Diploma thesis on Machining hardened steels is focused on the analysis of longitudinal turning of hardened steel 14 109 by using a tool from PKNB in terms of measuring the force load using a dynamometer and then evaluating the surface quality. The theoretical part deals with the issue of turning technology, cutting materials and heat treatment of steel. In the practical part, the influence of cutting conditions on the resulting values was assessed during the experiment. Twelve samples with different combinations of cutting conditions were tested, then was selected a sample that met the criterion of combining minimum cutting forces values and surface quality. The experiment shows that force load values can be achieved twice less by combining cutting conditions with an appropriate combination.

Strength and strain analysis of high pressure compound vessel, which is used to produce superhard materials (for example synthetic diamond). This work was elaborated to compare the stresses and strains calculated by Prof. Jan Vrbka making use of the FEM program ‘Prokop’17 years ago with those gained with the contemporary FEM Ansys program. The vessel is loaded by internal pressure of size 6 GPa. The elastic-plastic material be-haviour is taken into account. Real value of friction between rings and non-uniform temperature field is included into the calculation. The process of assembling the compound vessel is simulated step by step.

Diploma thesis is focused on the superhard cutting materials (polycrystalline diamond, polycrystalline boron nitride) and presents their physico-mechanical properties, production, efficient use, new trends. It assesses the range of cutting tool materials and individual front world producers in terms of optimum cutting conditions for turning operations and type of material to be machined. Further, these cutting materials are compared between different manufacturers to bring out thein differences in cutting conditions.

In this thesis, we investigate optical and electrical properties of dilute nitride semiconductors GaAsN in pulsed magnetic fields up to 62 T. For the most part, the experiments are performed at the Dresden High Magnetic Field Laboratory (HLD). In the first part of this thesis, the electron effective mass of GaAsN is determined with a direct method for the first time. Cyclotron resonance (CR) absorption spectroscopy is performed in Si-doped GaAsN epilayers with a nitrogen content up to 0.2%. For the CR absorption study, we use the combination of the free-electron laser FELBE and pulsed magnetic fields at the HLD, both located at the Helmholtz-Zentrum Dresden-Rossendorf. A slight increase of the CR electron effective mass with N content is obtained. This result is in excellent agreement with calculations based on the band anticrossing model and the empirical tight-binding method. We also find an increase of the band nonparabolicity with increasing N concentration in agreement with our calculations of the energy dependent momentum effective mass. In the second part of this thesis, the photoluminescence (PL) characteristics of intrinsic GaAsN and n-doped GaAsN:Si is studied. The PL of intrinsic and very dilute GaAsN is characterized by both GaAs-related transitions and N-induced features. These distinct peaks merge into a broad spectral band of localized excitons (LEs) when the N content is increased. This so-called LE-band exhibits a partially delocalized character because of overlapping exciton wave functions and an efficient interexcitonic population transfer. Merged spectra dominate the PL of all Si-doped GaAsN samples. They have contributions of free and localized excitons and are consequently blue-shifted with respect to LE-bands of intrinsic GaAsN. The highly merged PL profiles of GaAsN:Si are studied systematically for the first time with temperature-dependent time-resolved PL. The PL decay is predominantly monoexponential and has a strong energy dispersion. In comparison to formerly reported values of intrinsic GaAsN epilayers, the determined decay times of GaAsN:Si are reduced by a factor of 10 because of enhanced Shockley-Read-Hall and possibly Auger recombinations. In the third part of this thesis, intrinsic and Si-doped GaAsN are investigated with magneto-PL in fields up to 62 T. A magneto-PL setup for pulsed magnetic fields of the HLD was built for this purpose. The blue-shift of LE-bands is studied in high magnetic fields in order to investigate its delocalized character. The blue-shift is diminished in intrinsic GaAsN at higher temperatures, which indicates that the interexcitonic population transfer is only active below a critical temperature 20 K < T < 50 K. A similar increase of the temperature has no significant impact on the partially delocalized character of the merged spectral band of GaAsN:Si. We conclude that the interexcitonic transfer of Si-doped GaAsN is more complex than in undoped GaAsN. In order to determine reduced masses of undoped GaAsN and GaAs:Si, the field-induced shift of the free exciton transition is studied in the high-field limit. We find an excellent agreement of GaAs:Si with a formerly published value of intrinsic GaAs which was determined with the same method. In both cases, the reduced mass values are enhanced by 20% in comparison to the accepted reduced mass values of GaAs. The determined GaAsN masses are 1.5 times larger than in GaAs:Si and match the rising trend of formerly reported electron effective masses of GaAsN.

