Atomic/plasma polymerization technology is widely used in various technical fields. This work is focused to use the PE-CVD technology in the field of formation of interphase and adhesive layers, which are developed into layered nanostructures. To ensure reproducible chemical and physical properties of the materials, the deposition process was monitored by mass spectrometry. Vapours of the pure tetravinylsilane, or a mixture of these vapours with oxygen, was used as a precursor for atomic polymerization, which results in the thin films with a large variability of properties. Physical and chemical properties were varied by the effective power delivered to the plasma discharge. The deposited films were analyzed from different perspectives using several methods (in situ spectroscopic ellipsometry, FTIR, nanoindentation, AFM). The removal of hydrogen atoms from the carbon-silicon network results in increased crosslinking of the material, which controls the mechanical and optical properties of the deposited layers. From the precisely defined a-CSi:H and a-CSiO:H materials, layered nanostructures composed of 3 and 7 individual layers was subsequently constructed. These nanostructures were analyzed by XPS and RBS to determine the atomic concentrations of carbon, silicon, oxygen and their binding states.

The work is aimed at preparation and characterization of thin films deposited by Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) on silicon wafers. A comprehensive characterization of the deposition system in order to determine the range of deposition conditions was a part of the study. Subsequently, the single and multi-layers were deposited from tetravinylsilane monomer. The deposition process was monitored by spectroscopic ellipsometry and mass spectroscopy. Layers and layered structures were characterized by microscopic and spectroscopic techniques. The physical and chemical properties of deposited films were studied with respect to the deposition conditions and monomer fragmentation in low-temperature plasma.

Theoretical part of diploma thesis was focused on the search of the state of knowledge in the area of plasma, plasma polymerization and characterization of thin films. Plasma-enhanced chemical vapor deposition (PECVD) was described in the experimental part together with selected analytical techniques. The technology with high level of reproducibility was reached by precise control of deposition conditions, monitoring of plasma, and analysis of plasma products using mass spectrometry. The obtained results demonstrated that the elemental composition, chemical structure, optical and mechanical properties of films were influenced by effective power used.

In Chapter 1, evidence is presented to correlate the vibronic progression in steady-state optical absorption spectra of a dimeric, organic material to its performance in field-effect transistor devices. The organic material, hPDI2, is fitted with solubilizing side chains of varying structure and length to investigate the effects that side chains have on both the optical and electronic properties of hPDI2. In solution, these side chains influence the character of aggregation and in thin films, the side chains influence film morphology. The character of aggregation in solution is determined by the change in relative peak intensities in optical absorption spectra with increasing concentration in solution. The change in relative peak intensity with increasing concentration in solution is a result of intermolecular electronic coupling, which alters the transitional symmetry of optical excitations. The character of aggregation in solution and the morphology of an organic material in thin films are akin to one another. In thin films, the intermolecular electronic coupling can facilitate the charge-transfer characteristics of an organic material in field-effect transistors. It is concluded that the structure and length of molecular side chains do indeed influence the optical and electronic properties of organic materials as a function of aggregation in solution and morphology in thin films. However, more evidence is necessary to elucidate a convincing correlation between the relative peak intensities in optical absorption spectra to the performance of the organic material in field-effect transistors. In Chapter 2, the fundamental electronic and chiroptical properties of a helical, polyaromatic molecule are demonstrated. Structurally, the organic material, NP3H, is a helix of helicenes, which generates intense circular dichroism. The circular dichroism is measured in spin-cast thin films. Electronic transfer characteristics are also presented for enantiopure NP3H as well as the racemic mixture. Upon fabricating field-effect transistors using spin-cast thin films of NP3H, the racemic mixture exhibits a marginally superior electron mobility over the enantiopure material. However, single crystals of enantiopure NP3H were grown and exhibited a two-fold increase in electron mobility when fabricated into a field-effect transistor device in comparison to its amorphous, spin-cast counterpart. It is concluded that enantiopure NP3H exhibits the necessary physical prerequisites to be useful in chiral device applications such as electron spin-filters and chiral light detectors. In Chapter 3, hPDI2 and NP3H are investigated for their ability to aggregate and form ordered films at the air-water interface of a Langmuir-Blodgett trough. Isotherms are presented and compared for each side chain derivative of hPDI2 as well as enantiopure and racemic NP3H. Additionally, an enhancement in circular dichroism is observed when a system of ordered layers of enantiopure NP3H are deposited from the Langmuir-Blodgett trough in comparison to its amorphous, spin-cast counterpart. Furthermore, ordered layers of enantiopure NP3H exhibit an enhancement in electron mobility when fabricated into field-effect transistor devices. The electron mobility is also demonstrated to enhance as the number of ordered layers that increases up to five layers. When ten ordered layers are deposited, a slight decrease is observed. Lastly, single crystals of hPDI2 were grown by solvent annealing a system of ordered layers deposited from the Langmuir-Blodgett trough, which is significant because, to the best of the author’s knowledge, a similar technique for single crystal growth of an organic material from ordered layers of Langmuir-Blodgett films has not yet been published in peer-reviewed scientific literature. It is concluded that the increased order that is induced by the Langmuir-Blodgett technique does indeed enhance the optical and electronic properties of organic materials in comparison to amorphous, spin-cast films and that this enhancement could be advantageous in device applications.

