59 research outputs found
Roughening of the (1+1) interfaces in two-component surface growth with an admixture of random deposition
We simulate competitive two-component growth on a one dimensional substrate
of sites. One component is a Poisson-type deposition that generates
Kardar-Parisi-Zhang (KPZ) correlations. The other is random deposition (RD). We
derive the universal scaling function of the interface width for this model and
show that the RD admixture acts as a dilatation mechanism to the fundamental
time and height scales, but leaves the KPZ correlations intact. This
observation is generalized to other growth models. It is shown that the
flat-substrate initial condition is responsible for the existence of an early
non-scaling phase in the interface evolution. The length of this initial phase
is a non-universal parameter, but its presence is universal. In application to
parallel and distributed computations, the important consequence of the derived
scaling is the existence of the upper bound for the desynchronization in a
conservative update algorithm for parallel discrete-event simulations. It is
shown that such algorithms are generally scalable in a ring communication
topology.Comment: 16 pages, 16 figures, 77 reference
Continuous and correlated nucleation during nonstandard island growth at Ag/Si(111)-7x7 heteroepitaxy
We present a combined experimental and theoretical study of submonolayer
heteroepitaxial growth of Ag on Si(111)-7x7 at temperatures from 420 K to 550 K
when Ag atoms can easily diffuse on the surface and the reconstruction 7x7
remains stable. STM measurements for coverages from 0.05 ML to 0.6 ML show that
there is an excess of smallest islands (each of them fills up just one
half-unit cell - HUC) in all stages of growth. Formation of 2D wetting layer
proceeds by continuous nucleation of the smallest islands in the proximity of
larger 2D islands (extended over several HUCs) and following coalescence with
them. Such a growth scenario is verified by kinetic Monte Carlo simulation
which uses a coarse-grained model based on a limited capacity of HUC and a
mechanism which increases nucleation probability in a neighbourhood of already
saturated HUCs (correlated nucleation). The model provides a good fit for
experimental dependences of the relative number of Ag-occupied HUCs and the
preference in occupation of faulted HUCs on temperature and amount of deposited
Ag. Parameters obtained for the hopping of Ag adatoms between HUCs agree with
those reported earlier for initial stages of growth. The model provides two new
parameters - maximum number of Ag atoms inside HUC, and on HUC boundary.Comment: LaTeX2e, BibTeX, 9 pages, 7 images, accepted to Phys. Rev.
Reconstructed Rough Growing Interfaces; Ridgeline Trapping of Domain Walls
We investigate whether surface reconstruction order exists in stationary
growing states, at all length scales or only below a crossover length, . The later would be similar to surface roughness in growing crystal
surfaces; below the equilibrium roughening temperature they evolve in a
layer-by-layer mode within a crossover length scale , but are always
rough at large length scales. We investigate this issue in the context of KPZ
type dynamics and a checker board type reconstruction, using the restricted
solid-on-solid model with negative mono-atomic step energies. This is a
topology where surface reconstruction order is compatible with surface
roughness and where a so-called reconstructed rough phase exists in
equilibrium. We find that during growth, reconstruction order is absent in the
thermodynamic limit, but exists below a crossover length , and that this local order fluctuates critically. Domain walls become
trapped at the ridge lines of the rough surface, and thus the reconstruction
order fluctuations are slaved to the KPZ dynamics
Soft versus Hard Dynamics for Field-driven Solid-on-Solid Interfaces
Analytical arguments and dynamic Monte Carlo simulations show that the
microstructure of field-driven Solid-on-Solid interfaces depends strongly on
the dynamics. For nonconservative dynamics with transition rates that factorize
into parts dependent only on the changes in interaction energy and field
energy, respectively (soft dynamics), the intrinsic interface width is
field-independent. For non-factorizing rates, such as the standard Glauber and
Metropolis algorithms (hard dynamics), it increases with the field.
