The structure of the Ni(1 0 0)c(2 × 2)–N 2 surface: a chemical-state-specific scanned-energy mode photoelectron diffraction determination

Abstract

Using the chemical shift in the N 1s photoemission peak from the two inequivalent N atoms of N 2 adsorbed on Ni(1 0 0) we have performed a scanned-energy mode photoelectron diffraction (PhD) structure determination of the Ni(1 0 0)c(2 × 2)–N 2 weak chemisorption system. The N 2 is found to adsorb atop surface Ni atoms with the N–N axis perpendicular to the surface at a Ni–N nearest-neighbour distance of 1.81 ± 0.02 Å. This is very significantly shorter than the value (2.25 Å) found in an earlier published study. An independent density-functional theory slab calculation yields a value of 1.79 Å, in excellent agreement with the results of the current experiment. Analysis of the PhD modulations of the N 1s photoemission satellite peak show that these are consistent with this comprising separable components localised at the two N atoms as has previously been assumed in an earlier investigation based on (angle-scan) X-ray photoelectron diffraction. Both experiment and theory indicate a small extension of the N–N distance due to the adsorption (0.03 ± 0.03 Å and 0.02 Å respectively).