
processes, surfaces and interfaces at the nanoscale, when organic radicals are deposited on metal
and metal oxide surfaces. We suggest how to design organic radicals bearing in mind thethermodynamic factors that govern thin film stability, with the purpose of obtaining not only achemically stable radical, but also stable thin films. We investigate the thermal and air stabilityof the deposited films, and we explore the influence of the surface/radical chemical bond and therole of surface defects on the magnetic moment at the interface. We find that organic radicals are
physisorbed and keep their magnetic moment on inert and passivated surfaces, while defective
sites such as oxygen vacancies or presence of OH groups lead to chemisorption of the organic
radicals on the surface with quenching of their magnetic moment.
Our work shows that the use of X-ray based techniques represents a powerful approach to reveal
the mechanisms governing complex interfaces, such as radical/metal and radical/metal-oxide
where it is important to describe both charge and spin behavior (spinterfaces). A deep
understanding of stable radical/inorganic spinterfaces may open the way to use radicals in solidstate devices, or as quantum bits with dedicated configurations, as proposed for other molecularquantum bits, and in spin-based electronics.

[1] M.B. Casu, Acc. Chem. Res. 51, 753 (2018).

37

Thursday 17:55

Introduction to JSPS and its international programs
1

Nobuo Ueno1,2
Japan Society for the Promotion of Science – London, London, NW1 2HD, UK
2
Chiba University, Chiba 263-8522, Japan
E-mail: uenon@jsps.org and uenon@faculty.chiba-u.jp

In this workshop I will briefly introduce Japan Society for the Promotion of Science (JSPS) and
its international programs for Japan-over sea countries research collaboration. JSPS wasestablished in 1932. Through open competitive research grants and research fellowships for all
research fields, now JSPS is recognized as the largest funding agency with the longest history inJapan.
JSPS’s three main supports are(1) Grant to research projects: Grant-in-Aid, well known as “KAKENHI”, with
€1,000,000,000/80,000 projects)(2) Fellowships: 6,000 Japanese pre-/post-docs, for researchers at Japanese Institutions,regardless of their nationality.
(3) International programs:(i)International scholarships from research students, postdocs to established researchers(ii) Bi-lateral programs(iii) Core-to-core program (multi-lateral program).
There are other programs for creating diverse world-level knowledge and enhancing education
and research functions of universities etc. The JSPS budget and its transition are shown in the
figure. International collaborations are also supported through KAKENHI to researchers in Japan
as well as through the international programs (3).

Year
[URL]:<JSPS-Bonn: http://www.jsps-bonn.de><JSPS-London: http://www.jsps.org><JSPS-Strasbourg, http://jsps.unistra.fr/><JSPS-Stockholm: http://www.jsps-sto.com><JSPS-Tokyo: http://www.jsps.go.jp>38Schluchsee 2018 – ASOMEA-IX

Oral Abstracts Friday

39

40

Schluchsee 2018 – ASOMEA-IX

Friday 09:00

Dispersive states at molecule-metal interfaces
F. Stefan Tautz1,2Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
2
Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology,
52425 Jülich, Germany
e-mail: s.tautz@fz-juelich.de1

When molecules adsorb on metal surfaces, their localized states interact with the extended statesof the metal. In special circumstances, this can result in molecule-derived states acquiring a kspace dispersion. Such cases are of considerable interest, because they indicate a strong lateralinteraction between molecules.
While the measurement of the dispersion as such is standard in angle-resolved photoelectron
spectroscopy, the unambiguous identification of a dispersing state as being of molecular origin
requires additional information on the corresponding wave functions. As I will illustrate with thehelp of two examples, this information can come from either photoelectron tomography (PT) orfrom scanning tunneling spectroscopy/microscopy (STS/STM), both of them adapted for the
specific task of addressing dispersing states.
The first example is PTCDA/Cu(100). Here we apply an extension of PT beyond the plane wave
approximation that is able to deal with dispersing states. We show that the interaction andhybridization of the lowest unoccupied molecular orbital with substrate states leads to its
occupation and the formation of a strongly dispersing intermolecular band (1.1 eV band width)[1].
The second example is the well-known PTCDA/Ag(111) interface state. Here we revisit thequestion of whether this state is just the up-shifted Shockley surface state of the bare Ag(111)
surface, or whether this state has some intrinsic molecular component in its wave function. To
study this question, we introduce a new variant of STS, so-called Feature-Detection STS (FDSTS). Our results suggest that the presently accepted model for the metal-molecule interface
state at PTCDA/Ag(111) and similar interfaces is incomplete [2].

[1] D. Lüftner et al., Phys. Rev. B 96, 125402 (2017).
[2] A. Sabitova et al., submitted.

41

Friday 09:35

Formation of occupied and unoccupied hybrid bands atinterfaces between metals and organic molecules
Petra Tegeder
Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Germany
e-mail: tegeder@uni-heidelberg.de

Efficient charge transport in organic semiconductors and sufficient charge injection at theirinterfaces with electrodes is crucial for the performance of organic molecule-based electronic
devices. Band formation fosters effective transport properties and can be found in organic single
crystals of large -stacking aromatic molecules. However, at molecule/metal interfaces hybrid
band formation and band dispersion is a rarely observed phenomenon. Using angle-resolved twophoton photoemission (see Fig. 1) supported by density functional theory calculations wedemonstrate such band formation for three different molecule/metal systems in the energy regionof occupied as well as unoccupied electronic states. In all cases, strong adsorbate/substrateinteractions result in formation of interface states due to hybridization between localized
molecular states and delocalized metal bands (sp- or d-bands). These interface states exhibit
significant dispersions. Our study reveals that hybridization in combination with an extended
well-ordered adsorption structure of the -conjugated organic molecules is a striking concept toreceive and experimentally observe band formation at molecule/metal interfaces.

Fig.1 Angle-resolved two-photon photoemission is utilized to gain information
about the dispersion (viz. electron localization/delocalization) of electronic statesat organic molecule/metal interfaces.

42Friday 10:10

Schluchsee 2018 – ASOMEA-IX

Unoccupied electronic states and excited
dimer formation at the perylene/graphite interface
Takashi Yamada, Natsumi Ito, Noriaki Kawakita, Kento Araragi,
Hiroyuki S. Kato, Toshiaki Munakata
Dept. of Chem., Gr. Sch. of Sci., Osaka Univ., Jpn; e-mail: tyamada@chem.sci.osaka-u.ac.jp

Perylene (see Fig.1) and its derivatives have attracted widespread interest with regard to
applications in various electronic devices. In this study, perylene monolayer films on a graphite
substrate have been investigated by a combination of two-photon photoemission (2PPE)
spectroscopy, low energy electron diffraction (LEED), scanning tunneling microscopy (STM),
and photoluminescence spectroscopy.
When the graphite substrate was covered with a monolayer perylene film, visible light emission
was observed in response to incident laser light used for 2PPE. Fig. 1 shows photographs taken
during the 2PPE experiments, in which green-yellowish and orange light emissions wereobserved for room temperature (RT) and low temperature (LT, 90K) samples, respectively. At
low temperature, visible light with a wavelength at around 630 nm was observed. The overall
spectral features are very similar to those reported for perylene α crystals [1], and the origin of
the 630 nm peak can be ascribed to the photon emission from an excited state of a moleculardimer (that is, an excimer). Actually, dimerized pairs consisting of single molecular protrusions
are seen in the STM image in Fig. 1. The mechanism for the photon emission was examined byacquiring the photon-energy dependent 2PPE spectra of a 1 ML perylene film (Fig. 2). At 90 K,
the strong peak “EXCIMER” appeared +1.05 eV above the Fermi level (EF). Therefore, we
propose that the photon emission in Fig. 1 results from transition between the EXCIMER and
HOMO levels. To date, visible photon emission from ultrathin 2 ML (or thicker) films has beenreported for perylene [2] and its derivatives [3]. The difference between the present data and thatobtained from previous studies is that luminescence quenching by the substrate is suppressed on
the graphite substrate used in the work reported herein, due to the reduced substrate-moleculeinteraction as compared to that with a metallic substrate [2,3]. Instead, intermolecularinteractions contributed strongly to the formation of a bulk-like structure, as evidenced by thegeneration of a dimerized configuration having an α crystal-like structure. At room temperature,
the strong EXCIMER peak changed to an unoccupied feature with tail component toward higher
energy side, and this resulted in the broadened luminescence spectrum in Fig. 1.
Fig. 1 Photolumineccencefrom the perylene 1 ML film.
Excited at a photon energy of
4.77 eV.

Fig. 2 Photon energy
dependent 2PPE spectraof perylene 1 ML
acquired at 90 K.

[1] H. Nishimura et al., J. Phys. Soc. Jpn. 53, 3999 (1984).
[2] Q. Chen, J. Phys. Chem. C 114, 6062 (2010).
[3] W. Gebauer et al., Phys. Rev. B 69, 155431 (2004).

43

Friday 11:00

Critical interplay of atomic structure and level alignment
in organic/inorganic interfaces
Mariana Rossi
Fritz Haber Institut of the Max Planck Society, Berlin, Germany
e-mail: rossi.at.fhi-berlin.mpg.de

The versatile tunability of hybrid inorganic/organic materials makes them promising candidates
for more efficient photovoltaic and electronic devices. One aspect that hinders advances in thisfield is the lack of knowledge or understanding about how the electronic and atomic degrees of
freedom cooperate or compete in the final, desired, interface properties. Here we show how work
function changes and level alignments are modulated by the structure of the organic components
in model hybrid systems comprising strong electron acceptor molecules and acenes, both
adsorbed on H/Si(111). We can explain the geometry adsorption preferences quantitatively
through the competition between molecule-molecule and molecule-surface interactions.
Furthermore, we show that temperature induces large fluctuations in the interface dipole and thatfor certain systems, the consideration of large commensurate cells is necessary for a quantitativedescription of level alignment.

44

Schluchsee 2018 – ASOMEA-IX

Friday 11:35

Spectroscopy and imaging of photocarriers in organic
functional films probed by two-photon photoemission
Masahiro Shibuta
Keio Institute of Pure and Applied Sciences, Keio University, Japane-mail: shibuta@sepia.chem.keio.ac.jp

Understanding of carrier dynamics at organic functional films is essentially important for further
achievement of organic electronics. We have employed two-photon photoemission (2PPE)
spectroscopy for the organic films deposited on several substrates, which can sensitively detect
the photoexcited electron in the molecular unoccupied states (e.g. the lowest unoccupied
molecular orbitals (LUMOs)) with high energy and time resolutions.
In case of C60 fullerene thin films deposited on an inert HOPG graphite substrate, photocarrier
electrons in LUMO and LUMO+1 are clearly resolved with intense signals (Fig. 1(a)) exhibiting
the decay dynamics with a fs-ps regime [1]. In contrast, C60 deposited on a metal Au(111)substrate shows broader 2PPE spectral features due to a strong organic-metal interaction [2].
Furthermore, it has also been demonstrated that the energies of LUMOs (as well as HOMOs) of
C60 can be designed by chemical modifycation of depositing an alkanethiolate self-assembled
monolayer on an interface [3].
In addition, the 2PPE spectroscopy can be extended to 2PPE electron microscopy (2P-PEEM) to
detect spatially resolved photocarrier dynamics. Figs. 1(b) and 1(c) compare the standard (onephoton) and 2P-PEEM for 0.2 monolayer C60/HOPG, showing the successful imaging of thephotocarrer electrons generated in the C60 nanostructured islands [4].

Fig. 1 (a) 2PPE spectra for 0.6 monolayer (ML) C60 film on HOPG, (b) standard (one-photon) photoelectron
emission microscopy (PEEM) for 0.2 ML C60/HOPG, and (c) 2P-PEEM for the same
area of (b) [4]. Photocarriers occupying LUMOs in the C60 islands are imaged in 2P-PEEM.
[1]
[2]
[3]
[4]

M. Shibuta et al., Sci. Rep. 6, 35853 (2016).
M. Shibuta et al., Chem. Lett. 46, 1528 (2017).
M. Shibuta et al., J. Phys. Chem. C 121, 27399 (2017).
M. Shibuta et al., Appl. Phys. Lett. 109, 203111 (2016).

45

Friday 12:10

Organic-inorganic energy-level alignment:
From academic interfaces to devices
Steffen Duhm
Institute of Functional Nano & Soft Materials (FUNSOM),
Soochow University, Suzhou, P.R. Chinae-mail: duhm@suda.edu.cn

Contact formation at organic-inorganic interfaces is of utmost importance for the performance oforganic electronic devices. Organic-metal interfaces serve as well-defined model systems andinterface energetics and chemical reactions are accessed by ultraviolet- and X-ray photoelectron
spectroscopy (UPS and XPS) [1]. Metal work functions -and thus the energy-level alignment tosubsequently deposited organic layers- can be tuned by strongly coupled molecular monolayers[2]. However, molecular diffusion can counteract this effect and we developed UPS and XPSbased indicators to predict the actual arrangement of organic heterostructures on metal substrates[3]. The work function of transition metal oxides can be controlled by oxygen vacancies and by
careful preparation the work function of VO2 can reach up to 6.7 eV [4]. Likewise, the propertiesof organic-inorganic perovskite thin films depend critically on the preparation conditions and weshow how beneficial energy-alignment for photovoltaic applications can be achieved for both,
solution processed and vacuum-sublimed perovskite films [5]. Moreover, deposition of MoOx on
hybrid perovskite leads to p–n junctions induced by local electronic doping [6]. In a similar way,
an inversion layer can be induced in n-Si and consequently a dopant-free p-n junction is formed
[7].

[1]
[2]
[3]
[4]
[5]
[6]
[7]

S. Kera et al., J. Phys. Soc. Jpn. 87, 061008 (2018).
O. T. Hofmann et al., J. Phys. Chem. C 121, 24657 (2017).
Q. Wang et al., J. Phys. Chem. C, 122, 9480 (2018).
K.-K. Fu et al., ACS Appl. Mater. Interfaces 10 (2018), 10552.
R.-B. Wang et al., ACS Appl. Mater. Interfaces 9 (2017), 7859.
Q.-D. Ou et al., Adv. Mater. 30, 1705792 (2018).
T. Sun et al., Phys. Status Solidi RRL, 11, 1700107 (2017).

