V. Boev

Glass formation in the Ge–Se–AgI ternary

Abstract The glass-forming region in the Ge–Se–AgI ternary has been identified, based on the results of X-ray diffraction examinations, electron microscope investigations, Raman scattering studies and modulated differential scanning calorimetry (MDSC) analysis. Depending on the Ge–Se backbone hosting the AgI clusters, the glasses with larger Se content appear phase separated, while glasses based on Ge–Se face sharing tetrahedra units are quite homogeneous with AgI completing, most probably, a common structure with the Ge–Se backbone. These assumptions are confirmed by the crystal phases emerging from the glasses, spectral and thermal properties as well as the molar volume of the vitreous material.

Nanovoids in Glasses and Polymers Probed by Positron Annihilation Lifetime Spectroscopy

Nanovoids in As2S3-based glasses (As2S3, (As2S3)85Ag15, and (As2S3)85(AgI)15), a polymer and a As2S3-polymer nanocomposite were studied using the positron annihilation lifetime spectroscopy (PALS) technique. After computer treatment of the PALS data recorded, it was found that only two components τ 1 (short-lived) near 0.2 ns and τ 2 (long-lived) near 0.4 ns are resolved for the As2S3-based glasses. At the same time, in the case of the polymer sample two components τ 2 near 0.3 ns and τ 3 (pick-off annihilation of ortho-positronium) near 2.8 ns were detected, while for the As2S3-polymer nanocomposite three components τ 1 near 0.2–0.3 ns, τ 2 near 0.4–0.5 ns and τ 3 near 2.4 ns were established. The volume of nanovoids in the materials studied was determined, and the fractional free volumes of the As2S3-polymer nanocomposite and the polymer matrix were compared. The results obtained are important to utilize As2S3-based glasses and polymer nanocomposites for advanced sensor applications.

Nanostructured Diamond Electrodes for Energy Conversion Applications

The subject of our work is the investigation of boron doped nanocrystalline diamond (NCD) layers functionalized with photosensitive molecules of manganese phthalocyanine. The functionalized NCD sample was used as a working electrode in a three electrode cell and electrochemically studied. The two methods applied were stationary volt-ampere (VA) measurements and cyclic voltammetry (CV) in dark and under illumination. The VA and CV measurements showed that the electrode has a wide potential range and a high photosensitivity. The results obtained are promising for future application of functionalized diamond electrodes in light conversion systems.

Photoinduced changes in As-Se-Ag amorphous films

Thin films from the As-Se-Ag system have been prepared on glass and silicon substrates by thermal vacuum evaporation from previously fabricated bulk glassy samples. The amorphous state of the samples has been proved by X-ray diffraction. Some optical properties of the amorphous As-Se-Ag thin films have been studied in relation to the Ag concentration in the sample. In order to investigate the photoinduced changes due to irradiation by with He-Ne laser light, transmission spectra of the thin films have been measured before and after irradiation. The optical characteristics as a function of the composition have been studied.

Glass formation in the Se-Ag-Br and Se-Ag-Cl systems

Abstract The possibilities of obtaining glassy phases in the systems Se-Ag-Br and Se-Ag-Cl are investigated, proving, on the basis of theoretical suggestions, that glass formation can be expected in these systems. Strongly immiscible solid media are produced and their physico-chemical properties — transformation temperature, microhardness, density, molar volume and chemical resistance — are studied. On the basis of these properties and X-ray analysis, a structural model of the glasses is proposed.

Ureasil-Based Polymer Matrices As Sensitive Layers for the Construction of Amperometric Biosensors

Ureasil and ureasil-chalcogenide glass composites of different history (fresh and aged during 1 year) were used for the immobilization of laccase and the construction of amperometric biosensors. A correlation between the microscopical free-volume of the polymer matrices as revealed by low-temperature positron annihilation lifetime spectroscopy and biosensor characteristics of the laccase-containing ureasil based biosensors is established. The observed findings could be applied for improvement of the operational parameters of the constructed biosensors, which may have potential for monitoring the level of pollution of wastewater.

Polymer Nanocomposites with Silver Nanoparticles Formed by Low-Energy Ion Implantation: Slow Positron Beam Spectroscopy Studies

Polymer nanocomposites formed by low-energy ion implantation were studied by means of positron annihilation spectroscopy with a variable-energy positron beam or slow positron beam spectroscopy. Silver ion implantation into polymethylmethacrylate (Ag:PMMA) and hybrid organic-inorganic ureasil (Ag:ureasil) was performed at different ion fluences with a constant energy of 30 keV and a current density of 1 μA/cm2 in order to prepare Ag nanoparticles in the near-surface region of polymer matrix. Contribution of Doppler broadening slow positron beam spectroscopy technique for understanding Ag nanoparticles formation in Ag:PMMA and Ag:ureasil nanocomposite films is demonstrated.

Stress Measurements and Optical Studies of (AsSe)100−xAgx Films for Optical Sensor Applications

Thin (AsSe)100–xAgx (x = 0–25 mol.%) films have been deposited on glass substrates and silicon cantilevers by vacuum thermal evaporation from the corresponding bulk materials. The mechanical stability was investigated by measuring the stress of the films deposited on silicon cantilevers. The correlation between the stress and the composition has been investigated and will be discussed.

Doppler Broadening of the Annihilation Line Study of Organic-Inorganic Hybrid Ureasil-Based Composites

The organic-inorganic hybrid ureasil-based composites, containing polyether chains covalently linked to a silica framework through urea bridges, referred as ureasilicates or ureasils, and semiconducting As2S3 clusters, are investigated using Doppler broadening of annihilation line technique. It is established that the Doppler S and W parameters show significant structural difference between the pure ureasil and the As2S3-ureasil composites, the effect is more essential as the loading fraction of As2S3 increases. The new Doppler broadening results obtained in this work are found to be in consistent with the earlier reported results of positron annihilation lifetime measurements of the same materials.

Effect of the preparation method on the optical properties of GeS 1.2 — AgI films

Thin films from Ge-S-AgI system with various amount of AgI prepared by pulsed laser deposition and vacuum thermal evaporation method have been studied. The films are analysed with respect to their morphology, structure and roughness. The optical properties are investigated as a function of the composition and preparation method.