In der vorliegenden Arbeit werden verschiedene Aspekte des Einflusses von Lokalisation, Unordnung und Polarisationsfeldern auf Elektron-Loch Zustände in Quantengräben (QWs von engl. quantum wells) aus Halbleitern mit großer Bandlücke theoretisch untersucht. Unter Verwendung eines Schwerpunktseparationsansatzes wird das Verhalten von QW Exzitonen und Biexzitonen im Grenzfall schwacher Lokalisation beschrieben. Es zeigt sich, daß die Lokalisationsenergie des Biexzitons mehr als doppelt so groß ist wie die des Exzitons. Dies wird verursacht durch ein universelles Gesetz der Lokalisation in schwachen zwei-dimensionalen Potentialen, welches lediglich durch das "Potentialvolumen" und die Masse des lokalisierten Teilchens bestimmt wird. Ein einfaches Modell des QW Biexzitons wird entwickelt, dessen Ergebnisse gut mit jenen übereinstimmen, die man mit Hilfe eines aufwendigeren numerischen Modells erhält. Der Grenzfall starker Lokalisation von QW Exzitonen und höheren Exzitonenkomplexen wird mittels einer Dichtefunktionalrechnung untersucht. Es wird gezeigt, daß Zustände bis mindestens zum X4 in den nm-großen Potentialminima lokalisieren können, die durch Phasenseparation in (In,Ga)N/GaN QWs enstehen. Es wird das Übergangsspektrum des sukzessiven Zerfalls eines lokalisierten X4 berechnet. Auf Grundlage der selbstkonsistenten Lösung von Poisson- und Schrödinger-Gleichung wird der Einfluß des Probendesigns von (In,Ga)N/GaN QW-Strukturen auf den makroskopischen Verlauf des Polarisationsfeldes in Wachstumsrichtung und somit auf optische Übergangsenergie und Oszillatorstärke systematisch untersucht. Besondere Bedeutung kommt dabei der Abschirmung der Felder durch Raumladungszonen zu. Es wird gezeigt, daß die Position des QW bezüglich einer ausgedehnten Oberflächen-Verarmungszone - die in n-dotierten, Ga-polarisierten Proben auftritt - erheblichen Einfluß auf Übergangsenergie und Oszillatorstärke hat. Durch die räumliche Variation der Polarisationsfeldstärke in dieser Verarmungszone kann das optische Übergangsspektrum eines Mehrfach-QW Schultern oder mehrere Maxima aufweisen. Indium Oberflächen-Segregation ruft eine Blauverschiebung der Übergangsenergie hervor, die bis zu einem Drittel der vom Polarisationsfeld verursachten quantum confined Stark-Verschiebung kompensiert. Diese Blauverschiebung wird von einer Verringerung des Elektron-Loch Überlapps begleitet. Die Polarisationsfelder in (In,Ga)N/GaN Mehrfach-QWs verschmieren das stufenförmige Einteilchen-Absorptionsspektrum. Durch die Aufhebung der näherungsweisen Diagonalität von Inter-Subband Übergängen und durch die Miniband-Dispersion in höheren, gekoppelten Zuständen haben diese Felder, neben dem Beitrag von Potentialfluktuationen, einen entscheidenden Einfluß auf die Form des Absorptionsspektrums. Ein in der Literatur diskutierter Mechanismus, der allein durch Polarisationsfelder eine Verbreiterung optischer Spektren hervorruft, kann nicht bestätigt werden. Unter Annahme einer unkorrelierten Zusammensetzung von (In,Ga)N und einer lateral korrelierten Grenzflächenrauhigkeit von einer Monolage in jeder Grenzfläche zeigt die spektrale Breite des Exzitonen-Schwerpunktpotentials eine Verschmälerung mit zunehmendem Feld. Diese wird verursacht durch das Eindringen der Teilchen in die binären Barrieren und durch ein vergrößertes Exzitonenvolumen. Im Fall einer langreichweitigen Grenzfächenrauhigkeit findet man eine Aufspaltung des Spektrums in einzelne Linien. / In this thesis, various aspects of the influence of localization, disorder, and polarization fields on electron-hole states in wide-gap semiconductor quantum wells (QWs) are investigated theoretically. A theoretical treatment of quantum well exciton and biexciton states in the limit of weak localization is presented, using a center-of-mass separation ansatz. It shows that the localization energy of the biexciton is more than twice as large as that of the exciton due to the universal behaviour of localization in weak two-dimensional potentials which is ruled only by the potential "volume" and the mass of the localized particle. A useful simple model of the QW biexciton wavefunction is developed which provides good agreement with the results obtained with an extensive numerical solution. The limit of strong localization of QW excitons and higher exciton complexes is investigated with a density functional calculation. It is demonstrated that states at least up to X4 may localize in nm-scale potential boxes caused by indium phase separation in (In,Ga)N/GaN QWs. The transition spectrum of the successive recombination of a localized X4 is calculated. A systematic investigation of the influence of the sample design of (In,Ga)N/GaN QW structures on optical transition energy and oscillator strength reveals the importance of space charge layers with regard to screening of polarization fields along the QW-axis. Based on a self-consistent solution of the Schrödinger-Poisson equations, the overall situation of the macroscopic spontaneous and piezoelectric polarization fields is discussed in dependence on various substantial sample parameters. It is found that the position of a QW in the sample with respect to an extended surface depletion layer - which is shown to exist in n-type Ga-face grown material - severely affects transition energy and electron-hole overlap. Due to the spatial variation of the field strength in this surface depletion layer, the optical transition spectrum of a Ga-face grown multiple-QW can display shoulders or even a multiple-peak structure. Indium surface segregation results in a blueshift of the transition energy compensating up to one third of the quantum confined Stark shift produced by the polarization field. This blueshift is accompanied by a decrease of the electron-hole overlap. Polarization fields in (In,Ga)N/GaN multiple-QWs result in a smoothing of the step-like single-particle absorption spectrum. Apart from the contribution of compositional fluctuations, the fields have significant influence on the shape of the spectrum via the abrogation of the nearly diagonality of inter-subband transitions and via the mini-band dispersion of higher coupled states in case of a periodic structure. A line broadening-mechanism due to polarization fields in (In,Ga)N/GaN QWs, as sometimes discussed in literature, could not be confirmed. Assuming uncorrelated (In,Ga)N alloy and in-plane-correlated interface roughness of one monolayer in each interface, the calculation of the spectral width of the QW exciton center-of-mass potential yields a narrowing with increasing average field. This is a result of the penetration of the carriers into the barriers and of an increasing exciton volume. In case of a long-range interface roughness, a splitting of the spectrum into individual lines can be predicted.

