Thin-film sensors based on evaporated chalcogenide glasses

Thin-film sensors based upon evaporated layers of chalcogenide glasses and sensitive to silver, copper, and lead ions have been developed. The optimal contents of the membranes were established and the electrochemical characteristics were investigated. It was shown that the sensitivity, detection limit, response time, reproducibility, and selectivity to interfering ions are in good agreement with those for traditional bulk ion-selective electrodes.     

Kinetics of laser-induced photodarkening in arsenic based chalcogenide glasses

Photoinduced changes in the optical properties of chalcogenide glass thin films have been studied extensively but usually only permanent changes were recorded through measurements before and after exposure to pump light. To understand the progression of such effects, in this paper we report in situ measurement of transient changes in the optical transmission of amorphous As₂Se₃, As₅Se₅ and As₄Se₃ thin films during their exposure to a He-Ne laser which has photon energy close to the bandgap of the studied compositions. Mathematical expressions are established, which describe accurately both the light intensity and time dependences of photodarkening. The structural origin of the observed changes is discussed briefly.     

Physical aging of chalcogenide glasses

Physical aging effects are shown to be typical of chalcogenide glasses with an under- or overconstrained network and to influence their physicochemical properties. The natural physical aging of glasses can be accelerated by gamma irradiation or exposure to light.     

High-purity chalcogenide glasses for fiber optics

The data on the present degree of purity of chalcogenide glasses for fiber optics, on their methods of production and on the properties, which are essential for their actual application, are generalized. The content of limiting impurities in the best samples of chalcogenide glasses is 10–100 ppb wt.; of heterophase inclusions with size of about 100 nm is less than 10³ cm^?3. On the basis of chalcogenide glasses the multimode and single mode optical fibers are produced with technical and operation characteristics sufficient for a number of actual applications. The minimum optical losses of 12–14 dB/km at 3–5 µm are attained in the optical fiber from arsenic-sulfide glass. The level of losses in standard chalcogenide optical fibers is 50–300 dB/km in 2–9 µm spectral range. The factors, affecting the optical absorption of glasses and optical fibers, are analyzed, and the main directions in further development of chalcogenide glasses as the materials for fiber optics are considered.     

Effect of high pressure on chalcogenide glasses

The effect of high pressures on the various properties of the chalcogenide glasses is reviewed. The properties discussed include the mechanical, electrical, optical and magnetic properties. The phenomena of the crystallization of the chalcogenide glasses under high pressure is also discussed. This article is dedicated to the memory of late Dr N S Satya Murthy who had been intimately associated directly and indirectly with the development of condensed matter physics in India.     

Ag doped chalcogenide glasses and their applications

Ag-doped chalcogenide glasses and amorphous thin films, their preparation, properties, photodoping, photoinduced surface deposition and applications, are reviewed, expanding on the results obtained recently. The progress obtained is not only connected with better understanding of their structure, chemical bonding and properties but also in application of Ag-containing glasses and films in solid-state batteries, electrochemical sensors and optoelectronics (gratings, microlenses, waveguides, optical memories, non-linear effects).     

Near infrared quazi-omnidirectional reflector in chalcogenide glasses

The quazi-omnidirectional reflector was designed as a planar quarter wave stack consisting of the alternating amorphous chalcogenide Ge₂₅S₇₅ and Sb₄₀Se₆₀ films. Photonic bandgap calculation of the intended reflector predicted 240 nm omnidirectional and 450 nm normal incidence first-order bandgaps centred near 1.55 μm for appropriate values of the index of refraction and thickness of the films. The TEM and HR-TEM images of the prepared 7.5 pairs reflector verified good periodicity, smooth interface and amorphous structure of the chalcogenide films deposited by thermal and flash evaporation, respectively. The optical reflectivity measurements revealed 98.8% normal incidence stopband of the reflector at 1.55 μm. We also report the ellipsometry study of the prepared reflector. The TEM and ellipsometry studies confirmed the thickness variation of prepared individual layers to be ±7 and ±9 nm, respectively, compared to theoretical predictions.     

Thermodynamic predictions of the formation of chalcogenide glasses

The understanding of glass forming ability requires quantitative information on the stable and metastable phase equilibria of binary and multicomponent systems, particularly as a function of composition and temperature. This paper discusses the success of the use of Gibbs free energy curves for the supercooled liquid relative to the stable crystalline phases to describe glass forming ability. Applications are reported for the systems GeSe₂-Se, Sb₂Se₃-Se and GeSe₂-Sb₂Se₃ for which experimental minimal quenching rates are available. A strongly associated regular solution model for the liquid phase gives a predicted behaviour consistent with experimental data. The method is intended to apply to glass forming liquids both in equilibrium with a solid and in a supercooled state.     

Microhardness of chalcogenide glasses of the system Se-Ge-As

The microhardness of chalcogenide glasses of the system Se-Ge-As was investigated for twelve different compositions. An apparatus was constructed which was capable of recording loading and unloading curves, and the results evaluated according to the method of Fröhlich and Grau. The Vickers microhardness valuesL _2(vh) obtained were independent of load and are thought to be material constants. TheseL _2(vh) values varied between 700 and 1400 N mm^–2 in the Se-Ge-As system and showed a non-linear dependence on composition. This is explained structurally by the existence of varying proportions of different short-range order units in the different glasses. The elastic recovery after unloading varied between 45 and 61% for a maximum load of 1.96 N.     

