bluuebunny/crossref_metadata_2025_split huggingface dataset:
(Invited) Excited State Dynamics and Ultrafast Electron Transfer in β-Iodo Substituted Bdp and ADP Donor-Acceptor Systems Featuring Fullerene.
Authors: Gobeze Haptom B. , Shao Shuai , D'Souza Francis 
Published: February 2020

Novel donor-acceptor systems featuring, as electron donors, triplet sensitizers, viz., β-iodo substituted BDP and ADP, and fullerene as an electron acceptor are designed and synthesized. Iodination of meso-phenyl-tetramethyl-BDP and tetraphenyl-ADP bearing catechol aldehyde groups at the boron center is achieved by treating the precursors with N-iodosuccinimide (NIS) in dry DCM and dry chloroform, respectively, and stirring them for 24 hours under nitrogen at room temperature. Following successful synthesis of pure diiodo-BDP-CHO and diiodo-ADP-CHO, the final donor-acceptor dyads I2BDP-C60 (1) and I2ADP-C60 (2) are synthesized by following Prato reaction using sarcosine in dry toluene and refluxing under nitrogen for 24 hours. The final products which are purified over silica column are achieved as pink-reddish and bluish solid, respectively. Their structural integrity is arrived by both 1H and 13C-NMR, and HR-Mass spectral analysis.
The steady-state and time-resolved excited state study of the dyads and control compounds using UV-vis absorption, fluorescence, phosphorescence, TCSPC and transient absorption both in the femtosecond and nanosecond time domain, in both toluene and benzonitrile, reveals very interesting photochemistry. The interplay of the thermodynamics and the kinetics of the singlet to triplet state intersystem crossing in the donor compounds is found to be decisive to the formation and quantum yield of the charge separated state in the dyads 1 and 2. In the case of dyad 1, with a slower rate of intersystem crossing, kISC= 5.18 x 10 9 S-1 in benzonitrile, the electron transfer seems to out compete the intersystem crossing and an ultrafast electron transfer is observed in benzonitrile with kCS= 1.9 x 1011 S-1. In the case of dyad 2 on the other hand, the fast intersystem crossing in diiodo-ADP seems to aggressively compete with the electron transfer especially for excitation initiated from S1 state while a better electron transfer dynamic is observed for electron transfer originating from the higher excited state. The charge separated states are found to persist up to ca. 1 ns, especially in the case of dyad 1 with a life time of 992.5 ps and a kCR= 1.0 x 109 S-1.

Figure 1
(Invited) Chemical Purification of Nanotubular Fullerenes: Separating Buckyballs from Buckytubes
Authors: Koenig Ryan M. , Tepper Katelyn R. , Franklin Hannah M. , Seeler Tiffany L. , Stevenson Steven 
Published: February 2020

The existence of structural isomers is well known for fullerenes. Thousands of publications relate to the “spheroidal” fullerenes. Yet only a trace of experimental findings have been reported for the predicted “tubular” fullerene isomers. There are several reasons. First, the yield of nanotubular fullerenes is less than 0.05 percent in a typical soot extract. Second, there is a purification challenge to overcome. The currently published method necessitate the use of multiple HPLC columns having a variety of stationary phases to resolve co-eluting spheroidal and nanotubular fullerenes.
In this presentation, we discuss our recent results since the Seattle meeting. We will demonstrate that differences in the chemical reactivity of spheroidal versus tubular fullerenes can be used as a separation tool. Using this approach, we now have purified several isomers of nanotubular fullerenes.
(Invited) New Approaches in Computational Modeling of Fullerene/Metallofullerenes
Authors: Liu Xiaoyang , Dorn Harry C 
Published: February 2020

Today, computational models are extensively applied in scientific research to address fundamental as well as practical issues in material science. Fullerenes and metallofullerenes are well recognized as potential materials for next-generation electronic devices, such as quantum computers. The rapid advance in fullerene/metallofullerene research requires improved theoretical tools to understand fundamental as well as practical applications of these new members of fullerene/metallofullerene family. In this presentation, we will describe the extension of the famous spiral program by Fowler and Manolopoulos1 to generate new non-classical isomers. We have extended this approach beyond 5 and 6 membered fullerene structures to other polygon faces, such as, heptagons. In addition, we have developed a machine learning tool based on a general relationship between the structure patterns and physical properties. Finally, we will describe our current modeling studies regarding chromatographic retention mechanism(s) of fullerene/metallofullerene molecules.
Reference:

