The mechanical and biocompatibility properties of DLC-Si films prepared by pulsed DC plasma activated chemical vapor deposition

Films of diamond-like carbon containing up to 22 at.% silicon (DLC-Si) were deposited on to silicon substrates by low-frequency pulsed DC plasma activated chemical vapor deposition (PACVD). The influence of silicon doping on deposition rate, composition, bonding structure, hardness, stress, surface roughness and biocompatibility was investigated and correlated with silicon content. A mixture of methane and tetramethylsilane (TMS) was used for the deposition of DLC-Si films at a pressure of 200 Pa. The deposition rate increased with increasing TMS flow. The addition of silicon into the DLC film leads to an increase of sp3 bonding, as measured by Raman spectroscopy, and also resulted in lower stress and hardness values. The RMS surface roughness of the films was measured by atomic force microscopy and increased from 0.35 nm for DLC to 6.7 nm for DLC-Si (14 at.% Si) due to the surface etching by the H atoms. Biocompatibility tests were performed using MG-63 osteoblast-like cell cultures that were left to grow for 3 days and their proliferations were assessed by scanning electron microscopy. The results indicated a homogeneous and optimal tissue integration for both the DLC and the DLC-Si surfaces. This pulsed PACVD technique has been shown to produce biocompatible DLC and DLC-Si coating with potential for large area applications.