Nanostructural transformation and formation of heterojunctions from Si nanowires.

Si nanowires coated with Ni showed interesting structural transformation behaviors as observed by in situ transmission electron microscopy. Owing to the presence of the native oxide on Si nanowire surfaces, the Ni thin shells initially segregated into nanosized droplets on the oxide surfaces. The native oxide shells protected the Si cores from reacting with Ni at temperatures below 1350 °C. Ni started the reaction with Si nanowires preferentially at the defects or bending regions of the nanowires. Because the reaction temperature was sufficiently high, the structural transformation was extremely fast and completed within 0.1 s. The resulting nanowires were single crystalline NiSi(2), the most desirable Ni silicide structure for potential applications. Nanowire junctions of NiSi(2)/Si and nanowire-nanotube junctions of NiSi(2)/SiC have been obtained upon further annealing.