Symposium F
Graphene and Other Emerging 2D-layered Nanomaterials: Synthesis, Properties and Potential Applications


Session F-1 - General Physical and Chemical Properties

F-1:KL  2D Materials: Standards, Science, and Technology
A.H. CASTRO NETO, National University of Singapore, Singapore

The field of 2D materials is one of the fastest growing fields in Physics. The scientific developments in the last few months have shown that one can reach unprecedent control of the electronic properties of these materials. Nevertheless, the technological development of new applications has been stalled by the lack of clear standards for characterization and processing. I will review the evolution in this exciting field and discuss what lies ahead.

F-1:L01  Optoelectronic Properties of Transition Metal Dichalcogenides
L. BALICAS, D. RHODES, National High Magnetic Field Lab, Florida State University, Tallahassee, FL, USA

Here, we will discuss a broad range of optoelectronic properties measured from transition metal dichalcogenides, ranging from photoconductivity, photovoltaic response, a density of carriers induced metal-insulator transition, new functionalities associated with the intrinsic Schottky barrier at the level of the electrical contacts, and the electronic structure at the Fermi level of semi metallic systems. For example, photo-transistors based upon a few atomic layers of these systems can show extremely high photo-responsivities with reasonable although optimizable photo-responsive times while PN-junctions can display photovoltaic responses approaching 12 to 14 %. Through a scaling analysis of the conductivity as a function of the temperature we show that the metal insulator transition observed in these systems is ascribable to a second-order phase-transition driven by electronic correlations. We also show that in ambipolar systems a gate voltage can modulate the relative size of the Schottky barriers, which upon illumination leads to a novel type of optoelectronic switch. Finally, we show that the electronic structure at the Fermi level of semi metallic compounds cannot be captured by band structure calculations.

F-1:IL02  Role of Edge Geometry and Chemistry in Electronic and Magnetic Structures of Nanographenes
TOSHIAKI ENOKI, Tokyo Institute of Technology, Tokyo, Japan

The electronic structures of graphene nanostructures depend crucially on their edge geometries, in which zigzag and armchair edges are two fundamental components. In armchair-edged nanostructures, electron wave interference gives rise to the formation of a standing wave, resulting in energetically stabilizing these nanostructures. In contrast, spin-polarized nonbonding edge states are created at zigzag edges, giving the electronic, magnetic and chemical activities to zigzag-edged nanostructures. The electronic structures depend also on how edges are terminated with foreign chemical species. We have investigated the electronic structures of graphene nanostructures using STM/STS and AFM observations together with DFT calculations. Monohydrogenated and dihydrogenated linear zigzag edges were found to possess edge states well localized and less localized in the vicinity of zigzag edges, respectively. In contrast, an edge consisting of a mixture of mono- and di-hydrogenated carbon atoms has no edge state, instead it is subjected to the formation of standing wave similar to armchair-edged nanostructures. Oxygen-terminated linear zigzag edges have less localized edge state owing to charge transfer from edge carbon atoms to oxygen atoms.

F-1:IL03  Raman Spectroscopy of Graphene-related Materials
C. CASIRAGHI, School of Chemistry, University of Manchester, UK

Raman Spectroscopy is the most used technique to probe the properties of graphene and related materials. In this talk I will give an overview on the use of this technique to identify graphene, and to probe amount of defects, doping, strain and superlattices [1-5]. I will also show that Raman spectroscopy is able to identify ultra-narrow and atomically precise graphene nanoribbons [6-8].
1 Ferrari et al. (2006), Phys. Rev. Lett. 97, 18740; 2 Pisana et al (2007), Nature Materials, 6, 198; 3 Zabel et al (2011), Nano Letters, 12, 617; 4 Eckmann et al (2012), Nano Letters, 12, 3925; 5 Eckmann et al (2013), Nano Letters, 13, 5242; 6 Narita et al (2014), Nature Chemistry, 6, 126; 7 Narita et al (2014), ACS Nano, 8, 11622; 8 Verzhbitskiy et al, submitted

F-1:L05  Understanding the Structural Evolution of Graphene Heated with Electrical Current in Air

In various applications of graphene, understanding the mechanism of the changes of the graphene in harsh environments should precede many activities in tamed conditions. In this presentation, we report the unusual structural evolution of microbridge graphene in air near the electrical current-breakdown limit. In-situ micro-Raman study revealed broad D and G peaks in Raman spectra taken under high-electrical currents. The broad Raman peaks show partially reversible behavior under electrical currents below the breakdown limit. The reversible portion of the broad Raman peak seems to be due to the physical changes due to the thermal stress, and the irreversible portion is due to chemical changes in graphene structure producing amorphous-carbon like phase. Our calculations suggest that the irreversible phase is originated from the broken symmetry caused by defect formations, in particular, bonds of carbon-oxygen and vacancies-oxygen. A collection of energetically favorable vacancies-oxygen pairs results in porous graphene, and its evolution can be the key to understanding how the breakdown starts and propagates in graphene under high current density in air. In summary, we investigate structural changes and breakdown of graphene with increasing the electrical current.

F-1:L06  Super-low Friction Property of Si-doped Diamond-like Carbon by the Generation of Graphene Structure: Quantum Chemical Molecular Dynamics Simulations
M. KUBO, S. BAI, M. NAKAMURA, Y. HIGUCHI, N. OZAWA, Institute for Materials Research, Tohoku University, Sendai, Japan

Si-doped diamond-like carbon (DLC) has gained much attention as super-low friction materials for automotive engines, aerospace equipments, etc. However, the mechanism of its super-low friction property has not been clarified yet. Therefore, we applied our quantum chemical molecular dynamics simulator [1,2] to clarifying the origin of its super-low friction property. Our simulation results indicate that Si doping in the DLC generates the graphene structure on the DLC surface and it leads to the super-low friction coefficient. We also elucidated that the stress around the doped Si atom changes the six-membered carbon ring to the five-membered carbon ring and this structure change leads to the C-C bond dissociation of its neighboring six-membered carbon ring. Then, this C-C bond dissociation generates graphene structure. We also suggest how to increase the number of graphene structure on the DLC surface.
[1] K. Hayashi, M. Kubo et al., Faraday Discuss., 156 (2012) 137. [2] S. Bai, M. Kubo et al., RSC Adv., 4 (2014) 33739.

F-1:IL07  Emission and Detection of THz Radiation in Double-graphene-layered van der Waals Heterostructures via Photon-assisted Plasmonic Resonant Tunneling
TAIICHI OTSUJI, Research Institute of Electrical Communication, Tohoku University, Sendai, Japan

This paper reviews recent advances in the research of graphene-based van der Waals heterostructures for emission and detection of terahertz radiation. A gated double-graphene-layer (G-DGL) nanocapacitor is the core shell under consideration, in which a thin tunnel barrier layer is sandwiched by outer graphene layers at both sides. A dc bias voltage between the GLs induces charges (electrons (hole) in the negatively (positively) biased GL), resulting in band-offset energy between the GLs. The gate bias voltage can tune the band offset. By applying a pertinent gate bias voltage photon emission or photon absorption, whose energy coincides with the band offset, can assist the inter-GL resonant tunneling. Preliminary experimental results demonstrate the occurrence of THz photon emission and detection in the G-DGL. The DGL can excite symmetric optical and anti-symmetric acoustic coupled plasmon modes in the GLs. The latter mode can modulate the band-offset between the GL, giving rise to modulation of the inter-GL-layer resonant tunneling. This can dramatically enhance the THz gain or responsivity via plasmon-assisted inter-GL resonant tunneling.

