Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Concentration dependence of the fluorescence decay profile in transition metal doped chalcogenide glass  [PDF]
M. Hughes,D. W. Hewak,R. J. Curry
Physics , 2014,
Abstract: In this paper we present the fluorescence decay profiles of vanadium and titanium doped gallium lanthanum sulphide (GLS) glass at various doping concentrations between 0.01 and 1% (molar). We demonstrate that below a critical doping concentration the fluorescence decay profile can be fitted with the stretched exponential function: exp[-(t/{\tau})\b{eta}], where {\tau} is the fluorescence lifetime and \b{eta} is the stretch factor. At low concentrations the lifetime for vanadium and titanium doped GLS was 30 {\mu}s and 67 {\mu}s respectively. We validate the use of the stretched exponential model and discuss the possible microscopic phenomenon it arises from. We also demonstrate that above a critical doping concentration of around 0.1% (molar) the fluorescence decay profile can be fitted with the double exponential function: a*exp-(t/{\tau}1)+ b*exp-(t/{\tau}2), where {\tau}1and {\tau}2 are characteristic fast and slow components of the fluorescence decay profile, for vanadium the fast and slow components are 5 {\mu}s and 30 {\mu}s respectively and for titanium they are 15 {\mu}s and 67 {\mu}s respectively. We also show that the fluorescence lifetime of vanadium and titanium at low concentrations in the oxide rich host gallium lanthanum oxy-sulphide (GLSO) is 43 {\mu}s and 97 {\mu}s respectively, which is longer than that in GLS. From this we deduce that vanadium and titanium fluorescing ions preferentially substitute into high efficiency oxide sites until at a critical concentration they become saturated and low efficiency sulphide sites start to be filled.
Modified chalcogenide glasses for optical device applications  [PDF]
Mark A. Hughes
Physics , 2014,
Abstract: This thesis focuses on two different, but complementary, aspects of the modification of gallium lanthanum sulphide (GLS) glasses. Firstly the addition of transition metal ions as dopants is examined and their potential for use as active optical materials is explored. It is also argued that the spectroscopic analysis of transition metal ions is a useful tool for evaluating the local environment of their host. Secondly femtosecond (fs) laser modification of GLS is investigated as a method for waveguide formation.
Optical properties of two-dimensional gallium chalcogenide films  [PDF]
O. Del Pozo-Zamudio,S. Schwarz,M. Sich,I. A. Akimov,M. Bayer,R. C. Schofield,E. A. Chekhovich,B. J. Robinson,N. D. Kay,O. V. Kolosov,A. I. Dmitriev,G. V. Lashkarev,D. N. Borisenko,N. N. Kolesnikov,A. I. Tartakovskii
Physics , 2015,
Abstract: Gallium chalcogenides are promising building blocks for novel van der Waals heterostructures. We report low-temperature micro-photoluminescence (PL) of GaTe and GaSe films with thickness ranging from from 200 nm to a single unit cell. In both materials, PL shows dramatic decrease by 10$^4$-10$^5$ when film thickness is reduced from 200 to 10 nm. Based on evidence from cw and time-resolved PL, we propose a model explaining the PL decrease as a result of non-radiative carrier escape via surface states.
V. Dumitrescu,Nina Dumitrescu,Dana Anghel
Analele Universitatii Bucuresti : Chimie , 2004,
Abstract: Sulphide anion was determined indirectly, by potentiometric titration. For thispurpose, a known concentration of Ce4+ and sulphide ions was added into the electrochemicalcell. Ce4+ remained in the cell after his reduction by the sulphide ions was titrated with a Fe2+solution having a known concentration. The difference between total Ce4+ and the titrated Ce4+corresponds to the amount of Ce4+ reduced by the sulphide ion. The proposed method isreproducible, fast and allows the determination of sulphide ion in waters.
