4,622 research outputs found
Kinetics of step bunching during growth: A minimal model
We study a minimal stochastic model of step bunching during growth on a
one-dimensional vicinal surface. The formation of bunches is controlled by the
preferential attachment of atoms to descending steps (inverse Ehrlich-Schwoebel
effect) and the ratio of the attachment rate to the terrace diffusion
coefficient. For generic parameters () the model exhibits a very slow
crossover to a nontrivial asymptotic coarsening exponent .
In the limit of infinitely fast terrace diffusion () linear coarsening
( = 1) is observed instead. The different coarsening behaviors are
related to the fact that bunches attain a finite speed in the limit of large
size when , whereas the speed vanishes with increasing size when .
For an analytic description of the speed and profile of stationary
bunches is developed.Comment: 8 pages, 10 figure
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
Breakdown of step-flow growth in unstable homoepitaxy
Two mechanisms for the breakdown of step flow growth, in the sense of the
appearance of steps of opposite sign to the original vicinality, are studied by
kinetic Monte Carlo simulations and scaling arguments. The first mechanism is
the nucleation of islands on the terraces, which leads to mound formation if
interlayer transport is sufficiently inhibited. The second mechanism is the
formation of vacancy islands due to the self-crossing of strongly meandering
steps. The competing roles of the growth of the meander amplitude and the
synchronization of the meander phase are emphasized. The distance between
vacancy islands along the step direction appears to be proportional to the
square of the meander wavelengthComment: 7 pages, 9 figure
Drift causes anomalous exponents in growth processes
The effect of a drift term in the presence of fixed boundaries is studied for
the one-dimensional Edwards-Wilkinson equation, to reveal a general mechanism
that causes a change of exponents for a very broad class of growth processes.
This mechanism represents a relevant perturbation and therefore is important
for the interpretation of experimental and numerical results. In effect, the
mechanism leads to the roughness exponent assuming the same value as the growth
exponent. In the case of the Edwards-Wilkinson equation this implies exponents
deviating from those expected by dimensional analysis.Comment: 4 pages, 1 figure, REVTeX; accepted for publication in PRL; added
note and reference
New mechanism for impurity-induced step bunching
Codeposition of impurities during the growth of a vicinal surface leads to an
impurity concentration gradient on the terraces, which induces corresponding
gradients in the mobility and the chemical potential of the adatoms. Here it is
shown that the two types of gradients have opposing effects on the stability of
the surface: Step bunching can be caused by impurities which either lower the
adatom mobility, or increase the adatom chemical potential. In particular,
impurities acting as random barriers (without affecting the adatom binding)
cause step bunching, while for impurities acting as random traps the
combination of the two effects reduces to a modification of the attachment
boundary conditions at the steps. In this case attachment to descending steps,
and thus step bunching, is favored if the impurities bind adatoms more weakly
than the substrate.Comment: 7 pages, 3 figures. Substantial revisions and correction
Records and sequences of records from random variables with a linear trend
We consider records and sequences of records drawn from discrete time series
of the form , where the are independent and identically
distributed random variables and is a constant drift. For very small and
very large drift velocities, we investigate the asymptotic behavior of the
probability of a record occurring in the th step and the
probability that all entries are records, i.e. that . Our work is motivated by the analysis of temperature time series in
climatology, and by the study of mutational pathways in evolutionary biology.Comment: 21 pages, 7 figure
Spiral Growth and Step Edge Barriers
The growth of spiral mounds containing a screw dislocation is compared to the
growth of wedding cakes by two-dimensional nucleation. Using phase field
simulations and homoepitaxial growth experiments on the Pt(111) surface we show
that both structures attain the same characteristic large scale shape when a
significant step edge barrier suppresses interlayer transport. The higher
vertical growth rate observed for the spiral mounds on Pt(111) reflects the
different incorporation mechanisms for atoms in the top region and can be
formally represented by an enhanced apparent step edge barrier.Comment: 11 pages, 4 figures, partly in colo
Driven Lattice Gases with Quenched Disorder: Exact Results and Different Macroscopic Regimes
We study the effect of quenched spatial disorder on the steady states of
driven systems of interacting particles. Two sorts of models are studied:
disordered drop-push processes and their generalizations, and the disordered
asymmetric simple exclusion process. We write down the exact steady-state
measure, and consequently a number of physical quantities explicitly, for the
drop-push dynamics in any dimensions for arbitrary disorder. We find that three
qualitatively different regimes of behaviour are possible in 1- disordered
driven systems. In the Vanishing-Current regime, the steady-state current
approaches zero in the thermodynamic limit. A system with a non-zero current
can either be in the Homogeneous regime, chracterized by a single macroscopic
density, or the Segregated-Density regime, with macroscopic regions of
different densities. We comment on certain important constraints to be taken
care of in any field theory of disordered systems.Comment: RevTex, 17pages, 18 figures included using psfig.st
Bottleneck-induced transitions in a minimal model for intracellular transport
We consider the influence of disorder on the non-equilibrium steady state of
a minimal model for intracellular transport. In this model particles move
unidirectionally according to the \emph{totally asymmetric exclusion process}
(TASEP) and are coupled to a bulk reservoir by \emph{Langmuir kinetics}. Our
discussion focuses on localized point defects acting as a bottleneck for the
particle transport. Combining analytic methods and numerical simulations, we
identify a rich phase behavior as a function of the defect strength. Our
analytical approach relies on an effective mean-field theory obtained by
splitting the lattice into two subsystems, which are effectively connected
exploiting the local current conservation. Introducing the key concept of a
carrying capacity, the maximal current which can flow through the bulk of the
system (including the defect), we discriminate between the cases where the
defect is irrelevant and those where it acts as a bottleneck and induces
various novel phases (called {\it bottleneck phases}). Contrary to the simple
TASEP in the presence of inhomogeneities, many scenarios emerge and translate
into rich underlying phase-diagrams, the topological properties of which are
discussed.Comment: 14 pages, 15 figures, 1 tabl
An Exactly Solved Model of Three Dimensional Surface Growth in the Anisotropic KPZ Regime
We generalize the surface growth model of Gates and Westcott to arbitrary
inclination. The exact steady growth velocity is of saddle type with principal
curvatures of opposite sign. According to Wolf this implies logarithmic height
correlations, which we prove by mapping the steady state of the surface to
world lines of free fermions with chiral boundary conditions.Comment: 9 pages, REVTEX, epsf, 3 postscript figures, submitted to J. Stat.
Phys, a wrong character is corrected in eqs. (31) and (32
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