Browsing by Author "Boev V."

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    Compositional dependence of the optical properties of silver containing As2Se3 thin films
    (2012-01-01) Ilcheva V.; Petkov P.; Petkova T.; Boev V.; Monchev B.
    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. © Published under licence by IOP Publishing Ltd.
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    Optical properties of thermally evaporated (As2Se 3)100-xAgx thin films
    (2013-01-01) Ilcheva V.; Petkov P.; Boev V.; Petkova T.
    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 extrapolation the values of n in the region of strong absorption (whereα ≥104 cm-1) and its spectral distribution was discussed. The dispersion of the refractive index was analyzed in terms of single-oscillator Wemple-DiDomenico model. The shift of the optical absorption edge was described using the non-direct transition model, proposed by Tauc. Optical band gap was calculated from the Tauc plot αhν =B(EgTauc - hν )2 and the compositional dependence of the optical gap was discussed. In order to realize photoinduced changes in the films, they were illuminated by He-Ne laser and their transmission spectra were measured before and after illumination. The shift of the absorption edge of as - deposited and illuminated films was investigated and discussed as a function of the films composition. © 2013 The Authors.
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    Photoinduced changes in As-Se-Ag amorphous films
    (2008-05-01) Ilcheva V.; Boev V.; Roussev D.; Petkov P.; Petkova T.; Sharlandjiev P.; Nasarova D.
    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. © 2008 IOP Publishing Ltd.
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    Silver nanoparticles synthesis and their effect on the SOPC lipid structure
    (2022-04-04) Slavkova Z.; Genova J.; Chamati H.; Boev V.; Yancheva D.
    We focus our attention on the influence of hydrophobic silver nanoparticles (Ag NPs) on the 1-Stearoyl-2-oleoylsn-glycero-3-phosphocholine (SOPC) model system. Results obtained by differential scanning calorimetry (DSC) and infrared (IR) spectroscopy were compared to their counterpart for lipid systems with incorporated hydrophobic gold nanoparticles (AuNPs) and pure SOPC lipid in a water environment. The results show a strong effect of hindering the gel-to-liquid crystalline phase transition for both types of noble metal hydrophobic NPs. The effect of the phase transitions shift to the lower temperatures is more pronounced for the silver particles for the concentrations studied. According to the IR spectral analyses, no negative effect is observed of the NPs on the lipid hydration for the concentration studied, and the plasmon effect of the Ag NPs appears to be more pronounced.