4,217 research outputs found
Scaling properties of step bunches induced by sublimation and related mechanisms: A unified perspective
This work provides a ground for a quantitative interpretation of experiments
on step bunching during sublimation of crystals with a pronounced
Ehrlich-Schwoebel (ES) barrier in the regime of weak desorption. A strong step
bunching instability takes place when the kinetic length is larger than the
average distance between the steps on the vicinal surface. In the opposite
limit the instability is weak and step bunching can occur only when the
magnitude of step-step repulsion is small. The central result are power law
relations of the between the width, the height, and the minimum interstep
distance of a bunch. These relations are obtained from a continuum evolution
equation for the surface profile, which is derived from the discrete step
dynamical equations for. The analysis of the continuum equation reveals the
existence of two types of stationary bunch profiles with different scaling
properties. Through a mathematical equivalence on the level of the discrete
step equations as well as on the continuum level, our results carry over to the
problems of step bunching induced by growth with a strong inverse ES effect,
and by electromigration in the attachment/detachment limited regime. Thus our
work provides support for the existence of universality classes of step
bunching instabilities [A. Pimpinelli et al., Phys. Rev. Lett. 88, 206103
(2002)], but some aspects of the universality scenario need to be revised.Comment: 21 pages, 8 figure
Lonely adatoms in space
There is a close relation between the problems of second layer nucleation in
epitaxial crystal growth and chemical surface reactions, such as hydrogen
recombination, on interstellar dust grains. In both cases standard rate
equation analysis has been found to fail because the process takes place in a
confined geometry. Using scaling arguments developed in the context of second
layer nucleation, I present a simple derivation of the hydrogen recombination
rate for small and large grains. I clarify the reasons for the failure of rate
equations for small grains, and point out a logarithmic correction to the
reaction rate when the reaction is limited by the desorption of hydrogen atoms
(the second order reaction regime)
Kinetic Monte Carlo simulations of oscillatory shape evolution for electromigration-driven islands
The shape evolution of two-dimensional islands under electromigration-driven
periphery diffusion is studied by kinetic Monte Carlo (KMC) simulations and
continuum theory. The energetics of the KMC model is adapted to the Cu(100)
surface, and the continuum model is matched to the KMC model by a suitably
parametrized choice of the orientation-dependent step stiffness and step atom
mobility. At 700 K shape oscillations predicted by continuum theory are
quantitatively verified by the KMC simulations, while at 500 K qualitative
differences between the two modeling approaches are found.Comment: 7 pages, 6 figure
Kinetic Roughening in Deposition with Suppressed Screening
Models of irreversible surface deposition of k-mers on a linear lattice, with
screening suppressed by disallowing overhangs blocking large gaps, are studied
by extensive Monte Carlo simulations of the temporal and size dependence of the
growing interface width. Despite earlier finding that for such models the
deposit density tends to increase away from the substrate, our numerical
results place them clearly within the standard KPZ universality class.Comment: nine pages, plain TeX (4 figures not included
Symmetry analysis of magneto-optical effects: The case of x-ray diffraction and x-ray absorption at the transition metal L23 edge
A general symmetry analysis of the optical conductivity or scattering tensor
is used to rewrite the conductivity tensor as a sum of fundamental spectra
multiplied by simple functions depending on the local magnetization direction.
Using this formalism, we present several numerical examples at the transition
metal L23 edge. From these numerical calculations we can conclude that large
deviations from the magneto-optical effects in spherical symmetry are found.
These findings are in particular important for resonant x-ray diffraction
experiments where the polarization dependence and azimuthal dependence of the
scattered Bragg intensity is used to determine the local ordered magnetization
direction
Interfaces with a single growth inhomogeneity and anchored boundaries
The dynamics of a one dimensional growth model involving attachment and
detachment of particles is studied in the presence of a localized growth
inhomogeneity along with anchored boundary conditions. At large times, the
latter enforce an equilibrium stationary regime which allows for an exact
calculation of roughening exponents. The stochastic evolution is related to a
spin Hamiltonian whose spectrum gap embodies the dynamic scaling exponent of
late stages. For vanishing gaps the interface can exhibit a slow morphological
transition followed by a change of scaling regimes which are studied
numerically. Instead, a faceting dynamics arises for gapful situations.Comment: REVTeX, 11 pages, 9 Postscript figure
Linear theory of unstable growth on rough surfaces
Unstable homoepitaxy on rough substrates is treated within a linear continuum
theory. The time dependence of the surface width is governed by three
length scales: The characteristic scale of the substrate roughness, the
terrace size and the Ehrlich-Schwoebel length . If (weak step edge barriers) and ,
then displays a minimum at a coverage , where the initial surface width is reduced by a factor
. The r\^{o}le of deposition and diffusion noise is analyzed. The
results are applied to recent experiments on the growth of InAs buffer layers
[M.F. Gyure {\em et al.}, Phys. Rev. Lett. {\bf 81}, 4931 (1998)]. The overall
features of the observed roughness evolution are captured by the linear theory,
but the detailed time dependence shows distinct deviations which suggest a
significant influence of nonlinearities
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