bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Axially Assembled Photosynthetic Antenna-Reaction Center Mimics
Authors: Obondi Christopher , Lim Gary N. , Karr Paul , Pilkington Melanie , van der Est ARt , Poddutoori Prashanth K. , D'Souza Francis
Published: February 2020

A series of porphyrin based donor-acceptor conjugates in which the arrangement of various components are in perpendicular orientation to the porphyrin plane have been constructed and used to study the pathways of electron and energy transfer processes. The employed aluminum(III) porphyrin in these studies is found to be synthetically more advantageous as it provides reaction site on both faces of the porphyrin plane. The axial hydroxyl group on one side of the aluminum(III) porphyrin plane is able to form a covalent ester or ether bond with an energy harvester or electron acceptor while Lewis bases such as pyridine or an imidazole group form a metal-ligand axial coordination on other side of the plane hosting an electron donor or acceptor. The advantage of this configuration of the conjugates is that the donor and acceptor sides of the complex are located on opposite faces of the porphyrin which minimizes the rate of charge recombination. Moreover, the excited state 𝜋* orbital of porphyrin and axially coordinated ligand lie in the same space which causes an increase in the electronic coupling thus facilitating the electron/energy transfer processes. The distance dependence of sequential electron transfer in vertical, linear supramolecular triads constructed using tetrathiafulvalene (TTF), aluminum(III) porphyrin (AlPor) and fullerene (C60) entities will be discussed. Further, results of photoinduced energy transfer followed by electron transfer in antenna-reaction center mimicking BODIPY-AlPor-C60 supramolecular triads will be highlighted.

Figure 1
(Invited) Excited State of Y-Nitride Clusterfullerene: Luminescence and EPR Spectroscopy Study
Authors: Krylov Denis , Zalibera Michal , Schiemenz Sandra , Ziegs Frank , Rosenkranz Marco , Savitsky Anton , Popov Alexey A.
Published: February 2020

Empty fullerenes are known to have very fast intersystem crossing with near 100% yield of the T1 state, which results in very low quantum yield of fluorescence and relatively short fluorescence lifetimes (less than 1 ns). In endohedral metallofullerenes, the intersystem crossing is even faster due to the internal heavy-atom effect, and hence fluorescence can hardly be expected. However, Y3N@C80 is known to exhibit reasonably high yield of fluorescence (1%) and unusually long lifetimes of 800 ns.1, 2 Such unusual photophysical parameters indicate that simple fluorescence mechanism cannot explain experimental facts. In this contribution we describe steady-state and lifetime luminescence as well as light-induced electron paramagnetic resonance studies of Y3N@C80 at different temperatures aimed at clarification of photophysical properties of Y3N@C80.

1. Bharadwaj, L.; Novotny, L., Plasmon-Enhanced Photoemission from a Single Y3N@C80 Fullerene. J. Phys. Chem. C 2010, 114, 7444-7447.

2. Toth, K.; Molloy, J. K.; Matta, M.; Heinrich, B.; Guillon, D.; Bergamini, G.; Zerbetto, F.; Donnio, B.; Ceroni, P.; Felder-Flesch, D., A Strongly Emitting Liquid-Crystalline Derivative of Y3N@C80: Bright and Long-Lived Near-IR Luminescence from a Charge Transfer State. Angew. Chem.-Int. Edit. Engl. 2013, 52, 12303-12307.
Enhancing the Ion Detection of Graphene Field Effect Transistors at the Quantum Capacitance Limit
Authors: Fakih Ibrahim , Mahvash Farzaneh , Siaj Mohamed , Szkopek Thomas
Published: February 2020

Graphene field effect transistors (FETs) are attractive candidates for sensing applications because of their high charge carrier mobility and the ideal coupling between graphene charge carriers and surface potential. However, depositing a selective layer on the graphene for these sensing applications can degrade graphene’s electrical properties, increase hysteresis, and present a challenge for maintaining its sensitivity and stability. Here, we protect the graphene by encapsulating it with an ultrathin layer (4-8 nm) of parylene, a hydrophobic polymer, and then deposit 3-5 nm sensing layers, either aluminum oxide or tantalum pentoxide for sensing pH. We demonstrate gate capacitances approaching the quantum limit with 0.6 uF/cm2 and near Nernstian pH sensitivities of 55.2 mV/pH. We also observe significant improvements in field effect mobilities of 7000 cm2V-1s-1 and in transconductance with limited hysteresis compared to previous work. The improvements due to encapsulation have resulted in a detection limit of 0.1 mpH at a 60 Hz electrical bandwidth. We demonstrated our pH response by monitoring the change in acidity of carbonated water in real time.

Figure 1
Holey Graphene for Energy Storage
Authors: Kanungo Rohit , Radich James
Published: February 2020

Reduced graphene oxide (RGO) with modified morphologies has shown potential application as electrode material for electrochemical capacitors. By creating nanopores within the RGO sheets, the specific surface area of electrode and diffusion of electroactive species can be improved. Here, we present a simple solution based process to make holey graphene from graphene oxide (GO) via microwave (MW) radiations. GO aqueous dispersion prepared by modified Hummer’s method can be converted to RGO via thermal, chemical or photochemical methods. Then, RGO in presence of hydrogen peroxide is irradiated with microwaves. The MW generated OH• radicals etch away the carbon atoms present at the active defective sites on RGO, leaving behind carbon vacancy, which extends to form the nanopores. This holey graphene is characterized using TEM, XPS, BET, Raman & FTIR. Further, the material is used to make an electrochemical capacitor and tested to show improved energy density.
Morphological Varied and Scalable MoS2 for Electrochemical Energy Storage Devices
Authors: Patel Mumukshu D. , Cha Eunho , Choudhary Nitin , Kang Chiwon , Choi Wonbong
Published: February 2020

