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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.
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SMV-2014-04: Micro-stereolithography writer
Šerý, Mojmír
Contractual research is dealing with experimental development of apparatus for creating of microstructures with strongly focused laser beams. The microstructures are written into photoresist material by two-photon process. It is possible to write details in the range of hundreds of nanometers.
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Ultrafast processes in semiconductor nanocrystals
Dzurňák, Branislav ; Trojánek, František (advisor) ; Dohnalová, Kateřina (referee)
This diploma thesis deals with optical properties of silicon nanocrystals implanted in silicon oxide substrate. We examined samples with various concentrations of nanocrystals. We measured Raman spectra of our samples and identified size of nanocrystals and distance between them as function of depth. We measured absorption and reflection of samples and calculated the energy of band gap. For various implantation doses we examined temperature dependence of luminescence spectra. Two peaks were observed for excitation wavelength of 408 nm, the first shifts towards longer wavelength with increasing temperature, the second one stays unchanging. We observed low-temperature resonant luminescence in order to identify fonon structure. During observation of time-resolved luminescence two components of fast luminescence appeared - the slower in scale of nanoseconds, the faster in scale of picoseconds. We devoted to study of the faster component. For the faster component we observed up-converted luminescence. Intensity dependence of this component is quadratic. We also observe degradation of luminescence owing to strong laser beam. In conclusion we discussed origin of each component of luminescence spectra.
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An apparatus with a horizontal capillary tube intended for measurement of the surface tension of supercooled liquids
Vinš, Václav ; Hošek, Jan ; Hykl, Jiří ; Hrubý, Jan
New experimental apparatus for measurement of the surface tension of liquids under the metastable supercooled state has been designed and assembled in the study. The measuring technique is similar to the method employed by P.T. Hacker [NACA TN 2510, 1951]. A short liquid thread of the liquid sample was located in a horizontal capillary tube partly placed in a temperature-controlled chamber. One end of the capillary tube was connected to a setup with inert gas which allowed for precise tuning of the gas overpressure. The open end of the capillary tube was precisely grinded and polished in order to assure its planarity and perpendicularity. The liquid meniscus at the open end was illuminated by a laser beam and observed by a digital camera. Application of an increasing overpressure of the inert gas at the inner meniscus of the liquid thread caused variation of the outer meniscus such that it gradually changed from concave to flat and subsequently convex shape. The surface tension at the temperature of the inner meniscus could be evaluated from the overpressure corresponding to exactly planar outer meniscus.
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SMV-2013-19: Nanolithography system based on two-photon photopolymerization
Jákl, Petr ; Šerý, Mojmír ; Zemánek, Pavel
The reasearch contract deals with development of experimental setup for dynamic shaping of laser beams. Using computer generated holographic phase masks, it is possible to create independent foci of laser beams in the sample space, change their intensity profiles and power of each diffracted beam. By employing fast acousto-optic modulator, the complex procedure allows control of sample irradiation within microsecond resolution. It is possible to precisely select sample region for laser impact using computer-controlled nano-positioning stage.
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