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Shiv Nadar University

(SoNS) School of Natural Sciences

We present the microstructural evolution in Ge-rich SiO2 doped with Er under different fabrication conditions. At sufficiently high Er contents and annealing temperatures, the Er2 O3 and Er2 Ge2 O7 phases are eventually formed, leading to an electroluminescence quenching of Ge-related oxygen-deficiency centers. The correlation between the microstructure and electroluminescence is discussed based on: (i) an Er doping dependent fragmentation/amorphization of Ge nanocrystals, (ii) a temperature dependent Ge diffusion toward the Si/ SiO2 interface, and (iii) the formation of different Er phases. © 2009 The American Physical Society.

Physics

World University root node

Physical Review B - Condensed Matter and Materials Physics

Probing the impact of microstructure on the electroluminescence properties of Ge-nanocrystal enriched Er-doped SiO2 layers

Temperature-dependent photoluminescence of Ge-rich SiO2 in the presence or absence of Er shows a crossover between defect-related (15-150 K) and Er-related (150-295 K) emission within 1525 and 1440 nm. The origin of the near-infrared defect-related bands is discussed in the light of recombination of localized excitons in luminescence centers at the Ge cluster/ SiO2 interface. Time-resolved photoluminescence further enables us to illustrate the observed 1.53μm Er emission above 150 K in terms of a phonon-assisted nonradiative energy-transfer process from the luminescence centers to the Er3+ ions. © 2009 The American Physical Society.

Temperature dependence of the crossover between the near-infrared Er and defect-related photoluminescence bands of Ge-rich Er-doped SiO2 layers

The composition, electronic structure and molecular orientation of a self-assembled monolayer (SAM) of benzenethiolate on the Cu(1 0 0) surface have been investigated by means of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). An ordered benzenethiolate SAM with c(2 × 6) superstructure has been obtained by the reaction of diphenyldisulfide with the Cu(1 0 0) surface at room temperature. S 2p and C 1s XP spectra show S-Cu bond formation without significant thiolate decomposition. The strong dichroic signal of C K-edge NEXAFS upon varying polarization angle indicates upstanding of the adsorbed molecules with the benzene ring tilted by 20° from the surface normal. © 2009 Elsevier B.V. All rights reserved.

Journal of Electron Spectroscopy and Related Phenomena

Characterization of benzenethiolate self-assembled monolayer on Cu(1 0 0) by XPS and NEXAFS

We give a short direct proof of Agler's factorization theorem that uses the Blecher-Ruan-Sinclair characterization of operator algebras. The key ingredient of this proof is an operator algebra factorization theorem. Our proof provides some additional information about these factorizations in the case of polynomials. © 2009 American Mathematical Society.

Mathematics

Fulltext

Proceedings of the American Mathematical Society

An operator algebraic proof of Agler's factorization theorem

We develop a systematic approach to construct novel completely solvable rational potentials. Second-order supersymmetric quantum mechanics dictates the latter to be isospectral to some well-studied quantum systems. PT symmetry may facilitate reconciling our approach to the requirement that the rationally extended potentials be singularity free. Some examples are shown. © Indian Academy of Sciences.

Pramana - Journal of Physics

Isospectrality of conventional and new extended potentials, second-order supersymmetry and role of PT symmetry

Optical response of a rare earth (RE)-doped SiO2 layer is known to deteriorate markedly at room temperature due to RE clustering. The key challenge is therefore to probe the ongoing processes at the microscopic level and the subsequent impact on the luminescence properties with increasing RE concentration. Here, we report how the Er electroluminescence in a metal-oxide-semiconductor structure has been affected by increasing Er content. Our results indicate that the Er oxide clustering is anticipated by the formation of Si-based oxygen-deficiency centers during postimplantation annealing and leads to a strong quenching of the short-wavelength (350-500 nm) Er electroluminescence. © 2009 American Institute of Physics.

Applied Physics Letters

Correlation between the microstructure and electroluminescence properties of Er-doped metal-oxide semiconductor structures

It is generally believed that the 1.5 μm Er luminescence is enhanced by transferring energy from Si nanocrystals to the nearest Er3+ ions in Er-doped Si-rich SiO2 layers during optical pumping. Here, the influence of Ge nanocrystals instead of excess Si in the same environment is studied using electroluminescence technique on metal-oxide-semiconductor structures. An increase of the 400 nm electroluminescence intensity with a concomitant reduction of the Er-related emission is observed. This is explained in the light of an inverse energy transfer process from Er3+ to the Ge-related oxygen-deficiency centers. © 2009 American Institute of Physics.

Enhanced blue-violet emission by inverse energy transfer to the Ge-related oxygen deficiency centers via Er3+ ions in metal-oxide semiconductor structures

This paper reports on structural, optical, vibrational, and morphological properties of cobalt-doped CdS thin films, prepared by 90 keV Co+ implantation at room temperature. In this work, we have used cobalt concentration in the range of 0.34-10.8 at. %. Cobalt doping does not lead to the formation of any secondary phase, either in the form of metallic clusters or impurity complexes. However, with increasing cobalt concentration a decrease in the optical band gap, from 2.39 to 2.26 eV, is observed. This reduction is addressed on the basis of band tailing due to the creation of localized energy states in association with Urbach energy calculations. In addition, implantation gives rise to grain growth and increase in the surface roughness. Size and shape fluctuations of individual CdS grains, at higher fluences, give rise to inhomogeneity in strain. The results are discussed in the light of ion-matter interaction in the keV regime. © 2009 American Institute of Physics.

Journal of Applied Physics

Implantation-assisted Co-doped CdS thin films: Structural, optical, and vibrational properties

Type A N-fold supercharge admits a one-parameter family of factorizations into product of N first-order linear differential operators due to an underlying GL (2, C) symmetry. As a consequence, a type A N-fold supersymmetric system can have different intermediate Hamiltonians corresponding to different factorizations. We derive the necessary and sufficient conditions for the latter system to possess intermediate Hamiltonians for the N = 2 case. We then show that whenever it has (at least) one intermediate Hamiltonian, it can admit second-order parasupersymmetry and a generalized 2-fold superalgebra. As an illustration, we construct a set of generalized Pöschl-Teller potentials of this kind. © 2009 Elsevier Inc. All rights reserved.

Annals of Physics

Existence of different intermediate Hamiltonians in type A N-fold supersymmetry

The fundamental building blocks of any ecosystem, the food webs, which are assemblages of species through various interconnections, provide a central concept in ecology. The study of a food web allows abstractions of the complexity and interconnectedness of natural communities that transcend the specific details of the underlying systems. For example, Fig. 1 shows a typical food web, where the species are connected through their feeding relationships. The top predator, Heliaster (starfish) feeds on many gastropods like Hexaplex, Morula, Cantharus, etc., some of whom predate on each other [129]. Interactions between species in a food web can be of many types, such as predation, competition, mutualism, commensalism, and ammensalism (see Section 1.1, Fig. 2). © Birkhäuser Boston, a part of Springer Science+Business Media, LLC 2009.