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Study of physical properties of Heusler alloys
Beran, Lukáš ; Veis, Martin (advisor)
This diploma thesis is devoted to systematic study of structural trans- formations of Heusler alloys by means of spectroscopic ellipsometry and magneto-optical spectroscopy. Structural transformations in these alloys are induced by different microscopic mechanisms. Obtained experimental results were confronted with theoretical calculations. This allowed the discussion of obtained results and suggestion of their interpretation. In the case of Co- Fe-Si alloys, changes in optical and magneto-optical properties with change of Co-Fe ratio were observer. This was explained by lowering of the gap for minority spins with increasing Fe concentrations. Temperature dependent optical and magneto-optical properties of Ni-Mn-Ga alloy showed the pres- ence of so-called Martensitic transformation from cubic to tetragonal phase. A study of Mn-Rh-Co-Sn alloys did not show a clear dependence of physical properties upon the concentration of Rh and Mn. This was explained by strong strain inside the samples, which distorted obtained results. 1
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Physics of interfaces in magnetic nano structures
Ohnoutek, Lukáš ; Veis, Martin (advisor) ; Urbánek, Michal (referee)
Modification of interfaces in nanostructures can significantly influence their overall properties. Magneto-optical spectroscopy and spectroscopic ellipsometry are ideal for studying these phenomena thanks to their in-depth sensitivity and contactless measurements. Two methods of nonreversible modification of magnetic properties, especially the magnetic anisotropy, are investigated. The measured spectral dependence of magneto-optical Kerr effect is compared to a theoretical calculation in order to determine the profile of the samples for different levels and methods of modification. In addition to this, ellipsometric measurements are performed on a device whose optical properties change by voltage application.
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Optical and magneto-optical properties of Heusler compounds
Král, Daniel ; Veis, Martin (advisor) ; Mistrík, Jan (referee)
Cílem této práce bylo studium Heuslrových sloučenin pomocí optických a magneto-optických (MO) metod. V případě první sloučeniny, Co2FeGa0.5Ge0.5, jsme studovali výskyt strukturálního disorderu za pomoci spektroskopické elipsometrie, MO spektroskopie a MO Kerrovy magnetome- trie. Experimentální výsledky jsme poté porovnali s teoretickými modely. Doplnili jsme také výsledky našich spolupracovník·, a to včetně X-ray difrakce, atomic-force mikroskopie a ab initio výpočt·, abych potvrdili naši interpretaci naměřených výsledk·. Bylo zjištěno, že strukturální disorder je vskutku pozorovatelný pomocí metod, kterých jsme využili. Jeho výskyt se projevil změnou elektronové struktury vzork·. V případě druhé sloučeniny, Fe2MnGa, jsme vyšetřovali vliv obsahu Fe složky na optické a MO vlastnosti tohoto materiálu. Zjistili jsme, že atomy Fe ovlivňují koncentraci volných elektron·, čímž dodávají sloučenině kovový charakter (v porovnání s Ni2MnGa). Zároveň zvyšují optickou a MO odezvu v blízké infra-červené oblasti spektra. Dále bylo zjištěno, že vzorek s nejvyšším obsahem Fe má nulovou magnetizaci. 1
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Studium fyzikálních vlastností Heuslerových slitin
Beran, Lukáš ; Veis, Martin (advisor) ; Mistrík, Jan (referee)
This diploma thesis is devoted to systematic study of structural trans- formations of Heusler alloys by means of spectroscopic ellipsometry and magneto-optical spectroscopy. Structural transformations in these alloys are induced by different microscopic mechanisms. Obtained experimental results were confronted with theoretical calculations. This allowed the discussion of obtained results and suggestion of their interpretation. In the case of Co- Fe-Si alloys, changes in optical and magneto-optical properties with change of Co-Fe ratio were observer. This was explained by lowering of the gap for minority spins with increasing Fe concentrations. Temperature dependent optical and magneto-optical properties of Ni-Mn-Ga alloy showed the pres- ence of so-called Martensitic transformation from cubic to tetragonal phase. A study of Mn-Rh-Co-Sn alloys did not show a clear dependence of physical properties upon the concentration of Rh and Mn. This was explained by strong strain inside the samples, which distorted obtained results. 1
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Characterization of a new deposition system for coating the fibers
Zvonek, Milan ; Salyk, Ota (referee) ; Čech, Vladimír (advisor)
Cieľom bakalárskej práce je charakterizácia depozičného systému na výrobu tenkých vrstiev. Teoretická časť je zameraná na literárnu rešerš o plazme, plazmovej polymerácií, tenkých vrstvách a ich analýzu pomocou infračervenej spektroskopie a spektroskopickej elipsometrie. Experimentálna časť popisuje použité materiály a aparaturu použitú na prípravu tenkých vrstiev pomocou plazmovej polymerácie. Posledná časť popisuje výsledky merania depozícií tenkých vrstiev a ich vyhodnotenie vzhľadom na depozičné podmienky.
