STRUCTURAL DETERMINATION OF C(2X2)N CU(100) - A MULTIPLE-SCATTERING SURFACE-EXAFS STUDY/

The adsorption of 0.5 monolayer of atomic nitrogen on a Cu(100) surfac e has been studied by means of temperature- and angle-dependent surfac e-extended x-ray-absorption fine-structure (SEXAFS) measurements. The c (2 x 2) surface structure on the Cu(100) surface was obtained both b y (i) adsorption of ion-gun-activated nitrogen at room temperature and by (ii) thermal dissociation of NH3 adsorbed at 50 K. The measured da ta were directly analyzed by means of Fourier-filtering techniques and were also compared to multiple-scattering calculations. It can be sho wn that for both preparation methods the nitrogen adsorbs in a fourfol d hollow site with a vertical distance of 0.4 angstrom towards the top most Cu layer which undergoes an outward relaxation of 4% with respect to the bulk value. Evidence for a corrugation of 0.1 angstrom in the second Cu layer is found.