Investigation of the oxide-assisted growth mechanism for nanowire growth and a model for this mechanism

Abstract

Oxide-assisted growth (OAG) mechanism produces high-density nonowires (NWs). Salient features of the existing models for this OAG mechanism and the fundamentals underlying this mechanism have been investigated in some detail. A simple, novel, malleable model for the OAG mechanism has been developed, and the concept of droplet used to develop this model has been articulated. The concept takes into consideration the size-dependent melting temperature depression. Two important elements of the model are (1) the attraction between the vapor-phase NW species and the droplet species, which leads to landing of the NW species on the droplet surface, and (2) the diffusion of the NW species through the droplet species to the liquid/solid interface, which leads to supersaturation and nucleation. The present investigation, together with our model, indicates that the assistance of a suitable oxide, the formation of nanoclusters/seeds, and the creation of droplets are all central to the OAG mechanism, which is essentially self-catalytic in nature. Various chemical reactions taking place on the droplet surface and the temperature range for these reactions are also important. The formation of a core and sheath during nucleation are the inevitable results of the use of oxide. The role of the droplet surface tension and the electrostatic forces between the droplet and the reactive (source) NW vapor species are crucial for OAG. Possible participation of a foreign element catalytic agent (FECA) in the NW growth by OAG mechanism has been examined. Based on these investigations, the present model appears to explain many of the OAG-grown NW characteristics. The experimentally observed oxide sheath has been addressed. Also, the basic causes of higher growth rates of the NWs grown by the OAG and FECA-mediated OAG mechanisms have been explained.