Physics

<p>Shiv Nadar University is a comprehensive, multidisciplinary, research-focused, and student-centric University offering a full range of academic programs at the undergraduate, postgraduate and doctoral level. With state-of-the-art infrastructure, the University comprises of academic wings, sophisticated labs, international standard sports facilities, amphitheaters, auditorium, conference rooms and smart classrooms. The University&rsquo;s goal is to become internationally recognized for the quality of its research and creative endeavors and their applicability to improving quality of life, generating new insights and expanding the boundaries of human knowledge creativity. Committed to excellence in teaching, research and service, the University aims to serve the higher education needs of India and the world beyond.</p>

Shiv Nadar University

Implanting photoactive ions into quartz or silica is a simple and efficient way to tune the luminescence light used for various optoelectronic applications. However, such ion implantation damages or even destroys the crystalline order in quartz. We report here on cathodoluminescence of α-quartz after 175 keV Rb-ion implantation and epitaxial growth when annealing the samples in air or 18 O 2. In the cathodoluminescence spectra taken at room temperature, five bands were identified. In addition to three intrinsic bands at 2.40, 2.79, and 4.30 eV, which are related to the quartz and/or silica matrix, two strong violet sub-bands at 3.25 and 3.65 eV were observed, which appear to be strongly correlated with the presence of alkali ions and/or the degree of epitaxy of the matrix. Their properties and origin are discussed in relation to similar bands observed after Ba, Ge, and Na ion implantation.

World University root node

(SoNS) School of Natural Sciences

Applied Physics B: Lasers and Optics

Cathodoluminescence during epitaxy in Rb-ion irradiated α-quartz

Even at low fluences doping of quartz by ion implantation results in amorphization. Here we report on the measurement of cathodoluminescence and surface structures during solid phase epitaxy in Na-implanted α-quartz annealed in 18O2 atmosphere. Complete epitaxy was achieved under appropriate conditions of ion fluence, annealing temperature and time. The crystalline structure of the samples was studied by Rutherford backscattering channelling spectroscopy and the 18O-16O exchange between the matrix and 18O2 annealing gas by elastic recoil detection analysis. In the cathodoluminescence spectra taken at room temperature, five bands were identified and assigned to various defect centres. Two of the bands in the violet region at 3.25 and 3.65 eV strongly vary in intensity at 843-1173 K annealing temperature and appear to be intimately correlated with the presence of Na-ions in the implanted region of the matrix. Finally, atomic force microscopy enabled, for the first time, the observation of the correlation of surface structures and epitaxy. © 2006 Elsevier B.V. All rights reserved.

Journal of Non-Crystalline Solids

Solid phase epitaxy of Na-ion irradiated α-quartz: Cathodoluminescence, kinetics and surface morphology

It is shown that dilute niobium doping has a significant effect on the ferromagnetism and microstructure of dilutely cobalt-doped anatase TiO 2 films. Epitaxial films of anatase TiO 2 with 3% Co, without and with 1% niobium doping were grown by pulsed-laser deposition at 875°C at different oxygen pressures. For growth at 10 -5 Torr niobium doping suppresses the ferromagnetism, while it enhances the same in films grown at 10 -4 Torr. High-resolution Z-contrast scanning transmission electron microscopy and electron energy loss spectroscopy show uniform surface segregation of cobalt-rich Ti 1-x-yCo xNb yO 2-δ phase, but without cobalt metal clusters. © 2006 American Institute of Physics.

Fulltext

Applied Physics Letters

Consequences of niobium doping for the ferromagnetism and microstructure of anatase Co:TiO 2 films

The simplest purely imaginary and piecewise constant PT-symmetric potential located inside a larger box is studied. Unless its strength exceeds a certain critical value, all the spectrum of its bound states remains real and discrete. We interpret such a model as an initial element of the generalized non-Hermitian Witten's hierarchy of solvable Hamiltonians and construct its first supersymmetric partner in closed form. © World Scientific Publishing Company.

International Journal of Modern Physics A

PT-symmetric supersymmetry in a solvable short-range model

Thin films of Nb-doped SrTiO 3 (NSTO) are grown via pulsed laser deposition (PLD) on LaAlO 3 (LAO,001), Mg Al 2O 4 (MAO,001), SrTiO 3 (STO,001), and Y-stabilized ZrO 2 (YSZ,001) substrates. The effects of the film-substrate lattice mismatch, film thickness, and substrate temperature during growth on the film properties are investigated. The electrical transport in NSTO films is shown to exhibit a strong sensitivity to strain, which is suggested to arise from the dependence of carrier mobility on bond distortions/stretching and related changes in phonon modes. © 2006 American Institute of Physics.

Substrate-induced strain effects on the transport properties of pulsed laser-deposited Nb-doped SrTiO 3 films

Thin films of (0.5%, 1%) Nb:SrTiO 3 dilutely doped with (2 at. %) magnetic transition elements (Cr, Co, Fe, Mn) are examined for ferromagnetism. X-ray diffraction, Rutherford backscattering ion channeling, scanning transmission electron microscopy Z-contrast imaging, and electron energy loss spectroscopy techniques establish high crystalline quality of the films with no impurity phase(s) and highly uniform dopant distribution. Although the film conductivity improves dramatically by Nb doping, no ferromagnetism is found in any of our samples over the temperature range of 365 down to 5 K. This is contrasted to the case of ferromagnetism reported in cobalt doped (La, Sr)TiO 3. © 2006 American Institute of Physics.

Search for ferromagnetism in conductive Nb:SrTiO 3 with magnetic transition element (Cr, Co, Fe, Mn) dopants

We formulate a systematic algorithm for constructing a whole class of Hermitian position-dependent-mass Hamiltonians which, to lowest order of perturbation theory, allow a description in terms of -symmetric Hamiltonians. The method is applied to the Hermitian analogue of the -symmetric cubic anharmonic oscillator. A new example is provided by a Hamiltonian (approximately) equivalent to a -symmetric extension of the one-parameter trigonometric Pöschl-Teller potential. © 2006 IOP Publishing Ltd.

Journal of Physics A: Mathematical and General

Pseudo-Hermitian versus Hermitian position-dependent-mass Hamiltonians in a perturbative framework

Physical Review-Section B-Condensed Matter

Electronic structure: Wide-band, narrow-band, and strongly correlated systems-Ab initio real-space Hartree-Fock and correlated approach to optical dielectric constants of crystalline insulators (4

Physical Review B

Ab initio real-space Hartree-Fock and correlated approach to optical dielectric constants of crystalline insulators

Light-emitting centers in alkali-ion-implanted α quartz have been investigated with respect to the solid phase epitaxial growth of the ion irradiation induced amorphous zone. Cathodoluminescence was studied under the conditions of chemical epitaxy in annealing the samples, implanted with 2.5 × 10 16 50 keV Na ions/cm 2 or 175 keV Rb ions/cm 2, in 18O 2 atmosphere in the temperature range of 673-1173 K. In addition to the known intrinsic subbands at 2.40, 2.79, and 4.30 eV, which previously were associated with specific defects in the silica matrix, a strong violet band at 3.65 eV and a band at 3.25 eV have been identified. Both are intimately correlated with the presence of the implanted alkali atoms and recrystallization process. With respect to the 3.25 eV band reported in the literature, they are discussed to be correlated with the presence of nanoclusters in Si-enriched, and Ge- and Sn-implanted SiO 2 structures. © 2006 American Institute of Physics.