Off-normal photoelectron diffraction study of thec(2×2)selenium overlayer on Ni(001)

Abstract

Off-normal energy-dependent photoelectron diffraction data are presented for the $c(2\mathrm{}\times 2)$ Se-Ni(001) system, and compared with calculations to confirm the accepted four-fold hollow-site geometry. The best agreement is found for a $d_{\perp }$ spacing of 1.55 Å, confirming earlier normal photoelectron diffraction and low-energy electron diffraction results. The size of the photoelectron diffraction modulations decreases with increasing polar angle of emission. An $R$-factor analysis indicates that the theory-to-experiment fit is very good, especially at smaller polar angles. Off-normal photoelectron diffraction is shown to be capable of distinguishing the correct site geometry for cases in which theoretical normal photoelectron diffraction curves for two geometries exhibit an "accidental coincidence" in peak positions.