Metallic Cr film coatings of 1.2μm thickness were prepared by DC magnetron sputter deposition method on c-plane sapphire substrates. The thin Cr films were ammoniated during horizontal furnace thermal annealing for 10-240 min in NH3 gas flow conditions between 400 and 900˚C. After annealing, changes in the crystal phase and chemical constituents of the films were characterized using X-ray diffraction (XRD) and energy dispersive X-ray photoelectron spectroscopy (XPS) surface analysis. Nitridation of the metallic Cr films begins at 500˚C and with further increases in annealing temperature not only chromium nitrides (Cr2N and CrN) but also chromium oxide (Cr2O3) was detected. The oxygen in the films originated from contamination during the film formation. With further increase of temperature above 800˚C, the nitrogen species were sufficiently supplied to the film's surface and transformed to the single-phase of CrN. However, the CrN phase was only available in a very small process window owing to the oxygen contamination during the sputter deposition. From the XPS analysis, the atomic concentration of oxygen in the as-deposited film was about 40 at% and decreased to the value of 15 at% with increase in annealing temperature up to 900˚C, while the nitrogen concentration was increased to 42 at%.

The ZnO thin films were grown on GaN template substrates by RF magnetron sputtering at different RF powers and n-ZnO/p-GaN heterojunction LEDs were fabricated to investigate the effect of the RF power on the characteristics of the n-ZnO/p-GaN LEDs. For the growth of the ZnO thin films, the substrate temperature was kept constant at 200˚C and the RF power was varied within the range of 200 to 500W at different growth times to deposit films of 100 nm thick. The electrical, optical and structural properties of ZnO thin films were investigated by ellipsometry, X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and by assessing the Hall effect. The characteristics of the n-ZnO/p-GaN LEDs were evaluated by current-voltage (I-V) and electroluminescence (EL) measurements. ZnO thin films were grown with a preferred c-axis orientation along the (0002) plane. The XRD peaks shifted to low angles and the surface roughness became non-uniform with an increase in the RF power. Also, the PL emission peak was red-shifted. The carrier density and the mobility decreased with the RF power. For the n-ZnO/p-GaN LED, the forward current at 20 V decreased and the threshold voltage increased with the RF power. The EL emission peak was observed at approximately 435 nm and the luminescence intensity decreased. Consequently, the crystallinity of the ZnO thin films grown with RF sputtering powers were improved. However, excess Zn affected the structural, electrical and optical properties of the ZnO thin films when the optimal RF power was exceeded. This excess RF power will degrade the characteristics of light emitting devices.

In this study, GaN powders were synthesized from gallium oxide-hydroxide (GaOOH) through an ammonification process in an NH3 flow with the variation of B2O3 additives within a temperature range of 300-1050˚C. The additive effect of B2O3 on the hexagonal phase GaN powder synthesis route was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transformation infrared transmission (FTIR) spectroscopy. With increasing the mol% of B2O3 additive in the GaOOH precursor powder, the transition temperature and the activation energy for GaN powder formation increased while the GaN synthesis limit-time (tc) shortened. The XPS results showed that Boron compounds of B2O3 and BN coexisted in the synthesized GaN powders. From the FTIR spectra, we were able to confirm that the GaN powder consisted of an amorphous or cubic phase B2O3 due to bond formation between B and O and the amorphous phase BN due to B-N bonds. The GaN powder synthesized from GaOOH and B2O3 mixed powder by an ammonification route through β-Ga2O3 intermediate state. During the ammonification process, boron compounds of B2O3 and BN coated β-Ga2O3 and GaN particles limited further nitridation processes.

The purpose of this study is to investigate the crystalline structure and optical properties of (GaZn)(NO) powders prepared by solid-state reaction between GaOOH and ZnO mixture under NH3 gas flow. While ammoniation of the GaOOH and ZnO mixture successfully produces the single phase of (GaZn)(NO) solid solution within a GaOOH rich composition of under 50 mol% of ZnO content, this process also produces a powder with coexisting (GaZn)(NO) and ZnO in a ZnO rich composition over 50 mol%. The GaOOH in the starting material was phase-transformed to α-, β-Ga2O3 in the NH3 environment; it was then reacted with ZnO to produce ZnGa2O4. Finally, the exchange reaction between nitrogen and oxygen atoms at the ZnGa2O4 powder surface forms a (GaZn)(NO) solid solution. Photoluminescence spectra from the (GaZn)(NO) solid solution consisted of oxygen-related red-emission bands and yellow-, green- and blue-emission bands from the Zn acceptor energy levels in the energy bandgap of the (GaZn)(NO) solid solutions.

