Surface structures of cesium on Mo(1 1 0) surface investigated by RHEED

The surface structures of cesium deposited on a Mo(1 1 0) surface have been investigated by reflection high energy electron diffraction (RHEED), and three kinds of surface structures were observed. Nearly at 1.0 ML of Cs deposition thickness, a commensurate structure expressed as the [5 2, 2 4] structure in matrix notation appeared from room temperature (RT) to 350 °C. The lengths of unit vectors of this structure are aα=5.04 Å and bα=5.11 Å and the angle between them is 119.5°. With elevating temperatures of the substrate ranging from 350 to 450 °C, this commensurate structure changed to a hexagonal structure in which the lengths of the unit vectors are aβ=bβ=5.94 Å. In the temperatures ranging from 450 to 900 °C, rotated structures by maximum ±5° from the hexagonal structure appeared. Up to 0.75 ML of deposition thicknesses, these rotated structure was also observed in wide temperature range of the substrate. Three-dimensional crystallites did not grow on these surface phases at room temperature because of high vapor pressure of cesium.