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Carbon nanotube (CNT) growth was carried out on SiO2/Si substrates with a Co catalyst using an alcohol gas source method in an ultra-high vacuum chamber. The resulting CNTs were characterized by scanning electron microscopy (SEM), Raman spectroscopy and transmission electron microscopy (TEM). Reducing the ethanol pressure decreased the optimum growth temperature for maximum yield, enabling single-walled carbon nanotube (SWNT) growth at 400 degrees C. By employing an Al2Ox buffer layer, SWNT yield increased several times, even at 400 degrees C. Under TEM observation, the Co particle size on the Al2Ox layers did not show a significant dependence on the growth temperature between 400 and 700 degrees C. Raman and TEM results confirmed activation of Co particles with larger diameter (>1 nm) by the Al2Ox buffer layer.

The Raman spectra of carbon nanotubes (CNTs) formed on a 6H–SiC(0001) C-face substrate by surface decomposition were acquired using a 1064 nm Nd:YAG laser as the excitation source. Intense radial-breathing-mode Raman bands were successfully detected under resonant excitation from CNTs formed by the surface decomposition of SiC. Fine CNTs having diameters between 0.7 and 1.3 nm were observed on SiC after heating at 1700 °C in a vacuum electric furnace. These diameters are considerably smaller than those previously observed for CNTs grown by this technique.

Aluminum oxide (Al2Ox) buffer layers were employed in carbon nanotube (CNT) growth using an alcohol gas source and Co catalyst. The CNT yield was strongly dependent on the Al2Ox buffer layer thickness. By optimizing the thickness of deposited Al, vertically aligned single-walled nanotubes (SWNTs) were grown on Si substrates, even under an ethanol pressure of 10(-1) Pa. Transmission electron microscopy (TEM) revealed that Co particle size was strongly dependent on Al thickness. Dense Co particles about 2-4 nm in diameter were formed at the optimal Al thickness. Surface flatness of oxide layers was relatively independent of oxide thickness, and could be easily maintained up to the onset of CNT growth. Thus, Al2Ox layers promote formation of nanosized Co particles suitable for SWNT growth, providing a significant enhancement to yield. At the higher Al thickness, the yield was reduced, which was due to the diffusion of Co particles into the Al2Ox layer. Therefore, control of Al thickness is important to obtain efficient CNT growth.

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