46

Schluchsee 2018 – ASOMEA-IX

Poster Abstracts

47

48

Schluchsee 2018 – ASOMEA-IX

Poster Session, Wednesday, 24.10.2018
1

Rachana Acharya, MPI Stuttgart
Alkyl- and fluoroalkyl-phosphonic acid self-assembled monolayer hybrid dielectrics
for organic transistors

2

Mohsen Ajdari, Uni Heidelberg
High resolution electron energy loss spectroscopy of N-heteropolycycles on metal
surfaces

3

Kenichi Aoyama, Tokyo Univ. of Science
Characterizing chemical and electronic structure of graphitic carbon nitride withphotoelectron spectroscopy

4

Axel Belser, Uni Tübingen
Interaction channels between perfluorinated iron phthalocyanine and Cu(111)5James Borchert, MPI Stuttgart
Organic TFTs with low contact resistance

6

Giulio d'Acunto, Lund Univ.
ALD of HfO2 on SiO2: Identification of surface species by ambient pressure XPS andIR spectroscopy

7

Michael Geiger, MPI Stuttgart
Quantitative analysis of the density of trap states in organic semiconductors byelectrical transport measurements on low-voltage thin-film transistors

8

Katharina Greulich, Uni Tübingen
Interface properties of FePcF16 on MoS2

9

Jan Hagenlocher, Uni Tübingen
Influence of structural defects on the energy level alignment in planar pentaceneperfluoropentacene heterojunctions

10

Sebastian Hammon, Uni Bayreuth
Simulating the pump-probe photoemission process from organic semiconductors inreal-time

11

Martin Hantusch, IFW Dresden
Photoelectron spectroscopy of F6TCNNQ-polycyclic hydrocarbon interfaces

12

Philipp Hurdax, Uni Graz, Austria
Charge transfer and molecular level alignment on dielectric interlayers on metals

49

13

Masato Iwasawa, Tsukuba Univ.
Thermal stability of the surfaces of organic single crystals under UHV

14

Hiroyuki Ichikawa, Chiba Univ.
Interface dipole of the bulk-heterojunction of organic solar cell

15

Svenja Janke, Duke Univ., NC/USA
Level alignment prediction of hybrid inorganic-organic systems: Tetracene andpentacene on H/Si(111)

16

Tobias Junghöfer, Uni Tübingen
Organic radical films investigated by X-ray-based spectroscopies

17

Reimer Karstens, Uni Tübingen
Iron-phthalocyanine on rutile: Main interaction channel oxygen vacancies at thesurfaces

18

Benedikt Klein, Uni Marburg
Molecular topology and surface chemical bond: Alternant vs. non-alternant aromatic
molecules

19

Michael Kothe, Uni Marburg
Evolution of TiOPc-films on Ag(111): Bilayer stacking enables ultra-smooth layers

20

Christian Kumpf, FZ Jülich
Two-dimensional growth of dendritic islands: NTCDA on Cu(001) studied in real time

21

Christian Kumpf, FZ Jülich
Steering the growth of multiple ordered hetero-molecular phases by utilizing
intermolecular repulsion

22

Alexander Lerch, Uni Marburg
Time-resolved spectroscopy of electron transfer processes at metal/organic interfaces

23

Xianjie Liu, Linköping Univ.
Energetic degradation of organometal halide perovskite films upon oxygen, water andillumination

24

Ahmed Mansour, HU Berlin
Investigating the electronic structure and chemical interactions in doped poly(3hexylthiophene) with the Lewis acid dopant tris(pentafluorophenyl)borane

25

Matthias Meissner, NIMS-IMS, Okazaki
Orbital tomography of a strong hole-vibration coupling molecule

26

Christian Metzger, Uni Würzburg
Orbital imaging of the non-planar molecules

50Schluchsee 2018 – ASOMEA-IX

27

Andreas Opitz, HU Berlin
Exciton binding energy of organic materials: Valence vs. core excitation

28

Maryline Ralaiarisoa, HU Berlin
Influence of water, oxygen, and air exposure on the electronic structure of methyl
ammonium lead mixed iodide-chloride CH3NH3PbI3-xClx perovskite films

29

Foqia Rehman, Lund Univ.
Monitoring of atomic layer deposition by synchrotron-based ambient pressure XPS:
Towards millisecond time resolution

30

Haruki Sato, Chiba Univ.
Development of angle-resolved low energy inverse photoelectron spectroscopy
apparatus

31

Thorsten Schultz, HU Berlin
Importance of homogeneous substrates for ionization potential determination by
ultraviolet photoelectron spectroscopy

32

Mathias Schwendt, Uni Graz
Photoemission tomography for π-extended peri-xanthenoxanthene on Cu(111)33

Kohei Shimizu, Chiba Univ.
"Shallow states" of organic films observed by hν-dependent high-sensitivity
photoemission

34

Vipilan Sivanesan, Uni Heidelberg
Exciton dynamics in pentacene-perfluoropentacene heterostructures

35

Serguei Soubatch, FZ Jülich
Dependence of the adsorption height of graphenelike adsorbates on theirdimensionality

36

Stefan Tautz, FZ Jülich
Nanoscale engineering with molecules at surfaces

37

Ryohei Tsuruta, Tokyo Univ. of Science
Epitaxial growth of the organic pn heterojunctions

38

Yuki Uemura, Chiba Univ.
Impact of the molecular quadrupole moment in the molecularly mixed film of organic
semiconductors

51

39

Ryota Usui, Chiba Univ.
Enhancement of signal intensity for the inverse photoelectron spectroscopy by thesurface plasmon resonance of the Ag nanoparticles

40

Ana Valencia, HU Berlin
Electronic and optical properties of oligothiophene/F4TCNQ charge-transfer
complexes: The role of donor conjugation length41

Qiankun Wang, HU Berlin
Switching the surface electronic properties of polar ZnO crystals with photochromic
pyridine-dihydropyrene molecular layers

42

Rongbin Wang, HU Berlin
Solution-processing vs. vacuum-sublimation: Impact on the electronic structure of
methylammonium lead iodide perovskite thin films

43

Berthold Wegner, HZB & HU Berlin
Predicting ion pair formation yield in molecular electrical doping from redoxpotentials

44

Xiaomin Xu, HU Berlin
Microstructure and elastic constants of transition metal dichalcogenide monolayers
from friction and shear force microscopy

45

Jin-Peng Yang, Yangzhou Univ.
Band dispersion of CH3NH3PbI3 single crystal

46

Xiaosheng Yang, FZ Jülich
Identifying molecular orbitals and on-surface reaction products with photoemission
tomography

47

Koki Yoshida, Tokyo Univ. of Science
Structural and electronic characterization on organic semiconductor homojunctions

48

Fengshuo Zu, HU BerlinBand structure of CH3NH3PbI3 and CH3NH3PbBr3 perovskite single crystals fromangle-resolved photoelectron spectroscopy

52

P1

Schluchsee 2018 – ASOMEA-IX

Alkyl- and fluoroalkyl-phosphonic acidself-assembled monolayer hybrid dielectrics
for organic transistors
Rachana Acharya1,2, Guido Schmitz2, Hagen Klauk1
Max Planck Institute for Solid State Research, Stuttgart, Germany
2
Institute of Materials Science, University of Stuttgart, Stuttgart, Germany
e-mail: R.Acharya@fkf.mpg.de
1

Hybrid gate dielectrics composed of a thin metal oxide and an organic self-assembled monolayer(SAM) are useful for low-voltage organic thin-film transistors (TFTs) by providing a large
dielectric capacitance while minimizing gate leakage and improving overall TFT performance.
We have fabricated and characterized organic TFTs with gate dielectrics composed of a plasmagrown AlOx layer and a solution-processed phosphonic acid (PA) SAM, in which the terminalgroup and the alkyl chain length of the molecule forming the SAM were varied. Two different
terminal groups, namely alkyl and fluoroalkyl groups, and a chain length ranging from 6 to 18
carbon atoms for the alkyl and 6 to 14 carbon atoms (in steps of 2 carbon atoms) for the
fluoroalkyl PA molecules were used to form the SAMs. Optimum TFT characteristics are found
for the medium chain length molecules in both alkyl and fluoroalkyl-phosphonic acid SAMs,
which could potentially be due to maximum ordering and packing density in the SAMs. We
explore the possibility of verifying these results with various spectroscopic measurements.

Fig.1 Alkyl- and fluoroalkyl-phosphonic acid molecules

53

P2

High resolution electron energy loss spectroscopy of
N-Heteropolycycles on metal surfaces
Mohsen Ajdari1, Friedrich Maass1, Benjamin Günther2,
L. Hahn2, Lutz H. Gade2, Petra Tegeder1
1
Physikalisch-Chemisches Institut, 2Anorganisch-Chemisches Institut,
Ruprecht-Karls-Universität Heidelberg, Heidelberg, Germany
e-mail: mohsen.ajdari89@gmail.com

Understanding the adsorption and electronic properties of organic molecules on inorganic
substrates provides important insights into the charge transport properties at organic/inorganicinterface, which is crucial in determining the performance of electronic devices based on organic
semiconductors. High resolution electron energy loss spectroscopy (HREELS) is a powerful toolfor investigating both the adsorption geometry via vibrational excitations and electronic
properties of the molecules by utilizing electrons with sufficient energy to excite electronictransitions. We successfully employed HREELS to investigate the adsorption and electronic
properties of several tetraazaperopyrene (TAPP) derivatives as a function of coverage on
Au(111). TAPPs belong to N-Heteropolycyclic aromatic compounds that are promising
candidates for n-channel semiconductors which are of great interest especially for field effecttransistors [1, 2]. We found that TAPPs without bulky substituents adopt a planar geometry withrespect to the substrate in both the monolayer (ML) and thin films (up to 10 ML). Contrary, intheir crystal structure the molecules are tilted up to 35° between the molecular planes inneighboring stacks. This adsorption behavior is attributed to the ability of the plane Au(111)
surface in adsorbing the planar molecules in a flat adsorption geometry to maximize thesubstrate/adsorbate interactions and thereby the binding energy. This substrate-induced strictly
planar growth, results in the formation of a ”flat” monolayer, on which additional molecules also
adsorb in a planar fashion.
a)

b)

c)
35°

vs.

Au(111)

Fig. 1 a) Schematic of TAPP molecule; b) Crystal structure of TAPP;c) Geometry of TAPP on Au(111) in comparison to its crystal structure [2].

[1] F. Maass et al., J. Phys. Chem. C 120, 2866 (2016).
[2] L. Hahn et al., Chem. Eur. J. 21, 17691 (2015).

54

crystalP3

Schluchsee 2018 – ASOMEA-IX

Characterizing chemical and electronic structure ofgraphitic carbon nitride with photoelectron spectroscopy
Kenichi Aoyama, Kouki Akaike, Shunsuke Dekubo, Kaname Kanai
Dept. of Physics, Fac. of Science & Technology, Tokyo University of Science, Japane-mail : 6217601@ed.tus.ac.jp

Graphitic carbon nitride [g-CN, Fig. 1(a)] has attracted enormous interests since it is found thatg-CN exhibits the photocatalytic activity under the irradiation of visible light, such as hydrogen
evolution via water splitting [1]. g-CN was believed to be g-C3N4, where the two dimensional
covalent sheets of melem, the repeating unit of g-CN [Fig. 1(a)], are formed. However, therecent structural investigations revealed that g-CN is the linear polymer of melem, melon [Fig.
1(a)] [2–4]. Nevertheless, the interpretation of X-ray photoelectron spectra of g-CN appears to beincomprehensive in previous literature. Moreover, the electronic structure near the energy gap,
which is indeed important for understanding the photocatalytic reaction, has not been
investigated.
In this work, by utilizing the g-CN and melem films, we reappraised the N 1s X-ray
photoelectron spectra of g-CN and identified g-CN as melon [Fig. 1(b)]. The analysis withultraviolet photoelectron spectroscopy and inverse photoemission spectroscopy revealed theenergy levels preferable to water splitting. Theoretical calculations suggest that, along thepolymer chain, only the LUMO exhibits the energy dispersion, whereas both the energy
dispersions of the HOMO and LUMO are present along π-stacking [5].

Fig. 1 (a) Process of thermal polycondensation of melem (gray, blue and white balls represent carbon, nitrogen andhydrogen, respectively). (b) XPS N1s spectra of melem (top) and melon films (bottom). Black dots are the measured
spectra after subtracting Shirley backgrounds. The peaks labeled S at higher binding energy might be attributed toshake-up satellites.

[1]
[2]
[3]
[4]
[5]

X. Wang et al., Nat. Mater. 8, 76-80 (2009).
V. B. Lostch et al., Chem. Eur. J. 13, 4649-4680 (2007).
T. Tyborski et al., J. Phys. Condens. Matter. 25, 395402(7pp), (2013)
F. Fina et al., Chem. Mater. 27, 2612-2618 (2015).
K. Akaike, K. Aoyama et al., Chem. Mater. 30, 2342-2351 (2018).

55

P4

Interaction channels between
perfluorinated iron phthalocyanine and Cu(111)Axel Belser, Reimer Karstens, Thomas Chassé, Heiko Peisert
Institute of Physical and Theoretical Chemistry, University of Tübingen, Germany
e-mail: axel.belser@uni-tuebingen.de

The initial growth and interfacial electronic structure of perfluorinated iron phthalocyanine(FePcF16) on Cu(111) has been studied using X-ray photoelectron spectroscopy (XPS) andpolarization dependent X-ray absorption spectroscopy (XAS). The planar molecules are oriented
preferred flat lying on the substrate surface during the growth of the first layers while the tilt
angle is increased in thicker films. A clear interaction at the interface is observed, involving boththe central metal ion and the macrocycle. At monolayer coverages, the Fe2p spectrum shows aninterface signal at 707.1 eV, while the C-N component of the C1s spectrum is distinctly shiftedwith respect to the thicker films. Also the nitrogen atom is involved in the interaction, bestvisible in the * resonance of N K edge spectra recorded from molecules at the interface. [1]Fig. 1 X-ray photoemission spectra of the Fe2p (left) and C1s (right) core levels. Both thecentral metal atom and the macrocycle take part in the interaction at the interface.

[1] A. Belser et al., physica solidi status b, submitted.

56

P5

Schluchsee 2018 – ASOMEA-IX

Organic TFTs with low contact resistanceJames W. Borchert1,2, Florian Letzkus3, Joachim N. Burghartz3,
Ute Zschieschang1, Sabine Ludwigs2, and Hagen Klauk1
1
Max Planck Institute for Solid State Research, Heisenbergstr.1, Stuttgart, Germany
2
Universität Stuttgart, Pfaffenwaldring 55, Stuttgart, Germany
3Institut für Mikroelektronik (IMS CHIPS), Allmandring 30a, Stuttgart, Germany
e-mail: j.borchert@fkf.mpg.de

The performance of organic thin-film transistors (TFTs) can depend significantly on the device
architecture. Organic TFTs fabricated in the bottom-gate, bottom-contact (BC) architecture often
suffer from larger contact resistances than otherwise similar top-contact (TC) TFTs due to poor
morphology of the organic semiconductor layer on the contact-metal surface and lack of a gatefield-induced charge density above the contacts, both of which limit the area for charge exchange[1]. To combat these issues, the surface of the bottom-contacts can be modified with a molecularmonolayer, e.g. pentafluorobenzenethiol (PFBT), to increase the work function and improve thesemiconductor morphology on the metal surfaces [1,2]. Interestingly, recent simulations [3]predict that with a sufficiently thin gate dielectric and sufficiently small injection barrier, thecontact resistance of BC TFTs will be as small as (and even smaller than) that of TC TFTs.
Therefore, we fabricated BC and TC TFTs using 2,9-diphenyl-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DPh-DNTT) [4] with various gate dielectric thicknesses and analyzed
the contact resistances. The results confirm that BC TFTs can indeed have smaller contact
resistances than TC TFTs when (1) a sufficiently thin gate dielectric is used and (2) the bottomcontacts are treated with PFBT. We show optimized BC TFTs fabricated on flexible PEN
substrates with a record-low contact resistance of 29 Ωcm, along with large on/off current ratio(109), large effective carrier mobility (4.7 cm2/Vs), steep subthreshold slope (62 mV/decade) andvery short signal propagation delay (138 ns per stage at a supply voltage of 3.7 V, measured
using 11-stage ring oscillators).

Fig. 1 Comparison of top-contact and bottom-contact DPh-DNTT TFTs: (a) transfer characteristics (b) contact
resistance (c) signal propagation delay measured on 11-stage unipolar ring oscillators.

[1]
[2]
[3]
[4]

D.J. Gundlach et al., J. Appl. Phys. 100, 024509 (2006).
S. Choi et al., ACS Appl. Mater. Interfaces 8, 24744 (2016).
K. Zojer et al., Phys. Rev. Appl. 4, 044002 (2015).
K. Niimi et al., Org. Lett. 13, 3430 (2011).

