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Ultrafast dynamics of charge carriers in 2D materials
Koutenský, Petr ; Kozák, Martin (advisor) ; Galář, Pavel (referee)
Title: Ultrafast dynamics of charge carriers in 2D materials Author: Bc. Petr Koutenský Department: Department of Chemical Physics and Optics Supervisor: RNDr. Martin Kozák, Ph.D., Department of Chemical Physics and Optics Abstract: The goal of this thesis was to study ultrafast dynamics of excitons in monolayers of transient metal dichalcogenides WSe2 and MoS2 using methods of ultrafast laser spectroscopy. We focus on two types of processes in this thesis. We measured ultrafast dynamics of carrier recombination and inter-valley scattering of excitons. We also focused on ultrafast manipulation with excitonic energy levels which allows us to remove the energy degeneracy in different minima of the band structure using coherent optical effects (optical Stark effect and Bloch-Siegert shifts). In the future, the observed phenomena could contribute to developement of new utrafast optical and optoelectronical devices exploting so called valley polarization of electrons in the studied materials. Keywords: Ultrashort laser puses, time-resolved laser spectroscopy, nonlinear op- tics, 2D crystals iii
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Photochromic effect in nanoporous titanium dioxide film with Ag nanocrystals
Galář, Pavel ; Malý, Petr (advisor) ; Dohnalová, Kateřina (referee)
The diploma thesis is devoted to multicolour photochromic effect in nanocomposite material Ag-TiO2, which is caused by a spectrally selective photoinduced decrease in extinction. The Thesis introduces briefly the theory of particle plasmons which are of fundamental significance for the investigated phenomenon. A short summary of the models and results published on photochromic effect in Ag-TiO2 is than given. The core of thesis deals with the optimization of this nanocomposite material towards a high photochromatic response. The influence of concentration of the TiO2 solution and of the speed of its spin coating deposition on a substrate was measured. Also the effect of AgNO3 quality used for sample preparation was monitored. A change in the extinction was found to depend on parameters of the excitation laser beam too. As a part of the optimization process, also the alternative TiO2 matrixes produced on basis of lamellar micelles were tested. The photochromic effect was monitored by measurements of the light extinction and scattering in dependence on the sample photoexposition. The properties of a set of the high-quality samples were studied using photoluminescence spectroscopy. Measurements of the photoluminescence decay with subpicosecond time resolution by up-conversion technique as well as of the...
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Nanoscopy, spectroscopy and modication of individual nanoobjects in liquid environment
Smísitel, Petr ; Valenta, Jan (advisor) ; Galář, Pavel (referee)
In this diploma thesis we will study the luminescence properties of nanocrystals. We will summarize the basic division according to size and standard method of theoretical description of semiconductor and metal nanocrystals. We will describe the luminescence properties of nanocrystals and the influence of the surrounding environment. In the se- cond part of the thesis we will follow up the construction of an apparatus for imaging luminescence spectroscopy intended for the measurement of individual nanoobjects in a liquid environment. Finally, we will study luminescence properties of organixally passi- vated metal clusters in a liquid environment with changes in temperature and excitation intensity. We compare the luminescence of gold nanocrystals with and without long po- lyethylene glycol chains bound on the surface. 1
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Ultrafast spectroscopy of hybrid nanosystems
Galář, Pavel ; Malý, Petr (advisor) ; Herynková, Kateřina (referee) ; Vrňata, Martin (referee)
Title: Ultrafast spectroscopy of hybrid nanosystems Author: RNDr. Pavel Galář Department: Department of Chemical Physics and Optics Supervisor: prof. RNDr. Petr Malý, DrSc. Abstract: This Ph. D. thesis is focused on physical phenomena located at the interface of hybrid nanostructure composed of polycrystalline diamond and polymer polypyrrole. The main method used in our experimental study was ultrafast laser spectroscopy that allowed us to gain new findings about electron recombination processes in polycrystalline diamond layers, polypyrrole and in their hybrid structures. The research was focused on mutual influence of both components, especially through energy and charge transfer. In the first step of our research we carried out optical characterisation of different kinds of polypyrrole and complex study of recombination processes dynamics of photoexcited charge carriers in polycrystalline diamond. The measurements were realized by the methods of time-resolved photoluminescence and transmission spectroscopy in the time scale from picoseconds to milliseconds. On the basis of the obtained results the model explaining the origin of luminescence signal related to the different kinds of electron recombination processes in non- diamond phase and on surface defects of diamond grains in polycrystalline layers was...
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Photochromic effect in nanoporous titanium dioxide film with Ag nanocrystals
Galář, Pavel
The diploma thesis is devoted to multicolour photochromic effect in nanocomposite material Ag-TiO2, which is caused by a spectrally selective photoinduced decrease in extinction. The Thesis introduces briefly the theory of particle plasmons which are of fundamental significance for the investigated phenomenon. A short summary of the models and results published on photochromic effect in Ag-TiO2 is than given. The core of thesis deals with the optimization of this nanocomposite material towards a high photochromatic response. The influence of concentration of the TiO2 solution and of the speed of its spin coating deposition on a substrate was measured. Also the effect of AgNO3 quality used for sample preparation was monitored. A change in the extinction was found to depend on parameters of the excitation laser beam too. As a part of the optimization process, also the alternative TiO2 matrixes produced on basis of lamellar micelles were tested. The photochromic effect was monitored by measurements of the light extinction and scattering in dependence on the sample photoexposition. The properties of a set of the high-quality samples were studied using photoluminescence spectroscopy. Measurements of the photoluminescence decay with subpicosecond time resolution by up-conversion technique as well as of the...
