<p>This thesis report is focused on the growth of Pt/Mg multilayers and the studies of the sputter yield amplification effect in these. The main application is to use the multilayers as X-ray mirrors reflecting an X-ray wavelength of 17 Å. This wavelength is important for astronomical applications in general, and solar imaging applications in particular.</p><p>For periodic X-ray multilayer mirrors only a certain specific wavelength of X-rays can be reflected. What wavelength that is reflected depends on the individual layer thicknesses of the materials that are constituting the multilayer. These thicknesses can be determined using modified Bragg’s law and are approximately a quarter of the wavelength.</p><p>In order to obtain the exact desired layer thickness of each individual layer it is necessary to understand the growth processes and the effects that are going on during deposition of such multilayer mirrors. It has been shown that when depositing multilayers consisting of one very light and one very heavy material, like e.g. Pt and Mg, the deposition rate of the light element is non-linear with deposition time for thin layers. This is because of backscattered energetic neutrals from the heavy target material, which affects the growing film. Furthermore, a sputter yield amplification is present for thin layers when a light element is grown on top of a heavy element, i.e. for Mg on top of Pt.</p><p>Dual DC magnetron sputtering has been used to grow the Pt/Mg multilayers, and the influence of the backscattered energetic neutrals and the sputter yield amplification effect has been studied for Ar and Kr sputtering gases at pressures ranging from 3 up to 9 mTorr. The individual layer thicknesses have been obtained from simulations of hard X-ray reflectivity measurements using the IMD program. The number of backscattered energetic neutrals and their energies at the target have been calculated using the TRIM code.</p><p>Using the results obtained it is now possible to predict and compensate for the non-linear deposition rate of Mg.</p>

<p>This thesis reports on the development of low-temperature processes for transition metal carbide and MAX-phase thin film growth. Magnetron sputtering and evaporation, far from thermodynamical equilibrium, have been utilised to engineer the properties of the films by physical and chemical control. Deposition of W, W₂C and β-WC_1-x films with controlled microstructure, from nanocrystalline to epitaxial, is shown in the W-C system down to 100 ^oC. W films with upto 20 at% C exhibited an extreme solid-solution hardening effect, with a nanoindentation hardness maximum of 35 GPa. Furthermore, the design of epitaxial ternary carbide films is demonstrated in the Ti_1-xV_xC_y system in the form of controlled unit-cell parameters, strain-free films with a perfect match to the substrate, and ternary epitaxial gradient films. Moreover, phase stabilisation and pseudomorphic growth can be tuned in (Nb,Mo)C and (Ti,W)C films. The results obtained can be used for example to optimise electrical contacts in SiC high-power semiconductor devices. </p><p>A large part of this thesis focuses on the deposition of MAX-phases. These compounds constitute a family of thermally stable nanolaminates with composition M_n+1AX_n, n=1, 2 or 3, where M is an early transition metal, A is generally a group 13-14 element, and X is C or N. They show a combination of typical ceramic and metallic properties and are also machinable by virtue of the unique deformation behaviour observed only in laminates. So far, the MAX-phases have almost exclusively been prepared by high-temperature sintering and studied in bulk form. However, this thesis establishes a patented seed layer approach for successful MAX-phase thin film depositions down to 750 ^oC. For the first time, single-phase and epitaxial films of Ti₃SiC₂, Ti₃AlC₂ and Ti₂AlC have been grown. The method has also been used to synthesise a new MAX-phase, Ti₄SiC₃. In addition, two previously unreported intergrown MAX-type structures are presented, Ti₅Si₂C₃ and Ti₇Si₂C₅. Combined theoretical and experimental results show the possibility to deposit films with very low bulk resistivity and designed mechanical properties. Furthermore, the demonstration of MAX-phase and carbide multilayer films paves the way for macrostructure engineering, for example, in coatings for low-friction or wear applications.</p>

