19 research outputs found
Segregation in noninteracting binary mixture
Process of stripe formation is analyzed numerically in a binary mixture. The
system consists of particles of two sizes, without any direct mutual
interactions. Overlapping of large particles, surrounded by a dense system of
smaller particles induces indirect entropy driven interactions between large
particles. Under an influence of an external driving force the system orders
and stripes are formed. Mean width of stripes grows logarithmically with time,
in contrast to a typical power law temporal increase observed for driven
interacting lattice gas systems. We describe the mechanism responsible for this
behavior and attribute the logarithmic growth to a random walk of large
particles in a random potential due to the small ones.Comment: 5 pages, 4 figure
Double step structure and meandering due to the many body interaction at GaN(0001) surface in N-rich conditions
Growth of gallium nitride on GaN(0001) surface is modeled by Monte Carlo
method. Simulated growth is conducted in N-rich conditions, hence it is
controlled by Ga atoms surface diffusion. It is shown that dominating four-body
interactions of Ga atoms can cause step flow anisotropy. Kinetic Monte Carlo
simulations show that parallel steps with periodic boundary conditions form
double terrace structures, whereas initially V -shaped parallel step train
initially bends and then every second step moves forward, building regular,
stationary ordering as observed during MOVPE or HVPE growth of GaN layers.
These two phenomena recover surface meandered pair step pattern observed, since
1953, on many semiconductor surfaces, such as SiC, Si or GaN. Change of terrace
width or step orientation particle diffusion jump barriers leads either to step
meandering or surface roughening. Additionally it is shown that step behavior
changes with the Schwoebel barrier height. Furthermore, simulations under
conditions corresponding to very high external particle flux result in
triangular islands grown at the terraces. All structures, emerging in the
simulations, have their corresponding cases in the experimental results.Comment: 25 pages, 8 figure
Step bunching with both directions of the current: Vicinal W(110) surfaces versus atomistic scale model
We report for the first time the observation of bunching of monoatomic steps
on vicinal W(110) surfaces induced by step up or step down currents across the
steps. Measurements reveal that the size scaling exponent {\gamma}, connecting
the maximal slope of a bunch with its height, differs depending on the current
direction. We provide a numerical perspective by using an atomistic scale model
with a conserved surface flux to mimic experimental conditions, and also for
the first time show that there is an interval of parameters in which the
vicinal surface is unstable against step bunching for both directions of the
adatom drift.Comment: 17 pages, 10 figure