Fowler, Patrick W., and D. E. Manolopoulos. An Atlas of Fullerenes. Clarendon Press-Oxford, 1995.
(Invited) Synthesis and Properties of Giant Molecular Carbon Nanorings and Nanocrowns Based on Nanographenes
Authors: Du Pingwu , Huang Qiang , Jia Hongxing 
Published: February 2020

Carbon exists as a variety of nanometer-sized allotropes, such as 0D fullerenes, 1D carbon nanotubes (CNTs), and 2D graphene. So far, it is still a great challenge to construct CNTs with a fixed length and diameter-specified single-chirality. We have synthesized a series of novel large π-extended molecular carbon nanorings and nanocrowns based on nanographene hexa-peri-hexabenzocoronene (HBC) unit (named as [n]CHBCs) and other nanographenes as a finite model of armchair CNTs, including [n]CHBCs (n=4,6,8), TCR, and HCR, et al (Figure 1).1-3 Their tubular structures of these [n]CHBCs have also been characterized using various physical methods, including NMR, STM, PL, crystallographic analysis, and STM images. In addition, the photophysical properties of these nanocarbons are studied in solution and explained by theoretical calculations. TCR and HCR can selectively capture fullerene C60 due to strong supramolecular interactions and the molecular structure of C60@TCR is unambiguously determined by single-crystal X-ray diffraction. Compared to the HBC monomer, obvious redshift in absorption and emission spectra has been observed in these HBC carbon nanorings and nanocrowns. More recently, we constructed a three-dimensional capsule-like HBC-containing carbon nanocage,4 which can be considered as a novel synthetic model of the capped zigzag [12,0] carbon nanotubes.
1. Lu, D. P.; Wu, H. T.; Dai, Y. F.; Shi, H.; Shao, X.; Yang, S. F.; Yang, J. L.; Du, P. W. Chem.
Commun.
2016, 52, 7164-7167.
2. Lu, D.P.; Zhuang, G. L.; Wu, H. T.; Wang, S.; Yang, S. F.; Du, P. W. Angew.
Chem., Int. Ed.
2017, 56, 158-162.
3. Jia, H. X.; Zhuang, G. L.; Wang, J. Y.; Huang, Q.; Wu, Y. Y.; Zhou, Y.; Yang, S. F.; Du, P. W. submitted for publication, 2019.
4. Cui, S. S.; Zhuang, G. L.; Lu, D. P.; Jia, H. X.; Wang, Y.; Yang, S. F.; Du, P. W. Angew.
Chem., Int. Ed.
2018, 57, 9330-9335.

Figure 1
Enhancing Electrical and Contact Properties of WSe2 ­­field-Effect Transistors Via Vacuum-Annealed Pt-W Alloy Contacts
Authors: Kim Hyun , Park Hyunik , Kim Jihyun 
Published: February 2020

Two-dimensional (2D) materials have been extensively studied as one of the promising post-silicon materials for nano-sized field effect transistors to overcome physical limits of Si-based electronic devices. Semiconducting transition metal dichalcogenides (TMDs) have been studied as attractive candidates with sizeable band structure, in contrast to graphene with zero band gap limiting its implementation into electronics due to large off-currents and low drain-current modulation. Among all, tungsten diselenide (WSe2) has attracted attention as a p-type conducting material with its high current on/off ratio, hole mobility, and environmental stability. Despite the superior electrical properties of WSe2, difficulty in forming of a stable Ohmic contact with a low contact resistance has posed a significant limitation in fabricating WSe2-based devices. It creates van der Waals (vdW) gaps with contact metal and additional tunneling barrier, which increases contact resistance and affects device performance. Efforts have been made to reduce contact resistance such as by work function engineering and charge transfer methods employing various novel technical strategies. However, such approaches still need industrial fabrication compatibility and environmental stability.
In this work, a simple one-step vacuum annealing was used to address vdW gaps and reduce contact resistance. Thermal annealing is extensively incorporated in conventional compound semiconductor fabrication process to facilitate alloying or inter-diffusion of metal to semiconductors and enhance contact properties. Plus, thermal annealing can eliminate interlayer residues originated from the repeated exfoliation and dry transfer processes, which would deteriorate electrical contact between metals and TMDs. Herein, few-layered WSe2 was transferred on to platinum (Pt) electrodes with high work function (>5 eV) to facilitate hole injection. Effects of vacuum annealing on the performance of WSe2 FETs were then investigated. With improved contact properties from the removal of interlayer residues, the device performance including on-current density, hole mobility, and current on/off ratio enhanced up to the temperature of 650 ℃. Especially, p-type conduction was greatly improved after vacuum-annealed at 600 ℃, confirmed by selenium vacancy-aided formation of interlayer PtxW1-x alloy. The alloyed contacts occupied between WSe2 and Pt played a role in improving contact properties and lowering contact resistance. The device performance started to deteriorate when vacuum-annealed above 650 ℃, which is attributed to thermal degradation of WSe2 channel from high annealing temperature. Our work would further pave the way for achieving methods in fabricating a reliable TMDs based devices. Details will be discussed at the presentation.