F-1:L08  Graphene-boron Nitride 2D Heterosystems Functionalized with Hydrogen: Structure, Vibrations, Optical Response and Electron Band Engineering and Bonding
A.I. SHKREBTII, B. WILK, Z.A. IBRAHIM, R. MINNINGS, University of Ontario, Institute of Technology, Oshawa, ON, Canada; I.M. KUPCHAK, Institute of Semiconductor Physics, Academy of Sciences, Kiev, Ukraine; R. ZAPATA-PENÃ, S.M. ANDERSON, B.S. MENDOZA, Centro de Investigaciones en Óptica, León, Guanajuato, México

We characterize from first principles the structure and bonding in 2D heterosystems made of bilayers or trilayers of graphene and graphene-like-materials (GLMs), stacked on top of each other, and functionalized using low hydrogen dose. The effects of electron band gap opening and tuning, as well as formation of strongly bonded multilayers have been predicted. Optical and vibrational spectra were modelled for alternating graphene monolayers with insulating BN films, modified by low H coverage. The simulated response, electron and atomic structures indicate that submonolayer hydrogenation of the outer surfaces of multilayer systems induces covalent interlayer bonds and results in the possibility of electron gap engineering in otherwise gapless graphene. Calculated structural, vibrational, electronic and optical properties of the systems of interest aim to enabling in-situ noninvasive characterization of graphene based multilayers. Hydrogenated hetero-layers of graphene – incommensurate SiC film were also simulated, as we proved previously, graphene-like SiC is thermally stable and can be created experimentally. Finally, partially hydrogenated on one side graphene, which shows nonzero gap and is covalently bonded to silicon carbide substrates, was considered from the same footing.

Session F-2 - Novel Properties

F-2:KL  Charge and Spin in Layered Materials and Topological Insulators
A. BANSIL, Physics Department, Northeastern University, Boston, MA, USA

I will discuss how charge and spin states evolve in quantum matter through spin-orbit coupling effects in the presence of protections provided by time-reversal, crystalline and particle-hole symmetries, and highlight our recent work aimed at predicting new classes of 2D and 3D topological materials. [1-6] Surfaces of three-dimensional (3D) topological materials and edges of two-dimensional (2D) topological materials support novel electronic states. For example, in 2D topological insulators, also called quantum spin Hall insulators, the 1D topological edge states are not allowed to scatter since the only available backscattering channel is forbidden by constraints of time-reversal symmetry. The special symmetry protected electronic states in topological materials hold the exciting promise of providing revolutionary new platforms for exploring fundamental science questions and for the realization of multifunctional topological devices for applications.
[1] I. Zeljkovic et al., Nature Materials 14, 318 (2015). [2] J. He et al., Nature Materials 14, 577 (2015). [3] S.-Y. Xu et al., Science 349, 613 (2015). [4] S.-M. Huang et al., Nature Comm. 6, 7373 (2015). [5] C. P. Crisostomo et al., Nano Letters (2015) [6] A. Bansil, H. Lin, T. Das, Reviews of Modern Physics (2015).

F-2:IL02  Ultrafast Dynamics of Spin-valley Coupled Polarization in Monolayer MoS2
CHIH-WEI LUO, Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan

The inherent valley-contrasting optical selection rules for interband transitions at the K and K’ valleys in monolayer MoS2 have attracted extensive interest. Carriers in these two valleys can be selectively excited by circularly polarized optical fields. The comprehensive dynamics of spin valley coupled polarization and polarized exciton are completely resolved in this work. Here, we present a systematic study of the ultrafast dynamics of monolayer MoS2 including spin randomization, excitons dissociation, free carriers relaxation, and electron-hole recombination by helicity- and photon energy-resolved transient spectroscopy. The time constants for these processes are 60 fs, 1 ps, 25 ps, and ~300 ps, respectively. The ultrafast dynamics of spin polarization, valley population, and exciton dissociation provides the desired information about the mechanism of radiationless transitions in various applications of 2D transition metal dichalcogenides. For example, spin valley coupled polarization provides a promising way to build optically selective-driven ultrafast valleytronics at room temperature. Therefore, a full understanding of the ultrafast dynamics in MoS2 is expected to provide important fundamental and technological perspectives.

F-2:IL03  Lateral Heterostructure Field Effect Transistors
G. FIORI, G. IANNACCONE, Dipartimento Ingegneria dell'Informazione, University of Pisa, Pisa, Italy

The complete switch-off of the channel of a Field Effect Transistors is one of the main requirements for digital applications. This is the main reason, which prevents graphene to be exploited in electronic applications as a possible substitute to Silicon in CMOS technology. Recently, vertical and lateral heterostructures have been proposed as a technological option in order to circumvent the above mentioned problems, and they are generally referred as tunneling devices. Here we will show that the main mechanism at play is indeed not tunneling of carriers through the barrier, but rather thermionic emission over the barrier. Through a multi-scale simulation approach, based on ab-initio and atomistic calculations, we will assess the device performance against Industry requirements, showing which are the most promising options, and which are those to discard.

F-2:IL04  Spectral Response of 2D Materials based Photodiodes
M. LEMME, A.BABLICH, Graphene-based Nanotechnology, University of Siegen, Siegen, Germany

This talk will discuss the spectral response of 2D materials based photodiodes. Hybrid structures of graphene / silicon and molybdenum diselenide (MoS2) / silicon diodes are investigated over a broad spectrum. High responsivity is achieved in graphene / silicon hybrid diodes within the silicon band gap: up to 50% of the responsivity of commercial calibrated diodes. This value drops severely at energies below the band gap of silicon, where only graphene can absorb the radiation.  The spectral response of MoS2 / silicon diodes clearly shows a fingerprint of the hybrid materials' band structure. This method therefore provides easy access to the physics of (2D) heterostructures. Further results on other 2D heterostructure will also be discussed.

F-2:IL05  Ultrafast and Nonlinear Dynamics in 2D Materials and their Heterostructures
K.M. DANI, M. MAN, Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University, Onna-son, Okinawa, Japan

The discovery of a variety of 2D materials from semi-metallic graphene to semiconducting MoS2 to insulating hexagonal Boron Nitride has spawned a vigorous field of research in condensed matter physics.  In particular, the semiconducting 2D materials and their heterostructures provide a unique opportunity for light-matter interactions in low dimensions. Due to strong optical activity, and the potential for rapid transfer of electrons from one 2D crystal to another, they allow for novel technological applications as well as the study of new phenomena occurring at the interfaces of two dissimilar crystals. Here, we explore the nonlinear optical properties and the ultrafast dynamics of photocarriers created in 2D semiconducting heterostructures using ultrafast pump-probe techniques and time-resolved photoemission spectroscopy.

F-2:IL06  Quantum Confinement in Black Phosphorus through Strain-engineered Rippling
J. QUEREDA1, V. PARENTE2, P. SAN-JOSÉ3, N. AGRAÏT1,2,4, G. RUBIO-BOLLINGER1,4, F. GUINEA2, R. ROLDÁN2,3, A. CASTELLANOS-GOMEZ2, 1Dpto. de Física de la Materia Condensada, Universidad Autónoma de Madrid, Madrid, Spain; 2Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-nanociencia), Campus de Cantoblanco, Madrid, Spain; 3Instituto de Ciencia de Materiales de Madrid, CSIC, Madrid, Spain; 4Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Madrid, Spain

The recent isolation of black phosphorus has unleashed the interest of the community working on 2D materials because of its interesting electronic and optical properties: narrow intrinsic gap, ambipolar field effect and high carrier mobility. Black phosphorus is composed of phosphorus atoms held together by strong bonds forming layers that interact through weak van der Waals forces holding the layers stacked on top of each other. This structure, without surface dangling bonds, allows black phosphorus susceptible to withstand very large localized deformations without breaking. Its outstanding mechanical resilience makes black phosphorus a prospective candidate for strain engineering, modification of a material’s optical/electrical properties by means of mechanical stress, in contrast to conventional 3D semiconductors that tend to break for moderate deformations. Here we explore the effect of periodic strain profiles to modulate the electronic and optical properties of black phosphorus by combining hyperspectral imaging spectroscopy experiments and tight-binding calculations.

