The Decomposition of Molybdenum Hexacarbonyl on Thin Alumina Films at High Temperatures: Formation and Reduction of Carbides

Film growth by reaction of molybdenum hexacarbonyl with an alumina film deposited onto a Mo(100) substrate is investigated under ultrahigh vacuum where a significant deposition rate is found only for substrate temperatures above ∼670 K. Auger and X-ray photoelectron spectroscopy measurements reveal that a monolayer of molybdenum carbide (MoC) is deposited onto the alumina surface forming a monolayer after an exposure of ∼40 L. This layer is reduced to the metal by heating to ∼1500 K by reaction with the alumina substrate to evolve CO and form metallic molybdenum. The carbide can be re-formed by heating the metal-covered alumina sample in ethylene at 900 K, and the carbide can once again be reduced to the metal by heating to 1500 K. This process can be repeated so that the carbide can be regrown by reaction with ethylene and reduced by annealing in vacuo to 1500 K.