Nanowires are anisotropic structures which have diameters of several to tens of nm’s while their lengths could be μm’s long. Thus they have a very high aspect ratio, large surface-area-to-volumeratio and allow carrier/photon confinement in two dimensions, which lead to their unique properties.They are usually grown by the so-called vapour-liquid-solid mechanism, which relies on a metal nanoparticle to catalyze and seed the growth. An alternative technique to grow the nanowires is by selective area growth, where a dielectric mask is first patterned on the substrate prior to growth.Inverse opals are highly ordered macroporous materials consisting of a face-centered cubic crystal,formed through the infiltration of another material into a sacrificial opal template, and followed by the removal of the spheres. They are ideal for photocatalysis due to their inherent structural properties such as a large surface area, tunable macroporosity, and stability. The interconnected macroporous architecture allows accessibility of the electrolyte to the active sites of the photocatalyst, and also provide long-range ordered paths for electron transport throughout the electrode, thus improving charge migration.
In this talk, I will present the III-V semiconductor nanowire activities at The Australian National University. Various issues related to nanowire growth such as crystal structure, tapering, crystalline defects and formation of axial and radial heterostructures will be discussed. Results from three types of device - nanowire lasers, solar cells and photoelectrodes for solar water splitting will then be presented. I will also show and discuss our results of using TiO2 inverse opal structure as the photoelectrode and also as a template for CdS for photoelectrochemical water splitting, including tandem devices.
Finally, I will introduce some of the new research activities in my group, such as the growth of shape engineered nanostructures, van der Waal epitaxy and the growth of hexagonal hBN, which is a of 2-D material.