Session F-3 - Synthesis, Processing and Integration of Graphene and other 2D Layered Compounds

F-3:KL  Defect Engineering in 2-Dimensional Materials: From Theory to Applications
M. TERRONES, Department of Physics, Department of Chemistry, Department of Materials Science and Engineering and Center for 2-Dimensional & Layered Materials, The Pennsylvania State University, University Park, PA, USA & Institute of Carbon Science and Technology, Shinshu University, Japan

We will provide an overview of different defects in 2-Dimensional materials such as graphene and Chalcogenides. We will then discuss the synthesis of large-area, high-quality monolayers of nitrogen- and boron-doped graphene sheets on Cu foils using ambient-pressure chemical vapor deposition (AP-CVD). Scanning tunneling microscopy (STM) and spectroscopy (STS) reveal that the defects in the doped graphene samples arrange in different geometrical configurations exhibiting different electronic and magnetic properties. Interestingly, these doped layers could be used as efficient molecular sensors and electronic devices. In addition, the synthesis of hybrid carbon materials consisting of sandwich layers of graphene layers and carbon nanotubes by a self-assembly route will be discussed. These films are energetically stable and could well find important applications as field emission sources, catalytic supports, gas adsorption materials and super capacitors. Beyond graphene, the synthesis and defect engineering of Chalcogenides will be described. In particular, we will discuss the defects and their characterization using state-of-the-art techniques and theory. Applications of these defective materials will also be described.

F-3:IL02  Black-phosphorus, Graphene and 2D Binary Transition Metal Dichalcogenides for Device Applications
A. KAUL, University of Texas, El Paso, TX, USA

Complimentary to graphene, other elemental 2D layered materials have emerged in recent years which includes black phosphorus, as well as binary transition metal dichalcogenides such as 2D molybdenum disulfide (MoS2), niobium diselenide (NbSe2), tungsten disulphide (WS2) and tungsten diselenide (WSe2), which exhibit interesting optical and electronic properties. In this work I will present our efforts in the synthesis and characterization of these materials and discuss some of our device related efforts in harnessing the novel properties of these materials.

F-3:IL04  2D Magnetic Materials based on Coordination Chemistry 
S. MAÑAS-VALERO, M. CLEMENTE-LEÓN, E. CORONADO, ICMol, University of Valencia, Spain

In the area of 2D-layered materials the study of 2D magnetic materials has been largely ignored so far. However, coordination chemistry has shown to provide many examples of layered coordination polymers showing cooperative magnetism. Still, these layers are often charged so as the resulting layered material contains  counter-ions in the interlamellar space. As a result, these charged layers are difficult to exfoliate using a micromechanical method. To overcome this problem we have designed a honeycomb layer with large pores which are able to accommodate inside them the charge-compensating counter-ions. The result is a crystal formed by neutral layers assembled through van der Waals interactions, which can be easily exfoliated. Here we report the design and exfoliation of this new class of insulating layered magnets. The magnetic layer exhibits a 2D anionic network formed by Mn(II) and Cr(III) ions linked through anilate ligands. The counter-ions are molecular spin-crossover complexes of the type [FeIII(acac2-trien)]+. In bulk, these materials behave as ferrimagnets with a Tc = 11 K. As for graphene, they can be exfoliated in atomically-thin layers with heights down to 2 nm.

F-3:L05  Epitaxial Growth of Large Area MoS2 Few Layers by Sputtering Process
TAEKYUNG OH, HYUNGSEOB MIN, HYUNSU JU, JEON-KOOK LEE, Center of Opto-Electronic Materials and Devices, Korea Institute of Science and Techniology, Seoul, Korea

Two-dimensional (2D) atomic sheets are atomically thin, layered crystalline solids with the defining characteristics of intra-layer covalent bonding and inter-layer van der Waals Bonding. These materials are considered 2D because they represent the thinnest unsupported crystalline solids that can be realized, possess no dangling surface bonds and show superior intra-layer transport of fundamental excitations (charge, heat, spin and light). Therefore atomically thin two-dimensional (2D) transition metal Dichalcogenides (TMDs), MX2 (M = Mo, W; X = S, Se, Te), were expected to offer rich collection of physical properties and functionalities in the area of Nano-electronics, optoelectronics, catalysis, photo-detection, photovoltaics and photo-catalysis. As a prototype of TMDs, molybdenum disulfide (MoS2) has been demonstrated to exhibit high current on/off ratio, high mobility and negligible off current. This indicates that the sensitivity can be significantly improved with MoS2-based field effect transistors (FETs). In addition to its good electronic properties, the inherent band gap (1.8 eV for monolayer and 1.2 eV for bulk), excellent mechanical and optical properties permit its applications in large-area flexible optoelectronics. To facilitate the integration of this fascinating material into macroscopic electronic applications, it is essential to develop a large-area growth technique that is compatible with current micro- or Nano-fabrication processes. Our study is based on off-axis sputtering, and is, therefore, easily scalable to allow growth of very thin TMD films over very large areas. All MoS2 thin films were grown via off axis-sputtering on SiO2, GaN and Al2O3 using a solid poly-MoS2 target of 99.9% purity. After sputtering MoS2, we annealed samples by varying atmosphere (Sulfur fraction) and temperature. MoS2 few-layer samples were analyzed by Raman Spectroscopy, Atomic Force Microscopy (AFM), Optical Microscopy, Scanning Electron Microscope (SEM), and Transmission Electron Microscope (TEM).

F-3:L06  Rapid and Catalyst-free van der Waals Epitaxy of Graphene on Hexagonal Boron Nitride
N. MISHRA1, V. MISEIKIS1, D. CONVERTINO1, M. GEMMI1, V. PIAZZA1, C. COLETTI1,2, 1Center for Nanotechnology Innovation @ NEST, Istituto Italiano di Tecnologia, Pisa, Italy; 2Graphene Labs, Istituto Italiano di Tecnologia, Genova, Italy

Recently, hexagonal boron nitride (h-BN) has been shown to act as an ideal substrate to graphene by greatly improving the material transport properties. Chemical vapour deposition (CVD) is presently considered the most scalable approach to grow graphene directly on h-BN. However, for the catalyst-free approach, poor control over the shape and crystallinity of the graphene grains and low growth rates are typically reported. In this work we investigate the crystallinity of differently shaped grains and identify a path towards a real van der Waals epitaxy of graphene on h-BN by adopting a catalyst-free CVD process. We demonstrate the polycrystalline nature of circular-shaped pads and attribute the stemming of different oriented grains to airborne contamination of the h-BN flakes. Single-crystal grains with six-fold symmetry can be obtained by adopting high hydrogen partial pressures during growth. Notably, growth rates as high as 100 nm/min are obtained by optimizing growth temperature and pressure [1]. The possibility of synthesizing single-crystal graphene on h-BN with appreciable growth rates by adopting a simple CVD approach is a step towards an increased accessibility of this promising van der Waals heterostructure.
[1] N. Mishra et al., Carbon 96, 497–502 (2016).

F-3:IL07  Direct Fabrication of Functionalized Graphenes and their Hybrids Inks  via  Submerged Liquid Plasma [SLP] and Electrochemical Exfoliation [ECE] under Ambient Conditions
M. YOSHIMURA, J. SENTHILNATHAN, K. SANJEEVARAO, Promotion Centre for Global Materials Research (PCGMR), Dept. of Material Science and Engineering, National Cheng Kung University, Tainan, Taiwan

Nano-carbons like Grapnenes have greatly been interested  in various fields of researches,where the large scale synthesis of nano-carbon should be free from using excess energies for firing, sintering, melting,vaporizing and/or expensive equipments. We, propose here Soft processing of functionalized Graphenes at ambient conditions. The Soft processing provides number of advantages which includes (a) simple reaction set up,(b) at ambient conditions, (c) simple procedure and (d)less operating costs and wastes. In the present study, we have utilized “Submerged Liquid Plasma [SLP]” and “Electrocemical Exfoliation[ECE] methods. SLP methods resulted the direct synthesis of Nitrogen functionalized Graphene Nano-sheets from Graphene suspension and/or Graphite electrode in acetonitrile liquids.[1,2] Products contains few layers (< 5) Graphene nanosheets. Unsaturated or high energy functional group (e.g. C=C, C=N and C≡N) have formed in the products. We could confirm those functionalized Graphenes are electrochemically active. Using pencil rods instead of Graphite rods we have also succeeded to prepare the Nano-clay/Graphene hybrids by this SLP methods [3]. Reduction and functionalization of Graphene oxides [2] and Synthesis of Graphene/Au Hybrids [4] also realized by SLP. In the ECE, graphite anode is exfoliated electrochemically by H2O2-NaOH[5,6] or Glycine-H2SO4[7] aqueous solutions under ambient temperature and pressure,for 5-30 min with +1-+5 volt, into 3-6 layers Graphene Nanosheets[GNs]. Those conditions are much milder than those reported before using other chemicals like ionic liquids and/or H2SO4-KMnO4,etc.,because O22- ions or ionic complex like Glycine-HSO4- would assist the exfoliation of graphite layers. Our products:GNs suspended in solutions can be transformed in the 2nd step in the same container using BrCH2CN/dioxane into N-FG, further into Au-Hybridized N-FG by the sonification with Au nanoparticles. We have confirmed the excellent catalytic performance of those hybrids[5,6] It should be noted that Soft Processing can directly produce “Graphene Ink”;Graphenes dispersed in various liquids, under mild conditions.
1) J. Mater Chem A,(2014) 2, 3332; 2) Scientific Reports, 4(2014), 04395; 3) Carbon,78 (2014),446; 4) J. Mater Chem A, 2015, 3,3035-30435) Sci. Rep. 4 ,4237 (2014); 6) Nanoscale (2014) 6,12758; 7) Adv. Funct. Mater. 2015, 25, 298-305.

