Invited Paper IS+NC-ThA7
Kinetics of Individual Nucleation Events during Nanoscale Vapor-Liquid-Solid Growth

Thursday, October 23, 2008, 4:00 pm, Room 310

The growth of self-assembled nanostructures, such as nanowires, must be carried out with a high degree of control if electronic and optoelectronic devices are to be fabricated reliably. In particular, nucleation must be well controlled if a single nanostructure is to form at each location over a wafer. Using ultra high vacuum TEM, we have therefore examined nucleation in the model vapor-liquid-solid systems Si-Au and Ge-Au. We will present a quantitative analysis of both the initial transformation from solid Au to liquid Au-Si or Au-Ge eutectic and the subsequent formation of the nanowire nucleus. Quantitative measurements of nucleation and growth kinetics agree well with a simple model that provides a unified picture of the growth process. Nucleation is heterogeneous, occurring consistently at the edge of the liquid droplet, yet it is intrinsic and highly reproducible. We estimate the critical supersaturation required for nucleation, and find that size effects are surprisingly small, even for systems down to 12 nm in diameter. Nucleation is also important when forming nanowire heterostructures, and we examine this process in situ by observing the epitaxial nucleation of Si and Ge on wires formed of dissimilar materials such as GaP and GaAs. The observation and analysis of individual nucleation events in nanoscale systems leads to results that may be relevant to the formation of nanostructures for real-world applications.