Structural determination ofc(2×2)N/Cu(100): A multiple-scattering surface-EXAFS study

The adsorption of 0.5 monolayer of atomic nitrogen on a Cu(100) surface has been studied by means of temperature- and angle-dependent surface-extended x-ray-absorption fine-structure (SEXAFS) measurements. The c(2×2) surface structure on the Cu(100) surface was obtained both by (i) adsorption of ion-gun-activated nitrogen at room temperature and by (ii) thermal dissociation of ${\mathrm{NH}}_3$ adsorbed at 50 K. The measured data were directly analyzed by means of Fourier-filtering techniques and were also compared to multiple-scattering calculations. It can be shown that for both preparation methods the nitrogen adsorbs in a fourfold hollow site with a vertical distance of 0.4 Å towards the topmost Cu layer which undergoes an outward relaxation of 4% with respect to the bulk value. Evidence for a corrugation of 0.1 Å in the second Cu layer is found.