This thesis addresses the evolution of nanoscale ripple patterns on solid surfaces during low-energy ion sputtering. Particular attention is paid to the long-time regime in which the surface evolution is dominated by nonlinear processes. This is explored in simulation and experiment. In numerical simulations, the influence of anisotropy on the evolution of the surface patterns in the anisotropic stochastic Kuramoto-Sivashinsky (KS) equation with and without damping is studied. For a strong nonlinear anisotropy, a 90 rotation of the initial ripple pattern is observed and explained by anisotropic renormalization properties of the anisotropic KS equation. This explanation is supported by comparison with analytical predictions. In contrast to the isotropic stochastic KS equation, interrupted ripple coarsening is found in the presence of low damping. This coarsening seems to be a nonlinear anisotropy effect that occurs only in a narrow range of the nonlinear anisotropy parameter. Ex-situ atomic force microscopy (AFM) investigations of Si(100) surfaces sputtered with sub-keV Ar ions under oblique ion incidence show the formation of a periodic ripple pattern. This pattern is oriented normal to the direction of the ion beam and has a periodicity well below 100 nm. With increasing ion fluence, the ripple pattern is superposed by larger corrugations that form another quasi-periodic pattern at high fluences. This ripple-like pattern is oriented parallel to the direction of the ion beam and has a periodicity of around one micrometer. Interrupted wavelength coarsening is observed for both patterns. A dynamic scaling analysis of the AFM images shows the appearance of anisotropic scaling at large lateral scales and high fluences. Based on comparison with the predictions of different nonlinear continuum models, the recent hydrodynamic model of ion erosion, a generalization of the anisotropic KS equation, is considered as a potentially powerful continuum description of this experiment. In further in-situ experiments, the dependence of the dynamic scaling behavior of the sputtered Si surface on small variations of the angle of incidence is investigated by grazing incidence small angle X-ray scattering (GISAXS). A transition from strongly anisotropic to isotropic scaling is observed. This indicates the presence of at least two fixed points in the system, an anisotropic and an isotropic one. The dynamic scaling exponents of the isotropic fixed point are in reasonable agreement with those of the Kardar-Parisi-Zhang (KPZ) equation. It remains to be seen whether the hydrodynamic model is able to show such a transition from anisotropic to isotropic KPZ-like scaling.

Reactive Sputtering is a widely used technique in processing of thin compound films. Such films can be sputtered from metal targets, which are comparatively cost efficient. Also the fact that sputtering from metal targets can ccur in the dc mode reduces the cost of the sputtering equipment. To keep the deposition process stable, its necessary to know the effects of target poisoning including its hyteresis behavior. The aim of this work was to nvestigate the evolution of reactive gas coverage on a titanium magnetron target surface, by real time, in-situ ion beam analysis during magnetron sputtering. A cylindrical 2 inch magnetron was used for reactive sputtering of TiN. It was operated in an Ar/N2 gas mixture at achamber pressure of about 3∙10-3 mbar. The argon/nitrogen flux ratio was variated between 0 and 20%. The nitrogen concentration on the target was determinated using the 14N(d, α)12C, nuclear reaction at a deuterium beam energy of 1.8 MeV. Depending on the adjusted nitrogen flow the target incorporation varies between 0 and about 1∙1016 N∙cm-2. Further the expected hysteresis behaviour ofnitrogen partial pressure, target voltage and nitrogen concentration at increasing/decreasing nitrogen gas flow is confirmed. The lateral distribution of nitrogen was measured across the diameter of target surface. In the zone of higher erosion (the \"race track\") the nitrogen concentration is 50% lower than in the middle or the edge of the target. A deposition zone in the center of the target could not be detected. By increasing the nitrogen flow into the chamber a saturation in nitrogen content in the target was found at an Ar/N2 flow ratio of about 10%. Assuming nitrogen implantation with a depth of 2.5 nm under the influence of typical target voltage during magnetron sputtering, this saturation is at a concentration value where stoichiomtric TiN is formed. Within the precision of the measurements, a mobile fraction of nitrogen could not determined. The concentration in the target remains unchanged after switching off the magnetron.