Figure 1
Synthesis and Surface Modification of Two-Dimensional Mxenes As Potential Magnesium Battery Cathodes
Authors: Fagerli Frode Håskjold , Kaland Henning , Hadler-Jacobsen Jacob , Boge Lars-Arne , Selbach Sverre Magnus , Wang Zhaohui , Vullum-Bruer Fride 
Published: February 2020

Rechargeable magnesium batteries may allow for safer and cheaper batteries compared to those based on Li-ion technology, mostly due to the possibility of utilizing magnesium metal as anode material without forming dendrites [1]. However, since the first prototype was reported in 2000 [2], limited improvements on the cathode side have been achieved, where either trapping of magnesium ions or low operating potentials limit the performance [3]. After its discovery in 2011 [4], a new group of two-dimensional materials, known as MXenes, has been proposed as possible cathode materials for rechargeable magnesium batteries, due to their good electronic properties and ion hosting capabilities [5]. Various MXenes have already shown promising behavior in Li-ion batteries [6].
Here, we present data from several compositions of MXenes formed by the selective etching of Al from the initial MAX phase precursor in concentrated HF acid. The MAX phases were produced by solid state reaction synthesis through careful control of temperature and stoichiometry to obtain the desired end compositions. After successful etching, different treatment methods have been investigated in order to control the surface termination groups together with the interlayer distance between the flakes. The materials were characterized by SEM, EDX, XRD and XPS to map out the elemental and structural changes resulting from these treatments. Electrochemical properties have also been assessed through cyclic voltammetry and galvanostatic charge/discharge analysis.

References:

[1] M. Masaki, Journal of Power Sources 196 (2011), 7048-7055
[2] D. Aurbach et al., Nature 407 (2000) 724-727
[3] P. Canepa et al., Chemical Reviews 117 (2017) 4287-4341
[4] Naguib et al., Adv. Mater. 23 (2011) 4248-4253.
[5] Naguib et al., J. Am. Chem. Soc. 135 (2013) 15966-15969
[6] C. Eames, M. S. Islam, J. Am. Chem. Soc. 136 (2015) 16270-16276
(Invited) Atomic Level Investigation of Resistance Switching in 2D Memory Devices
Authors: Hus Saban , Ge Ruijing , Wu Xiaohan , Gu Yuqian , Lee Jack C. , Li An-Ping , Akinwande Deji 
Published: February 2020

The last few years have witnessed significant developments in non-volatile resistance switching (NVRS) devices which employ layered 2D materials such as hexagonal Boron Nitride (hBN) and Transitional Metal Dichalcogenides (TMDs) as the active medium. Among these developments, the demonstration of NVRS in vertical metal-insulator-metal (MIM) devices with single layer atomic sheets used as the insulating layer, is particularly intriguing. While it was long believed that leakage currents would prevent observation of this phenomenon for atomically thin insulating layers our previous studies on mesoscopic scale devices demonstrated stable unipolar and bipolar operations. Furthermore, these studies suggest that localized defects and other atomic-scale multiphysics mechanisms are likely to have a key role in NVRS observed in these 2D devices.
Here, we present our current research on the atomic level details of the relationship between the NVRS and heterogeneities in 2D materials. For these investigations, we utilize both single probe and multi-probe scanning electron microscopy (STM) methods, first, to identify the atomic level details of the heterogeneity and then to conduct transport experiments in the vicinity of specific heterogeneities. These studies aim to provide one to one correlation between the structural properties of the heterogeneity and its role on the transport properties of the material. Through these studies, we seek to deduce which particular defect structures are most desirable for NVRS and utilize this information for the development of extremely high-density data storage devices as well as neuromorphic applications and low power RF switches.
Molybdenum Disulfides and Diselenides By Atomic Layer Deposition
Authors: Zazpe Raul , Prikryl Jan , Krbal Milos , Ng Siowwoon , Dvorak Filip , Bures Filip , Macak Jan M. 
Published: February 2020

