The idea of half-metallic ferromagnets was first introduced by de Groot et al. in 1983 based on their calculations. The density of state at the Fermi level for half-metallic ferromagnet is completely polarized, meaning that only one of the spin up or spin down channel exists and has metallic behaviour while the other spin channel behaves as a semiconductor or insulator. This unusual electronic structure can be seen in different materials including Sr2FeMoO6, CrO2 and Mn-based Heusler alloys. The high spin polarization degree of the half-metallic ferromagnets makes them a perfect candidate to be used as a spin-injector/detector in spin-based electronics device (spintronics). However, the degree of spin polarization of these materials, particularly in the multilayered structure spintronic devices, strongly depends on the surface/interface quality and the presence of defects, which was the subject of the present study. Pulsed laser deposition (PLD) has been used to grow two examples of the half-metallic ferromagnets, namely, Sr2FeMoO6 and CrO2. The effects of the growth conditions (deposition temperature, gas pressure, laser power, target-to-substrate distance, post-annealing) and of the substrate lattice mismatch and thickness evolution have been studied. By optimizing the growth conditions, nanocrystalline Sr2FeMoO6 films have been grown on a Si(100) substrate for the first time. This single-phase Sr2FeMoO6 film was obtained at a temperature as low as 600°C, and it exhibits a high saturation magnetic moment of 3.4 μB per formula unit at 77 K. By using glancing-incidence X-ray diffraction with different incident beam angles, the crystal structure of the film was sampled as a function of depth. Despite the lack of good lattice matching with the Si substrate, a preferential orientation of the nanocrystals in the film was observed for the as-grown Sr2FeMoO6 films thicker than 60 nm. Furthermore, effects of the deposition temperature on the epitaxial growth of the Sr2FeMoO6 films on MgO(001) have been studied by means of high-resolution X-ray diffraction. The film grown at 800°C was post-annealed in oxygen, producing epitaxial films of SrMoO4 on top of the Sr2FeMoO6 film. The corresponding magnetization data showed that the post-annealing treatment lowered the saturation magnetic moment from 3.4 µB per formula unit (or /f.u.) for the as-grown Sr2FeMoO6 film to 1.4 µB/f.u. after annealing. X-ray photoemission measurements as a function of sputtering time further revealed the presence of SrMoO4 on both the as-grown and annealed films, and their corresponding depth profiles indicated a thicker SrMoO4 overlayer on the annealed film. The intensity ratios of the 3d features of Mo4+, Mo5+, and Mo6+ for Sr2FeMoO6 remained unchanged with sputtering depth (after 160 s of sputtering), supporting the conclusion that the observed secondary phase (SrMoO4) was formed predominantly on the surface and not in the sub-grain boundaries of the as-grown Sr2FeMoO6 film. The epitaxial growth evolution of Sr2FeMoO6 films of different thickness on substrates of MgO(001), SrTiO3(100) and LaAlO3(100) have also been studied. For each thickness, surface morphology, grain size, film epitaxy, and crystal quality were determined by atomic force microscopy and X-ray diffraction (-2θ scan and reciprocal space mapping). For thicker films (~120 nm), high resolution X-ray diffraction studies revealed that SrMoO4 and other parasitic phases tend to forms on SrTiO3 and LaAlO3 substrates, but not on those grown on MgO substrates. As a second part of the project, single-phase CrO2 nanostructured thin films have been grown for the first time directly on MgO(001) by PLD from a metallic Cr target in an O2 environment. X-ray diffraction shows that these films are strained and consist of CrO2 crystallites with two possible epitaxial relationships to the substrate: either CrO2(110) or CrO2(200) is parallel to MgO(001). X-ray photoemission further confirms that the films are primarily CrO2 covered with a thin CrO3 overlayer, and indicates its complete synthesis without any residual metallic Cr.

