LEED Studies of the Adsorption Systems W(100) +N2 and W(100) +N2 +CO

Low-energy electron-diffraction (LEED) techniques have been used to study the room-temperature interaction of nitrogen with a tungsten (100) surface. Adsorption to saturation results in the formation of a c(2×2)—N structure in which half of the surface sites are occupied, and coverage determinations show the adsorption to be atomic. The complete c(2×2) structure lowers the work function of the surface by 0.65 eV. Rapid desorption occurs at temperatures above ∼1200°K and gives only a single β peak. With simultaneous adsorption of N2 and CO the adsorbed species interact to give a series of LEED patterns, none of which can be formed by the individual gases. CO adsorption on the c(2×2)—N structure causes the ½½ diffraction spots to disappear and raises the work function to +0.30 eV above that of the clean surface. Subsequent heating of the saturated surface produces a ¼-order LEED pattern. From these results it is concluded that the interaction of CO gives rise to a new binding state β* for nitrogen.