F-3:L09  How the Nanostructure of Layered Titanates Influences the Mechanical Properties
P. GONZALEZ2, W. LETTE3, D.J. SCHIPPER3, J.E. TEN ELSHOF2, 1Materials innovation institute (M2i), Delft, the Netherlands; 2Inorganic Materials Science Group, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands; 3Faculty of Engineering Technology, University of Twente, Enschede, The Netherlands

Layered materials find many applications in electronics, coatings or lubrication. One example are titanium oxide nanosheets, which can be obtained through the exfoliation of protonated layered titanates with lepidocrocite-like structures (H1.07Ti1.73O4). Layered titanates are constituted by negatively charged oxide layers that can be intercalated by a wide range of cations. Here, they were functionalized with linear alkylamines. The amines are weak bases that react with the protons of the layered host. This reaction is the driving force for molecular intercalation and swelling of the layered structure. Small Angle X-ray Scattering was performed to investigate the dynamic swelling and exfoliation behavior of these layered systems in aqueous solution. The ratios of amine to layered host and the carbon chain length were varied. Layered compounds find an important application in lubrication. The mechanical tests of the new solid lubricants helped to establish a relationship between the nanostructure of the layered material and its lubricating properties. Pin-on-disc tests showed low friction coefficients (from µ ≈ 0.05). The results suggest that the chemical modification decreased the electrostatic interactions between the titania planes, making the layered compound easily deformable.

F-3:L11  Lessons learned from Carbon Nanotube Growth can be applied to Graphene: 100% Reproducibility and Improved Graphene Quality by Preheating Precursor Gases using Thermal Chemical Vapor Deposition
G.D. NESSIM, Bar Ilan University, Department of Chemistry and Center for Nanotechnology and Advanced Materials, Ramat Gan, Israel

Years ago, we showed how preheating precursor gases helped to synthesize carbon nanotubes (CNTs) at lower temperature and with increased crystallinity. We now demonstrate how by applying a similar technique, we synthesized high quality, few-layer graphene at reduced temperature with full reproducibility on nickel thin films. Raman spectroscopy showed that the graphene films synthesized using gas preheating exhibited 50% less defects compared to those obtained without gas preheating. However, the most important outcome is that all experiments performed using gas preheating were fully reproducible, while less than 15% of the experiments performed without gas preheating led to graphene of only acceptable quality. Gas chromatography/mass spectrometry (GC-MS) of the preheated gases showed an increased formation of polycyclic aromatic hydrocarbons (PAHs), as it did in our previous studies on CNTs. >From the results obtained, we postulated a new growth mechanism that fits previous density functional theory (DFT) reports of hydrocarbon stability on a nickel surface. The results presented are an important step in the direction of graphene synthesis at lower temperatures with full reproducibility. In this presentation, we will focus on the parallels between CNT and graphene synthesis.

F-3:L12  One-pot Electrochemical Exfoliation and Functionalization of Graphene Sheets
D.B. OSSONON, D. BELANGER, Université du Québec à Montréal, Département de Chimie, Montréal, Canada

Graphene can be prepared in large scale by the classical Hummers' method and subsequent chemical reduction. A major drawback of this widely used method is that it is a multi-steps process that requires aggressive chemicals. On the other hand, graphene sheets can be also prepared by electrochemical exfoliation of graphite. In this work, graphene was produced by electrochemical exfoliation of graphite in aqueous electrolyte. Acidic and neutral electrolyte were used. With this procedure, graphene sheets with low oxygen content is produced. Graphene sheets were also functionalized with specific organic molecules during the electrochemical exfoliation process by using appropriate reagants and experimental conditions. The resulting materials were characterized by several techniques such as Fourier transform infrared, X-ray photoelectron and Raman spectroscopy, thermogravimetric analysis, elemental analysis, electronic conductivity measurements and electrochemical techniques.

F-3:L14  Selective Modification of as-grown CVD Graphene on Cu by Oxygen Plasma for Flexible Electronics Applications
A.M. ALEXEEV, M.D. BARNES, V.K. NAGAREDDY, M.F. CRACIUN, C.D. WRIGHT, College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, UK

The global market of flexible electronics is currently reaching the $4 billion mark and is estimated to become $13 billion by 2020. However, the market still has a high demand for new flexible materials. Graphene and other 2D materials offer an exciting route for the realization of flexible devices – they are light, strong, and possess high bending endurance. Electronic and optical properties of these materials can be tailored by functionalization with chemical elements such as fluorine, hydrogen, or oxygen[1]. In the present work we utilise plasma treatment[2] as a novel technique for functionalization of as-grown CVD graphene directly on Cu. Exposure of graphene to oxygen plasma results in modification of graphene surface with epoxy, hydroxyl, and carbonyl groups as we confirm by XPS, Raman, and AFM measurements. We apply the developed technique to oxidise lithographically defined regions of continuous graphene film before transferring it from Cu onto an arbitrary substrate. The developed method can be used for large-scale patterning of CVD graphene devices, such as touch screen electrodes or flexible transistors, directly on Cu with subsequent transfer onto desired substrates.
[1]M.F. Craciun et al, J Phys Cond Matt 25, 423201 (2013) [2]T. Gokus et al, ACSNano 3, 3963 (2009)

F-3:L15  Langmuir-Blodgett Films of 2D Oxide Nanosheets for Oriented and Epitaxial Growth of Functional Oxide Thin Films
J.E. TEN ELSHOF, HUIYU YUAN, M. NIJLAND, M. NGUYEN, G. RIJNDERS, G. KOSTER, MESA+ Institute for Nanotechnology, University of Twente,  Enschede, the Netherlands

Oxide nanosheets are the oxide equivalents of graphene. They have a thickness of ~1 nm and lateral sizes up to tens of micrometers. They are made by exfoliation of layered oxides in water using a combined acid-base & ion exchange reaction. We investigated the mechanism and kinetics of exfoliation of lepidocrocite-type titanates into Ti1-xO2 nanosheets using time-resolved techniques. In contrast to common knowledge, we found that the exfoliation process is rapid and occurs within minutes, opening up possibilities for large-scale synthesis. Dense nanosheet monolayer films were made by Langmuir-Blodgett (LB) deposition. The conditions for LB deposition of nanosheets on glass and silicon were optimized. The nanosheet films were used as seed layers to form preferentially oriented nanoelectronic oxide films by pulsed laser deposition. SrRuO3, (La,Sr)MnO3 and Pb(Zr,Ti)O3 films were grown on Ca2Nb3O10 and Ti0.87O2 nanosheets. Depending on nature of the seed layer, either [001] or [110] oriented films were formed, which influenced their functional properties. Nanosheet flake size is also shown to have an effect. Micropatterns of different nanosheets by photolithography and lift-off are demonstrated, illustrating the possibility to locally control the orientation of functional films.

