32 research outputs found
Formation of atomic nanoclusters on graphene sheets
The formation of atomic nanoclusters on suspended graphene sheets have been
investigated by employing a Molecular dynamics simulation at finite
temperature. Our systematic study is based on temperature dependent Molecular
dynamics simulations of some transition and alkali atoms on suspended graphene
sheets. We find that the transition atoms aggregate and make various size
nanoclusters distributed randomly on graphene surface. We also report that most
alkali atoms make one atomic layer on graphene sheets. Interestingly, the
potassium atoms almost deposit regularly on the surface at low temperature. We
expect from this behavior that the electrical conductivity of a suspended
graphene doped by potassium atoms would be much higher than the case doped by
the other atoms at low temperature.Comment: High quality figures can be requested to the author
The surface science of quasicrystals
The surfaces of quasicrystals have been extensively studied since about 1990. In this paper we review work on the structure and morphology of clean surfaces, and their electronic and phonon structure. We also describe progress in adsorption and epitaxy studies. The paper is illustrated throughout with examples from the literature. We offer some reflections on the wider impact of this body of work and anticipate areas for future development.
(Some figures in this article are in colour only in the electronic version
Diffusive Charge Transport in Graphene on SiO2
We review our recent work on the physical mechanisms limiting the mobility of
graphene on SiO2. We have used intentional addition of charged scattering
impurities and systematic variation of the dielectric environment to
differentiate the effects of charged impurities and short-range scatterers. The
results show that charged impurities indeed lead to a conductivity linear in
density in graphene, with a scattering magnitude that agrees quantitatively
with theoretical estimates [1]; increased dielectric screening reduces
scattering from charged impurities, but increases scattering from short-range
scatterers [2]. We evaluate the effects of the corrugations (ripples) of
graphene on SiO2 on transport by measuring the height-height correlation
function. The results show that the corrugations cannot mimic long-range
(charged impurity) scattering effects, and have too small an
amplitude-to-wavelength ratio to significantly affect the observed mobility via
short-range scattering [3, 4]. Temperature-dependent measurements show that
longitudinal acoustic phonons in graphene produce a resistivity linear in
temperature and independent of carrier density [5]; at higher temperatures,
polar optical phonons of the SiO2 substrate give rise to an activated, carrier
density-dependent resistivity [5]. Together the results paint a complete
picture of charge carrier transport in graphene on SiO2 in the diffusive
regime.Comment: 28 pages, 7 figures, submitted to Graphene Week proceeding
LEED and STM study of Cs on Cu(211)
A low-temperature (25 K) STM study of Cs adsorption on Cu(211) indicates that Cs forms variable-density structures which align along the step edges of the Cu(211) surface. The density of the overlayer increases with Cs coverage, forming a quasihexagonal c(2×2) structure at a coverage of 0.17. A dynamical LEED study of that structure at 130 K indicates that the Cs atoms are adsorbed on top of the Cu atoms in the center of the terraces, with a Cs–Cu nearest-neighbor distance of 3.56± 0.04 Å. This structure is accompanied by a significant rumpling of the Cu(211) surface. </jats:p
Phonon-mediated superconductivity in graphene by lithium deposition
Graphene(1) is the physical realization of many fundamental concepts and phenomena in solid-state physics(2). However, in the list of graphene's many remarkable properties(3-6), superconductivity is notably absent. If it were possible to find a way to induce superconductivity, it could improve the performance and enable more efficient integration of a variety of promising device concepts including nanoscale superconducting quantum interference devices, single-electron superconductor-quantum dot devices(7,8), nanometre-scale superconducting transistors(9) and cryogenic solid-state coolers(10). To this end, we explore the possibility of inducing superconductivity in a graphene sheet by doping its surface with alkaline metal adatoms, in a manner analogous to which superconductivity is induced in graphite intercalated compounds(11,12) (GICs). As for GICs, we find that the electrical characteristics of graphene are sensitive to the species of adatom used. However, contrary to what happens in GICs, Li-covered graphene is superconducting at a much higher temperature with respect to Ca-covered graphene