The idea of half-metallic ferromagnets was first introduced by de Groot et al. in 1983 based on their calculations. The density of state at the Fermi level for half-metallic ferromagnet is completely polarized, meaning that only one of the spin up or spin down channel exists and has metallic behaviour while the other spin channel behaves as a semiconductor or insulator. This unusual electronic structure can be seen in different materials including Sr2FeMoO6, CrO2 and Mn-based Heusler alloys. The high spin polarization degree of the half-metallic ferromagnets makes them a perfect candidate to be used as a spin-injector/detector in spin-based electronics device (spintronics). However, the degree of spin polarization of these materials, particularly in the multilayered structure spintronic devices, strongly depends on the surface/interface quality and the presence of defects, which was the subject of the present study. Pulsed laser deposition (PLD) has been used to grow two examples of the half-metallic ferromagnets, namely, Sr2FeMoO6 and CrO2. The effects of the growth conditions (deposition temperature, gas pressure, laser power, target-to-substrate distance, post-annealing) and of the substrate lattice mismatch and thickness evolution have been studied. By optimizing the growth conditions, nanocrystalline Sr2FeMoO6 films have been grown on a Si(100) substrate for the first time. This single-phase Sr2FeMoO6 film was obtained at a temperature as low as 600°C, and it exhibits a high saturation magnetic moment of 3.4 μB per formula unit at 77 K. By using glancing-incidence X-ray diffraction with different incident beam angles, the crystal structure of the film was sampled as a function of depth. Despite the lack of good lattice matching with the Si substrate, a preferential orientation of the nanocrystals in the film was observed for the as-grown Sr2FeMoO6 films thicker than 60 nm. Furthermore, effects of the deposition temperature on the epitaxial growth of the Sr2FeMoO6 films on MgO(001) have been studied by means of high-resolution X-ray diffraction. The film grown at 800°C was post-annealed in oxygen, producing epitaxial films of SrMoO4 on top of the Sr2FeMoO6 film. The corresponding magnetization data showed that the post-annealing treatment lowered the saturation magnetic moment from 3.4 µB per formula unit (or /f.u.) for the as-grown Sr2FeMoO6 film to 1.4 µB/f.u. after annealing. X-ray photoemission measurements as a function of sputtering time further revealed the presence of SrMoO4 on both the as-grown and annealed films, and their corresponding depth profiles indicated a thicker SrMoO4 overlayer on the annealed film. The intensity ratios of the 3d features of Mo4+, Mo5+, and Mo6+ for Sr2FeMoO6 remained unchanged with sputtering depth (after 160 s of sputtering), supporting the conclusion that the observed secondary phase (SrMoO4) was formed predominantly on the surface and not in the sub-grain boundaries of the as-grown Sr2FeMoO6 film. The epitaxial growth evolution of Sr2FeMoO6 films of different thickness on substrates of MgO(001), SrTiO3(100) and LaAlO3(100) have also been studied. For each thickness, surface morphology, grain size, film epitaxy, and crystal quality were determined by atomic force microscopy and X-ray diffraction (-2θ scan and reciprocal space mapping). For thicker films (~120 nm), high resolution X-ray diffraction studies revealed that SrMoO4 and other parasitic phases tend to forms on SrTiO3 and LaAlO3 substrates, but not on those grown on MgO substrates. As a second part of the project, single-phase CrO2 nanostructured thin films have been grown for the first time directly on MgO(001) by PLD from a metallic Cr target in an O2 environment. X-ray diffraction shows that these films are strained and consist of CrO2 crystallites with two possible epitaxial relationships to the substrate: either CrO2(110) or CrO2(200) is parallel to MgO(001). X-ray photoemission further confirms that the films are primarily CrO2 covered with a thin CrO3 overlayer, and indicates its complete synthesis without any residual metallic Cr.

Made available in DSpace on 2014-06-12T18:08:10Z (GMT). No. of bitstreams: 2 arquivo8041_1.pdf: 1032286 bytes, checksum: cb40cd20e21c163acad02ddabf34f51f (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2002 / Neste trabalho foi projetado e montado um sistema de evaporação de filmes finos utilizando um laser de Nd:YAG como a fonte de energia de evaporação com comprimentos de onda de 1064 nm e 532 nm. Esta técnica é conhecida como: Deposição com Laser Pulsado (Pulsed Laser Deposition, PLD). O material escolhido para evaporação foi o CdS. A caracterização dos filmes foi feita através de técnicas como difração de raios-X, microscopia eletrônica, transmissão, fotoluminescência, e absorção no infravermelho médio e distante por transformada de Fourier. Verificamos a obtenção de filmes cristalinos com estrutura wurtzita e com eixo c altamente orientado na direção perpendicular à superfície do substrato. Até onde conhecemos este é um resultado original para filmes evaporados com 532 nm. Através dos espectros de absorção e transmissão foram obtidos parâmetros importantes como espessura do filme, índice de refração, gap óptico e variação relativa da concentração de impurezas. Foi constatada uma diminuição na concentração de impurezas por excesso de Cd com o aumento da fluência e a diminuição do comprimento de onda de evaporação. O aumento da fluência também acarretou uma diminuição do gap do material como reflexo das variações na concentração de impurezas. As bandas de impurezas foram estudadas pela técnica de absorção no infravermelho médio e distante por transformada de Fourier. Os espectros de fotoluminescência obtidos mostraram picos de máxima intensidade no verde. Este aspecto é um indicador da alta qualidade dos filmes evaporados