Microwave materials have been widely used in a variety of applications ranging from communication devices to military satellite services, and the study of materials properties at microwave frequencies and the development of functional microwave materials have always been among the most active areas in solid-state physics, materials science, electrical and electronic engineering. In recent years, the increasing requirements for the development of high speed, high frequency circuits and systems require complete understanding of the properties of materials function at microwave frequencies. Ferroelectric materials usually have high dielectric constant, and their dielectric properties are temperature and electric field dependent. The change in permittivity as a function of electric field is the key to a wide range of applications. Ferroelectric materials can be used to fabricate capacitors for electronic industry because of their high dielectric constant, and this is important in the trend toward miniaturization and high functionality of electronic products. The simple tunable passive component based on ferroelectric films is a varactor which can be made as a planar structure and used for electrically tunable microwave integrated circuits. It is an important task to sinter highly tunable and low loss ferroelectrics, fabricate and test the properties of microwave ferroelectric components. This thesis shows experimental results on growth, crystalline and microwave properties of Na0.5K0.5NbO3 (NKN), AgTa0.5Nb0.5O3 (ATN), Ba0.5Sr0.5TiO3 (BST) as well as AgTaO3 (ATO), and AgNbO3 (ANO) thin films. The films were grown by Pulsed Laser Deposition (PLD) and rf-magnetron sputtering techniques from stoichiometric high density ceramic NKN, ATN, ATO, ANO and BST targets onto LaAlO3 (LAO), Al2O3 (r-cut sapphire), Nd:YAlO3 single crystals and amorphous glass substrates. Advanced X-ray diffraction examinations showed NKN, ATN, BST films on LAO substrates grow epitaxially, whereas films on r-cut sapphire were found to be preferentially (00l) oriented. Coplanar waveguide 2 µm finger gap interdigital capacitor (CPWIDC) structures were fabricated by photolithography process and metal lift-off technique. On-wafer tests up to 40 GHz were performed to characterize microwave properties of the ferromagnetic film CPWIDC devices. The measurement setup is composed of network analyzer, probe station, and microwave G-S-G probes. External electric field was applied to planar capacitors to measure tunability. Original de-embedding technique has been developed to calculate capacitance, loss tan δ, and tunability of varactors from the measured S-parameters. NKN film interdigital capacitors on Nd:YAlO3 showed superior performance compared to ATN in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40V, 200 kV/cm) was about 29%, loss tangent ~ 0.13, K-factor = tunability/tan δ from 152% @ 10GHz to 46% @ 40GHz. The ATN/sapphire CPWIDCs showed the lowest dispersion ~ 4.3% in whole frequency range from 1 to 40 GHz, voltage tunability 4.7% @ 20GHz and 200 kV/cm, lowest loss tangent ~ 0.068 @ 20GHz, K-factor = tunability/tan δ ranged from 124% @ 10GHz to 35% @ 40GHz. BST film CPWIDCs on sapphire showed frequency about 17%, the highest voltage tunability ~ 22.2%, loss tangent ~ 0.137 @ 20GHz, and K-factor = 281% @ 10GHz to 95% @ 40GHz. / QC 20100906

Ferroelectric oxides are a group of advanced electronic materials with a wide variety of properties useful in applications such as memory devices, resonators and filters, infrared sensors, microelectromechanical systems, and optical waveguides and modulators. Among the oxide perovskite-structured ferroelectric thin film materials, sodium potassium niobate or Na0.5K0.5NbO3 (NKN) has recently emerged as one of the most promising materials in radio frequency (rf) and microwave applications due to high dielectric tenability and low dielectric loss. This thesis presents results on growth and structural, optical, and electrical characterization of NKN thin films. The films were deposited by rf-magnetron sputtering of a stoichiometric, high density, ceramic Na0.5K0.5NbO3 target onto single crystal LaAlO3 (LAO), Al2O3 (sapphire), SrTiO3, and Nd:YAlO3, and polycrystalline Pt80Ir20 substrates. By x-ray diffractometry, NKN films on c-axis oriented LaAlO3, SrTiO3 and Nd:YAlO3 substrates were found to grow epitaxially, whereas films on r-cut sapphire and polycrystalline Pt80Ir20 substrates were found to be preferentially (00l) oriented. The surface morphology was explored using atomic force microscopy. Optical and waveguiding properties of the Na0.5K0.5NbO3/substrate heterostructures were characterized using prism-coupling technique. Sharp and distinguishable transverse magnetic and electric propagation modes were observed for NKN thicknesses up to 2.0 μm. The extraordinary and ordinary refractive indices were calculated together with the birefringence of the NKN material. The electro-optic effect in transverse geometry was measured in transmission, where the effective linear electro-optic response was determined to reff = 28 pm/V for NKN/Al2O3 with an applied dc field up to 18 kV/cm. The ferroelectric state in NKN films on Pt80Ir20 at room temperature was indicated by a polarization loop with saturated polarization as high as 33.4 μC/cm2 at 700 kV/cm, remnant polarization of 10 μC/cm2, and coercive field of 90 kV/cm. Current-voltage characteristics of vertical Au/NKN/PtIr capacitive cells and planar Au/NKN/LAO interdigital capacitors (IDCs) showed very good insulating properties, with the leakage current density for an NKN IDC on the order of 30 nA/cm2 at 400 kV/cm. Rf dielectric spectroscopy demonstrated low loss, low frequency dispersion, and high voltage tunability. At 1 MHz, NKN/LAO showed a dissipation factor tan δ = 0.010 and a tunability of 16.5 % at 200 kV/cm. For the same structure the frequency dispersion was Δεr = 8.5 % between 1 kHz and 1 MHz. / QC 20100928

