National Repository of Grey Literature 21 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Ultrafast laser spectroscopy of antiferromagnets
Saidl, Vít ; Němec, Petr (advisor) ; Kužel, Petr (referee) ; Hamrle, Jaroslav (referee)
This work is dedicated to the study of two antiferromagnetic materials that are suitable for use in spintronic devices. In series of FeRh samples we studied the transition temperature between the antiferromagnetic and ferromagnetic phases. We developed a method based on material optical response for a quick determination of this temperature, which enabled us to study with a spatial resolution of 1 μm a magnetic inhomogeneity of prepared samples.We also developed a method for a determination of the Néel temperature and the magnetization easy axis position in thin films prepared from compensated antiferromagnetic metal. We successfully applied this method on an uniaxial sample of CuMnAs and we discussed its applicability for a research of samples with a biaxial magnetic anisotropy.
Ultrafast response of electrons in nanostructured and disordered semiconductor systems studied by time-resolved terahertz spectroscopy
Zajac, Vít ; Kužel, Petr (advisor) ; Lloyd-Hughes, James (referee) ; Ostatnický, Tomáš (referee)
of Doctoral Thesis Title: Ultrafast response of electrons in nanostructured and disordered semiconductor systems studied by time-resolved terahertz spectroscopy Author: Vít Zajac Department / Institute: Institute of Physics of the Czech Academy of Sciences Supervisor of the doctoral thesis: doc. RNDr. Petr Kužel, Ph.D., Institute of Physics of the Czech Academy of Sciences Abstract: This thesis deals with charge transport in semiconducting nanomaterials on the picosecond time scale studied by time-resolved terahertz spectroscopy. The problematics of the effective response of composite materials is reviewed and the VBD effective medium model is formulated. The wave equation for the THz probing pulse propagating through inhomogeneously excited percolated and non-percolated semiconducting nanomaterials is solved. This theory is used to investigate charge transport in samples of nanoporous-Si-derived nanocrystals and in epitaxial Si nanocrystal superlattices. The experimental spectra are successfully modeled with the use of Monte Carlo calculations of charge carrier mobility in nanocrystals of corresponding sizes and degrees of percolation within the VBD approximation. It is found that nanocrystals from different regions of the nanocrystal size distribution of the sample dominate the signal in THz and...
Socio-economic transformation of kicker societies and formation of football clubs in Prague cities and suburbs before The Great War
Kužel, Petr ; Čechurová, Jana (advisor) ; Kvaček, Robert (referee)
The most popular game all over the world has entered the territory of Bohemia already in the last decades of the 19th century, when especially in the cities and suburbs of Prague many Czech or German societies, engaged in new game from England called "football", was founded. Sudden and long lasting interruption of positive development of young sport by mobilization in the summer of 1914 and deep political and social changes after conflict isolated prewar events and made unique relict environment that creates the main sources for ideas of work. However chapters leaving sport performances aside and try to describe the period culminating after year 1900, when profesional player was born of student-enthusiast and when club loyalities based on nationality or social inclusion of spectator have been created. To achive a comprehensive view is also important to describe ideological orientation and economy of clubs, topography of Prague grounds or relationships between biggest clubs SK Slavia, AC Sparta, SK Viktoria Žižkov and DFC Prag, which was litmus paper of attitudes with German etnicity. Keywords Football, Prague, Czechs, Germans, Slavia, Sparta, The Great War
Studium a využití povrchových plazmonů v terahertzové spektrální oblasti
Darebník, Peter ; Kužel, Petr (advisor) ; Postava, Kamil (referee)
Title: Study and application of surface plasmons in terahertz spectral range Author: Peter Darebník Department: Department of Chemical Physics and Optics Supervisor: doc. RNDr. Petr Kužel, Dr., department of Chemical Physics and Optics - external employee Abstract: The goal of this thesis is analytical, numerical and experimental study of surface plasmons in terahertz spectral range The description of the surface plasmon propagation along metal/dielectric interface can be done purely analytically. Our goal is to obtain the description of the surface plasmon propagating in more complex dielectric layered structures which are in contact with metallic layer. Analysis of the surface plasmon dispersion curves in anisotropic layered structure was done numerically. Existing transmission terahertz spectroscopy experiment was expanded by an arrangement that allows us to excite the surface plasmon on the metallic layer and allows us to measure its characteristics after the transmission of samples, that are in contact with this layer. Obtained theoretical and experimental data were then evaluated, so we could conclude to which extent can the surface plasmon be used for spectroscopic purposes in terahertz range. We concluded, that we were able to describe surface plasmons in layered structures including anisotropic...
