T. Wagner

Controlling the optical constants of thermally-evaporated Ge10Sb30S60 chalcogenide glass films by photodoping with silver

Abstract We have analysed the effect of silver content on the optical properties of Ag-doped Ge 10 Sb 30 S 60 chalcogenide glass films; the chalcogenide host layers were prepared by vacuum thermal evaporation. Films of compositions Ag x (Ge 0.1 Sb 0.3 S 0.6 ) 100− x , with x ≲8 at.%, were obtained by successively photodissolving thin (around 10 nm) layers of silver. The optical constants ( n , k ) have been determined by a method based on the envelope curves of the optical transmission spectrum at normal incidence. The dispersion of the refractive index of the Ag-photodoped chalcogenide films is analysed within the single-effective-oscillator approach. The optical-absorption data indicate that the absorption mechanism is non-direct transition. We found that the refractive index of the Ag-doped samples increases with the Ag content, whereas the optical band gap, E g opt , decreases from 1.97xa0±xa00.01 to 1.67xa0±xa00.01 eV. These results are consistent with the hypothesis that the photodoped Ag is a structure modifier in the a -Ge 10 Sb 30 S 60 films.

Application of As40S60−xSex layers for high-efficiency grating production

Abstract Here we investigate image formation properties of As 40 S 60− x Se x layers and their application for gratings fabrication. The light sensitivity of layers, the dissolution kinetics of as-evaporated and exposed layers in amine-based etching solutions have been studied. The surface relief formation was investigated by means of numerical simulation and experimental investigations. The aim was to optimize treatment conditions to increase the efficiency of gratings. Transmission gratings with line periodicity 6–12 μm were prepared by exposure to a halogen-lamp through Cr masks and subsequent etching achieved diffraction efficiencies from 20% to 26%. The recording of holographic gratings was carried out by exposure with Ar or He–Ne laser. Diffraction efficiencies of reflection gratings with spatial frequencies 1800–2400 mm −1 in polarized light were 80–90%. Polymer copies were obtained using the master gratings on the base of As–S–Se layers.

Photoinduced changes of the structure and physical properties of amorphous chalcogenides

Abstract The recent results of the study of photoinduced effects in chalcogenide glasses and layers were reviewed and discussed. The main attention was paid to changes of structure, optical transmissivity and reflectivity and to photoinduced optical anisotropy.

Kinetics of the thermally and photoinduced solid state reaction of Ag with As33S67 films

The kinetics of the solid state chemical reaction of silver with amorphous As33S67 films in a conventional sandwich structure was measured by optically monitoring the change in thickness of the undoped chalcogenide. For the thermally stimulated process, the kinetics data indicate a two-stage process, with the second stage having a sublinear time dependence. The effect of broadband illumination is to reduce the activation energy by approximately one order of magnitude, but the photoinduced process still has two identifiable stages. In the case of the photostimulated process, rate coefficients and activation energies have been measured and the composition and structure of the reaction products have been determined by Rutherford backscattering spectroscopy (RBS). The RBS spectra obtained at different stages of the photoinduced reaction process show a step-like form for the Ag concentration profile during the course of the reaction and indicated a homogeneous distribution of Ag in the final reaction products,...

Structure and imaging properties of As40S60−xSex glasses

Abstract Compositional dependence of photo- and thermally induced structural changes in As 40 S 60− x Se x layers ( x =0,20,30,40,60) have been measured. Dispersion of the refractive index was obtained from the transmission data. Single-oscillator model parameters (oscillator energy, dispersion energy) were estimated. The evolution of the optical dielectric constant was analyzed using the Penn model. Raman measurements have shown that two-phase structures characteristic of glasses are preserved in As 40 S 60− x Se x layers and indicate different bonding structures for as-evaporated, exposed, and annealed layers. These correspond to photo- and thermally induced changes. The single-oscillator energy changes linearly with composition. The compositional dependencies of such structurally determined parameters as glass transition temperature, relaxation enthalpy, specific heat capacity and dispersion energy are explained by a small deviation from the statistical effects of substitution of Se atoms by S in the composition change.