This thesis report is focused on the growth of Pt/Mg multilayers and the studies of the sputter yield amplification effect in these. The main application is to use the multilayers as X-ray mirrors reflecting an X-ray wavelength of 17 Å. This wavelength is important for astronomical applications in general, and solar imaging applications in particular. For periodic X-ray multilayer mirrors only a certain specific wavelength of X-rays can be reflected. What wavelength that is reflected depends on the individual layer thicknesses of the materials that are constituting the multilayer. These thicknesses can be determined using modified Bragg’s law and are approximately a quarter of the wavelength. In order to obtain the exact desired layer thickness of each individual layer it is necessary to understand the growth processes and the effects that are going on during deposition of such multilayer mirrors. It has been shown that when depositing multilayers consisting of one very light and one very heavy material, like e.g. Pt and Mg, the deposition rate of the light element is non-linear with deposition time for thin layers. This is because of backscattered energetic neutrals from the heavy target material, which affects the growing film. Furthermore, a sputter yield amplification is present for thin layers when a light element is grown on top of a heavy element, i.e. for Mg on top of Pt. Dual DC magnetron sputtering has been used to grow the Pt/Mg multilayers, and the influence of the backscattered energetic neutrals and the sputter yield amplification effect has been studied for Ar and Kr sputtering gases at pressures ranging from 3 up to 9 mTorr. The individual layer thicknesses have been obtained from simulations of hard X-ray reflectivity measurements using the IMD program. The number of backscattered energetic neutrals and their energies at the target have been calculated using the TRIM code. Using the results obtained it is now possible to predict and compensate for the non-linear deposition rate of Mg.

This dissertation presents a comprehensive study of the intrinsic room temperature ferromagnetism, RTFM, in technologically important thin films of ZnO, MgO, Mg@ZnO, the so-called d0–magnets that do not contain any intrinsic magnetic elements. We also present the first report on magnetism in Mn doped MgO films fabricated by dc magnetron sputtering. We have just published (April 2013 ‘on-line’) a state of the art review entitled ‘p-type ZnO Theory, growth, properties, and devices’ in the prestigious journal ‘Progress in Materials Science’, summarizing the recent advances of the studies on p-type ZnO thin films and pointing out the major challenges that remain in the field. The experimental work then focuses on the magnetic properties of band gap engineered Mg@ZnO films exploiting the fact that by substitutional doping of Mg for Zn in ZnO it is possible to tailor new materials with bandgap energy in the range 3.3 eV to 7.2 eV, thus extending the possibilities for new magnetic and optical device applications. In addition, we show that by doping Mn in MgO its magnetic properties can be enhanced to saturation values as high as 38.5 emu/cm3 in a 92 nm thick film. These studies involve extensive characterization of the high quality films in the thickness range of nanometers, using SQUID magnetometer for magnetic properties, XRD for structural analysis, Dual beam HRSEM/FIB and AFM for accurate film cross-sectioning and surface morphology, EDXS for elemental analysis, UV-VIS NIR for measuring the band gap of MgxZn(1-x)O films, Mg K-edge NEXAFS experiment in order to understand electronic structure of specific cations present in the thin films The origin of the observed room temperature feerromaganetism is attributed to cation vacancies and its consequences on the polarization about these vacancies in the oxides... ZnO films are promising materials for optoelectronic device applications, and the fabrications of high quality p-type ZnO and p–n junction are the key steps to realize these applications. However, reliable p-type doping of the material remains a major challenge because of the self-compensation from native donor defects (VO and Zni) and/or hydrogen incorporation. Considerable efforts to obtain p-type ZnO by doping different elements with various techniques have resulted in remarkable progress in the field both from theoretical and experimental point of view. In our paper, we discuss p-type ZnO materials: theory, growth, properties and devices, comprehensively. We first discuss the native defects in ZnO. Among the native defects in ZnO, VZn and Oi act as acceptors. We then present the theory of p-type doping in ZnO, and summarize the growth techniques for p-type ZnO and the properties of p-type ZnO materials. Experimentally, besides the intrinsic p-type ZnO grown at O-rich ambient, p-type ZnO (MgZnO) materials have been prepared by various techniques using Group-I, IV and V elements. We pay a special attention to the band gap of p-type ZnO by band gap engineering and room temperature ferro magnetism observed in p-type ZnO. Finally, we summarize the devices based on p-type ZnO materials. In presenting the current studies, we first focus on the sputtering process in order to produce high quality films. From a comparative study of RTFM, in MgO films deposited by sputtering from 99.999% pure metallic Mg, Vs MgO targets respectively on glass/Si substrates under identical ambience during deposition it is found that the metallic targets give the best magnetic properties (e.g: with maximum Ms values of ~13.75 emu/g vs ~ 4.2 emu/g respectively on Si substrates.(supplement 2). Furthermore, the Ms values are strongly film thickness dependent with Mg target while it is weakly so for films from MgO target. Also, the as deposited MgO films using metallic Mg target are found to be amorphous, while it is nanocrystalline when the films are sputtered off MgO targets. The overall Ms values are found to be dependent on the oxygen content in the atmosphere during deposition, increasing to 2.69 emu/g at a oxygen partial pressure of 40% of the total working gas pressure. On annealing to nanocrystallize these films in the temperature range 600 to 8000C strong XRD peaks corresponding to (200) orientation are observed, and Ms values decrease proportionately. (supplement 3). With the above information on studies for optimizing the effect of sputtering gas, film thickness, and oxygen partial pressure, PO2, comprehensive investigations on band gap engineering and magnetism in MgxZn(1-x)O co-sputtered thin films from Mg and Zn targets are then closely examined. The optical band gap calculated from absorption spectra shows that the band gaps of Mg-doped ZnO thin films increased linearly from 3.33 to 4.074 eV. Our studies indicate that both the magnetic properties and the band gap of the film can be tailored by tuning the film thickness and PO2 in the working gas. In summary, RTFM ordering in the thin films originates from cation vacancies which couple ferromagnetically and establish long range magnetic order. The ferromagnetic ordering in these materials is shown to arise from defects situated at the cation sites. Electronic structure studies of some selected films disclose that the unoccupied O 2p states exist and this unoccupied state results from cation vacancy (VMg). / <p>QC 20130524</p>

