Plasma-enhanced chemical vapor deposition of carbon nanotubes using alcohol vapor

We have successfully grown carbon nanotubes (CNTs) by alcohol plasma-enhanced chemical vapor deposition (PECVD). When 0.01 wt% ferrocene was added to alcohol, vertically-aligned CNTs could be grown using RF (= 13.56 MHz) plasma at 650ºC. In contrast, no CNTs were obtained by pure alcohol PECVD. To understand the plasma properties for CNT growth, especially plasma species containing a gas phase of alcohol plasma, we analyzed the plasma using optical emission spectroscopy (OES) and quadrupole mass spectrometry (QMS). From the OES measurement, one could identify the emission peaks from the excitation states of CHO, CO, C 2 , O 2 , H, CH + , and H 2 O + , while the QMS measurement also showed the existence of CO, H 2 O, and C x H y (x≥2, y≥2). It is considered that such plasma species affect CNT growth by changing the oxidation state of the catalyst or by adjusting the amount of precursor species in the plasma. Comparing this PECVD experiment with thermal alcohol CVD (without plasma), only PECVD can be used to grow CNTs under the reported experimental conditions. It is considered that thermal alcohol CVD requires more energy to grow CNTs because 650ºC is a little lower than the temperature required for CNT growth. These results indicate that in alcohol plasma, the active species produced by decomposition and recombination reactions have a possibility to promote/suppress CNT growth depending on the process conditions.