Center for Functional Nanomaterials Seminar

Crucial to the application of nanostructured materials is control over their nucleation and growth, as these aspects determine their structure and thus properties. We will review our work concerning these issues in both semiconductor nanowires and carbon nanotubes. These studies exploit a combination of environmental and ultra-high vacuum transmission electron microscopy approaches to observe these processes in real time and at high resolutions. Interestingly, nanowire and nanotube growth share many similarities. In each case small metal nanoparticles are used to catalyze the decomposition of relatively simple source gas. This decomposition leads to incorporation of the growth element (Si, Ge, C, …) into the particle until supersaturation is reached and the new nanostructure nucleates and grows. We will present measurements of the nucleation and growth process in Si nanowires, quantifying the process as it proceeds from the initial solid Au nanoparticle, through the creation of the AuSi eutectic liquid and finally towards Si nanowire nucleation and growth. The observations will demonstrate the reproducibility of the process, and allow determination of the rate limiting steps for nanowire growth. In the case of carbon nanotube growth, we will demonstrate that both Ostwald ripening and atomistic diffusion of the Fe catalytic nanoparticles lead to growth termination and we will present early results that suggest a pathway towards the creation of an ‘immortal’ catalyst to support continuous nanotube growth. Recent observations suggesting a route towards chirality control will also be described and future directions in both nanostructure nucleation and general catalysis experimentation will be outlined.