Arcanobacterium haemolyticum, a Gram-positive bacterium, is an under-reportedagent of disease, causing pharyngitis, wound infections and a variety of invasive diseases.This work characterized a known A. haemolyticum toxin, phospholipase D (PLD), anddetermined its possible role in bacterial virulence. In addition, a novel toxin, arcanolysin(ALN), was identified and characterized. A draft genome sequence was determined andseveral additional virulence factors that may aid in disease pathogenesis were identified.PLD was present in all strains of A. haemolyticum tested, and was expressedmaximally during logarithmic growth. Recombinant PLD caused lipid raftrearrangement on the surface of HeLa cells in a dose-dependent manner. Thisrearrangement allowed maximal bacterial adhesion to the host, with a pld knockoutadhering only 39.7% to HeLa cells as compared to wildtype. Loss of production of PLDdid not affect bacterial invasion. However, PLD expressed by intracellular bacteria wascytotoxic to host cells, as determined by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium/phenazine methosulfate(MTS/PMS) viability assays. PLD caused host cell death via necrosis as determined bytransmission electron microscopy. PLD did not induce apoptosis, as caspases 3/7 and 9were not elevated in HeLa cells infected with wildtype A. haemolyticum.A. haemolyticum also expresses a Cholesterol-Dependent Cytolysin (CDC), ALN.Like pld, aln was present in all strains tested. ALN displays a variant undecapeptide andan unusual N-terminal extension not found in most other CDCs. Recombinant ALN11shows significantly increased activity against cultured cells and erythrocytes of humanorigin, compared with intermediate activity on rabbit and hamster cells, and low to noactivity on bovine and ovine cells as measured by hemolysis, cytotoxicity and membranebinding assays. ALN was less inhibited by free cholesterol when compared with otherCDCs, indicating the possibility of alternative receptor binding.The A. haemolyticum genome was sequenced to >20X coverage, and assembled to50 contigs covering ~95% of the genome. The genome is ~1.95Mb with a mol %G+C of53.1% and contained no plasmids. pld and aln have a reduced mol %G+C of 47.2% and46.5%, respectively, indicating the possibility of gene acquisition by horizontal transfer.Initial bioinformatics analysis identified genes encoding a protease, an extracellularDNase, two neuraminidases and three fimbrial biosynthetic operons were also identifiedwithin the genome.

In this thesis, the growth of c-axis oriented Sr2RuO4 thin films using pulsed laser deposition and their electrical transport properties are systematically discussed. The deposition and optimization process involved several progressive steps. Specifically, the first focus was on the Sr2RuO4 phase optimization in films grown on lattice-matched (LaAlO3)0.3(SrAl0.5Ta0.5O3)0.7 (LSAT) substrates. Film composition was found to be greatly influenced by changes in oxygen pressure, substrate temperature, target to substrate distance, and laser fluence. High oxygen pressure, low substrate temperature, large target to substrate distance, and high laser fluence increased the tendency to form the Ru-rich SrRuO3 phase in the film. The second focus was on improving the electrical transport properties of Sr2RuO4 from metal-insulating to fully metallic and eventually to superconducting behavior. It was observed that the full width at half maximum (FWHM) of the Sr2RuO4 (006) rocking curves in x-ray diffraction (XRD) scan was related to the quality of the electrical transport response. By fine tuning the deposition parameters to obtain low FWHM values, the electrical transport behavior of the Sr2RuO4 thin films was consistently improved from metal-insulating to fully metallic. In addition, localized superconductivity with enhanced superconducting transition temperature Tc onset was also observed among the fully metallic film. An in-depth study of the XRD results in fully metallic films indicated the existence of defects (intergrowths) along the c-axis direction, which caused localized c-axis tensile strain. The existence of structural defects within the film was likely to be responsible for the fact that only localized superconductivity was observed in the films. Furthermore, the enhanced superconducting transition temperature (Tc) relative to bulk single crystals is likely to be associated to localized strain in the film. Finally, Nb doped SrTiO3 substrates were used to achieve better quality growth of partial superconducting Sr2RuO4 thin films. Sr2RuO4 films grown on Nb doped SrTiO3 substrates had smaller FWHM values and lower level of c-axis tensile strain compared to those on LSAT substrates. Various partially superconducting films with different thicknesses and different superconducting Tc values are presented, and correlations between fabrication process, film crystalline quality as well as transport properties are discussed. This work provides better understanding of the importance of maximizing crystalline quality by delicate fine tuning of PLD deposition parameters to achieve high quality superconducting films.

