In der vorliegenden Arbeit wurde die Verwendung der kostengünstigen aber sauerstoffaffinen Legierungselemente Mangan, Silizium und Chrom in pulvermetallurgisch hergestellten Sinterstählen untersucht. Das Einbringen der Legierungselemente erfolgte mit Hilfe unterschiedlicher Masteralloysysteme. In der vorliegenden Arbeit wurden insgesamt 18 chemisch unterschiedliche, niedriglegierte Sinterstähle entwickelt und untersucht.

The work described herein deals with the synthesis and characterization of lead chalcogenide thin films and nanocrystals. The first part of thesis describes the properties of semiconductors followed by an analysis on the chemical vapour deposition and nanoparticulate formation. In the next part of thesis, single-source precursors of type thioselenophosphinato, selenoureato, dithiocarbamato and dithiocarbanato complexes of lead have been synthesised and characterised. As-synthesised compounds have been utilised for the fabrication of lead sulfide and lead selenide thin films by aerosol-assisted chemical vapour deposition as well as nanocrystals by colloidal injection method. Lead sulfide thin films were also deposited by liquid-liquid interface from lead dithiocarbanato at room temperature. The as grown thin films of lead sulfide and lead selenide have been characterised by XRD, SEM and energy dispersive x-ray (EDX) analysis. In the second part of the thesis, preparation of lead sulfide and lead selenide nanocrystals in olive oil at low growth temperatures (50-60°C) is described and have shown that by controlling experimental conditions, well-defined particles with tunable emission in mid and far-infrared region can be synthesised. Furthermore, compositionally-tuned PbSxSe1-x nanocrystals has also been prepared by adding controlled amount of sulur and selenium ingredients into lead oxide. Homogenous distribution of sulfur and selenium within alloyed nanocrystals is confirmed by transmission electron microscope studies. Moreover, attempts have been made to prepare quaternary (PbTe/Se/S) nanocrystals of lead chalcogenides and depth (1.9-5.8 nm) profile analysis by x-ray photoelectron spectroscopy confirmed the formation of core/shell/shell type structure i.e. PbTe/S/Se.

Design of flat pallet for automatic parking garage. Parking and description of automatic parking systems. Welding and weldability of materials. Electric arc welding and welding by melting electrode in protective gas by MIG/MAG method, welding instruments. Design of parking palette calculation and calculation this palette by MKP method. Process of drawing documentation for parking palette. Design of welding process and WPS. Description of annealing and zinc coating. Economic-technical analysis of palette for automatic parking system production.

In der vorliegenden Arbeit wurde die Verwendung der kostengünstigen aber sauerstoffaffinen Legierungselemente Mangan, Silizium und Chrom in pulvermetallurgisch hergestellten Sinterstählen untersucht. Das Einbringen der Legierungselemente erfolgte mit Hilfe unterschiedlicher Masteralloysysteme. In der vorliegenden Arbeit wurden insgesamt 18 chemisch unterschiedliche, niedriglegierte Sinterstähle entwickelt und untersucht.

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Metal nanoparticles have recently gained popularity in many research areas due to their nanosize-related properties. Depending on the size of the metal nanoparticle, their mode of interaction with electromagnetic radiation and the outcome of this interaction vary; in turn the effect exerted on a protein which is conjugated to a nanoparticle varies, because different sized nanoparticles demonstrate different modes of energy transfer with electromagnetic radiation and molecules conjugated to them. Very small cluster with sizes around 1 – 1.2 nm tend to get excited by incident light and emit fluorescence, whereas larger nanoparticles absorb the incoming light very strongly due to their LSPR. In this study we observed the outcomes of the interaction between two types of nanoparticles, namely gold and gold/silver alloyed nanoparticles with the fluorescence emission of two fluorophores, namely eGFP and rPhiYFP; and demonstrated a bioassay where the fluorescence modulation by gold nanoparticles can be used as the sensing strategy. Lastly, we demonstrated the potential of autofluorescent gold nanoparticles as intracellular reporters.

