T. Petkova - Academia.edu (original) (raw)

Papers by T. Petkova

Bulk glasses of Ge-Se-In system were synthesized by melt-quenching technique. Thin films from the... more Bulk glasses of Ge-Se-In system were synthesized by melt-quenching technique. Thin films from the respective bulk materials were prepared by vacuum evaporation and the composition was determined by Auger electron spectroscopy. The films structure was investigated by transmission electron microscopy and the films surface roughness was examined by atomic force microscopy. The current-voltage characteristics of the sandwich structures Cu-(GeSe5)1−xIn-Cu, x = 020 at.% were measured at a linear increasing electrical field applied up to 10 9 V.m −1 at room temperature. Basic electrical constants of the films-dielectric permittivity, effective electron mass and electron work function on the interface metal-chalcogenide were derived from the current-voltage characteristics. The experimental data obtained show good correlation with the Christov's theory of injected electron currents. Two regions have been observed: extended thermionic emission region and intermediate emission region. The...

NiCo2O4-spinel has been prepared by three different techniques: The Pechini method, a hydrotherma... more NiCo2O4-spinel has been prepared by three different techniques: The Pechini method, a hydrothermal method and a precipitation reaction. The obtained samples have been examined by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM). The results reveal that materials prepared by the Pechini method possess two phases (Co3O4 and NiO), those obtained by the hydrothermal method have phases of NixCo3-xO4. Single-phase NiCo2O4 material is obtained only by the precipitation reaction. The obtained NiCo2O4 material is nanosized, exhibiting thermal stability up to 700 °C, where thermal decomposition of NiCo2O4 to Co3O4 and NiO takes place. In the region of thermal stability, a linear thermal expansion of the elementary cell has been observed.

Boron doped nanocrystalline diamond films (BDD) immobilized with photosensitive molecules have be... more Boron doped nanocrystalline diamond films (BDD) immobilized with photosensitive molecules have been studied as electrode material for reduction of nitrate in waste water. This process is one of the most important goals of the modern electrochemistry. The diamond thin films were deposited on silicon substrate by Hot Filament Chemical Vapour Deposition (HFCVD) technique. Manganese phthalocyanine has been used as photosensitive material for immobilization. The BDD electrode has been electrochemically studied in three electrode cell. The electrochemical properties have been studied by Cyclic Voltammetry (CV) at different experimental conditions in dark and under illumination. The results approve that the boron doped diamond electrode grafted with phthalocyanine serves as an efficient and stable electrode for nitrate reduction. The diamond electrode has wide potential range. The obtained results are promising for future electrochemical application.

Acta Physica Polonica A, Nov 1, 2017

Network properties of ureasil-based polymer matrixes suitable for construction of amperometric bi... more Network properties of ureasil-based polymer matrixes suitable for construction of amperometric biosensors were probed by positron annihilation lifetime spectroscopy and swelling experiments. Temperature dependences of the ortho-positronium (o-Ps) lifetimes and their relative intensities were measured in a temperature range of 15-350 K. Glass transition temperatures and expansion coefficients of microscopical free-volume for the investigated polymers were determined. Differences in network behavior for the aged samples and the effect of chalcogenide (As2S3) particles on the free volume of ureasil network were observed. Swelling experiments using ethyl alcohol showed that the structure of the aged sample network had less swelling ability for the pure ureasil as well as composite. This suggests that the one of factors influencing swelling is the change of the basic ureasil network due to ageing. It is supposed that the network properties obtained by positron annihilation lifetime spectroscopy and swelling experiments could be very helpful to understand better the bio-functionality of the constructed biosensor based on the ureasil-chalcogenide glass composite.

INTERNATIONAL CONFERENCE ON SCIENCE AND APPLIED SCIENCE (ICSAS) 2019

Gold Bulletin

Synthesis of gold nanoparticles (Au-NPs) was performed using method of an inorganic chemical redu... more Synthesis of gold nanoparticles (Au-NPs) was performed using method of an inorganic chemical reduction. The synthesized Au-NPs showed an intensive surface plasmon resonance band at 525 nm that is typical for corresponding Au-NPs reported in literature. The structural and morphology characterizations of the obtained Au-NPs were carried out using SEM, AFM, TEM, and X-ray spectral analysis. The possibility of usage of Au-NPs as a carrier for covalent immobilization of commercial laccase and the combination of the obtained bio-Au-NPs with ureasil polymers as host matrixes for formation of bio-nanocomposite films was studied. The prospect of using the obtained bio-nanocomposite films in biosensor technologies in order to improve the bioanalytical characteristics of sensory elements has been proved.

Thin Solid Films

Abstract The main purpose of this study is to obtain transparent and conductive As-doped SnO2 thi... more Abstract The main purpose of this study is to obtain transparent and conductive As-doped SnO2 thin films and their application for large area position sensitive structure Si-SiO2-SnO2:As, acting on the base of lateral photoeffect. The films were deposited over n-type silicon substrate with native SiO2 surface by spray pyrolysis technique, using 0.25 M water-ethanol solution of SnCl4 consisting As2O5 as dopant. The films were characterized by X-ray diffraction; scanning electron microscopy and atomic force microscopy. Si-SiO2-SnO2:As structures were prepared and the lateral photoeffect was investigated. Under nonuniform irradiation with a laser beam, a lateral photovoltage (LPV) appeared, with high sensitivity to the spot position on the plane of the metal oxide film. The LPV depends on the conductivity and optical transmittance of the films. The position sensitivity shows a peak about 36 mV/mm for the films of SnO2 doped with As. The position characteristic shows good linearity and resolution and could be useful for practical applications.

