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.

We have developed Fe-In-Sn-O fine particle or powder catalysts for synthesizing carbon nanocoils by catalytic thermal chemical vapor deposition. The coprecipitation technique was used to produce the powder catalysts. By optimizing the composition ratios of Fe, In (between 10 and 33% of Fe), and Sn (less than 3.3% of Fe), carbon nanocoils could be grown in high yield. From the study of optimizing the compositions of In and Sn and the study of crystal structures of the catalysts using X-ray diffraction measurements, it was also found that Sn in the catalysts was required to grow carbon nanocoils and that In plays roles in increasing the yield of carbon nanocoils and controlling the coil diameters. This study will lead to the mass production of carbon nanocoils and therefore widen their applications.

The nonlinear I/V characteristics of a molecular rectifier structure of the form Au/20 layers of C16H33Q-3CNQ/Au have been explored from 8 to 300 K. At 8 K the voltage-controlled nonlinear conduction is explored in the absence of thermal effects. At the highest voltages (±15 V) at 8 K the rectification ratio was about 4 with current densities as high as 1000 A m−2 and log I varying as |V|0.5, indicating voltage-controlled hopping. The likely explanation for the complete I/V characteristics rests with the insulating aliphatic tails, which provide substantial electrical barriers within the structure.

Multiwalled carbon nanocoils (CNCs) have been synthesized by a method of thermal chemical vapor deposition (CVD) using a codeposited thin film consisting of Fe and Sn as catalysts. It has been found that the multiwalled CNCs are thinner and have a higher crystallinity than conventional CNCs. The catalyst particles are observed at the roots of CNCs, with diameters much larger than the line diameters of the coils. These large particles are formed by the aggregation of Sn and Fe reduced by the C 2 H 2 gas in CVD. These results indicate that Sn plays a crucial role in the growth of the multiwalled CNCs, and a base growth mechanism that differs from conventional growth mechanisms has been experimentally observed and analyzed.