Co-doped ZnO (ZnO:Co) thin film with room temperature ferromagnetism and spin polarized carriers is one of the advance materials and highly applicable in future development in spintronics. When ZnO:Co films deposited by a £_ growth method in a ion sputtering system, low solubility of Co (3.75%) limits further applications such that a single-guns sputtering thin film growth technique is employed in this study to outreach this limitation. A ZnO:Co bulk with 5 at% of Co was formed by a solid reaction method and used as a target. ZnO:Co films were grown in a single-gun RF sputtering system. However, all films grown at room temperature were insulator which might because sufficient oxygen content in the target and the negative charge of oxygen ion moving toward substrate making the films of full oxygen content. In this study, the post annealing in vacuum environment and the deposition of films in hydrogenation environment are conducted to try to produce various level of oxygen vacancies in the films for understanding the interplay between the oxygen vacancies and the electric transport and magnetic coupling. The present experiment contains two parts: (1) grow films with various thicknesses by controlling deposition time and then applying post annealing process, and (2) grow the films in oxygen reduced environment by introducing hydrogen during growth and taking out partial oxygen content in the plasma and the films. In the first part, the grain sizes of the films are near constant while the crystal quality is improved with the thickness of films. The worse crystal quality of grains, the better the electric transport and the stronger the magnetic coupling after post annealing processes. This indicates that the electric transport and magnetic coupling could be improved when the thin films was formed by crystals with certain disordering and contained a certain level of oxygen vacancies. In the second part, the introduced hydrogen may combine with the oxygen sputtered out from the target before deposition on substrates. It means that the films are grown in oxygen deficient conditions and result in various degrees of oxygen vacancies. Zn clusters precipitate in films when the concentration of hydrogen is over 20%, and at the meantime, they increase the conductivity and suppress the magnetic coupling in the films. These discoveries provide new perspective in understand the electric transport and ferromagnetism mechanics in DMS materials.

