Hydrogen adsorption site on the Ni 1115- 2=2/–H: a TOF-LERS study

The adsorption site of hydrogen on the Ni 1114- 2=2.–H surface resulting from the H2 exposure at low temperature was investigated by time-of-flight low energy recoil spectrometry TOF-LERS.. Recoiling spectra induced by pulsed 1 keV Neq primary-ion beams were monitored as a function of polar and azimuth angles. From classical trajectory calculations and shadowing and blocking analyses, it was found that the H atoms occupy both the fcc- and hcp-adsorption sites on the Ni 111. terraces at a height of approximately 1.1–1.5 A° above the plane of the first layer of Ni atoms. Furthermore, adsorption and desorption measurements show that the initial sticking coefficient of a H atom is s u.f0.45 and the activation energy of H atoms adsorbed on the surface is evaluated to be 0.42 eV. The onset temperature for desorption was found to be around 250 K. q1999 Elsevier Science B.V. All rights reserved.