Session F-4 - Synthesis and Processing of Composites

F-4:IL02  Fabrication Processes and Properties of Multi-functional Graphene and Carbon Nanotube Nanocompositess
SOON HYUNG HONG, Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, Korea

Carbon nanomaterials such as graphene and carbon nanotube (CNT) have been received high attention as new materials to overcome the limitation of traditional reinforcements in composites due to their excellent mechanical, thermal, electrical and chemical properties. Most important issues of carbon nanomaterials filled nanocomposites, regarding their synthesis process, are homogeneous dispersion of carbon nanomaterials in matrices and enhancement of interfacial bonding between reinforcements and matrices. In order to solve these important issues, a new fabrication process, named “molecular level mixing process”, has been developed based on functionalization followed by chemical bonding between molecules. The carbon nanomaterials filled nanocomposites fabricated by molecular level mixing process show an ideally homogenous dispersion of carbon nanomaterials in matrices as well as strong interfacial bonding between carbon nanomaterials and various matrices. The characterizations of microstructures and properties of graphene and carbon nanotube nanocomposites are discussed for multi-functional applications such as structural, electronic and energy related materials.

F-4:IL04  A Polymer Chemistry of Graphenes: Synthesis, Processing, Applications
K. MUELLEN, Max Planck Institute for Polymer Research, Mainz, Germany

Graphene is praised as multifunctional wonder material and rich playground for physics. Above all, it is a two-dimensional polymer and thus a true challenge for materials synthesis. Herein we present, both, “bottom-up” precision synthesis and “top-down” fabrication protocols toward graphene. The resulting materials properties cover an enormous breadth ranging from batteries, supercapacitors, oxygen reduction catalysts, photodetectors and spin-walves to semiconductors. Another question is whether graphene holds promise for robust technologies. An attempt will be made at providing answers.
Nature 2010, 466, 470; Nature Chem. 2011, 3, 61; Nature Nanotech. 2011, 6, 226; Nature Chem. 2012, 4, 699; Angew. Chem. Int. Ed. 2012, 51, 7640; Nature Commun. 2013, DOI: 10.1038/ncomms3646; Nature Commun. 2013, DOI: 10.1038/ncomms3487; Adv. Polym. Sci. 2013, 262, 61; Angew. Chem. Int. Ed. 2014, 53, 1570; J. Am. Chem. Soc. 2014, 136, 6083; Angew. Chem. Int. Ed. 2014, 53, 1538; Nature Nanotech. 2014, 9, 182; Nature Nanotech. 2014, 9, 131; Nature Chem. 2014, 6, 126; Nature Commun. 2014, DOI:10.1038/ncomms5973; Nature Nanotech. 2014, 9, 896; Nature Commun. 2014, DOI:10.1038/ncomms5253; Adv. Mater. 2015, 27, 669; ACS Nano 2015, 9, 1360; Angew. Chem. Int. Ed. 2015, 54, 2927; J. Am. Chem. Soc. 2015, 137, 6097; Nature Commun. 2015, DOI: 10.1038/ncomms8992; Nature Commun. 2015, DOI: 10.1038/ncomms8655.

F-4:IL05  Graphene Oxide Composite 3D Materials obtained by Self-assembly Process using Biological Macromolecules
R. IPPOLITI, M. ARDINI, L. OTTAVIANO, S. SANTUCCI, F. PERROZZI, G. FIORAVANTI, G. PANELLA, A.CIMINI, E. BENEDETTI, F. ANGELUCCI, University of L'Aquila, Italy; G. FABRIZI, University of Rome La Sapienza, Rome, Italy; V. MORANDI, L. ORTOLANI, M. CHRISTIAN, V. PALERMO, CNR, Bologna, Italy; L. PALOMBI, University of Salerno, Salerno, Italy

Graphene oxide (GO) is considered a breakthrough precursor material for next-generation devices, for which the transition of its 2D layered structure into more accessible 3D arrays is demanded. Peroxiredoxins (Prx) are multi-tasking redox enzymes, self-assembling into ring-like architectures. Taking advantage of both Prx symmetric structure and function, 3D rGO-based composites have been built up. Prx rings can adhere flat on single GO layers and partially reduce them, driving their stacking into 3D multi-layer rGO-Prx composites at very low GO concentration. Further, protein engineering allows the Prx ring to bind metal ions inside its lumen capturing pre-synthesized gold nanoparticles and growing in situ palladium nanoparticles, generating 3D rGO-metal composite materials using “green” routes. Further evolution of GO-based 3D materials with self-assembled structures induced by other biological macromolecules will be discussed, together with applications as bio-compatible scaffold, chemical catalysts and bio-sensors.

Session F-5 - Novel Characterizations

F-5:KL  Electronic and Optoelectronic Physics in the van der Waals Heterojunctions
PHILIP KIM, Department of Physics, Harvard University, Cambridge, MA, USA

Recent advance of van der Waals (vdW) materials and their heterostructures provide a new opportunity to realize atomically sharp interfaces in the ultimate quantum limit. By assembling atomic layers of vdW materials, such as hexa boronitride, transition metal chalcogenide and graphene, we can construct novel quantum structures. Unlike conventional semiconductor heterostructures, charge transport of the devices are found to critically depend on the interlayer charge transport, electron-hole recombination process mediated by tunneling across the interface. We demonstrate the enhanced electronic optoelectronic performances in the vdW heterostructures, tuned by applied gate voltages, suggesting that these a few atom thick interfaces may provide a fundamental platform to realize novel physical phenomena, such as hydrodynamic charge flows, cross-Andreev reflection across the quantum Hall edges states, and interlayer exciton formation and manipulations.

F-5:IL01  Photoconductivity in 2D Layers of Transition Metal Dichalcogenides
S. TALAPATRA, Department of Physics, Southern Illinois University, Carbondale, IL, USA

Single- and few-layers of atomically thin Transition Metal Dichalcogenides (TMDCs) such as Molybdenum Disulphide (MoS2), Tungsten Disulphide (WS2), etc. possess fascinating and lucrative physicochemical properties. For example, the presence of inherent band gap in these materials is a huge advantage over Graphene, a zero band gap material. Though innovative synthesis approaches such as confining graphene into nano-ribbons (GNRs), production of bilayer graphene, doping graphene etc. are used for opening band gap in them, these synthesis routes are often complicated. In that context, the ability to produce few layered TMDCs (through simple liquid phase exfoliation process, and or mechanical exfoliation) with inherent optical gaps opens up a huge possibility in utilizing these materials for optoelectronics applications. Thus in order to assess the viability of these materials for utilization in next generation photo detectors, ultrafast light modulators, optical switches etc. a clear understanding of photo conduction mechanism in these materials is necessary. In this presentation, several aspects of photoconductive properties of TMDC obtained using liquid phase as well as mechanical exfoliation will be discussed.
Funding support: US DoD-ARO-W911NF-11-1-0362.

Session F-6 - Application of Graphene and other 2D Layered Materials and Composites

F-6:KL  Origin and Impact of Noise in Multifunctional 2D Electronics
A. GHOSH, Department of Physics, Indian Institute of Science, Bangalore, India

Two-dimensional (2D) Van der Waals materials, such as graphene and its analogues, transition metal dichalcogenides and Bi-based topological insulators, form a unique platform for multifunctional electronic applications. The performance limit of these applications, which is determined by the intrinsic level of noise, is hence an important parameter that requires a close scrutiny. The noise in electronic devices from 2D materials, however, not only depends on the internal disorder and the nature of electronic states but also on the kinetics of charge disorder of the local environment, especially that of the supporting substrate. In this talk an account of the microscopic origin and performance impact of low-frequency electrical noise in a variety of devices from 2D materials and their hybrids will be presented. For graphene transistors, noise arises primarily from mobility fluctuations that depend critically on the substrate charge traps, nature of electrical leads and existence of grain boundaries. In dichalcogenide field-effect devices, on the other hand, carrier number fluctuation constitutes the dominant source of noise. I shall present a comprehensive study of noise in hybrid devices as well, including those based on graphene, hexagonal boron nitride and molybdenum disulphide.

