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Structural Defects in Graphene
"... t is the second law of thermodynamics that dictates the presence of a certain amount of disorder in crystalline mate-rials. But it is also due to the imperfection of material production processes that impuri-ties and defects are always present in crys-tals. Such lattice imperfections have a strong i ..."
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t is the second law of thermodynamics that dictates the presence of a certain amount of disorder in crystalline mate-rials. But it is also due to the imperfection of material production processes that impuri-ties and defects are always present in crys-tals. Such lattice imperfections have a strong influence on the electronic, optical, thermal, and mechanical properties of the solid. In fact, many of the characteristics of technologically important materials such as the conductance of semiconductors or the mechanical strength and ductility of metals are governed by defects.1 Defects in bulk crystals have been stud-
Plasmons in graphene: fundamental properties and potential applications
- Proceedings of the IEEE
, 2013
"... In graphene, plasmons are expected to provide valuable insights into many-body effects that include electron-phonon, electron-electron, and plasmon-phonon interactions. This paper provides a critical review of the state of research in this area. By Marinko Jablan, Marin Soljačić, and Hrvoje Buljan ..."
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In graphene, plasmons are expected to provide valuable insights into many-body effects that include electron-phonon, electron-electron, and plasmon-phonon interactions. This paper provides a critical review of the state of research in this area. By Marinko Jablan, Marin Soljačić, and Hrvoje Buljan ABSTRACT | Plasmons in graphene have intriguing fundamental properties and hold great potential for applications. They enable strong confinement of electromagnetic energy at subwavelength scales, which can be tuned and controlled via gate voltage, providing an advantage for graphene's plasmons over surface plasmons (SPs) on a metal-dielectric interface. They have been described for a large span of frequencies from terahertz up to infrared and even in the visible. We provide a critical review of the current knowledge of graphene plasmon properties (dispersion and linewidth) with particular emphasis on plasmonic losses and the competition between different decay channels, which are not yet fully understood. Plasmons in graphene provide an insight into interesting many-body effects such as those arising from the electron-phonon interaction and electron-electron interactions, including hybrid plasmon-phonon collective excitations (either with intrinsic or substrate phonons) and plasmarons. We provide a comparison of SPs on a metal-dielectric interface with plasmons in graphene and 2-D metallic monolayers. We finally outline the potential for graphene's plasmons for applications.
Corrugation in Exfoliated Graphene: An Electron Microscopy and Diffraction Study
"... raphene, a single monolayer of car-bon atoms arranged in a honey-comb lattice, is attracting excep-tional attention in view of potential applications that exploit its unique elec-tronic and transport properties.13 This zero-gap semiconductor is characterized by the linear dispersion of its valence a ..."
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raphene, a single monolayer of car-bon atoms arranged in a honey-comb lattice, is attracting excep-tional attention in view of potential applications that exploit its unique elec-tronic and transport properties.13 This zero-gap semiconductor is characterized by the linear dispersion of its valence and conduction bands, which meet at inequiva-lent charge-neutral points in momentum space. Graphene shows an ambipolar electric-field effect and an extremely high mobility of charge carriers, described as relativistic massless fermions, which results in unique transport properties. For instance,
In Situ Imaging of Layer-by-Layer Sublimation of Suspended Graphene
, 2010
"... ABSTRACT An individual suspended graphene sheet was connected to a scanning tunneling microscopy probe inside a transmission electron microscope, and Joule heated to high temperatures. At high temperatures and under electron beam irradiation, the few-layer graphene sheets were removed layer-by-laye ..."
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ABSTRACT An individual suspended graphene sheet was connected to a scanning tunneling microscopy probe inside a transmission electron microscope, and Joule heated to high temperatures. At high temperatures and under electron beam irradiation, the few-layer graphene sheets were removed layer-by-layer in the viewing area until a monolayer graphene was formed. The layer-by-layer peeling was initiated at vacancies in individual graphene layers. The vacancies expanded to form nanometer-sized holes, which then grew along the perimeter and propagated to both the top and bottom layers of a bilayer graphene joined by a bilayer edge. The layer-by-layer peeling was induced by atom sublimation caused by Joule heating and facilitated by atom displacement caused by high-energy electron irradiation, and may be harnessed to control the layer thickness of graphene for device applications.
Impact of Vacancies on Diffusive and Pseudodiffusive Electronic Transport in Graphene
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C 2011 American Chemical Society Stability of Graphene Edges under Electron Beam: Equilibrium Energetics versus Dynamic Effects
, 2011
"... heoretical predictions1,2 and subse-quent experiments3,4 demonstrated that a tunable band gap can be open-ed in graphene;the two-dimensional one-atomic-layer thick carbon membrane5;by confining it to a ribbon, thus opening a potential route toward applications of this novel material in nanoelectroni ..."