Electronic and optical properties of semiconducting nanocrystals, that can be engineered and manipulated by various ways like varying size, shape, composition, structure, has been a subject of intense research for more than last two decades. The size dependency of these properties in semiconductor nanocrystals is direct manifestation of the quantum confinement effect. Study of electronic and optical properties in smaller dimensions provides a platform to understand the evolution of fundamental bulk properties in the semiconductors, often leading to realization and exploration of entirely new and novel properties. Not only of fundamental interests, the semiconductor nanocrystals are also shown to have great technological implications in diverse areas. Besides size tunable properties, introduction of impurities, like transition metal ions, gives rise to new functionalities in the semicon-ductor nanocrystals. These materials, termed as doped semiconductor nanocrystals, have been the subject of great interest, mainly due to the their interesting optical properties. Among different transition metal doped semiconductor nanocrystals, manganese doped systems have drawn a lot on attention due to their certain advantages over other dopants. One of the major advantages of Mn doped semiconductor nanocrystals is that they do not suffer from the problem of self-absorption of emission, which quite often, is consid-ered detrimental in their undoped counterparts. The doped nanocrystals are known to produce a characteristic yellow-orange emission upon photoexcitation of the host that is relatively insensitive to the surface degradation of the host. This emission, originating from an atomic d-d transition of Mn2+ ions, has been a subject of extensive research in the recent past. In spite of the spin forbidden nature of the specific d-d transition, namely 6A1 −4 T1, these doped nanocrystals yield intense phosphorescence. However, one major drawback of utilizing this system for a wide range application has been the substantial inability of the community to tune the emission color of Mn-doped systems in spite of an intense effort over the years; the relative constancy of the emission color in these systems has been attributed to the essentially atomic nature of the optical transition involving localized Mn d levels. Interestingly, however, the Mn emission has a very broad spectral line-width in spite of its atomic-like origin. While the long (∼ 1 ms) emission life-time of the de-excitation process is well-studied and understood in terms of the spin and orbitally forbidden nature of the transition, there is little known concerning the process of energy transfer to the Mn from the host in the excitation step. In this thesis, we have studied the ultrafast dynamic processes involved in Mn emission and addressed the issues related to its tunability and spectral purity. Chapter 1 provides a brief introduction to the fundamental concepts relevant to the studies carried out in the subsequent chapters of this thesis. This chapter is started with a small preview of the nanomaterials in general, followed by a discussion on semiconducting nanomaterials, evolution of their electronic structure with dimensions and size as well as the effect of quantum confinement on their optical properties. As all the semiconducting nanomaterials studied in the thesis are synthesized via colloidal synthesis routes, a separate section is devoted on colloidal semiconducting nanomaterials, describing various ways of modifying or tuning their optical properties. This is followed by an introduction to the important class of materials “doped semiconductor nanocrystals”. With a general overview and brief history of these materials, we proceed to discuss about various aspects of manganese doped semiconductor nanocrystals in great details, highlighting the origin of the manganese emission and the associated carrier dynamics as well as different reported synthetic strategies to prepare these materials. The chapter is closed with the open questions related to manganese doped semiconductor nanocrystals and the scope of the present work. Chapter 2 describes different experimental and theoretical methods that have been employed to carry out different studies presented in the thesis. It includes common experimental techniques like UV-Vis absorption spectroscopy, steady-state and time-resolved photoluminescence spectroscopy used for optical measurements, X-ray diffraction, trans-mission electron microscopy and atomic absorption spectroscopy used for structural and elemental analysis. Experimental tools to perform special studies like transient absorption and single nanocrystal spectroscopy are also discussed. Finally, theoretical fitting method used to analyse various spectral data has been discussed briefly. Chapter 3 deals with the dynamic processes involved in the photoexcitation and emission in manganese doped semiconductor nanocrystals. For this study, Mn doped ZnCdS alloyed nanocrystal has been chosen as a model system. There are various radiative and nonrdiative recombination pathways of the photogenerated carriers and they often compete with each other. We have studied the dynamics of all possible pathways of carrier relaxation, viz. excitonic recombination, surface state emission and Mn d-d transition. The main highlight of this chapter is the determination of the time-scale to populate surface states and the Mn d-states after the photoexcitation of the host. Employing femtosecond pump-probe based transient absorption study we have shown that the Mn dopant states are populated within sub-picosecond of the host excitation, while it takes a few picoseconds to populate the surface states. Keeping in mind the