Characterization of crystalline structure and morphology of NiO thin films.

We investigated the relation of sputtering powers with structural and morphological properties of nickel oxide (NiO) thin films. NiO thin films were fabricated by using an rf-reactive sputtering method on Si(100) substrates with a Ni target in a partial pressure of oxygen and argon. The films were deposited by various rf-sputtering powers from 100 to 200 W at room temperature. The phases and crystalline structures of the deposited films were investigated by using grazing incident X-ray diffraction (XRD). The thickness and surface morphology of the films were investigated by using a field emission-scanning electron microscopy (FE-SEM). The different sputtering conditions drastically affected the crystallinity and the surface morphology of NiO thin films. A combined analysis of the data obtained from X-ray diffraction and SEM images demonstrates that the preferred orientation of NiO films tends to grow from (111) to (200) direction as increasing the sputtering power, which can be explained by in terms of the surface energy along the indexing plane in an fcc structure. As increasing the rf power, lattice constants decreased from 4.26 to 4.20 angstroms and samples became high-quality crystals. Under our experimental condition, NiO films prepared at 150 W with 20% partial pressure of oxygen and 7 cm distance from the sample to the target show the best quality of the crystal.

Structural stability and kinetics of hydrogen in TiZrNi quasicrystals.

When hydrogen atoms slowly diffuse into a metastable structure, a coherence length of thin TiZrNi quasicrystal metallic ribbons is increased. Improved atomic order with addition of hydrogen is an uncommon phenomenon in metals, and may reflect the unordinary structural property of quasicrystals. Metastable TiZrNi quasicrystals prepared by rapid quenching of molten ingots were hydrogenated in a low pressure of hydrogen (lower than 1000 Torr) at high temperature. After completion of the pressure-composition-temperature measurements between 200 to 300 degrees C, X-ray diffraction data revealed that the full width at half maximum values of the diffraction peaks were decreased suggesting that the quasicrystal phase may stabilized by hydrogen inclusion. Annealing of the same sample at 200 degrees C without hydrogen yields no change of the relative intensity of diffraction peaks.

Structural and magnetic properties of TiZrNi thin films prepared by magnetron sputtering and thermal annealing.

Distinctive thin layers of TiZr and Ni were deposited by using a magnetron sputtering method and a thermal annealing was applied to discover metallic films of quasicrystals. After a heat treatment in vacuum, 70 nm thick deposited layers were well mixed with nominal compositions of 49.7, 29.3 and 21.0 for Ti, Zr and Ni, respectively, which is very close with the one forming a quasicrystalline phase. The magnetization values were significantly decreased from 0.286 to 0.142 emu/mm3 at 2000 Oe, after annealing, while a shape of magnetic hysteresis was maintained. It is believed that a different magnetic behavior after thermal annealing is due to the homogeneous mixing of atomic elements and possible existence of a metastable phase.