Recent progress in layered transition metal dichalcogenides (TMDs) has led to various promising electronic and optoelectronic applications. However, the structure of materials plays a critical role in electronic and optoelectronic devices, and determines performance. Electronic and optoelectronic devices typically consist of multiple layers that form electrical homojunctions or heterojunctions. Therefore, in a device it can be expected that a WS2 layer may serve as the substrate for a subsequent layer in a multilayer device stack and determine how the layer grows. In transistor structures, roughness at the channel/gate dielectric interface introduces field variations and charge scattering. Therefore, understanding the relations between processing, surface morphology and properties is important. In this project, the effects of pulsed laser deposition (PLD) processing conditions on the surface morphology of few layered WS2 films were studied. WS2 films were synthesized under processing conditions that represent the extremes of surface supersaturation and kinetic energy transfer from the flux to the growing films, and evolution of the surface morphology was studied. The specific conditions were 1Hz/50mJ, 10Hz/50mJ, 1Hz/300mJ, and 10Hz/300mJ respectively. Combining AFM, XRD and Raman analyses, it was determined that deposition at 10Hz/300mJ, provided the best structural properties and surface morphology. Growth appeared to be 3D-cluster, and was governed by supersaturation rather than by surface diffusion processes. No clear correlation between mobility and surface roughness was found. Hall measurements and XPS data show the highest mobility was obtained with the highest S/W ratio, indicating that point defect scattering rather than scattering from surface roughness was dominant.

High tunability and low loss tangent of ferroelectric thinfilms offer unique opportunity for the development of variousmicrowave devices. Silver tantalate niobate, which showsexcellent microwave properties, was selected for this study.Ag(Ta,Nb)O3(ATN) showed week dielectric dispersion in a widefrequency range from 1 kHz up to 100 GHz, negligible losses upto 30 GHz, and ease to tailor paraelectric state in a widetemperature range by Ta:Nb ratio. This thesis is mainly based on the synthesis andcharacterization of niobate ferroelectric ATN thin films. Thinfilms for various measurements were prepared by pulsed laserdeposition and rf-magnetron sputtering techniques. X-ray diffraction (XRD) pattern show that ATN/Pt80Ir20films have been found to be (001) preferentiallyoriented, while the epitaxial quality of ATN/LaAlO3heterostructures have been ascertained. Dielectricproperties were analyzed by measuring the relationship betweendielectric permittivity and frequency as well as dielectricpermittivity and temperature. Reliable tracing of theferroelectric hysteresis polarization versus electric loopsindicate the ferroelectric state in ATN films at temperaturebelow 125 K and yields the remanant polarization of 0.4µC/cm2@ 77 K. The fundamental current-voltage behavior in Ag(Ta,Nb)O3ferroelectric films was measured usingMe/Ag(Ta,Nb)O3/Pt80Ir20, Me = Pd, Au, Cr, and Al, vertical capacitivecell structures with different top electrodes. Various kinds ofconduction mechanisms such as Schottky emission, Poole-Frenkel,Fowler-Nordheim, and ionic conduction were classified. Finally, by fabricating interdigital capacitors on the oxidesubstrates, the characteristics and performances of Ag(Ta,Nb)O3varactors were examined. Au/Cr/ATN/LaAlO3interdigital capacitors exhibited loss tangent aslow as 0.0033 @ 1 MHz, weak frequency dispersion of 5.8 % in 1kHz to 1 MHz range, tunability as high as 16.4 %,K-factor (tunability/tanδ) higher than 48.