A versatile non-graphene 2D material (MoS2) has recently attracted great research attention owing to their novel structure-property relation for high performance energy storage devices. The unique hexagonal layered family of transition metal dichalcogenides (TMDs-MX2) composed of X-M-X layers; are stacked together by van der Waals bonding. Different fabrication methods including mechanical/chemical exfoliation, chemical vapor deposition, co-evaporation, and hydrothermal reactions have been employed to fabricate different thickness of MoS2. However, there is continuous pursuit to explore various novel methods for uniform and large-scale synthesis of MoS2 on different substrate. Here in, we present two different applications of MoS2for electrochemical energy storage devices:

Firstly, MoS2 nanomaterials are very efficient supercapacitor electrode due to its sheet like structure providing high surface area for double layer charge storage and exhibits multiple oxidation states for pseudo capacitive charge transfer due to intercalation of H+ and Li+ into MoS2 structure. We have synthesized large scale and flexible MoS2 electrodes just by using direct magnetron sputtering technique. The novel three-dimensional (3D) porous structure of the MoS2 on copper film exhibits an excellent capacitance of 330 F /cm3 along with a high volumetric power and energy density of 40–80 W/cm3 and 1.6–2.4 mWh/cm3, respectively. Additionally, it shows excellent cycling stability upto 5000 cycles with capacitance retention of 97%.

Secondly,a unique binder-free electrode of 3-dimensional carbon nanotubes (3D CNTs) coated by MoS2 has been fabricated by a chemical vapor deposition (CVD) and direct magnetron sputtering method. The unique vertically oriented nanoflakes of MoS2 are strongly bonded on 3D CNTs with diameter of 50-100nm. The 3D geometry for the accommodation of active material (MoS2) provides high surface area with active electrochemical sites, enhances ion diffusivity, and compensates volumetric expansion of MoS2. The electrochemical performance of the binder-free 3D CNTs-MoS2 electrode shows very high areal capacity of ~1.65mAh/cm2 with an areal density (of MoS2) of ~0.35mg/cm2 at 0.5C rate; it also shows capacity retention of ~82% after 50 cycles. The unique architecture of 3D CNTs-MoS2 is suggestive to be a promising anode for next generation Li-ion batteries with high capacity and long cycle life.

References:

(a) N. Choudhary+, M. Patel+ (+ First Authors), Y.H. Ho, N.B. Dahotre, W.Lee, J.Y. Hwang, W.Choi, Directly deposited MoS2 thin film electrodes for high performance supercapacitors, J. Mater. Chem. A 3 (2015) 24049-24054

(b) M.D. Patel, E. cha, N. Choudhary, C. Kang, W. Lee, J. Hwang, W. Choi, Vertically oriented MoS2 nanoflakes coated on 3D carbon nanotubes for next generation Li-ion batteries, Nanotechnology 27 (2016) 495401-495410
Modulation of the Electrostatic and Quantum Capacitances of Few Layered Graphenes through Plasma Processing
Authors: Bandaru Prabhakar R , Narayanan Rajaram , Yamada Hidenori , Rao Apparao M. , Podila Ramakrishna , Karakaya Mehmet
Published: February 2020

A comprehensive understanding of the characteristics of graphene, with regard to its unique electrical and structural attributes, would be incomplete unless the inevitable presence of defects have been considered. While such imperfections may limit the realization of theoretically predicted characteristics, they may also be vital for uncovering new fundamental phenomena and related applications. Here we show that the charged defect generation, through argon ion based plasma processing, in few layer graphene (FLG) could be integral to the substantial enhancement of the electrical capacitance, and be of potential use in electrochemical (EC) energy storage. By combining EC characterization techniques with detailed Raman spectroscopic analysis, we elucidate the contributions of plasma-induced defects to electrostatic and quantum capacitance.

We then show that charged defect generation, through argon ion based plasma processing, in FLG could substantially enhance the electrical capacitance, and could be used for electrochemical energy storage. Detailed consideration of the constituent space charge and quantum capacitances were used to delineate a new length scale, correlated to electrically active defects contributing to the capacitance, and which was found to be smaller than a structural correlation length determined through Raman spectroscopy. The study offers insights into an industrially viable method (i.e., plasma processing) for modifying and enhancing the energy density of graphene-based electrochemical capacitors.
Photovoltaic Properties of Monolayer 2D Lateral Heterojunction Devices
Authors: Tsai Meng-Lin , Li Ming-Yang , Li Lain-Jong , He Jr-Hau
Published: February 2020

The recent development of two-dimensional (2D) monolayer lateral semiconductor has created new paradigm to develop p-n heterojunctions, the building block of electronic devices. Albeit, the growth methods of these heterostructures typically result in alloy structures at the interface, limiting the development for high efficiency photovoltaic (PV) devices. Here, we explore the PV properties of sequentially-grown alloy-free 2D monolayer WSe2-MoS2 lateral p-n heterojunction. Our PV devices show extraordinary power conversion efficiencies of 1.07. Moreover, the large surface active area of our PV devices enables the full exposure of the depletion region, leading to excellent omnidirectional light harvesting characteristic with only 10% reduction of efficiency at incident angles up to 75°—unachievable by conventional vertical solar cells. Modeling studies also demonstrate the PV devices comply with typical principles, greatly increasing the feasibility for further development. Furthermore, our appropriate electrode-spacing design led to environment-independent PV properties. These robust PV properties deriving from the atomically-sharp lateral p-n interface can help develop next-generation 2D monolayer-based electronic devices.
Metallic Phase MoS2-Graphene Composite for High Performance Coin Cells Supercapacitors
Authors: Aynalem Andinet Ejigu , Dryfe Robert AW , Kinloch Ian A
Published: February 2020

