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Gas sensing properties of tungsten oxide thin films
Vojík, Jiří ; Mašek, Karel (advisor) ; Haviar, Stanislav (referee)
The purpose of this thesis is a study of sensing properties of pure, platinum-doped and gold-doped tungsten oxide thin films. Required films were prepared by magnetron sputtering on glass and passivated silicon. Their chemical composition was investigated by XPS. The morphology of the films was measured using AFM and SEM. Sensing response of these films to hydrogen was investigated in the range from 1,000 to 10,000 ppm and temperatures between 100 and 350 řC. It was found that platinum oxides PtO2 and PtO were partially reduced during the sensing tests. The possible encapsulation of the platinum by the tungsten oxide was discovered. The sensitivity of the metal doped films was much higher than the sensitivity of the pure films. In the case of platinum-doped films the sensitivity decreased with increasing temperature in contrast to the gold-doped films where the sensitivity increased. The gold was present in two metallic and oxidized states. The gold was reduced during the reactions with hydrogen. After the sensing tests, the size of crystalline grains increased and the platinum-doped films became coarser.
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Studium fyzikálně-chemických vlastností povrchově modifikovaného oxidu wolframu
Polášek, Jan ; Mašek, Karel (advisor) ; Novák, Stanislav (referee) ; Plšek, Jan (referee)
This work can be divided into two parts. In the first part, we examine possibilities of preparation of monocrystalline tungsten and tungsten oxide nanoclusters by means of magnetron sputtering with gas aggregation. Clusters are prepared in the non-reactive (Ar) and reactive (Ar + O2) atmosphere and heated after the deposition or during the flight by IR radiation. Influence of oxygen in the aggre- gation process was described and possibilities of generating crystalline tungsten and tungsten oxide clusters were found. In the second part, we study reactivity of tungsten oxide layers, pure and doped with rare metals (Pt, Au), deposited on the silicon wafer and etched carbon, towards partial methanol oxidation. Influence of carbon substrate and metal doppants on reactivity was found and described, along with mofrological and chemical changes that occurs in the sample during the proces. 1
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Study of physical and chemical properties of surface-modified tungsten oxide
Polášek, Jan ; Mašek, Karel (advisor)
Title: Study of physical and chemical properties of surface-modified tungsten oxide Author: Jan Polášek Department: Department of Surface and Plasma Science Supervisor: Doc. RNDr. Karel Mašek, Dr., Department of Surface and Plasma Science Abstract: This work can be divided into two parts. In the first part, we examine possibilities of preparation of monocrystalline tungsten and tungsten oxide na- noclusters by means of magnetron sputtering with gas aggregation. Clusters are prepared in the non-reactive (Ar) and reactive (Ar + O2) atmosphere and heated after the deposition or during the flight by IR radiation. Influence of oxygen in the aggregation process was described and possibilities of generating crystalline tungsten and tungsten oxide clusters were found. In the second part, we study reactivity of tungsten oxide layers, pure and doped with rare metals (Pt, Au), deposited on the silicon wafer and etched carbon, towards partial methanol oxi- dation. Influence of carbon substrate and metal doppants on reactivity was found and described, along with mofrological and chemical changes that occurs in the sample during the proces. Keywords: catalysis, tungsten oxide, clusters, partial oxidation of methanol, etched carbon 1
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Study of the structural properties of model ceria based catalysts
Beran, Jan ; Mašek, Karel (advisor) ; Olejník, Kamil (referee) ; Lykhach, Yaroslava (referee)
This work is concerning the study of model ceria based calalysts structure by methods of electron diffraction RHEED and photoelectron spectroscopy XPS. The influence of deposition conditions and substrate on the growth of epitaxial cerium oxide films on copper single crystals is described in detail. The work then describes the interaction of cerium and tin in model systems and the creation of SnCeOx mixed oxide and its structure. In the last chapter, the interaction of palladium with cerium and tin oxide layers is examined, and the creation of paladium bimetallic alloys is described. Powered by TCPDF (www.tcpdf.org)
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Study of gas sensing properties of tungsten oxide thin films
Vojík, Jiří ; Mašek, Karel (advisor) ; Ševčíková, Klára (referee)
Purpose of this thesis is a study of gas sensing properties of pure and platinum doped tungsten oxide thin films, which are deposited on a glass substrate. Needed films were prepared by magnetron sputtering method. Chemical composition and morphology of the films were investigated by means of XPS and SEM. It was discovered that prepared films are relatively flat and homogenous. They consist of polycrystalline WO3. It emerged that platinum which is present in modified films is in form of the PtO2 and PtO oxides. During subsequent heating of the films in air, which is needed for right function of films as sensors, PtO2 partially reduced. The resistance of the films decreased after heating. Sensing properties of the films were studied at 300 řC. The platinum doped film was more sensitive to exposition of hydrogen than the pure film.
