Vertically aligned boron nanowires in self‐assembled large‐scale arrays with excellent uniformity and high density have been fabricated using radio‐frequency magnetron sputtering of boron and B2O3 powder onto various substrates. The nanowires thus produced are several tens of micrometers long and 20–80 nm wide, with typically platform‐shaped tips (see Figure for a high‐magnification SEM image).

Electron acceleration from the interaction of an intense short-pulse laser with low density plasma is considered. The relation between direct electron acceleration within the laser pulse and that in the wake is investigated analytically. The magnitude and location of the ponderomotive-force-caused charge separation field with respect to that of the pulse determine the relative effectiveness of the two acceleration mechanisms. It is shown that there is an optimum condition for acceleration in the wake. Electron acceleration within the pulse dominates as the pulse becomes sufficiently short, and the latter directly drives and even traps the electrons. The latter can reach ultrahigh energies and can be extracted by impinging the pulse on a solid target.

Effects of relaxation on glass transition and crystallization of ZrTiCuNiBe bulk metallic glassZr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass ͑BMG͒ was prepared by shock-wave quenching. Differences in property, structure, and thermal stability were found between the BMGs prepared by the shock-wave quenching and water quenching. The glass transition temperature of the shock-wave-quenched BMG is about 13 K higher than that of the water-quenched one. Although the density of the shock-wave-quenched BMG is decreased, the acoustic velocities in it are increased. Shock-wave quenching is possibly a promising method for preparing BMG.

The low-temperature behavior of tetragonal copper sulfide, Cu 2 S, was investigated by powder and singlecrystal x-ray diffraction, calorimetry, electrical resistance measurements, and ambient temperature optical absorption spectroscopy. The experiments were complemented by density-functional-theory-based calculations. High-quality, polycrystalline samples and single crystals of tetragonal copper sulfide were synthesized at 5 GPa and 700 K in a large volume multianvil press. Tetragonal Cu 2 S undergoes a temperature-induced phase transition to an orthorhombic structure at around 202 K with a hysteresis of ±21 K, an enthalpy of reaction of 1.3(2) kJ mol −1 , and an entropy of reaction of 6.5(2) J mol −1 K −1. The temperature dependence of the heat capacity at the transition temperature indicates that the transition from the tetragonal to the low-temperature polymorph is not a single process. The structure of the low-temperature polymorph at 100 K was solved in space group P na2 1. The structure is based on a slightly distorted cubic close packing of sulfur with copper in threefold coordination similar to the structure of tetragonal copper sulfide. The electrical resistance changes several orders of magnitude at the transition following the temperature hysteresis. The activation energy of the conductivity for the tetragonal phase and the low-temperature polymorph are 0.15(2) and 0.22(1) eV, respectively. The direct band gap of the tetragonal polymorph is found to be 1.04(2) eV with the absorption spectrum following Urbach's law. The activation energies and the band gaps of both phases are discussed with respect to the results of the calculated electronic band structures.

Glass transition behavior, crystallization kinetics, and microstructure change of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass under high pressure Crystallization of Zr 41 Ti 14 Cu 12.5 Ni 10 Be 22.5 bulk metallic glass under high temperature and high pressure has been investigated by in situ synchrotron radiation x-ray diffraction. The onset temperature of crystallization was found to increase with pressure, but with a sudden drop at about 5.6 GPa. Though the primarily precipitated phase is the same at different pressures, the sequences of the following phase precipitation are different.