57

P6

ALD of HfO2 on SiO2: Identification of surface species byambient pressure XPS and IR spectroscopy
G. D’Acunto1, P. Shayesteh1, M. Van Daele2, F. Rehman1, A.R. Head3, F. Rochet4,
F. Bournel4, R. Tsyshevskiy5, C. Detavernier2, C. Dendooven2, J.-J. Gallet4, J. Schnadt1
1
Lund University, Sweden; 2 University of Ghent, Belgium; 3 Brookhaven National Laboratory,
USA; 4 Sorbonne Université, Paris, France; 5 University of Maryland, USAe-mail: giulio.dacunto@sljus.lu.se
Atomic layer deposition (ALD) is a powerful technique for the deposition of thin film materials
with atomic scale precision. Ideal ALD schemes, which always rely on the assumption of a selflimiting nature of the growth, provide guidelines to understand how the ALD growth proceeds
and which structures are produced. However, in most case, the detailed surface chemistry of the
ALD process is not fully understood, as a result of side reactions, possible non-self-limiting
nature of the growth, influence of surface defects and gas phase reactions [1]. In our work, we
explore possibilities to gain an exact knowledge of the surface chemistry of the ALD processfrom the application of in situ and operando methods, which allow the investigation of surfaces
during the reaction.
The ALD of HfO2 on a native oxide-covered Si(111) surface as well as on an anatase TiO2(101)surface from tetrakis(dimethylamido)hafnium (TDMAHf) and H2O was studied using ambientpressure x-ray photoelectron spectroscopy (APXPS) and in situ fourier transform infrared
spectroscopy (FTIR) with second time resolution. The ALD was carried out at temperatures in
between 200 and 280°C, and the surfaced species during the process were investigated. The
FTIR data show that the adsorption and reactions of TDMAHf and H2O on the native oxidecovered Si(111) surface is self-limiting at this temperature (Fig. 1 a). All spectra used have beenreferenced to the previous spectrum. Operando APXPS at high temporal resolution illustrates theevolution of the C 1s, N 1s and Hf 4f core levels (cf. Fig 2). From these, Hf-amido adsorbates aswell as methyl methyleneimine surface species were identified. Our study illuminates thepotential of surface sensitive in situ and operando methods to gain a detailed understanding of
the ALD surface process during growth.

Fig.1 a) Integrated peak area vs number of pulses for the CH3
stretching modes (2650-3050 cm-1). b) FTIR differential
absorbance spectra for ALD of HfO2 on SiO2/Si(111).
[1] F. Zaera, Coord. Chem. Rev. 257, 3177 (2013).
[2] A.R. Head et al., J. Phys. Chem. C 120, 243 (2016).

58

Fig.2 XPS analysis of the first half cycle of
HfO2 ALD on SiO2/Si(111).

P7

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Quantitative analysis of the density of trap states inorganic semiconductors by electrical transportmeasurements on low-voltage thin-film transistors
Michael Geiger,1 Lukas Schwarz,1 Ute Zschieschang,1 Dirk Manske,1Jens Pflaum,2 Jürgen Weis,1 Hagen Klauk,1 Ralf Thomas Weitz3
1
MPI for Solid State Research, Stuttgart, Germany; 2 Exper. Physics VI,
Univ. Würzburg, Germany; 3 Dept. of Physics, LMU München, Germany
E-Mail: M.Geiger@fkf.mpg.de

The electrical characteristics of thin-film transistors (TFTs) based on disordered semiconductors
are greatly influenced by the density and energetic distribution of localized electronic states inthe energy gap of the semiconductor. In the 1980s, Michael Grünewald et al. developed amethod to convert a measured transfer curve of a field-effect transistor to the underlying densityof-trap-states (trap DOS) function.1 The Grünewald method has been employed with great
success, however, in all previous publications, a critical simplification was made, whereby thepotential drop across the semiconductor layer was ignored.2-4 For high-voltage TFTs, in which
the applied gate-source voltage drops almost entirely across the gate dielectric, thissimplification is indeed justified. However, for TFTs employed in real applications, low-voltage
operation is a critical prerequisite, in which case the above-mentioned simplification is no longer
valid. Therefore, we have explored an extension of the Grünewald method by performing thederivation without this simplification. Our results confirm the validity of the original Grünewald
method for high-voltage TFTs, but also the need for the extended Grünewald method for lowvoltage TFTs. Furthermore, we used this method to investigate the correlation between thesurface roughness of the gate dielectric and the trap DOS of the organic semiconductor, and theimplications of the surface roughness for the TFT performance.

Fig. 1 Density of trap states as a function ofenergy above the transport level. (a) For the
TFT with the high operating voltage theresults show that the original Grünewald
method is indeed valid. (b) For the TFT withthe low operating voltage the trap DOS
functions obtained with and without thesimplification deviate substantially.

[1]
[2]
[3]
[4]

M. Grünewald et al., Phys. Stat. Sol. B 100, K139 (1980).
W.L. Kalb et al., Phys. Rev. B 76, 184112 (2007).
P.J. Diemer et al., Appl. Phys. Lett. 107, 103303 (2015).
N.K. Za’aba et al., Org. Electronics 45, 174 (2017).

59

P8

Interface properties of FePcF16 on MoS2
Katharina Greulich, Axel Belser, Reimer Karstens, Peter Grüninger,
Thomas Chassé, Heiko Peisert
Institute of Physical and Theoretical Chemistry, University of Tübingen, Germany
e-mail: k.greulich@uni-tuebingen.de

The recently increasing research efforts devoted to layered transition metal dichalcogenides(TMDCs) derives from their novel electronic and magnetic properties. As example, in MoS2, thesize of the bandgap and their nature (indirect to a direct) depends on the number of trilayers.[1]Moreover, even in the bulk material, MoS2 shows regions of high spin-polarization.[2] Electronic
properties of TMDC surfaces might be tuned by the adsorption of molecules. On the other hand,electronic and magnetic properties of transition metal phthalocyanines (TMPcs) can be tuned
over a wide range. Thus, TMDC/TMPc heterostructures may exhibit novel electronic properties,
which could be of high interest for efficient and flexible electronics and spintronics.
We studied interface properties of FePcF16 on a MoS2 single crystal using photoemission, x-ray
absorption (XAS) and scanning tunneling microscopy (STM). Band structure measurements
before and after FePcF16 deposition were carried out using the ARTOF analyzer at the PM4
beamline at HZB Berlin (Figure 1). Because of the very high electron transmission (300 times
higher compared to hemispherical analyzers) a very limited photon flux, radiation damage oforganic molecules can be avoided.[3] Our results indicate that uniform large-area heterostructures
can be prepared. The spin state of FePcF16 in films of about 1 nm is comparable to thick films of
FePc on single crystalline substrates but different to thick films of FePcF16 on Ag(111) andCu(111).[4] Generally, a weak interaction was observed between FePcF16 and MoS2.
b)

a)

high

low

Fig. 2 ARPES band map along the K-Γ-M high symmetry line of a) MoS2 andb) a thin layer of FePcF16 on MoS2. Upon adsorption of FePcF16, the band structure of
the substrate is attenuated, but still visible.
[1]
[2]
[3]
[4]

Q.H. Wang et al., Nat. Nanotechnol. 7, 699 (2012).
M. Gehlmann et al., Scientific Reports 6 (2016).
A. Vollmer et al., J. Electron Spectrosc. 185, 55 (2012).
A. Belser et al., J. Phys. Chem. C 122, 15390 (2018).

60

P9

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Influence of structural defects on theenergy level alignment in planarpentacene-perfluoropentacene heterojunctions
Jan Hagenlocher1, Alexander Hinderhofer1, Satoshi Kera2, Frank Schreiber1
1
Institut für Angewandte Physik, Eberhard Karls Universität Tübingen, Germany
2
Institute for Molecular Science, Myodaiji, Okazaki, Japane-mail: jan.hagenlocher@uni-tuebingen.de

We studied the Energy Level Alignment in planar Pentacene-Perfluoropentacene
Heterostructures grown on a native silicon substrate using high-resolution Ultraviolet
Photoelectron Spectroscopy (UPS). The films were grown at different substrate temperatures tointroduce structural defects which were further studied analyzed by surface x-ray scattering
techniques [1]. We found a connection between the magnitude of the interface dipole and thesize of the crystallites within the film. We explain this behavior with the film quality dependentarising of gap states which are responsible for the number of transferred charges [2].

[1] K. Yonezawa et al., Adv. Mater. Interfaces 1.5, 1400004 (2014).
[2] M. Oehzelt et al., Nature Comm. 5, 4174 (2014).

61

P 10

Simulating the pump-probe photoemission process fromorganic semiconductors in real-timeSebastian Hammon, Stephan Kümmel
Department of Physics, University of Bayreuth, Germany
e-mail: sebastian.hammon@uni-bayreuth.de

Simulating the pump-probe photoemission process in real-time, we apply a first principles timedependent density functional theory (TDDFT) approach. Within this theoretical framework weare able to calculate (angle-resolved) photoemission directly as a time-dependent process.
Firstly, applying our pump-probe method to the one-electron hydrogen system, we are able toverify our TDDFT approach within this transparent test scenario. Secondly, following thissuccessful test, we present first angle-resolved photoemission spectroscopy (ARPES) results (cp.
Fig. 1) for the real-time pump-probe simulation of the organic benchmark molecule perylene3,4,9,10-tetracarboxylic dianhydride (PTCDA).

Fig. 1 ARPES intensity momentum map obtained from the real-time simulation of thepump-probe process for PTCDA: Photoemission was recorded after
a first pulse with an energy of 2.1 eV, followed by a second pulse
with an energy of 6.0 eV and a delay of 10 fs.

62

P 11

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Photoelectron spectroscopy of
F6TCNNQ-polycyclic hydrocarbon interfaces
Martin Hantusch, Daniel Waas, Florian Rückerl, Martin Knupfer
Leibniz Institute for Solid State and Materials Research, D-01171 Dresden, Germany
e-mail: m.hantusch@ifw-dresden.de

The doping of polycyclic hydrocarbons, e.g. pentacene, with hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ) offers the opportunity for new organic electrical devices [1].
While doping affects the bulk system, examining the physical processes at the interfaces oforganic semiconductors in more detail is also in the focus of recent research in order to enhance
the performance of organic electrical devices. Our work investigates the charge transfer acrossthese interfaces.
We present results for thin film systems consisting of pentacene or di-benz-pentacene (DBP) andF6TCNNQ, deposited in a multi-step process and analysed after each deposition step byphotoelectron spectroscopy. Significant changes are observed in the valence, the nitrogen and thecarbon core levels. The intensity ratio of the characteristic F6TCNNQ-C1s-peaks (286.3 eV;
287.2 eV), as shown in Figure 1, is varying with the layer thickness which indicates a reductionof the electron acceptor in the interface area. The subtraction of the pristine spectra of
F6TCNNQ and of the polycyclic hydrocarbon from the hetero-junction spectrum reveals twoclear peaks (285.3 eV; 286.5 eV) which correspond to F6TCNNQ--ions [2]. Hence, the changes
in the photoelectron spectra are directly correlated with the charge transfer processes across theinterface.

Fig. 1 C1s-core levels of F6TCNNQ/pentacene and F6TCNNQ/DBP systems withvarious deposition times (same rates) and an analysis of two similar systems.

[1] B. Lüssem et al., Nature Comm., 4, 2775 (2013).
[2] D. Waas et al., physica status solidi c, submitted (2018).

63

P 12

Charge transfer and molecular level alignment
on dielectric interlayers on metals
Philipp Hurdax1, Michael Hollerer1, Daniel Lüftner1, Thomas Ules1,
Sergey Soubatch2,3, F. Stefan Tautz2,3, Georg Koller1, Peter Puschnig1,
Martin Sterrer1, Michael G. Ramsey1
1
Institute of Physics, University of Graz, 8010 Graz, Austria
2Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
3
Jülich Aachen Research Alliance (JARA), Fundamentals of Future Information Technology,
52425 Jülich, Germany
e-mail: philipp.hurdax@uni-graz.at

It is becoming accepted that ultrathin dielectric layers on metals are not merely passive
decoupling layers, but can actively influence orbital energy level alignment and charge transfer
at interfaces. As such, they can be important in applications ranging from catalysis to organic
electronics. However, the details at the molecular level are still under debate. Here, we present acomprehensive analysis of the phenomenon of charge transfer promoted by a dielectric interlayer
with a comparative study of pentacene adsorbed on Ag(100) with and without an ultrathin MgO
interlayer. Using scanning tunneling microscopy and photoemission tomography supported bydensity functional theory we are able to unambiguously identify the orbitals involved andquantify the degree of charge transfer in both cases. Fractional charge transfer occurs forpentacene adsorbed on Ag(100), while the presence of the ultrathin MgO interlayer promotes
integer charge transfer with the LUMO transforming into a singly occupied (SOMO) and singly
unoccupied (SUMO) state separated by a large gap around the Fermi energy. We show that bycontrolling the work function of the dielectric layer we can control the number of charged
molecules in the monolayer.

[1] M. Hollerer et al., ACS Nano 11, 6252 (2017).

64

P 13

Schluchsee 2018 – ASOMEA-IXInterface dipole of thebulk-heterojunction of organic solar cell
Hiroyuki Ichikawa1, Itaru Osaka2, Hiroyuki Yoshida3
1Grad. School of Science and Engineering, Chiba Univ., Japan; 2Dept. of Applied Chemistry,
Hiroshima Univ., Japan; 3Grad.School of Engineering, Chiba Univ., Japane-mail: hi-ichikawa@chiba-u.jp

intensity (arb. units)

In order to improve the power conversion efficiency (PCE) of the organic solar cell (OSC), great
efforts have been made to reduce the energy loss and increase the open circuit voltage (VOC). For
this purpose, the energy of each step of the OSC process is indispensable. Although the energiesof the exciton and charge-transfer (CT) state has been precisely determined, the energy of theseparated free holes and electrons state (CS state) are only ambiguously evaluated using theultraviolet photoelectron spectroscopy (UPS) and optical gap, or the oxidation/reduction
potentials of individual materials. Further, the interface dipole between the donor (D) andacceptor (A) layers are often ignored. The recent OSC with low-energy loss shows small
difference in energy between the CT and CS states, even the CT states is lower than the CS
states. To explain the charge separation from the lower CT to higher CS states, the entropy gain
is proposed [1].
A
In this study, we demonstrated a procedure to determine the
C1sDenergy of the CS states and applied it to the bulkD+A
heterojunction of the low-energy loss OSC, PNOz4T and
Exp
PCBM [2]. At first, we precisely determined ionizationenergy (IE) and electron affinity (EA) of each materialusing ultraviolet photoelectron spectroscopy (UPS) and low
energy inverse photo-electron spectroscopy (LEIPS) [3],respectively. Then the interface dipole between the D and A
layers Δ was estimated from the shift of the core levels
using
X-ray
photoelectron
spectroscopy(XPS).
Unfortunately, the core level shift was not able to be
286
284
282
energy from EF (eV)directly determined because all the elements in the PCBM
molecule (C, N, O, H) are common in PNOz4T. We applied Fig. 1 Decomposed XPS spectrum
the classical least squares to the angle-resolved XPS data to of PNOz4T (D) and PCBM (A).
decompose the C1s spectra (Fig. 1) to determine Δ. Basedon the values of Δ, IE, and EA, we obtained the energy
level diagram (Fig. 2).
The energy of the CS state was found to be 1.33 eV which
is lower than that of the CT states, 1.52 eV [2]. As a result,
the transition from the CT state to the CS state can proceedwithout considering the entropy [1].

[1] T. Burke et al., Adv. Energy Mater. 5, 123 (2015).
[2] I. Osaka et al., Nat. Commun. 6, 10085 (2015).
[3] H. Yoshida, Chem. Phys. Lett. 539-540, 180 (2012).

Fig. 2 Energy level diagram.

65

P 14

Thermal stability of the surfaces oforganic single crystals under UHV
Masato Iwasawa1, Masahiro Sasaki1, Ryohei Tsuruta2,
Yasuo Nakayama2, Yoichi Yamada1
1
Institute of Applied Physics, University of Tsukuba, Japan2
Department of Pure and Applied Chemistry, Tokyo University of Science, Japane-mail: mstiwsw@gmail.com

The organic single crystals (OSCs) have been widely utilized due to its high crystallinity andresulting charge mobility. Although the electronic structure of the OSCs have been graduallyclarified, the surface/interface properties of OSCs that directly impact on the device performance
are yet to be provided. Recent reports have revealed that the electronic properties of OSCs can besignificantly affected by the microscopic surface features such as steps.
In order to obtain the more insight into the cleanliness and stability of the surface of OSCs,
especially that in UHV condition, we fabricated single crystals with well-known organic
semiconductors, such as Pentacene, Rubrene, Tetracene, Perylene, and TCNQ, and investigatedtheir surface under UHV condition.
The surfaces of the single crystals used in this work had inert and clean step-terrace structure at
RT in the air. The surfaces of Pentacene and Rubrene-SC were stable even in UHV at RT(Fig.1(a)). However, the surface molecules desorped from both terraces and step edges at
45 /UHV, resulting in the layer-by-layer removal.
By contrast, the surface structures of Tetracene, Perylene, and TCNQ-SC cannot be maintainedat UHV, as shown in Fig.2 (b). The surface flatness of these crystals were gradually lost under
UHV on account of the desorption and the cohesion. The surface roughness was more than 30
nm and original step-terrace structure was not observed after 24h under UHV. On the other hand,
the roughening of the surface of TCNQ-SC was suppressed at low temperature of -160 .
These findings indicate that the surface stability show no obvious relation with the molecularweight or the melting point of OSCs. Therefore, we have to pay particular attention to thesurface conditions when utilizing OSCs under vacuum.