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Preparation and characterization of epitaxial tungsten oxide thin films
Pavlíková, Romana ; Mašek, Karel (advisor) ; Olejník, Kamil (referee)
Tungsten oxide thin films were prepared by vacuum evaporation on surfaces of Pd(111), Cu(111), Cu(110) and Cu(100) single crystals and studied by RHEED, XPS and AFM methods. The tungsten oxide deposition was done at temperatures from 300 řC to 400 řC in UHV or in oxygen atmosphere. The best deposition conditions - substrate temperature of 400 řC and oxygen atmosphere - were found resulting in growth of epitaxial and only partially reduced thin films. Thin films grown on the Pd(111) and Cu(111) surfaces consisted of two phases: a nearly atomically flat phase with (100) epitaxial plane and a phase formed by three dimensional particles with (111) epitaxial plane. Thin film deposited on Cu(100) also consisted of two phases: a flat film with (100) epitaxial plane and self-organised 1D structures parallel to Cu[010] and Cu[001] directions. Thin film prepared on the Cu(110) surface contained solely 1D structures parallel to Cu[1-10] surface direction. Capability of the partially reduced thin films for oxidation was studied. We applied oxidation using RF oxygen plasma, O2 exposure at elevated temperature and exposure to atmosphere. Thermal stability of the WO3/Cu(110) system was also investigated by heating up to 620 řC.
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Digitizing of video and radio broadcasting in the Czech republic
Endris, Petr ; Slámová, Hana (advisor) ; Mašek, Karel (referee)
Cílem bakalářské práce je podat ucelený přehled procesu digitalizace televizního a rozhlasového vysílání v České republice. V úvodu jsou vysvětleny základní pojmy. V druhé kapitole je pojednáno o televizi jako novém médiu a o funkci médií ve společnosti. Třetí kapitola je věnována standardům a specifikacím digitálních zařízení. Jsou zde popsány televizní normy, rozdíl mezi HDTV a SDTV. Jsou také popsány možnosti příjmu vysílání v HD kvalitě a interaktivní služby. Čtvrtá kapitola je věnována institucionálnímu zabezpečení digitalizace - konkrétně Českému telekomunikačnímu úřadu, Radě pro rozhlasové a televizní vysílání a Národní koordinační skupině. V páté kapitole je vysvětlen samotný průběh digitalizace televizního a rozhlasového vysílání [Autorský abstrakt]. Powered by TCPDF (www.tcpdf.org)
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Study of metal- tungsten oxide model system by methods of electron spectroscopy and diffraction
Polášek, Jan ; Mašek, Karel (advisor) ; Starý, Vladimír (referee)
In the present thesis structure, morphology, chemical and electronic properties of the Pt - Au/tungsten oxide model system were investigated by means of RHEED, AFM and PES. The epitaxial tungsten oxide thin films were prepared by oxidation of W(110) single-crystal surface using a RF oxygen plasma source followed by thermal annealing. Gold and Platinum were deposited "in-situ" by evaporation. Gold or platinum deposition led to the growth of oriented particles having (111) epitaxial plane as well as to the growth of polycrystalline phase. Platinum encapsulation was proved by CO adsorption observed by SRPES. Deposition of the second metal led to the formation of core - shell bimetallic clusters. Detail structure of the bimetallic system depends on the order of deposited metals and the substrate temperature. Thermal stability of the system was investigated by heating up to 600 řC.
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Study of influence of the substrate temperature on the structure of epitaxial tungsten oxide layers
Pavlíková, Romana ; Mašek, Karel (advisor) ; Veltruská, Kateřina (referee)
Purpose of this thesis is a study of substrate temperature influence on structure, chemical composition and morphology of tungsten oxide thin films prepared by oxidation of a tungsten single crystal W(110) using a radio frequency plasma source. Thin film's parameters were observed by RHEED, XPS, AFM snad SEM. The substrate was oxidized at room temperature (RT) and at temperatures of 400ř C, 500ř C and 550ř C. In the first and the second case, produced thin films were amorphous and epitaxial structure was obtained by recrystallization. At the temperature of 500ř C, an epitaxial thin film was produced directly. After further heating at the temperature of 550ř C we got polycrystalline thin film without orientation of the crystal grains. All the epitaxial thin films had (111) crystallographic plane parallel to substrate surface. The tungsten oxide layers grew with relatively hight surface roughness in the order of several nanometers.
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