We have examined the formation of silicon nanowires grown by self-assembly from Si substrates with thin aluminum films. Postgrowth and in situ investigations using various Al deposition and annealing conditions suggest that nanowire growth takes place with a supercooled liquid droplet (i.e., the vapor-liquid-solid system), even though the growth temperatures are below the bulk Al/Si eutectic temperature. Wire morphology as a function of processing conditions is also described. It is shown that when Al environmental exposure is prevented before wire growth a wide process window for wire formation can be achieved. Under optimum growth conditions, it is possible to produce excellent crystal quality nanowires with rapid growth rates, high surface densities, low diameter dispersion, and controlled tapering. Photoelectron spectroscopy measurements indicate that the use of Al leads to active doping levels that depend on the growth temperature in as-grown nanowires and increase when annealed. We suggest that these structural and electronic properties will be relevant to photovoltaic and other applications, where the more common use of Au is believed to be detrimental to performance.

Raman microscopy has been used to investigate phase transitions within Vickers diamond residual indentations, made at room temperature and at 77 K, in single crystal Si(100) and 0.3 µm thick amorphous silicon film deposited on a sapphire single crystal. It has been found that for room temperature residual indentations in the single crystal silicon (Si-I) and amorphous silicon film phase transition to the Si-III phase occurs, as indicated by the existence of Raman peaks corresponding to this phase. On the other hand, in the case of the indentations made at 77 K, only the Si-I crystalline phase and amorphous silicon were found within the residual indentations. It has been suggested that when Vickers diamond indentations are made at 77 K, there is no phase transition to the Si-II (i.e. the β-Sn phase) during indenter loading, which would give rise to the Si-III phase on the removal of indenter load. Moreover, the existence of a very strong peak due to the Si-I phase gives further support to the suggestion that during Vickers indentations in single crystal silicon and in amorphous silicon at 77 K there is no structural phase transition. It has also been suggested that during room temperature indentations there is a substantial temperature rise, which may help to cause structural phase transitions.

It has been known for about 15 years that when a Vickers indenter is loaded on to a crystalline semiconductor, such as silicon, a semiconductor to metallic phase transition occurs during indenter loading and on removal of the indenter the material within the residual indentation becomes amorphous. Here we report a completely opposite effect: when a Berkovich or Vickers diamond indenter is loaded onto a submicrometer thick film of amorphous germanium, it crystallizes and undergoes structural phase transitions. These observations are based on our transmission electron microscopy and Raman scattering investigations, which have been described. It has also been shown that the indentation-induced crystallization and phase transitions occur close to the indenter tip, where the plastic strains are the highest.

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Mapping the three-dimensional strain field around a microindentation on silicon using polishing and Raman spectroscopy Using four-terminal in-situ dc electrical resistance measurements and Raman spectra of residual Vickers indentations in single crystals of Si ͑100͒, it has been shown that the sample temperature, in the range of 150 to 300 K, at which a Vickers diamond indentation is made, has a strong influence on the occurrence of indentation-induced phase transitions within the plastically deformed zone around the indentation. A consistent explanation of the experimental results, based on an existing theoretical pressure-temperature phase diagram of silicon, has been provided.