October 11, 2013
October 11, 2013
One major focus of my research is the combination of carbon nanotubes and few-layered graphene (FLG) into a hybrid nanostructured material. In the Nanomaterials and Thin Films lab, we have the unique capability of creating graphenated carbon nanotubes (g-CNTs), which are carbon nanotubes with leaf-like graphene “foliates” along the sidewalls, in a one-step PECVD process. In a recent set of parametric studies, the importance of various process parameters on the growth of carbon nanostructures in our 915 MHz microwave PECVD reactor, including carbon nanotubes (CNTs), g-CNTs, and vertically oriented carbon nanosheets, revealed an intriguing morphological dependence on temperature. As seen in the figure below, a range of morphologies is attainable by solely adjusting the deposition temperature, demonstrating a close connection between deposition temperature, graphene edge density, and specific capacitance.
In addition, I have recently studied the growth kinetics of carbon nanotubes deposited on a polycrystalline silicon substrate for applications in microelectromechanical systems (MEMS) devices. A set of experiments was performed to determine the activation energies associated with diffusion in different stages of growth on crystalline silicon and poly-silicon, namely diffusion into the catalyst nanoparticles during nucleation, and diffusion through the CNT forest to the substrate-affixed catalyst as deposition proceeds. A theoretical model was carefully employed to determine the diffusion-limited nature of CNT growth in our system and the nature of the diffusion process, supported by experimental data. Morphological features of CNT films grown on poly-Si, especially a reduction in film thickness, were tied to the polycrystalline grain structure of the substrate and the subsequent distribution of the catalyst nanoparticle array. We hope to make use of our new understanding of growth on this substrate to improve the quality of MEMS devices for use as cold cathode field emission sources.