MERCURY ADSORPTION ON NI(111) .1. ADSORPTION AT ROOM-TEMPERATURE AND ABOVE

The adsorption of mercury on Ni(111) has been studied in the temperature range 323-403 K using LEED, angle resolved Auger and angle resolved photoelectron spectroscopy. Under equilibrium adsorption conditions using a pressure of 2 × 10-8 mbar of mercury, a ( 3 × 3)R30 °, 1 3 ML structure was observed at 351 K, and a p(2 × 2), 0.5 ML structure at 323 K. Δφ values for these surfaces were -0.36 ± 0.04 and -0.34 ± 0.04 eV respectively. The isosteric heat of adsorption, determined using adsorption isotherms, was 110 ± 40 kJ mol-1 at zero coverage, rising to 200 ± 40 kJ mol-1 for the 3 structure, and falling precipitately to 80 ± 40 kJ mol-1 for the p(2 × 2) structure. UPS showed a Ni(111) surface resonance, the intensity of which was linearly dependent on coverage up to the 3 structure, and a split Hg 2D 5 2 peak, the behaviour of which depended on the aggregation of the surface mercury. Precursor state adsorption kinetics were observed and the 2D 5 2 peak was used to deduce that compact islands were formed during non-equilibrium adsorption at 323 K, while less compact islands formed during adsorption at 351 K. For equilibrium adsorption at T > 380 K a dispersed phase was formed. Surface structures are suggested for the ( 3 × 3)R30 ° and p(2 × 2), 0.5 ML structures. © 1990.