862 research outputs found
Distinguishing step relaxation mechanisms via pair correlation functions
Theoretical predictions of coupled step motion are tested by direct STM
measurement of the fluctuations of near-neighbor pairs of steps on
Si(111)-root3 x root3 R30 - Al at 970K. The average magnitude of the
pair-correlation function is within one standard deviation of zero, consistent
with uncorrelated near-neighbor step fluctuations. The time dependence of the
pair-correlation function shows no statistically significant agreement with the
predicted t^1/2 growth of pair correlations via rate-limiting atomic diffusion
between adjacent steps. The physical considerations governing uncorrelated step
fluctuations occurring via random attachment/detachment events at the step edge
are discussed.Comment: 17 pages, 4 figure
Defect Formation and Kinetics of Atomic Terrace Merging
Pairs of atomic scale terraces on a single crystal metal surface can be made
to merge controllably under suitable conditions to yield steps of double height
and width. We study the effect of various physical parameters on the formation
of defects in a kinetic model of step doubling. We treat this manifestly non-
equilibrium problem by mapping the model onto a 1-D random sequential
adsorption problem and solving this analytically. We also do simulations to
check the validity of our treatment. We find that our treatment effectively
captures the dynamic evolution and the final state of the surface morphology.
We show that the number and nature of the defects formed is controlled by a
single dimensionless parameter . For close to one we show that the
fraction of defects rises linearly with as . We also show that one can arrive at the final state faster and with
fewer defects by changing the parameter with time.Comment: 17 pages, 8 figures. To be submitted to Phys. Rev.
Fluctuations, line tensions, and correlation times of nanoscale islands on surfaces
We analyze in detail the fluctuations and correlations of the (spatial)
Fourier modes of nano-scale single-layer islands on (111) fcc crystal surfaces.
We analytically show that the Fourier modes of the fluctuations couple due to
the anisotropy of the crystal, changing the power spectrum of the fluctuations,
and that the actual eigenmodes of the fluctuations are the appropriate linear
combinations of the Fourier modes. Using kinetic Monte Carlo simulations with
bond-counting parameters that best match realistic energy barriers for hopping
rates, we deduce absolute line tensions as a function of azimuthal orientation
from the analyses of the fluctuation of each individual mode. The
autocorrelation functions of these modes give the scaling of the correlation
times with wavelength, providing us with the rate-limiting kinetics driving the
fluctuations, here step-edge diffusion. The results for the energetic
parameters are in reasonable agreement with available experimental data for
Pb(111) surfaces, and we compare the correlation times of island-edge
fluctuations to relaxation times of quenched Pb crystallites.Comment: 11 pages, 8 figures; to appear in PRB 70, xxx (15 Dec 2004), changes
in MC and its implication
Labyrinthine Island Growth during Pd/Ru(0001) Heteroepitaxy
Using low energy electron microscopy we observe that Pd deposited on Ru only
attaches to small sections of the atomic step edges surrounding Pd islands.
This causes a novel epitaxial growth mode in which islands advance in a
snakelike motion, giving rise to labyrinthine patterns. Based on density
functional theory together with scanning tunneling microscopy and low energy
electron microscopy we propose that this growth mode is caused by a surface
alloy forming around growing islands. This alloy gradually reduces step
attachment rates, resulting in an instability that favors adatom attachment at
fast advancing step sections
Nanoscale periodicity in stripe-forming systems at high temperature: Au/W(110)
We observe using low-energy electron microscopy the self-assembly of
monolayer-thick stripes of Au on W(110) near the transition temperature between
stripes and the non-patterned (homogeneous) phase. We demonstrate that the
amplitude of this Au stripe phase decreases with increasing temperature and
vanishes at the order-disorder transition (ODT). The wavelength varies much
more slowly with temperature and coverage than theories of stress-domain
patterns with sharp phase boundaries would predict, and maintains a finite
value of about 100 nm at the ODT. We argue that such nanometer-scale stripes
should often appear near the ODT.Comment: 5 page
Fractal formation and ordering in random sequential adsorption
We reveal the fractal nature of patterns arising in random sequential
adsorption of particles with continuum power-law size distribution, , . We find that the patterns become more and
more ordered as increases, and that the Apollonian packing is obtained
at limit. We introduce the entropy production rate as a
quantitative criteria of regularity and observe a transition from an irregular
regime of the pattern formation to a regular one. We develop a scaling theory
that relates kinetic and structural properties of the system.Comment: 4 pages, RevTex, 4 postscript figures. To appear in Phys.Rev.Let
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