Le nitrure de silicium est largement utilisé dans l’industrie verrière au sein d’empilements de couches minces permettant de fonctionnaliser le vitrage. Le dépôt de ces couches est réalisé par pulvérisation cathodique magnétron sur une large gamme de surfaces. Cette technique de dépôt génère cependant des pores nanométriques dans ces couches amorphes au détriment de la durabilité des produits au sein desquels elles sont employées. Cette thèse de doctorat présente le développement d’une approche multi-échelles de la caractérisation de cette nano-porosité en se basant sur l’association de deux techniques : la Microscopie Electronique en Transmission (TEM/STEM) et la Spectroscopie d’Impédance Electrochimique (EIS). Cette démarche est appliquée à l’étude de couches de nitrure de silicium de différentes épaisseurs. Par ailleurs, l’impact de certains paramètres comme la pression de dépôt, la pression partielle en azote ou encore la nature de la sous-couche de croissance a été investigué.La nano-porosité de ces couches est fortement dépendante des conditions de dépôt utilisées : la pression et l’épaisseur semblent déterminantes sur leur nanostructure. Dans la plupart des cas la morphologie de ces couches de nitrure de silicium se divisent en deux principales zones dans l’épaisseur : une couche homogène proche du substrat et une structure colonnaire occupant la partie supérieure de la couche. Une description quantitative de la porosité de cette zone colonnaire est proposée et comprend l’estimation du diamètre et de la densité des pores, l’évolution de leur morphologie dans l’épaisseur, leur percolation, ou encore la surface accessible en fond des pores traversant la couche. / Silicon nitride is widely used in glass industry embedded in stacks of thin layers applied to functionalize glass for thermal, optical (antireflection) or self-cleaning applications. The deposition of these layers is made by magnetron sputtering on large surfaces with a great versatility. However, nanometric pores can be produced in these amorphous layers deposited with this technique which is detrimental for the durability of the products containing theses layers. This PhD thesis presents the development of a multiscale approach in order to characterize this nano-porosity combining two techniques: Transmission Electron Microscopy (TEM/STEM) and Electrochemical Impedance Spectroscopy (EIS). This analysis route is applied to study silicon nitride layers of different thicknesses. Furthermore, the impact of several parameters like the deposition pressure, the nitrogen partial pressure or the nature of the seed layer has been investigated.The nano-porosity of these layers is strongly dependent on the deposition conditions: pressure and thickness seem to be crucial for their nanostructure. For most of the cases, the morphology of this silicon nitride layer is divided in two main areas: a homogeneous area near the substrate and a columnar structure in the upper part of the layer. A quantitative description of the columnar area porosity is proposed and includes the estimation of the pores diameter and density, their change in morphology with the layer thickness, their percolation and the substrate accessible surface at the bottom of the through pores.

