Cobalt Chemical Vapor Deposition Process on Molybdenite Basal Plane Observed by Ultrahigh-Vacuum Scanning Tunneling Microscopy

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The processes of high-temperature (473 K) resulfidation and cobalt carbonyl adsorption by chemical vapor deposition (CVD) on a cleaved basal plane of a natural molybdenite (MoS2) single crystal were examined by ultrahigh-vacuum scanning tunneling microscopy (UHV-STM) on the nanometer scale. The resulfided cleaved molybdenite basal plane showed a displacement of upper terraces, and a sinusoidal structure at step edges, both of which may be caused by the electronic effect at the surface. Cobalt carbonyl appeared to be adsorbed at both the S- and Mo-terminated edges, resulting in an agglomeration at the step edges on lower terraces with a width of a few tens of nanometers. When this surface with adsorbed carbonyl was sulfided at 513 K for 1 h, most of the adsorbed carbonyl clusters appeared to be desorbed while a small part were dispersed on the terraces in small clusters of 10–20 nm in size. The obtained results are discussed in terms of the preparation of Co-Mo hydrodesulfurization (HDS) catalysts.
2005-07-15