S. Boycheva

Glass formation in the GeSe2 (As2Se3)–Sb2Se3–CdTe systems

Abstract Glass-forming regions in GeSe 2 –Sb 2 Se 3 –CdTe (I) and As 2 Se 3 –Sb 2 Se 3 –CdTe (II) systems have been determined by visual, X-ray diffraction and electron microscope analyses. Glasses have been obtained in the GeSe 2 -rich region in system I and As 2 Se 3 -rich region in system II, respectively. Glassformation has been observed along the tie-lines GeSe 2 –Sb 2 Se 3 -line (30–100 mol% GeSe 2 ) and As 2 Se 3 –CdTe-line (45–100 mol% As 2 Se 3 ). In the binary GeSe 2 –CdTe and As 2 Se 3 –CdTe systems, glasses has found homogeneous in the concentration ranges 0–5 mol% CdTe (I) and 0–7 mol% CdTe (II), respectively. Up to 15 mol% CdTe are dissolved in the system GeSe 2 –Sb 2 Se 3 and in the system As 2 Se 3 –Sb 2 Se 3 , up to 12 mol% CdTe are dissolved. The basic physical–chemical characteristics of the glasses are investigated—density, microhardness, transformation temperature, crystallization temperature, melting temperature. A compositional dependence of these properties is shown. IR spectra of the samples are investigated.

Electrical and optical properties of thin films in the Ag2Te–CdTe system

Abstract Some optical and electrical properties of thin films in the Ag2Te–CdTe system are studied as a function of the cadmium content. In order to determine the optical band-gap, Eg, the transmission spectra of films are analysed. From the transmission and the refraction spectra, the relationship between the absorption coefficient α and the wavelength λ at different CdTe contents is derived. The temperature dependence of the electrical conductivity is measured and the thermal band-gap, Ea, is determined. The relation between these parameters and the composition of the samples is discussed.

Influence of the Gas Phase Composition on Nanocrystalline Diamond Films Prepared by MWCVD

Nanocrystalline diamond (NCD) films have been prepared by microwave plasma chemical vapor deposition (MWCVD) from methane/nitrogen mixtures, and the influence of the gas phase composition on the basic properties of the films (composition, morphology, topography, crystallinity and bonding structure) was investigated.

New Chemical Sensors for Fast and Reliable Analytical Control of Sn2+ and Pb2+ Ions in Water and Waste Water

Chemical sensors selective to Pb2+ and Sn2+ ions were developed on the base of chalcogenide glasses (ChG) from the GeSe2-PbSe-PbTe and GeSe2-Sb2Se3-SnSe systems. All-solid-state sensors of the ‘coated wire’ type were designed consisting of inner Ag/AgCl reference electrode uniformly coated with composite mixture of binding polymer and Pb- and Sn- ChG powder. Pb(II)- and Sn(II)-sensors were tested in aqua solutions with respect to their basic analytical characteristics: stability, linearity and slope of the calibration function, working pH-range, limits of detection, response time and selectivity. The proposed sensors guarantee reliable analytical performance for water and waste water control with detection limits of the order of 10−6 mol/L, selectivity and chemical stability in aggressive media.

AZO films prepared by r.f. magnetron sputtering: structural, electrical, and optical properties

Aluminium-doped zinc oxide films with 91% transmittance in the visible range and electrical resistivity of the order of 10-3 Ωcm were fabricated by radio frequency magnetron sputtering in Ar atmosphere starting from a target of ZnO mixed with 2% wt Al2O3. A systematic study of the deposition conditions such as substrate temperature, working gas pressure, radio frequency power, magnetron strength, target to substrate distance, etc., was performed when searching for improved electrical and optical performances of the films. Several deposition conditions govern the film characteristics, so that films with same good optical and electrical properties can be obtained by opportunely combining different deposition parameters.

Multicomponent Chalcogenide Glasses: Advanced Membrane Materials for Chemical Sensors and Nanosensors

The present report describes the development of chemical sensors selective to heavy metal ions with membranes based on multicomponent chalcogenide glasses (ChGs). ChGs containing a GeSe2-glass-former, a Sb2Se3(Sb2Te3)-network-modifier and heavy metal chalcogenides MeCh (Me = Zn, Cd, Sn, Pb; Ch = Se, Te) were synthesized and applied as active membrane components in chemical sensors. The main aspects of material synthesis, sensor design and analytical test results as well as concepts for the potential-generating mechanisms are discussed.

New Chalcohalide Glasses from the GeSe2–Ag2Se–AgI System for Nanostructured Sensors

New chalcohalide glasses from the GeSe2–Ag2Se–AgI system with potential application as active materials for sensor elements have been synthesized. The glass forming region was determined by means of XRD and electron microscopic analyses. The main physicochemical properties, the density d, Vickers microhardness HV and the temperatures of glass-transition Tg, crystallization Tcr and melting Tm were determined. A correlation between these properties and the composition of the investigated glasses is established and discussed.