|
|
Optical and magneto-optical properties of Heusler compounds
Král, Daniel ; Veis, Martin (advisor)
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
|
|
|
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
|
|
|
Study of ferrimagnetic garnets thin films for photonic applications
Tázlarů, Stáňa ; Veis, Martin (advisor) ; Antoš, Roman (referee)
The aim of this thesis was an optical and magneto-optical characterization of thin layers of iron garnets prepared on silicon substrate by pulsed laser deposition method with emphasis on determining their suitability for use as materials for integrated optical isolators. The work is primarily dedicated to study of a single-layer terbium iron garnet samples and the influence of bismuth and cerium substitutions on their properties. Pre- sented values of a quality parameter, the figure of merit, are comparable with previously published results of two-layer structures of yttrium iron garnets and up to an order of magnitude higher than other available published values in this field. 1
|
|
|
Optical and magneto-optical properties of thin films of topological insulator Bi2Se3
Jambrich, Jakub ; Veis, Martin (advisor) ; Hamrle, Jaroslav (referee)
Topological insulators have attracted intensive research interest in the field of material research in the last two decades. Their main advantage is that metallic conductive states are formed on their surface, in which the electrons can move as if their effective mass is nearly zero. This feature has huge potential for use in the new generation of high-speed electronics. In this work, we investigate the optical and magneto-optical properties of the topological insulator Bi2Se3, which are key to its further potential use. By measuring the absorption at Landau levels in a high magnetic field, we determine the shape of the dispersion of the electronic structure as well as the bandgap. Subsequently, by spectroscopic ellipsometry in the range of the visible and near-ultraviolet spectrum, we measure the energy dependence of complex relative permittivity, which is the key for the description of optical properties.
|
|
|
Dynamic change in optical response of nanostructures
Vančík, Michal ; Veis, Martin (advisor) ; Zázvorka, Jakub (referee)
Title: Dynamic change in optical response of nanostructures Author: Michal Vančík Institute: Institute of Physics of Charles University Supervisor: RNDr. Martin Veis, Ph.D., Institute of Physics of Charles University Abstract: At the present time, properties of thin layers and multilayered nanos- tructures are intensively reseacrched. Because of different properties than bulk materials, thin layers have found application in various fields and play a key role in many technologies. Nanostructures containing GdOxare intensively studied since their properties can be modified by voltage application. It is assumed, that this change is caused by migration of ions in the structure. This thesis conducts re- search on multilayered structures, whose optical response changes reversibly by applying voltage. In these samples, the change is likely caused by migration of hydrogen ions into the GdOx layer. The goal of this thesis is to describe the opti- cal properties of individual layers of the structure and to describe the dynamic change in optical properties. The measurements were conducted with the help of spectroscopic ellipsometry, which allowed in situ voltage application. Keywords: spectroscopic ellipsometry, gadolinium oxide, multilayered nanostruc- tures, in situ
|
|
|
Study of the optical properties of graphene oxide thin films
Smolková, Denisa ; Zmeškal, Oldřich (referee) ; Schmiedová, Veronika (advisor)
This thesis examines the preparation of thin layers and determining their optical properties. It is focused on graphene oxide. In the theoretical part, basic information about the thin layers and their preparation is supplied. That is followed by a description of various methods of determining their optical properties and properties of light. Experimental part and results are focused on the preparation of thin layers by spin-coating and evaluation of measured values using optical microscopy, profilometry, spectroscopic ellipsometry and UV VIS spectroscopy. The conclusion summarizes the results of these methods.
|
|
|
Functional organic-inorganic nanostructures
Kelíšek, Petr ; Zmeškal, Oldřich (referee) ; Čech, Vladimír (advisor)
Diploma thesis deals with preparation of multilayered organic-inorganic nanostructures via PECVD technology and analysis of optical properties of these layers by spectroscopic ellipsometry. The theoretical part handles the definition of thin layers, layered and gradient nanostructures, plasma enhanced chemical vapor deposition and principles of spectroscopic ellipsometry. In the experimental part, used materials and chemicals are described, afterwards follow a complete description of the apparatus used for sample preparation and a description of the sample preparation procedure. The results part consists of methodology of preparing material models necessary for ellipsometric measurements and evaluation of optical properties of deposited nanolayers.
|
|
|
Study of the optical properties of titanium dioxide thin films
Rackovská, Anna Patrícia ; Schmiedová, Veronika (referee) ; Zmeškal, Oldřich (advisor)
The bachelor thesis is focused on the acquirement of thin film layers optical properties characterisation methods, done on inject printed titanium dioxide layers deposed on soda lime glass. Its main emphasis was on spectroscopic ellipsometry that was used to determine the refractive indices and the extinction coefficients of the samples in range of wavelengths from 200 nm to 850 nm and layer thickness. This thesis also shows another options of thin film layers preparation and several other methods to characterise properties of samples, specifically optical microscopy, used to set sample boundary as rough, mechanical profilometry which defined thickness of layers in range of 80 nm for the most thin sample to 250 nm for the most thick sample, and UV-VIS spectroscopy.
|
|
|
Optical and magneto-optical properties of Heusler compounds
Král, Daniel ; Veis, Martin (advisor)
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
|
|
|
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
|
guest ::