typical life-time of the excitonic emission (∼ a few ns), the ultra-fast process of energy transfer from the host to the Mn ions explains why the presence of Mn dopant ions quenches the excitonic as well as the surface state emissions so efficiently. Chapter 4 presents a study of manganese emission in ZnS nanocrystals of different sizes. By varying the size of the ZnS host nanocrystal, we show that one can tune the Mn emission over a limited range. In particular, with a decrease in host size, the Mn emission has been observed to red-shift. We have attributed this shift in Mn emission to the change in the ratio of surface to bulk dopant ions with the variation of the host size, noting that the strength of the ligand field at the Mn site should depend on the position of the Mn ion relative to the surface due to a systematic lattice relaxation in such nanocrystals. The ligand field affects the emission wavelength directly by controlling the splitting of the t2 and e levels of Mn2+ ions. The surface dopant ions experience a strong ligand field due to distorted tetrahedral environment which leads to larger splitting of these t2 and e states. We further corroborated these results by performing doping concentration dependent emission and life-time studies. In Chapter 5 addresses two fundamental challenges related to manganese photolumines-cence, namely the lack of a substantial emission tunability and presence of a very broad spectral width (∼ 180-270 meV). The large spectral width is incompatible with atomic-like manganese 4T1 −6 A1 transition. On the other hand, if this emission is atomic in nature, it should be relatively unaffected by the nature of the host, though it can be manipulated to some extent as discussed in Chapter 3. The lack of Mn emission tunability and spectral purity together seriously limit the usefulness of Mn doped semiconductor nanocrystals. To understand why the Mn emission tunability range is very limited (typically 565-630 nm) and to understand the true nature of this emission, we carried out single nanocrystal imaging and spectroscopy on Mn doped ZnCdS alloyed nanocrystals. This study reveals that Mn emission, in fact, can vary over a much wider range (∼ 370 meV) and exhibits widths substantially lower (∼ 60-75 meV) than reported so far. We explained the occur-rence of Mn emission in this broad spectral range in terms of the possibility of a large number of symmetry inequivalent sites resulting from random substitution of Cd and Zn ions that leads to differing extent of ligand field contributions towards the splitting of Mn d-levels. The broad Mn emission observed in ensemble-averaged measurements is the result of contribution from Mn ions at different sites of varying ligand field strengths inside the NC. Chapter 6 presents a synthetic strategy to strain-engineer a nanocrystal host lattice for a controlled tuning of the ligand field effect of the doped Mn sites. It is realized synthesizing a strained quantum dot system with the structure ZnSe/CdSe/ZnSe. A larger lattice parameter of CdSe compared to that of ZnSe causes a strain field that is maximum near the interface, gradually decreasing towards the surface. We control the positioning of Mn dopant ions at different distances from the interface, thereby doping Mn at different predetermined strain fields. With the help of this strain engineering, we are able to tune Mn emission across the entire range of the visible spectrum. This strain induced tuning of Mn emission is accompanied by life-times that is dependent on the emission energy which has been explained in terms of perturbation effect on the Mn center due to the strain generated inside the quantum dot. The spectacular emission tuning has been explained by modelling the quantum dot system as an elastic continuum containing three distinct layers under hydrostatic pressure. From this modelling, we found that the strain is max-imum at the interface and decreases continuously as one goes away from the interface. We also show that the Mn emission maximum red shifts with increasing distance of the dopants from the maximum strained region. In summary, we have performed a study on the photophysical processes in manganese doped semiconductor nanocrystals. We have emphasized in understanding of different dynamic processes associated with the manganese emission and tried to understand the true nature of manganese emission in a nanocrystal. This study has brought out some new aspects of manganese emission and opened up possibilities to tune and control manganese emission by proper design of the host material.

Metal nanoparticles have recently gained popularity in many research areas due to their nanosize-related properties. Depending on the size of the metal nanoparticle, their mode of interaction with electromagnetic radiation and the outcome of this interaction vary; in turn the effect exerted on a protein which is conjugated to a nanoparticle varies, because different sized nanoparticles demonstrate different modes of energy transfer with electromagnetic radiation and molecules conjugated to them. Very small cluster with sizes around 1 – 1.2 nm tend to get excited by incident light and emit fluorescence, whereas larger nanoparticles absorb the incoming light very strongly due to their LSPR. In this study we observed the outcomes of the interaction between two types of nanoparticles, namely gold and gold/silver alloyed nanoparticles with the fluorescence emission of two fluorophores, namely eGFP and rPhiYFP; and demonstrated a bioassay where the fluorescence modulation by gold nanoparticles can be used as the sensing strategy. Lastly, we demonstrated the potential of autofluorescent gold nanoparticles as intracellular reporters.