This study focuses on various aspects of nanocrystals embedded in a dielectric matrix. In the first part of this work, a new approach with the use of Fourier Transform Infrared spectroscopy (FTIR) in the nanocrystal analysis was developed and presented. Si and Ge nanocrystals embedded in SiO2 matrix were mainly studied. This new approach is based on the analysis of structural variations of SiO2 matrix during the formation of semiconductor nanocrystlas. It is shown that the chemical and structural variations of the host matrix are directly related to the precipitation of nanocrystals in it. This correlation provides valuable information about the presences of nanocrystals in the matrix. In the second part of this work, fabrication of SiC films with and without Si nanocrystals inclusions was studied. With this aim, stoichiometric SiC and Si rich SiC thin films were fabricated by using magnetron co-sputtering and Plasma Enhanced Chemical Vapor Deposition (PECVD) techniques. For SiC films, the structural and optical analyses were performed. For Si rich SiC films, the formation conditions of Si nanocrystals were investigated. Post annealing studies were carried out to track the evolution of the SiC matrix and formation of Si nanocrystals at different temperatures. Chemical and structural properties of the SiC host matrix were investigated with FTIR spectroscopy. Optimum conditions for the fabrication of stoichiometric SiC layers were determined. The crystallography of the nanocrystals was investigated by X-Ray Diffraction (XRD). The variation of the atomic concentrations and bond formations were investigated with X-Ray Photoelectron Spectroscopy (XPS). Raman spectroscopy and Transmission Electron Microscopy (TEM) were used to verify the formation of Si nanocrystals. We have shown that both single and multilayer Si nanocrystals can be fabricated in the amorphous SiC matrix for applications such as light emitting diodes and solar cells.

In der vorliegenden Arbeit wird das Wachstum von Ta- und TaN-Schichten auf Si- und SiO_2-Substraten untersucht Die Schichten werden dabei unter technologienahen Bedingungen mittels Magnetron-Sputtern abgeschieden. Die Untersuchungen erfolgen hauptsächlich mit winkelaufgelöster röntgenstrahlungsangeregter Photoelektronenspektroskopie (ARXPS). Die Analysen erfolgen in situ, ohne Unterbrechung des Ultrahochvakuums, um die Deposite vor Oxidation und Kontamination zu schützen. Zur zerstörungsfreien Tiefenprofilanalyse wird ein Quantifizierungsalgoritmus beschrieben und angewandt. Für die Kombination Ta/Si wird die Bildung einer zunächst unvollständigen TaSi_2-Schicht, danach das Aufwachsen von Ta auf diese Zwischenschicht beobachtet. Für die Kombination Ta/SiO_2 wird eine Reduktion des SiO_2-Substrates bei gleichzeitigem Aufwachsen von Ta-Oxiden beobachtet. Auf dem durchmischten Schichtstapel wächst danach Ta auf. Für die Kombination TaN/Si wird die Bildung einer Si-N-Zwischenschicht bei gleichzeitigem Wachsen einer TaN-Schicht beobachtet. Für die Kombination TaN/SiO_2 wird das Aufwachsen einer TaN-Schicht ohne Ausbilung von Zwischenschichten beobachtet. Das Wachstumsverhalten des Ta/Si-Systems wird zusätzlich mit in situ Rastertunnelmikroskopie und -spektroskopie untersucht. Es wurden Untersuchungen zur thermischen Stabilität von abgeschiedenen Schichten an den Systemen Ta/Si und TaN/SiO_2 durchgeführt. Als mögliche Alternative zur winkelaufgelösten XPS wurden Untersuchungen mittels synchrotronstrahlungsangeregter Photoelektronenspektroskopie bei variierter Anregungsenergie durchgeführt.

Vibration control requires high dynamic stiffness in mechanical structures for a reliable performance under extreme conditions. Dynamic stiffness composes the parameters of stiffness (K) and damping (η) that are usually in a trade-off relationship. This thesis study aims to break the trade-off relationship. After identifying the underlying mechanism of damping in composite materials and joint interfaces, this thesis studies the deposition technique and physical characteristics of nano-structured HDS (high dynamic stiffness) composite thick-layer coatings. The HDS composite were created by enlarging the internal grain boundary surface area through reduced grain size in nano scale (≤ 40 nm). The deposition process utilizes a PECVD (Plasma Enhanced Chemical Vapour Deposition) method combined with the HiPIMS (High Power Impulse Magnetron Sputtering) technology. The HDS composite exhibited significantly higher surface hardness and higher elastic modulus compared to Poly(methyl methacrylate) (PMMA), yet similar damping property. The HDS composites successfully realized vibration control of cutting tools while applied in their clamping interfaces. Compression preload at essential joint interfaces was found to play a major role in stability of cutting processes and a method was provided for characterizing joint interface properties directly on assembled structures. The detailed analysis of a build-up structure showed that the vibrational mode energy is shifted by varying the joint interface’s compression preload. In a build-up structure, the location shift of vibration mode’s strain energy affects the dynamic responses together with the stiffness and damping properties of joint interfaces. The thesis demonstrates that it is possible to achieve high stiffness and high damping simultaneously in materials and structures. Analysis of the vibrational strain energy distribution was found essential for the success of vibration control.