The catalyst droplet plays a fundamental role in determining the structure of nanowires, and the remarkable range of structures enabled by the vapor-liquid-solid (VLS) growth mode can be thought of as the result of engineered changes to the droplet. For example, changing the droplet contact angle by varying its volume can alter the nanowire diameter, the sidewall structure and even, in some materials, switch between growth of one crystal structure and another. A new approach to droplet engineering, consist in the application of an external electric field during growth. The electric field deforms the droplet, directly altering its shape, contact angle and position, without affecting other aspects of growth.
We explore electric field effects by growing nanowires inside a microfabricated growth system that can be operated in an in situ transmission electron microscope (TEM). We image the changes in droplet geometry and nanowire growth as voltage is applied. With this approach, we explore strategies to create new types of complex, three dimensional nanostructures.
Movie caption. A voltage is applied between a silicon nanowire and a counter electrode at a distance of 170 nm. The generated electric field stretches the nanowire droplet. This was used to control the nanowire diameter and growth direction. Using in situ transmission electron microscopy, we record in real time the deformation of the AuSi droplet.