<p>  </p> <p>In this study, VO2 films were grown on conducting oxide SrRuO3 layers. Apart from applications in magnetism, SrRuO3 is a widely studied template material to create multi-functional oxide heterostructures. Here, SrRuO3 buffered SrTiO3 (111) and Si/SiO2 were selected as platforms for VO2 growth. The properties of VO2 thin films grown on SrRuO3 buffer layers, as well as thermally and electric-field induced metal-insulator transition were systematically studied. Numerous growth experiments were conducted to identify the optimal growth conditions. Utilizing the current shunting associated with the conductive underlayer, electric-field induced metal-insulator transition was investigated in both the in-plane and out-of-plane configurations. A distributed resistance network with general applicability to understanding metal-insulator transitions is proposed to predict the electrical behavior of VO2 grown on conducting layers.</p>

Emission of electromagnetic radiation due to the temperature of a body is an inherent property in nature. Electromagnetic radiation sources relying on thermal emission are critical in application of energy harvesting, lighting, spectroscopy and sensing. However, many of these sources, typically made of several hundreds of microns thick bulk objects, are inefficient and radiate much less power than an ideal blackbody. In the first part of this work, we demonstrate an efficient thermal emitter based on material films that are nanometers thin. Nano-film based thermal sources are generally poor emitters, but have received much interest lately since they require significantly lower heating power compared to their bulk counterparts. We show a novel approach for realizing thin-film based blackbody emitters by placing them inside an external optical cavity, engineered to provide enhancement of thermal emission while maintaining a constant temperature. Our approach is independent of the emitter material and can be tuned to operate at any temperature since the optical elements and the emitter are physically disconnected. The work opens new avenues for realizing blackbody-type thermal sources consuming significantly lower heating power than the current state-of-art, thus suggesting direct applications in lighting, spectroscopy and energy harvesting. Furthermore, we utilize the nano-film broadband emitters for demonstrating heat transfer that beats conventional blackbody limit at deep-subwavelength distances. We demonstrate the first of its kind, fully integrated and re-configurable thermo-photovoltaic on silicon platform. We report over an order of magnitude increase in generated electrical power by electro-statically tuning the distance between a suspended hot emitter TE ~ 880 K) and an underlying detector (maintained at TD ~ 300 K) from ~500 nm to ~100 nm. We believe this demonstration will be influential for the fields of active energy harvesting as well as in realizing integrated thermal control systems. In the third part of this work, we shift our focus away from broadband emitters, towards spectrally narrow band thermal emitters and propose a novel technique for long-distance transport of thermal radiation. In order to do so, we rely on enhanced near-field heat transfer over blackbody limits aided by surface plasmon polaritions (SPP). We then show that a dispersion engineered sub-wavelength waveguide can allow required states for SPP aided electromagnetic emission to propagate. We show computational analysis of the a composite structure using the open-source electromagnetic solvers SCUFF-EM that captures the effects of surface current distribution induced electromagnetic field effects inside and outside the emitter. We furthermore show a prototype structure of the proposed thermal-waveguide with doped silicon emitters that support SPP. We discuss the measurement technique and present preliminary results of thermal transport over a waveguide that is ~34 μm long. We believe that our proposed approach shown here could advance the field towards development of novel devices for thermal control.