The goal of this work was to evaluate the electrochemical properties of TiZrNbTa thin films deposited by magnetron sputtering using an industrial physical vapor deposition system. Samples were deposited on both Si(001) and 316L stainless steel. The samples deposited on Si(001) were either crystalline (bcc reflections) or amorphous, depending on the sputtering parameters. The crystalline films were composed of thin films with two different layers. The upper layer was nanocolumnar composed of elongated nanocolumns, while the lower was dense. The amorphous films had only one nanocolumnar layer and higher porosity. Polarization curves revealed that all samples had low corrosion current densities, in the order of 10-8 A/cm2. The samples showed an extended passive region up to 3.0 V vs Ag/AgCl due to the growth of a passivating oxide. The surface of the samples consisted of Nb2O5, ZrO2, TiO2 and Ta2O5. The chronoamperometry tests showed current oscillations, related to a break-down and reformation of the passive film. Electrochemical impedance spectroscopy revealed that all samples behaved similarly in all three electrolytes, and the simulated electrical circuits were indicating no corrosion reactions. A decrease in capacitance values after polarization was observed and was related to the formed surface oxide. Samples deposited on 316L stainless steel showed a passive regime for a shorter potential window, probably related to surface defects of the films. Heat treatments at 400 and 800 Celsius for 20 hours could not trigger the phase transformation from single bcc to hcp or dual bcc, as predicted by the Thermo-Calc software.

Micro-electro-mechanical systems (MEMS) have become an essential component of a wide range ofelectronic devices over the last decades such as accelerometers, microphones, gas sensors, and filters.During this new millennium, a new radio frequency (RF) technology has been developed to satisfy thetough demands that arose due to the implementation of 5G wireless communication: bulk acoustic wave(BAW) filters.BAW devices use the piezoelectric effect, converting mechanical vibrations to electrical signals, topower wireless devices. BAW filters can operate between 3.5 GHz and 6 GHz, therefore, within therange of the new 5G. BAW technology offers lower insertion loss, higher heat dissipation, andperformances at higher power and frequency which increases the data speed considerably.This thesis will be focused on the study of the materials used in BAW devices. A common BAW filteris made from different layers distributed in a stack, from the bottom to the upper part, the BAW filteris composed of a substrate, a transducer layer made of a piezoelectric layer in between of two electrodes,and intermediate layers that can enhance the addition of the deposited layers on top called buffer layers,or the crystal quality of the films on top called seed layers.The main characteristic that a buffer layer must possess is an intermediate lattice parameter betweenthat of the substrate and the top layer. When these two layers present a high lattice mismatch, theinterface quality is rather poor. By using a buffer layer, and therefore, by adding two different interfaces,the crystal quality is improved by decreasing the internal stress and the crystal distortion. Buffer layermaterials depend on the type of materials that will be in contact with them.A seed layer is usually used to improve the crystal quality of a layer that requires extreme sputteringparameters to be used to be deposited possessing a high crystal quality and a preferred orientation. Seedlayers used in BAW devices, whose piezoelectric layer is made of AlScN or AlN, are usually made ofhighly c-axis oriented and highly crystalline AlN.The objective of this study is to analyze the deposition of AlN and HfN by means of reactive radiofrequency magnetron sputtering and reactive pulsed-direct current magnetron sputtering, respectively.AlN is largely used as a buffer layer and as a seed layer, however, the new approach of this report is tostudy the sputtering of HfN and compare it as a possible candidate to replace AlN as a seed layer.

