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Über dieses Buch

This book presents selected papers from the fourth edition of the GraphX conference series, GraphITA 2015. Its content range from fundamentals to applications of graphene and other 2D material such as silicene, BN and MoS2. The newest technological challenges in the field are described in this book, written by worldwide known scientists working with 2D materials.The chapter 'Morphing Graphene-Based Systems for Applications: Perspectives from Simulations' is published open access under a CC BY 4.0 license.



Thermal Transport in Nanocrystalline Graphene: The Role of Grain Boundaries

Single grain boundaries of crystalline graphene with varying mismatch angles from 3° to 16° have been investigated using molecular dynamics simulations. Four- to eight-atomic rings are found to be the most abundant non-hexagonal polygons in the grain boundary for all mismatch angles. Tetra- and octagons are predominant for mismatch angles of 4.1° and 6.6° in contrast to nanocrystalline samples where penta- and heptagons are dominating. Out-of-plane buckling at the grain boundary is most pronounced for a mismatch angle of 3.0° and it tends to decrease with increasing mismatch angle. At 16.1°, the out-of-plane buckling vanishes. Analysis of the vibrational density of states of boundary atoms revealed a significant decrease of the main peak of optical vibrations and the evolution of secondary peaks below and above the major frequency attributed to vibrations of non-hexagonal rings. The thermal boundary resistance in single graphene interfaces has been approximated. It tends to increase with increasing mismatch angle, indicating reduced thermal conductivity when such interfaces are present in crystalline graphene. In nanocrystalline graphene samples, the thermal conductivity is significantly reduced with respect to crystalline graphene and it decreases with decreasing grain size according to an increasing number of single boundaries.
K. R. Hahn, C. Melis, L. Colombo

Raman Spectroscopy of Graphene Nanoribbons: A Review

In the last few years, several methods have been proposed for the production of ultra-narrow stripes of graphene, called graphene nanoribbons, which could find several applications in nano- and opto-electronics. However, every production method gives rise to different types of ribbons, in terms of structural quality, width, edge pattern, and type of functional groups. In this review, we compare the Raman spectrum of graphene nanoribbons produced by different techniques by focusing on the effect of different structural parameters, such as width and edge-patterns. Effects due to changes in the lateral dimension are also discussed by comparing the Raman spectrum of ultra-narrow graphene nanoribbons with the spectrum of polycyclic aromatic hydrocarbons and defective graphene.
C. Casiraghi, D. Prezzi

Electron–Phonon Coupling in Two-Dimensional Superconductors: Doped Graphene and Phosphorene

The advent of two-dimensional materials with the possibility to vary their physical properties by means of doping, strain, electric, and magnetic fields allows to explore novel physical effects in the two-dimensional limit, where electronic, magnetic, and structural properties can be very different with respect to three-dimensional case. For example, the possibility to synthesize a two-dimensional superconductor will open the doors to new and unexplored applications in present nanotechnology. In this respect, reliable predictions of the superconducting critical temperature from first-principles and in real materials are important prerequisite to make important advances along this line of research. In this work, we review the results of recent theoretical predictions of superconductivity in experimentally realized two-dimensional superconductors: doped graphene and doped phosphorene. And for the latter system, we also present an analysis of several realistic dopants that could induce a superconducting state.
G. Profeta, C. Tresca, A. Sanna

Elastic Properties and Electron–Phonon Coupling of Graphene/Metal Interfaces Probed by Phonon Dispersion

High-resolution electron energy loss spectroscopy is a suitable tool for investigating phonons in graphene, due to its exceptional energy resolution in both the energy and momentum domains. In this chapter, we show that the experimental phonon dispersion of graphene can be used to estimate elastic properties and electron–phonon coupling. Novel coupling mechanisms of Dirac cone electrons in graphene with out-of-plane optical phonons of the graphene lattice, activated only whenever the graphene sheet is supported by a solid substrate, are also discussed.
M. Alfano, C. Lamuta, G. Chiarello, A. Politano

Ab Initio Calculations and Kinetic Process Simulations of Nitrogen-Doped Graphene

The precise control of the doping characteristics of graphene-based systems is a key parameter for successful integration in devices and applications. Doping can tune graphene’s carrier density, which is important for the optimization of graphene-based flexible and transparent electrodes. Moreover, if doping is confined within one out of the two equivalent graphene sublattices, considerable band gaps can open that could serve for switching devices on and off. We use the density functional theory to explore the conditions of sublattice symmetry breaking in nitrogen-doped graphene. We show that the nucleation of graphene grains and their growth through the propagation of unpassivated zigzag edges could give rise to a highly unbalanced doping, due to exothermic substitutions on edge sites. Based on our ab initio results, we calibrate an event-driven kinetic Monte Carlo model that simulates the growth kinetics and investigates the N incorporation mechanism in real-process conditions. We demonstrate that the degree of symmetry breaking strongly depends on the growing conditions.
I. Deretzis, A. La Magna

From Point to Line Defects in Two-Dimensional Transition Metal Dichalcogenides: Insights from Transmission Electron Microscopy and First-Principles Calculations

