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Study of the structure and of interaction with gas molecules of Rh-Sn and Rh-SnO2
Janeček, Petr ; Nehasil, Václav (advisor) ; Jirka, Ivan (referee) ; Bartoš, Igor (referee)
In this work we present the results of the analysis of the surface structures and absorption properties with respect to the CO and O2 molecules of the Sn/Rh and Rh/SnO2 model systems. In the part dedicated to the Sn structures on Rh surfaces with two different orientations - Rh(110) and Rh(111) - we have investigated the development of the core electron levels and valence band during the development of surface reconstructions and absorption of CO molecules. The surface reconstructions of the Sn/Rh(110) systems were studied for the first time. Difference in behaviour w.r.t. Sn/Rh(111) was observed and explanation offered. Finally, on in-situ prepared epitaxial SnO2 layers, the surface reconstruction (4×1) was observed. The CO adsorp- tion properties of Rh on polycrystalline and epitaxial SnO2 layers were also studied and difference in behaviour explained.
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Physically chemical properties of epitaxial films CeO2/Cu(110)
Aulická, Marie ; Veltruská, Kateřina (advisor) ; Nehasil, Václav (referee)
In this work ways of preparation of thin epitaxial cerium oxide film on Cu(110) surface were studied. X-ray photoelectron spectroscopy (XPS), X-ray photoelectron difraction (XPD), low energy electron difraction (LEED), ion scattering spectroscopy (ISS) and scanning tunneling microscopy (STM) were used for the characterization of prepared systems. The island structure of CeO2 was prepared by the method of reactive evaporation in oxygen atmosphere. The influence of temperature on the electronic structure and morphology was studied. At the temperature above 550 ˚C partial reduction to Ce2O3 and reordering of the islands to the CeO2(331) structure was observed. The ceria promoted oxidation of copper surface was approved, since the clean c(6x2) reconstruction of the surface was observed at the oxygen exposure 1,5 order of magnitude lower then on Cu(110) alone. The other model system was prepared by cerium evaporation to the oxygen precovered Cu(110) surface. The mix of (2x1) and c(6x2) surface reconstruction was formed by oxygen exposition at 300 ˚C. Cerium was deposited on this surface, also at 300 ˚C. During the following heating to 500 ˚C the formation of epitaxial film Ce2O3(0001) was observed, accompanied by the formation of large hundreds nm long smooth band structures in the [11̄0] direction.
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Study of gas molecule - surface interaction
Kettner, Miroslav ; Nehasil, Václav (advisor) ; Johánek, Viktor (referee)
Title: Study of gas molecule - surface interaction Author: Miroslav Kettner Department: Department of surface and plasma science Supervisor: doc. RNDr. Václav Nehasil, Dr., Department of surface and plasma science Abstract: In this work, we examined the suitability of rhodium deposited on a plasma sprayed substrate of titanium dioxide for catalysis reactions. With X-ray photoelectron spectroscopy method, the thermal stability of TiO2 prepared with plasma spray technology on aluminum plate was tested at first. Then, rhodium was evaporated on substrate and thermal stability of the whole system Rh/TiO2 was determined. Further methods of thermal desorption spectroscopy and molecular beam were used to study adsorption and desorption of CO and reaction of CO with oxygen. It was verified that the system Rh/TiO2 ceases to adsorbing CO after heating above 620 K, also the CO reaction with oxygen exhibits considerably lower intensity after heating above 620 K. After calibrating on rhodium plate, it was determined that the intensity of CO2 creation on Rh/TiO2 is four times lower than intensity on the rhodium plate. Unprompted adsorption and desorption passivation of the system, however, seems to be the most significant problem. Therefore, the system was assessed as unsuitable for further research. Keywords: Rh, TiO2,...
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Laboratory Study of Field Ion Emission from Dust Grain
Jeřáb, Martin ; Šafránková, Jana (advisor) ; Stöckel, Jan (referee) ; Nehasil, Václav (referee)
Title: Laboratory study of field ion emission from dust grains Author: Martin Jeřáb Department: Department of Surface and Plasma Science Supervisor: Prof. RNDr. Jana Šafránková, DrSc., KFPP Abstract: Dust particles are common objects in space environment. As a dust particles, we call objects with typical sizes of several atoms up to approximately 100 µm. However, a total mass of dust particles is only about 1% of total mass of our galaxy, the presence of dust particles significantly affects environment. The most interesting is dynamics of dust particles and attached dust charging processes. The presented thesis consists of two main parts. The first part deals with the experimental study of field ion emission. Our measurements have been performed using gold and carbon spherical dust grains. It has been found that during the charging of dust particle using ion gun are the primary ions implanted under the surface of the dust particle from where they are release in the form of neutral gas. This releasing of implanted ions affects field ion emission for several hours. The second part of the thesis describes a development of new experimental apparatus determined to the study of photoemission dust charging and con- sequently to the "true" field ion emission study. Keywords: dust, dusty plasmas, charging properties, field...