The Journal of Physical Chemistry, 1992

Photoinduced changes in thin films from the Se-Ag-I system are investigated firstly, employing va... more Photoinduced changes in thin films from the Se-Ag-I system are investigated firstly, employing various methods-holography, microscopy, electron microscopy, X-ray analysis, and Auger electron spectroscopy. The influence of the composition on the photoinduced changes, as well as the possibility of inducing considerable photoanisotropy, is demonstrated. The mechanism of the processes is discussed on the basis of the experimental data, the phenomena being related to Weigert effect in silver halide system, photocrystallization, and orientation of defects in chalcogenide systems. 14 refs., 8 figs.

NATO Science for Peace and Security Series B: Physics and Biophysics, 2011

Chapter 22 Thin As-Se-Sb Films as Potential Medium for Optics and Sensor Application Vania Ilchev... more Chapter 22 Thin As-Se-Sb Films as Potential Medium for Optics and Sensor Application Vania Ilcheva, V. Boev, T. Petkova, Plamen Petkov, Emil Petkov, G. Socol3 and IN Mihailescu Abstract Thin films have been deposited onto quartz substrates by the pulsed laser deposition ...

Electrochimica Acta, 2005

Applied Physics Letters, 1997

Bulk samples of the ternary system TiO2-V2O5-P2O5 have been synthesized by standard melt quenchin... more Bulk samples of the ternary system TiO2-V2O5-P2O5 have been synthesized by standard melt quenching technique. The structure of the materials has been studied by X-ray diffraction. The obtained samples possess glassy-crystalline structure. Impedance investigations have been performed by using impedance spectroscopy at different temperatures. The spectra are analyzed by two phase concept: crystalline grains distributed in glassy matrix The conductivity is obtained using fitting procedure. The conductivity is most likely caused by polaron hopping between aliovalent vanadium ions.

Materials Letters, 2002

Optical and electrical properties of Ag 2 À 2x Zn x Te thin films have been investigated. Optical... more Optical and electrical properties of Ag 2 À 2x Zn x Te thin films have been investigated. Optical band gap has been determined from the transmission spectra using Swanepoel's method and Tauc's procedure. The calculated values increase with ZnTe content from 0.08 to 0.46 eV. The thermal activation energy of the films with different ZnTe concentration is determined by investigating the temperature dependence of conductivity. The increase of ZnTe content leads to increase in the thermal band gap from 0.06 to 0.44 eV.

2014 Tenth International Vacuum Electron Sources Conference (IVESC), 2014

Physics Procedia, 2013

In this research we report deposition of thin films from the already synthesized chalcohalide (Ge... more In this research we report deposition of thin films from the already synthesized chalcohalide (GeS 1.5) 1-x (AgI) x glasses, where x=5, 10, 20 mol.%. The bulk samples used and the corresponding layers are checked by XRD analysis which reveals only a diluted halo on the respective diffractograms. Some basic optical parameters of the investigated Ge-S-AgI thin films are estimated and their relation with materials' composition is determined. The influence of the third component on the optical absorption is discussed. The optical energy gap (E g) is determined from the Tauc plot h =B(E g Tauc-h) 2 and E g 04 is found from the relationship =f(h). The E g values calculated by both methods reveal slight increase with silver iodide addition probably due to structural changes.

Proceedings of the Second International Symposium of Trans Black Sea Region on Applied Electromagnetism (Cat. No.00TH8519), 2000

Thin films of glassy (GeS2)1-x (AgI)x system have been studied. The films have been coated on can... more Thin films of glassy (GeS2)1-x (AgI)x system have been studied. The films have been coated on cantilever-based gas sensors and studied upon exposure to water, acetone, and ammonia vapours. The results reveal that the sensor acted like a resonance microbalance, showing highest sensitivity towards the analyte with the highest molecular weight, i.e. towards acetone. Modification of the surface of the sensitive layer after the exposure to ammonia is associated with chemisorption of the analyte molecules on it and results in increase sensitivity towards water due to the chemisorbed NH3 molecules.

Thin (As2Se3)100-xAgx (x = 0-25 mol.%) films have been obtained on glassy and silicon substrates ... more Thin (As2Se3)100-xAgx (x = 0-25 mol.%) films have been obtained on glassy and silicon substrates by vacuum thermal evaporation and pulsed laser deposition from the corresponding bulk materials. The stress of the layers deposited on silicon cantilevers was measured by a cantilever technique, which is commonly applied to solid inorganic thin films. The correlation between the stress and the composition as a function of the film preparation methods has been investigated and discussed. We showed that the addition of silver leads to changes in the glass properties, such as an increase of the density and compactness, related to the modification of the stress values.