In Situ Study of Iron Catalysts for Carbon Nanotube Growth Using X-Ray Diffraction Analysis

We have investigated how an iron catalyst changes during the growth of vertically aligned carbon nanotubes by in situ measurement of X-ray diffraction. It is found that heating the catalyst film to a growth temperature of 700°C in He atmosphere induces its oxidation beyond 100°C due to adsorbed moisture and changes the film to particles at approximately 600°C. At 700°C, the catalyst particles consist mainly of iron oxide with a cubic system. By feeding C2H2, the catalyst starts to be deoxidized and then absorbs carbon atoms to form Fe-C and Fe3C. The growth mechanism of nanotubes is discussed in terms of the crystalline phase and orientation of the catalyst.