Real time observations of nanowire nucleation

Semiconductor nanowires are key materials in the field of nanotechnology, as they provide the opportunity to create new types of functionality in the area of electronic devices.

In this work, we have utilized the technique of transmission electron microscopy to investigate the fundamental mechanisms of how they form.  The most common technique for creating nanowires uses a small (<100 nm) metal particle (“catalyst”) to convert a gas source of a semiconductor material (e.g. silicon from the gas disilane) into a solid silicon crystal of small size.  This process requires “nucleation” to occur, much like the process of freezing ice in water.

Each of the steps required are shown in the animation above.  The solid metal particle (here a gold “Au” catalyst) helps to break apart the source gas into its constituents, Si and H2. The silicon becomes absorbed into the gold, resulting in the liquification of the alloy.  With continuing supply of Si into the liquid, the system becomes supersaturated, resulting in the formation of a new solid Si phase: the ‘nanowire’.

These studies provide insight into fundamental processes in the creation of crystalline materials.  By observing individual nucleation events at previously unattainable levels of magnification and resolution, one can carefully understand each step of the process.  We have found that the nucleation events are highly repeatable, implying that it may be possible to create these materials with the high demands for control on size and length required for the electronics industry.