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. Understanding how to control the morphology, rational design and predictable synthesis of nanowires is vital in order to deterministically integrate such nanostructures into various technologies. A remarkably elegant approach to produce 1-dimensional (1D) nanostructures is by metal-catalyzed nanowire formation via the vapor-liquid-solid (VLS) mechanism. Our results demonstrated the successful synthesis of unusual silicon carbide (SiC) nanocones and Y, T branched heterostructures as catalyzed by an iron nanoparticle originally encapsulated within a graphite-like carbon shell. At high temperature, the Fe nanoparticles leave the C-shell, migrate and combine with other Fe to form larger Fe nanoclusters. The increasing cross-sectional diameter of the SiC is due to the increasing diameter of the exposed Fe surface, that catalyzes the SiC growth, which could be caused by the release of the nanocluster from the C-shell and/or the coalescence with later released Fe particles. The released Fe can migrate onto an existing SiC nanowire, which catalyzes the nucleation and growth of a secondary SiC nanowire. Consequently, different Y and T branched structures and more complex hierarchical SiC nanostructures can be realized from this unique catalytic process. The migration of iron nanocrystal from the graphitic carbon shell is visualized by in situ transmission electron microscopy (TEM). The resultant SiC nanocones and heterostructures are analyzed systematically by different electron microscopy techniques, including Z-contrast imaging, energy dispersive X-ray emission (EDX) and electron energy-loss spectroscopy (EELS) techniques, electron diffraction and high-resolution electron microscopy (HREM).