F-6:IL01  Strong Light-matter Interactions at Graphene-heterostructures for Photonics and Photovoltaics
CHUN-WEI CHEN1, CHIA-CHUN CHEN2, PO-HSUN HO1, 1Department of Materials Science and Engineering, National Taiwan University, Taipei, Taiwan; 2Department of Chemistry, National Taiwan Normal University, Taipei, Taiwan

Graphene, consisting of a single atom-thick plane of carbon atoms arranged in a honeycomb lattice, has exhibited excellent carrier transport attributed to its unique two-dimensional (2D) energy dispersion. In this talk, I would like to present the strong light-matter interactions at graphene/heterostructure for photonics and photovoltaics. I would like to introduce photoinduced modulation doping based on graphene/TiOx heterostructure, where trap-state-mediated photoinduced charge transfer from the remote bulk TiOx ultrathin film to graphene resulted in a strikingly high n-type doping level  (>1013 cm-2), showing both unique advantages of using the conventional chemical doping (high doping concentrations) and photoinduced doping (reversible and controllable).[1] I would like to demonstrate a novel approach to precisely control the band gap opening of a bilayer graphene/TiOx heterostructure by optical modulation. In addition, I would like to demonstrate interesting optically controllable graphene electronics due to strong light-matter interactions at graphene heterostructure. For example, the dual carrier-typed transport behavior of a graphene transistor by wavelength-selective illumination will be demonstrated [2]. A new concept of photoactive graphene/TiOx heterostructure transparent electrode for photovoltaic application will be also shown [3]. Finally, I would also like to present our recent discovery of crack-filled graphene (CFG) films and clean lifting transfer of graphene for the large-area electronics application.[4,5] 
[1] Advanced Materials, (2015), in press. [2] Advanced Materials, Vol.27, 282, (2015). [3] Energy & Environmental Science, 8, 2085, (2015). [4] Advanced Materials Vol.25, 4521, (2013). [5] Advanced Materials Vol.27, 1724, (2015)

F-6:IL03  A New Paradigm for Selective NO2 Gas Sensing with Physisorption based Two Dimensional SnS2
K. KALANTAR-ZADEH1, J.Z. OU1, W. GE2, W. SHAN2, S.P. RUSSO3, Y. X. LI1,2, 1School of Electrical and Computer Engineering, RMIT University, Melbourne, Australia; 2The Key Laboratory of Inorganic Functional Materials and Devices, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, P.R. China; 3School of Applied Sciences, RMIT University, Melbourne, Australia

Nitrogen dioxide (NO2) gas plays an important role in certain industrial, farming and healthcare sectors. However, there are still significant challenges for NO2 sensing at low detection limits, especially in the presence of other interfering gases. We present a breakthrough for NO2 sensing based on an economical sensing platform with charge transfer between selectively physisorbed NO2 gas molecules and two-dimensional (2D) tin disulphide (SnS2) flakes. The device shows high sensitivity and superior selectivity to NO2 at operating temperatures of less than 160ºC which are well below those of chemisorptive and ion conductive NO2 sensors with much poorer selectivity.
Ou J. Z., Ge W., Carey B., Daeneke T., Rotbart A., Shan W., Wang Y., Fu Z., Chrimes A. F., Wlodarski W., Russo S. P., Li Y. X., Kalantar-zadeh K., 2015, ACS Nano, vol. 9, pp. 10313-10323

F-6:IL05  Highly Efficient Photocatalytic CO2 Conversion to Selective Hydrocarbons using Graphene Oxides and Related 2D Hybrids
LI-CHYONG CHEN, Center for Condensed Matter Sciences, National Taiwan University, Taipei, Taiwan; KUEI-HSIEN CHEN, Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan

Photocatalytic conversion of carbon dioxide (CO2) to hydrocarbons makes possible simultaneous solar energy/fuel harvesting and CO2 reduction, two birds with one stone for the energy and environmental issues. Here, we describe a highly efficient photocatalytic conversion of CO2 to selective hydrocarbons using GOs and their related 2D hybrids as photo-catalysts. Several approaches have been employed to synthesize GOs and reduced GOs (rGOs) with tunable bandgap and band alignment with respect to the CO2 reduction level. Under visible light, the photocatalytic conversion of CO2 to methanol of GOs/rGOs is several-fold higher than that of TiO2 (commercial P-25). Further, metal and metal sulfides, especially the 2D materials such as MoS2 were deposited onto GO as co-catalysts to enhance the photocatalysis reaction. Besides methanol, other selective hydrocarbons including acetaldehyde were also detected. Total solar to fuel yield of ~200 times enhancement over that of P-25 has been achieved. In all these GOs-2D hybrids, the photo-catalytic performance is always much better than that of constituent component when used alone. Detailed preparation and characterization of the catalysts will be presented. The role and interplay of the constituent components will also be discussed.

F-6:IL06  The Route to the Silicene Field Effect Transistor
A. MOLLE1, E. CINQUANTA1, C. GRAZIANETTI1, L. TAO2, D. AKINWANDE2, 1CNR-IMM, Laboratorio MDM, Agrate Brianza (MB), Italy; 2The University of Texas at Austin, TX, USA

Silicene, a honeycomb-like Si lattice, attracts an enormous interest as emerging research material for the semiconductor technology roadmap and for its natural affinity with the ubiquitous silicon technology. Self-organization of a silicene lattice is made possible via epitaxial growth of a Si monolayer on commensurate substrates. However, silicene undergoes hybridization with its hosting substrates and easy oxidation in environmental conditions, these facts strongly limiting its “portability” and integration in devices. We here exposed a methodology to address both issues and then integrate the silicene in a field effect transistor operating at room temperature and exhibiting a graphene-like ambipolar behavior [1]. In detail, Ag-supported silicene is synthesized on cleavable substrates and then encapsulated with Al2O3 for subsequent delamination and transfer into a device-friendly platform by pattering contacts from the native Ag. The transport behavior is discussed in relation with the intrinsic silicene features. Stability issues are also taken into account, and a further outlook on the integration of silicene multilayer is proposed.
[1] L. Tao et al., Nat. Nanotech. 10, 227 (2015).

F-6:L07  Light Detection from Nanocrystal Sensitized Graphene Photodetectors at kHz Frequencies
D. SPIRITO, S. KUDERA, R. KRAHNE, Istituto Italiano di Tecnologia, Nanochemistry department and Graphene Labs, Genoa, Italy; V. MISEIKIS, C. COLETTI, Istituto Italiano di Tecnologia, Center for Nanotechnology Innovation and Graphene Labs, Pisa, Italy; C. GIANSANTE, Center for Biomolecular Nanotechnologies @UNILE, Istituto Italiano di Tecnologia and CNR NANOTEC-Istituto di Nanotecnologia, Lecce, Italy

Hybrid devices based on graphene and sensitizer materials have proved to be promising platform to detect light in the visible and near UV range; in particular, the use of colloidal semiconductor nanocrystals (NCs) has given very good results. In this hybrid system, photoexcited charges in the NCs are transferred to graphene, inducing a sizeable change in its resistivity. This allow to exploit high absorption in the NCs and high mobility in graphene for photoconductive gain. However, the relaxation processes of the photoexcited charges can be slow and limit high frequency performance of the device. In this contribution, we report on photodetectors made using CVD-graphene based field-effect transistors and a thin film of CdS NCs deposited onto it by spin coating. The spectral response follows the NCs absorption, with high sensitivity in near UV range, and a maximum responsivity of about 4 10^4 A/W at 349 nm. Using a pulsed laser, we could detect ns-pulses up to 2 kHz repetition rate, thus demonstrating that fast relaxation processes can be exploited. We discuss the effective mechanisms of charge transfer from NCs to graphene, and the role of surface states and adsorbed molecules. Finally, we discuss the use of different materials to extend the operating wavelength range.

