Characteristics of Palladium Doped Amorphous Carbon Films Fabricated by Unbalanced Magnetron Sputtering System

Generally, hydrogenated amorphous carbon (a-C:H) has been shown to have a low friction coefficient, high hardness, and low abrasive wear rate. In this study, Pd doped hydrogenated amorphous carbon (a-C:H:Pd) fabricated by the closed-field unbalanced magnetron sputtering (CFUBMS) system with two targets of carbon and palladium in Ar/C2H2 plasma. The tribological and lubricant characteristics for a-C:H:Pd fabricated with various DC bias voltage from 0 to −200 V were investigated. We obtained a hardness up to 27.5 GPa and friction coefficient lower than 0.1. The atomic percentage of Pd related to the lubricant properties increased up to 22% at −200 V. In the results, the Pd doping in the a-C:H films improved the tribological and lubricant properties. The friction coefficient value of a-C:H:Pd films was decreased, the hardness and elastic modulus were increased, and also the adhesion properties was improved with the increase of negative DC bias voltage.

Electrical Conduction Properties of Hydrogenated Amorphous Carbon Films with Different Structures

Hydrogenated amorphous carbon (a-C:H) films have optical and electrical properties that vary widely depending on deposition conditions; however, the electrical conduction mechanism, which is dependent on the film structure, has not yet been fully revealed. To understand the relationship between the film structure and electrical conduction mechanism, three types of a-C:H films were prepared and their film structures and electrical properties were evaluated. The sp2/(sp2 + sp3) ratios were measured by a near-edge X-ray absorption fine structure technique. From the conductivity–temperature relationship, variable-range hopping (VRH) conduction was shown to be the dominant conduction mechanism at low temperatures, and the electrical conduction mechanism changed at a transition temperature from VRH conduction to thermally activated band conduction. On the basis of structural analyses, a model of the microstructure of a-C:H that consists of sp2 and sp3-bonded carbon clusters, hydrogen atoms and dangling bonds was built. Furthermore, it is explained how several electrical conduction parameters are affected by the carrier transportation path among the clusters.