Synthesis of β-Mo2C Thin Films

Thin films of stoichiometric β-Mo2C were fabricated using a two-step synthesis process. Dense molybdenum oxide films were first deposited by plasma-enhanced chemical vapor deposition using mixtures of MoF6, H2, and O2. The dependence of operating parameters with respect to deposition rate and quality is reviewed. Oxide films 100−500 nm in thickness were then converted into molybdenum carbide using temperature-programmed reaction using mixtures of H2 and CH4. X-ray diffraction confirmed that molybdenum oxide is completely transformed into the β-Mo2C phase when heated to 700 °C in mixtures of 20% CH4 in H2. The films remained well-adhered to the underlying silicon substrate after carburization. X-ray photoelectron spectroscopy detected no impurities in the films, and Mo was found to exist in a single oxidation state. Microscopy revealed that the as-deposited oxide films were featureless, whereas the carbide films display a complex nanostructure.