Molybdenum disulphide exhibits two possible crystal states, the naturally occurring semiconducting phase (2H-MoS2), and the non-naturally occurring metallic state (1T-MoS2) which can be prepared by intercalation chemistry.1 The metallic 1T phase has a conductivity up to 107 times higher than the 2H phase.2 Consequently, metallic phase MoS2 nanosheets are very attractive for a number of electrochemical applications including supercapacitor electrodes and catalysts for hydrogen evolution.2
,
3 For example, Acerce et al. recently demonstrated that the gravimetric capacitance of chemically exfoliated 1T-MoS2 was 20 times higher than the gravimetric capacitance of the 2H-MoS2.2

In this work, we compare the capacitive behaviour of 1T-MoS2, 2H-MoS2, graphene and 1T-MoS2/graphene composite using symmetrical coin cell architecture. The electrodes were prepared by filtering a known volume of the respective dispersion over pre-weighed polyvinylidene fluoride membrane using syringe pump dispenser. The gravimetric capacitance of 1T-MoS2 was over 100 F g-1 in aqueous solution which is higher than the gravimetric capacitance obtained using 2H-MoS2 or graphene electrodes. The capacitance performance of 1T-MoS2 was further enhanced by making a composite electrode with highly conducting graphene. A volumetric capacitance of over 560 F cm-3 in an aqueous solution and 250 F cm-3 in a non-aqueous solution were achieved using these composite electrodes. The composite electrode displayed capacity retention of over 90 % after 5,000 cycles. The enhanced capacitance in the composite material was probably due to a synergistic effect between 1T-MoS2 and graphene where graphene enhances the overall conductivity of the composite whilst also reducing the re-aggregation of the sheets.

1. M. A. Py and R. R. Haering, Can. J. Phys., 1983, 61, 76-84.

2. M. Acerce, D. Voiry and M. Chhowalla, Nat. Nanotechnol., 2015, 10, 313-318.

3. M. A. Lukowski, A. S. Daniel, F. Meng, A. Forticaux, L. S. Li and S. Jin, J. Am. Chem. Soc., 2013, 135, 10274-10277.
Investigating Properties of Graphene Oxide As a Drug Delivery/Imaging Platform
Authors: Sizemore Elizabeth , Hasan Md Tanvir , Culp Marais , Naumov Anton V
Published: February 2020

Graphene and its derivatives are novel materials with a number of unique properties that can be applied in electronics, sensing and biotechnology. Particularly, graphene oxide (GO) is an exceptional system that, unlike graphene, can be chemically mass-produced at low cost and possesses physical properties that are critical for biomedical applications. GO exhibits pH-dependent fluorescence emission in the visible/near-infrared, providing a possibility of molecular imaging and pH-sensing. It is also water soluble and has a substantial platform for functionalization, which allows for the delivery of multiple therapeutics, or the attachment of different sensing moieties. Some of these properties can be adjusted by the means of chemical/physical processing to fit the desired therapeutic delivery or sensing approaches. We utilize and modify these properties to yield a multifunctional delivery/imaging/sensing platform geared toward the analysis of cancer therapeutics delivery in vitro. In our work GO serves as a drug transport agent when paired with cancer therapeutic drugs and as a molecular marker for imaging the delivery pathways. The optimal emission and excitation of the graphene oxide flakes are selected to maximize the imaging modality in the spectrally-confined region and reduce the effects of biological autofluorescence. We also modify GO physical properties via controlled oxidation to maximize the emission and reduce the cytotoxicity to low/negligible levels: we report over 90% cell viability with GO concentration levels of 15 ug/mL based on the MTT assay in HEK-293 cells. GO emission in healthy (HEK-293) and cancer (HeLa) cells is quantified for a variety of pH environments, as well as flake sizes, to identify the ideal conditions for cellular internalization and pH-sensing of acidic cancerous environments. In addition, in-vitro fluorescence microscopy analysis provide quantitative assessment of the drug delivery and preferential targeting for cancer versus healthy cells. The results of this work suggest GO as an innovative and effective multifunctional platform for cancer therapeutics.
Heterostructures Beyond Van Der Waals
Authors: Perez Emilio M
Published: February 2020

One of the most attractive areas of research in Nanoscience is the combination of 2D materials through van der Waals forces heterostructures.1 Here, we present strategies beyond dispersion forces to interface 0D-2D and 2D-2D materials.

We will show examples of 0D-2D heterostructures connected through covalent and noncovalent chemistry. In the first example, we will show a method to functionalize graphene covalently with exquisite (>98%) atomic selectivity.2 In the second example, we will show that the photoresponse of MoS2 photodetectors can be enhanced by simple and reversible supramolecular functionalization with organic dyes.3 Finally, we will also the unique example of franckeite, a naturally occuring van der Waals heterostructure that can be thinned down to very few layers, both mechanically and through liquid-phase exfoliation.4

References:

(1) Novoselov, K. S.; Mishchenko, A.; Carvalho, A.; Castro Neto, A. H. Science
2016, 353, DOI: 10.1126/science.aac9439

(2) Navarro, J. J.; Leret, S.; Calleja, F.; Stradi, D.; Black, A.; Bernardo-Gavito, R.; Garnica, M.; Granados, D.; Vazquez de Parga, A. L.; Pérez, E. M.; Miranda, R. Nano Lett.
2016, 16, 355.

(3) Molina-Mendoza, A. J.; Vaquero-Garzon, L.; Leret, S.; de Juan-Fernandez, L.; Pérez, E. M.; Castellanos-Gomez, A. Chem. Commun.
2016, 52, 14365.

