Center for Functional Nanomaterials Seminar

Nanowires represent an important and broad class of one-dimensional (1D) nanostructures at the forefront of nanoscience and nanotechnology. Nanowires are also attractive building blocks for functional nanoscale electronics, optoelectronic, electrochemical, and electromechanical devices. A remarkably elegant approach to produce those 1D nanowires is by metal-catalyzed formations via the vapor-liquid-solid (VLS) mechanism. Deeper understanding of nanowire formation mechanisms is vital for better control the morphology, rational design and predictable synthesis of nanowires, ultimately benefits deterministically to integrate such nanostructures into various technologies.
In situ TEM, a specialized technique, allows one to observe dynamic microstructural changes at atomic level as they occur, thereby validating conventional TEM experiments and inspiring new experimental approaches and theories. By encapsulating metal catalyst in a carbon cage, it is allowed the metal catalyst specie slowly to escape at high temperature. Thus, a situation is created where the amount of catalyst available for growth changes with time and temperature, termed Release Catalysis. It was demonstrated that more complex unusual silicon carbide (SiC) nanostructures such as cones, Y and T-shaped junction structures, can result from this unique procedure. With the aid of in situ TEM techniques, it is revealed that how different nanostructures grow from such time-varying catalysts in response to the dynamic behavior/ motion of the catalyst. This concept of “released catalysts” may be applicable for a range of different catalytic systems. The findings provide an approach for the formation of complex nanostructures that is much more versatile than previous techniques - including the nanowire growth techniques that are commonly studying - where the amount, geometry and activity of the catalyst do not change during growth.