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently received great deal of attention due to their unique properties associated with the reduced dimensionality of the system. The properties of these materials have been shown to be affected by atomic defects in the atomic network. The very structure of these materials which are composed from three atomic layers only, combined with dramatic improvements in microscopy techniques, made it possible to study the behavior of defects in these systems with unprecedented accuracy. Various point and line defects were identified, and their effects on the properties of the systems were accessed. It was demonstrated that point defects induced by electron beam irradiation coalesce in line defects, but their quasi-one dimensional atomic structure varies from member to member in the transition metal dichalcogenides family. In this review, we summarize recent experimental and theoretical findings in this area, discuss how the line structures appear due to the agglomeration of point defects, and dwell upon how line defects can be used to engineer properties of 2D TMDs. Finally, we address the challenges in this field and issues which still lack the explanation.
H.-P. Komsa, A. V. Krasheninnikov

Open Access

Morphing Graphene-Based Systems for Applications: Perspectives from Simulations

Graphene, the one-atom-thick sp2-hybridized carbon crystal, displays unique electronic, structural and mechanical properties, which promise a large number of interesting applications in diverse high-tech fields. Many of these applications require its functionalization, e.g., with substitution of carbon atoms or adhesion of chemical species, creation of defects, modification of structure or morphology, to open an electronic band gap to use it in electronics, or to create 3D frameworks for volumetric applications. Understanding the morphology–properties relationship is the first step to efficiently functionalize graphene. Therefore, a great theoretical effort has been recently devoted to model graphene in different conditions and with different approaches involving different levels of accuracy and resolution. Here, we review the modeling approaches to graphene systems, with a special focus on atomistic level methods, but extending our analysis onto coarser scales. We illustrate the methods by means of applications with possible potential impact.
T. Cavallucci, K. Kakhiani, R. Farchioni, V. Tozzini

Perfecting the Growth and Transfer of Large Single-Crystal CVD Graphene: A Platform Material for Optoelectronic Applications

In this work, we demonstrate the synthesis of millimetre-sized single-crystals of graphene, achievable in a commercially available cold-wall CVD reactor, and several different approaches to transfer it from the growth substrate to a target substrate of choice. We confirm the high crystal quality of this material using various characterisation techniques, including optical and scanning electron microscopy as well as Raman spectroscopy. By performing field effect and quantum Hall effect measurements, we demonstrate that the electronic properties of such single crystals are comparable to those of ideal mechanically exfoliated flakes of graphene. Several applications of this high-quality material are also reviewed.
V. Miseikis, S. Xiang, S. Roddaro, S. Heun, C. Coletti

Advances in the Fabrication of Large-Area Back-Gated Graphene Field-Effect Transistors on Plastics: Platform for Flexible Electronics and Sensing

Graphene (Gr) is currently one of the most appealing materials as conductive transparent electrode for flexible electronics, thanks to its bendability/stretchability accompanied by small variations of the electrical properties after mechanical deformations. In addition, the field-effect tunable carrier density combined to a high mobility and saturation velocity make it an excellent channel material for field-effect transistors (FETs) even on flexible substrates. By proper design of the device structure (channel length, top- or back-gate configuration), Gr-FETs can be used for high-frequency (RF) electronics or for high-sensitivity chemical, biological, and environmental sensors exploiting transconductance variations in response to the chemi/physisorption of molecular species on Gr channel. In particular, miniaturized and flexible Gr-FET sensors can represent a strong advance with respect to current sensors technology and will be extremely useful for “in situ” applications. Here we report a wafer scale and semiconductor fab compatible processing strategy to fabricate arrays of Gr-FETs on a PEN substrate, adopting a local back-gate configuration, with a thin Al2O3 gate dielectric film deposited at low temperature (100 °C) by plasma-assisted Atomic Layer Deposition (ALD) and transfer of large-area Gr grown by chemical vapor deposition on copper foils. Electrical characterization of the fabricated devices is presented and their suitability for solid ion sensing FET (IS-FET) applications is discussed.
G. Fisichella, S. Lo Verso, S. Di Marco, V. Vinciguerra, E. Schilirò, S. Di Franco, R. Lo Nigro, F. Roccaforte, A. Zurutuza, A. Centeno, S. Ravesi, F. Giannazzo

Silicene in the Flatland

Since the rise of graphene, the flatland of two-dimensional (2D) materials continues to expand its borders including more and more members with complementary properties. An overview of the more relevant members is proposed which accounts for the class of 2D layered transition metal dichalcogenides and elementary 2D materials. Amidst the latter ones is silicene, a honeycomb-like Si lattice. Silicene has recently attracted an enormous interest as emerging research material for the semiconductor technology roadmap because of its intrinsic affinity with the ubiquitous silicon technology. Free-standing silicene is energetically allowed provided that the chemical bonds are vertically buckled rather than being perfectly planar as in graphene. Nonetheless, a stable graphite-like Si allotrope does not exist in nature. Artificially forcing silicon atoms into a silicene lattice is made possible by the epitaxy of a silicon monolayer on substrates therein giving rise to a quite rich variety of surface phases. Here we review the phase diagram of silicene on Ag(111) as a paradigmatic case of the silicene-on-substrate. Attention is also paid to identify templates for the silicene growth enabling the silicene transfer to technological platforms targeting device integration.
C. Grazianetti, A. Molle

