Growth of metal-free carbon nanotubes on glass substrate with an amorphous carbon catalyst layer.

We have investigated the direct growth of metal-free carbon nanotubes (CNTs) on glass substrates with microwave-plasma enhanced chemical vapor deposition (MPECVD). Amorphous carbon (a-C) films were used as a catalyst layer to grow metal-free CNTs. The a-C films were deposited on Corning glass substrates using RF magnetron sputtering with the use of a carbon target (99.99%) at room temperature. They were pretreated with hydrogen plasma using a microwave PECVD at 600 degrees C. Then, CNTs were prepared using microwave PECVD with a mixture of methane (CH4) and hydrogen (H2) gases. The CNTs were grown at different substrate temperatures (400 degrees C, 500 degrees C, and 600 degrees C) for 30 minutes. Other conditions were fixed. The growth trends of CNTs against substrate temperature were observed by field emission scanning electron microscopy (FE-SEM). The structure of a-C catalyst layer and grown CNTs were measured by Raman spectroscopy. High-resolution transmission electron microscopy (HR-TEM) images showed that the CNTs had bamboo-like multi-walled structures. Energy dispersive spectroscopy (EDS) measurements confirmed that the CNTs consisted of only carbon.