Socio-economic Transformation of Sport Societies and Formation of Football Clubs in Prague Cities and Suburbs before 1914
Kužel, Petr ; Čechurová, Jana (advisor) ; Kvaček, Robert (referee)
The most popular game all over the world has entered the territory of Bohemia already in the last decades of the 19th century, when especially in the cities and suburbs of Prague many Czech or German societies engaged in new game from England called "football" was founded. Sudden and long lasting interruption of positive development of young sport by mobilization in the summer of 1914 and deep political and social changes after conflict isolated prewar events and made quite unique relict environment that creates the main sources for ideas of work. However chapters leaving sport performances aside and try to describe the period culminating after year 1900, when profesional player was born of student-enthusiast and when club loyalities based on nationality or social inclusion of spectator have been created. To achive a comprehensive view is also important to describe ideological orientation and economy of clubs, topography of Prague grounds or relationships between biggest clubs - SK Slavia, AC Sparta, SK Viktoria Žižkov and Deutscher Fussball Club Prag, which was litmus paper of attitudes with German etnicity. Keywords Football, Prague, Czechs, Germans, SK Slavia, AC Sparta, DFC Prag, First Word War
Studium optických nelinearit v polovodičích a polovodičových nanostrukturách
Kozák, Martin ; Trojánek, František (advisor) ; Herynková, Kateřina (referee) ; Kužel, Petr (referee)
This Ph.D. thesis is focused on the study of optical nonlinearities and dynamics of excited charge carriers in monocrystalline diamond, nanocrystalline diamond and silicon. The dynamics of high density carriers in bulk diamond is investigated in detail (the transition from excitons and free carriers to electron-hole liquid or plasma). We study the picosecond dynamics of electron-hole liquid condensation using several techniques of time-resolved optical spectroscopy and demonstrate its evaporation by femtosecond laser pulses. We also propose two new optical techniques for measurement of lifetime, diffusion coefficient and surface recombination velocity of excitons in diamond. The results obtained by these techniques are described theoretically using diffusion equation and compared with the results obtained by the transient grating diffraction measurement. Further we study two- and three- photon absorption and nonlinear refractive index in diamond. In nanocrystalline diamond we study the second and third harmonic generation and its physical origin. In superlattices of silicon nanocrystals in SiO2 matrix we investigate the nonlinear transient absorption dynamics and carrier diffusion.
Philosophy of Louis Althusser in his ‚theoreticist' period
Kužel, Petr ; Hauser, Michael (advisor) ; Hohoš, Ladislav (referee) ; Zouhar, Jan (referee)
TITLE: The Philosophy of Louis Althusser in his ‚theoreticist' period AUTHOR: Petr Kužel DEPARTMENT: Social Sciences and Philosophy, Department SUPERVISOR: Mgr. Michael Hauser Ph.D. ABSTRACT: The thesis focuses on a philosophy of Louis Althusser in his "teoreticist" period, i.e. 1960-1967. The work is divided to four essentials sections: epistemology, ontology, psychoanalyse and ideology. We put accent on epistemological problematic, which is in this period of a development of Althusser's philosophy unequivocally dominant. In introduction of this text is explained historical and political context, in which Althusser realized his "theoretical intervention". The thesis treat on Althusser's conviction, that inadequate theory leads to deformed political practice and that Marxist theory exists till now in his "applied form", notably in The Capital. According to Althusser this Marxist theory wasn't adequately theoretically formed. Our work characterises Althusser's tentative to create and theoretically formulate this theory. This Althusser's tentative is connected with an effort to draw a "line of demarcation" between the Marxism and the pre-Marxist idealist notions, which are foreign to authentic Marxism. Althusser's critique focuses on Stalinism, "theoretical humanism", empiricism and Hegelianism. In present...