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heoretical predictions1,2 and subse-quent experiments3,4 demonstrated that a tunable band gap can be open-ed in graphene;the two-dimensional one-atomic-layer thick carbon membrane5;by confining it to a ribbon, thus opening a potential route toward applications of this novel material in nanoelectronics. It oc-curred, however, that electronic and trans-port properties of the ribbons are governed by not only ribbon width, but also the morphology of the edges.6 In fact, control-ling the atomic structure of the edges is crucial for any graphene-based electronics. Although many techniques have been sug-
C 2014 American Chemical Society Deep Ultraviolet to Near-Infrared Emission and Photoresponse in Layered N‑Doped Graphene Quantum Dots
, 2014
"... aterials that exhibit broadband absorption and emission covering deep ultraviolet (DUV), visible, and near-infrared (NIR) spectral range are of scientific and technological importance due to their valuable applications in the fields of broadband photodetectors, solar cells, and bioimaging. Currently ..."
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aterials that exhibit broadband absorption and emission covering deep ultraviolet (DUV), visible, and near-infrared (NIR) spectral range are of scientific and technological importance due to their valuable applications in the fields of broadband photodetectors, solar cells, and bioimaging. Currently, different semiconductor materials are required to cover these broad spectral ranges. Narrow-gap inorganic semiconductors such as PbS,1 PbSe,2 PbTe,3 HgTe,4 and InGaAs5 show infrared optical properties, but their toxicity and chemical instability limit their applica-tions. The wide band gap semiconductors
Electrical Properties of Chemically Derived Graphene
, 2011
"... Graphene, an atomically thin sheet of carbon, is the most recent endeavor for the application of carbon nanostructures in conventional electronics. The envisioned creation of devices completely carved out of graphene could lead to the revolution of electronic circuitry. However, the most established ..."
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Graphene, an atomically thin sheet of carbon, is the most recent endeavor for the application of carbon nanostructures in conventional electronics. The envisioned creation of devices completely carved out of graphene could lead to the revolution of electronic circuitry. However, the most established tech-nique to obtain high quality graphene sheets, i.e, by micromechanical cleav-age cannot be easily upscaled., serving as an impediment towards technolog-ical applications. The present thesis is dedicated to the study of graphene prepared via an alternative scalable, high yield and cost effective method which involves the chemical reduction of graphene oxide. The first part of this thesis describes in detail the atomic structure of graphene obtained by this method. Raman spectroscopy was used for this purpose followed by Transmission Electron Microscopy (TEM) and Near Edge X-Ray and Fine Structure (NEXAFS) measurements locally probe these sheets with atomic resolution. This revealed a highly disordered struc-
Chemical Versus Thermal Folding of Graphene Edges
, 2011
"... Using molecular dynamics (MD) simulations, we have investigated the kinetics of the graphene edge folding process. The lower limit of the energy barrier is found to be ~380 meV/Å (or about 800 meV per edge atom) and ~50 meV/Å (or about 120 meV per edge atom) for folding the edges of intrinsic clean ..."
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Using molecular dynamics (MD) simulations, we have investigated the kinetics of the graphene edge folding process. The lower limit of the energy barrier is found to be ~380 meV/Å (or about 800 meV per edge atom) and ~50 meV/Å (or about 120 meV per edge atom) for folding the edges of intrinsic clean single-layer graphene (SLG) and double-layer graphene (DLG), respectively. However, the edge folding barriers can be substantially reduced by imbalanced chemical adsorption, such as of H atoms, on the two sides of graphene along the edges. Our studies indicate that thermal folding is not feasible at room temperature (RT) for clean SLG and DLG edges and is feasible at high temperature only for DLG edges, whereas chemical folding (with adsorbates) of both SLG and DLG edges can be spontaneous at RT. These findings suggest that the folded edge structures of suspended graphene observed in some experiments are possibly due to the presence of adsorbates at the edges.
TRANSMISSION ELECTRON MICROSCOPY OF STRUCTURAL DISORDER IN TWO-DIMENSIONAL MATERIALS
, 2014
"... Transmission electron microscopy (TEM) of two-dimensional materials (2D) offers an unprecedented opportunity to study disordered systems down to the single-atom level. The reduced dimensionality of these systems provides a two-fold opportunity: first, 2D materials serve as model systems for explorin ..."
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Transmission electron microscopy (TEM) of two-dimensional materials (2D) offers an unprecedented opportunity to study disordered systems down to the single-atom level. The reduced dimensionality of these systems provides a two-fold opportunity: first, 2D materials serve as model systems for exploring direct correlations between the structure and properties of individual atomic features. Second, these studies enable the development of new 2D materials and devices with precisely tailored optical, electronic, and mechanical properties. The experiments presented in this thesis show the first atomic-resolution images of extended one- and two-dimensional disorder in 2D materials and the extraordi-nary range of consequences they have on the local materials properties. The thesis begins with studies that probe the structure and properties of the 1D defects that make up grain boundaries in atomically-thin layers of graphene and molybdenum disulfide. These experiments span length scales across five orders of magnitude to image every atom at the grain boundaries through atomic-resolution scanning TEM and rapidly map the location, orientation, and shape of several
