6,729 research outputs found
A Reaction Diffusion Model Of Pattern Formation In Clustering Of Adatoms On Silicon Surfaces
We study a reaction diffusion model which describes the formation of patterns on surfaces having defects. Through this model, the primary goal is to study the growth process of Ge on Si surface. We consider a two species reaction diffusion process where the reacting species are assumed to diffuse on the two dimensional surface with first order interconversion reaction occuring at various defect sites which we call reaction centers. Two models of defects, namely a ring defect and a point defect are considered separately. As reaction centers are assumed to be strongly localized in space, the proposed reaction-diffusion model is found to be exactly solvable. We use Green's function method to study the dynamics of reaction diffusion processes. Further we explore this model through Monte Carlo (MC) simulations to study the growth processes in the presence of a large number of defects. The first passage time statistics has been studied numerically. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.4757592]Microelectronics Research Cente
Dark Energy and the Statistical Study of the Observed Image Separations of the Multiply Imaged Systems in the CLASS Statistical Sample
The present day observations favour a universe which is flat, accelerated and
composed of matter (baryonic + dark) and of a negative
pressure component, usually referred to as dark energy or quintessence. The
Cosmic Lens All Sky Survey (CLASS), the largest radio-selected galactic mass
scale gravitational lens search project to date, has resulted in the largest
sample suitable for statistical analyses. In the work presented here, we
exploit observed image separations of the multiply imaged lensed radio sources
in the sample. We use two different tests: (1) image separation distribution
function of the lensed radio sources and (2)
{\dtheta}_{\mathrm{pred}} vs {\dtheta}_{\mathrm{obs}} as observational
tools to constrain the cosmological parameters and \Om. The results are
in concordance with the bounds imposed by other cosmological tests.Comment: 20 pages latex; Modified " Results and Discussion " section, new
references adde
X-ray standing wave and reflectometric characterization of multilayer structures
Microstructural characterization of synthetic periodic multilayers by x-ray
standing waves have been presented. It has been shown that the analysis of
multilayers by combined x-ray reflectometry (XRR) and x-ray standing wave (XSW)
techniques can overcome the deficiencies of the individual techniques in
microstructural analysis. While interface roughnesses are more accurately
determined by the XRR technique, layer composition is more accurately
determined by the XSW technique where an element is directly identified by its
characteristic emission. These aspects have been explained with an example of a
20 period Pt/C multilayer. The composition of the C-layers due to Pt
dissolution in the C-layers, PtC, has been determined by the XSW
technique. In the XSW analysis when the whole amount of Pt present in the
C-layers is assumed to be within the broadened interface, it l eads to larger
interface roughness values, inconsistent with those determined by the XRR
technique. Constraining the interface roughness values to those determined by
the XRR technique, requires an additional amount of dissolved Pt in the
C-layers to expl ain the Pt fluorescence yield excited by the standing wave
field. This analysis provides the average composition PtC of the
C-layers .Comment: 12 pages RevTex, 10 eps figures embedde
Determining the CP properties of the Higgs boson
The search and the probe of the fundamental properties of Higgs boson(s) and,
in particular, the determination of their charge conjugation and parity (CP)
quantum numbers, is one of the main tasks of future high-energy colliders. We
demonstrate that the CP properties of a Standard Model-like Higgs particle can
be unambiguously assessed by measuring just the total cross section and the top
polarization in associated Higgs production with top quark pairs in e+e-
collisions.Comment: 4 pages, revtex, uses axodraw (style file included in the submission
Replicating Nanostructures on Silicon by Low Energy Ion Beams
We report on a nanoscale patterning method on Si substrates using
self-assembled metal islands and low-energy ion-beam irradiation. The Si
nanostructures produced on the Si substrate have a one-to-one correspondence
with the self-assembled metal (Ag, Au, Pt) nanoislands initially grown on the
substrate. The surface morphology and the structure of the irradiated surface
were studied by high-resolution transmission electron microscopy (HRTEM). TEM
images of ion-beam irradiated samples show the formation of sawtooth-like
structures on Si. Removing metal islands and the ion-beam induced amorphous Si
by etching, we obtain a crystalline nanostructure of Si. The smallest
structures emit red light when exposed to a UV light. The size of the
nanostructures on Si is governed by the size of the self-assembled metal
nanoparticles grown on the substrate for this replica nanopatterning. The
method can easily be extended for tuning the size of the Si nanostructures by
the proper choice of the metal nanoparticles and the ion energy in
ion-irradiation. It is suggested that off-normal irradiation can also be used
for tuning the size of the nanostructures.Comment: 12 pages, 7 figures, regular paper submitted to Nanotechnolog
Analytic Coulomb matrix elements in the lowest Landau level in disk geometry
Using Darling's theorem on products of generalized hypergeometric series an
analytic expression is obtained for the Coulomb matrix elements in the lowest
Landau level in the representation of angular momentum. The result is important
in the studies of Fractional Quantum Hall effect (FQHE) in disk geometry.
Matrix elements are expressed as simple finite sums of positive terms,
eliminating the need to approximate these quantities with slowly-convergent
series. As a by-product, an analytic representation for certain integals of
products of Laguerre polynomials is obtained.Comment: Accepted to J. Math. Phys.; 3 pages revtex, no figure
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