Mechanical properties of silicon-doped diamond-like carbon films prepared by pulse-plasma chemical vapor deposition

Silicon-doped diamond-like carbon (Si-DLC) films were prepared by dc pulse-plasma chemical vapor deposition (CVD), using a mixture of acetylene (C(2)H(2)) and tetramethylsilane (TMS) as the material gas. The pulse voltage was varied from -2 to -5 kV, and the TMS flow ratio (TMS/(C(2)H(2) + TMS)) was varied from 0 to 40%. At a pulse voltage of -2 kV, an increase in TMS flow ratio leads to a decrease in hardness. In contrast, at a pulse voltage of -5 kV, an increase in TMS flow ratio leads to a slight increase in hardness. The high hydrogen concentration in the films due to an increase in TMS flow ratio promotes the formation of polymeric sp(3) C-H bonds, resulting in the fabrication of soft films at a low pulse voltage of -2 kV. However, an increase in the effect of ion peening on the growth face results in the formation of hard films at a high pulse voltage of -5 kV. Then, at a pulse voltage of -5 kV fabricating hard Si-DLC films, an increase in TMS flow ratio leads to an increase in the silicon content in the films, resulting in a decrease in the friction coefficient. Therefore, it is clarified that Si-DLC films fabricated by dc pulse-plasma CVD under a high pulse voltage and high TMS flow ratio exhibit high hardness and a low friction coefficient. Moreover, to investigate the friction coefficient of Si-DLC films fabricated by dc pulse-plasma CVD, films deposited by dc plasma CVD were also evaluated. To obtain the same low friction coefficient, dc pulse-plasma CVD requires less TMS than dc plasma CVD. Hence, it is also clarified that Si-DLC films can be fabricated at a low cost by dc pulse-plasma CVD. (C) 2011 Elsevier B.V. All rights reserved.