Fig.1 AFM images of Pentacene-SC

Fig.2 AFM images of TCNQ-SC

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Level alignment prediction of
hybrid inorganic-organic systems:
Tetracene and pentacene on H/Si(111)
Svenja M. Janke1,2, Mariana Rossi2, Sergey Levchenko2,
Matthias Scheffler2, Volker Blum1
1
Mechanical Engineering & Materials Science, Duke University, Durham, USA
2
Theory Department, Fritz Haber Institute of the Max Planck Society, Berlin, Germany
e-mail: svenjamaria.janke@gmail.com

Hybrid organic inorganic systems allow to combine the properties of organic and inorganic
substances at the nanoscale and hence open up a wide area for construction of new materials
with tunable properties. The position of carrier levels and their alignment determine electronic
properties of semiconductor interfaces. In the present work, we address the fundamental question ofelectronic level alignment from first principles at the level of hybrid functionals within all electron, fullpotential density functional theory (FHI-aims [1]) for two paradigmatic organic-inorganic semiconductor
interfaces, the singlet fission materials tetracene and pentacene on H/Si(111). We investigate thestructure of either interface in the low-coverage and in the monolayer regimes and demonstratethat a large coincidence cell between the organic film and inorganic substrate, comprising up to~1200 atoms, is necessary to describe the correct level alignment quantitatively. We find that a
type-I heterojunction is formed in the low-coverage regime, while a type-II heterojunction ispredicted in the monolayer regime that allows a potential charge separation between organic andinorganic components.

Fig. 3 Schematic energy level alignment of the frontier orbitals of apentacene monolayer film (blue) on H/Si(111) (grey) calculated with HSE06 for aunit cell with ~1000 atoms. Electrons can transfer from the monolayer to the substrate whileholes remain on the monolayer, allowing a potential charge separation.
[1] V. Blum et al., Comp. Phys. Comm. 180, 2175, (2009).

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Organic radical films investigatedby X-ray-based spectroscopies
1

T. Junghöfer,1 M. B. Casu1
Institute of Physical and Theoretical Chemistry, University of Tübingen, Germany
e-mail: tobias.junghoefer@uni-tuebingen.de

Organic radicals are fascinating materials because of their unique properties, which make themsuitable for a variety of possible applications. Their synthesis may be challenging and big efforts
have focused on chemical stability. However, introducing a new material in electronics surely
requires chemically stable molecules but also stable thin films in view of their use in devices.
In this work we present the results obtained evaporating thin films of stable purely organic
radicals. The films were investigated by using a multi-technique approach. We have investigatedelectronic structure, paramagnetic character, and stability of the obtained films under ultra highvacuum (UHV) and ambient conditions, by X-ray photoelectron spectroscopy, X-ray absorption
spectroscopy, atomic force microscopy, and electron paramagnetic resonance spectroscopy [1-4].

[1]
[2]
[3]
[4]

S.-A. Savu et al., Chem. Eur. J. 19, 3445 (2013).
R. Kakavandi et al., ACS Appl. Mater. Interfaces 7, 1685 (2015).
F. Ciccullo et al., ACS Appl. Mater. Interfaces 8, 1805 (2016).
T. Junghöfer et al., in preparation.

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Iron-phthalocyanine on rutile:
Main interaction channel oxygen vacancies at the surfaces
Reimer Karstens, Axel Belser, Thomas Chassé, Heiko Peisert
Institute of Physical and Theoretical Chemistry, University of Tübingen, Germany
e-mail: nikolaus-reimer.karstens@uni-tuebingen.dePrevious results in the literature show different interaction strength for phthalocyanines on TiO2
(rutile) obviously depending on the crystal orientation, preparation conditions andphthalocyanine’s metal center. [1, 2]
We studied iron phthalocyanine (FePc) and iron hexadecafluoro-phthalocyanine (FePcF16) on therutile (100) and (110) crystal surfaces using photoemission and X-ray absorption spectroscopy(XAS). Almost no interaction was observed, if the rutile is prepared with few defects (few
sputtering and annealing cycles at moderate conditions) and the annealing takes place at anoxygen partial pressure of 1x10-6 mbar (especially the shape of the N1s PES spectra is similar to
TMPcs on non-interacting oxide surfaces [3]).
If some and especially the last annealing steps are done without oxygen, FePcF16 show strong
interaction involving the iron metal center and the nitrogen, which is clearly visible by acomponent at higher binding energy in the N1s photoelectron spectrum (Fig. 1).
We conclude that the interaction of investigated phthalocyanines is considerably influenced byoxygen vacancies at the rutile surface, which can be controlled by the preparation conditions.
FePcF16/TiO2(100)a)

norm. Intensity (arb. units)

norm. Intensity (arb. units)

prepared without O2

5.3 nm

3.1 nm

0.6 nm404

FePcF16/TiO2(100)

b)

N 1s

prepared with O2

N 1s

5.6 nm

0.6 nminterface component

0.3 nm

402

400

398

404

396

Binding energy (eV)

402

400
Binding energy (eV)398

Fig. 1 FePcF16 on rutile (100): N1s PES spectra of a) rutile prepared with few defects
and O2 while the annealing; measured with Eexc= 650 eV and b) rutile prepared with many defects
and no O2 while the last annealing; measured with Eexc=1486.6 eV.

[1] P. Palmgren et al., J. Phys. Chem. C 112, 5972 (2008).
[2] S. Sinha et al., J. Phys. Chem. C 121, 3365 (2017).
[3] M. Glaser et al., J. Phys. Chem. C 119, 27569 (2015).

69

396

P 18

Molecular topology and surface chemical bond:
Alternant vs. non-alternant aromatic molecules
Benedikt P. Klein,1 Nadine van der Heijden,2 Markus Franke,3 Stefan R. Kachel,1François C. Bocquet,3 Martin Schmid,1 Ralf Tonner,1 Ingmar Swart,2
Christian Kumpf,3 Reinhard J. Maurer,4 J. Michael Gottfried 1
1
Fachbereich Chemie, Philipps-Universität Marburg, Germany
2
Debye Institute for Nanomaterial Science, Utrecht University, The Netherlands
3Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, Germany
4
Dept. of Chem. and Centre for Scientific Computing, Univ. of Warwick, United Kingdom
e-mail: kleinbe@students.uni-marburg.de

In organic light-emitting diodes and related organic-electronic devices, molecular organic
semiconductors are typically contacted by metal electrodes. The resulting metal/organicinterfaces have a large impact on the performance of these devices, which makes theunderstanding of their chemical, electronic and geometric structure indispensable for the further
rational development of organic electronics. Accordingly, model metal/organic interfaces witharomatic molecules have been a major research topic during the past decade. Up to now, thefocus has been almost exclusively on aromatic systems with alternant topology such aspentacene, which have a uniform charge distribution and highly delocalized frontier orbitals. In
contrast, aromatic systems with non-alternant topology have non-uniform charge distributions,which can result in considerable in-plane dipole moments, and more localized frontier orbitals.
They also violate the Coulson-Rushbrooke pairing theorem and thus have shifted valence levels
compared to the isomers with alternant topology. In this contribution, we present the firstsystematic studies of a non-alternant aromatic molecule on the (111) surfaces of Ag and Cu. In
particular, we focus on naphthalene, which has as an alternant topology, and its non-alternant
counterpart azulene. On the basis of extensive NEXAFS, PES, TPD, nc-AFM, STM and NIXSW
studies, we show that the non-alternant topology results in much stronger interaction with metal
surfaces, especially in the case of Cu(111), and that the interaction is more localized.
Complementary periodic DFT calculations provide detailed insight into the surface chemicalbond and charge redistribution between surface and molecule. A major part of the localizedinteraction is the donation of electron density into the molecular LUMO. This leads in turn toconsiderable in-plane and out-of-plane deformations of the adsorbed non-alternant species, while
the alternant molecule remains largely undeformed.

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Evolution of TiOPc-films on Ag(111):
Bilayer stacking enables ultra-smooth layers
Michael Kothe, Felix Widdascheck, Gregor Witte
Department of Physics, Philipps-Universität Marburg, Germany
e-mail: michael.kothe@physik.uni-marburg.de

The chemical and thermal robustness of titanyl-phthalocyanine (TiOPc) in combination with its
high optical absorption favours its application as photoconductor or chromophore for lightharvesting in organic photovoltaic applications [1]. Beside such device application there is alarge interest in the controlled fabrication of smooth molecular spacer layers of controlled
thickness in order to prepare molecular hetero-structures. While many -conjugated materials
form highly ordered mono- and bilayer films on metallic (single crystalline) substrates, the films
exhibit a notable roughness upon increasing film thickness [2]. Here, we demonstrate that TiOPc
forms extremely smooth films on Ag(111), not only in the mono- and bilayer regime [3-5] but
also for thicker films exceeding a thickness of 10nm. Combining various analytical techniques
including atomic force and scanning tunnelling microscopy (AFM, STM), with X-ray
photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure spectroscopy(NEXAFS) and X-ray diffraction (XRD), we show that for substrate temperatures below 450 K
TiOPc forms molecularly smooth films with a rather small overall film roughness. The detailed
analysis shows that the films are stabilized by the characteristic molecular bilayers ofalternatingly (up and down) oriented titanyl units. Finally, we show that even the thick films are
epitaxially oriented with respect to the azimuth direction of the supporting Ag(111) surface.

Fig. 1 a) Schematic drawing of the TiOPc multilayer growth mode on Ag(111).
b) NEXAFS data of 10nm TiOPc on Ag(111)
[1]
[2]
[3]
[4]
[5]

K. Xiao et al., Appl. Phys. A 77, 367 (2003).
J. Krug et al., Phys. Rev. Lett. 90, 016104 (2003)
I. Kröger et al., New J. Phys. 18, 113022 (2016).
L. Fernandez et al., J. Phys. Chem. C 121, 1608 (2017).
L. Fernandez et al., Phys. Chem. Chem. Phys. 19, 2495 (2017).

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Two-dimensional growth of dendritic islands:
NTCDA on Cu(001) studied in real timeJanina Felter, Markus Franke, Jana Wolters, Caroline Henneke, Christian Kumpf
Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
Jülich-Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology
e-mail: c.kumpf@fz-juelich.de

Real time growth studies of thin films are very rare in the literature, which is quite surprisingsince they enable an otherwise unrivalled level of control in the growth process of (e.g.) organic
thin films and adsorbate systems. In this context, we report a LEEM-based growth study of
NTCDA on Cu(001). Figure 1 summarizes the very surprising growth results for this system:
In bright-field LEEM, no contrast but only a decreasing overall intensity is found with increasing
coverage (Fig. 1a), while at the same time LEED clearly indicates an ordered structure already at~0.3 ML (b). Dark-field LEEM, however, shows a very clear contrast between two rotational
domains at 0.4 ML. Most remarkably, it appears as if the domains were occupying the entire
surface already at the small coverage of 0.4 ML and were not growing in size upon further
deposition (Fig. 1c).
We explain this surprising finding with fractal structures, formed due to a strongly preferred onedimensional growth mode at small coverages. This growth mode leads to a long-range ordered
network of thin molecular chains spanning over the entire surface already at small coverages.
Later in the growth process, voids in this network structure are incrementally filled. Thisdendritic growth model is supported by energetic arguments based on pair-potential calculations
that can explain the preferred growth of one-dimensional structures.

Fig. 1 NTCDA/Cu(001): (a) BF-LEEM, (b) LEED and (c) DF-LEEM images (false-color images of the tworotational domains) at different coverages. While in BF-LEEM no contrast is visible in the entire sub-monolayer
regime, the LEED images indicate a well ordered structure arising at ~0.3ML. DF-LEEM also shows the formationof ordered domains covering the entire surface already at 0.4 ML coverage.

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Steering the growth of multiple ordered hetero-molecularphases by utilizing intermolecular repulsion
Caroline Henneke, Daniel Schwarz, Janina Felter, F. Stefan Tautz, Christian Kumpf
Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
Jülich-Aachen Research Alliance (JARA)-Fundamentals of Future Information Technology
e-mail: c.kumpf@fz-juelich.de

In characterizing interfaces between organic semiconductors and metals, the formation ofmolecular blends (i.e., heteromolecular layers containing two types of molecules, usually charge
donors und acceptors) is of great interest. In this context, we report a novel thermodynamic
phase diagram found for molecular blends formed by PTCDA and CuPc in submonolayers on
Ag(111) [1]. Our comprehensive LEEM study identifies five crystalline phases with different
stoichiometries. Large eutectic regions exist in the phase diagram, caused by the opposite
intermolecular interaction of its components – repulsive for CuPc, attractive for PTCDA. We
find that the repulsive species forms a two-dimensional lattice gas, the density of which
determines the stability of all other crystalline phases. The existence of critical gas-phasedensities is the basis for understanding the constant-volume phase diagram. We anticipate thegeneral validity of this type of phase diagram for binary systems containing 2D gas phases, andemphasize that the density of the gas phase allows engineering of the interface structure.

Fig. 1 (a) Bright-field LEEM images recorded during a binary deposition experiment: Initially, 0.17 ML PTCDA
form compact islands (upper left image). The following LEEM images were recorded during subsequent depositionof 0.7 ML CuPc. The PTCDA islands (green) are sequentially transformed into MBW (yellow), M121 (red) and
MZZ islands (blue), according to the stoichiometry sequence. (b) Corresponding phase diagram for thesubmonolayer regime: Data points and colored areas mark the regimes of pure and eutectic phases as obtained fromexperiment and thermodynamic model, respectively. The path of the experiment shown in (a) is indicated by adotted black arrow. The model is based on more than 20 LEEM experiments with different initial coverages. Abbr.:
P = PTCDA, C = CuPc; Sequence and stoichiometry of the phases: PTCDA (P) – MBW (P2C) – M121 (PC) –MZZ (PC2) – CuPc (C).
[1] C. Henneke et al., Nature Materials 16, 628 (2017)

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Time-resolved spectroscopy ofelectron transfer processes at metal/organic interfaces
Alexander Lerch1, Klaus Stallberg1, Jonas Zimmermann1,
Frederik Schiller2, Ulrich Höfer1
1
Department of Physics, Philipps-Universität Marburg, Germany
2
Centro de Física de Materiales (CSIC-UPV-EHU) andMaterials Physics Center (MPC), 20018 San Sebastián, Spaine-mail: alexander.lerch@physik.uni-marburg.de

Interfaces between ordered organic thin films on single-crystal metals constitute well-definedmodel systems for electrical contacts of organic semiconductor devices. Time-resolved twophoton photoemission (2PPE), a method that combines femtosecond laser pump-probe
techniques with photoelectron spectroscopy, can provide detailed microscopic information about
electron transfer processes at such model contacts. Specific emphasis of this talk will be on therole of interface-specific electronic sates for the charge transfer [1-8].
Experiments with organic bilayer systems, such as CuPc/ PTCDA/Ag(111) or
PCTDA/TiOPc/Ag(111), unambiguously show that normally unoccupied interface states (IS)can be optically excited from the metal side as well as from the LUMO of the second and eventhird organic monolayer. Transfer times of electrons from the LUMO into the IS and from the IS
to the metal range from 20 to 100 fs. These values indicate that the IS wave function has goodoverlap with both, the delocalized electron system of the metal and the relevant molecularorbitals. Interface states located between the Fermi level of the metal and the molecular LUMOs
are thus able to mediate the charge transfer. The results show that not only the molecular levelalignment at the interface, but also the properties of interface-specific electronic states play animportant role for the efficiency of organic/metal contacts.