Chalcogenide Thin Film Substrate for Protein Biochip Application  [PDF]
A. S. Tveryanovich,A. S. Vasileva,A. V. Belykh,E. N. Borisov,Yu. S. Tveryanovich
Journal of Applied Chemistry , 2014, DOI: 10.1155/2014/152734
Abstract: Diagnostic of pathogen in the human biological liquids by biochip technology is an intensively developed methodic now. The main and the most important part of biochip is the adsorbing layer. Adsorption properties of chalcogenide films to protein (rat monoclonal antibodies) were tested. The films were prepared by conventional thermal deposition technique and by pulsed laser deposition technique. Two methods were used for forming in the films the two-dimensional map of adsorbing places for probe testing. One is using photoresist properties of chalcogenide films; another is using photo-induced oxidation of chalcogenide films. It was shown Good selectivity of the developed structures to protein markers was shown. 1. Introduction Diagnostic of pathogen in the human biological liquids by biochip technology is an intensively developed methodic now. The most important part of biochip is the adsorbing layer. There are two main problems in developing this layer. One is creation of pattern on the film-surface and the second is achievement of selectivity of adsorption of protein or DNA to the created pattern [1]. Chalcogenide glasses have ability to adsorb biological materials [2]. Besides, chalcogenide glasses, for example, of the As-S system have photostructural transformations under irradiation of light with energy above band gap [3]. These transformations are characterized by changes in the chemical short-range structure and some properties. It can be used for creation of precision island structure with photoresist technology. Also, Ge-Ga-S glassy films undergo photo-induced oxidation under exposure to photons with energy above the band gap [4]. It results in fundamental changes in the chemical structure. Both these effects can be used for forming two-dimensional map of places for adsorbing of probe at the films taking into account supposition that chalcogenide and oxide glasses have different ability to adsorb amine groups of proteins or DNA. Methods of patterning and adsorption properties of chalcogenide films to protein or DNA were investigated in this work for the biochip application. 2. Experimental The glasses of As39S61 and Ge26Ga9S65 compositions were synthesized in evacuated quartz ampoules from elementary arsenic and sulfur or elementary germanium, gallium, and sulfur. The prepared As39S61 glass was used to deposition of thin films onto standard glass slide by thermal deposition. The film thickness was about 500?nm. The synthesized Ge26Ga9S65 glass was used for preparation of the thin films by pulsed laser deposition (XeCl laser was used). Pulsed
Three-dimensional mid-infrared photonic circuits in chalcogenide glass  [PDF]
Airan Rodenas,Guillermo Martin,Brahim Arezki,Nicholas D. Psaila,Gin Jose,Animesh Jha,Lucas Labadie,Piern Kern,Ajoy K. Kar,Robert R. Thomson
Physics , 2011, DOI: 10.1364/OL.37.000392
Abstract: We report the fabrication of single mode buried channel waveguides for the whole mid-infrared transparency range of chalcogenide sulphide glasses by means of direct laser writing. We have explored the potential of this technology by fabricating a prototype three-dimensional three-beam combiner for future application in stellar interferometry, which delivers a monochromatic interference visibility of 99.89% at 10.6 \mum, and an ultrahigh bandwidth (3-11 \mum) interference visibility of 21.3%. These results demonstrate that it is possible to harness the whole transparency range offered by chalcogenide glasses on a single on-chip instrument by means of direct laser writing, a finding that may be of key significance in future technologies such as astrophotonics and biochemical sensing.