Kinetics of light-assisted physical ageing in chalcogenide glasses

A fundamental understanding of glass relaxation under ambient temperatures, as well as under the external influences is vital to the glass and polymer science communities. Our results show that kinetics of light-assisted physical aging in Se-based glasses can be well fitted with stretch-exponential Kohlrausch type function, which exponent β and the effective time relaxation constant τ depend on the wavelength of incident photons. The obtained β values for Se-rich glasses group around 3/7 and 1/3 values, predicted by Phillips field-free and field-forced axiomatic diffusion-to-traps models.     

Some optical properties of Se-Ge-As amorphous chalcogenide glasses

The effects of composition, film thickness, substrate temperature, and annealing of amorphous thin films of Se₇₅Ge_25−x As _x (5⩽x⩽20) on their optical properties have been investigated. X-ray diffraction revealed the formation of amorphous films. The absorbance and transmission of vacuum-evaporated thin films were used to determine the band gap and refractive index. Optical absorption measurements showed that the fundamental absorption edge is a function of glass composition and the optical absorption is due to indirect transition. The energy gap increases linearly with increasing arsenic content. The optical band gap,E _opt, was found to be almost thickness independent. The shapes of the absorption edge of annealed samples displayed roughly the same characteristic as those of the unannealed films, but were shifted towards shorter wavelengths; as a result,E _opt increased andE _e, the width of the band tails, decreases. The increase inE _opt is believed to be associated with void removal and microstructural re-arrangement during annealing. The influence of substrate temperature on the optical parameters is discussed.     

Temperature-modulated differential scanning calorimetry studies of the structure of bulk and film GexAsyS60 chalcogenide glasses

The recent novel temperature-modulated differential scanning calorimetry (TA Instruments MDSCTM) technique has been applied to the measurement of thermal properties of GexAsyS60 chalcogenide glasses in the glass transition region in bulk glasses and in their thin films. The reversing and non-reversing heat flows through the glass transformation region during both heating and cooling schedules were measured and the values of the parameters, Tg, ΔH, Cp and ΔCp, which characterize the thermal events in the glass transition region, were determined. The structurally determined parameters, Tg, ΔH, Cp and ΔCp, reveal significant changes with composition because in the GexAsyS60 glasses the average coordination number, 〈r〉, increases from 2.4 to 2.8 with increasing x from 0 to 40 at% Ge. A maximum in Tg, ΔH and Cp and a minimum in the heat capacity change, ΔCp, at Tg occur near the composition for which x≈30 at% Ge. These extrema which appear in both films and bulk glasses are ascribed to a change in the network function of Ge atoms replacing As atoms in a covalent network. Recent structural models for chalcogenide glasses have been considered to explain the observed thermal properties. This revised version was published online in November 2006 with corrections to the Cover Date.     

硫系锂离子导电玻璃及微晶玻璃的研究

硫系锂离子导电玻璃及微晶玻璃具有离子电导率高、成形简单、组成和性能在一定范围内连续可调、不可燃等特点,被视为实现全固态锂离子电池的理想电解质材料。综述了硫系锂离子导电玻璃及微晶玻璃的制备工艺、结构、导电性能以及在锂离子电池中的应用,最后指出了其发展趋势。     

Optical properties of chalcogenide glasses with ion-synthesized copper nanoparticles

Substrates of chalcogenide glassy semiconductors As₂S₃ and Ge_15.8As₂₁S_63.2 are implanted with Cu⁺ ions (energy 40 keV, radiation dose 1.5 × 10¹⁷ ion/cm², fixed current density in the ion beam 1 μA/cm²). The composite layers are analyzed by measuring linear optical transmittance and recording nonlinear optical absorption using the Z-scan technique at 780 nm (probe laser radiation with 150-fs pulses; intensity of 25–100 mW). It is ascertained for the irradiated materials that (1) the linear transmission characteristic of the optical surface plasmon resonance (SPR) band, which indicates the formation of copper nanoparticles in the near-surface region, has emerged and (2) there are simultaneously saturated and two-photon nonlinear absorption types; the latter prevails as the intensity of laser irradiation is increased.     

Dielectric properties of some berate glasses

The dielectric constant, epsilon', and the dielectric loss, epsilon ", for some selected lead berate glasses within the frequency band 10(5) to 10(7) Hz and the temperature range (20 similar to 50)degreesC were measured. The dielectric dispersion and the dielectric loss absorption bands were observed. the relaxation time, the activation enthalpy and entropy change of the dielectric relaxation were calculated. The results obtained were discussed and correlated to the internal network structure of the glasses studied.     

Dielectric properties of silver borophosphate glasses

Dynamic behaviour of electrical conduction and polarization in silver borophosphate glasses has been studied over wide range of frequencies and temperatures. The dielectric spectrum showed a strong dispersion in C() with rise in temperature which distinguishes the conduction process from a pure steady state. The observed behaviour was found to be temperature activated with an activation energy of 0.39 eV. The data have been analysed in terms of admittance plots and a model has been proposed on the basis of this analysis.