The success of graphene opened a door for a new class of chalcogenide materials with unique properties that can be applied in the semiconductor technology [1]. Monolayers of two-dimensional transition metal dichalcogenides (2D TMDCs) possess a direct band gap [2] that is crucial for optoelectronic applications. Additionally, the direct band gap can be easily tuned by either chemical composition or external stimuli. Next to the optoelectronic applications, where a monolayer planar structure is necessary to employ, a layer of standing flakes, which possesses a large surface area, can be used for hydrogen evolution [3] a photodegradation of organic dyes [4] or as electrodes in Li ion batteries [5].
In principle, TMDCs can be prepared by various top-down (e.g. exfoliation) and bottom-up techniques, such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) growth techniques [1]. MoS2, a typical representative of TMDCs, has been widely studied for many applications. Recently, the possibility to employ ALD as a technique to grow MoS2 has been reported. In these works (CH3)2S2 [6] or H2S [7, 8] were used as the S precursor and Mo(CO)6 [6], MoCl5 [7] or Mo(thd)3 [8] as the Mo precursors. From the practical point of view, MoSe2 is even more interesting than MoS2 since MoSe2 possesses a higher electrical conductivity than MoS2 [9, 10]. Recently, we have shown that ALD deposition of MoSe2 [11] or Mo-O-Se [12] using ((CH3)3Si)2Se as the Se precursor and the MoCl5 or Mo(CO)6, respectively, as the Mo precursors is feasible.
The presentation will focus on the synthesis of MoS2 and MoSe2 by ALD, their characterization and applications in various fields. Experimental details and some recent photocatalytic and hydrogen evolution results will be presented and discussed.
References:
[1] A. V. Kolobov, J. Tominaga, Two-Dimensional Transition-Metal, Dichalcogenides. Springer Series in Materials Science, Springer International Publishing AG, Switzerland 2016

[2] B. Radisavljevic, A. Radenovic, J. Brivio, V. Giacometti, A. Kis, Nat. Nanotechnol. 2011, 6, 147.
[3] L. Wang, Z. Sofer, J. Luxa, M. Pumera, Adv. Mater. Interfaces
2015, 2, 1500041
[4] Y. Wu, M. Xu, X. Chen, S. Yang, H. Wu, J. Pan, X. Xiong, Nanoscale
2016, 8, 440
[5] D. Ilic, K. Wiesener, W. Schneider, H. Oppermann, G. Krabbes, J.Power Sources
1985, 14, 223
[6] Z. Jin, S.Shin,D.H.Kwon, S. J.Han,Y. S.Min,Nanoscale
2014, 6, 14453.
[7] L. K. Tan, B. Liu, J. H. Teng, S. Guo, H. Y. Low, K. P. Loh, Nanoscale
2014, 6, 10584
[8] M. Mattinen et al., Adv. Mater. Interfaces
2017, 4, 1700123.
[9] D. Kong, H. Wang, J. J. Cha, M. Pasta, K. J. Koski, J. Yao, Y. Cui, Nano Lett. 2013, 13, 1341.
[10] A. Eftekhari, Appl. Mater. Today
2017, 8.
[11] M. Krbal et al., Phys. Stat. Sol. RRL,
2018, 12, 1800023
[12] S. Ng et al., Adv. Mater. Interfaces
2017, 1701146.
(Invited) Towards High-Performance Field-Effect Transistors with Atomically Precise Graphene Nanoribbons
Authors: Llinas Juan Pablo 
Published: February 2020

