Quantitative structural study of the coadsorption of CO and K on Ni(111) using photoelectron diffraction

Abstract

Scanned energy mode photoelectron diffraction measurements from the K 2p, O 1s and C 1s states of a Ni(111)(2 × 2)-K/ nCO ( n ≈ 2) coadsorption structure have been coupled with multiple scattering simulations to determine the local adsorption structure. This structure is compared with the structure of the Ni(111)c(4 × 2)-CO phase obtained from a similar analysis of C 1s and O 1s photoelectron diffraction data (which extends earlier work based on the C 1s signal alone), and of the structure of the Ni(111)(2 × 2)-K phase based on a previously-published analysis of K 2p and K 2s photoelectron diffraction. In the CO coadsorption phase the K atoms retain the atop site of the (2 × 2)-K phase but with a K Ni bondlength increased by 0.15 ±0.05 Å, and with the outermost Ni layer contraction of the (2 × 2)-K phase replaced by an outer layer expansion. The CO molecules occupy both types of hollow site on the surface with a C Ni outermost layer spacing of approximately 1.30Å, but the inferred C O bondlength shows no statistically significant change from its value in the absence of coadsorbed K.