Effects of Process Parameters on the Microstructural Characteristics of DC Magnetron Sputtered Molybdenum Films on Graphite Substrate

Graphite, due to its extreme purity and high-temperature stability, is considered as the material of choice for nuclear fusion reactors. However, it undergoes rapid oxidation and erosion at extreme environmental conditions like those experienced by the plasma-facing components (PFCs) of a fusion reactor. On the other hand, molybdenum (Mo) does offer a combination of thermal, mechanical, and chemical properties that make it an aspirant candidate for PFCs and other applications demanding substantial physical, chemical, and thermal stability as well as significant thermal conductivity. Mo films on graphite is one of the attractive options to sustain against such harsh environmental conditions. Here, in this work, we develop Mo films over graphite substrate through sputter deposition and analyze the effects of process parameters like the sputter power and the substrate temperature on the morphology and film quality. It is shown that an increase in sputter power, as well as substrate temperature, induces significant changes in the topography of the films. For low-temperature depositions, the grain morphology does not change with increasing sputter power, however, for relatively higher substrate temperatures, significant changes in morphology are observed with increasing sputter power. Similarly, dependences of crystallite size, film roughness, and electrical conductivity are discussed with changing sputter power and substrate temperature. Our results suggest that the kinetic energy of the sputtered Mo particles plays a crucial role in determining the final film quality. This study manifests that optimum sputter parameters guarantee quality Mo films over graphite substrate.