Normal Photoelectron Diffraction of the Se3dLevel in Se Overlayers on Ni(100)

Modulations of up to a factor of 2 were observed in the Se $3d$ photoelectron intensity normal to the surface, for selenium overlayers on Ni(100), as the photon energy was varied from 90 to 240 eV. Excellent agreement of peak energies with predictions by Tong and Li was obtained for both the $c(2\mathrm{}\times 2)$ and $p(2\mathrm{}\times 2)$ structures, using the hollow-site geometry. Normal photoelectron diffraction appears to have promise as a surface structural method.