Decorated and Modified Graphenes as Electrodes in Na and Li-Ion Batteries

Nowadays, rechargeable Li-ion batteries represent the state of the art for the power supply in technological devices. However, the wide-scale implementation of this technology, for example in the automotive field or for large stationary applications, could raise issues, i.e. concerning the limited lithium mineral reserves. The investigation of alternatives to lithium is hence highly desirable, although it requires the identification of new materials suitable as components for new batteries, displaying similar or possibly even better performances with respect to the current systems. Here we show that electrodes based on graphene derivatives are able not only to support the insertion of Li+, but also of Na+ ions, with high capacity and stability upon cycling, leading to the development of novel Na-ion batteries.
D. Pontiroli, G. Magnani, M. Gaboardi, M. Riccò, C. Milanese, J. C. Pramudita, N. Sharma

Chemically Exfoliated Layered Materials for Practical Gas Sensing Applications

In the last decade two-dimensional materials have attracted great interest for a wide range of applications, from optoelectronics to nanobiotechnology. Between the possible applications, the use of two-dimensional materials for the production of gas sensors has proved to be very promising. In this work we report on the fabrication and the characterization of gas sensors obtained from chemically exfoliated graphene oxide, black phosphorous, MoS2 and WS2. All the sensors were prepared by simply drop casting the flakes dispersed in a solution on a Pt interdigitated substrate. The sensors have shown excellent electrical responses to both oxidizing and reducing gases, demonstrating that the use of chemically exfoliated two-dimensional materials is a practical and cheap way to produce high-quality gas sensing devices.
F. Perrozzi, C. Cantalini, L. Ottaviano

Solutions of Reduced Carbon Allotropes and Their Utilization for Functional Material Generation

Despite their reactive nature, the properties of solutions of reduced carbon allotropes have been studied in detail and remarkable research regarding their possible utilization have been conducted in recent years. Solutions of reduced carbon allotropes are an excellent basis for the generation of functional architectures. Solutions of reduced carbon nanotubides have been used to enrich metallic SWCNTS in solution, to fabricate transparent conductive films and to generate macroscopic fibers of aligned CNTs. GICs have been used to produce potassium batteries and to synthesize carbon nanodots with photoluminescence behavior. We foresee a bright future for these solutions because predominantly single components are present, e.g., single-layer graphene and their properties are now well understood.
F. Hof, A. Pénicaud

Synthesis of High-Density Graphene Foams Using Nanoparticle Templates

Graphene foams grown by CVD on commercially available Ni foam templates were first reported in 2011. Since then they have been investigated widely due to their ability to transfer many of the unique properties of graphene to the macroscopic scale, with high surface area, high electrical conductivity and good structural integrity. However, the pore-size range is typically 200–400 μm, so much of the volume is unoccupied by the functional graphene material. We report a new synthesis procedure that produces graphene foams with pore sizes in the range of 1–10 μm, by using a sacrificial template of metal nanoparticles sintered together to form a network. These materials could have wide-ranging applications in fields such as high-density energy storage, membranes and sensing.
M. Christian, L. Venturi, L. Ortolani, F. Liscio, R. Rizzoli, V. Palermo, V. Morandi

Protein-Based Nanostructures and Their Self-assembly with Graphene Oxide

Proteins are hetero-polymers made-up of single building blocks (aminoacids) whose composition determines folding and final architecture. Some proteins are able to undergo self-assembly process enabling the formation of ordered molecular aggregates that in some cases assume conformations particularly suitable to nanotechnological applications. In this work we describe the properties of a ring-like decameric protein, Peroxiredoxin (Prx), to build composite materials interacting with or catalyzing the formation of selectively metal nanoparticles that can be trapped over the surface of nanostructured graphene oxide (GO) sheets. We demonstrate furthermore the ability of Prx to guide the formation of 3D layers of GO embedding metal nanoparticles in the composite material. These composites are discussed as possible precursors to electronic and chemical devices.
R. Ippoliti, M. Ardini, L. Di Leandro, F. Giansanti, A. Cimini, L. Ottaviano, V. Morandi, L. Ortolani, F. Angelucci

Graphene- and Carbon Nanotubes-Yeast Bionicomposites

Nature offers us an enormous amount of ready-to-use templates with various morphologies and functionalities, which can be successfully utilized in fabrication of biosensors, tissue engineering, and microelectronics. The directed combination of such natural templates with graphene or carbon nanotubes results in the development of a novel material which uses the features of both. We produced hybrid materials by giving to microorganisms the nutrient to grow together with graphene nanoplatelets and carbon nanotubes. Such hybrid materials can be considered as bionic because they have the benefits of both biological world which can self-organize and that of non-living materials, which couple functions such as self-healing and electronic transport.
L. Valentini, S. Bittolo Bon, S. Signetti, N. M. Pugno
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