Представлен литературный обзор в области свойств сплавов из сложнолегированных латуней и заготовок из них. В экспериментальной части работы представлены результаты исследований, направленных на изучение механических свойств сложнолегированной латуни CuZnMnAlSiNiCr в горячепрессованном состоянии. Выполнена статистическая обработка результатов измерений. Наблюдается значительная дисперсия механических свойств, что объяснено сложностью химического состава, фазового и структурного состояния сплава. Обнаружено проявление анизотропии. / A literature review is given in the field of properties of alloys from complex-alloyed brasses and blanks from them. The experimental part of the paper presents the results of studies aimed at studying the mechanical properties of complex-alloyed brass CuZn30Al2Mn3SiNiCr in the hot-extruded state. Statistical processing of measurement results is performed. A significant dispersion of mechanical properties is observed, which is explained by the complexity of the chemical composition, phase and structural state of the alloy. Anisotropy is observed.

Investigations on size dependent phase stability and transformations in isolated nanoparticles have gained momentum in recent times. Size dependent phase stability generates size specific particle microstructure which consequently yields size specific functionality. One important prerequisite for conducting studies on nanoparticles is their synthesis. A substantial amount of research effort has therefore been focused on devising methodologies for synthesizing nanoparticles with controlled shapes and sizes. The present thesis deals with both these two aspects: (a) synthesis of nanoparticles and (b) phase transformations in nanoparticles. The system chosen in this study is AuCu intermetallic nanoparticles. The choice of AuCu nanoparticle was due to the fact that the literature contains abundance of structural and thermodynamic data on Au–Cu system which makes it a model system for investigating size dependence of phase transformations. With respect to synthesis, the present thesis provides methodologies for synthesizing alloyed Au–Cu nanoparticles of different sizes, Au–Cu nano-chain network structures and uniform Au–Cu2S hybrid nanoparticles. For every type, results are obtained from a detailed investigation of their formation mechanisms which are also presented in the thesis. With respect to phase transformation, the thesis presents results on the size dependence of fcc to L10 transformation onset in Au–Cu nanoparticles under isothermal annealing conditions. The present thesis is divided into eight chapters. A summary of results and key conclusions of work presented in each chapter are as follows. The ‘introduction’ chapter (chapter I) describes the organization of the thesis. Chapter II (literature study) presents a review of the research work reported in the literature on the various methodologies used for synthesizing Au–Cu based nanoparticles of different shapes and sizes and on ordering transformation in AuCu nanoparticles. The chapter also presents a brief discussion on the reaction variables that control the process of nucleation and growth of the nanoparticles in solution. Chapter III titled ‘experimental details and instrumentation’ describes the synthesis procedures that were used for producing various nanoparticles in the present work. The chapter also briefly describes the various characterization techniques that were used to investigate the nanoparticles. The fourth chapter titled ‘synthesis and mechanistic study of different sizes of AuCu nanoparticles’ provides two different methodologies for synthesis, referred as ‘two-stage process’ and ‘two-step process’ that have been used for producing alloyed AuCu nanoparticles of different sizes (5, 7, 10, 14, 17, 25 nm). The ‘two-stage’ process involved sequential reduction of Au and Cu precursors in a one pot synthesis process. Whereas, the ‘two-step’ process involved a two-pot synthesis in which separately synthesized Au nanoparticles were coated with Cu to generate alloyed AuCu nanoparticles. In the two-stage synthesis process it was observed that by changing the total surfactant-to-metal precursor molar ratio, sizes of the alloyed AuCu nanoparticles can be varied. ‘Total surfactants’ here include equal molar amounts of oleic acid and oleylamine surfactants. Interestingly, it was observed that there exists a limitation with respect to the minimum nanoparticle size that can be achieved by using the two-stage process. The minimum AuCu nanoparticle size achieved using the two-stage synthesis process was 14 nm. Mechanism of formation of AuCu nanoparticles in the two-stage synthesis process was investigated to find out the reason for this size limitation and also to determine how the synthesis process can be engineered to synthesize alloyed AuCu nanoparticles with smaller (<14nm) sizes. Studies to evaluate mechanism of synthesis were conducted by investigating phase and size of nanoparticles present in the reaction mixture extracted at various stages of the synthesis process. Their studies revealed that (a) the nanoparticle formation mechanism in the two-stage synthesis process involves initial formation of Au nanoparticles followed by a heterogeneous nucleation and diffusion of Cu atoms into these Au rich seeds to form Au–Cu intermetallic nanoparticles and (b) by increasing the relative molar amount of the oleylamine surfactant, size of the initial Au seed nanoparticles can be