(4) Molina-Mendoza, A. J.; Giovanelli, E.; Paz, W. S.; Nino, M. A.; Island, J. O.; Evangeli, C.; Aballe, L.; Foerster, M.; Van der Zant, H. S. J.; Rubio-Bollinger, G.; Agrait, N.; Palacios, J. J.; Perez, E. M.; Castellanos-Gomez, A. 2016, arXiv:1606.06651 (final version accepted in Nature Comms.)
Substrate Modulated Reductive Graphene Functionalization
Authors: Hirsch Andreas
Published: February 2020

Covalently functionalizing mechanical exfoliated monolayer and bilayer graphenides with λ-iodanes led to the discovery that the monolayers supported on a SiO2 substrate are considerably more reactive than bilayers as demonstrated by statistical Raman spectroscopy/microscopy. Supported by DFT calculations we show that ditopic addend binding leads to much more stable products than the corresponding monotopic reactions due to much lower lattice strain of the reactions products. The chemical nature of the substrate (graphene versus SiO2) plays a crucial role.
>24h Stabilization of Silicon Photoanode Operation in Aqueous Media Using a Fluorinated Graphene Protection Layer
Authors: Thompson Annelise C. , Nielander Adam C. , Lewis Nathan S
Published: February 2020

Development of efficient and robust photoelectrochemical systems compromised of semiconductor electrodes which harness light to drive useful chemical transformations is hindered by a paucity of appropriate protective coatings to enable operation in aqueous media. Optically transparent, electrically conductive and physically stable coatings must be generated in order to avoid deleterious surface reactions associated with the corrosion and passivation of the semiconductor in solution. Graphene is the thinnest protective coating (0.3 nm) shown to extend stability of a semiconductor in aqueous solution, due in part to its relative impermeability to most gases and liquids. However, large-scale graphene growth via chemical vapor deposition – vital to integration of graphene into commercial devices – yields polycrystalline graphene, which contains a number of defects, such as dangling bonds found at grain boundaries and the edges of a sheet or point dislocations found within the sheet. This work demonstrated that capping these defects utilizing fluorine moieties can lead to significantly enhanced stability of silicon photoanodes under anodic conditions in aqueous media, which are typically too harsh for carbon-based layers to withstand for extended periods of time. N-type silicon (n-Si) (111) photoelectrodes with a hydride surface functionalization were biased anodically at short-circuit in aqueous Fe(CN)6
3-/4- under illumination (∼33 mW cm–2 ENH-type W-halogen lamp), and the generated photocurrent was observed to decay almost to zero within 100s, consistent with rapid corrosion of the semiconductor. In comparison, identical photoelectrodes protected with a single sheet of fluorinated graphene (F–Gr) demonstrated photocurrent densities of ~ 10 mA cm-2 for > 100,000s (> 24h). X-ray photoelectron spectra collected before and after exposure to aqueous anodic conditions showed that oxide formation was significantly inhibited for the n-Si electrodes covered with F–Gr in comparison with bare n-Si–H electrodes tested under the same conditions. Variations in the open-circuit voltage (VOC) in contact with several different redox couples with formal potentials that span the bandgap of silicon indicated that the photoanodes coated with F–Gr did not form a buried junction with respect to solution, which shows promise for the use of F–Gr as a protective layer for semiconductors beyond silicon. In addition, n-Si photoanodes coated with F–Gr exposed to a HBr/Br2 electrolyte solution under anodic conditions showed enhanced stability and formed a halide-splitting cell with up to 5% efficiency with the addition of a platinum catalyst, demonstrating that these protective layers can successfully be integrated into devices for the production of chemical fuels.
(Invited) New Functionalities of 2-Dimensional Materials: Graphene, Doped-Graphene, Tough Fibers and Beyond
Authors: Terrones Maurcio
Published: February 2020

This talk will first provide an overview of different defects in 2-Dimensional materials including graphene and Chalcogenides. In particular, we will focus on: 1) defining the dimensionalities and atomic structures of defects; 2) pathways to generating structural defects during and after synthesis and, 3) the effects of having defects on the physico-chemical properties and applications. We will then discuss the synthesis of large-area, high-quality monolayers of nitrogen-, boron- and silicon-doped graphene sheets on Cu foils using ambient-pressure chemical vapor deposition (AP-CVD). Scanning tunneling microscopy (STM) and spectroscopy (STS) demonstrate that defects in doped graphenes arrange in different geometrical configurations exhibiting different electronic and chemical properties. Interestingly, these doped layers can be used as efficient molecular sensors and electronic devices. In this context, Graphene enhanced Raman spectroscopy will be introduced and it will explained that by doping graphene with Nitrogen, the Fermi level (EF) of graphene shifts, and if this shift aligns with the lower unoccupied molecular orbital (LUMO) of a molecule, charge transfer would be enhanced, thus significantly amplifying the molecule's vibrational Raman modes. Concentrations as low as 10-11 mol/L of different dye molecules can be detected using GERS. Finally, we will discuss the controlled synthesis and assembly of chalcogenide monolayers on different substrates. The electronic performance of monolayers of MoS2, WS2 and hetero-systems operating under flexural strain will also be presented. Our findings demonstrates that it is now possible to use chalcogenide layers for the fabrication of flexible electronic devices, however, defect control is required to tailor their performance. Finally, we will talk about the transformation of graphite into graphene oxide (GO). This material could be used in the fabrication of robust and super-tough films and fibers, as well as 3-Dimensional graphene foams; all exhibiting fascinating mechanical, and electronic properties. These GO materials could also be incorporated in ceramics and polymers, and recent exciting progress in these areas will be introduced.
A Wafer-Scale Bernal Stacked Bilayer Graphene Film Obtained on a Cu(0.5 %at Ni) Foil Using Atmpspheric Pressure Vapour Deposition
Authors: Manyala Ncholu , Madito Jack
Published: February 2020

