2ND-HARMONIC GENERATION AND SURFACE RECONSTRUCTION - CS ON AG(110)

The Cs induced reconstruction of the Ag(110) surface has been investig ated by second-harmonic generation (SHG), combined with measurements o f the work function change (DELTAphi) and thermal desorption spectrosc opy (TDS). Adsorption of one monolayer of Cs at 100 K leads to a SHG a mplification of 1100 compared to the signal level of the clean surface . Through annealing the sample, a local reconstruction can be obtained at temperatures between 165 and 220 K, as a precursor to the long ran ge ordered (1 x 3) and (1 x 2) missing row reconstruction. The onset o f the local reconstruction is identified by a sharp decline of the SH intensity. For theta(Cs) < 0.24 this can be understood as a variation in the conditions for the resonance of the radiation field with optica l transitions between Cs derived resonant levels, caused by a modified adsorption geometry.