[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]

C.H. Schwalb et al., Phys. Rev. Lett. 101, 146801 (2008).
M. Marks et al., Phys. Rev. B 84, 081301 (2011).
M.C.E. Galbraith et al., J. Phys. Chem. Lett. 5, 50 (2014).
M. Marks et al., J. Electr. Spectrosc. 195, 263 (2014).
S.S. Tsirkin et al., Phys. Rev. B 92, 235434 (2015).
P. Jakob et al., Phys. Rev. B 94, 125436 (2016).
N. Armbrust et al., Sci. Rep. 7, 46561 (2017).
A. Lerch et al., J. Phys. Chem. C 121, 25353 (2017).

Work performed in the framework of the Collaborative Research Centre "Structure and Dynamics of InternalInterfaces" (SFB 1083).

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Energetic degradation of organometal halide perovskite
films upon oxygen, water and illumination
Xianjie Liu1, QinyeBao1,2, Jianming Yang2, Zhongcheng Yuan1, Mats Fahlman1
1
IFM, Linköping University SE-58183 Linköping, Sweden
2
Key Laboratory of Polar Materials and Devices, East China Normal University, 200241,
Shanghai, P.R. Chinae-mail: xjliu@ifm.liu.se

Due to their large absorption coefficients, tunable band gaps, long carrier diffusion lengths,
ambipolar charge transports and low defect concentrations, hybrid organic-inorganic perovskite
semiconductors have attracted tremendous attention upon the perspective applications on
optoelectronics [1]. Organometal halide perovskites, as a promising photovoltaics materials,
have reached a power conversion efficiency over 22% [2] surpassing that of dye-sensitized andorganic photovoltaics within a very short timescale. However, the long-term stability remains amajor challenge for their commercialization. Understanding the influence from water, oxygen,light illumination and heating upon organometal halide perovskites themselves will besignificantly helpful to shed light on their degradation mechanism and to realize a better
performance of the corresponding photovoltaic devices.
Here, we present our recent spectroscopic studies of energetic degradation of organometal halide
perovskite films by in-situ oxygen, water, and light exposure in a controlled manner [3-4]. We
found that oxygen molecules induce an upwards shift of the vacuum level of the perovskite films
from formation of an oxygen-induced surface dipole. However, water vapor downshifts thevacuum level significantly, meanwhile, edge of the valence band maximum increases
simultaneously, as results, the ionization potential of the perovskite films is kept unchanged.
On light illumination on cationic compositional engineered organometal perovskites, i.e.,
MAPb(I0.83Br0.17)3, FA0.83MA0.17Pb(I0.83Br0.17)3 and Cs0.1(FA0.83MA0.17)0.9Pb(I0.83Br0.17)3, allundergo severe degradation under white light illumination in ultrahigh vacuum (UHV)
environment, but the degradation rate in the mixed cation perovskites is significantly lower [4].
From the change of their atomic contents and vibration mode with illumination, we attribute thisto the defect-induced trap states that trigger the strong coupling between the photo-excited
carriers and the crystal lattice. Our results support UHV environment remarkably accelerates thedegradation from illumination, and the mixed cations can suppress the photoinduced
degradation. Moreover, the applied UHV environment could be an accelerated test method toestimate the photostability of the perovskites.

[1]
[2]
[3]
[4]

S.D. Stranks et al., Science, 342, 341 (2013).
W.S. Yang et al., Science, 356, 1376 (2017).
J. Yang et al., ACS Appl. Mater. Interfaces, 10, 16225 (2018).
J. Yang et al., Advanced Optical Materials, (in press).

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Investigating the electronic structure andchemical interactions in doped poly(3-hexylthiophene)
with the Lewis acid dopant tris(pentafluorophenyl)borane
Ahmed E. Mansour1, Dominique Lungwitz1, Andreas Opitz1, Norbert Koch1,21Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
2
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
e-mail: amansour@physik.hu-berlin.deTris(pentafluorophenyl)-borane (BCF) has been introduced as a strong Lewis acid dopant fororganic semiconductors (OSC). The doping mechanism is proposed to be due to the formation
Lewis acid-base adducts, in which lone pair electrons transfer from the OSC to the boron atom of
the dopant.[1] More recently, BCF has been demonstrated as a p-dopant to P3HT resulting in
improved electrical conductivity which has been ascribed to integer charge transfer. [2]In this contribution, we investigate the electronic and chemical changes in BCF doped P3HT
using photoemission spectroscopy, aiming to improve the current understanding of theunderlying mechanism of Lewis acid doping of OSC. Ultraviolet photoemission spectroscopy(UPS) is used to probe the changes to the valence band of P3HT upon doping and monitor thechanges in the work function of the film. As a result of p-doping, the work function of P3HT
increases by ~0.7 eV as the occupied states shift towards the Fermi level. We employ X-ray
photoelectron spectroscopy (XPS) to investigate the core levels of P3HT and monitor the dopant
concentration and chemical changes resulting from interacting with BCF. Deconvolution of the S
2p core levels (Fig. 1) shows an increase of sulfur in a positively charged environment ascompared to neutral sulfur. However, this increase is larger than the measured dopant ratio, andscales by different factors with dopant ratio pointing towards a change in the delocalization
length of the polaron as the amount of dopant in the film changes. In addition, we provide an
overall picture of the changes in the energy of both valence and core levels with doping.

Fig. 1 S 2p core level measured from XPS[1] G.C. Welch et al., J. Am. Chem. Soc. 131, 10802 (2009)[2] P. Pingel et al., Adv. Electron. Mater. 2, 1600204 (2016)

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Schluchsee 2018 – ASOMEA-IX

Orbital tomography of a strong
hole-vibration coupling molecule
Matthias Meissner1, Takuma Yamaguchi1, Takahiro Ueba1, Naoki Komiya2,
Christian Metzger3, Achim Schöll3, Friedrich Reinert3, Kaori Niki2, Satoshi Kera1
1
Institute for Molecular Science, Okazaki, Japan
2
Graduate School of Science, Chiba University, Chiba, Japan
3
Experimentelle Physik VII, Julius-Maximilians-Universität Würzburg, Germany
e-mail: meissner@ims.ac.jp

Photoemission experiments on organic semiconductors have been carried out for many years
now. Yet, improvements in experimental technologies and simulation techniques open up new
possibilities to study photoemission processes at the interface between organic molecules andsubstrates that were hardly accessible before.
Here, we present the experimental and computational characterization of the perfluoro-pentacene(PFP)/Ag(111) interface, using the k-space resolving PEEM (photoemission electron
microscope) of the NanoESCA beamline at Elettra, Italy, in combination with a structuralcharacterization by low-energy electron diffraction (LEED) and photoemission simulations
based on an independent atomic center approximation for final state [1]. This allows us todiscuss the effects of the strong hole-vibration coupling of PFP [2] on the photoemission maps
and electronic interaction within molecular monolayers and bilayers, respectively.

Fig. 1 Comparison between the photoemission maps of a PFP monolayer on Ag(111), as obtained experimentally(left) at 76 K with p-polarized photons (30 eV) and by simulation (right).

[1] N. Komiya et al., J. Electron Spectrosc. Relat. Phenom. 220, 21 (2017).
[2] S. Kera et al., J. Phys. Chem. C 117, 22428 (2013).

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Orbital imaging of the non-planar molecules
C. Metzger1, M. Graus1, M. Grimm1, K. Baumgärtner1, G. Zamborlini2, V. Feyer2,
M. Schwendt3, D. Lüftner3, P. Puschnig3, A. Schöll1, F. Reinert1
1
Experimentelle Physik VII, Julius-Maximilians-Universität Würzburg, Germany
2Peter Grünberg Institut, Forschungszentrum Jülich, Germany
3Institut für Physik, Karl-Franzens-Universität Graz, Austria
e-mail: christian.metzger@physik.uni-wuerzburg.de

We present experimental and simulated data on the photoemission intensity ofbuckminsterfullerene C60 within an evaporated molecular thin film utilizing ARPES
measurements combined with the theoretical calculation of the full interface and simulations of
the entire photoemission process. The experimental data was acquired by a photoemission
electron microscope in Fourier-space imaging mode (kPEEM) which enables the efficient
detection of photoelectrons emitted into the entire hemisphere above the sample [1]. The
symmetry of the recorded photoemission intensity demonstrates the molecules adsorb with asingle alignment and do not rotate on the silver substrate at room temperature. We perform
simulations of the photoemission matrix elements within a framework of independent atomic
centers (IAC), where the final states is assembled from composite contributions of the individual
atoms within the molecule [2],[3]. The comparison between theory and experiment enables thedetermination of the adsorption geometry and orientation of the C60 molecules in agreement with
DFT-based structure relaxation of the full interface. Additionally, we characterize thehybridization of the partially occupied LUMO, whose degeneracy is lifted due to symmetry
breaking upon adsorption.

Fig. 1 Experimental (a) and simulated (b) angular photoemission intensity distribution fromthe degenerate HOMO of buckminsterfullerene C60 at a photon energy of 40 eV.
Note that the intensity is cut beyond the detector plate in the experiment.

[1] C. Tusche et al., Ultramic. 159, 520-529 (2015).
[2] W.D. Grobman, PRB 17, 4573-4585 (1978).
[3] S. Hasegawa et al., PRB 48, 2596-2600 (1993).

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Exciton binding energy of organic materials:
Valence vs. core excitation
Andreas Opitz1, Paul Beyer1, Raphael Schlesinger1, Konstantin Lion1,
Caterina Cocchi1,2, Claudia Draxl1,2, Norbert Koch1,2,3
1
Institut für Physik, Humboldt-Universität zu Berlin, Germany
2
IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
3Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
e-mail: Andreas.Opitz@hu-berlin.de

Organic semiconductors are well known as materials with high exciton binding energy (EBE).
This energy can be considered as the difference between the electronic gap (sometimes referred
to as charge transport gap) and the excitation energy [1]. In recent years, substantial efforts havebeen made to determine the EBE of valence excitations and to relate it to fundamental processes
in devices, particularly the exciton dissociation in photovoltaic cells [2]. Core excitations, inturn, are widely used for fine structure spectroscopy of organic materials [3] and more recently
also from ab-initio theory perspective [4].
In this contribution, the EBE is investigated for pristine organic semiconductors with valence(HOMO-LUMO transition) and core excitations (C1s-LUMO transition). We compare thesetransition energies determined from absorption related measurements with the transport gaps
obtained from measurements by direct and inverse photoelectron spectroscopy. The experimental
results are compared to first-principles calculations of the x-ray absorption spectra through thesolution of the Bethe-Salpeter equation, including a relativistic treatment of the core states [5].
While the EBEs measured for valence excitations of α-sexithiophene and diindenoperylene are in
the range of several hundred meV, the EBEs for core excitations are higher than one eV andtherefore significantly higher than the value for valence excitations. This comparison shows that
the EBE for core excitations is strongly increased and related to the core-hole localization andthe poor screening of the electron-hole interaction through intermediate charges as also shown by
theoretical investigations of comparable molecular materials [4,6].

[1]
[2]
[3]
[4]
[5]
[6]

J.-L. Bredas, Mater. Horiz. 1, 17 (2014).
T.M. Clarke, J. R. Durrant, Chem. Rev. 110, 6736 (2010).
J. Stöhr, D. Outka, Phys. Rev. B 36, 7891 (1987).
C. Cocchi, C. Draxl, Phys. Rev. B 92, 205105 (2015).
C. Vorwerk et al., Phys. Rev. B 95, 155121 (2017).
C. Cocchi et al., J. Chem. Phys. 145, 234701 (2016).

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Influence of water, oxygen, and air exposure on theelectronic structure of methyl ammonium lead mixed iodidechloride CH3NH3PbI3-xClx perovskite films
Maryline Ralaiarisoa1,2, Ingo Salzmann3, Feng-Shuo Zu1,2, Nobert Koch1,2Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
2
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
3
Department of Physics, Department of Chemistry & Biochemistry, Concordia University,
Montreal, Quebec, Canadae-mail: ralaiarr@physik.hu-berlin.de1

During the last few years the class of organic-inorganic perovskite materials has attracted muchattention from the photovoltaic community, particularly due to their application in highefficiency solar cells. However, the rapid progresses in terms of attainable high efficiencies withthese materials contrast with stability and reproducibility issues that still represent a serious
obstacle for their reliable long-term application. One central aspect related to these stability
issues is the effect of environmental conditions that can affect the properties of the perovskite.
To gain a better understanding of the processes underlying the effect of environmental
conditions, we investigated the surface electronic properties of solution-processed CH3NH3PbI3xClx perovskite thin films upon exposure to water, oxygen, and air – as experienced during
typical device fabrication and operation conditions.
By means of photoelectron spectroscopy (PES), we characterized perovskite films that were kept
in inert-gas (nitrogen) atmosphere of a glove-box or UHV and that exhibit a pronounced n-typesurface character mostly due to Pb-related defects [1], where the Fermi-level is closer to the
conduction band edge than to the valence band edge. Upon exposure to water vapor, thepronounced n-type surface character was accentuated. This change is mostly reversible after mild
heating or drying in UHV. Importantly, a water partial pressure as low as 10-6 mbar, as
encountered in inert-gas glove boxes and in high vacuum, already decreases the work function,
likely due to physisorbed water. Pure oxygen exposure leads to a shift of the Fermi-level towards
a mid-gap position, i.e., the surface became significantly less n-type, while the ionization energy(IE) remains unchanged. Comparably, the exposure to ambient air results in a shift of the Fermilevel towards mid-gap position by 0.6 eV, which implies the prevailing effect of oxygen uponthat of water in air. Such variations of the electronic structure of perovskite film surfaces willaffect the energy-level alignment at the subsequently formed interface between the perovskite
and typical charge transport materials on top.

[1] F. Zu et al., Adv. Opt. Mater. 5, 1700139 (2017).

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Monitoring of atomic layer deposition bysynchrotron-based ambient pressure XPS:
Towards millisecond time resolution
F. Rehman1, P. Shayesteh1, A. Troian1, G. D’Acunto1, S.Yngman1,
E. Kokkonen2, J. Knudsen1,2, S. Urpelainen2, F. Rochet3, F. Bournel3,
J.-J. Gallet3, R. Timm1, J. Schnadt1,2
1
Department of Physics, Lund University, Lund, Sweden
2
MAX IV Laboratory, Lund University, Lund, Sweden
3
LPCMR, Sorbonne Université, Paris, France
e-mail: foqia.rehman@sljus.lu.se

Atomic layer deposition (ALD) is a thin film deposition technique for depositing uniform andconformal layers on complex three-dimensional topographies. ALD is highly used in different
fields of technology, e.g. in microelectronics for metal-oxide semiconductor field effecttransistors, in the formation of catalyst materials and in solar cell technology. The understandingof the atomic and molecular surface processes underlying the ALD growth are, however, farfrom complete, which implies difficulties in further advancing the technology. A thoroughinvestigation for the identification and role of surface species, surfaces defects, impurities andvapour phase reactions is therefore very much needed [1].
Here we have applied ambient pressure x-ray photoelectron spectroscopy (APXPS) to study the
ALD growth of metal oxides on the clean native oxide-covered surfaces with different time
resolution. APXPS has the advantage that it can be carried out during thin film growth, i.e. underoperando conditions. Our investigation focuses on the dynamic nature of the ALD process, and
it is for the first time that APXPS has been applied to this subject with millisecond time
resolution. This is illustrated in Fig. 1, which shows APXP spectra taken during the ALD of
HfO2 on an InAs(100) surface at different time resolution. It is possible to in detail follow theevolution the core levels during ALD.

Fig. 1 (a) As 3d spectra taken during the exposure of a native oxide-covered InAs(100) surface
during exposure to TDMAT at 10-2 mbar. In total 1200 spectra were taken in around 70 s.
(b) Hf 4f spectra taken in the same kind of experiment, measured at 0.07 Hz frequency.
[1] F. Zaera, Coord. Chem. Rev. 257, 3177 (2013).

