Crystal tilts in the epitaxial lateral overgrown (ELO) GaN region over SiO2 mask by hydride vapor phase epitaxial away from the opening region were investigated by scanning electron microscope and the four-circle x-ray diffraction method. The increased mask width and ratio of stripe opening width to stripe period (fill factor) lead to increased wing tilts. The introduction of additional HCl and C3H8 /H2 can decrease wing tilts and improve the ELO GaN surface morphologies significantly. Moreover, it has been observed that a high growth rate will bring more defects and large wing tilts into the GaN materials.

Thin YBa2Cu3O7-d/La0.67Ca0.33MnO3 (YBCO/LCMO) films were grown on SrTiO3 (STO) substrates by magnetron sputtering technique. The microstructures of the bilayers were characterized and a standard four-probe technique was applied to measure the resistivity of the samples. The interdiffusions at the YBCO/LCMO and LCMO/STO interfaces formed two transient layers with the thickness of about 3 and 2nm, respectively. All the bilayers were well textured along the c axis. At low temperature, the superconductivity can only be observed when the thickness of YBCO is more than 25nm. When the ickness of YBCO is less than 8nm, the bilayers show only ferromagnetism. The superconductivity and ferromagnetism perhaps coexist in the bilayer with the YBCO thickness of 12.5nm. These interesting properties are related to the interaction between spin polarized electrons in the manganites and the cooper pairs in the cuprates.

A dynamic model of anisotropic x-ray diffraction is developed using two-wave approximation. A dispersion surface equation is derived for the screw-axis and glide-plane forbidden reflections. Propagation and polarization phenomena of waves are discussed. The deductions show that all these forbidden reflections may be excited except the 00l (l52n11) reflections for a 63 screw axis and the 00l (l56n13) reflections for 61 and 65 screw axes. The general methods are illustrated by their application to the rutile structure. [S0163-1829(99)3330-5]

The discovery of colossal magnetoresistance (CMR) 1 in thin film perovskite-like manganites has renewed interest in their possible use in device applications. 2 One of the crucial issues in thin film CMR manganites is the role of finite size effects related to structure on the thin film properties. Due to the restricted geometrical dimensionality of a thin film, a change in the layer thickness changes the metal-to-insulator transition temperature Tc. There exist several key areas for which we do not have a fundamental understanding of the physical processes that are occurring. Many of the problems arise from a poor understanding of the magnetism and structure at, or close to the interface region between the layer and the substrate.

We we have successfully fabricated ceramic superconductors of Hg-1223 with substitution of Pb for Hg, i. e. Hg1-xPbxBa2Ca2Cu3ov, by using encapsulation and short time annealing techniques. Samples fabricated in this manner may have nearly single phase structure and some enhancement ofTc can be achieved through this method. The materials of this ceramic with x ranging from 0 to 0.5 exhibit high-temperature superconductivity at temperatures falling in the range from 103 to 135K. The sample with optimum doping of Pb of x=0.34 and 6=0.40 has a highest Tc of 135K and its diamagnetic onset temperatureTdiac=143K. The composition of this sample has been found experimentally and is specified by a formula of Hg0.66Pb0.34Ba2Cal. 98Cu2.9708.4. The valence number for the copper constituent is given byvcu=2.30