F-6:L09  Epitaxial Graphene on SiC as a Platform for Extremely Sensitive and Selective Gas Sensors
J. ERIKSSON, C. STRANDQVIST, R. GUNNARSON, S. EKEROTH, U. HELMERSON, I.G. IVANOV, R. YAKIMOVA, A. LLOYD SPETZ, Linköping University, Linköping, Sweden; C. Strandqvist, Graphensic AB, Linköping, Sweden

We report on graphene surface modifications with metal or metal-oxide (MOx) nanostructures including nanoparticles (NPs) and monolayers, formed by reproducible thin film deposition techniques, and their effect on the electronic properties of the graphene and on gas interactions at the graphene surface. The scope is to exploit the sensing properties of MOx materials for selectivity tuning while utilizing the unique electronic properties of graphene as an ultra-sensitive transducer. Chemiresistor sensors based on epitaxial graphene on SiC decorated with Au, Pt, TiO2, and Fe3O4 core-shell NPs were tested from ppm down to low ppb concentrations of common air pollutants like NO, NO2, CO, H2, NH3, CH2O, and C6H6. The effect of decoration on the sensor performance strongly depends on the choice, thickness, surface coverage, and size of the NPs. We found that decoration with TiO2 or Fe3O4 NPs can yield selective detection of CH2O and C6H6, while pristine EG/SiC showed no response to the tested volatile organic compounds (CH2O and C6H6). Decoration with nanoporous Au improved the detection limit and selectivity for NO2. Our results show that graphene decoration can be an effective strategy for tuning the sensor performance in terms of sensitivity and selectivity.

F-6:L11  Alkali Metal Insertion in TiO2- and Li4Ti5O12-graphene Composites for Battery Applications
M. ZUKALOVA, A. ZUKAL, B. PITNA LASKOVA, L. KAVAN, J. Heyrovský Institute of Physical Chemistry, v.v.i., AS CR, Prague, Czech Republic

Li4Ti5O12 (spinel, LTO) has attracted attention as a promising candidate for Li-ion battery anode material due to its excellent Li-ion insertion/extraction reversibility with zero structural change and a relatively high operating voltage. Recently several reports on Na storage in LTO and TiO2 have been published as well. However, there are still issues to be addressed; poor electrical conductivity and sluggish Li/Na ion diffusion resulting in poor rate capability. Efforts to improve the rate capability of LTO include a synthesis of nanosized particles to shorten the Li+/Na+ diffusion path and LTO coating with conductive species. Graphene has superior electronic conductivity and is an ideal conductive additive for hybrid nanostructured electrodes. In our work we analyzed morphology and tested electrochemical performance of LTO-graphene and TiO2-graphene composites prepared by both dry and wet coating with graphene oxide by cyclic voltammetry of Li/Na insertion and chronopotentiometry. The LTO-graphene composite containing 5% of graphene made by wet coating exhibited improved specific capacity of 169mAh/g as compared to that of pure LTO (143 mAh/g).
This work was supported by the Grant Agency of the Czech Republic (contract No. 15-06511S).

F-6:L12  Failure of Self Lubricating Properties of MoS2: Oxidation or Water Molecules Adsorption?
E. SERPINI1,2, A. ROTA2, D. MARCHETTO1,2, S. VALERI1,2,3, 1Dipartimento di Scienze Fisiche, Informatiche e Matematiche - Università di Modena e Reggio Emilia, Modena, Italy; 2Istituto CNR-NANO S3, Modena, Italy; 3Centro Interdipartimentale per la Ricerca Applicata e i Servizi nella Meccanica Avanzata e nella Motoristica Intermech-Mo.Re., Università di Modena e Reggio Emilia, Modena, Italy

In inert environments, at room temperature, MoS2 shows exceptional lubrication properties [1]. During sliding a transfer film forms on the counterpart and the basal planes of MoS2 crystallites realign in the direction of motion causing easy shear between lamellae [2,3]. Oxygen and water vapour cause the deterioration of these processes, but it is not clear whether the dominant mechanism is oxidation or water molecule adsorption [4]. Trying to clarify this point we performed ball-on-disc friction tests of MoS2 thin coatings deposited on Si(111) by RF magnetron sputtering. The effect of environmental humidity and surface temperature was investigated. Reduction of friction was observed in dry air, nitrogen and also humid air upon sample heating. The obtained results suggested that environmental humidity and not oxidation plays the major role in inhibiting the lubrication properties of MoS2. Finally, we studied the role of transfer film formation vs. crystallite orientation for thin films, which exhibit a different microstructure with respect to thicker films.
[1] Donnet, C. et al, Tribol. Int. 29(2) (1993) 123–128. [2] M.R. Hilton et al, Surf. Coat. Technol. 435 (1992) 54-55. [3] A.R. Landsdown, Tribology Series 35 (1999). [4] H. S. Khare et al, Tribol Lett DOI 10.1007/s11249-013

F-6:L14  Graphene Lubrication of Steel-steel Contacts
D. MARCHETTO1, P. RESTUCCIA1, C. RIGHI2, S. VALERI1,2,3, 1Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Università di Modena e Reggio Emilia, Modena, Italy; 2Istituto CNR-NANO S3, Modena, Italy; 3Centro Interdipartimentale per la Ricerca Applicata e i Servizi nella Meccanica Avanzata e nella Motoristica Intermech-Mo.Re., Università di Modena e Reggio Emilia, Modena, Italy

In a recent study a solution of graphene flakes was used with success to lubricate a steel-steel sliding contact [1]. The reduction of friction was explained by the low shear and highly protective nature of the graphene. A theoretical work published in 2014 [2] explained the reduction of friction with the ability of graphene to increase the load carrying capacity of the surface. They also conclude that, “when the graphene ruptures it loses its low friction and wear properties”. In the light of the results reported above and in order to take the explanation of graphene properties to a further level we studied the behavior of graphene coated steel surfaces. Graphene was deposited onto the samples applying an alcohol solution in which flakes were dispersed. Pin-on-disc tests were performed. Solutions with different concentrations of graphene flakes were used in order to study the effect of a partial surface coverage. The effect of load and speed was also studied. Finally a theoretical model was developed. The model shows that the graphene flakes cover the metal, in particular the highly reactive Fe bonds, reducing the interaction between the sliding surfaces and therefore the friction force.
- D. Berman et al. Carbon 59 (2013) 167 - Klementz A et al, Nanoletters, 14 (2014) 7145

Poster Presentations

F:P02  Electromagnetic Properties in Multilayer Graphene within the Ritus Formalism: Transverse Electrical Conductivity
G. MURGUIA-ROMERO, A. SÁNCHEZ, R. ZAVALETA-MADRID, Facultad de Ciencias, Universidad Nacional Autónoma de México, Distrito Federal, México

Within the framework of the Quantum Field Theory, we discuss how to study electromagnetic properties of a multilayer graphene sample in presence of an electric field parallel to a magnetic field, both perpendicular to the graphene planes. We deal with the multilayer system by taking into account the quantum mechanical supersymmetric property of the monolayer Hamiltonian. We solve the Dirac equation for the graphene charge carriers by using the Ritus formalism. This formalism consists in the diagonalization of the operator (γμ Πμ)2 with Πμ = pμ - eAμ and γμ the Dirac gamma matrices which contain information about spin. We calculate the charge carrier propagator and we obtain the photon polarization operator, the leading quantum correction to the classical Lagrangian density, that encodes the electromagnetic properties of the system through the constitutive equations.

F:P05  Maximyzing the Potential of Layered Compounds for Hydrogen Production
O.E. MEIRON1, L. HOUBEN2, M. BAR-SADAN1, 1Ben Gurion University of the Negev, the chemistry department, Beer Sheba, Israel; 2Chemical Research Support, Weizmann Institute of Science, Rehovot, Israel

Layered transition metal dichalcogenides (TMDs) gained much attention in recent years. Layer edges were identified as the catalytic sites, making edge oriented morphologies a desired design. In addition, first principle calculations showed that doping and alloying of TMDs can be used to modify their electronic properties. To date, TMD alloying is primeraly performed at high temperature, solid state reactions, such as chemical vapor deposition (CVD) or chemical vapor transport (CVT) which limit morphology and composition control. We used low temperature, controllable colloidal synthesis to produce nanoflower alloyed TMDs. Specifically Mo(SxSe1-x)2 nanoflowers with edge oriented nanostructures. A range of alloy compositions were prepared. The Materials were analyzed using TEM, XRD, UV-Vis, ICP-MS spectroscopy and electron tomography. We found that the produced nanoflowers were molybdenum rich, in agreement with previous reports. The composition closely follows the feed ratio enabling the production of precisely controlled compositions. XRD and UV-Vis spectra results suggests the formation of a homogeneous solid solution rather than two sepa-rate phases of MoS2 and MoSe2. Tunable bandgap was achieved as a function of alloying de-gree, as measured by UV-Vis.