Tunable materials and structures for terahertz spectral range
Skoromets, Volodymyr ; Kužel, Petr (advisor) ; Hlídek, Pavel (referee) ; Pashkin, Alexei (referee)
This thesis is devoted to an experimental study of dielectric properties of incipient fer- roelectrics. The terahertz time-domain spectroscopy was used to investigate the complex permittivity spectra in both single crystals and various strained thin film structures versus temperature and applied electric bias. Namely, it allowed characterizing the ferroelectric soft-mode dynamics and its coupling to a central mode. An electric-field tunability of bulk single crystals of SrTiO3 was determined up to room temperature for the first time. The phenomenon is governed by soft-mode stiffening under applied field. As an application we proposed and characterized a tunable one-dimensional photonic structure with a thin SrTiO3 plate inserted as a defect layer. The importance of the soft-mode dynamics was stressed also in the study of bulk high density KTaO3 ceramics. A systematic study was performed of a KTaO3 thin film and especially of a set of strained multilayers consisting of SrTiO3/DyScO3 bilayers grown on DyScO3 substrate. Strain-induced ferroelectric transition was observed in these films governed by the soft mode coupled to a lower-frequency relaxation. A general model was developed describing the whole family of the studied samples. Effect of the composition stoichiometry of SrTiO3 films grown on DyScO3 was...
Dynamics of delocalized states in molecular systems studied by time-resolved THz spectroscopy
Mics, Zoltán ; Kužel, Petr (advisor) ; Jepsen, Peter Uhd (referee) ; Kůsová, Kateřina (referee)
This thesis is devoted to a study of the conductivity of confined charge carriers in various nanocrystalline materials. The experimental method -- THz spectroscopy -- involves measurements of the conductivity of carriers generated by doping or by optical excitation. In the theoretical interpretation of measured data we address important aspects of carrier transport, connected to the microscopic inhomogeneity of samples and the nanoscale confinement of carriers. We focus on the study of nanocrystalline ZnO and CdS using simulations and experiments in a wide range of carrier densities and for several temperatures. In ZnO, the interplay of highly mobile electron-hole gas, dense electron-hole plasma and population of excitons was observed. In CdS the investigation reveals the importance of clusters of nanocrystals in the electron confinement. The dynamics of the electron mobility at different carrier densities show the role of the kinetic energy of electrons and its relaxation in the carrier transport in nanostructured systems. At temperatures 20 K and at low carrier densities a crossover between localized transport and Drude-like free electron behaviour was observed for the first time.
Spin dynamics in GaAs-based semiconductor structures
Schmoranzerová, Eva ; Němec, Petr (advisor) ; Postava, Kamil (referee) ; Kužel, Petr (referee)
This work is dedicated to the study of spin dynamics in systems based on the semiconductor gallium arsenide (GaAs) that are suitable for use in spintronic devices. We explored two types of model structures using experimental methods of ultrafast laser spectroscopy and transport measurements. In the ferromagnetic semiconductor (Ga,Mn)As, we investigated laser-induced magnetization precession. We found out that transfer of both energy and angular momentum from the circularly polarized laser light can trigger magnetization precession, the latter one being identified as a new phenomenon, the "optical spin transfer torque". Furthermore, we demonstrate the possibility to control the energy-transfer-induced magnetization dynamics both optically and electrically using piezo-stressing. When dealing with purely non-magnetic structures for spintronics, we studied the Spin-Injection Hall Effect (SIHE) in GaAs/AlGaAs heterostructures with a special type of spin- orbit (SO) coupling that are lithographically patterned to create nanodevices. We managed to observe precession of the electron spin in the SO field directly in the space domain by extending the original detection method. This finding, together with the direct detection of a pure spin current, helped to propose a working spin Hall effect transistor.

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