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Development of angle-resolved low energy
inverse photoelectron spectroscopy apparatus
Haruki Sato1, Yuki Kashimoto1, Satoshi Ideta1, Hiroyuki Yoshida2,3
Graduate School of Science and Engineering, Chiba-University, Japan
2
Graduate School of Engineering, Chiba-University, Japan3
Molecular Chirality Research Center, Chiba-University, Japane-mail: h.sato@chiba-u.jp

1

Band dispersions of the occupied and unoccupied states of metals and semiconductors areindispensable information for understanding the charge transport mechanism of the holes andelectrons, respectively. The angle-resolved photoelectron spectroscopy is frequently used as astandard technique for the occupied states. On the other hand, the unoccupied states of metals
and inorganic semiconductors has been reported by angle-resolved inverse photoelectron
spectroscopy (ARIPES).1 However, the band dispersion of the unoccupied states of the organic
semiconductors has not been observed owing to sample damage due to the electron
bombardment and the low energy resolution of 0.5 eV comparable to the bandwidth of molecularsolids.
In 2012, we developed low energy inverse photoelectron spectroscopy(LEIPS) making it possible to measure the unoccupied states oforganic semiconductors without damaging the sample while
maintaining high resolution.2 In this study, we have developed theangle-resolved LEIPS apparatus aiming at the measurements of theband dispersion of the unoccupied states of the organic
semiconductors. However, to focus the low energy electron beam withkinetic energy between 2 and 5 eV was difficult. To overcome thisproblem, we developed an optimized electron source and thoroughly
shielded the stray magnetic and electric fields which enabled us tomake the angle-resolved measurement.
Fig. 1 shows the spectra of the unoccupied states of graphite measured
by this apparatus. The image potential state was observed at the energy
between 3 and 4 eV. The peak energy shifted as the angle of incident
electron changed. The relation is consistent with the free-electron
nature of the image potential state and the effective mass is calculated
to be 0.99 ± 0.10 excellent agreement with the previous value
measured by two-photon photoelectron spectroscopy.3

Fig.1 AR-LEIPS spectraof graphite surface

[1]
[2]
[3]
[4]

I. Schäfer et al., Phys. Rev. B 35, 7663 (1987).
H. Yoshida, Chem. Phys. Lett. 539-540, 180 (2012).
H. Yoshida, J. Electron Spectrosc. Relat. Phenom. 204, 116 (2015).
K.Takahashi et al, Phys.Rev. B 85, 075325 (2012).

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Importance of homogeneous substrates
for ionization potential determination by
ultraviolet photoelectron spectroscopy
Thorsten Schultz1, Patrick Amsalem1, Naresh Kotadiya2, Thomas Lenz2,
Paul W.M. Blom2, Norbert Koch1
1
Department of Physics, Humboldt-Universität zu Berlin, Germany
2

Max Planck Institute for Polymer Research, Mainz, Germany

e-mail: tschultz@physik.hu-berlin.de

Ultraviolet photoemission spectroscopy (UPS) is probably the most widely used technique
nowadays to determine the ionization energy (IE) of materials, especially for newly synthesizedmolecules. Usually these are evaporated onto a substrate and then measured by UPS. For
homogeneous substrates the determination of IE from the measured UPS data is straight forward.
However, if the used substrate is heterogeneous (intentionally or unintentionally) the
conventional method to determine IE yields wrong results and a more elaborated data evaluationis necessary. In an earlier work we demonstrated the effect of a heterogeneous surface on thework function determination by UPS [1]. In this work we now demonstrate the pitfalls of using
heterogeneous substrates to determine the IE of molecules by means of well-controlled model
systems and show how a more in depth data analysis can still yield correct results.

[1] T. Schultz et al., Adv. Mater. Interfaces 4, 1700324 (2017).

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Photoemission tomography for
π-extended peri-xanthenoxanthene on Cu(111)
M. Schwendt1, P. Puschnig1, D. Lüftner1, T. Miletic2, D. Bonifazi2,
G. Di Santo3, L. Petaccia3
1
Institut für Physik, Karl-Franzens-Universität Graz, Austria
2
School of Chemistry, Cardiff University, Park Place, CF10 3AT, Cardiff, UK
3
ELETTRA - Sincrotrone Trieste, S.S. 14, AREA Science Park 34149 Basovizza, Trieste ITALY
e-mail: mathias.schwendt@uni-graz.at

Organic molecules on metal surfaces often form ordered overlayer structures that are ideallysuited for angle-resolved ultraviolet photoelectron spectroscopy (ARUPS) studies. On thetheoretical side much information on these systems can be gained by assuming a plane wave forthe final state and modelling the initial state within density functional theory (DFT). Thisapproach is called Photoemission Tomography, and here we report a new application of thesemethod for a π-extended peri-xanthenoxanthene (PXX) derivative adsorbed on Cu(111).
The adsorption geometry is determined via DFT calculations and subsequently used for the
calculation of momentum maps within the plane wave approximation for the final state. The
results of this simulation are compared to experiment. This allows us to assign molecular orbitals
to the observed emission features (see Fig. 1 for an example) and to study the charge transfer
between the molecule and the substrate.

Fig. 1 Experimental momentum map (left) compared to simulated HOMO momentum map (right).

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Schluchsee 2018 – ASOMEA-IX"Shallow states" of organic films observed byhν-dependent high-sensitivity photoemission
Kohei Shimizu1, Yuki Yamaguchi1, Junki Yamazaki1, Tomoya Sato1,
Kinjo Hiroumi1, Hisao Ishii1,2,3
1
Graduate School of Science and Engineering, Chiba University, Japan
2
Center for Frontier Science, Chiba University, Japan3
Molecular Chirality Research Center, Chiba University, Japane-mail: acfa2458@chiba-u.jp

In organic electronics, gap states as well as HOMO and LUMO have considerable impact on theperformance of devices. Therefore, direct and precise measurement of gap states is integral forfurther understanding of device physics. For that purpose, we have developed a new variation ofultraviolet photoemission spectroscopy (UPS), hν-dependent high-sensitivity UPS (hν-HS-UPS)[1-4]. In this method, a series of UPS measurements with various incident photon energies hν areperformed. Then, the spectra are combined by overlapping spectral parts with similar line shapes
between adjacent hν, which removes the effect of photoionization cross section. In the case of
UPS with a single hν, a wide dynamic range and a strict suppression of ghost signals are required
to measure small DOS precisely. In contrast, our method only requires a dynamic range of a twoorder magnitude for connecting the adjacent spectra and thus the ghost signals can be excluded.
We have applied this method to various organic materials including small molecules andpolymers.
By using this technique, not only we successfully acquired a wide range of DOS [1,2] but also
we frequently observed “shallow states” above the Fermi level, indicating that excess electrons
are in the organic film. The origins of excess electrons can be classified into three types. i)
excess electrons are in localized states, so-called trap states. We observed trap states extended tojust 2.98 eV below the vacuum level in an alkane (C44H90) film. ii) excess electrons are in
LUMO, forming anions. A film of Alq3 with positive polarization charge on the film surface wasfound to accumulate anions at the surface, hence anion states were clearly observed [3]. This
result proposes hν-HS-UPS as a novel method to observe LUMO and carrier states. iii) excess
electrons are in LUMO under the attractive potential of holes, forming excitons. In the case of
CBP, a shallow peak was observed at the energy where the triplet exciton is expected. The
ability to observe DOS of excitonic states will help the understanding on the charge transfer
process in optoelectronic devices.
In conclusion, hν-HS-UPS succeeded to detect various type of shallow states as mentioned
above. The detailed information of these shallow states would facilitate the understanding on thephysics of organic devices.

[1]
[2]
[3]
[4]

T. Sato et al., Appl. Phys. Express 10, 011602 (2017).
T. Sato et al., Appl. Phys. Lett. 110, 111102 (2017).
H. Kinjo et al., Appl. Phys. Express 9, 021601 (2016).
K. Shimizu et al., MRS Advances 2, 2261 (2017).

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Exciton dynamics inpentacene-perfluoropentacene heterostructures
Vipilan Sivanesan1, Frank Schreiber2, Katharina Broch2, Petra Tegeder1
1
Physikalisch-Chemisches Institut, Universität Heidelberg, Germany
2
Institut für Angewandte Physik, Universität Tübingen, Germany
e-mail: vipilan.sivanesan@uni-heidelberg.de

Understanding the ultrafast electronically excited state dynamics in organic semiconductors after
optical excitation is crucial for the optimization of organic optoelectronic devices. Moreover, theknowledge of the morphology and energetics at donor-acceptor interfaces is important for
efficient charge separation in organic solar cells [1, 2]. Thereby, charge transfer (CT) states playa decisive role. To analyse the ultrafast processes at the interface more precisely, both welldefined structures of the samples and a very high time resolution in the experiment are required.
In this work we investigated thin films of pentacene (PEN), perfluoropentacene (PFP), andvarious heterostructures of PEN and PFP by means of femtosecond time-resolved second
harmonic generation (TR-SHG). For the donor/acceptor configurations, depending on themolecular orientations at the interface and the excitation energies, the dynamics of chargetransfer states were investigated.

Fig. 1 Schematics of TR-SHG at PEN/PFP heterostructure.

[1] K. Broch et al., Phys. Status Solidi RRL, 1700064 (2017)[1] A. Rinn et al., ACS Appl. Mater. Interfaces, 9, 42020−42028 (2017)

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Dependence of the adsorption height ofgraphenelike adsorbates on their dimensionality
S. Weiß1, D. Gerbert2, A. Stein2, A. K. Schenk3, X. Yang1, C. Brülke4,
R. Kremring4, S. Feldmann2, F. C. Bocquet1, M. Gille5, S. Hecht5,
M. Sokolowski4, P. Tegeder2, S. Soubatch1, and F. S. Tautz1
1
Forschungszentrum Jülich, Jülich, Germany
2
Heidelberg University, Heidelberg, Germany
3
La Trobe University, La Trobe, Australia
4
University of Bonn, Bonn, Germany
5
Humboldt University of Berlin, Berlin, Germany
e-mail: s.subach@fz-juelich.deComparing the adsorption heights of various graphene nanoribbons on Cu(111) and Au(111)
surfaces to those of graphene and π-conjugated planar organic molecules using the x-ray
standing waves technique, we observe that two-dimensional graphene adsorbs much further
away from the surface than both one-dimensional graphene nanoribbons and π-conjugated planarmolecules—which represent zero-dimensional graphene flakes. We show that this is a directconsequence of the adsorbates’ dimensionality [1]. Our results provide insights into the interplayof Pauli repulsion, pushback effect, and chemical interaction for graphenelike adsorbates of any
dimensionality on metal surfaces.

Fig. 1 Charge redistributions at the nanoribbon/metal interface. (a) Schematic illustration of the spill-out charge
redistribution (blue arrows) for adsorption of planar molecules and graphene nanoribbons. (b) Schematic illustrationof the annealing-induced change of the (3,1)-GNR/Cu(111) geometry.

[1] S. Weiß et al., Phys. Rev. B, 98, 075410 (2018).

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Nanoscale engineering with molecules at surfaces
N. Friedrich1,2, Matthew F. B. Green1,2, Philipp Leinen1,2, Taner Esat1,2,
Christian Wagner1,2, Ruslan Temirov1,2, F. Stefan Tautz1,2
1Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, 52425 Jülich, Germany
2
Jülich Aachen Research Alliance (JARA), Fundamental of Future Information Technology,
52425 Jülich, Germany
e-mail: s.tautz@fz-juelich.deThe study of molecular adsorption at surfaces has long been a focus of surface science. With
increasing molecular complexity, new properties and phenomena emerge, and the design offunctional single-molecule devices becomes possible. We present recent examples from ourresearch that illustrate the intriguing physics of complex molecules at surfaces.
First, we demonstrate the emergence of a topologically protected quantum critical point in aspin-carrying molecular structure [1, 2]. Among many others, this example may serve as
motivation to develop a methodology for crafting molecular “designer structures”. Next, wereport our recent advances towards such a methodology [3-6]. Finally, we show that evenrelatively simple designer structures show intriguing functionalities, including quantum dot
behaviour [7], electrostatic potential sensing [8], and coherent single-electron field emission [9].

[1]
[2]
[3]
[4]
[5]
[6]

T. Esat et al., Phys. Rev. B 91, 144415 (2015).
T. Esat et al., Nature Physics 12, 867 (2016).
P. Leinen et al., Beilstein J Nanotechnol. 5, 1926 (2014).
C. Wagner et al., Nat. Comm. 5, 5568 (2014).
P. Leinen et al., Beilstein J of Nanotechnol. 6, 2148 (2015).
C. Wagner et al., Perspectives of Molecular Manipulation and Fabrication. In Molecular Architectonics,
Advances in Atom and Single Molecule Machines (Ed. T. Ogawa), Springer 2017.
[7] R. Temirov et al., Phys. Rev. Lett. 120, 206801 (2018).
[8] C. Wagner et al., Phys. Rev. Lett. 115, 026101 (2015).
[9] T. Esat et al., Nature 558, 573 (2018).

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Epitaxial growth of the organic pn heterojunctions
Ryohei Tsuruta1, Masaki Iwashita1, Kana Takahashi1, Takuya Hosokai2,
Tomoyuki Koganezawa3, Yasuo Nakayama1
1
Dept. of Pure & Applied Chem., Tokyo Univ. of Sci., Japan; 2 Nat. Inst. of Adv. Ind. Sci. &Technol. (AIST), Japan; 3 Jap. Synchrotron Rad. Res. Inst. (JASRI), SPring-8, Japane-mail: 7218705@ed.tus.ac.jp

Organic electronics is attracting attention as next generation semiconductor electronic devices.
Functionalities of most semiconductor devices are originated from charge carrier exchange at p-njunctions. The p-n junctions in the organic electronic devices such as organic photovoltaics areheterojunctions constituted with donor (p-type) and acceptor (n-type) molecules, and thus
designing of the molcular contacts is important for improving the device performance. However,detailed mechanisms how the molecules form the donor-acceptor interfaces have not yet been
understood thoroughly. Our group has unveiled the crystallographic structures of well-definedorganic semiconductor interfaces between epitaxial overlayers of fullerene (C60), an n-typemolecule, on single crystal substrates of pentacene (Pn), a p-type organic semiconductor, which
provides hints for understanding formation mechanisms of the molecular contacts [1-3]. In thiswork, we investigated evolution of epitaxial overlayers of C60 on single crystal surfaces of avariety organic semiconductors, e.g. rubrene, tetracene, and perylene, by means of grazing
incidence X-ray diffraction (GIXD) and atomic force microscopy (AFM).
The C60 overlayers of 20 nm-thick were grown by vacuum deposition on the organic single
crystal substrates prepared by a physical vapor transport method. GIXD measurements wereconducted at BL19B2 or BL46XU, Spring-8.
Two-dimensional GIXD results showed that C60 grows in the face-centered cubic_ (fcc) phase inthe (111)-orientation on the rubrene single crystals (Rub-SCs) and the fcc-C60 {220} diffraction
spots appeared at every 30° of the in-plane azimuthal angle of the sample. This means that the
fcc-C60 crystallites were not randomly oriented but grew epitaxially on Rub-SC, while theirlattice orientations were not unique but there were two nonequivalent crystal domains rotating
their in-plane lattice directions by 90° each other, as shown in Fig. 1. This result is contrasting to
the previous case of C60 on Pn-SC exhibiting the single domain growth [1]. High-resolution
GIXD spot profiles revealed that the in-plane mean
crystallite size of the epitaxial C60 overlayers extended as
elevating temperature during the growth. Interestingly,
equivalent or rather greater mean crystallite sizes wereobtained for the C60/Rub-SC cases in comparison to C60/PnSC, despite crystal domains of inequivalent orientations
coexisted for the former heterojunction. Interface structures Fig. 1 Schematic drawings indicatingof C60 on tetracene and perylene single crystals are also lattice orientations of C60 (circles) on
the surface of Rub-SC (bars).
discussed in this presentation.
[1] Y. Nakayama et al., ACS Appl. Mater. Interf. 8, 13499 (2016).
[2] R. Tsuruta et al., J. Cryst. Growth 468, 770 (2017).
[3] Y. Nakayama et al., Adv. Mater. Interf. 5, 1800084 (2018).

