Invited Paper NS+EM-WeM3
In Situ Kinetic Measurements during the Nucleation and Growth of Si and Ge Nanowires

Wednesday, October 17, 2007, 8:40 am, Room 616

In this presentation we will discuss the growth of epitaxial nanowires in Si and Ge using Au as the catalyst, focusing on the kinetic processes that influence nucleation and wire shape. We grow wires in an environmental TEM, which has capabilities for evaporating Au onto a clean Si substrate and for introducing the precursor gases while the sample remains under observation. In situ video rate imaging allows us to measure nucleation events and growth kinetics and to observe structures during growth. We will start by showing the nucleation of Si nanowires within the catalyst particles, and will discuss the buildup of supersaturation that leads to nucleation. After nucleation, the variation of growth rate with pressure, temperature and droplet size allows us to determine the rate limiting step and evaluate the relevance of curvature-driven effects to wire growth. For Si wires, the simple picture that results is complicated by some interesting phenomena caused by the high mobility of Au on the wire surface. And for Ge wires, we show that the growth-driven supersaturation can stabilise the droplets and allow growth far below the eutectic temperature. We finally discuss the growth of hybrid nanowires composed of group IV and group III-V components, showing how the balance of interface energies determines the overall structure. Thus we find that nanowires provide a unique window into fundamental crystal growth processes, as well as an opportunity to fabricate precisely controlled structures for novel applications.