Fabrication & Characterisation of Si Nanowire/ Carbon Nanotube Heterostructure Devices

Nanometre scale electronic structures are of both fundamental and technological interest. They provide a link between molecular and solid state physics and have potential to reach far higher device densities than is possible with conventional semiconductor technology. Nanoscale heterojunctions between SiNWs and CNTs may have important applications in nanoscale devices and as interfaces between new nanomaterials and conventional silicon electronics.

The first stage of this three-year project is to develop a solid-state process for growing SiNWs and understand and correlate the growth parameters to the properties of the wires produced. The solid-state reaction we have chosen uses the Ni/Ti/SiO2/Si-substrate layered system. This is because this system yields SiNWs with nickel catalyst particulates at the tip of the wires. We will use this nickel to further catalyse the growth of CNTs, therefore making the heterostructures.
The SiNWs solid-state reaction is being   characterised in terms of the metal layer structures and layer thicknesses. The metal layers are deposited by conventional magnetron sputtering using a system from JLS. After metal deposition, the structures are transferred to a furnace for annealing at 1000°C, where nanowire growth occurs. The Scanning Electron microscopy images show different kinds of wires that can be obtained from this process, by adjusting the initial metal-layer structure before growth.
 
We have grown SiNWs from these metal-structures. The nanowires were studied by SEM, TEM and Raman. Their structure and property dependencies on the Ni, Ti and oxide thicknesses are being correlated. Initial investigations show a strong dependency on the oxide layer. However, this also gives rise to a high proportion of silicon-dioxide wires, with an amorphous structure.