Consequences for the interface velocity and its anisotropy are discussed.Comment: 9 pages LaTex with imbedded .eps figs. Minor revision
Atomic step motion during the dewetting of ultra-thin films
We report on three key processes involving atomic step motion during the
dewetting of thin solid films: (i) the growth of an isolated island nucleated
far from a hole, (ii) the spreading of a monolayer rim, and (iii) the zipping
of a monolayer island along a straight dewetting front. Kinetic Monte Carlo
results are in good agreement with simple analytical models assuming
diffusion-limited dynamics.Comment: 7 pages, 5 figure
Island diffusion on metal fcc(100) surfaces
We present Monte Carlo simulations for the size and temperature dependence of
the diffusion coefficient of adatom islands on the Cu(100) surface. We show
that the scaling exponent for the size dependence is not a constant but a
decreasing function of the island size and approaches unity for very large
islands. This is due to a crossover from periphery dominated mass transport to
a regime where vacancies diffuse inside the island. The effective scaling
exponents are in good agreement with theory and experiments.Comment: 13 pages, 2 figures, to be published in Phys. Rev. Let
Extremal dynamics model on evolving networks
We investigate an extremal dynamics model of evolution with a variable number
of units. Due to addition and removal of the units, the topology of the network
evolves and the network splits into several clusters. The activity is mostly
concentrated in the largest cluster. The time dependence of the number of units
exhibits intermittent structure. The self-organized criticality is manifested
by a power-law distribution of forward avalanches, but two regimes with
distinct exponents tau = 1.98 +- 0.04 and tau^prime = 1.65 +- 0.05 are found.
The distribution of extinction sizes obeys a power law with exponent 2.32 +-
0.05.Comment: 4 pages, 5 figure
Electron-correlation effects in appearance-potential spectra of Ni
Spin-resolved and temperature-dependent appearance-potential spectra of
ferromagnetic Nickel are measured and analyzed theoretically. The Lander
self-convolution model which relates the line shape to the unoccupied part of
the local density of states turns out to be insufficient. Electron correlations
and orbitally resolved transition-matrix elements are shown to be essential for
a quantitative agreement between experiment and theory.Comment: LaTeX, 6 pages, 2 eps figures included, Phys. Rev. B (in press
A Simple Model for Anisotropic Step Growth
We consider a simple model for the growth of isolated steps on a vicinal
crystal surface. It incorporates diffusion and drift of adatoms on the terrace,
and strong step and kink edge barriers. Using a combination of analytic methods
and Monte Carlo simulations, we study the morphology of growing steps in
detail. In particular, under typical Molecular Beam Epitaxy conditions the step
morphology is linearly unstable in the model and develops fingers separated by
deep cracks. The vertical roughness of the step grows linearly in time, while
horizontally the fingers coarsen proportional to . We develop scaling
arguments to study the saturation of the ledge morphology for a finite width
and length of the terrace.Comment: 20 pages, 12 figures; [email protected]
Theory of Spin-Resolved Auger-Electron Spectroscopy from Ferromagnetic 3d-Transition Metals
CVV Auger electron spectra are calculated for a multi-band Hubbard model
including correlations among the valence electrons as well as correlations
between core and valence electrons. The interest is focused on the
ferromagnetic 3d-transition metals. The Auger line shape is calculated from a
three-particle Green function. A realistic one-particle input is taken from
tight-binding band-structure calculations. Within a diagrammatic approach we
can distinguish between the \textit{direct} correlations among those electrons
participating in the Auger process and the \textit{indirect} correlations in
the rest system. The indirect correlations are treated within second-order
perturbation theory for the self-energy. The direct correlations are treated
using the valence-valence ladder approximation and the first-order perturbation
theory with respect to valence-valence and core-valence interactions. The
theory is evaluated numerically for ferromagnetic Ni. We discuss the
spin-resolved quasi-particle band structure and the Auger spectra and
investigate the influence of the core hole.Comment: LaTeX, 12 pages, 8 eps figures included, Phys. Rev. B (in press
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