Spectroscopic characterization of thin vanadium carbide films on a vanadium (110) surface: Formation, stability, and reactivities

The surface properties of thin vanadium carbide films, produced on a V(110) surface, have been investigated by using a combination of high-resolution electron energy-loss spectroscopy, fluorescence-yield near-edge x-ray absorption spectroscopy (FYNES), and Auger electron spectroscopy (AES). Our results indicate that thin carbide films with a stoichiometry of VC can be produced by exposing V(110) to olefin molecules at 600 K. A comparison of the bulk-sensitive FYNES data with the relatively surface-sensitive AES results suggests that the average thickness of the VC film is greater than the penetration depth of Auger electrons for the C(KLL) and V(LMM) transitions. Upon heating to 600–1050 K, the thin VC films most likely undergo a thermally induced clustering process, which is followed by a diffusion of carbon atoms into the bulk V(110). The surface reactivities of the carbide-modified surfaces are significantly different from those of either clean V(110) or oxygen-modified V(110), as will be demonstrated by the interactions of these surfaces with CO and ethylene molecules.