This dissertation documents the development and demonstration of a new laser crystallization process called spot-beam annealing (SBA). The SBA method is a partial-melting-based laser-annealing method, which converts as-deposited amorphous Si films into high-mobility TFT-enabling polycrystalline films. SBA builds on the thermally additive utilization of multiple short-lived low-energy ultra-high-frequency pulses, achieved via substantially overlapped scanning of a small spot beam to incrementally and gradually heat and partially melt the beam-irradiated region. After a brief review of other laser crystallization technologies, the conceptual framework for the SBA process is introduced, and various possible implementation schemes and development paths are discussed. In the present work, the SBA method is implemented using a new class of ultra-high-frequency (>100 MHz), low-pulse energy (<1 𝜇J), short-pulse-duration (<1 ns) UV fiber lasers. The first half of the thesis (chapters 4 and 5) presents, the simulation- and calculation-based studies of the SBA process. A simple but relevant one-dimensional thermal analysis identifies the "dwell time" (associated with the overall intensity temporal profile defined by the collection of those pulses that irradiate a point in the film) as a key SBA parameter. Provided that a sufficient number of multiple shots are involved in irradiating the point in the film, this parameter dictates the overall thermal and transformation cycle of heating, primary melting, and solidification that enables the ultra-short-pulse-based SBA method to mimic the physical conditions encountered previously only using pulsed lasers with pulse duration in the range of tens to hundreds of nanoseconds; the precise range needed for optimally generating laser-annealed polycrystalline materials on glass and plastic substrates. Additionally, we also identify and examine an important differentiating feature of the SBA method, namely the highly transient temperature spikes that arise from the individual pulses incident onto a point on the film during overlapped scanning. By simultaneously considering the preliminary experimental results that are presented in this thesis (chapters 6 and 7), we suggest that these periodic temperature spikes, the specific degree of which depends on the temporal profile and energy density of individual pulses, can potentially play a key role in dictating certain important details of melting and solidification transitions encountered in SBA. In particular, we identify and elaborate on how the temperature fluctuations can affect how explosive crystallization of a-Si films is manifested in a different manner than has previously been observed. In addition, we point out how the fluctuations can control the degree to which the melting scenarios in SBA can deviate from the grain-boundary-melting-dominated 2-D transition scenario (as for instance encountered in pulsed-laser irradiation of columnar-grained polycrystalline films), where lateral melting is exclusively initiated at grain boundaries and propagates predominantly laterally into the superheated and defect-free interior of the grains. In the second half of the thesis, the experimental results that are obtained from a recently constructed research SBA system are presented, characterized, and evaluated. Specifically, the examination of single-scan and multiple-scan exposed Si films conducted using OM, AFM, and TEM material characterization techniques reveals that the method is capable of not only generating uniform polycrystalline Si films consisting of ordered grains with tight grain-size distribution around the beam wavelength, but it can furthermore be configured to produce polycrystalline films with an enhanced level of ordering as manifested in the films with a highly parallel ridge (HPR) pattern.

The design of biocompatible synthetic surfaces is an important issue for medical applications. Surface modification techniques provide good approaches to control the interactions between living systems and implanted materials by modifying the surface characteristics. This thesis work demonstrates the feasibility and effectiveness of the novel and low-cost electrostatic self-assembly (ESA) technique for the manufacturing of biocompatible thin film coatings. The ESA process is based on the alternating adsorption of molecular layers of oppositely charged polymers/nanoparticles, and can be applied in the fabrication of well-organized multilayer thin films possessing various biocompatible properties. ESA multilayer assemblies incorporating various biomaterials including metal oxides and polymers were fabricated, the uniformity, thickness, layer-by-layer linearity, and surface morphology of the films were characterized by UV/vis spectroscopy, ellipsometry, and AFM imaging. Preliminary biocompatibility testing was conducted, concentrating on contact angle surface characterization and the in vitro measurements of protein adsorption. The use of Fourier Transform Infrared Reflection-Absorption Spectroscopy (FT-IRAS) for the investigation of the protein adsorption behavior upon the ESA multilayer films is presented. / Master of Science

In the present work atom probe tomography (APT) was applied to analyze thin films used in semiconductor industry to investigate the capability of atom probe tomography as well as the dopant redistribution in thin silicide layer stacks. Different titanium silicide layer stacks are investigated and titanium diboride precipitates are identified by APT. Arsenic grain boundary segregation is verified by APT in cobalt silicide layer stacks. Furthermore APT measurements are compared to commonly used methods such as TEM and SIMS and found in good agreement. Each method exhibits its own advantages depending on the sample and the question. Atom probe tomography offers some unique features enabling three-dimensional analysis on the nanometer scale as shown on the mentioned thin film layer stacks.

Within this thesis, a comprehensive study of the initial growth process of pure Fe3O4 films and Fe3O4/NiO bilayers on Nb:SrTiO3(001) substrates including the thermal interdiffusion behavior of these bilayers is presented. The sensitive interplay between magnetic, electronic and structural properties of these materials has been investigated in detail. In the first study, the initial growth behavior of high-quality ultrathin magnetite films on SrTiO3(001) deposited by reactive molecular beam epitaxy depending on the deposition temperature has been analyzed. For this purpose, the growth process has been monitored in situ and during the deposition by grazing incidence x-ray diffraction (GIXRD). The second part provides a comparative study of Fe3O4/NiO bilayers grown on both MgO(001) and Nb:SrTiO3(001) substrates exploring morphological, structural and magnetic properties. These structures have been investigated by means of x-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED), x-ray reflectivity (XRR) and diffraction (XRD), as well as vibrating sample magnetometry (VSM). Subsequently, thermal stability of these bilayers and the thermally induced interdiffusion process have been studied successively accompanied by a comprehensive characterization of the fundamental electronic, structural and magnetic properties using additional techniques such as angle resolved hard x-ray photoelectron spectroscopy (AR-HAXPES) and x-ray magnetic circular dichroism (XMCD). Finally, an alternative pathway for the preparation of ultrathin nickel ferrite films through interdiffusion is provided.