2,459 research outputs found
Single-Particle Tunneling in Doped Graphene-Insulator-Graphene Junctions
The characteristics of tunnel junctions formed between n- and p-doped
graphene are investigated theoretically. The single-particle tunnel current
that flows between the two-dimensional electronic states of the graphene (2D-2D
tunneling) is evaluated. At a voltage bias such that the Dirac points of the
two electrodes are aligned, a large resonant current peak is produced. The
magnitude and width of this peak is computed, and its use for devices is
discussed. The influence of both rotational alignment of the graphene
electrodes and structural perfection of the graphene is discussed.Comment: 23 pages, 9 figures; added Section II(E) and associated figures, and
made other minor typographical correction
Inelastic Effects in Low-Energy Electron Reflectivity of Two-dimensional Materials
A simple method is proposed for inclusion of inelastic effects (electron
absorption) in computations of low-energy electron reflectivity (LEER) spectra.
The theoretical spectra are formulated by matching of electron wavefunctions
obtained from first-principles computations in a repeated vacuum-slab-vacuum
geometry. Inelastic effects are included by allowing these states to decay in
time in accordance with an imaginary term in the potential of the slab, and by
mixing of the slab states in accordance with the same type of distribution as
occurs in a free-electron model. LEER spectra are computed for various
two-dimensional materials, including free-standing multilayer graphene,
graphene on copper substrates, and hexagonal boron nitride (h-BN) on cobalt
substrates.Comment: 21 pages, 7 figure
Study of interface asymmetry in InAsâGaSb heterojunctions
We present reflection high energy electron diffraction, secondary ion mass spectroscopy, scanning tunneling microscopy and xâray photoelectron spectroscopy studies of the abruptness of InAsâGaSb interfaces. We find that the interface abruptness depends on growth order: InAs grown on GaSb is extended, while GaSb grown on InAs is more abrupt. We first present observations of the interfacial asymmetry, including measurements of band alignments as a function of growth order. We then examine more detailed studies of the InAsâGaSb interface to determine the mechanisms causing the extended interface. Our results show that Sb incorporation into the InAs overlayer and As exchange for Sb in the GaSb underlayer are the most likely causes of the interfacial asymmetry
Scanning tunneling microscopy of lnAs/GaSb superlattices: Subbands, interface roughness, and interface asymmetry
Scanning tunneling microscopy and spectroscopy is used to characterize InAs/GaSb superlattices, grown by molecular-beam epitaxy. Roughness at the interfaces between InAs and GaSb layers is directly observed in the images, and a quantitative spectrum of this roughness is obtained. Electron subbands in the InAs layers are resolved in spectroscopy. Asymmetry between the interfaces of InAs grown on GaSb compared with GaSb grown on In As is seen in voltage-dependent imaging. Detailed
spectroscopic study of the interfaces reveals some subtle differences between the two in terms of their valence-band onsets and conduction-band state density. These differences are interpreted in a model in which the GaSb on InAs interface has an abrupt InSb-like structure, but at the InAs on GaSb interface some Sb grading occurs into the InAs overlayer
Formation of Graphene on SiC(000-1) Surfaces in Disilane and Neon Environments
The formation of graphene on the SiC(000-1) surface (the C-face of the {0001}
surfaces) has been studied, utilizing both disilane and neon environments. In
both cases, the interface between the graphene and the SiC is found to be
different than for graphene formation in vacuum. A complex low-energy electron
diffraction pattern with rt(43) x rt(43)-R\pm7.6{\deg} symmetry is found to
form at the interface. An interface layer consisting essentially of graphene is
observed, and it is argued that the manner in which this layer covalently bonds
to the underlying SiC produces the rt(43) x rt(43)-R\pm7.6{\deg} structure
[i.e. analogous to the 6rt(3) x 6rt(3)-R30{\deg} "buffer layer" that forms on
the SiC(0001) surface (the Si-face)]. Oxidation of the surface is found to
modify (eliminate) the rt(43) x rt(43)-R\pm7.6{\deg} structure, which is
interpreted in the same manner as the known "decoupling" that occurs for the
Si-face buffer layer.Comment: 12 pages, 6 figures; to to be published in J. Vac. Sci. Technol.
Formation of a Buffer Layer for Graphene on C-face SiC{0001}
Graphene films prepared by heating the SiC(000-1) surface (the C-face of the
{0001} surfaces) in a Si-rich environment are studied using low-energy electron
diffraction (LEED) and low-energy electron microscopy (LEEM). Upon
graphitization, an interface with rt(43) x rt(43)-R7.6 degree symmetry is
observed by in situ LEED. After oxidation, the interface displays rt(3) x
rt(3)-R30 degree symmetry. Electron reflectivity measurements indicate that
these interface structures arise from a graphene-like "buffer layer" that forms
between the graphene and the SiC, similar to that observed on Si-face SiC. From
a dynamical LEED structure calculation for the oxidized C-face surface, it is
found to consist of a graphene layer sitting on top of a silicate (Si2O3)
layer, with the silicate layer having the well-known structure as previously
studied on bare SiC(000-1) surfaces. Based on this result, the structure of the
interface prior to oxidation is discussed.Comment: 12 pages, 5 figure
Morphology of Graphene on SiC(000-1) Surfaces
Graphene is formed on SiC(000-1) surfaces (the so-called C-face of the
crystal) by annealing in vacuum, with the resulting films characterized by
atomic force microscopy, Auger electron spectroscopy, scanning Auger microscopy
and Raman spectroscopy. Morphology of these films is compared with the graphene
films grown on SiC(0001) surfaces (the Si-face). Graphene forms a terraced
morphology on the C-face, whereas it forms with a flatter morphology on the
Si-face. It is argued that this difference occurs because of differing
interface structures in the two cases. For certain SiC wafers, nanocrystalline
graphite is found to form on top of the graphene.Comment: Submitted to Applied Physics Letters; 9 pages, 3 figures; corrected
the stated location of Raman G line for NCG spectrum, to 1596 cm^-
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