The study of photo- and thermally-induced diffusion and dissolution of Ag in As30S70 amorphous films and its reaction products

Kinetics of photo- and thermally-induced diffusion and dissolution (PIDD and TIDD) of silver in a-As30S70 films were measured by monitoring the change in thickness of the undoped chalcogenide using a modified computer-controlled reflectivity technique. Silver-concentration profiles during photo- and thermally-induced solid-state reactions were traced by means of Rutherford backscattering spectroscopy (RBS). The enthalpy of photo- and thermally-induced reactions was measured by means of differential photocalorimetry and quasi-isothermal temperature-modulated differential scanning calorimetry (DSC), which are shown to be connected with the chemical reaction: Ag+As3S7=AgAsS2+As2S5.

Photo-induced dissolution effect in Ag/As33S67 multilayer structures and its potential application

Abstract A new technique for preparing metal-doped layers using photo-induced metal dissolution in chalcogenide glasses is presented. This technique is based on multilayer structures formed by alternating metal (Ag) and chalcogenide (As 33 S 67 ) layers prepared by vacuum evaporation. Such multilayer structures have a greater sensitivity to illumination and a larger photo-dissolution rate in comparison to the conventional double layer structure Ag/As 33 S 67 . The multilayer structure was used to fabricate a phase grating for operation in the IR region.

Optical properties and structure of amorphous (As0.33S0.67)100−xTex and GexSb40−xS60 chalcogenide semiconducting alloy films deposited by vacuum thermal evaporation

Amorphous films with compositions (As0.33S0.67)100−xTex (x = 0, 1, 5 and 10 at.%) and GexSb40−xS60 (x = 10, 20 and 30 at.%) have been prepared by thermal evaporation. The compositional dependences of their optical properties, with increasing Te and Ge content, respectively, are explained in terms of the modifications occurring in the film structure: Te joins the glassy network through the substitution of S atoms in the AsS3 pyramidal units, to form new AsS2Te mixed pyramidal units, on the one hand, and, on the other hand, there is a presence of GeS4 and S3Ge–GeS3 structural units, when the Ge content is increased. The refractive-index dispersion has been analysed on the basis of the Wemple–DiDomenico single-oscillator approach. It has been found that the refractive index increases in the As–S–Te system, with increasing Te content, while it decreases instead, in the Ge–Sb–S system, with increasing Ge content. The behaviour of the Tauc gap, when the composition of the material is varied, shows, as expected, just the opposite trends.

The preparation of the Agx (As0.33S0.67)100−x amorphous films by optically-induced solid state reaction and the films properties

Abstract The technique of step-by-step optically-induced solid state reaction (OSSR) of Ag with As 33 S 67 amorphous films, which has allowed to design films with exact silver concentration, is reported. The host As 33 S 67 films were photodoped by consecutive dissolving thin (∼10xa0nm) layers of silver, which resulted in a single-phase optically homogeneous film. It was possible to prepare amorphous Ag x (AS 0.33 S 0.67 ) 100− x films with defined silver concentrations of amorphous solid solutions ranging from 1 to 41xa0at.%. We have analyzed the effect of the silver doping in the host material on optical, thermal and mechanical properties, and its structure by means of optical spectroscopy, temperature-modulated differential scanning calorimetry, microhardness measurements and Raman spectroscopy, respectively. The photodoped films with a silver concentration close to 25xa0at.%, i.e. with composition of the stoichiometric AgAsS 2 compound, showed distinct features of their optical, thermal, mechanical properties and their structure.

Kinetics and reaction products of the photo-induced solid state chemical reaction between silver and amorphous As33S67 layers

The kinetics of the photo-induced solid state chemical reaction of silver with a-As 33 S 67 films in a conventional sandwich structure was measured by monitoring the change in the thickness of the undoped chalcogenide using a modified reflection technique. The kinetics data obtained show there are two stages to the photo-reaction (PR) process. The rate coefficients and activation energies characterising each stage have been measured and a complementary study of the composition and structure of the reaction products has been made