Gallium interstitial contributions to diffusion in gallium arsenide  [PDF]
J. T. Schick,C. G. Morgan,P. Papoulias
Physics , 2011,
Abstract: Enthalpies of formation of gallium interstitials and all the other native point defects in gallium arsenide are calculated using the same well-converged \emph{ab initio} techniques. Using these results, equilibrium concentrations of these defects are computed as a function of chemical potential from the arsenic rich limit to the gallium rich limit and as a function of the doping level from $p$-type to $n$-type. Gallium interstitial diffusion paths and migration barriers for diffusion are determined for all the interstitial charge states which are favored for Fermi levels anywhere in the gap, and the charge states which dominate diffusion as a function of Fermi level are identified. The effects of chemical potential, doping level, and non-equilibrium defect concentrations produced by ion implantation or irradiation on gallium self-diffusion are examined. Results are consistent with experimental results across the ranges of doping and stoichometry where comparisons can be made. Finally, these calculations shed some light on the complex situation for gallium diffusion in gallium arsenide that is gallium-rich and doped heavily $p$-type.
Chalcogenide optical parametric oscillator  [PDF]
Raja Ahmad,Martin Rochette
Physics , 2012, DOI: 10.1364/OE.20.010095
Abstract: We demonstrate the first optical parametric oscillator (OPO) based on chalcogenide glass. The parametric gain medium is an As2Se3 chalcogenide microwire coated with a layer of polymer. The doubly-resonant OPO oscillates simultaneously at a Stokes and an anti Stokes wavelength shift of >50 nm from the pump wavelength that lies at {\lambda}P = 1552 nm. The oscillator has a peak power threshold of 21.6 dBm and a conversion efficiency of >19 %. This OPO experiment provides an additional application of the chalcogenide microwire technology; and considering the transparency of As2Se3 glass extending far in the mid-infrared (mid-IR) wavelengths, the device holds promise for realizing mid IR OPOs utilizing existing optical sources in the telecommunications wavelength region.
Gallium interstitial contributions to diffusion in gallium arsenide
Joseph T. Schick,Caroline G. Morgan
AIP Advances , 2011, DOI: 10.1063/1.3644937
Abstract: A new diffusion path is identified for gallium interstitials, which involves lower barriers than the barriers for previously identified diffusion paths [K. Levasseur-Smith and N. Mousseau, J. Appl. Phys. 103, 113502 (2008), P. A. Schultz and O. A. von Lilienfeld, Modelling and Simulation in Materials Science and Engineering 17, 084007 (2009)] for the charge states which dominate diffusion over most of the available range of Fermi energies. This path passes through the 110 gallium-gallium split interstitial configuration, and has a particularly low diffusion barrier of 0.35 eV for diffusion in the neutral charge state. As a part of this work, the character of the charge states for the gallium interstitials which are most important for diffusion is investigated, and it is shown that the last electron bound to the neutral interstitial occupies a shallow hydrogenic bound state composed of conduction band states for the hexagonal interstitial and both tetrahedral interstitials. How to properly account for the contributions of such interstitials is discussed for density-functional calculations with a k-point mesh not including the conduction band edge point. Diffusion barriers for gallium interstitials are calculated in all the charge states which can be important for a Fermi level anywhere in the gap, q = 0, +1, +2, and +3, for diffusion via the 110 gallium-gallium split interstitial configuration and via the hexagonal interstitial configuration. The lowest activation enthalpies over most of the available range of Fermi energies are found to correspond to diffusion in the neutral or singly positive state via the 110 gallium-gallium split interstitial configuration. It is shown that several different charge states and diffusion paths contribute significantly for Fermi levels within 0.2 eV above the valence band edge, which may help to explain some of the difficulties [H. Bracht and S. Brotzmann, Phys. Rev. B 71, 115216 (2005)] which have been encountered in fitting experimental results for heavily p-type, Ga-rich gallium arsenide by simply extending a model for gallium interstitial diffusion which has been used for less p-doped material.
Bipolaron Model of Superconductivity in Chalcogenide Glasses  [PDF]
Liang-You Zheng,Bo-Cheng Wang,Shan T. Lai
Physics , 2010,
Abstract: In this paper we propose a small bipolaron model for the superconductivity in the Chalcogenide glasses (c-As2Te3 and c-GeTe). The results are agree with the experiments.
Page 1 /100
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.