Fabrications of Carbon Nanotube Devices using Thermal Chemical Vapour Deposition

Carbon nanotubes have been investigated over a long period of time due to their potential applications. For the synthesis of carbon nanotubes, catalytic chemical vapour deposition (CCVD) has attracted many scientists because it enables us to grow carbon nanotubes directly on to substrates and allows us to control the growth positions and the directions by employing catalytically patterned substrates and electric fields. However, not many carbon nanotube products have been commercialised yet due to the lack of understanding for the growth mechanism of carbon nanotubes. Further efforts are necessary to investigate the growth mechanism to obtain better control of crystallinity, chirality and other structural properties.
Carbon nanotubes are grown using thermal chemical vapour depositions and thin catalyst films which are deposited on silicon oxide/silicon wafers by sputterring. For the synthesis of carbon nanotubes, methane, hydrogen and helium were introduced in the furnace and the pressure, the gas flow and the growth temperature were varied during the growth and pre-treatment. For the patterning of catalyst films, e-beam lithography, conventional photo-lithography, and forcused ion beam were used.
Electric fields can be applied between the two electrodes during growth to control the growth direction of carbon nanotubes.

The carbon nanotubes were grown with the variations of the growth temperature and the procedure of pre-treatment. The structure of carbon nanofibres has changed from amorphous to graphitic as the concentration of hydrogen decreased in the initial periods of growth time. We considered the effects of the temperature and the role of gas species during the carbon nanotube growth from the point of view of gas and catalyst chemistry.

Scanning (a) and Transmission (b) Electron microscopy images of CNTs