68,308 research outputs found
Fast diffusion of graphene flake on graphene layer
Diffusion of a graphene flake on a graphene layer is analyzed and a new
diffusion mechanism is proposed for the system under consideration. According
to this mechanism, rotational transition of the flake from commensurate to
incommensurate states takes place with subsequent simultaneous rotation and
translational motion until the commensurate state is reached again, and so on.
The molecular dynamics simulations and analytic estimates based on ab initio
and semi-empirical calculations demonstrate that the proposed diffusion
mechanism is dominant at temperatures T ~ Tcom, where Tcom corresponds to the
barrier for transitions of the flake between adjacent energy minima in the
commensurate states. For example, for the flake consisting of ~ 40, 200 and 700
atoms the contribution of the proposed diffusion mechanism through rotation of
the flake to the incommensurate states exceeds that for diffusion of the flake
in the commensurate states by one-two orders of magnitude at temperatures 50 -
150 K, 200 - 600 K and 800 - 2400 K, respectively. The possibility to
experimentally measure the barriers to relative motion of graphene layers based
on the study of diffusion of a graphene flake is considered. The results
obtained are also relevant for understanding of dynamic behavior of polycyclic
aromatic molecules on graphene and should be qualitatively valid for a set of
commensurate adsorbate-adsorbent systems.Comment: 33 pages, 6 figure
Pseudo-magnetic field distribution and pseudo-Landau levels in suspended graphene flakes
Combining the tight-binding approximation and linear elasticity theory for a
planar membrane, we investigate stretching of a graphene flake assuming that
two opposite edges of the sample are clamped by the contacts. We show that,
depending on the aspect ratio of the flake and its orientation, gapped states
may form in the membrane in the vicinity of the contacts. This gap in the
pre-contact region should be biggest for the armchair orientation of the flake
and width to length ratio of around 1.Comment: 7 pages + 3 figure
Gender Differences in the Intergenerational Earnings Mobility of Second-Generation Migrants
This study analyzes gender diff erences in the intergenerational earnings mobility of second-generation migrants in Germany. The analysis takes into account potential infl uences like assortative mating in the form of ethnic marriages and the parental integration measured by parents’ years since migration. First, intergenerational earnings elasticities are estimated at the mean and along the earnings distribution. The results do not reveal large diff erences in the intergenerational mobility – neither between natives and migrants nor between men and women. Second, intergenerational changes in the relative earnings position are analyzed. The results show that migrants are less likely than natives to worsen their relative earnings position while they have the same probability as natives to improve their earnings position. In summary, migrants are mostly as (im)mobile as the native population.International migration; second-generation migrants; intergenerational mobility; marriage
Diamondlike flake composites
A carbon coating is vacuum arc deposited on a smooth surface of a target which is simultaneously ion beam sputtered. The bombarding ions have sufficient energy to create diamond bonds. Spalling occurs as the carbon deposit thickens. The resulting diamond-like carbon flakes are mixed with a binder or matrix material to form a composite material having improved thermal, electrical, mechanical, and tribological properties when used in aerospace structures and components
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