V. Ilcheva

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.

Ge-Chalcogenide Glasses – Properties and Application as Optical Material

The great interest toward chalcogenide materials is due to the simple technology of preparation in bulk forms and thin films; good thermal and mechanical properties; transparency and photo-sensibility in the IR spectral range. These advantages determine the possibilities for potential application of these materials like optical storage media, memory devices, optical elements (lenses, waveguides, gratings, etc). The idea of present study is to trace the impact of gallium or indium as metal introduction on the behaviors of the glasses from germanium - chalcogenide system.

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.

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.

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.

Compositional dependence of the optical properties of silver containing As2Se3 thin films

We obtained amorphous thin films by evaporation and condensation in three-component systems based on As, Se and Ag. The aim was to investigate the influence of the third component on the thin film structure and optical properties. The refractive index and the film thickness were determined from the upper and lower envelopes of the optical transmission spectra measured in the spectral range 400 – 2500 nm. The absorption coefficient (α) was determined after extrapolating the values of n in the region of strong absorption (where α ≥ 104 cm−1); its spectral distribution is discussed. The dispersion of the refractive index was analyzed in terms of the single-oscillator Wemple-DiDomenico model. The shift of the optical absorption edge was described using the non-direct transition model proposed by Tauc. The optical band gap was calculated from the Tauc plot ahv = B(Egopt – hv)2; the compositional dependence of the optical gap is also discussed.

Thin As-Se-Sb Films as Potential Medium for Optics and Sensor Application

Thin films have been deposited onto quartz substrates by the pulsed laser deposition (PLD) method from the corresponding glassy bulk As-Se-Sb chalcogenide materials. Photoinduced changes have been observed after illumination of the films with a Xe lamp. The transmission spectra of the thin films have been measured before and after irradiation and the optical constants have been derived by the Swanepoel method. The results suggest feasible applications of these materials for waveguide-sensors.

PHYSICO-CHEMICAL CHARACTERIZATION OF NANOSTRUCTURED As-Se-Ag GLASSY MATERIALS

Bulk glasses from the systems (AsSe)1−xAgx and (As2Se3)1−xAgx have been prepared by the melt-quenching technique. Basic physico-chemical characteristics like density, microhardness, and compactness have been investigated. The correlation between the composition and the properties of the AsSeAg glasses is established and comprehensively discussed.

STUDY OF (As2Se3)100-X(AgI)X THIN FILMS PREPARED BY PLD AND VTE METHODS

Amorphous chalcogenide (As2Se3)100-x(AgI)x thin films with x = 5, 10, 15, 20, 25, 30 and 35 mol % have been deposited by pulsed laser deposition (PLD) and vacuum thermal evaporation (VTE). The films were characterized by various techniques with respect to their structure, composi- tion and morphology. The optical properties were studied by transmission spectroscopy; the optical band gap Eg was determined from Tauc plots and as Eg 04 in the strong absorption region (by α ≥10 4 cm −1 ) from the relation- ship α  (hν). The variation of the band gap is discussed with respect to the influence of the AgI content and the methods of film preparation.

Photoinduced changes in amorphous gallium doped GeTe4 chalcogenides

Chalcogenide thin films from the system Ge-Te-Ga were deposited by thermal vacuum evaporation on glass substrates from initial bulk synthesized materials. Optical measurements on as-deposited and irradiated thin films were performed. The optical constants - refractive index (n) and extinction coefficient (k) were evaluated from the transmission and reflectance spectra. Irradiation of the films for 3 hours through an interference filter with pass-band centered at 1,06 μm led to changes in the transmission spectra of the samples. A shift of the absorption edge was observed depending on the gallium content. The most significant change in the absorption edge was obtained in films with composition (GeTe4)95Ga5 with estimated coordination number 2.43. According to the covalent network model in glasses with coordination number close to 2.43, a floppy-rigid transition occurs. The spectral distribution of the refractive index change showed a sign inversion - from negative to positive. Changes in the physical thickness of the samples investigated due to the irradiation were not established.