Title: Bioapplications of novel nanostructured materials Author: Anna Fučíková Department / Institute: Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University in Prague Supervisor of the doctoral thesis: Doc. RNDr. Jan Valenta, Ph.D., Department of Chemical Physics and Optics, Faculty of Mathematics and Physics, Charles University in Prague Abstract: This work is aimed at development of new fluorescent labels based on silicon nanocrystals. Nanodiamonds and commercial CdSe quantum dots have been used as comparative materials. Silicon nanocrystals are relatively small (1-4 nm) compared to other studied nanomaterials. They are prepared by electro-chemical etching and their surface can be activated by various molecules which strongly influences luminescence properties. Luminescence quantum efficiency can be as high as 30 % and perfectly photostable even in biological environment. Si nanocrystals are biodegradable in a living organism within reasonable time scale and non-toxic. We are able to detect luminescence of single nanocrystals, even inside living cells, with use of our micro-spectroscopy apparatus. Nanodiamonds have weak luminescence; they are toxic at higher dosages and very stable in living bodies (without available technique how to remove them). Studied CdSe...

Thesis is aimed at studying of magnetic iron oxide particles of submicron and nanoscale dimensions by means of nuclear magnetic resonance (NMR). 57 Fe NMR inves- tigations were carried out in composite bentonite/maghemite with respect to tempera- ture of calcination (Tcalc) during the sample preparation and in magnetite submicron powders with respect to various range of the particles size. One of the main findings is that increasing Tcalc improves resolution in the NMR spectra, which is most likely connected with higher degree of atomic ordering in the spinel structure. Evaluating the integral intensities of NMR spectra allowed us to determine the relative content of maghemite phase in particular samples of the series: the content rapidly grows for Tcalc up to ∼420 deg. An approach to distinguish signal from tetrahedral and octahedral irons was developed and tested on pure maghemite sample. Analysis based on vacancy- distribution models was performed in the spinel structure and the results were compared to the experiment. 57 Fe NMR spectra in submicron magnetite samples were found to differ markedly from spectrum of a single crystal. It was concluded that the investigated powders possess high amount of defects in the crystal structure or contain additional phase (probably closely related to the maghemite phase).

Silicon nanocrystals (SiNCs) of sizes below approximately 5 nm are a material with an efficient room-temperature photoluminescence (PL) and optical gain. Optical gain is a pre- requisite for obtaining stimulated emission from a pumped material, and the achievement of stimulated emission (and lasing) from Si-based nanostructures is of particular interest of the field of silicon photonics. The aim of this work was (i) to investigate fundamental optical properties of SiNCs, (ii) to design and prepare a photonic crystal with enhanced light ex- traction efficiency and (iii) to explore a possibility of enhancing optical gain of light-emitting SiNCs by combining them with a two-dimensional photonic crystal. First, free-standing oxide (SiOx/SiO2)-passivated SiNCs were prepared by electrochemical etching of a Si wafer. Their optical properties were studied by employing time-resolved spectroscopy, also at cryogenic temperatures. The fast blue-green emission band of these SiNCs was linked with the quasi- direct recombination of hot electrons and holes in the vicinity of the Γ-point. Furthermore, the spectral shift of the slow orange-red band (of these SiNCs) as a function of temperature was explained on the basis of an interplay between tensile strain and bulk Si temperature-induced indirect bandgap shift. The...

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.

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...

This diploma thesis deals with the design and optimization of the device for measurement of field emission from gallium nitride (GaN) nanocrystals surface. The first part of the thesis is the topic review, which contains the introduction to the problematics of field emissio focused on GaN. Then there were designed, constructed and optimized two versions of the device for the measurement of field emission. Through the optimization phase, the first successful test has been performed with zinc oxide (ZnO) nanowires. Simultaneously GaN nanocrystals were fabricated on the silicon substrate Si(111) with 2 nm of silicon dioxide SiO2 and also on the copper foil covered by graphene by molecular beam epitaxy (MBE). In the last chapter, there are presented the results of the measurement for emission of GaN nanocrystals. Finally, this study is comparing results with the current research in the area of field emission, which displays the improved characteristics for field emission of GaN nanocrystals on the copper foil covered by graphene.

Nanočástice perovskitů halogenidů kovů vykazují unikátní vlastnosti, především výjimečně vysoké hodnoty kvantových výtěžků fluorescence, které předurčují tyto materiály pro aplikace v optoelektronických a fotonických zařízeních. Tato práce popisuje přípravu nanočástic perovskitů halogenidů kovů pomocí stabilizačních činidel inspirovaných přírodou. Stabilizační činidla zde slouží nejen ke stabilizaci, ale i k modifikaci povrchu nanočástic za účelem zvýšení funkčnosti výsledných nanostruktur. Úvod práce popisuje optimalizaci přípravy nanočástic precipitační technikou za použití stabilizačních činidel; jako stabilizační činidlo byl zvolen adamantan-1-amin spolu s hexanovou kyselinou. Bylo prokázáno, že klíčový vliv na optické vlastnosti výsledných koloidních roztoků má volba rozpouštědel a teploty při precipitaci. Mimo jiné byl zkoumán vliv koncentrace prekurzorů na výslednou morfologii a optické vlastnosti nanočástic a jejich koloidních roztoků. V neposlední řadě byly nanočástice stabilizovány adamantan-1-aminem spolu s různými karboxylovými kyselinami a byly studovány optické vlastnosti a koloidní stabilita výsledných koloidních roztoků. V dalším kroku byly nanočástice perovskitů stabilizovány pomocí proetogenních aminokyselin L-lysinu and L-argininu. Takto stabilizované nanočástice vykazovaly úzká emisní spektra ve viditelné oblasti a kvantové výtěžky fluorescence dosahující hodnot téměř 100 %. Stabilizace nanočástic prostřednictvím postranních skupin aminokyselin byla prokázána navázáním chránící terc-butoxykarbonylové skupiny na -amino skupinu. Nanočástice stabilizované modifikovaným lysinem v průběhu jejich přípravy vykazovaly závislost optických vlastností na přítomnosti vody. Předpokládá se, že molekuly vody jsou schopné kontrolovat růst krystalové mřížky po navázání na prekurzory perovskitů a ovlivňovat tak výslednou velikost nanočástic, což vede k projevení kvantových jevů. Spojení nanočástic perovskitů s peptidy představuje nový typ materiálů kombinujících výjimečné optické vlastnosti se samoorganizačními a senzorickými vlastnostmi. Tento koncept byl představen přípravou nanočástic perovskitů stabilizovaných cyklo(RGDFK) pentapeptidem. Vzhledem k citlivosti peptidů na jejich byly nanočástice stabilizovány peptidovými nukleovými kyselinami, robustními analogy nukleových kyselin. Ke stabilizaci nanočástic byl připraven monomer a trimer peptidové nukleové kyseliny obsahující thymin jako dusíkatou bázi. Thymin byl na povrchu nanočástic dostupný k interakci s adeninem přes vodíkové můstky umožňující přenos náboje. Kombinace peptidových nukleových kyselin a perovskitů s unikátními optickými vlastnostmi otevírá aplikační možnosti zejména v oblasti optických senzorů.