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Impact of the molecular quadrupole moment in themolecularly mixed film of organic semiconductors
Yuki Uemura, Abdullah Syed, Hiroyuki Yoshida
Chiba University, Japan
E-mail: y.uemura@chiba-u.jp

Recently, it has been reported that the electronic level of thin films of organic semiconductors
can be tuned continuously by changing the mixing ratio of the two constituent molecules having
quadrupoles with opposite direction [1]. Based on the results from the ultraviolet photoelectron
spectroscopy (UPS) experiment and the density functional theory (DFT) calculation, they
concluded that the electrostatic effect which can be approximated by the interaction between the
cation generated by UPS process and the molecular quadrupole moments plays a central role.
Recently, we demonstrated that the electrostatic energy can be obtained solely from theexperimental data [2] by UPS and low energy inverse photoelectron spectroscopy (LEIPS) [3].
In this study, this method is applied to a mixed film of copper phthalocyanine (CuPc) and its
fluorinated compound (F16CuPc) with different mixing ratio of molecules to elucidate themechanism of the continuous change of the energy levels.
The gray circles in Fig.1 represent the combined UPS and LEIPS spectra. The peak of the mixed
films can be decomposed into the spectral components of the CuPc and F16CuPc shown bydashed and dotted lines in Fig. 1, respectively. The HOMO and LUMO levels shift rigidly withthe molecular ratio without changing the bandgap suggesting that the continuous shift isoriginate from the electrostatic energy. The electrostatic and electronic polarization energies
were evaluated quantitatively from the results.

Fig. 1 UPS(left) and LEIPS(right) spectra of the CuPc and F16CuPc co-deposited films.

[1] M. Schwarze et al., Science, 352, 1446 (2016).
[2] K. Yamada et al., Phys. Rev. B, 97, 245206 (2018).
[3] H. Yoshida, Chem. Phys. Lett. 539-540, 180 (2012).

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Enhancement of signal intensity for the
inverse photoelectron spectroscopy by thesurface plasmon resonance of the Ag nanoparticles
Ryota Usui1, Koki Shibata 2, Tomoko Sugita1, Norihisa Kobayashi 3,4,
Hiroyuki Yoshida3,4
1
Graduate School of Science and Engineering, Chiba-University, Japan
2
Faculty of Engineering, Chiba-University, Japan
3
Graduate School of Engineering, Chiba-University, Japan
4
Molecular Chirality Research Center, Chiba-University, Japane-mail: r.usui@chiba-u.jp

intensity (cps)The most direct and thorough information about the unoccupied states can be obtained byinverse photoelectron spectroscopy (IPES), which can be regarded as the time-inversion processof photoelectron spectroscopy (PES). However, the cross section of the IPES process is 5 ordersof magnitude smaller than that of PES [1], which impedes the wide use of IPES. In this study,
the intensity of the IPES signal is enhanced by SPR. This was, however, impossible because thephoton energy involved in conventional IPES exceeds 9 eV and is much higher than the SPR
energy of existing materials. In 2012, we developed low-energy IPES (LEIPS) [2]. The energies
of detected photons are less than 5 eV, which can be matched with the SPR energy.
Figure 1 shows the setup of LEIPS of the SPR. As the SPR media, we adopted Ag nanoparticles
which were prepared by vacuum deposition or electrodeposition with voltage-step method [3].
We observed as much as the 3-fold enhancement of LEIPS signal of Ag nanoparticles. Then an
organic semiconductor, cupper phthalocyanine (CuPc), was deposited on the Ag nanoparticles.
The signal intensity was also enhanced by a factor of 5 (Fig. 2). The wavelength dependence of
the LEIPS intensities is similar to the extinction spectra confirming that the signal enhancements
are indeed caused by the SPR of Ag nanoparticles.

CuPc / Ag

300
200

CuPc / ITO

100
0
4

3
2
1
energy from Evac (eV)0

Fig.2 LEIPS spectra of 20-nm thick CuPc filmwith and without the Ag nanoparticles.

Fig.1 Experimental setup of LEIPS[1] J. Pendry, Phys. Rev. Lett. 45, 1356 (1980).
[2] H. Yoshida, Chem. Phys. Lett. 539-540, 180 (2012).
[3] A. Tsuboi, Adv. Mater. 25, 3197 (2013).

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Electronic and optical properties ofoligothiophene/F4TCNQ charge-transfer complexes:
The role of donor conjugation length
Ana Valencia and Caterina Cocchi
Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
e-mail: ana.valencia@physik.hu-berlin.de

Doping in organic semiconductors remains a debated issue. Open questions concern theinteraction mechanisms between donors and acceptors, and also the role of the conjugation
length that can influence the charge transfer (CT) process [1]. To address this issue, weinvestigate electronic properties and optical excitations of a series of oligothiophene (nT)molecules doped by the strong acceptor F4TCNQ. In the framework of density-functional theory(DFT), and many-body perturbation theory, including the G0W0 approximation and the BetheSalpeter equation, we consider CT complexes formed by four different oligomers with increasing
length (4T, 6T, 8T and 10T). Based on the level alignment obtained from DFT adopting the
CAM-B3LYP hybrid functional [2] we find that the HOMO and the LUMO have CT characterin all complexes. On the other hand, occupied and virtual states above and below them arestrongly dependent on the nT length. The optical spectra reflect the electronic structure. For all
systems, the first bright excitation is dominated by the HOMO-LUMO transition. At increasing
donor length, higher-energy peaks exhibit different character, which again points to conjugationlength dependence. The rationale offered by our results contributes to clarify the excitation
processes in organic donor/acceptor complexes.

Fig. 4 (a) UV-vis spectra of 4T/F4TCNQ and 8T/F4TCNQ charge transfer complexes.
Results from BSE calculations, and the electronic G0W0 energy band gap is indicatedby dashed lines. (b) Selected molecular orbitals of both complexes.

[1] H. Mendez et al., Nat. Comms. 6, 8560 (2015).
[2] T. Yanai et al., Chem. Phys. Lett. 393, 51 (2004).

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Switching the surface electronic properties ofpolar ZnO crystals with photochromic
pyridine-dihydropyrene molecular layers
Qiankun Wang1, Giovanni Ligorio1,3, Raphael Schlesinger1, Valentin Diez-Cabanes2,
David Cornil2, Yves Garmshausen3, Stefan Hecht3, Jérôme Cornil2,
Emil J. W. List-Kratochvil1,3, Norbert Koch1
1
Department of Physics, Humboldt-Universität zu Berlin
2
Laboratory for Chemistry of Novel Materials, University of Mons
3
Department of Chemistry, Humboldt-Universität zu Berlin
e-mail: qiankun@physik.hu-berlin.de

Photoswitchable materials are attracting increasing interests for the development ofmultifunctional devices. A dynamic, light induced control of the electronic energy levels withsuch materials is a feasible pathway for realizing optoelectronic devices with multifunctional
properties in terms of the control of charge transfer and injection. Here, we demonstrate thatelectronic properties of polar ZnO surfaces can be reversibly modulated with a layer ofphotoswitches, i.e., pyridine-dihydropyrene (Py-DHP). This is due to the switching between the
two Py-DHP isomers (each with different conjugation) induced by illumination with green lightand proper heat treatment. Using photoemission spectroscopy and density functional theory(DFT) modelling, we show that the photochromic ring closure/opening reactions result indifferent valence electronic features of Py-DHP, leading to a reversible shift of the frontier
occupied orbitals by 0.7 eV with respect to Fermi level. This accordingly modulates the energy
injection barriers at the ZnO/Py-DHP interface. Moreover, upon switching, we observe an
increase of the ionization potential for Py-DHP multilayers compared to that of Py-DHP
monolayer. We attribute this observation to different molecular orientations existing between themonolayer and multilayer films. Our findings provide a pathway to tuning the interface energy
level alignments dynamically through a simple external stimulus, which can in the future be
employed in multifunctional optoelectronic devices.

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Solution-processing vs. vacuum-sublimation:
Impact on the electronic structure of
methylammonium lead iodide perovskite thin films
Rongbin Wang,1,2 Mingpeng Zhuo,1 Jitao Li,1 Tianshu Zhai,1 Jiacheng Yang,1Keke Fu,1 Liangsheng Liao,1 Lijia Liu,1 Steffen Duhm1, Norbert Koch1,21Institute of Functional Nano & Soft Materials, Soochow University, China
2
Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
e-mail: rongbin@physik.hu-berlin.de

CH3NH3PbI3 thin films were fabricated using several representative synthesis methods thatfrequently occur in reported literatures, which include spin-coating, [1] evaporation [2] and a
combination of the two.[3] We found that the surface morphology, composition and grain size ofthe films are highly dependent on how the PbI2 and CH3NH3I precursors are mixed, even when
the same stoichiometric ratio is used. X-ray photoelectron spectroscopy (XPS) reveals thatamount of CH3+-type defect, which is produced by CH3NH3I dissociation, is sensitive to both thephysical state of CH3NH3I and the order of mixing sequence. The variation of the
CH3NH3+:CH3+ ratio (Fig. 1) also affects the valence band and work function of thecorresponding films, as revealed by ultraviolet photoelectron spectroscopy (UPS). The chargetransport property of these films are further evaluated by examining the energy level alignment
between the perovskite film and a model hole transport layer, N,N′-di(1-naphthyl)-N,N′diphenylbenzidine (NPB). We find that CH3NH3+:CH3+ ratio (Fig. 1) shows correlation with theoffsets between the valence band maximum of perovskite film (VBM) and the highest occupied
molecular orbital (HOMO) of NPB as well, and the energy-level alignment with the dual-source,co-evaporated CH3NH3PbI3 film is most suitable for efficient hole transport. [4]Fig. 1 Plot of (a) work function and (b) VBM (perovskite)-HOMO (NPB) offsets as a function ofconcentration ratio between CH3NH3+ and CH3+ as measured by XPS.

[1]
[2]
[3]
[4]

R.B. Wang et al., ACS Appl. Mater. Interfaces 9, 7859 (2017).
L. Liu et al., Appl. Phys. Lett. 107, 061904 (2015).
F. Fu et al., Phys. Status Solidi A 212, 2708 (2015).
R.B. Wang et al., 2018, submitted.

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Predicting ion pair formation yield in
molecular electrical doping from redox-potentials
Berthold Wegner1,2, Lutz Grubert3, Dennis Chercka4, Andreas Opitz2,
Stefan Hecht3, Klaus Müllen4, Norbert Koch1,21Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
2
Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
3Institut für Chemie, Humboldt-Universität zu Berlin, Germany
4
Max-Planck-Institut für Polymerforschung, Mainz, Germany
e-mail: berthold.wegner@helmholtz-berlin.deElectrical molecular doping of organic semiconductors with strong molecular donors andacceptors is a key technological component to control the charge carrier density and Fermi levelof the organic semiconductor host. Its efficiency relies on identifying appropriate dopants thatare capable of ionizing the semiconductor molecules with a high yield, thereby creating mobile
charges. We explore the suitability of two different material parameters to predict ion pairformation in such systems: i) redox-potentials measured by cyclic voltammetry in solution andii) ionization energy (IE) / electron affinity (EA) measured on individual material thin films byultraviolet / inverse photoelectron spectroscopy for different sets of semiconductor-dopant
combinations using structurally similar molecules. The ion pair formation efficiency of thesematerial combination sets is qualitatively and quantitatively studied by use of optical absorption
spectroscopy performed on both solutions and solid thin films. While commonly IE/EA values
are employed to guide the selection of molecular dopants for organic hosts, our study provides
strong indications that redox-potentials are better suited to identify matching material pairs than
IE/EA values. This is ascribed to the strongly film-structure dependent IE/EA values ofmolecular assemblies on and above the meso-scale, whereas the relevant molecular length scale
dopant-semiconductor interaction appears to be better captured by cyclic voltammetry
measurements.

Fig. 1 Comparison of solid state ionization energies / electron affinities andredox-potentials for the prediction of possible charge transfer between
host and dopant molecules.

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Microstructure and elastic constants oftransition metal dichalcogenide monolayers
from friction and shear force microscopy
Xiaomin Xu1, Thorsten Schultz1, Ziyu Qin2, Nikolai Severin1, Benedikt Haas1,
Sumin Shen3, Jan N. Kirchhof4, Andreas Opitz1, Christoph T. Koch1,
Kirill Bolotin4, Jürgen P. Rabe1, Goki Eda2, Norbert Koch1,51Department of Physics & IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
2
Department of Physics, National University of Singapore, Singapore
3
Department of Statistics, Virginia Polytechnic Institute and State University, USA
4
Department of Physics, Freie Universität Berlin, Germany
5Helmholtz-Zentrum für Materialien und Energie GmbH,
Bereich Solarenergieforschung, Germany
e-mail:xiaomin@physik.hu-berlin.de

Optical and electrical properties of two-dimensional transition metal dichalcogenides (TMDCs)
grown by chemical vapor deposition (CVD) are strongly determined by their microstructure[1,2]. Consequently, the visualization of spatial structural variations is of paramount importancefor future applications [3,4]. Here we demonstrate how grain boundaries, crystal orientation, andstrain fields can unambiguously be identified with combined lateral force microscopy (LFM) andtransverse shear microscopy (TSM) for CVD-grown tungsten disulfide (WS2) monolayers, on
length scales that are relevant for optoelectronic applications. Further, angle-dependent TSM
measurements enable us to acquire the fourth-order elastic constants of monolayer WS2
experimentally. Our results facilitate high-throughput and nondestructive microstructure
visualization of monolayer TMDCs, insights into their elastic properties, thus providing anaccessible tool to support the development of advanced optoelectronic devices based on such
two-dimensional semiconductors [5].

[1]
[2]
[3]
[4]
[5]

A.M. van der Zande et al., Nat. Mater. 12, 554 (2013).
Z. Cai et al., Chem. Rev. 118, 6091 (2018).
X. Yin et al., Science 344, 488 (2014).
J. Wang et al., Nat. Commun. 8, 377 (2017).
X. Xu et al., Adv. Mater. in press (2018).

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Band dispersion of CH3NH3PbI3 single crystal
Jin-Peng Yang1, 2, Matthias Meissner 2, Takuma Yamaguchi3,
Nobuo Ueno4, Satoshi Kera2, 3, 4
1
College of Physical Science and Technology, Yangzhou University, Yangzhou, China
2
Institute for Molecular Science, Okazaki, Japan
3
SOKENDAI (The Graduate University for Advanced Studies), Hayama, Japan
4
Graduate School of Advanced Integration Science, Chiba University, Japane-mail: yangjp@yzu.edu.cn

Solar cells incorporating organic-inorganic perovskites, especially methylammonium lead iodide(CH3NH3PbI3), have shown remarkable performances and therefore attracted wide interest
recently. For understanding the origin of the high performance, the effective charge carriermasses of CH3NH3PbI3 are critical. However, direct experimental data on its electronic band
structure, which determines the effective mass, is yet to be provided. In this poster, we will
present the electronic structure of self-grown CH3NH3PbI3 single crystals studied by using angleresolved photoelectron spectroscopy on cleaved crystal surfaces after characterizing the surface
structure by low-energy electron diffraction. Sharp diffraction patterns agree well with the cubic
structure previously determined by X-ray diffraction and confirm a good sample quality.
Moreover, a clear band dispersion of the top valence band was observed along different highsymmetry directions, Γ-Χ and Γ-Μ directions, of the cubic structure in consistence withtheoretical calculations. Based on these values, the effective hole mass was then estimated to be
0.24 (±0.10) m0 at the M point and 0.35 (±0.15) m0 at the X point, which are significantly lower
than in organic semiconductors. Further, we expect an only slightly larger value at the R point byconsidering the theoretical band structure. Our results reveal the physical origin of the highperformance of solar cells incorporating perovskite materials compared to pure organic
semiconductors.