Titanium nitride coatings have been widely applied and studied as high temperature diffusion barrier for silicon devices in microelectronics, wear resistant coatings in turbine blade materials, and materials for future high temperature nuclear reactors. In order to enhance the material property, superlattices is one of artificially engineered protective coatings, such as AlN/TiN and TaN/TiN multilayered films. Epitaxial cubic multilayer films, TaN/TiN and AlN/TiN nanolayers were grown on Si(001) by Pulsed Laser Deposition (PLD) with various nanolayer thicknesses and number of interfaces. Microstructural studies include X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution TEM with ion-irradiation experiments. Electrical, mechanical and thermal property studies were conducted for the interface and size effects on the nanolayers by using nanoindentation and Transient Thermo-Reflectance (TTR) methods. The microstructural and hardness study on TaN/TiN films with ion irradiation (12 keV and 50 keV He ) suggest no obvious microstructural or mechanical behavior change due to ion irradiation. In addition, titanium nitride that serves as effective diffusion barrier to prevent the inter-diffusion between the nuclear fuel and the cladding material was studied in order to enhance the lifetime of the fuels and the reliability of the fuel claddings. The TiN has good adhesion with the stainless steel and higher hardness than that of bulk TiN on the stainless steel. Thermal conductivity test demonstrates that thin TiN film has compatible thermal conductivity as the MA957 and HT-9 bars. The size effect on electrical resistivity is dominant in both of the epitaxial cubic and the polycrystalline TiN thin films in the thickness ranged from ~60 nm down to ~35nm. In the TaN/TiN multilayer, the grain scattering effect on resistivity is dominant rather than interface influence on the resistivity with comparing epitaxial cubic phase and polycrystalline phase. The microstructure and hardness studies of the AlN/TiN multilayer films with He implantation present that the suppression of amorphization in AlN layers and the reduction of radiation-induced softening were achieved in all nanolayer films. Radiation tolerance was found to be size dependent and the layer thickness leading to the highest radiation tolerance was around 10 nm. In addition, the embedded epitaxial cubic AlN with cladding TiN nanolayers showed higher effective thermal conductivity than that of AlN single layer as well as the embedded polycrystalline AlN in the thickness ranged from 10 nm down to 2 nm. It confirms a suppressed size effect, which reduces the amount of decrease in through-plane thermal conductivity.

The purpose of this thesis is to design and fabricate Gigahertz range voltage controlled oscillator based on intrinsically tunable film bulk acoustic resonator.Modified Butterworth Van Dyke (MBVD) model was studied and implemented to simulate FBAR behavior. Advanced designed system (ADS) was used as the simulation tool.Oscillator theory is studied and an oscillator based on non-tunable FBAR at 2GHz is simulated which shows -132 dBc/Hz phase noise @ 100 kHz offset frequency.A 5.5 GHz Voltage controlled oscillator based on intrinsically tunable FBAR is designed. Frequency tuning of 129 MHz with phase noise of -106 dBc/Hz @ 100 kHz is achieved. The circuit is designed on a novel carrier substrate which includes integrated resonators and passive components. Bipolar junction transistors are mounted on the carrier substrate by silver epoxy. The thesis describes the design, development and processing of the carrier substrate, BSTO based resonators, and the oscillator circuit.

<p>High tunability and low loss tangent of ferroelectric thinfilms offer unique opportunity for the development of variousmicrowave devices. Silver tantalate niobate, which showsexcellent microwave properties, was selected for this study.Ag(Ta,Nb)O₃(ATN) showed week dielectric dispersion in a widefrequency range from 1 kHz up to 100 GHz, negligible losses upto 30 GHz, and ease to tailor paraelectric state in a widetemperature range by Ta:Nb ratio.</p><p>This thesis is mainly based on the synthesis andcharacterization of niobate ferroelectric ATN thin films. Thinfilms for various measurements were prepared by pulsed laserdeposition and rf-magnetron sputtering techniques.</p><p>X-ray diffraction (XRD) pattern show that ATN/Pt₈₀Ir₂₀films have been found to be (001) preferentiallyoriented, while the epitaxial quality of ATN/LaAlO₃heterostructures have been ascertained. Dielectricproperties were analyzed by measuring the relationship betweendielectric permittivity and frequency as well as dielectricpermittivity and temperature. Reliable tracing of theferroelectric hysteresis polarization versus electric loopsindicate the ferroelectric state in ATN films at temperaturebelow 125 K and yields the remanant polarization of 0.4µC/cm²@ 77 K.</p><p>The fundamental current-voltage behavior in Ag(Ta,Nb)O₃ferroelectric films was measured usingMe/Ag(Ta,Nb)O₃/Pt₈₀Ir₂₀, Me = Pd, Au, Cr, and Al, vertical capacitivecell structures with different top electrodes. Various kinds ofconduction mechanisms such as Schottky emission, Poole-Frenkel,Fowler-Nordheim, and ionic conduction were classified.</p><p>Finally, by fabricating interdigital capacitors on the oxidesubstrates, the characteristics and performances of Ag(Ta,Nb)O₃varactors were examined. Au/Cr/ATN/LaAlO₃interdigital capacitors exhibited loss tangent aslow as 0.0033 @ 1 MHz, weak frequency dispersion of 5.8 % in 1kHz to 1 MHz range, tunability as high as 16.4 %,<i>K</i>-factor (tunability/tanδ) higher than 48.</p>