87 research outputs found
Stochastic Model in the Kardar-Parisi-Zhang Universality With Minimal Finite Size Effects
We introduce a solid on solid lattice model for growth with conditional
evaporation. A measure of finite size effects is obtained by observing the time
invariance of distribution of local height fluctuations. The model parameters
are chosen so that the change in the distribution in time is minimum.
On a one dimensional substrate the results obtained from the model for the
roughness exponent from three different methods are same as predicted
for the Kardar-Parisi-Zhang (KPZ) equation. One of the unique feature of the
model is that the as obtained from the structure factor for
the one dimensional substrate growth exactly matches with the predicted value
of 0.5 within statistical errors. The model can be defined in any dimensions.
We have obtained results for this model on a 2 and 3 dimensional substrates.Comment: 8 pages, 7 figures, accepted in Phys. Rev.
Pulsed laser treatment at Fe/C<SUB>6</SUB>H<SUB>6</SUB> interface: a Mossbauer effect study
The pulsed ruby laser induced reactive-quenching process at Fe/C6H6 Ibenzenel has been investigated using conversion electron Mossbauer spectroscopy [CEMS]. It is shown that iron carbide phases can be synthesized when an iron foil immersed in benzene is treated with ruby Laser pulses [λ=694 nm, pulse width ~30 ns, energy density =15 J/cm2]. The results indicate the formation of ε-carbide and Fe5C2 phases in the as-treated sample and its transformation to Fe3C upon thermal treatment. The result of the CEMS measurements are supported by small angle X-ray diffractometry
A conversion electron Mossbauer spectroscopy study of ion beam mixing at Fe: polyethylene interface
The effects of ion beam induced atomic mixing at the Fe-Polyethylene interface have been investigated by means of conversion electron Mossbauer spectroscopy [CEMS]. It is shown that the as deposited and ion beam mixed composites exhibit distinctly different features. In particular, the ion beam mixed composite shows that presence of Fe2+ state in polyethylene matrix along with the Fe-C austenite like phase
Nonlinearities in Conservative Growth Equations
Using the dynamic renormalization group (DRG) technique, we analyze general
nonlinearities in a conservative nonlinear growth equation with non-conserved
gaussian white noise. We show that they fall in two classes only: the
Edwards-Wilkinson and Lai-Das Sarma types, by explicitly computing the
associated amputated two and three point functions at the first order in
perturbation parameter(s). We further generalize this analysis to higher order
nonlinearities and also suggest a physically meaningful geometric
interpretation of the same.Comment: REVTEX, will appear in Phys Rev E Rapid Comm. February 1996, .ps
figure file available upon request to [email protected]
Mounding Instability and Incoherent Surface Kinetics
Mounding instability in a conserved growth from vapor is analysed within the
framework of adatom kinetics on the growing surface. The analysis shows that
depending on the local structure on the surface, kinetics of adatoms may vary,
leading to disjoint regions in the sense of a continuum description. This is
manifested particularly under the conditions of instability. Mounds grow on
these disjoint regions and their lateral growth is governed by the flux of
adatoms hopping across the steps in the downward direction. Asymptotically
ln(t) dependence is expected in 1+1- dimensions. Simulation results confirm the
prediction. Growth in 2+1- dimensions is also discussed.Comment: 4 pages, 4 figure
Surface Kinetics and Generation of Different Terms in a Conservative Growth Equation
A method based on the kinetics of adatoms on a growing surface under
epitaxial growth at low temperature in (1+1) dimensions is proposed to obtain a
closed form of local growth equation. It can be generalized to any growth
problem as long as diffusion of adatoms govern the surface morphology. The
method can be easily extended to higher dimensions. The kinetic processes
contributing to various terms in the growth equation (GE) are identified from
the analysis of in-plane and downward hops. In particular, processes
corresponding to the (h -> -h) symmetry breaking term and curvature dependent
term are discussed. Consequence of these terms on the stable and unstable
transition in (1+1) dimensions is analyzed. In (2+1) dimensions it is shown
that an additional (h -> -h) symmetry breaking term is generated due to the
in-plane curvature associated with the mound like structures. This term is
independent of any diffusion barrier differences between in-plane and out
of-plane migration. It is argued that terms generated in the presence of
downward hops are the relevant terms in a GE. Growth equation in the closed
form is obtained for various growth models introduced to capture most of the
processes in experimental Molecular Beam Epitaxial growth. Effect of
dissociation is also considered and is seen to have stabilizing effect on the
growth. It is shown that for uphill current the GE approach fails to describe
the growth since a given GE is not valid over the entire substrate.Comment: 14 pages, 7 figure
Effect of strain on surface diffusion in semiconductor heteroepitaxy
We present a first-principles analysis of the strain renormalization of the
cation diffusivity on the GaAs(001) surface. For the example of
In/GaAs(001)-c(4x4) it is shown that the binding of In is increased when the
substrate lattice is expanded. The diffusion barrier \Delta E(e) has a
non-monotonic strain dependence with a maximum at compressive strain values (e
0) studied.
We discuss the consequences of spatial variations of both the binding energy
and the diffusion barrier of an adatom caused by the strain field around a
heteroepitaxial island. For a simplified geometry, we evaluate the speed of
growth of two coherently strained islands on the GaAs(001) surface and identify
a growth regime where island sizes tend to equalize during growth due to the
strain dependence of surface diffusion.Comment: 10 pages, 8 figures, LaTeX2e, to appear in Phys. Rev. B (2001). Other
related publications can be found at
http://www.rz-berlin.mpg.de/th/paper.htm
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