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Ordered and disordered arrays of colloidal nanoparticles for biomolecule detection
Ligmajer, Filip ; Rezek, Bohuslav (referee) ; Kolíbal, Miroslav (advisor)
This thesis deals with guided self-assembly of gold nanoparticles from their colloidal solutions onto silicon substrates and possible employment of nanoparticles for detection of biomolecules. It was found that by adjustment of solution pH and surface chemistry modification by means of electron beam irradiation it is possible to facilitate nanoparticle deposition to patterns with almost single particle precision. Spectroscopic ellipsometry was then employed in analysis of self-assembled layers of nanoparticles and its combination with a theory of effective medium approximation has proven the ability to assess nanoparticle dimensions and volume fractions. By experiments with thiolated oligonucleotides it has been shown that using ellipsometry one can detect even with very subtle changes in nanoparticle environment caused by biomolecules, thus promising its possible use in the field of biodetection.
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Ellipsometry of Thin Films
Novotný, Zbyněk ; Navrátil, Karel (referee) ; Nebojsa, Alois (advisor)
Diploma thesis deals with ageing process of thin films of Co and Cu on Si substrate, prepared by the IBAD method. The process of film ageing, which depends on time of exposition to the atmosphere at room conditions, was investigated with spectroscopic ellipsometry (VIS+UV) and atomic force microscopy. In case of thin Co films, approximately four days long incubation period was observed. During this time period, a change in the optical parameters of the film occurs without a measurable change of the film topography. Using non-contact atomic force microscopy, a growth of the transitional film in the island growth regime was observed. During the ageing of thin Cu films, two stages of growth of the transitional layer were observed - nucleation stage and growth stage. Both of these time periods of the transitional layer growth show direct logarithmic dependence. Using non-contact atomic force microscopy, the growth of the transitional film was observed. Using atomic force microscopy in non-contact regime, time dependent measurement was done and the process of forming of one monolayer of the transitional layer was documented. Within the diploma thesis, a series of experiments on ultra high vacuum system were performed in order to investigate phase transformation of thin Fe films (22 monolayers) on Cu(100) stabilized by CO absorption. The transformation from fcc phase to bcc phase was induced by Ar+ ion beam bombardment with the ion energy in the range (0.5-4) keV. The process of phase transformation was observed by surface magneto-optic Kerr effect, Auger electron spectroscopy and low energy electron diffraction.
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Thin films prepared in RF glow discharge and their physico-chemical properties
Bránecký, Martin ; Boušek, Jaroslav (referee) ; Čech, Vladimír (advisor)
Theoretical part of this master thesis was focused on literature recherché dealing with the formation of thin films, plasma, plasma analyses using mass spectrometry and plasma polymerization. Further, this section describes the analysis of thin films using optical methods such as spectroscopic ellipsometry and FT-IR spectrometry. Experimental part describes the materials which are used for the preparation of thin films as well as a description of the equipment for preparation of thin films using a technology of plasma-enhanced chemical vapor deposition (PE-CVD). Control of deposition conditions and monitoring of plasma with its products result in high reproducibility of thin films. The last part of the thesis describes the results of measurement of the first group of samples and their ellipsometric, mass spectrometry and FT-IR evaluation with respect to the deposition conditions.
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Deposition and optical properties of thin films and layered structures by PECVD
Kucharčík, Jan ; Boušek, Jaroslav (referee) ; Čech, Vladimír (advisor)
Thesis in theoretical part is focused on the principle of spectroscopic ellipsometry and formation of thin films by plasma-enhanced chemical vapor deposition (PECVD). In the experimental part we describe the deposition system, ellipsometer and mathematical evaluation of ellipsometric data, materials used for film formation and processing of the samples. Single-layer and multilayer structures of polymeric materials were prepared. We revealed that the optical properties of thin films are independent of film thickness. We also described the effect of the effective power and deposition gas mixture on optical properties of thin films.
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Adhesion of plasma polymer films deposited from tetravinylsilane monomer
Plichta, Tomáš ; Salyk, Ota (referee) ; Čech, Vladimír (advisor)
This bachelor thesis deals with the characterization of thin films of plasma polymers prepared from monomers of tetravinylsilane (TVS) and deposited on planar silicon substrates. Plasma enhanced chemical vapor deposition (PE CVD) was used as a method of thin films preparation. Three power series were prepared from pure TVS and two mixtures TVS with argon and oxygen. The main characterization methods were scratch tests and atomic force microscopy (AFM) is used to assess the adhesion degree of the layers and topography of scratches. To assess the characteristics and context the layer thickness was measured by spectroscopic ellipsometry (ELL) and elastic modulus using nanoindentation. The collected data were used to assess the reproducibility of the results with the regard to the purity of substrates and adhesion layers, depending on the deposition conditions and layers aging.
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