further reduced from the minimum size that can be achieved in the case when equal molar amounts of oleylamine and oleic acid surfactants are used. The information obtained from the mechanistic study was then utilized to design the two-step synthesis process. In the two-step process, Au nanoparticles were synthesized in a reaction mixture containing only the oleylamine surfactant. Use of only oleylamine resulted in production of pure Au nanoparticles with sizes that were well below 10 nm. These Au nanoparticles were washed and dispersed in a solution containing Cu precursor. Introduction of a reducing agent into this reaction mixture led to the heterogeneous nucleation of Cu onto the Au seed particles and their subsequent diffusion into them to form alloyed AuCu nanoparticles with sizes of ~5, 7 and 10 nm. The study present in this chapter essentially signified that the surfactants used in the reaction mixture not only prevent nanoparticles from agglomerating in the final dispersion but also control their nucleation and growth and therefore can be used as a tool to tune nanoparticle sizes. The fifth chapter titled ‘size dependent onset of FCC-to-L10 transformations in AuCu alloy nanoparticles’ illustrates the effect of AuCu nanoparticle size on the onset of ordering under isothermal annealing conditions. Nanoparticles in this study were annealed in-situ in a transmission electron microscope. Samples were prepared by drop drying a highly dilute dispersion of as-synthesized nanoparticles onto an electron transparent TEM grid. Nanoparticles sitting on the TEM grid were well separated from each other to minimize particle sintering during the annealing operation. It was however observed that during the isothermal annealing, particle coarsening due to atomic diffusion was appreciable for 5 nm particles but negligible for 7 and 10 nm particles. Therefore for this study only 7 nm and 10 nm sized particles were considered. Onset of ordering was determined from the time when first sign of the diffraction spot, corresponding to the ordered phase, appears in the selected area electron diffraction pattern from a region containing large number of AuCu nanoparticles. Through a series of isothermal experiments it was observed that the time for onset of ordering increased with decrease in size of the nanoparticles. It is speculated that the delay in onset of ordering may be due to the fact that with a decrease in nanoparticle size the probability of a nanoparticle containing a fluctuation that shall generate a thermodynamically stable nuclei of the ordered phase decreases. A sharp interface between the ordered and the disordered phase inside the particle was also observed which suggested that the ordering transformation in as-synthesized fcc AuCu nanoparticles is a first order transformation. The sixth chapter titled ‘synthesis and characterization of Au1-xCux–Cu2S hybrid nanostructures: morphology control by reaction engineering’ provides a modified polyol method based synthesis strategy for producing uniform Au–Cu2S hybrid nanoparticles. Detailed compositional and structural characterization revealed that the hybrid nanoparticles are composed of cube shaped Au-rich, Au–Cu solid solution phase and hemispherical shaped Cu2S phase. Interestingly, the hemispherical Cu2S phase was attached to only one facet of the cube shaped phase. A study on the formation mechanism of hybrid nanoparticles was also conducted by characterizing specimens extracted from the reaction mixture at different stages of the synthesis process. The study revealed that the mechanism of formation of hybrid nanoparticles involved initial formation of isolated cube shaped pure Au nanoparticles and Cu–thiolate complex with a sheet morphology. With increase in time at 180°C, the Cu–thiolate complex decomposed and one part of the Cu atoms that were produced from the decomposition were utilized in forming the spherical Cu2S and other part diffused into the Au nanoparticles to form Au–Cu solid solution phase. The chapter also presents a study on the effect of dodecanethiol (DDT) on achieving the hemisphere-on-cube hybrid morphology. In this study it is illustrated that an optimum concentration of dodecanethiol is required both for achieving size and morphological uniformity of the participating phases and for their attachment to form a hybrid nanoparticle. The seventh chapter titled ‘synthesis of Au–Cu nano-chains network and effect of temperature on morphological evolution’ provides methodology for synthesizing fcc Au– Cu nano-chain network structures using polyvinylprrolidone (PVP) surfactant. It was observed that with increase in the molar amount of PVP in the reaction mixture, morphology of the as-synthesized product gradually changed from isolated nanoparticles to branched nano-chain like. The nano-chains contained twins which indicated an absence of continuous growth and possibility of growth by oriented attachment of initially formed Au–Cu nanoparticles. Both in-situ and ex-situ annealing of the nano-chains led to their decomposition into isolated nanoparticles of varying sizes. Annealing also caused fcc-to¬L10 phase transformation. Investigation of the wave length of perturbation leading to breaking of a nano-chain into particles indicated that the surface energy anisotropy affects the splitting of nano-chain network structure into nano-sized particles. The thesis ends with a last chapter where we have presented possible future extension of current work.