B.Q. Hu

Growth and luminescence characterization of large-scale zinc oxide nanowires

Large-scale zinc oxide (ZnO) nanowires were grown via a simple chemical reaction involving water vapour. Electron microscopy observations reveal that the ZnO nanowires are single crystalline and grow along the c-axis ([001]) direction. Room temperature photoluminescence measurements show a striking blue emission at 466 nm along with two other emissions in the ultraviolet and yellow regions. Annealing treatment of the as-grown ZnO nanowires results in an apparent reduction of the intensity of the blue emission, which indicates that the blue emission might be originating from the oxygen or zinc defects generated in the process of growth of the ZnO nanowires.

Defects in large single crystals Nd: YVO4

The exchange anisotropy in NiFe/NiMn bilayers was studied by using the planar Hall effect. The sputtered NiFe/NiMn films were patterned into strips of 1 mm in length and 200 mum in width and with six terminals for anisotropy magnetoresistance and planar Hall voltage measurements by a photolithographic process. It is shown that the planar Hall effect is an effective method to characterize the exchange anisotropy in ferromagnetic/antiferromagnetic (AF) systems. It can be used to accurately determine the exchange field and describe the magnetization reversal processes. The effective uniaxial anisotropy field H-K eff, the effective unidirectional anisotropy field H-ud, and AF domain wall energy H-w can be obtained by fitting the experimental results. We found that in the NiFe/NiMn bilayer system, the parameters H-K eff, H-ud, and H-w have the same values in reversible and irreversible measurements, and the domain wall energy in AF layer is larger than interfacial unidirectional anisotropy

New type of defects in SiC grown by the PVT method

The quality of SiC crystals grown by the physical vapour transport (PVT) method was studied by means of optical microscopy and scanning electron microscopy (SEM) observations with the aid of etching by molten KOH. New types of defects were found, including triangular etching pits, shallow hexagonal etching pits and dendritic silicon inclusions in 4H-SiC. The triangular etching pits usually appear on the C face with a size comparable with the irregular dark etching pits due to the micropipes, while the shallow hexagonal etching pits were observed on the Si face with a size comparable with that due to the micropipes. The silicon inclusions exhibit dendritic shape up to several microns like those usually observed in metal alloys. In addition, 4H-SiC and 6H-SiC domains with different polarities in the growth surface were found to develop from the same seed. The interface of 4H-SiC and 6H-SiC was one of the sources for inducing the micropipes.

Growth of single crystals of YB2 by a flux method

YB2 crystals with cross-sections of several square millimeters were prepared using Y flux in a pyrolytic BN crucible by a flux method. The as-grown crystals have good structural properties. The electrical resistivity and magnetic susceptibility of YB2 were measured. It is shown that YB2 is a paramagnetic compound and above 20 K the temperature dependence of magnetic susceptibility in YB2 obeys well with the Curie-Weiss law

Study on the structure and superconductivity of La2CuO4+δ chemically oxidized by NaClO at 50 °C

A series of La2CuO4+δ samples chemically oxidized at 50 °C with different oxidation times using NaClO as the oxidizing agent have been prepared. All the oxidized samples are single-phase bulk superconductors with an onset transition temperature at 42-45 K measured by dc magnetic susceptibility. X-ray powder diffraction indicates that all the oxidized samples are orthorhombic, and show an enhanced orthorhombic distortion with the oxidation time, compared with that of the starting material. The excess oxygen contents of the oxidized samples determined by iodometric titration are large and increase with the oxidation time. The fit to the experimental data reveals that the excess oxygen content versus the oxidation time obeys the law of the second-order exponential decay. No obvious changes in the grains of the samples before and after oxidation have been observed by scanning electron microscopy.