TPD, AES, DELTA-PHI AND LEED INVESTIGATIONS OF CESIUM ADSORBED ON AG(100)

The basic properties of Cs adsorPtion on a Ag(100) single-crystal surface have been investigated using standard surface analysis methods. In TPD the first monolayer of Cs shows a very broad desorption spectrum ranging from 300 to about 900 K. For higher exposures a narrow condensation peak is growing at 300 K. The appearance of this multilayer peak corresponds to a kink in the Cs AES uptake curve, which is interpreted as completion of the first layer. Cesium adsorption at 80 K yields a typical alkali/ metal DELTAphi curve with a minimum of -2.9 eV at theta(Cs) = 0.43 ML and saturation at theta(Cs) greater-than-or-equal-to 1 ML, corresponding to the work-function value of bulk Cs. Cs adsorbed at 300 K shows the same initial decrease of DELTAphi, but at theta(Cs) greater than or similar to 0.2 ML distinct, temperature-dependent differences are observed indicating a change in the adsorbate structure or a Cs-induced substrate reconstruction. The first monolayer of cesium forms an incommensurate hexagonal superlattice. Its density is slightly compressed (d(Cs-Cs) = 4.89, instead of 5.25 angstrom for bulk Cs) corresponding to a coverage of theta(Cs) = 0.40 with respect to the Ag(100) substrate, calibrated by observed c(4 x 2) and c(2 square-root 2 x 4 square-root 2)R45-degrees LEED structures at theta(Cs) = 0.62 and 0.31 ML, respectively.