Effect of Hydrogen on Carbon Nanowall Growth by Microwave Plasma-Enhanced Chemical Vapor Deposition

概要

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The effect of hydrogen on the growth of carbon nanowalls (CNWs) with different hydrogen-to-carbon (H2/CH4) flow ratios in chemical vapor deposition was investigated using scanning electron microscopy (SEM) and Raman spectroscopy. The CNWs were synthesized on catalyst-free substrates (Si or SiO2) by microwave plasma-enhanced chemical vapor deposition (MPECVD). At low H2/CH4 flow rate ratios (0--2), the wall size increased with increasing H2/CH4 flow rate ratio while the $I_{\text{G}}/I_{\text{D}}$ remained constant; however, at high H2/CH4 flow rate ratios (2--4), the wall size decreased and $I_{\text{G}}/I_{\text{D}}$ increased with increasing H2/CH4 flow rate ratios. This indicates that hydrogen plays different roles in the two ranges: reduction of nucleation density resulting in the larger CNWs for the former range and removal of amorphous carbon resulting in a higher $I_{\text{G}}/I_{\text{D}}$ for the latter range. Note that the present growth method provides an extremely high growth rate of CNWs reaching 23 μm/h.
2011-01-25