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Optical characterization of InAs nanowires
Hošková, Michaela ; Ligmajer, Filip (referee) ; Musálek, Tomáš (advisor)
This bachelor thesis deals with the fabrication and optical characterization of InAs nanowires. Physical vapor deposition is used for the fabrication of nanowires via method selective epitaxy in the MBE chamber. The growth conditions for the formation of nanowires are optimized and their dimensions are characterized by a scanning electron microscope. Confocal spectroscopy and electron energy loss spectroscopy are employed for measurement of the optical response and the influence of the geometry of individual nanowires is studied. The motivation is the development of a new optical method that monitors nanowires directly during growth in the MBE apparatus.
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GaN deposition on a tungsten substrate
Pikna, Štěpán ; Piastek, Jakub (referee) ; Čalkovský, Vojtěch (advisor)
This bachelor thesis is focused on deposition of GaN nanocrystals on the etched tungsten tips. Motivation was to prepare these GaN structures on the Schottky cathode made by company ThermoFisher Scientific and measure its field emission. In the theoretical part of the thesis GaN and tungsten field emission properties are introduced. The experimental part begins with tungsten tip etching optimalization, where the right values for best tips are temperature 20 °C, depth of the tip 2,5 mm and solution NaOH used. Further the gallium structures were prepared on these tips using molecular beam epitaxy (MBE). The right temperature to prepare GaN nanocrystals was determined as 200 °C. The deposition of gallium was set to 2 hours and following nitridation was 3 hours. Finally, the field emission from GaN prepared on copper foil with graphene was measured and compared with other experiments.
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Optical spectroscopy of magnetic semiconductors suitable for spintronic applications
Saidl, Vít ; Němec, Petr (advisor) ; Mics, Zoltán (referee)
In this work we investigate optical properties of new antiferromagnetic semiconductor - LiMnAs. This semiconductor oxidizes easily in air. This fact complicates significantly the investigation of its properties by the optical spectroscopy. This problem was solved by a construction of the optical setup that enables measurements of the reflectivity spectra directly in the chamber where this semiconductor is prepared by a molecular beam epitaxy (MBE). Firstly, the reliability of this optical setup was tested by the measurements of the reflectivity spectra of the well known semiconductors (GaAs and InAs). Secondly, the first measurements of LiMnAs reflectivity directly in the MBE chamber was performed.
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The oxygen modification of the graphene structures for biosensors
Mikerásek, Vojtěch ; Bartošík, Miroslav (referee) ; Mach, Jindřich (advisor)
The bachelor thesis deals with the modification of CVD graphene by oxygen atoms. The theoretical part describe the structure of graphene oxide and its physical properties. Methods of production of this material and its use in biosensors are also described. The practical part describes the preparation of monolayer graphene on a silicon wafer. The main attention was paid to the oxidation of graphene by atomic oxygen and its modification in oxygen plasma. The samples were measured during process of oxidation at individual time intervals using XPS.
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Deposition of Ga nanostructures on graphene membranes
Severa, Jiří ; Mikulík, Petr (referee) ; Mach, Jindřich (advisor)
This diploma thesis deals with the preparation of the graphene membranes for depo-sition of gallium atoms by the molecular beam epitaxy. In the first part properties ofgraphene and methods of its production are described. Second part focuses on the gra-phene membranes, their specific properties, applications and methods of production. Thirdpart describes growth theory of the thin films. Practical part is focused on preparationof graphene membranes, which consists of covering the holes in the silicon substrate bygraphene layer. For that mechanical exfoliated and chemical vapor deposited graphenewere used. Subsequently, gallium atoms were deposited on these membranes by molecularbeam epitaxy and in situ observed by scanning electron microscopy.
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Preparation of low-dimensional III-V semiconductors
Stanislav, Silvestr ; Detz, Hermann (referee) ; Kolíbal, Miroslav (advisor)
Tato diplomová práce se zabývá přípravou nanostruktur z indium arsenidu (InAs) pomocí metody molekulární svazkové epitaxe (MBE). Důraz je kladen na výrobu struktur ve formě nanodrátů na křemíkovém substrátu. V úvodní části práce je popsána motivace pro studium III-V polovodičů a konkrétně InAs. Následující kapitoly vysvětlují dva základní princpy tvorby nanodrátů. Experimentální část práce diskutuje možnost přípravy indiového katalyzátoru pro samokatalyzovaný růst InAs nanodrátů v konkrétní aparatuře MBE. Následuje prezentace výsledků růstu InAs nanodrátů mechanismem selektivní epitaxe (SAE). Nanodráty byly vyrobeny na substrátu s termálně dekomponovaným oxidem a rovněž na substrátech s litograficky připravenou oxidovou maskou.
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The deposition of CaF2 ultrathin layers on graphene substrate
Caesar, Radek ; Nebojsa, Alois (referee) ; Mach, Jindřich (advisor)
This master’s thesis is focused on preparation and analysis of ultrathin CaF2 (calcium fluoride) films on a graphene substrate. CaF2 was deposited in UHV conditions at substrate temperatures in the range from 20 °C to 400 °C. The material was deposited on Si(111) with a native SiO2 layer and on a substrate with a CVD graphene layer. The deposited films were analyzed by XPS, AFM and SEM. Moreover four different sample holders for deposition purposes were designed in this work.
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The deposition of germanium nanoparticles on hydrogenated amorphous silicon.
Stuchlík, J. ; Volodin, V.A. ; Shklyaev, A.A. ; Stuchlikova, T.H. ; Ledinsky, M. ; Čermák, J. ; Kupčík, Jaroslav ; Fajgar, R. ; Mortet, V. ; More-Chevalier, J. ; Ashcheulov, P. ; Purkrt, A. ; Remeš, Z.
We reveal the mechanism of Ge nanoparticles (NPs) formation on the surface of the hydrogenated amorphous silicon (a-Si:H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) on ITO and a on boron doped nanocrystalline diamond (BDD). The coating of Ge NPs on a-Si:H was performed by molecular beam epitaxy (MBE) at temperatures up to 450 degrees C. The Ge NPs were characterized by Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The nanocrystalline Ge particles are conglomerates of nanocrystals of size 10-15 nm and quantum dots (QDs) with size below 2 nm embedded in amorphous Ge phase. After coating with Ge NPs the a-Si:H thin films show better adhesion on BDD substrates then on ITO substrates.
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The deposition of germanium nanoparticles on hydrogenated amorphous silicon
Stuchlík, Jiří ; Volodin, V.A. ; Shklyaev, A.A. ; Stuchlíková, The-Ha ; Ledinský, Martin ; Čermák, Jan ; Kupčík, Jaroslav ; Fajgar, Radek ; Mortet, Vincent ; More Chevalier, Joris ; Ashcheulov, Petr ; Purkrt, Adam ; Remeš, Zdeněk
We reveal the mechanism of Ge nanoparticles (NPs) formation on the surface of the hydrogenated amorphous silicon (a-Si:H) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) on ITO and a on boron doped nanocrystalline diamond (BDD). The coating of Ge NPs on a-Si:H was performed by molecular beam epitaxy (MBE) at temperatures up to 450 °C. The Ge NPs were characterized by Raman spectroscopy, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The nanocrystalline Ge particles are conglomerates of nanocrystals of size 10-15 nm and quantum dots (QDs) with size below 2 nm embedded in amorphous Ge phase. After coating with Ge NPs the a-Si:H thin films show better adhesion on BDD substrates then on ITO substrates.
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