In this thesis, growth of ZrB2 thin films by direct current magnetron sputtering is investigatedusing a high vacuum industrial scale deposition system and an ultra-high vacuum laboratory scalesystem. The films were grown from ZrB2 compound targets at temperatures ranging from ambient (without external heating) to 900 °C and with substrate biases from -20 to -120 V. Short deposition times of typically 100 or 300 s and high growth rates of 80-180 nm/min were emphasized to yield films with thicknesses of 300-400 nm. The films were characterized by thinfilm X-ray diffraction with the techniques θ/2θ and ω scans, pole figure measurements andreciprocal space mapping, scanning and transmission electron microscopy, elastic recoil detection analysis and four point probe measurements. The substrates applied were Si(100), Si(111),4H-SiC(0001) and GaN(0001) epilayers grown on 4H-SiC. The Si(111), 4H-SiC(0001) substrates and GaN(0001) epilayers were chosen given their small lattice mismatches to ZrB2 making them suitable for epitaxial growth.The films deposited in the industrial system were found to be close to stoichiometric with a low degree of contaminants, with O being the most abundant at a level of < 1 at.%. Furthermore, the structure of the films is temperature dependent as films deposited in this system without external heating are fiber textured with a 0001-orientation while the films deposited at 550 °C exhibitrandom orientation. In contrast, epitaxial growth was demonstrated in the laboratory scale system on etched 4H-SiC(0001) and Si(111) deposited at 900 °C following outgassing of the substrates at 300 °C and in-situ heat treatment at the applied growth temperature to remove the native oxides. However, films grown on GaN(0001) were found to be 0001 textured at the applied deposition conditions, which make further studies necessary to enable epitaxial growth on this substrate material. Four point probe measurements on the films deposited in the industrial system show typical resistivity values ranging from ˜95 to 200 μΩcm with a trend to lower values for the films deposited at higher temperatures and at higher substrate bias voltages.

Ferroelectrics are a group of advanced electronic materialswith a wide variety of properties useful in applications suchas memory devices, resonators and filters, infrared sensors,microelectromechanical systems, and optical waveguides andmodulators. Among the oxide perovskite-structured ferroelectricthin film materials sodium potassium niobate or Na0.5K0.5NbO3(NKN) has recently emerged as one of the most promisingmaterials in microwave applications due to high dielectrictunability and low dielectric loss. This licentiate thesispresents results on growth and structural, optical, andelectrical characterization of Na0.5K0.5NbO3 thin films. Thefilms were deposited by rf-magnetron sputtering of astoichiometric, high density, ceramic Na0.5K0.5NbO3 target ontosingle crystal LaAlO3 and Al2O3, and polycrystalline Pt80Ir20substrates. By x-ray diffractometry, NKN films on c-axisoriented LaAlO3 substrates were found to grow epitaxially,whereas films on hexagonal sapphire and polycrystallinePt80Ir20 substrates were found to be preferentially (00l)oriented. Optical and waveguiding properties of theNa0.5K0.5NbO3/Al2O3 heterostructure were characterized using aprism-coupling technique. Sharp and distinguishable transversemagnetic (TM) and electric (TE) propagation modes wereobserved. The extraordinary and ordinary refractive indiceswere calculated to ne = 2.216±0.003 and no =2.247±0.002 for a 2.0 μm thick film at λ = 632.8nm. This implies a birefringence Δn = ne - no =-0.031±0.003 in the film. The ferroelectric state inNKN/Pt80Ir20 films at room temperature was indicated by apolarization loop with polarization as high as 33.4 μC/cm2at 700 kV/cm, remnant polarization of 9.9 μC/cm2 andcoercive field of 91 kV/cm. Current-voltage characteristics ofvertical Au/NKN/Pt80Ir20 capacitive cells and planar Au/NKN/LaAlO3 interdigital capacitors (IDCs) showed very goodinsulating properties, with the leakage current density for anNKN IDC on the order of 30 nA/cm2 at 400 kV/cm. Rf dielectricspectroscopy demonstrated low loss, low frequency dispersion,and high voltage tunability. At 1 MHz NKN/LaAlO3 showed adissipation factor tan δ of 0.010 and a tunability of 16.5% at 200 kV/cm. For the same structure the frequencydispersion, Δεr, between 1 kHz and 1 MHz was 8.5%. <b>Key words:</b>ferroelectrics, sodium potassium niobates,thin films, rf-magnetron sputtering, waveguiding, refractiveindex, prism coupling, dielectric tunability / NR 20140805

