Carbon nanotubes (CNT) are an important new class of technological materials that have numerous novel and useful properties. Most carbon nanotube synthesis techniques require the introduction of metal catalyst in the form of gas particulates or as a solid support. However, the main problem of using metal nanoparticles for CNT’s growth is presence of impurities and thus usually requires further CNT purification which normally introduces unavoidable defects along the tubes and the pentagonal structure at the tube ends.
To date the successful synthesis of metal-catalyst-free carbon nanotubes on Si/SiO2 substrates has only been achieved by using higher temperature (over 800 ºC) CVD methods. However, since almost all exiting developed electronics devices have electrical interconnections, almost of which are formed of aluminium having a melting point of 660 ºC, it is very important to develop the method of low temperature CVD synthesis of metal-catalyst-free CNTs.
In our research we demonstrate successful growth of CNTs at 500 ºC without high temperature pre-treatment. It was found that the chemical pre-treatment of the Si-substrate in liquid ethanol is critical for defect generation on a Si/SO2 surface which were found to be responsible for carbon precipitation and formation of the metal-catalyst-free CNTs. The role of separating ethanol vapour pyrolysis from the CNT formation in the two-zone CVD and the role of ethanol pre-treatment of the Si/SO2 surface are discussed.