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Shiv Nadar University

(SoNS) School of Natural Sciences

The migration of oxygen in ion-beam-amorphized c-SiO2 (α-quartz) was investigated by means of nuclear reaction analysis using the resonant reaction 18O(p, α) 15N for oxygen depth profiling. Only very small amounts of oxygen were observed to diffuse in crystalline or in Xe+-ion beam-amorphized α-quartz after high-temperature annealing. However, a dramatic migration of oxygen occurs in Cs+-implanted α-quartz in the same temperature range (600-900°C), where Cs diffuses out of the amorphized layer and epitaxial recrystallization occurs. These results point out to a strong correlation of all these processes. A mechanism to explain the observed indiffusion of 18O is proposed and is related to the Cs migration and the topological modification to achieve epitaxial regrowth of the SiO2 matrix. © 2000 American Institute of Physics.

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Physics

Fulltext

Applied Physics Letters

Oxygen migration during epitaxial regrowth in Cs+-irradiated α-quartz investigated by means of nuclear reaction analysis

We study two-mode squeezing in the framework of generalized quantum condition and derive pedagogically the result that the two-mode squeezed state is factorizable in terms of the component single modes. We also examine the related problem of two-mode squeezing in the system of a pair of coupled oscillators and consider the effects of a sudden switching-on of the intermode coupling for these quadrature modes.

Modern Physics Letters A

A reappraisal of two-mode squeezing and intermode coupling

The powerful group theoretical formalism of potential algebras is extended to non-Hermitian Hamiltonians with real eigenvalues by complexifying so(2,1), thereby getting the complex algebra s1(2,C) or A1. This leads to new types of both PT-symmetric and non-PT-symmetric Hamiltonians. (C) 2000 Elsevier Science B.V.

Physics Letters, Section A: General, Atomic and Solid State Physics

sl(2,C) as a complex lie algebra and the associated non-Hermitian Hamiltonians with real eigenvalues

The iron di-silicide β-FeSi2 is a promising direct band gap semiconductor but difficult to produce. Here, the successful direct synthesis of this phase by ion beam mixing of Fe/Si bilayers at temperatures in the range of 450 to 550°C is reported. The obtained single-phase β-FeSi2 layers and their structure are confirmed by Rutherford backscattering spectrometry, X-ray diffraction and conversion electron Mossbauer spectroscopy.

Applied Physics A: Materials Science and Processing

Direct synthesis of β-FeSi2 by ion beam mixing of Fe/Si bilayers

First-principles calculations are carried out with the objective of assigning a chemical identity to the variety of forms of molecular oxygen which are known to exist on a TiO2(110) surface. Six different geometries and spin configurations of O2 are shown to be stable in the bridging oxygen defect site. The relationship of these results to experimental observations is discussed. © 1999 American Institute of Physics.

Chemistry

Journal of Chemical Physics

Adsorption of O2 on TiO2(110): A theoretical study

Inspired by the possibility of factorizing the second derivative interwining operators using a modified form of the well-known Crum-Darboux transformation, we pressent a scheme for generating a new pair of isospectral potentials. We also consider the interesting problem of constructing coherent states for such factorizable operators.

Higher derivatives supersymmetry, a modified Crum-Darboux transformation and coherent state

We study the problem of pseudoscalar mixing in an (Formula presented) breaking framework. In this connection, we derive the condition of a vanishing (Formula presented) component in the η,(Formula presented) wave functions. We also obtain new constraints obeyed by the mixed decay constants (Formula presented) which determine the octet-singlet mixing angles. In the (Formula presented) sector we find from a fit to the radiative decay rates of mesons that the presence of a (Formula presented) admixture in (Formula presented) is small in disagreement with the point of view that the branching ratio of (Formula presented) is enhanced by (Formula presented) mixing. © 1999 The American Physical Society.

Physical Review D - Particles, Fields, Gravitation and Cosmology

Mixing angles and decay constants of η, [formula presented], and [formula presented]

We study the problem of pseudoscalar mixing in an SU(4)xSU(4)xUA(1) breaking framework. In this connection, we derive the condition of a vanishing cc̄ component in the η,η′ wave functions. We also obtain new constraints obeyed by the mixed decay constants fη,η′q (q=u,s), which determine the octet-singlet mixing angles. In the ηη′ ηc sector we find from a fit to the radiative decay rates of mesons that the presence of a cc̄ admixture in η′ is small in disagreement with the point of view that the branching ratio of B→η′ K is enhanced by η′ ηc mixing. ©1999 The American Physical Society.

Mixing angles and decay constants of η, η′, and ηc

We study chiral and UA(1) phase transition in the dilute gas approximation. A comprehensive analysis of the mass and mixing angel of η and η′ reveals that in the transition of the quark-gluon-plasma droplets to the hadrons, besides the chiral phase transition, the UA(1) phase transition also plays a significant and non-trivial role. © 1999 Elsevier Science B.V. All rights reserved.

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

Chiral and UA(1) phase transitions in QCD: An analysis of the I = 0 pseudoscalars

We report on the evaluation of ion-beam induced damage in α-quartz and its dynamic annealing behavior in the temperature range between 80 and 1050 K using Rutherford backscattering spectrometry in channeling geometry. The results illustrate that the critical temperature for inhibiting amorphization during irradiation is about Tc≈940 K. The critical fluence φc for amorphization is independent of the temperature up to 550 K, but strongly increases at higher temperatures. The activation energy for the diffusion of defects in the collision cascade or at the amorphous/crystalline interface is found to be 0.28±0.02 eV. The dynamic annealing mechanism is explained by the vacancy out-diffusion model of Morehead and Crowder. © 1999 American Institute of Physics.