Deuterated Diamond Like Carbon films (DDLC): Mechanical properties in relation with microstructure

The aim of this work is to study the mechanical properties of Deuterated Diamond Like Carbon (DDLC) in comparison with Diamond Like Carbon (DLC), to clarify the influence of hydrogen in amorphous carbon thin film (a-C:H) of DLC type. For this purpose we substitute hydrogen (H) in the film by its isotope deuterium (D) by replacing CH4 by CD4 and their mixture 1:1 in the plasma. To investigate the deuterium role in the film structure, both hydrogenated and deuterated carbon films are deposited onto silicon wafer and glass substrates using a radio frequency PECVD device. All the amorphous carbon thin films are prepared with a negative self-bias voltage in the range of 50 V to 600 V. We obtain thus a wide variation of chemical composition. Single layer is produced with a constant thickness of 200 nm, controlled by X-ray reflectivity. The effects of deposition parameters on mechanical and adhesion properties of the DLC films are investigated using nano-hardness and nano-scratch tests. Chemical compositions are determined by ions and electrons spectroscopies (RBS, ERDA, XPS). We find, among other results, that replacing hydrogen by deuterium in amorphous carbon structure enhanced hardness properties for low self-bias voltage.