Tuesday, April 17, 2007

Blessie Basilia, Daniel O. Cardiel, Alver M. Musca, and Mark Jason P. Tiangco

A PRELIMINARY INVESTIGATION ON THE SYNTHESIS OF CARBON NANOTUBES ON GOLD-COATED SILICON SUBSTRATE
BY CHEMICAL VAPOR DEPOSITION

Blessie A. Basilia, Daniel O. Cardiel, Alver M. Musca and Mark Jason P. Tiangco

School of Earth and Materials Science and Engineering
MAPUA Institute of Technology
Muralla St., Intramuros, Manila, Philippines 1002
(babasilia@mapua.edu.ph, blessie_basilia@yahoo.com)

Carbon nanotubes (CNTs) are new technological materials that have numerous novel and useful properties. They are now considered as the strongest engineered material in the field of nanoscience and nanotechnology. Their unique structural and electronic properties have generated great interest for use in a broad range of potential nanodevices. CNT is a cylindrical carbon molecule that is a member of the fullerene structural family which comes in a variety of diameter and length. Depending on the growth process, the length can be approximately 100 nanometers to several microns and the diameter varies from 1 to 20 nanometers. There are primarily three main methods to grow carbon nanotubes: arc discharge, laser ablation and chemical vapor deposition (CVD). The first two methods are high temperature processes (2500oC) that yield high quality but poor density of carbon nanotubes while the third method is considered the cheapest way to grow CNTs and the highest yield. Several researchers nowadays focused on developing CNT of various morphologies by searching for new catalyst, substrates and carbon sources for CVD. In this study, using gold (Au) as catalyst will be a new parameter in CNT growth because most authors use iron (Fe), nickel (Ni) and cobalt (Co).

The aim of this research was to conduct a preliminary investigation on the synthesis of carbon nanotube by CVD using Au-coated silicon (Si) wafer substrate. This involved the flowing of hydrocarbon precursor such as ethanol or methanol into a heated CVD chamber containing Au-coated and etched Si-substrates. The heating/annealing conditions and etching parameters on the substrates were varied. The quality of CNTs produced from this technique was characterized by optical microscopy, Scanning Electron Microscopy and Energy Dispersive X-ray.

Based from the results of the study, synthesis of carbon nanotubes by CVD using gold as a catalyst was possible using hydrocarbons such as methanol and ethanol. Processing parameters such as 240 seconds etching time of the Au-coated Si substrate and annealing at 750oC for 30 minutes resulted to CNT growth during CVD. Surface morphology confirmed that methanol was a better precursor because it had produced long CNTs than ethanol. Likewise, EDX analysis showed that higher carbon atom percentage in carbon nanotubes were obtained using methanol than ethanol. But besides carbon nanotubes, other fiber-like structures of micron-sized were found during the SEM analysis. A phenomenological behavior of CNT growth using Au-coated Si wafer substrate was also developed. It illustrated that CNT growth was propagated when the dissolved carbon from the dissociation of the hydrocarbon precursor precipitates out the base of the gold tip pushing itself horizontally resulting to a tubular carbon nanotube.

Keywords: Carbon Nanotubes, Chemical Vapor Deposition, Scanning Electron Microscope

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