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Ultrafast laser spectroscopy of semiconductor nanostructures
Chlouba, Tomáš ; Trojánek, František (advisor) ; Žídek, Karel (referee)
In this work we investigate changes in dynamics of CdSe nanocrystalline films caused by different annealing temperatures and different conditions during films growth. We use methods of time-resolved laser spectroscopy like time-resolved pump and probe and streak camera to study these dynamics. We also measured linear absorption and luminiscence. Our goal is to match measured dynamics with dynamics of other samples with different annealing temperatures and discuss the microscopic origin of these dynamics. Powered by TCPDF (www.tcpdf.org)
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Ultrafast laser spectroscopy of semiconductor nanostructures
Neudert, Karel ; Trojánek, František (advisor) ; Nikl, Martin (referee) ; Herynková, Kateřina (referee)
This doctoral thesis deals with analysis of carrier dynamics in semiconductor nanocrystals and nanostructures by methods of ultrafast laser spectroscopy. In three chapters silicon, InAs/GaAs, InAs/AlAs and CdSSe materials are studied. Silicon nanocrystals prepared by sol-gel method were measured by time-resolved luminescence method with various time resolutions, two-photon absorption and Z-scan method. A model describing findings was suggested. InAs was well measured by upconversion method and gained knowledge appeared to be fully consistent with quantum model. CdSe material was examined in two basic forms - thin films of nanocrystals prepared by chemical deposition and nanocrystals in comercial filters. In both cases all questions regarding influencing optical properties of nanocrystals by modification of their growth were answered.
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Optical properties of silicon nanostructures for photovoltaics
Salava, Jan ; Trojánek, František (advisor) ; Žídek, Karel (referee)
Název práce: Optické vlastnosti křemíkových nanostruktur pro fotovoltaiku Autor: Bc. Jan Salava Katedra: Katedra chemické fyziky a optiky Vedoucí diplomové práce: doc. RNDr. František Trojánek, Ph.D., katedra chemické fyziky a optiky Abstrakt: V předložené práci jsou studovány křemíkové nanokrystaly umístěné v SiC matrici - jednotlivé vzorky se odlišují přidáním dopantu (boru) do příslušné vrstvy struktury během depozice metodou PECVD a pasivací vodíkem. Křemíkové nanokrystaly jsou významné zejména tím, že oproti své objemové verzi vykazují účinnou fotoluminiscenci a absorpci ve viditelné oblasti spektra. Změnami parametr· při přípravě lze ladit jejich vlastnosti s ohledem na konkrétní aplikaci. Základní myšlenka integrace křemíkových nanostruktur do solárních článk· spočívá ve zvýšení účinnosti konverze slunečního spektra kombinací několika tenkých vrstev s nanokrystaly a objemového Si článku tak, aby každá vrstva sluneční cely absorbo- vala určitou část spektra. Procesy, které se v těchto strukturách dějí krátce po excitaci nosič· náboje, však stále nejsou zcela popsány. Cílem práce je charakterizace těchto jev· metodami ča- sově rozlišené spektroskopie. Dalším úkolem je popsat vliv dopování jednotlivých částí materiálu a jeho pasivace ve vodíkové atmosféře na chování fotoexcitovaných nosič· a intenzitu...
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Spectroscopy of semiconductors with ultra-high time resolution
Hanák, Martin ; Trojánek, František (advisor) ; Kozák, Martin (referee)
This thesis is aimed at building and optimization of a new experiment setup for measuring time-resolved transmittance using a pump-probe method. Test measurements were then conducted on a sample of SiV centers in diamond. The theoretical part contains a general description of luminescence of color centers. It then specifically focuses on SiV centers in diamond and describes their structure, electronic and spectral properties in detail. The description of our setup and its optimization is given at the beginning of the experimental part. The dependencies of differential transmittance of SiV centers in diamond on excitation intensity and wavelength were measured and the lifetime of SiV centers was then determined from our measurement results. 1
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Selection of femtosecond laser pulses
Bažíková, Sára ; Trojánek, František (advisor) ; Zázvorka, Jakub (referee)
Construction of the laser is one of the most important physical advances of modern times. Its use in practice is extremely common and desirable, therefore, it is necessary to push the boundaries of possibilities of this technique still further. Lasers generating ultrashort pulses are widely used in material research for the study of nonlinear effects and ultrafast processes. These lasers have a high repetition rate, which must be reduced for some applications. In this thesis we used femtosecond titanium -sapphire laser from Spectra Physics, whose repetition rate is 80 MHz. The aim of this thesis is to reduce this frequency by using a pulse selector. The key mechanism that utilizes the pulse selector is an acoustooptic modulator that is based on the principle of Bragg diffraction and it is able to select pulses with a frequency of 1 Hz-4 MHz. The end of thesis is measurement of the properties of this selector and its optimization.
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