Biphenyl derivatives

We report the observation of a dependence of the low field resistance of blue bronzes on the electrical and thermal history of the samples. We suggest that these phenomena are related to the motion of charge-density wave domains boundaries coupled to defects.     

Fabrication and characterization of n-ZnO on p-SiC heterojunction diodes on 4H-SiC substrates

We report on the growth and characterization of n-ZnO/p-4H-SiC heterojunction diodes. Our n-ZnO layers were grown with radical-source molecular beam epitaxy (RS-MBE) on p-4H-SiC epilayers, which was previously prepared in a horizontal hot-wall reactor by chemical vapour deposition (CVD) on the n-type 4H-SiC wafers. Details on the n-ZnO growth on 8-off 4H-SiC wafers, the quality of the layers and the nature of realized p–n structures are discussed. Mesa diode structures were fabricated. Al was sputtered through a circle mask with diameter 1 mm and annealed to form Ohmic contacts to p-SiC. Ohmic contacts to the n-ZnO were formed by 30 nm/300 nm Ti/Au sputtered by electron beam evaporation. Electrical properties of the structures obtained have been studied with Hall measurements, and current–voltage measurements (I–V). I–V measurements of the device showed good rectifying behavior, from which a turn-on voltage of about 2 V was obtained.     

Fabrication of ZnO nanorod-based p–n heterojunction on SiC substrate

Due to the special properties of ZnO and numerous envisaged areas of application of its nanostructures, much effort has been made in fabricating ZnO nanostructures. The next challenging step seems to be the processing and hence realisation of devices based on the nanostructure. We have grown ZnO nanorods of high crystal quality and good optical properties on 6H-SiC and 4H-SiC substrates. Considering the p–n junction as a basis for electronic and optoelectronic devices, we realised ohmic contacts on p-type 4H-SiC and fabricated ZnO nanorod-based p–n heterojunctions with the p-type 4H-SiC serving as the hole-conducting region. Nanorod-based p–n diodes with a turn-on voltage of 1.8 V and relatively large reverse-bias breakdown voltage were obtained, thus suggesting both the possibility of ZnO nanorod-based ultraviolet photodetectors and light-emitting devices, and the miniaturisation of device scales.     

Dihedral Angles of Convex Polyhedra

Convex polyhedra in H ³ are not determined by (their combinatorics and) their edge lengths. Convex space-like polyhedra in the de Sitter space S ³ ₁ are determined neither by their dihedral angles nor by their edge lengths. The same holds of convex polyhedra in S ³ . Received November 16, 1998, and in revised form March 8, 1999.