Dimitre Dimitrov

Oxygen sensing junctions based on yttria stabilized zirconia with platinum nanoparticles

We invent new types of ceramic sensor junctions for detection of oxygen. Their electrodes comprise thin films of yttria stabilized zirconia (YSZ) obtained by spray pyrolysis: pure YSZ and YSZ reinforced with platinum nanoparticles. The potential difference of the sensors is measured as a function of temperature and described by empirical equation. In dynamic conditions this difference exhibits a well pronounced cyclic behavior sensitive to the oxygen content. The potential difference logarithmically depends on the oxygen concentration at a fixed temperature, which is proven both experimentally and theoretically. This difference has a minimum at particular concentration of platinum in the ceramics.

Oxygen detection using yttria-stabilized zirconia thin films doped with platinum

Yttria stabilized zirconia (YSZ) thin films are obtained using both spray-pyrolysis and dip-coating. The ability of YSZ films incorporated with platinum nanospecies (Pt-YSZ) to detect oxygen is compared with that of pure YSZ thin films using a new experimental setup. With this system, the surface electrical resistance of the films as a function the oxygen content is measured at a fixed temperature. In addition, the effects of thermal annealing on the oxygen sensitivity of the films are observed. Platinum doped samples, Pt-YSZ, show different kinetics of carrier diffusion as compared to pure YSZ samples.

Temperature dependence of electron transmission through organized organic thin films

The temperature dependence of electron transmission through various organized organic thin films (OOTFs) was investigated. For most systems a strong dependence of the transmission efficiency on temperature was observed, even for a relatively small temperature range. The well defined structure of the OOTFs and the monitoring of the angular dependence of both the initial and the final velocities of photoelectrons were used to reveal the mechanism behind the temperature effect and further elucidate the transmission mechanism. A simple model, which assumes that the electron transmission yield is much higher along the organic chains than in any other direction, was able to reproduce the experimental observations. We find that the photoelectron transmission yield through OOTFs is extremely sensitive to the structural order in the film.

Green synthesis of UV and visible light active TiO2/WO3 powders and films for malachite green and ethylene photodegradation

Powder nanocomposites of TiO2/WO3 are prepared by a simple solid-state thermal procedure from commercial oxide powders and cast thereafter as a film coating on TLC substrate. The WO3 content in the powder composites is varied from 0.5 to 50%. The phase composition and morphology of titania/tungsten composites and films is characterized by SEM and X-ray analysis. The photocatalytic activity of TiO2/WO3 powders is tested in the degradation of malachite green dye in aqueous solutions under UV and visible light irradiation. The effect of preparation temperature on the photocatalytic activity is also investigated. It is found out that the mixed powder of 5%WO3 manifests the best photocatalytic performance. The prepared powder photocatalyst is deposited as a film coating on TLC sheet for gas-phase application. The as-obtained composite coated photocatalysts with 5%WO3 are tested for air purification from ethylene contamination under UV and visible light illumination. The TiO2/WO3 coated photocatalysts show always a higher efficiency in comparison to that of the pure TiO2.

Photoelectric properties of polycrystalline layers based on halogen doped PbTe

The preparation conditions of halogen doped (Cl,l) PbTe thin films have been studied. The influence of substrate and layer growth conditions on electrical and photoelectric properties are analyzed. The optimal regimens of growth of the initial layers are determined. Further, effective refraction coefficients of lead telluride films in dependence on the preparation methods were measured. It is estimated that the adding of halogen impurities into the charge increase the IR-sensitivity and makes possible a preparation of sensitive samples without annealing and reduces relaxation time. Besides, the data related to the interactions of a PbTe surface with an environment at room temperature testify to presence of the capture centers of a double nature.