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Identifying molecular orbitals and on-surface reaction
products with photoemission tomography
Xiaosheng Yang1, Daniel Lüftner2, Simon Weiß1, Philipp Hurdax2,
Larissa Egger2, Alexander Gottwald3, Mathias Richter3, Georg Koller2,
Michael G. Ramsey2, Peter Puschnig2, Sergeui Soubatch1, F. Stefan Tautz1
1Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich, Germany
2
Institute of Physics, University of Graz, NAWI Graz, Austria
3
Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany
e-mail: xia.yang@fz-juelich.de

Photoemission tomography [1] allows to directly correlate the momentum maps ofphotoemission intensity measured by angle-resolved photoemission spectroscopy (ARPES) andparticular electronic states of organic molecules via the plane wave final state approximation.
This simple correlation makes ARPES a quantitative tool for assigning molecular orbitals, 3D
orbital imaging, determining the structure of molecule layer, and quantifying the charge transfer
between metal substrate and organic adsorbate, and so on [2–5].
In this contribution we report two recent examples of this method. First, the electronic states andgeometric vertical structures of perylene-tetracarboxylic dianhydride (PTCDA) molecule on an
oxygen-reconstructed (√2×2√2)R45° Cu(100) surface are investigated. With photoemission
tomography measurement we found that, in contrast to PTCDA on intrinsic Cu(100) wherestrong molecule-substrate interaction is present [6], the oxygen adsorbed on Cu(100) preventschange transfer from metal substrate into the PTCDA molecule. The simultaneous electronic andstructural decoupling at the molecule-metal interface is further corroborated by X-ray standing
wave measurement and DFT calculation [7].
Second, photoemission tomography was used to investigate the thermally induced chemical
reaction of dibromo-bianthracene (DBBA) molecule deposited on Cu(110) [8]. We could clearly
identify the cyclodehydrogenation product of DBBA upon post-deposition annealing as
bisanthene molecules using orbital imaging. Moreover, the exact chemical state of bisanthene
can be defined comparing the measured momentum maps and the ones predicted by DFT fordifferent possible adsorption configurations.

[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]

P. Puschnig et al., Science 326, 702 (2009).
J. Ziroff et al., Phys. Rev. Lett. 104, 233004 (2010).
P. Puschnig et al., Phys. Rev. B 84, 235427 (2011).
S. Weiß et al., Nat. Commun. 6, 8287 (2015).
M. Hollerer et al., ACS Nano 11, 6252 (2017).
D. Lüftner et al., Phys. Rev. B 96, 125402 (2017).
X. Yang et al., Chem. Commun., in press (2018).
K.A. Simonov et al., J. Phys. Chem. C 118, 12532 (2014).

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Structural and electronic characterization
on organic semiconductor homojunctions
Koki Yoshida1, Ryohei Tsuruta1, Masataka Hikasa1, Soichiro Yamanaka1,
Masaki Iwashita1, Ko Tonami1, Tomoyuki Koganezawa2, Takuya Hosokai3,
Mitsuru Kikuchi4, Seiichiro Izawa4, Masahiro Hiramoto4, Yasuo Nakayama1
1
Dept. of Pure & Appl. Chem., Tokyo Univ. of Science, Japan; 2Japan Synchrotron Radiation
Res. Inst. (JASRI), SPring-8, Japan; 3 Nat. Inst. of Advanced Industrial Sci. & Technol. (AIST),
Japan; 4 Inst. for Molec. Sci., Nat. Inst. of Nat. Sci., Japane-mail: 7217672@ed.tus.ac.jp

In order to develop organic electronic devices, it is necessary to establish fundamental physicalproperties of organic semiconductors. Single crystalline molecular semiconductor materials aregood benchmarks for exploration into basic aspects of the materials as well as for indicating one
promising direction to overcome mobility drawbacks of general organic semiconductor devices.
Meanwhile, regulation of electric properties of organic semiconductor materials throughcontrolled doping has long been an important challenge in the organic electronics field. Whereas
tuning of energy level alignments at molecular-molecular and molecular-electrodeheterojunctions through doping at the interfaces has already been established as an essential
technology of the organic electronics, researches for regulating charge carrier properties of theorganic semiconductor materials themselves through doping into crystalline molecular
semiconductors, like the cases of Si, are quite limited. Recently, successful doping into single
crystal rubrene (C42H28) based on homoepitaxy of single crystalline ruburene thin films wasreported [1]. In this study, we investigated structural and electronic characterization on
homojunctions of two prototypical organic semiconductor materials, ruburene and pentacene(C22H14), formed on the single crystal surface of each molecule.
Two-dimensional grazing incidence X-ray diffraction (2D-GIXD) data on the homojunction
samples of rubrene revealed substantially identical patterns to those of bare rubrene single crystal
samples, as shown in Fig. 1, corroborating excellent crystallinity of the homoepitaxial rubrene
thin films grown on the single crystal rubrene [1]. In contrast, an existence of so-called “thinfilm phase” pentacene (Pn-TF) on the single crystal pentacene (Pn-SC) was detected indiffraction patterns of pentacene homojunctions (Fig. 2). Electronic structures of thesehomojunction samples are also presented in this contribution.

Fig. 1 2D-GIXD patterns of (a) single crystal
rubrene and (b) homoepitaxial rubrene samples.

Fig. 2 Out-of-plane diffraction profiles of apentacene homojunction sample.

[1] C. Ohashi et al., Adv. Mater. 29, 1605619 (2017).

99

P 48

Band structure of CH3NH3PbI3 andCH3NH3PbBr3 perovskite single crystals fromangle-resolved photoelectron spectroscopy
Fengshuo Zu,1,2 Patrick Amsalem,1 David A. Egger,3,4 Rongbin Wang,1,5
Christian M. Wolff,6 Honghua Fang,7 Maria Antonietta Loi,7 Dieter Neher,6Leeor Kronik,4 Steffen Duhm,5 Norbert Koch*1,2
1Institut für Physik & IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
2
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany
3Institute of Theoretical Physics, University of Regensburg, Germany
4
Department of Materials and Interfaces, Weizmann Institute of Science, Israel
5
FUNSOM, Soochow University, Suzhou, P. R. China
6
Institut für Physik und Astronomie, Universität Potsdam, Germany
7
Photophysics & OptoElectronics, University of Groningen, Netherlande-mail: fengshuo@physik.hu-berlin.de

Photovoltaic devices based on halide perovskites with outstanding optoelectronic properties haveexhibited tremendous progress in performance.[1] To understand the origin of these properties
comprehensively, detailed knowledge on the underlying electronic band structure is required.
Here, we present complementary results from low-energy electron diffraction (LEED), angleresolved photoelectron spectroscopy (ARPES), and density functional theory (DFT) calculations
for CH3NH3PbBr3 and CH3NH3PbI3 single crystals. For both, sharp LEED patterns
corresponding to the (001) surfaces of CH3NH3PbBr3 and CH3NH3PbI3 were observed together
with well-resolved, dispersive valence band (VB) features. Noteworthy, the LEED patterns of
CH3NH3PbI3 reveal a coexistence of the cubic and tetragonal phase at the sample surface alreadyat room temperature. From ARPES, we determined a bandwidth of ~1.0 eV and of ~1.3 eV along
the X-R direction in CH3NH3PbI3 and CH3NH3PbBr3 single crystals, respectively. In good
agreement with results from DFT calculations, the hole effective-mass, mh*, with values as small
as 0.18 m0 (CH3NH3PbI3) and 0.25 m0 (CH3NH3PbBr3) were found. Furthermore, thefundamental differences between linear and logarithmic methods in determining the VB onset
are discussed and addressed. These findings substantially enhance our understanding of the
intrinsic optoelectronic properties of halide perovskites.

[1] J. Berry et al., Adv. Mater. 27, 5102 (2015).

100

Schluchsee 2018 – ASOMEA-IX

Participants

101

102

Schluchsee 2018 – ASOMEA-IX

Acharya, Rachana

MPI Stuttgart

r.acharya@fkf.mpg.de

P-01

Ajdari, Mohsen

Uni Heidelberg

mohsen.ajdari89@gmail.com

P-02

Akaike, Kouki

Tokyo Univ. of Sci.

kouki.akaike@rs.tus.ac.jp

We 15:40

Aoyama, Kenichi

Tokyo Univ. of Sci.

6217601@ed.tus.ac.jp

P-03

Belser, Axel

Uni Tübingenaxel.belser@uni-tuebingen.de

P-04

Blumstengel, Sylke

HU Berlin

sylke.blumstengel@physik.hu-berlin.de

Thu 09:35

Borchert, JamesMPI Stuttgart

j.borchert@fkf.mpg.de

P-05

Broch, Katharina

Uni Tübingen

katharina-anna.broch@uni-tuebingen.de

We 09:35

Casu, Benedetta

Uni Tübingen

benedetta.casu@uni-tuebingen.de

Thu 17:35

Cocchi, Caterina

HU Berlincaterina.cocchi@physik.hu-berlin.de

We 10:10

d'Acunto, Giulio

Lund Univ.

giulio.dacunto@sljus.lu.se

P-06

Draxl, Claudia

HU Berlinclaudia.draxl@physik.hu-berlin.de

Thu 11:00

Duhm, Steffen

Soochow Univ., Suzhou

duhm@suda.edu.cn

Fri 12:10

Dürr, Michael

Uni Gießen

michael.duerr@ap.physik.uni-giessen.de

We 17:05

Fahlman, Mats

Linköping Univ

mafah@ifm.liu.se

We 14:30

Geiger, Michael

MPI Stuttgart

m.geiger@fkf.mpg.de

P-07

Gottfried, Michael

Uni Marburg

michael.gottfried@chemie.uni-marburg.de

Thu 10:10

Greulich, Katharina

Uni Tübingenk.greulich@uni-tuebingen.de

P-08

Hagenlocher, Jan

Uni Tübingenjan.hagenlocher@uni-tuebingen.deP-09

Hammon, SebastianUni Bayreuth

sebastian_hammon@hotmail.com

P-10

Hantusch, Martin

IFW Dresdenm.hantusch@ifw-dresden.de

P-11

Harada, Yoshihisa

Tokyo Univ.

harada@issp.u-tokyo.ac.jp

We 11:00

Höfer, Ulrich

Uni Marburg

ulrich.hoefer@physik.uni-marburg.de

Hurdax, Philipp

Uni Grazphilipp.hurdax@uni-graz.at

P-12

Ichikawa, Hiroyuki

Chiba Univ.

hi-ichikawa@chiba-u.jp

P-13

Iwasawa, Masato

Tsukuba Univ.

mstiwsw@gmail.com

P-14

Jakob, PeterUni Marburg

jakob.peter@physik.uni-marburg.de

Thu 12:10

Janke, Svenja M.

Duke Univ.

svenja.janke@duke.edu

P-15

Junghöfer, Tobias

Uni Tübingen

tobias.junghoefer@uni-tuebingen.de

P-16

Karstens, N. Reimer

Uni Tübingennikolaus-reimer.karstens@uni-tuebingen.de

P-17

Kera, Satoshi

NIMS-IMS, Okazaki

kera@ims.ac.jp

We 09:00

Klein, Benedikt

Uni Marburg

kleinbe@students.uni-marburg.de

P-18

Koch, Norbert

HU Berlin

nkoch@physik.hu-berlin.de

Kothe, Michael

Uni Marburg

michael.kothe@physik.uni-marburg.de

P-19

Kumpf, Christian

PGI-3, FZ Jülich

c.kumpf@fz-juelich.deP-20, P-21

Lyu, Jiong

Nat. Univ. Singapore

chmluj@nus.edu.sg

Thu 09:00

Lerch, Alexander

Uni Marburg

alexander.lerch@physik.uni-marburg.de

P-22

Liu, Xianjie

Linköping Univ

xjliu@ifm.liu.se

P-23

Mansour, Ahmed E.

HU Berlinamansour@physik.hu-berlin.de

P-24

Meissner, Matthias

NIMS-IMS, Okazaki

meissner@ims.ac.jp

P-25

Metzger, ChristianUni Würzburg

christian.metzger@physik.uni-wuerzburg.de

P-26

103

Nakayama, Yasuo

Tokyo Univ. of Sci.

nkym@rs.tus.ac.jp

We 16:30

Opitz, Andreas

HU Berlin

andreas.opitz@hu-berlin.de

P-27

Ozawa, Kenichi

Tokyo Inst. of Technol.

ozawa.k.ab@m.titech.ac.jp

We 11:35

Peisert, Heiko

Uni Tübingen

heiko.peisert@uni-tuebingen.de

We 17:40

Pucci, Annemarie

Uni Heidelberg

pucci@kip.uni-heidelberg.de

Thu 11:35

Ralaiarisoa, Maryline

HU Berlin

ralaiarr@physik.hu-berlin.de

P-28

Rehman, Foqia

Lund Univ.

foqia.rehman@sljus.lu.se

P-29

Rensmo, Håkan

Uppsala Univ.

hakan.rensmo@physics.uu.se

We 15:05

Rossi, Mariana

FHI Berlinrossi@fhi-berlin.mpg.de

Fri 11:00

Sato, Haruki

Chiba Univ.

h.sato@chiba-u.jp

P-30

Schultz, Thorsten

HU Berlintschultz@physik.hu-berlin.de

P-31

Schwendt, Mathias

Uni Graz

mathias.schwendt@uni-graz.at

P-32

Shibuta, Masahiro

Keio Inst.

shibuta@sepia.chem.keio.ac.jp

Fri 11:35

Shimizu, Kohei

Chiba Univ.

acfa2458@chiba-u.jp

P-33

Sivanesan, Vipilan

Uni Heidelberg

vipilan.sivanesan@uni-heidelberg.de

P-34

Soubatch, Serguei

PGI-3, FZ Jülich

s.subach@fz-juelich.de

P-35

Stadtmüller, Benjamin

Uni Kaiserslauternbstadtmueller@physik.uni-kl.de

We 12:10

Tautz, Stefan

PGI-3, FZ Jülich

s.tautz@fz-juelich.deP-36, Fri 09:00

Tegeder, PetraUni Heidelberg

tegeder@uni-heidelberg.de

Fri 09:35

Tsuruta, Ryohei

Tokyo Univ. of Sci.

7218705@ed.tus.ac.jp

P-37

Uemura, Yuki

Chiba Univ.

y.uemura@chiba-u.jp

P-38

Ueno, Nobuo

Chiba Univ.

uenon@faculty.chiba-u.jp

Thu 17:55

Usui, Ryota

Chiba Univ.

r.usui@chiba-u.jp

P-39

Valencia, Ana

HU Berlin

valencia@physik.hu-berlin.de

P-40

Wang, Qiankun

HU Berlin

qiankun@physik.hu-berlin.deP-41

Wang, Rongbin

HU Berlin

rongbin@physik.hu-berlin.deP-42

Wegner, Berthold

HU Berlin

berthold.wegner@helmholtz-berlin.deP-43

Witte, Gregor

Uni Marburg

gregor.witte@physik.uni-marburg.de

Thu 15:35

Xu, Xiaomin

HU Berlin

xiaomin@physik.hu-berlin.de

P-44

Yamada, Takashi

Osaka Univ.

tyamada@chem.sci.osaka-u.ac.jp

Fri 10:10

Yamada, Yoichi

Tsukuba Univ.

yamada@bk.tsukuba.ac.jp

Thu 15:00

Yang, Jinpeng

Yangzhou Univ.

yangjp@yzu.edu.cn

P-45

Yang, Xiaosheng

PGI-3, FZ Jülich

xia.yang@fz-juelich.de

P-46

Yoshida, Hiroyuki

Chiba Univ.

hyoshida@chida-u.jp

Thu 16:10

Yoshida, Koki

Tokyo Univ. of Sci.

7217672@ed.tus.ac.jp

P-47

Yoshinobu, Jun

Tokyo Univ.

junyoshi@issp.u-tokyo.ac.jp

Thu 17:00

Zu, Fengshuo

HU Berlin

fengshuo@physik.hu-berlin.de

P-48

104