Cesium on molybdenum (110)

Abstract

Surface structure, work function changes and plasma losses have been studied for the adsorption of Cs on a Mo(110) surface. At 77 K, up to the density of 2.2 × 10 14 cm −2, Cs is in a two-dimensional liquid state. At higher coverages the adlayer crystallizes, forming domains rotated 19° with respect to each other. The domains possess a hexagonal structure and undergo a rotation of 90° at a coverage of 3 × 10 14 cm −2. A full monolayer has a close-packed hexagonal array of adatoms with a density of 5.1 × 10 14 cm −2. The onset of condensation in the second layer results in the immediate formation of two-dimensional islands with a close-packed hexagonal structure of 4 × 10 14 cm −2 density. The work function passes through a minimum (1.42 eV) at a coverage of 3 × 10 14 cm −2. After completion of the first layer the work function continues to grow during Cs condensation in the second layer and levels up to 2.15 eV. The EEL spectrum for clean Mo(110) possesses a set of peaks which are identified with the surface and volume plasmons. The first feature to appear in the energy plasma loss spectrum due to Cs deposition is the 2.2 eV loss. It appears at the Cs adatom density corresponding to a work function minimum. This signal is interpreted as due to the surface plasmon loss in Cs. The Cs bulk plasmon loss at 4.6 eV appears at the beginning of the second layer.