Growth of carbon nanotubes and semiconductor nanowires on silicon by chemical vapor deposition.

摘要

Carbon nanotubes (CNTs) are a promising material for nano-electronic devices because of their electrical properties and very small diameter. However, controlling their electronic properties depending on chirality and tube diameter of the CNTs and growth direction of the CNTs has been a challenge for realizing nanotube-based electronic devices. Until now, the growth mechanism of CNTs was not fully understood and controlling the growth of CNTs completely is still a major challenge. Understanding of the growth mechanism of CNTs is an essential in order to achieve controllability in both growth direction and electrical properties of nanotubes by chemical vapor deposition (CVD). There are many variables, however, to consider in this process, including the type of gases, catalyst metals, and supporting substrates.; Supporting substrates of the catalyst metals are also an important factor in the growth of carbon nanotube. It is known that interaction between catalyst particle and support is required for catalytic activity. In particular, oxygen-containing materials are known as a suitable support for this purpose. Our study is focused on the growth mechanism of CNTs on silicon oxide by chemical vapor deposition (CVD). In particular, the chemical interaction between the vapor phase and the supporting oxide is investigated relating to the growth mechanism of CNTs.; Methane (CH4) and hydrogen (H2) are used as reaction gases and nickel is used as a catalyst. CO is generated by chemical interaction between the supporting oxide and the process gases; thereby complicates the composition of the gas components in CVD process. In order to modulate CO vapor concentration in the system, metal oxide powders, such as titanium oxide (TiO2), silicon oxide (SiO2) and silicon oxide/iron nitrate mixture are adopted based on the thermodynamic calculation of CO vapor pressure of the each oxide in the CH4-H2 system.; Nanotubes can be used individually or as an ensemble to build a functional device prototype. Ensembles of nanotubes have been used for field emission based flat panel display. Individual nanotubes have been used for field emission sources and as tips for scanning probes. Nanotubes also have significant potential as the central elements of nano-electronic devices including field effect transistors (FETs), single-electron transistors, and rectifying diodes. In an effort to find a way to align carbon nanotubes on silicon substrate, the growth orientation of carbon nanotube is investigated on single crystal iron nano particles on silicon wafer. The iron nano particles are adhered to the substrate by magnetic field from dispersion. Our study suggests the possibility of controlling the growth orientation of the CNTs. Furthermore, novel evidence is given for the growth mechanism of the CNTs by CVD.