In this report we establish cyclohexasilane (CHS) as a reliable precursor for non-thermal plasma synthesis of high quality photoluminescent silicon nanocrystals (SiNCs). We demonstrate that this synthesis approach can produce high quality, size tunable silicon quantum dots with quantum yields exceeding 60% as synthesized (subsequent work in our group has measured over 70% quantum yield after density gradient ultracentrifugation size purification).After a brief background on non-thermal plasma synthesis, the characterization methods used in this study, and an overview of CHS, we report at length on our development of the apparatus used, and our exploration of the controllable processing parameters of the synthesis method. We describe our successes and challenges with size tuning, sample collection, and passivation. Finally, we discuss preliminary studies we performed to identify promising future research areas. Novel reactor designs, blue light passivation, and magnetic confinement of plasma are described briefly to entice future researchers.

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The thesis is focused on the study of properties of GaN nanocrystals and Ga structures on the surface of silicon and graphene substrate. In the theoretical part of this thesis, the basic properties of Ga/GaN and graphene are described, as well as their applications or connection of both structures together in different devices. The ability of metal nanoparticles to enhance not only photoluminescence, due to the interaction of the material with surface plasmons, is also shown in several examples. The experimental part of the work first deals with the production and characterization of graphene sheets prepared by Chemical Vapor Deposition. Ga/GaN growth on both types of substrates was performed in a UHV chamber using an effusion cell for Ga deposition and an atomic ion source for nitridation. Prepared structures were characterized using various methods (XPS, SEM, AFM, Raman spectroscopy or photoluminescence). In the last step, GaN nanocrystals were coated with Ga islands to study the photoluminescence enhancement.

Title: Study of semiconductors by methods of time resolved laser spectroscopy: Luminescence spectroscopy of nanocrystalline diamond Author: Branislav Dzurňák Department: Department of Chemical Physics and Optics Supervisor: doc. RNDr. František Trojánek, Ph.D. Abstract: The PhD thesis is focused on optical properties of nanocrystalline diamond prepared by chemical vapour deposition method. Photoluminescence of nanocrystalline diamond samples and effects of ambient temperature, pressure, pH and UV irradiation on it are studied by laser spectroscopy. Results suggest the keyrole of water and air adsorbates which affect the energy states in the sub-bandgap region of diamond. Photoluminescence decay of samples of different surface termination and structure and its dependency on ambient pressure and temperature is studied by methods of ultrafast (picosecond and nanosecond scale) laser spectroscopy. Results are analysed by power-law decay function which fits well the luminescence decay curves and also describes the dynamics of charge carriers in states localised within the bandgap. The model of interaction of nanocrystalline diamond with air adsorbates is proposed. Non-linear optical properties of nanocrystalline diamond are also studied, namely the generation of second and third harmonic frequency. The thesis...

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...

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)

Aim of this work was, to investigate the preparation of Si NC memories by sputter deposition. The milestones are as follows: - Review of relevant literature. - Development of processes for an ultrathin tunnel-oxide and high quality sputtered SiO2 for use as control-oxide. - Evaluation of methods for the preparation of an oxygen-deficient silicon oxide inter-layer (the precursor of the Si NC layer). - Characterization of deposited films. - Establishment of techniques capable of probing the phase separation of SiOx and the formation of Si NC. - Establishment of annealing conditions compatible with the requirements of current CMOS technology based on experimental results and simulations of Si NC formation. - Preparation Si NC memory capacitors using the developed processes. - Characterization of these devices by suitable techniques. Demonstration of their memory functionality.

The application of silicon nanocrystals as non-toxic bio-labels and downconverters requires their uniform size distribution in order to minimize the inhomogeneous broadening of the photoluminescence peak. In this thesis, we set the basis for their size-separation via the density-gradient centrifugation method. To be more precise, we successfully apply this technique to separate 5 and 10 nm gold nanoparticles from an ensemble by using an engineered medium layer stack. In addition, we explain how atomic force microscopy is used to measure the size of the nanoparticles, with a particular attentionon the removal of unwanted solvent-related effects. As a future plan, we will implement the technique for the size-separation of silicon nanocrystals.

Silicon nanocrystals (SiNCs) are nanometer-sized semiconducting materials. Their small size endows them with unique photophysical properties. Efficient photoluminescence (PL) from silicon nanocrystal (SiNC) composites has important implications for emerging solar-energy collection technologies, yet a detailed understanding of PL relaxation in non-colloidal SiNCs is still materializing. In this dissertation, we examine the photophysical properties of silicon nanocrystal/off-stoichiometry thiol-ene composites (SiNCs/OSTE hybrids). The dissertation begins with an introduction to the photophysical properties of SiNCs, their photophysical properties, how SiNC/polymer composites are made, the various SiNC preparation techniques, and the most likely application areas for these nanocrystals. A description of experimental methods such as PL spectroscopy and transmission electron microscopy (TEM) follows, and SiNC/OSTE polymer preparation methods are then explained in detail. In the first study, TEM and photophysical characterization were performed on selected polydisperse SiNCs samples. These samples were synthesized in a nonthermal plasma reactor, using Si6H12 as precursor, and functionalized with R (where R is 1-dodecene). These SiNCs were dispersed in mesitylene:1-dodecene (5:1) as a colloid. Optical absorption, quantum efficiency, and PL lifetime of SiNCs were then investigated, as well as the relationship between quantum yield, lifetime, and PL peak. In the second study, we selected samples for size separation via the density gradient ultracentrifugation method (DGU). We successfully applied this technique to separate silicon nanocrystals with sizes from 2 nm to 4 nm from the ensemble samples using an engineered density medium layer stack, and photophysical characterization was performed on the DGU size–separated SiNCs. Lastly, we explored details of PL relaxation in photo-polymerized off-stoichiometric polymer/nanocrystal hybrids. We found time- and air-stable emission from dilute composites with up to 70% QY, and we investigated PL relaxation in the parameter space of nanocrystal size and temperature. In light of previous work, our results reveal similarities between the impacts of crosslinking and cooling to cryogenic temperature, but of which are characterized by a relative reduction in the available of phonons.

A wrinkling approach was used to study the mechanics of hybrid nanotube/nanocrystal coatings adhering to soft polymer (PDMS) substrates. We focused on three thicknesses: 10 nm, 30 nm, and 40 nm. The approach we used is the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIFMM) technique, which allows measurement of the SWCNT film mechanics by the buckling wavelength and the film thickness by inducing a compressive stress in the films at different strains; 2%, 4%, 6%, 8%, 10%, and 12%. In this thesis, dip-coating method with colloidal nanocrystals was used to enhance the rigidity of the carbon nanotube films by filling the pores of the nanotube network. Our results show an almost two-fold enhancement in the Young modulus of a thin SWCNT film related to the presence of a thin interpenetrating over-layer of the semiconductor nanocrystal.