Showing papers by "Peidong Yang published in 1996"

Nanorod-superconductor composites : A pathway to materials with high critical current densities

Abstract: Most large-scale applications of the high-temperature copper oxide superconductors (HTSCs) require high critical current densities (Jc9s) at temperatures near the boiling point of liquid nitrogen to be technologically useful, although thermally activated flux flow reduces Jc dramatically at these temperatures. This intrinsic limitation can be overcome by introducing nanometer-sized columnar defects into an HTSC. Nanorods of magnesium oxide were grown and incorporated into HTSCs to form nanorod-HTSC composites. In this way, a high density of nanorod columnar defects can be created with orientations perpendicular and parallel to the copper oxide planes. The Jc9s of the nanorod-HTSC composites are enhanced dramatically at high temperatures and magnetic fields as compared with reference samples; these composites may thus represent a technologically viable strategy for overcoming thermally activated flux flow in large-scale applications.

Pulsed Laser Deposition of Diamond-Like Carbon Thin Films: Ablation Dynamics and Growth

Abstract: Thin films of diamond-like carbon have been grown by pulsed laser deposition using a Nd:YAG laser at 532 nm. Time-of-flight mass spectroscopy was used to investigate the effects of laser power density and background gas pressure on the plume characteristics including the species in the plume and the kinetic energy distribution of each species. We found that with increasing laser power density (1) the relative amount of C+ ions increases, (2) the kinetic energy distributions of C+ get broader and can be deconvoluted into fast and slow components, and (3) the kinetic energy of the fast component of C+ ions increases from several to 40 eV. The resistivity and the local carbon bonding in films grown under these same conditions were also characterized. It was found that there is direct correlation between the characteristics of fast part of C+ ions in the plume and the diamond-like properties of the thin films. Under optimal growth conditions diamond-like carbon films with a large fraction of sp3 bonding can be prepared, although the maximum fraction appears to saturate at 70%. The implications of these results are discussed.