|
|
Study of magnetic nanostructures for spintronics
Kameš, Jaroslav ; Nebojsa, Alois (referee) ; Urbánek, Michal (advisor)
The Cu/NiFe/Cu/Co/(CoOx) spin-valves have been prepared by the ion-beam sputtering method. Their GMR ratio and the time stability have been investigated by the magnetoresistance and the MOKE measurements at room temperature. The reproducibility of the preparation of the samples have been studied as well, i.e. two identically configurations of the layers should have the same magnetotransport properties.
|
|
|
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.
|
|
|
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.
|
|
|
Improvement of IBAD apparatus
Urbánek, Ivan ; Nebojsa, Alois (referee) ; Spousta, Jiří (advisor)
This thesis is divided into three main parts dealing with ion beam assisted deposition. In the first part there is a brief description of the IBAD chamber at Institute of Physical Engineering of BUT. There is also a detailed description of control of the IBAD apparatus during deposition. Next part deals with measuring of deposition rates of ion sputtering in order to refine deposition of thin layers. Last part deals with planned and already finished changes that should improve quality and speed of thin layers deposition. Changes include the option of covering the substrate holder, change of the entry flange, design of new insertion chamber with multifunctional substrate holder and the option to control the deposition by computer.
|
|
|
Switching vortex chirality in magnetostatically coupled permalloy nanodisks
Balajka, Jan ; Nebojsa, Alois (referee) ; Urbánek, Michal (advisor)
The diploma thesis is concerned with switching of vortex circulation in magnetic nanodisks. The results of micromagnetic simulations of hysteresis loops of individual disks with different degrees of asymmetry are presented. The influence of geometric asymmetry of the disk on the shape of the hysteresis loop is discussed as well as switching of vortex circulation in asymmetric nanodisks by external in-plane magnetic field. Simulations of pairs of magnetostatically coupled nanodisks were carried out for different interdisk distances and degrees of asymmetry. By analysing the results of the simulations, the effects of magnetostatic coupling and the asymmetry on resultant circulation of individual vortices were compared and the range of magnetostatic interaction between nanodisks of given dimensions and asymmetry was estimated. Experimental techniques used for fabrication and measurement of the samples are briefly summarized.
|
|
| |
|
|
Influence of underetching of plasmonic antennas on their optical response
Novák, Martin ; Nebojsa, Alois (referee) ; Šamořil, Tomáš (advisor)
Influence optical response on underetching of plasmonic antennas is observed in this thesis. When light falls with resonant wavelength on the optical antennas, the electromagnetic field is amplified near this antennas. The resonant wavelength depends on the length of the antenna and on effective refractive index given by the ambient properties around the antenna. The contact surface with substrate (dielectric) is reduced by underetching the antenna and the effective refractive index is changed and thus the optical response of the antenna is changed.
|
|
|
Deposition of Ga and GaN ultrathin layers on graphene substrate
Dvořák, Martin ; Nebojsa, Alois (referee) ; Mach, Jindřich (advisor)
This diploma thesis deals with preparation of graphene samples for depositions of ultrathin layers of gallium and gallium nitride. Graphene substrates were prepared by chemical vapour deposition in home-build high temperature reactor. After graphene transfer to silicon wafers, a series of chemical and thermal treatments were performed. Obtained samples were suitable for the study of growth of ultrathin layers of Ga and GaN. The growth of Ga and GaN was realized in ultra high vacuum conditions. Molecular beam epitaxy technique was used for gallium depositions together with ion source for nitridation. Obtained ultrathin layers were studied with X-ray photoelectron spectroscopy, atomic force microscopy and with scanning electron microscopy.
|
|
| |
|
|
Noncontact temperature measurements using luminescent materials
Jedlička, Jindřich ; Nebojsa, Alois (referee) ; Ligmajer, Filip (advisor)
This diploma thesis deals with noncontact temperature measurement using luminescent materials. In the theoretical part of the thesis, luminescent materials were selected on the basis of a literature review with respect to sensitivity and operating temperature range. In the experimental part of the thesis, photoluminescence of CdSe/ZnS and GaAs quantum dots for various temperatures was measured and the relative change of luminescence parameters such as emission peak position, intensity, intensity ratio of two emission peaks, and lifetime of luminescence were determined from the measurements in agreement with expectations according to the literature. Achieving high spatial resolution would be made possible by measuring cathodoluminescence, where the luminescence spectra are obtained with an order of magnitude higher spatial resolution. These measurements and the influence of electron beam on the luminescence quality of selected materials will be subject of further experimental study.
|
guest ::