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Nanoscopy, spectroscopy and modication of individual nanoobjects in liquid environment
Smísitel, Petr ; Valenta, Jan (advisor) ; Galář, Pavel (referee)
In this diploma thesis we will study the luminescence properties of nanocrystals. We will summarize the basic division according to size and standard method of theoretical description of semiconductor and metal nanocrystals. We will describe the luminescence properties of nanocrystals and the influence of the surrounding environment. In the se- cond part of the thesis we will follow up the construction of an apparatus for imaging luminescence spectroscopy intended for the measurement of individual nanoobjects in a liquid environment. Finally, we will study luminescence properties of organixally passi- vated metal clusters in a liquid environment with changes in temperature and excitation intensity. We compare the luminescence of gold nanocrystals with and without long po- lyethylene glycol chains bound on the surface. 1
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Nonlinear optical frequency conversion of few-cycle laser pulses
Koutenský, Petr ; Kozák, Martin (advisor) ; Galář, Pavel (referee)
Title: Nonlinear optical frequency conversion of few-cycle laser pulses Author: Petr Koutenský Department: Department of Chemical Physics and Optics Supervisor: RNDr. Martin Kozák, Ph.D., Department of Chemical Physics and Optics Abstract: The goal of the thesis was to achieve generation of second harmonic frequency from ultrashort laser pulses with central wavelength of 780 nm and to compress the generated pulses to the shortest possible time duration. We have studied and optimized the efficiency of second harmonic frequency generation from wide spectrum laser, which generates ultrashort pulses with a duration of few femtoseconds. Firstly we have developed and optimized the experimental setup for the highest power output of the generated second harmonic frequency pulses. Afterwards we measured the duration of the generated pulses using nonlinear optical cross- correlation with the pulses at the fundamental frequency generated by the laser. Cross- correlation was obtained from sum frequency generation in a thin nonlinear BBO crystal. The pulses at the second harmonic frequency were compressed to a duration of 13 femtoseconds by combining wide spectrum mirrors with negative dispersion of group velocities and thin fused silica wedges. These ultrashort pulses will be used in experiments with high time...
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Ultrafast spectroscopy of hybrid nanosystems
Galář, Pavel ; Malý, Petr (advisor) ; Herynková, Kateřina (referee) ; Vrňata, Martin (referee)
Title: Ultrafast spectroscopy of hybrid nanosystems Author: RNDr. Pavel Galář Department: Department of Chemical Physics and Optics Supervisor: prof. RNDr. Petr Malý, DrSc. Abstract: This Ph. D. thesis is focused on physical phenomena located at the interface of hybrid nanostructure composed of polycrystalline diamond and polymer polypyrrole. The main method used in our experimental study was ultrafast laser spectroscopy that allowed us to gain new findings about electron recombination processes in polycrystalline diamond layers, polypyrrole and in their hybrid structures. The research was focused on mutual influence of both components, especially through energy and charge transfer. In the first step of our research we carried out optical characterisation of different kinds of polypyrrole and complex study of recombination processes dynamics of photoexcited charge carriers in polycrystalline diamond. The measurements were realized by the methods of time-resolved photoluminescence and transmission spectroscopy in the time scale from picoseconds to milliseconds. On the basis of the obtained results the model explaining the origin of luminescence signal related to the different kinds of electron recombination processes in non- diamond phase and on surface defects of diamond grains in polycrystalline layers was...
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Photochromic effect in nanoporous titanium dioxide film with Ag nanocrystals
Galář, Pavel
The diploma thesis is devoted to multicolour photochromic effect in nanocomposite material Ag-TiO2, which is caused by a spectrally selective photoinduced decrease in extinction. The Thesis introduces briefly the theory of particle plasmons which are of fundamental significance for the investigated phenomenon. A short summary of the models and results published on photochromic effect in Ag-TiO2 is than given. The core of thesis deals with the optimization of this nanocomposite material towards a high photochromatic response. The influence of concentration of the TiO2 solution and of the speed of its spin coating deposition on a substrate was measured. Also the effect of AgNO3 quality used for sample preparation was monitored. A change in the extinction was found to depend on parameters of the excitation laser beam too. As a part of the optimization process, also the alternative TiO2 matrixes produced on basis of lamellar micelles were tested. The photochromic effect was monitored by measurements of the light extinction and scattering in dependence on the sample photoexposition. The properties of a set of the high-quality samples were studied using photoluminescence spectroscopy. Measurements of the photoluminescence decay with subpicosecond time resolution by up-conversion technique as well as of the...
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