Graphene has attracted wide interest due to its promising potential applications in electronics and photonics. However, many of these applications are restricted by zero band gap of graphene. Nonetheless, a considerable band gap of up to 250 meV can be opened up in Bernal (AB) stacked bilayer graphene by applying a perpendicular electric field between the two superimposed layers. Hence, graphene synthesis has been focused on growing high-quality and large-area AB-stacked bilayer graphene. Chemical vapour deposition (CVD) is a favourable synthesis technique for graphene since it can grow high-quality and large-area or wafer-scale graphene, which is important for electronic devices. In addition, atmospheric-pressure CVD is technologically more accessible for graphene growth. The metallic substrate like Cu which mostly used for CVD grown graphene is found to be favouring to grow monolayer graphene because of limitation of C arbsorption in Cu, while Cu substrate engineered with Ni is found to grow multilayer graphene because of significant arbsorption of C in Ni and hence if it well controlled it can grow AB stacked graphene.

In this study we focuse on the AP-CVD synthesis and characterization of high-quality and wafer-scale (scale of an entire foil) AB-stacked bilayer graphene film obtained on a dilute Cu(0.61 at% Ni) foil and compared the growth to the results of AP-CVD growth under identical conditions on pure Cu foil. Atomic force microscopy (AFM) average step height analysis showed thickness of bilayer graphene, scanning electron microscopy (SEM) micrographs showed uniform and continuous graphene layers and the Raman optical microscopy images and spectroscopy data supported by selected area electron diffraction (SAED) data showed high-quality and continuous (wafer-scale) AB-stacked bilayer graphene for graphene film obtained on a dilute Cu(0.5 at% Ni) foil.
In Situ variable-Temperature Scanning Tunneling Microscopy Studies of 2D Graphene and Hexagonal Boron Nitride (hBN) Layer Growth Kinetic
Authors: Kodambaka Suneel
Published: February 2020

The rich physical phenomena and properties associated with two-dimensional (2D) graphene layers have led to a surge in research efforts focused on synthesis, characterization, and, even large-scale production of a variety of 2D crystals. In the newly emergent class of 2D layered materials (and devices), some of the highly exciting developments are a result of leveraging the properties of individual layers via stacking of dissimilar 2D materials held together by van der Waals (vdW) forces. Such vdW-layers exhibit new properties (e.g., valleytronics) and are ideal for ultrathin flexible devices.

Graphene is semi-metallic, while its insulating 2D layered analog is hexagonal boron nitride (hBN). Graphene and hBN are isostructural and nearly lattice matched. Composite, lateral, and vertical heterostructures of graphene and hBN layers are expected to exhibit new physical phenomena and properties: tunable bandgap, magnetism, unique electronic and thermal transport properties, robust half-metallic behavior without applied electric fields, and more. Access to such new properties and hence novel applications, hinge on the ability to assemble the 2D materials in desired architecture. This requires fundamental understanding of the mechanisms governing the formation of epitaxial stacks of desired stacking sequences and layer thicknesses, atomically-abrupt graphene-hBN interfaces and domain widths within a single atomic layer, and desired composition within a 2D sheet. As a first step toward this goal, we investigated the chemical vapor deposition (CVD) kinetics of monolayer graphene and hBN on Pd(111) using ultra-high vacuum (UHV) variable-temperature scanning tunneling microscopy (VT-STM).

In this talk, we present in situ VT-STM observations of graphene growth using ethylene and hBN growth using borazine on Pd(111) as a function of substrate temperature, borazine flux, and deposition time. We observe the formation of monolayer graphene islands bounded by Pd surface steps. Using scanning tunneling spectroscopy (STS) measurements along with density functional theory (DFT) calculations, we show that graphene/Pd(111) exhibits a bandgap due to the strong interaction between graphene and the Pd substrate. During the CVD of borazine, we observe the nucleation and growth of chemisorbed borazine islands on Pd(111). Using STS, we determined the effect of hBN domain orientation with respect to Pd(111) on its bandgap. From the STM experiments, we identified the growth parameters critical to the formation of single-domain hBN layers on Pd(111). Our studies, which provide new insights into the growth of graphene and hBN monolayers, are useful in developing recipes for the growth of heterostructures of desired architecture.
Graphene Nanoribbon Heterojunctions with Dbtp Precursors on Ag(111)
Authors: Miranda Rodolfo , Cirera Borja , Otero Roberto , Gallego Jose M. , Ecija David
Published: February 2020

The observed width (and edge) dependence of the electronic structure and band gap of graphene nanoribbons has generated a vivid interest in the possibility to generate optically active, graphene-based quantum dots that can play a role in optically driven solid state devices for quantum information. We describe a bottom-up approach to generate armchair graphene nanoribbons (AGNRs) of well defined width and atomically perfect edges on Ag(111) surfaces under UHV conditions by debromination of DBTP precursors, covalent reaction along 1D metal-organic structures and subsequent covalent lateral reaction with neighbouring wires, giving rise to 6-12 AGNRs. The resulting graphene nanoribbons are examined in situ by STM and STS revealing the electronic structure of wires, heterojunctions and quantum dots at the atomic scale.

