Browsing by Author "Lazarova V."

Now showing 1 - 4 of 4
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    Characterization of reactive sputtered molybdenum oxide thin films for gas sensors
    (2009-08-01) Boyadzhiev S.; Lazarova V.; Makita K.; Kotani Y.; Yordanova I.; Matsumura Y.; Rassovska M.
    Molybdenum oxide (MoOx) thin films were deposited by two different techniques of reactive sputtering and their properties were characterized in order to determinate their usage in gas sensors. For preparing the samples the methods of radio frequency (RF) and direct current (DC) magnetron reactive sputtering were used. The composition and microstructure of the films were studied by X-ray photoelectron spectroscopy (XPS), electron probe microanalyser (EPMA), X-ray diffraction (XRD) and Raman spectroscopy. The films' surface was observed by Scanning electron microscopy (SEM) and EPMA. The research was focused on the sensing behavior of the MoO3 thin films. In order to do that, films of various thickness were deposited on quartz resonators and the quartz crystal microbalance (QCM) method was used. Applying it can be build high sensitive gas sensor capable to detect changes in the molecular range. These prototype QCM sensing structures with MoOx sensitive films in as-deposited state and without heating the substrates showed good sensitivity to ammonia at room temperature. They are also being tested for sensitivity to other gases and with future development can be successfully introduced into advanced chemical sensing devices. © 2009 The Surface Science Society of Japan.
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    Preparation and characterization of SnO2 films for sensing applications
    (2008-01-01) Stefanov P.; Atanasova G.; Manolov E.; Raicheva Z.; Lazarova V.
    SnO2 thin films for gas sensing applications were deposited by RF sputtering in a mixture of oxygen and argon. The morphology, structure and composition of the SnO2 films were analysed by XRD, SEM and XPS. SnO2 thin films showed a crystalline structure with a submicron particle size of 200 nm. The electronic structure of the film surface was elucidated by analysis of the photoelectron core level and valence band spectra of Sn.
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    Surface modification of steels by electrical discharge treatment in electrolyte
    (2014-02-25) Krastev D.; Paunov V.; Yordanov B.; Lazarova V.
    In this work some experimental data about the influence of applied electrical discharge treatment in electrolyte on the surface structure of steels are discussed. The electrical discharge treatment of steel surface in electrolyte gives a modified structure with specific combination of characteristics as a result of nonequilibrium transformations. The modification is performed by a high energy thermal process in a very small volume on the metallic surface involving melting, vaporisation, activation and alloying in electrical discharges, and after that cooling of the surface with high rate in the electrolyte. The surface layer obtains a different structure in comparison to the metal matrix and it possesses higher hardness, wear resistance and corrosion resistance.
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    XPS characterization of TiO2 layers deposited on quartz plates
    (2008-03-01) Stefanov P.; Shipochka M.; Stefchev P.; Raicheva Z.; Lazarova V.; Spassov L.
    TiO2 layers for gas sensing applications were obtained by Liquid Phase Deposition (LPD). The layers were deposited on gold-coated piezoelectric quartz crystals. The surface structure, morphology and chemical properties were analysed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). SEM showed that the layers were porous and composed of uniform crystalline grains. XPS indicated them to be non-stoichiometric. © 2008 IOP Publishing Ltd.