Thermodynamic measurements for N2 adsorption on Ni(100)

We investigated the adsorption of molecular N2 on Ni(100) by LEED and thermodynamic measurements. From our data isosteric heats and the entropies in the adsorbed layer are calculated and compared to results for N2 on Ni(110) and supported nickel particles. Saturation coverage of N2 on Ni(100), as characterized by a c(2 × 2) LEED pattern, corresponds very closely to saturation coverage of N2 on Ni(110). Near saturation coverage on Ni(100) we observe a drop in the heat of adsorption and an strong increase in the differential entropy of the adsorbed layer. We believe this observation is being caused by the presence of antiphase boundaries in the c(2 × 2) structure which cause a softening of vibrational modes in the surface layer