Figure 1
(Invited) Black Phosphorus Field Effect Transistors: Passivation By Oxidation, and the Role of Anisotropy in Magnetotransport
Authors: Szkopek Thomas , Gervais Guillaume , Peruzzini Maurizio , Heun Stefan
Published: February 2020

Black phosphorus (bP) is an elemental allotrope with an anisotropic layered crystal structure consisting of a puckered honeycomb lattice that can be mechanically exfoliated down to atomic layer thickness. bP is the most thermodynamically stable allotrope of phosphorus but is nonetheless subject to photo-­oxidation in the presence of water, oxygen and visible light with a reaction rate that increases as bP layer thickness decreases [1]. In the first part of my talk, I will describe our experiments showing how oxidation can be used for passivation of black phosphorus field effect transistors. In the second part of my talk, I will describe magnetotransport measurements of black phosphorus transistors and their relation to the anisotropy of the bP crystal lattice.

Motivated by the experimental observation that reactive ion etching produces a phosphorus oxide / black phosphorus interface that does not inhibit photo-luminescence yield [2], we have fabricated bP field effect transistors with an encapsulating phosphorus oxide layer that acts as a passivation layer. X-ray photoemission spectroscopy (XPS) reveals the oxide layer to have a P205 stoichiometry. Air stable, top gated bP field effect transistors with room temperature field effect mobilities exceeding 100 cm2/Vs are demonstrated using a gate oxide formed by reactive ion etching and subsequent atomic layer deposition of aluminum oxide.

We have also investigated the magnetotransport properties of black phosphorus at modest fields. Weak localization was observed in a black phosphorus field-effect transistor 65 nm thick [3]. The weak localization behavior was found to be in excellent agreement with the Hikami-Larkin-Nagaoka [4] model for fields up to 1 T, from which characteristic scattering lengths could be inferred. The temperature dependence of the phase coherence length L

ϕ

 was investigated, and above 1 K, it was found to decrease weaker than the L

ϕ ~ T

−1/2 dependence characteristic of electron-electron scattering in the presence of elastic scattering in two dimensions. Rather, the observed power law was found to be close to that observed previously in quasi-one-dimensional systems such as metallic nanowires [5] and carbon nanotubes [6]. The potential role of strong in-plane anisotropy resulting from a puckered honyecomb structure on localization will be discussed.

[1] A. Favron et al., Nat. Mater. 14, 826 (2015).

[2] J. Pei et al., Nat. Comm. 7, 10450 (2016).

[3] N. Hemsworth et al., Phys. Rev. B 94, 245404 (2016).

[4] S. Hikami et al., Prog. Theor. Phys. 63, 707 (1980).

[5] D. Natelson et al., Phys. Rev. Lett. 86, 1821 (2001).

[6] J. Appenzeller et al., Phys. Rev. B 64, 121404(R) (2001).
Hyperbolic Cooling of a Graphene on BN Transistor in the Zener-Klein Regime
Authors: Yang Wei , Berthou Simon , Lu Xiaobo , Watanabe Kenji , Zhang Guangyu , Baudin Emmanuel , Placais Bernard , Voisin Christophe
Published: February 2020

Engineering of cooling mechanisms is a bottleneck in nanoelectronics. Whereas thermal exchanges in diffusive graphene are driven by defect-assisted supercollisions [1], the case of high-mobility graphene on hBN is radically different with a prominent contribution of remote phonons from the substrate. Here, we show that a bilayer graphene on hBN transistor can be driven in the Zener-Klein (ZK) tunnelling regime where current is fully saturated. Using sensitive GHz noise thermometry [2], we show that ZK-tunnelling triggers a new cooling pathway due to the emission of hyperbolic phonons polaritons (HPPs) in hBN by out-of-equilibrium electron-hole pairs (Figure 1). The most striking consequence is a reversal of the doping dependence of the electronic temperature due to the Pauli blocking of ZK-tunnelling at finite doping. HPP cooling is the most efficient mechanism in graphene and promotes graphene Zener-Klein transistors as a valuable route for RF power amplification.

A. Betz et al., Nat. Phys., 9 (2013) 109

W. Yang et al., submitted (2016)

Figure 1
Thickness Dependence of Graphene-Hexagonal Boron Nitride-Graphene Based 2D Capacitor
Authors: Stehle Yijing , Vlassiouk Ivan , Polyzos Georgios , Smirnov Sergie , Datskos Panos
Published: February 2020

In this paper, a nanoscale dielectric capacitor was fabricated through wet transfer of CVD growth hexagonal boron nitride hBN as dielectric materials between monolayer graphene electrodes. The specific capacitance, power, and energy the capacitor with different hBN layer number were evaluated through cyclic voltammetry test. Different to traditional capacitor, whose capacitance decrease with dielectric layer distance once electrode is set, the capacitance of graphene-hBN-graphene based nanocapacitor increase with layer number before the thickness goes above 3nm at low scan rate (<50mv/s) due to the strong influence of interface quantum capacitance. The thickness-dependent stacked hBN thin film’ effective permittivity between graphene electrode was analyzed by impedance spectroscopy. we experimentally reveal that the permittivity of hBN thin film first increase then decrease with it layer number increase, which is also observed in other layered structure dielectric materials. The fabricated capacitor also shows promising transparency and flexibility.
(Invited) Plasmonic Enhancement of Single- and Multi-Electron Transfer Reactions on Modified Electrodes
Authors: Ikeda Katsuyoshi
Published: February 2020

In a photo-energy conversion system, the efficiency of photon capture is one of key issues that determine the overall efficiency. Metal nanostructures are recently drawing attention due to their unique optical properties, which are known as localized surface plasmon resonance (LSPR). Since metal nanostructures can confine incoming photon energy into the nanoscale region through excitation of LSPR, they are expected to function as optical nano-antennas. Indeed, various optical processes such as Raman scattering or fluorescence can gain intensity from LSPR. Such plasmonic enhancement is theoretically well explained and various applications have been demonstrated. On the other hand, plasmonic enhancement of photochemical reactions is still under discussion because the efficiency of photochemical reactions is influenced by many factors. Moreover, kinetics of photochemical reactions may be much slower than the lifetime of LSPR; plasmonic effect is not straightforward in this case. We have reported that photo-induced uphill single-electron transfer reaction can be enhanced by forming plsmonic nano-antennas on top of porphyrin-linked molecular monolayers at an Au electrode. In this talk, plasmonic enhancement of multi-electron transfer reactions will also be discussed, which are governed by more complicated and slower kinetics.