F:P10  Interfacial Engineering for Enhancement of Electrical Characteristics in MoS2 Field-effect Transistors
DONGRI QIU, EUN KYU KIM, Quantum-Function Research Laboratory and Department of Physics, Hanyang University, Seoul, Korea

Molybdenum disulfide (MoS2) have been attracted much attention and becoming the most widely investigated two-dimensional (2D) materials in the transition metal dichalcogenide group. There are various device application have been realized based on the field-effect conductance transition of 2D channel. However two interfaces located at dielectric/MoS2 and metal/MoS2 limited the performance of the devices. Moreover ohmic contact at metal/MoS2 has been rarely realized which is restrict the efficiency of carrier injection from metal contact. In this aspects of view such interfaces are much important in further application and it need to be explored. In this work, we fabricated multi-layered graphene/MoS2 heterostructured devices and bridge-channel MoS2 field-effect-transistors (FETs) by using polydimethylsiloxane based 2D trasnsfer method. It showed that the bridge-channel MoS2 FETs has significant improvement mobility (66 cm2/Vs) and subthreshold swing (113 mV/decade) by neglecting all surrounding perturbations to provide the intrinsic carrier transport characteristics. The Schottky barrier height (SBH) of the graphene/MoS2 heterostructured FET has tunable negative barrier height, typically in a range of 300 to –46 meV as a function of back-gate voltage.

F:P12  Nanoperforated Graphenes for Energy Storage Applications
HYUN KYUNG KIM, SEOK WOO LEE, YEON JUN CHOI, KWANG BUM KIM, Department of Material Science and Engineering, Yonsei University, Seoul, Republic of Korea

Graphene nanomesh with nanoperforations on a graphene basal plane has distinctive properties owing a high concentration of edge sites and perforation to perforation distance as small as 10 and 20 nm. Edge sites of graphene are known to exhibit facile electron transport and higher electrocatalytic activity than the basal planes. Graphene nanomeshes with nanoscale periodic or quasi-periodic nanoholes are expected to possess superior electrochemical properties, including exceptionally high rate capability and high frequency response in supercapacitor applications. In this study, we report on the synthetic method to prepare graphene nanomeshes using reduced graphene oxide flakes and their applications to high power energy storage devices.

F:P13  Aerogels Based on Microwave Plasma Torch Synthesized Graphene
F.R. SULTANOV, Z.A. MANSUROV, Institute of Combustion Problems, Almaty, Kazakhstan; S.C. CHANG, S. XING, F. ROBLES-HERNANDEZ, S.S. PEI, Center for Advanced Materials University of Houston, Houston, TX,  USA; Y.W. CHI, K.P. HUANG, Mechanical and Systems Research Laboratories, Industrial Technology Research Institute Chutung, Hsinchu, Taiwan, R.O.C.

Recently, we have synthesized highly uniform graphene nanoplatelets using a microwave plasma torch. Aerogels synthesized with different mixtures of MPT graphene nanoplatlets and multi-wall carbon nanotubes have been studied. Instead of synthesizing the graphene nanoplatelets with the top-down approach by some form of exfoliation process, a microwave plasma torch was used in a microwave-enhanced chemical vapor deposition process to synthesize the nanoplatelets with a bottom up approach. The 2.45 GHz microwave source has an output power of 1200 W. The plasma temperature is about 350ºC. The flow rates of argon and methane gases are 10 L/min and 0.1 L/min, respectfully, which results in an output of 6 g/hr graphene nanoplatelets. The MPT graphene nanoplatelets synthesized are highly uniform. The typical thickness is 2 atomic layers comparing to ≥ 4 layers by the top-down process, which substantially increases the BET surface area to 2041 m2/g of the MPT graphene nanoplatelets. FTIR/ESCA/SSNMR studies show no function group on MPT graphene nanoplatelets. Resulting MTP graphene and chitosan based aerogels present porous structure and strong hydrophobicity with contact angle between water drop and surface of aerogel higher than 150º. 1 gram of aerogel can absorb 101.3 grams of diesel.

F:HP14  Self-assembled α-Fe2O3 Mesocrystals/Graphene Nanohybrid for Enhanced Electrochemical Capacitor
LIAN GAO, XUEFENG SONG, PENG ZHANG, LIPING ZHAO, Shanghai Jiao Tong University, School of Material Science and Engineering, Shanghai, China

Here we show a facile fabrication of short rod-like α-Fe2O3 mesocrystals/graphene nanohybrids by self-assembly of FeOOH nanorods as the primary building blocks on graphene under hydrothermal conditions, accompanied and promoted by concomitant phase transition from FeOOH to α-Fe2O3. A systematic study of the formation mechanism is also presented. The galvanostatic charge/discharge curve shows a superior specific capacitance of the as-prepared α-Fe2O3 mesocrystals/graphene nanohybrid (considering total mass of active materials), which is 306.9 F g-1 at 3 A g-1 in the aqueous electrolyte under voltage ranges of up to 1 V. The nanohybrid with unique sufficient porous structure and high electrical conductivity allows for effective ion and charge transport in the whole electrode.

F:HP15  Hollow Carbon Based Anode Materials for High Performance Lithium Ion Batteries
XUEFENG SONG, ZHUANG SUN, PENG ZHANG, LIAN GAO, Shanghai Jiao Tong University, School of Material Science and Engineering, Shanghai, China

For commercial rechargeable lithium ion batteries, graphite-based materials are widely used as the traditional anode materials by virtue of its low cost, low and flat electrochemical potential and long cycle life, etc. Nevertheless, it is suffered from two main disadvantages, including the limited storage capacity (372 mAh g-1) and the poor rate performance induced by low Li diffusion constant. To circumvent these issues, hollow/porous carbon based materials have attracted considerable attention, because they can provide the following characteristics: 1) the large surface area leads to sufficient electrode-electrolyte interface to absorb Li+ ions, promoting rapid charge-transfer reaction; 2) the ultrathin shell can reduce the transport length of Li+ ions, while the nanopores on their surface facilitate Li+ ions transfer via enormous channels; 3) the hollow interior can buffer against the structure strain associated with the local volume change. Herein, several kinds of novel hollow carbon based materials were elaborated with hard template methods, which show high reversible capacity and good cycle life. For instance, MoS2-carbon hybrid hollow spheres delivered high specific capacity (831 mAh g-1 at 1A g-1 up to 200 cycles) and excellent rate capability (831, 738.6, 675.7, 612.8 and 562.9 mAh g-1 at 1, 3, 5, 8 and 10A g-1, respectively).

F:HP17  Self-standing Film of Porous Mo2C Nanostructures as Electrodes for Flexible Energy Storage Devices
LIPING ZHAO, XUEFENG SONG, PENG ZHANG, LIAN GAO, Shanghai Jiao Tong University, School of Material Science and Engineering, Shanghai, China

A novel self-supported film of molybdenum carbide nanofibers (Mo2C NFs) has been obtained by a facile and effective strategy. Consequently, a self-standing hybrid film of manganese dioxide nanosheets@molybdenum carbide nanofibers (MnO2-Mo2C NFs) has been fabricated, in which the ultrathin MnO2 nanosheets are uniformly decorated on highly conductive Mo2C NFs to form cross-linked network morphology. This unique hybrid architecture not only ensures the high electrical conductivity and mechanical stability of the hybrid film, but also offers numerous channels to rapidly ionic diffusion and charge transport. As a result, the self-standing hybrid film can be directly applied as the electrode of SCs without any binder or conductive additives. The specific capacitance is able to reach as high as 430 F/g and 280 F/g when the current density is 0.1 A/g and 2 A/g, respectively. There is almost no capacitance decay after continuous charge/discharge processes for 5000 cycles in aqueous electrolyte. Remarkably, the self-standing hybrid film electrode exhibits good electrochemical behaviors in organic (ionic liquid) electrolyte, especially in allowing to operate a high working voltage of 2.5 V and delivering a specific capacitance of 106 F/g at current density of 1 A/g. It indicates a promising potential application of the hybrid film as effective binder-free electrode material for flexible and high-performance SCs.

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