Bond length and adsorbate vibrations of (2×3)N/Cu(110): A SEXAFS study

Temperature- and angle-dependent surface-extended x-ray-absorption fine-structure (SEXAFS) measurements on the system (2×{}3)N/Cu(110) are reported. Three inequivalent adsorption sites of the N atoms within the surface unit cell are identified. The successful separation of their contributions in the present SEXAFS analysis allows for a determination of N--Cu bond lengths not only within the surface plane but also to the second Cu layer. The temperature-dependent measurements between 60 and 300 K enable us to separate structural from dynamic effects in the SEXAFS amplitude, leading to a reliable determination of coordination numbers. A strong anisotropy is found in the adsorbate vibrations parallel versus perpendicular to the surface. The relative motion of the N atom relative to the first three Cu neighbor shells is characterized by means of the corresponding Einstein temperatures. These indicate that the N atom is primarily bonded only to four Cu atoms, and not to five as previously suggested. Anharmonic corrections are found necessary for a reliable distance determination of the N--Cu bonds to the second layer. The structural parameters are compared to the ones predicted by the pseudo--(100)--c(2×{}2)--N reconstruction. {} 1996 The American Physical Society.