Fig. local field enhancement near an Au nanoparticle deposited on molecular monolayer on an Au substrate

Figure 1
(Invited) Highly Concentrated CO Evolution for Photocatalytic Conversion of CO2 By H2o As an Electron Donor
Authors: Teramura Kentaro
Published: February 2020

We should therefore attempt to develop industrial processes using CO2 as a feedstock and H2O as an electron donor in order to build a sustainable society in the near future. If H2O does function as the electron donor, then it is important to obtain a stoichiometric ratio between the amount of O2 evolved and the amount of CO2 reduced. Moreover, the reduction of H+, released from H2O molecules, usually competes with CO2 reduction when several heterogeneous materials are used as photocatalysts for the reduction of CO2 with H2O. Generally, the production of H2 via the reduction of H+ is the dominant pathway. Therefore, to achieve high selectivity in the photocatalytic conversion of CO2 with H2O, the electrons generated through the oxidation of H2O must be controlled to selectively. These days, we found that Ag/ZnGa2O4/Ga2O3, Ag/La2Ti2O7, Ag/SrO/Ta2O5, Ag/ZnGa2O4, and Ag/ZnTa2O6 exhibit good conversion of CO2 and high selectivity toward CO evolution for the photocatalytic conversion of CO2 by H2O as an electron donor.
(Invited) Electronic and Photophysical Properties of Surface-Anchored Metal-Organic Frameworks (SURMOFs)
Authors: Wöll Christof
Published: February 2020

The huge versatility and unparalleled level of control in the design of metal-organic frameworks (MOFs) has recently been shown to also carry a huge potential for applications based on the electrical, electronic and photophysical properties of this rich class of materials. Recent examples are MOF-based electrochemical [1,2], photo-electrochemical [3] and photovoltaic devices [4,5], as well as photon-upconversion [6]. Since at present methods to provide reliable and reproducible contacts to MOF-materials are scarce, we have developed a method to produce well-defined, highly oriented and monolithic MOF thin films supported on different types of surfaces, also referred to as SURMOFs [7]. This procedure in particular allows the fabrication of hetero-multilayers (see Fig. 1). In this talk, we will describe the fabrication of such well-defined model systems as well as the results of detailed, multi-technique investigations of electrical [8] and photophysical properties exhibited by empty and loaded MOFs, including cyclic voltammetry, atomic force microscopy, quartz crystal microbalance and UV-Vis spectroscopy. In this talk, we will demonstrate that the huge size of the chemical space spanned by MOFs can be further drastically increased by loading MOFs with nanoparticles or quantum dots. In this context, SURMOFs offer particular advantages since the loading can be carried out in a layer-by-layer fashion, offering the potential to fabricate hetero-mulitlayers.

References:

[1] A. Dragässer, O. Shekhah, O. Zybaylo, C. Shen, M. Buck, Ch. Wöll, D. Schlettwein, Chem. Comm., 48, 663 (2012)

[2] J. Liu, M. Paradinas, L. Heinke, M. Buck, C. Ocal, V. Mugnaini, Ch. Wöll, Chem.Elektro.Chem., 3, 713 (2016)

[3] Lu Ye, J. Liu, Y. Gao, Ch. Gong, M. Addicoat, Th. Heine, Ch. Wöll, L. Sun, J. Mater. Chem. A, 4, 15320, (2016)

[4] J. Liu, W. Zhou, J. Liu, I. Howard, G. Kilibarda, S. Schlabach, D. Coupry, M. Addicoat, S. Yoneda, Y. Tsutsui, T. Sakurai, S. Seki, Zh. Wang, P. Lindemann, E. Redel, Th. Heine, Ch. Wöll, Angew. Chemie Intl. Ed., 54, 7441 (2015)

[5] J. Liu, W. Zhou, J. Liu, Y. Fujimori, T. Higashino, H. Imahori, X. Jiang, J. Zhao, T. Sakurai, Y. Hattori, W. Matsuda, Shu Seki, S. K. Garlapati, S. Dasgupta, E. Redel, L. Sun, Ch. Wöll, Journal of Mat. Chem. A, 4, 12739 (2016)

[6] M. Oldenburg, A. Turshatov, D. Busko, S. Wollgarten, M. Adams, N. Baroni, A. Welle, E. Redel, Ch. Wöll, B. S. Richards, I. A. Howard, Adv. Mater., 28, 8477 (2016)

[7] Jin-L. Zhuang, A. Terfort, C. Wöll, Coordination Chemistry Reviews, 307, 391, (2016)

[8] J. Liu, T. Wächter, A. Irmler, P.G. Weidler, H. Gliemann, F. Pauly, V. Mugnaini, M. Zharnikov, Ch. Wöll, ACS Applied Materials & Interfaces, 7, 9824, (2015)

Figure 1
(Invited) Synthesis of Ordered Semiconductor Nanostructures for Energy Conversion Using Anodic Porous Alumina
Authors: Masuda Hideki , Kondo Toshiaki , Yanagishita Takashi
Published: February 2020

