Electron stimulated desorption of CO from [formula omitted

Abstract

The electron impact behavior of CO adsorbed on Pd 1 W(110) was investigated. The desorption products observed were neutral CO, CO +, and O +. After massive electron impact residual carbon, C/ W = 0.15, but not oxygen was also found, suggesting that energetic neutral O, not detected in a mass analyzer must also have been formed. Formation of β-CO, i.e., dissociated CO with C and O on the surface was not seen. The total disappearance cross section varies only slightly with coverage, ranging from 9 × 10 −18 cm 2 at low to 5 × 10 −18 cm 2 at saturation ( CO/ W = 0.75). The cross section for CO + formation varies from ∼ 4 × 10 −22 cm 2 at satura to ∼ 2 × 10 −21 cm 2 at low coverage. That for O + formation is 1.4 × 10 −22 cm 2 at saturation and ∼ 2 × 10 −21 cm 2 Threshold energies are similar to those found previously [J.C. Lin and R. Gomer, Surf. Sci. 218 (1989) 406] for CO W(110) and CO/Cu 1/W(110) which suggests similar mechanisms for product formation, with the exception of β-CO on clean W(110). It is argued that the absence or presence of β-CO in ESD hinges on its formation or absence in thermal desorption, since electron impact is likely to present the surface with vibrationally and rotationally activated CO in all cases; β-CO formation only occurs on surfaces which can dissociate such CO. It was also found that ESD of CO led to a work function increase of the remaining Pd 1/W(110) surface of ∼ 500 meV, which could be annealed out only at 900 K. This is attributed to surface roughness, caused by recoil momentum of energetic desorbing entities.