Surface reconstruction and surface explosion phenomena in the nickel (110)/hydrogen system

• Published in: Surface science 1985-01, Vol.152, p.356-366
• Main Authors: Christmann, K., Chehab, F., Penka, V., Ertl, G.
• Format: Article
• Language: English
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/0039-6028(85)90165-7

Combined Video-LEED, work function (Δ∅), thermal desorption (TD) and UV photoelcctron spectroscopy (UPS) measurements revealed a variety of hydrogen assisted phase transformations on a Ni(110) surface between 120 and 250 K. Among others, a 2 × 1−2H lattice gas phase (at a coverage θ H = 1 ML) undergoes a first-order transition to a reconstructed 1 × 2 phase wisth θ H = 1.5 ML at saturation. In UPS this phase produces a strong extra emission near − 1.3 eV below the Fermi energy. All low temperature phases are however only metastable and suffer an irreversible transition to a merely one-dimensionally ordered “streak” phase (which is likewise reconstructed) as the surface is heated to beyond ∼ 200 K. The transition 1 × 2 →“streak” occurs very rapidly in a narrow temperature range and is characterised by a sudden break-down of the LEED intensity of the extra spots and a steplike decrease of the work function. Also, the photoemission features 1.3 eV below E F disappear completely. Moreover, the transition is 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 are presented and discussed in order to rationalise the experimental findings.