Adsorption of Li on Ni(110) surfaces at low and room temperature

We present the investigation of Li adsorption on Ni(110) surfaces at low temperature (LT) and room temperature (RT) by means of Auger electron spectroscopy, low-energy electron diffraction, thermal desorption spectroscopy and work function measurements, in ultrahigh vacuum. At RT, from the early stages of deposition (Θ≤0.1 ML) Li induces a (1×2) reconstruction of the Ni(110) surface. The (1×2) reconstruction is lifted at 0.5 ML. A further increase of Li coverage leads to a disordered surface, with an intermixing of Li adatoms and the Ni substrate with a tendency toward Li–Ni alloy formation. A gradual heating of the Li-covered Ni(110) surface gives an Li(3×1), an Li(5×1) structure and the (1×2) reconstruction before the complete desorption of Li. Near saturation (Θ≈2 ML), Li forms a nearly metallic overlayer. At LT (150 K), deposition of Li up to 1 ML gives a sequence of c(2×2), (7×2), (3×2), (4×2), (5×4) and finally (1×1) structures, which have been determined using structure factor calculations. These structures are attributed to a continuous stretching of deposited Li atoms along the [11̄0] direction of the Ni(110) surface. The Li–Ni interaction is a thermally activated process and decreases the stability of the Ni surface, leading to its reconstruction at RT. However, at LT the Li–Li interaction dominates and the effect of Li adatoms on the substrate structure is limited. The change of the (1×2) reconstruction to the ideal (1×1) bulk-like surface occurs at the beginning of the transition of ionic to metallic bonding of the Li overlayer.