It is now possible to grow graphene nanoribbons with atomically precision by employing on-surface organic synthesis techniques [1]. Bottom-up synthesized graphene nanoribbons have promising electronic properties for high performance field effect transistors (FETs) and ultra-low power devices such as tunneling FETs. However, the short length, wide band gap, and random orientation of GNRs have prevented the fabrication of devices with the expected performance and switching behavior [2]. In this talk, I will discuss our progress in integrating bottom-up synthesized graphene nanoribbons into devices. I will show our results on high on-current and high on-off ratio FETs with a 9-atom wide graphene nanoribbon as the channel material [3]. Furthermore, we also fabricated devices with parallel arrays of GNRs transferred from single crystal Au(788), which greatly improves device yield. Finally, I will discuss how we can use graphene nanoribbon heterostructures to design a low-voltage switch [4].
References
[1] Cai, J. et al. Nature
466, 470–473 (2010).
[2] Bennett, P. B. et al. Applied Physics Letters
103, 253114 (2013).
[3] Llinas, J. P. et al. Nature Communications
8, 633 (2017).
[4] Smith, S., Llinás, J. P., Bokor, J. & Salahuddin, S. IEEE Electron Device Letters
39, 143–146 (2018).
Scanning Photoelectron Spectroscopy of Tapered Cross Sections of Perovskite Solar Cells: Element Distribution, Band Alignment, Space Charge Layers and Photo-Voltage Distributions
Authors: Jaegermann Wolfram , Mayer Thomas 
Published: February 2020

Photoelectron spectroscopy is used for the characterization of chemical and electronic properties of semiconductor interfaces. As the information depth is extremely low, inner interfaces of device stacks are analyzed by depositing sequentially the respective contact material onto the base material in vacuum chambers integrated with the PES system. Thus elemental distribution including ionic state of the materials in contact as well as doping and electronic potential distribution induced by interface charge transfer can be monitored. For devices with non planar architecture or deposition processes not compatible with vacuum as both are given for perovskite solar cells, this procedure is not applicable.
In this paper we demonstrate the photoelectron spectroscopic analysis of a complete working perovskite solar cell ranging from crystalline TiO2 on FTO front contact over perovskite intermixed in meso-TiO2 and the perovskite layer to Spiro-MeoTAD and Au back contact by preparing a tapered cross section of the cell stack. A wet chemically prepared mixed FAPbI3 MAPbBr3 solar cell of 18% efficiency is analyzed. As the analyzed spot size is in the range of the layer thicknesses a small angle tapered edge is prepared by polishing in order to drastically increase the local resolution across the cell stack. The tapered cross section is measured in the dark and under open circuit operando conditions.
Using core level photoelectron spectroscopy the elemental distributions which forms in the wet chemical deposition process of the precursor solution are derived from the measured core level intensities. In addition, the electronic contact potentials are mapped, which allows conclusions on the band diagram of the full stack. We find that the perovskite absorber is n-type and a strong band bending in the p-type spiro-MeOTAD hole transport contact layer. Shifts of the core level emission binding energies under in situ illumination indicate that the cell photo-potential is induced to a large part at this back contact. We conclude that the diffusion voltage of the cells is not formed across the TiO2-perovskite front contact but mostly across the perovskite/SpiroMeOTAD/Au back contact.
This example demonstrates that the wealth of information that can be obtained on full devices applying the method of scanning photoelectron spectroscopy on device cross section using a tapered edge approach.
(Invited) Elucidating Proton Migration in Hybrid Organic Inorganic Perovskites and the Effect of Surface Passivation
Authors: Bassani Dario M. , Sadhu Subha , Buffeteau Thierry , Hirsch Lionel 
Published: February 2020

Perovskites in general are known to possess ionic conductivity and ion movement has been postulated to be directly or indirectly responsible for their lack of long-term stability and unusual behavior, including hysteresis. Therefore, understanding ion migration in perovskites is of major importance in improving their performance. Ion movement in HOIPs may occur extrinsically, i.e. from one of the contacts, or take the form of ion migration, where an ion is displaced from an occupied to a vacant site. Numerous studies confirmed the rotational movement of the MA ions within the inorganic cage formed by the PbI2octahedra, which has been associated to the temperature and frequency dependence of the complex permittivity.
To test the relationship between MA rotation and the frequency dispersion in the dielectric response in HOIP materials, we conducted a series of experiments in which the hydrogen atoms in MAI were selectively substituted with deuterium. Our results (Figure 1) unambiguously demonstrate that deuteration of the ammonium group leads to a large inverse kinetic isotope effect indicative of proton tunneling in HOIP materials. Deuteration of the methyl group in MA induces a normal secondary KIE that is consistent with these findings.1,2

REFERENCES
1. Y.-F. Chen, Y.-T. Tsai, L. Hirsch, D. M. Bassani J. Am. Chem. Soc., 2017, 139, 16359 – 16364.
2. S. Sadhu, K. Aqueche, T. Buffeteau,J.-M. Vincent,L. Hirsch,D. M. BassaniMat. Horiz., 2018, DOI: 10.1039/C8MH01119B.

Figure 1