Combined video-LEED, work function, thermal desorption and UV photo-electron spectroscopy measurements revealed various hydrogen-assisted phase transformations on a Ni(110) surface between 120 and 250K. Among others, a (2 x 1)2H lattice gas phase (at a coverage of 1ML) underwent a first-order transition to a reconstructed 1 x 2 phase with a coverage of 1.5ML at saturation. In UPS this phase produces a strong extra emission near − 1.3eV below the Fermi energy. All low temperature phases were however only metastable and suffer an irreversible transition to a merely one-dimensionally ordered “streak” phase (which was likewise reconstructed) as the surface was heated to beyond ≈200K. The transition 1 x 2 →“streak” occurred very rapidly in a narrow temperature range and was characterised by a sudden break-down of the low-energy electron diffraction intensity of the extra spots and a step-like decrease of the work function. Also, the photoemission features 1.3eV below EF disappear completely. Moreover, the transition was accompanied by an explosive evolution of hydrogen which desorbs in a sharp α-state thereby suggesting the decomposition of a surface compound. Structure models and mechanisms were presented and discussed in order to rationalise the experimental findings.

Surface Reconstruction and Surface Explosion Phenomena in the Nickel (110)/Hydrogen System. K.Christmann, F.Chehab, V.Penka, G.Ertl: Surface Science, 1985, 152-153[1], 356-66