Interactions of H 2 with the Ni(110) surface: EELS and LEED studies

Abstract

High-resolution vibrational electron energy loss spectroscopy (EELS) and low-energy electron diffraction (LEED) have been used to study the interactions of hydrogen with the Ni(110) surface in the temperature range from 100 to 300 K. H 2 is adsorbed dissociatively on the Ni(110) surface. At 100 K, the (2 × 1)-H and (1 × 2)-H structures are formed; the streaky (1 × 2)-H structure is formed by heating the H-covered surface to above ~ 220 K or by the exposure of the Ni(110) surface to H 2 at 300 K. For the (2 × 1)-H surface which is characterized by the vibrational losses at 79 and 130 meV, H atoms are adsorbed in the low-symmetry short-bridge sites of the bulk-like Ni(110) surface. Adsorbed sites of H atoms for the low-coverage phases (found by molecular beam diffraction and video-LEED) are similar to those for the (2 × 1)-H structure. For the (1 × 2)-H surface with losses at 76, 117 and 150 meV, H atoms are considered to be adsorbed in the low-symmetry short-bridge sites and high-symmetry short-bridge sites of the second layer Ni atoms. The streaky (1 × 2)-H surface with losses at ~ 80, 117 and 140 meV consists of the undistorted and distorted patches whose local structures are similar to those of the (2 × 1)-H and (1 × 2)-H surfaces, respectively. The (2 × 1) → (1 × 2) phase transition is considered to be the first-order transition.