The properties of surface carbides of tungsten single crystals were studied using LEED, AES, and thermal desorption spectroscopy. Carburization of W (100) produced a series of surface structures; at θ = 0.5 a c(2 × 2) structure was observed which compressed into a double row ( 3 -) structure at θ = 0.67. This surface was inert to further carburization below 1000 K. Heating the crystal to 1500 K in ethylene resulted in the formation of an interstitial carbon layer having the structure of ditungsten carbide at the surface. The dissociative adsorption of hydrogen and CO were inhibited by adsorbed carbon or oxygen occupying fourfold symmetry interstitial sites on the W (100) surface. Dissociative adsorption of CO was directly related to the number of pairs of unoccupied fourfold sites. Adsorption of molecular CO correlated with the number of surface sites passivated by adsorbed carbon or oxygen. A surface passivated by dissociatively adsorbed CO was found to behave qualitatively similarly to a carbide surface.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry