Raman and morphological characteristics of carbon nanotubes depending on substrate temperatures by chemical vapor deposition

Carbon nanotubes (CNTs) films were synthesized at low pressure using nickel as catalyst by thermal chemical vapor deposition with hydrogen-acetylene mixture. The Raman characteristics and morphological features of CNTs at different substrate temperatures were investigated. The variation of CNTs morphological feature mainly depends on the substrate temperatures. In the low temperature range (450-550degC), the film consists of graphite particles and CNTs mixture with some amorphous phase. With increase the temperature (550-650degC), the tube content increases, and the tube diameter decreases. At high temperature range (700-800degC), the film consists of CNTs and nanoparticles mixture. Raman spectroscopy results show that the intensity ratio I
_D
/I
_G
of the G- and D-band has a maximum at the medium temperature of 600degC, and the width of G band becomes narrow with the substrate temperature. The growth behaviors of CNTs at different temperatures are discussed based on the experimental results.