3,393 research outputs found
Optimisation of the parameters of an extended defect model applied to non-amorphizing implants
In this paper, we present the optimisation of the parameters of a physical model of the kinetics of extended defects and applied the model with the optimised parameters to non-amorphizing implants. The model describes the small clusters, the {113} defects and the dislocation loops. In the first part, we determine the formation energies of the small clusters, the fault energy of the {113} defects, their Burgers vector and the self-diffusivity of silicon using TEM measurements and extractions of the supersaturation from the spreading of boron marker layers in low-dose implanted silicon. The improvements of the simulations are presented for the fitted experiments and for other wafers annealed at intermediate temperatures. In the second part, we increase the dose and energy of the non-amorphizing implant, leading to the transformation of {113} defects into dislocation loops. The predictions obtained with the optimised model are shown to be in agreement with the measurements. (c) 2005 Elsevier B.V. All rights reserved
Slow dynamics in a primitive tetrahedral network model
We report extensive Monte Carlo and event-driven molecular dynamics
simulations of the fluid and liquid phase of a primitive model for silica
recently introduced by Ford, Auerbach and Monson [J. Chem. Phys. 17, 8415
(2004)]. We evaluate the iso-diffusivity lines in the temperature-density plane
to provide an indication of the shape of the glass transition line. Except for
large densities, arrest is driven by the onset of the tetrahedral bonding
pattern and the resulting dynamics is strong in the Angell's classification
scheme. We compare structural and dynamic properties with corresponding results
of two recently studied primitive models of network forming liquids -- a
primitive model for water and a angular-constraint free model of
four-coordinated particles -- to pin down the role of the geometric constraints
associated to the bonding. Eventually we discuss the similarities between
"glass" formation in network forming liquids and "gel" formation in colloidal
dispersions of patchy particles.Comment: 9 pages, 10 figure
Quantum squeezing generation versus photon localization in a disordered microcavity
We investigate theoretically the nonlinear dynamics induced by an intense
pump field in a disordered planar microcavity. Through a self-consistent
theory, we show how the generation of quantum optical noise squeezing is
affected by the breaking of the in-plane translational invariance and the
occurrence of photon localization. We find that the generation of single-mode
Kerr squeezing for the ideal planar case can be prevented by disorder as a
result of multimode nonlinear coupling, even when the other modes are in the
vacuum state. However, the excess noise is a non-monotonous function of the
disorder amplitude. In the strong localization limit, we show that the system
becomes protected with respect to this fundamental coupling mechanism and that
the ideal quadrature squeezing generation can be obtained
Structure formation from non-Gaussian initial conditions: multivariate biasing, statistics, and comparison with N-body simulations
We study structure formation in the presence of primordial non-Gaussianity of
the local type with parameters f_NL and g_NL. We show that the distribution of
dark-matter halos is naturally described by a multivariate bias scheme where
the halo overdensity depends not only on the underlying matter density
fluctuation delta, but also on the Gaussian part of the primordial
gravitational potential phi. This corresponds to a non-local bias scheme in
terms of delta only. We derive the coefficients of the bias expansion as a
function of the halo mass by applying the peak-background split to common
parametrizations for the halo mass function in the non-Gaussian scenario. We
then compute the halo power spectrum and halo-matter cross spectrum in the
framework of Eulerian perturbation theory up to third order. Comparing our
results against N-body simulations, we find that our model accurately describes
the numerical data for wavenumbers k < 0.1-0.3 h/Mpc depending on redshift and
halo mass. In our multivariate approach, perturbations in the halo counts trace
phi on large scales and this explains why the halo and matter power spectra
show different asymptotic trends for k -> 0. This strongly scale-dependent bias
originates from terms at leading order in our expansion. This is different from
what happens using the standard univariate local bias where the scale-dependent
terms come from badly behaved higher-order corrections. On the other hand, our
biasing scheme reduces to the usual local bias on smaller scales where |phi| is
typically much smaller than the density perturbations. We finally discuss the
halo bispectrum in the context of multivariate biasing and show that, due to
its strong scale and shape dependence, it is a powerful tool for the detection
of primordial non-Gaussianity from future galaxy surveys.Comment: 26 pages, 16 figures. Minor modifications, version accepted by Phys.
Rev.
String Inspired Brane World Cosmology
We consider brane world scenarios including the leading correction to the Einstein-Hilbert action suggested by superstring theory, the Gauss-Bonnet term. We obtain and study the complete set of equations governing the cosmological dynamics. We find they have the same form as those in Randall-Sundrum scenarios but with time-varying four-dimensional gravitational and cosmological constants. By studying the bulk geometry we show that this variation is produced by bulk curvature terms parametrized by the mass of a black hole. Finally, we show there is a coupling between these curvature terms and matter that can be relevant for early universe cosmology
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