Microstructure and nanomechanical properties of pulsed excimer laser deposited DLC:Ag films: Enhanced nanotribological response

Abstract

Diamond-like carbon:silver (DLC:Ag) thin films, with metal contents as high as 16.8 at.%, have been deposited on silicon substrates using pulsed excimer laser deposition; the produced DLC:Ag films sustain a substantial sp3 content (36%) in the DLC matrix even for the highest Ag content (~ 16.8 at.%), in contrast to previous reports. The morphological, topographical, crystallographic, compositional and mechanical/tribological characteristics of the films have been studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and nanoindentation/nanoscratch tests, respectively. The low miscibility between carbon and silver leads to a nanocomposite material that exhibits a reduced elastic modulus and hardness that scale inversely with the silver content. The mechanical capacity reduction is attributed to the incorporation of the soft/compliant silver phase and the subsequent graphitization of the amorphous carbon matrix, as quantified through XPS. This mechanical softening response, however, is coupled with an increased ductility and an enhanced tribomechanical response (70% increase in the critical load to film failure), making this class of DLC-metal nanocomposites of great interest for protective coatings and other functional applications.