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Adsorption of gas molecules on bimetallic systems
Ševčíková, Klára ; Nehasil, Václav (advisor) ; Libra, Jiří (referee)
Nazev prace: Adsorpce molekul plynu na bimctalickych systemech Autor: Klara Sevcikova Katedra: Katedra fyziky povrchu a plazmatu Vedouci bakalafske prace: Doc. RNDr. Vaclav Nehasil, Dr. e-mail vcdouciho: nchasif(o)m box.troja.mff.euni.cz Abslrakl: Mctodami termodesorpcnf speklroskopie a rnolekularnich svazku byla studovana adsorpce a desorpcc CO na system u rhodia deponovaneho na polykrystalickem oxidu ceru pro ruzne tloust'ky rhodiove vrstvy. Dale byly na techto systemcch zkoumany reakce molekul CO, zejinena jejich disociace a tvorba CO2. Byly pozorovany dva desorpcni slavy CO i CO2, jejichz dcsorpcni energie klesaji s rostouci tlousfkou deponovane vrstvy Rh. Tvorba CO2 se jevi zavisla na desorpci CO. Nfzkotcplotni desorpcni stav CO odpovida procesu adsorpce - desorpce. Vysokoteplotnf stav by! vysvellen redukci oxidu ceru pfi vysoke teplote, behem niz je z vrstvy uvolnovan kyslik, ktcry reagujc s atomarnim uhlfkem za vzniku CO, v mensf mi'fe i CO2. Z porovnani ploch desorpcm'ch pikti CO a CO2 nizkoteplotm'ho stavu vyplyva, ze nejvetsi procento adsorbovaneho CO disociuje na vzorku s nejvetsim rozhranim Rh/CeO,. Klfcova slova:CeON; Rh; adsorpce a desorpce CO, termodesorpcni spektroskopie Title: Adsorption of gas molecules on bimetallic systems Author: Klara Sevcikova Department: Department of Surface and...
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The study of gas molecule interaction with supported noncontinuous bimetallic films
Píš, Igor ; Nehasil, Václav (advisor) ; Veltruská, Kateřina (referee)
We deposited several submonolayer films of rhodium and vanadium onto polycrystalline -Al2O3 substrate. Prepared samples were different in ratio of deposited amount of rhodium and vanadium. XPS spectra of surface were measured after every particular step of metal deposition, sample annealing and CO, oxygen adsorption. Adsorption and temperature stimulated desorption of gas molecules were performed using Molecular Beam and Thermo Programmed Desorption methods. Furthermore, we studied a bimetallic system prepared by deposition of vanadium onto polycrytalline Rh foil and growth of vanadium on -Al2O3.
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Study of catalytic properties of metal-ceroxide system
Ševčíková, Klára ; Nehasil, Václav (advisor) ; Janovská, Michaela (referee)
System of cerium oxide and rhodium is used extensively in automotive emission control as a material suited for three-way catalysis. The prime for the activity of this catalyst is the oxidation state and a structure of CeOx. This study is focusing on CO oxidation and reactivity of the systems composed of polycrystalline layers of cerium oxide prepared by magnetron sputtering which approach well the real catalysts with their chemical and structural properties. Rhodium was evaporated on various CeOx layers differing in the oxygen concentration. X-ray Photoelectron Spectroscopy (XPS) was used to characterize an electronic and chemical state of a surface. Its reactivity toward CO was observed by Temperature Programmed Desorption (TPD) and Molecular Beams (MB). During steady - state reactions of CO and O2 molecular beams in temperature interval of 300 K - 770 K, there were observed three reaction mechanisms of CO2. Through the developement of reactivity of a catalyst caused by changes of partial pressure of O2 and by using isotopic labeled 13C16O, we can distinguish contributions of separate mechanisms to the total yield of CO2 and suggest the process of reactions. Polycrystalline cerium oxide plays the kye role due to its ability to release and adopt oxygen and due to the facility of oxygen migration through the...
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STM study of adsorption of metals on the Si(111) 7x7 surface
Setvín, Martin ; Ošťádal, Ivan (advisor) ; Nehasil, Václav (referee)
The work is focused on studying of a single silver adatom hopping inside a half unit cell of Si(111)-7×7 reconstruction. It is possible to estimate activation energies and frequency prefactors for hops between particular adsorption sites. It was necessary to make fundamental modifications on a low temperature STM as a part of the work. The modificaations have been made on top of a sample cooling system and on inertial motor for coarse approach of the sample to a tip. The vacuum properties of the STM chamber have been improved. A considerable progress in technology of electrochemically etched tungsten tip preparation has been achieved. Further treatement of the tips has been studied with accent on field emission effect on the tip apex. The 7×7 reconstruction could not be prepared inside the vacuum chamber. Reason is probably a poor degassing of the sample. Further planned experiments could not be performed so far. This thesis contains detailed theoretical analysis of the studying of adsorption sites. The tests of time dependent tunelling spectroscopy method are described in results.
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