Nanostructured amorphous carbon-metal films for protective and solid lubricant applications

Abstract

Amorphous carbon exhibits a great diversity in its properties originating from the tunable microstructure that can result in properties that range between the values of graphite and approaching those of diamond. Amorphous carbon with primarily sp2 hybridization bonds is termed glassy carbon, commonly abbreviated as a−C. As the sp3 content increases the material tends to approach the properties of diamond and consequently a−C with dominant sp3 microstructures are commonly referred to as diamond like carbon (DLC). Owing to their excellent mechanical, thermal, electrical, optical, chemical and physical properties, DLC films have been the subject of intense research with several existing applications. Their wide applicability ranges from optoelectronic devices like heterojunction devices, thin film transistors and field effect devices to protective coatings for tribological applications like MEMS, air bearing surfaces of read-write magnetic heads for data processing tapes, and hard disk drives. Incorporating transition metals into a−C or DLC matrices creates a nanocomposite with enhanced physical characteristics (i.e., reduced friction coefficient, enhanced toughness) and additional functionalities (i.e., solar harvesting, bactericidal). This thesis reports on the physical and chemical vapor deposition and systematic characterization of metal-containing hydrogenated and non-hydrogenated DLC thin films with various metal compositions and types: Ag, Ti, and Mo are tested in the atomic percent range of 0 – 17 at.%. The deposited a−C:Me and a−C:H:Me films are characterized for their microstructure, crystallinity, surface roughness, residual internal stresses and nanomechanical response. Particular emphasis is placed on the evolution of the nanotribological response of the material with metal content. Transition metals appear to resolve the brittle nature of the highly sp3 DLC matrix by creating a more ductile and tough nanocomposite while at the same time reduce the residual compressive stresses generated during growth that hinder the development of thicker and stable coatings. Furthermore, these materials exhibit enhanced nanotribological properties that could be exploited for protective coating and/or solid lubricant applications.