ZnO thin films were grown on a sapphire substrate by RF magnetron sputtering. The characteristics of the thin films were investigated by ellipsometry, X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL), and Hall effect. The substrate temperature and growth time were kept constant at 200˚C at 30 minutes, respectively. The RF power was varied within the range of 200 to 500 W. ZnO thin films on sapphire substrate were grown with a preferred C-axis orientation along the (0002) plan; X-ray diffraction peak shifted to low angles and PL emission peak was red-shifted with increasing RF power. In addition, the electrical characteristics of the carrier density and mobility decreased and the resistivity increased. In the electrical and optical properties of ZnO thin films under variation of RF power, the crystallinity improved and the roughness increased with increasing RF power due to decreased oxygen vacancies and the presence of excess zinc above the optimal range of RF power. Consequently, the crystallinity of the ZnO thin films grown on sapphire substrate was improved with RF sputtering power; however, excess Zn resulted because of the structural, electrical, and optical properties of the ZnO thin films. Thus, excess RF power will act as a factor that degrades the device characteristics.

The synthesis and consolidation of titanium silicide by electro-discharge-sintering has been investigated. As-received Ti powder was in flaky shape and the mean particle size was , whereas the mean particle size of the pre-milled Si powder with angular shape was . Single pulse of 2.5 to 5.0 kJ/0.34g-elemental Ti and pre-milled Si powder mixture with the composition of Si was applied using capacitor. The solid with phase has been successfully fabricated by the discharge with the input energy more than 2.5kJ in less than Hv values were found to be higher than . The formation of occurred through a fast solid state diffusion reaction.

Ti-37.5at%Si elemental powder mixtures were mechanically alloyed by a high-energy ball mill, followed by CIP (cold isostatic pressing) and HIP (hot isostatic pressing) for different processing conditions. Only elemental phases (Ti and Si) were observed for the 5 min mechanically alloyed (MA 5 min) powder, but only phase was observed for the 30 min mechanically alloyed (MA 30 min) powder. phase was observed for the HIPed compact of MA 5 min and 30 min powders at 150 and 190 MPa for 3 hr at . For the HIPed compacts, the highest sintered density was obtained to be 99.5% of theoretical density by a HIP step at at 190MPa for 3hr. The hardness values of the HIPed compacts at at 150/190 MPa for 3hr were higher than HRC 76. The densification and mechanical property of HIPed compacts was found to depend on more HIP temperature than HIP pressure.

Nickel silicides (Si, NiSi and NiSi) have been synthesized by mechanical alloying (MA) of Ni-27.9at.9at%Si, Ni-33.3at% and Ni-50.0at% powder mixtures, respectively. From in situ thermal analysis, eash citical milling period for the formation of the three phases was observed to be 40.2, 34.9 and 57.5 min, at which there was a rapid increase in temperature. This indicates that rapid, self-propagating high-temperature synthesis (SHS) reactions were observed to produce the three phases during room-temperature high-energy ball milling of elemental powders. Each Ni silicide, Ni and Si, however, coexisted for an extended milling time even after the critical milling period. The powders mechanically alloyed after the critical period showed the rapid increase in microhardness. The Hv values were found to be higher than 1000kgf/mm. The formation of nickel silicides by mechanical alloying and the relevant reaction rates appeared to be influenced by the critical milling period and the heat of formation of the products involved (Si-43.1kJ/mol.at., NiSi-47.6kJ/mol.at., NiSi-42.4kJ/mol.at).

Different sizes of Si powder and milling medium materials (steel and partially stabilized zirconia (PSZ)) were used to synthesize and by mechanical aollying (MA) of Ti-25.0.at.%Si and Ti-66.7at.% Si powder mixtures. the formation of each titanium silicide did not occur even after 360 min of MA of as-re-ceived Si and Ti powder mixtures due to the lack of homogeneity. , however, was synthesized after 240 min of MA of Ti and 60 min-premilled Si powder mixture. and were produced by jar milling of Ti and 60 min-premilled Si powder mixture for 48 hr and high -energy PSZ ball-milling in a steel vial for 360 min. The formation of each titanium silicide was characterized by a slow reaction rate as the reactants and product(s) coexisted for a certain period of time. The formation of and and the reaction rates appeared to be influenced by the Si particle size, the homogeneity of the powder mixtures and the milling medium materials.

The synthesis of titanium silicides (, , , and TiSi) by mechanical alloying has been investigated. Rapid, self-propagating high-temperature synthesis (SHS) reactions were observed to produce the last three phases during room-temperature high-energy ball milling of elemental powders. Such reactions appeared to be ignited by mechanical impact in an intimate, fine powder mixture formed after a critical milling period. During the high-energy ball milling, the repeated impact at contact points leads to a local concentration of energy which may ignite a self-propagating reaction. From in-situ thermal analysis, each critical milling period for the formation of , and TiSi was observed to be 22, 35.5 and 53.5 min, respectively. and , however, have not been produced even till the milling period of 360 min due to lack of the homogeneity of the powder mixtures. The formation of titanium silicides by mechanical alloying and the relevant reaction rates appeared to depend upon the critical milling period, the homogeneity of the powder mixtures, and the heat of formation of the products involved.