We present a comprehensive comparison of electrical properties of differently fabricated high quality Schottky contacts on ZnO thin films grown by pulsed laser deposition. Thermally evaporated Pd/ZnO Schottky contacts exhibit ideality factors as low as 1.06 due to their high lateral homogeneity. The effective Richardson constant determined using these homogeneous contacts is (7.7±4.8)A cm−2 K−2 close to the theoretical value of 32 A cm−2 K−2. However, their rectification ratio is at most five orders of magnitude due to their comparably small barrier height (≈0.7eV). The largest effective barrier height (1.11 eV) and rectification ratio(7×1010) was obtained for reactively sputtered PdOx/ZnO Schottky contacts. Eclipse pulsed laser deposited IrOx/ZnO Schottky contacts were found to combine very good lateral homogeneity (n≈1.1), with a reasonably large barrier height (0.96 eV) and large rectification ratio (≈9 orders of magnitude). Our results for differently fabricated Schottky contacts suggest that the barrier formation is highly dependent on the presence of oxygen vacancies close to the interface and the different compensation mechanisms involved.

High power impulse magnetron sputtering has shown a lot of promise as a way of depositing photocatalytic thin films of titanium dioxide at low temperatures, however, the films deposited are often amorphous and display uncertain photocatalytic abilities. This thesis explores the deposition and characterization of photocatalytic thin films deposited with high power impulse magnetron sputtering.  Multiple films were deposited with reactive sputtering in both the oxide and metal mode of operations at different temperatures, duty cycles and substrate biases. The crystal structure, microstructure and photocatalytic activity of the samples were then characterized in order to correlate to each other as well as the growth conditions. Crystallinities were determined via a combined use of gracing incidence x-ray diffraction and Raman spectroscopy, microstructures were explored in cross-sectional images taken using scanning electron microscopy and the photocatalytic ability was measured by quantifying the rate constant during degradation of stearic acid while under UV-illumination.  It was found that the crystal structure of the sputtered films was influenced by the deposition mode used: oxide mode depositions yielded an anatase structure while metal mode depositions resulted in rutile or mixed structures. The only crystalline films were formed with substrate heating, the application of bias was found to correlate with the formation of more rutile and the most crystalline films were deposited with a higher duty cycle.  Photocatalytic films were successfully deposited at room temperature, even though they were amorphous. Interestingly, the anatase samples were not found to be the most reactive, instead it was found that the crystal structure only displayed a weak correlation to the reactivity of the films. The findings in this work suggest that the reactivity was also heavily influenced by the surface roughness of the samples as well as their microstructures.

The goals of this research project were the design and construction of a carbon nanotube (CNT) reactor based on the plasma enhanced chemical vapor deposition (PECVD) principle and the development of a method for directed assembly of CNTs by catalyst patterning. PECVD was selected as the growth method due to the requirement of a catalyst for the growth process, thereby facilitating directed assembly and controlled diameter CNT growth at well-defined locations. The reactor was built in accord with horizontal flow design using standard ultra high vacuum components. The controllable parameters of the reactor include sample temperature, DC plasma intensity, chamber pressure, gas flow ratios, and total gas flow. The most favorable parameters for growing CNTs of well defined length, diameter, and separation were obtained by initially using parameter values obtained from literature, then optimized by changing a parameter and noting the effect on CNT growth. Catalyst patterns for the directed assembly of CNTs were prepared by electron-beam lithography (EBL). Experiments were performed that demonstrated the feasibility of using lithographic methods to achieve directed assembly of carbon nanotubes for the manufacture of CNT devices. Experiments focusing on growth interruption and regrowth of CNTs were conducted to investigate methods of introducing tailored branching points into carbon nanotubes during the growth process. These experiments clearly demonstrate that growth interruption increases the occurrence of CNT branching. An analysis of the relationships between CNT diameter, branching points, and the number of growth steps was conducted.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第18698号 / エネ博第310号 / 新制||エネ||63(附属図書館) / 31631 / 京都大学大学院エネルギー科学研究科エネルギー社会・環境科学専攻 / (主査)教授 石原 慶一, 教授 佐川 尚, 准教授 奥村 英之 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM