BOND-LENGTH AND ADSORBATE VIBRATIONS OF (2X3)N CU(110) - A SEXAFS STUDY/

Temperature- and angle-dependent surface-extended x-ray-absorption fin e-structure (SEXAFS) measurements on the system (2X3)N/Cu(110) are rep orted. Three inequivalent adsorption sites of the N atoms within the s urface unit cell are identified. The successful separation of their co ntributions 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 an d 300 K enable us to separate structural from dynamic effects in the S EXAFS amplitude, leading to a reliable determination of coordination n umbers. A strong anisotropy is found in the adsorbate vibrations paral lel versus perpendicular to the surface. The relative motion of the N atom relative to the first three Cu neighbor shells is characterized b y means of the corresponding Einstein temperatures. These indicate tha t the N atom is primarily bonded only to four Cu atoms, and not to fiv e 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(2X2)-N reconstruction.