Efficient synthesis of the ordered nanostructures of semiconductors is important issue to be solved for the preparation of the photo-energy conversion systems with high efficiency [1]. For the effective preparation of the ordered nanostructures of semiconductors, the use of the naturally occurring ordered nanomaterials is promising for the synthesis due to its capability of the preparation of ordered nanostructures with high efficiency. Among them, anodic porous alumina, which is formed by anodization of Al in acidic electrolyte, is one of promising material due to ist precisely controllable geometrical nanostructures [2]. In the present report, the synthesis of the ordered nanostructures of semiconductors using anodic porous alumina templates will be described. The template synthesis using highly ordered anodic porous alumina allows the preparation of ordered nanostructures of the semiconductors. In addition, the application of the highly ordered anodic porous alumina with reduced hole intervals (~25 nm) and hole sizes (~10 nm) prepared under the low voltage anodization [3] generated the ordered structures of semiconductors with small dimensions. In the experiment, semiconductor (ZnO [4,5], CdS) nanorod arrays were prepared by electrochemical or hydrothermal synthesis of semiconductors using anodic porous alumina templates. The geometrical structure of the obtained nanorod arrays of semiconductors could be precisely controlled based on the ordered structures of anodic porous alumna. The synthesis of the nanorod arrays on the conducting substrates (ITO etc.) could provide the current collection electrodes with large surface area. The present process will be used for the preparation of nanostructures of semiconductors, which are required for the preparation of various kinds of photoenergy conversion systems with high efficiency, such as organic photovoltaic solar cells [6].

1. T. Shinagawa, S. Watase, M. Izaki, Cryst. Growth Des., 11, 5533 (2011).

2. H. Masuda and K. Fukuda, Science, 268, 1466 (1995).

3. H. Masuda, K. Takenaka, T. Ishii, K. Nishio, Jpn. J. Appl. Phys., 45, L1165 (2006).

4. M. Izaki, T. Omi, Appl. Phys. Lett., 98, 2439 (1996).

5. T. Özdal, R. Taktakoğlu, H. Özdamar, M. Esen, D. K. Takҫi, H. Kavak, Thin Solid Films, 592, 143 (2015).

6. B. Kippelen, J.-L. Brédas, Energy Environ. Sci., 2, 251 (2009).
(Invited) Energy and Information Conversion Assisted By Electric Double Layers at Liquid-Solid Nano-Interfaces
Authors: Awaga Kunio
Published: February 2020

Electric double layers (EDLs) at liquid-solid interfaces have attracted much attention in soft-material electronics, because they can induce extremely large electric fields, through which effective carrier injection and charge separation can be realized. As representative EDL materials, ionic liquids possess excellent features for electronic application, such as a wide electrochemical window, low vapor pressure, and high chemical and physical stability. In this presentation, we describe our recent works on organic field-effect transistors with ionic liquids as gate dielectrics. Secondly, we describe the opto-electronic conversion in organic photocells with a [Metal | Semiconductor | Electrolyte | Metal] structure, which can be used to effectively produce a polarization current under modulated light stimulus. We discuss their application to the information conversion in the NIR light range, as biosensors, and as AC photovoltaic cells based on the layered Perovskite compounds.
(Invited) Organic-Inorganic Hybrid Solar Cells with Antimony Sulfide-Metal Composites
Authors: Yukawa Mayumi , Hayakawa Akinobu , Sagawa Takashi
Published: February 2020

Since antimony sulfide (Sb2S3) has much attraction for photovoltaics in terms of appropriate bandgap, high absorption coefficient, low toxicity, and abundance, it has been recently applied for organic-inorganic hybrid solar cells, which has been attained the power conversion efficiency (PCE) of 7.5%.[1] We also have prepared Sb2S3-based solar cells with TiO2 or ZnO nanoparticles for electron transporting layer in addition to poly(3-hexylthiophene)-2,5-diyl (P3HT)/ (3, 4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS), zinc phthalocyanine (ZnPc), or MoO3 for hole transporting layer and compared their photovoltaic performance. Among these hybrid solar cells, it was found that the combination with ZnPc and TiO2 has the highest durability with keeping the relative PCE of 90% after the stability test under 1 sun at 63 °C at a relative humidity of 50% for 1,500 h.[2] For further improvement of the photovoltaic performance, we newly added La or Zn into　the precursor of Sb2S3 to prepare Sb2S3–metal composites and applied them for organic-inorganic hybrid solar cells.

Remarkable enhancement of the open-circuit voltage for glass-FTO/TiO2/Sb2S3 + La/P3HT/poly[(3-carboxybutyl)thiophene-2,5-diyl] (P3CT)/Au was observed after the addition of La to Sb2S3 and 33% improvement of PCE was attained. Impedance analyses of the hybrid solar cells with or without La revealed that the resistance at the interface was effectively lowered through the addition of La though the bulk-resistance had not been changed. It was found that the added La was phase-separated and accumulated between the layers of TiO2 and SbS3 through the TEM-EDX observations of the cross-sectional views of the La-added device. In this context, La was not doped into Sb2S3 but inserted into the interface of TiO2 and SbS3.

On the contrary, addition of Zn into the Sb2S3 precursor resulted in the enlargement of the crystalline size of the Sb2S3 from 14 nm to 25 nm, which was estimated from XRD peaks. No phase-separation was confirmed by TEM observations of the cross-sectional views. Therefore, it was concluded that the Zn was doped into Sb2S3. By using the Zn-doped Sb2S3, remarkable increment of the current density was observed in addition to relatively high fill factor and 57% improvement of PCE. These results are ascribed to the effective lowering the bulk-resistance, which was confirmed by the impedance analyses.

[1] J. A. Chang, J. H. Rhee, S. H. Im, Y. H. Lee, H. J. Kim, S. I. Seok, M. K. Nazeeruddin, and M. Graetzel, Nano Lett., 2010, 10, 2609–2612.

[2] A. Hayakawa, M. Yukawa, and T. Sagawa, ECS Trans., ahead of print.