Polystyrene block polyethyleneimine (PS-b-PEI) copolymer prepared by combining PS and poly(2-methyl-2-oxazoline) (PMeOx) segments together through two strategies. Furthermore, PMeOx block was hydrolysis to produce PEI block which linked with PS block. Macroinitiator route is one of these two ways to prepare PS-b-PEI copolymer. Polystyrene macroinitiator or poly(2-methyl-2-oxazoline) macroinitiator prepared through Nitroxide Mediate Radical Polymerization (NMRP) or Cationic Ring Opening Polymerization (CROP) respectively. Each macroinitiator has active initiated terminal group toward another block monomer. Second strategy based on coupling of PS segment with PMeOx block through “click” coupling chemistry. Polystyrene modified with terminal azide moiety are combined with PMeOx functionalized with alkyne group via 1,3 dipolar cycloaddition reaction “click reaction”. PS-b-PMeOx was hydrolysis in alkaline medium to produce amphiphilic PS-b-PEI copolymer. A set of block copolymer with different block ratios was prepared and investigated to select suitable block copolymer for further applications. Stichiometric PS-b-PEI copolymer selected to stabilize gold nanoparticle (Au NPs) in polymer matrix. PEI segment work as reducing and stabilizing agent of gold precursor in aqueous solution. Various concentrations of gold precursor were loaded and its effect on UVVIS absorbance, particle size and particle distribution studied. In addition, reduction efficiency of PEI block was determined from XPS measurements. The thickness of Au NPs/PS-b-PEI thin film was determined with a novel model for composite system. On the other hand, Gallium nitride quantum dots (GaN QDs) stabilized in PS-b-PEI copolymer after annealing. Our amphiphilic block copolymer exhibit nice thermal stability under annealing conditions. GaN QDs prepared in narrow nano-size with fine particle distribution. Blue ray was observed as an indication to emission activity of GaN crystal. Over all, PS-b-PEI copolymer synthesized through macroinitiator and click coupling methods. It was successfully stabilized Au NPs and GaN QDs in polymer matrix with controlled particle size which can be post applied in tremendous industrial and researcher fields.

Real structure of heteroepitaxial GaN and AlGaN layers is studied by diffuse x-ray scattering. A new developed method based on Monte Carlo simulation enabling to determine densities of threading dislocations in c-plane GaN and stacking faults in a-plane GaN is presented. The results of Monte Carlo simulations are compared with ones obtained by use of other conventional techniques. The advantages and limitations of the new method are discussed in detail. The methods accuracy is estimated as about 15%. We have shown that our method is a reliable tool for threading dislocations and stacking faults densities determination.

Práce je zaměřena na výzkum nové struktury umožňující charakterizaci fyzikálních vlastností grafenu při přesně řízených podmínkách. Návrh spojuje MEMS piezoelektrický rezonátor spolu s Hall Bar/FET strukturou. Tento přístup umožňuje měnit vlastnosti grafenu odděleně nebo společně dvěma metodami. Mechanický způsob je založen na relativní deformaci způsobené rezonátorem, na kterém je umístěna grafenová monovrstva. Navrhovaná struktura umožňuje měřit vlastnosti grafenu vyvolané pouze změnou mechanického pnutí a frekvencí nucených kmitů bez vlivu vnějšího elektrického pole. Druhý přístup přidává možnost ovládat fyzikální vlastnosti grafenu pomocí elektrického pole FET struktury. Tato technika využívá grafenovou monovrstvu jako laditelný sensor pro molekulární detekci. Měření koncentrace v jednotkách ppb není konstrukčně ničím limitováno. Realizované frekvenčně laditelné piezoelektrické MEMS rezonátory s monovrstvou grafenu budou využitelné v mnoha oblastech pro detekci na molekulové úrovni. Výsledné struktury budou vyrobeny v souladu s požadavky na bio- a CMOS kompatibilitu.

This master’s thesis deals with the design and realization of a functional sample power inverter for an electric compressor, which is used in hybrid cars. The electric compressor powered by the inverter is E-compressor by Garrett Advancing Motion. An inverter will be using modern High Electron Mobility Transistors which are based on gallium nitride (GaN). The purpose of this thesis is to find if GaN transistors can be used in E-boosting application.