Low temperature carbon nanotube and hexagonal diamond deposition with photo-enhanced chemical vapor deposition

Abstract

Deposition of carbon nanotube and hexagonal diamond thin films at low substrate temperature with photo-enhanced chemical vapor deposition is described here. Extensive experimentation is conducted to optimize the catalyst layer utilized for deposition by varying Al/Ni/Al metal layer thicknesses on SiO2 coated Si substrates. The coated substrates are annealed to transform the thin metal layers into nanoparticles. Suitable catalyst layer thicknesses obtained are 3/2/3, 5/1/5 and 5/3/5 nm for Al/Ni/Al sandwich metal layers. Suitable annealing conditions are in the range of 350---450 °C for substrate temperature and from 0.22 to 10 Torr for chamber pressure in ammonia ambient for 25 min. Carbon tetrachloride (CCl4) is used as a carbon precursor in this work. Argon to CCl4 flow ratio is varied in 1.5---19 range, chamber pressure is varied in 3---10 Torr range, and the substrate temperature is varied in 350---450 °C range. Carbon nanotubes (CNT) growth is observed at lower chamber pressure, lower partial pressure of CCl4, lower substrate temperature and for thin Ni catalyst layer. The optimal CNT deposition condition observed is 5 Torr total chamber pressure, 9:1 partial pressure ratio of Ar to CCl4, 400 °C substrate temperature and 5/1/5 nm thick Al/Ni/Al catalyst layers. The hexagonal diamond deposition is observed at a higher chamber pressure, higher partial pressure of CCl4, higher substrate temperature and for a thicker Ni catalyst layer. The optimal condition for hexagonal diamond deposition observed is 10 Torr total chamber pressure, 7:3 partial pressure ratio of Ar to CCl4, 450 °C substrate temperature and 5/3/5 nm thick Al/Ni/Al catalyst sandwich layers.