Patterned aligned growth of carbon nanotubes on porous structure templates using chemical vapor deposition methods

Abstract

In order to synthesize carbon nanotubes (CNTs) on the templates for diameter, density or alignment control, we prepared porous structure templates by electrochemical method. The p-Si(100) wafer was anodized in hydrofluoric acid (HF) aqueous solution under constant current density. The HF solution concentration is varied for controlling desired pore size and density. Following the anodization process, patterned Ni-catalyst of thickness 10 nm by e-gun evaporation and lift-off process were prepared. After 900 °C thermal pre-treatment process, the density of catalytic metal particles on porous silicon template was dramatically dropped off in each pattern because the catalyst particles only formed on edges of some pore mouths, and most of the nickel cleaved into the porous structure. After the thermal pre-treament process, CNTs were grown by thermal-CVD method using argon (Ar), ammonia (NH 3), methane (CH 4) mixing gas and by high-density-plasma (HDP)-CVD method using acetylene (C 2H 2) and hydrogen (H 2), respectively. For thermal-CVD method, the ratio of NH 3/CH 4 was found very sensitive in CNTs growth on plain silicon, but not on porous silicon. It was also discovered that CNTs grew on plain silicon by base growth mechanism in thermal-CVD, whereas they grew on porous template by tip growth mechanism, which suggested that porous structure effectively provided channels to help methane reaching the nickel catalyst particles from the top surfaces before they were passivated by amorphous carbon. On contrast, CNTs grew on both plain and porous template by tip growth in HDP-CVD.