Resonances in electron stimulated desorption yield of cesium atoms from germanium monolayer-covered tungsten

Abstract

The electron-stimulated desorption (ESD) yields and energy distributions for Cs atoms from a cesium layer adsorbed on germanium monolayer-covered tungsten surfaces have been measured as a function of electron energy, cesium coverage Θ, and substrate temperature. Cs is adsorbed at low temperature, 160K. The measurements have been carried out using a time-of-flight method and surface ionization detector. The Cs atom appearance threshold is about 24eV at Θ 0.15 ML which can be associated with the Ge 3d level excitation energy; a resonantlike peak with a maximum at Ee about 38eV that can be associated with the W 5p3∕2 level excitation energy also appears. This peak is seen only at Θ 0.3 and at Ee about 50eV. A third resonantlike peak is observed at Θ>0.5 ML, at Ee about 80eV. The positions of these two peaks can be associated with W 5p1∕2 and W 5s level excitation energies, respectively. The intensities of all resonant features pass through maxima at Θ=1 as the cesium coverage increases and are almost independent of the substrate temperature. The energy distribution for Cs atoms consists of a bell-shaped peak with a maximum at a kinetic energy of 0.55eV at Θ 0.15: a wide one with a maximum at a kinetic energy of 0.5eV and a narrow one with a maximum at a kinetic energy of 0.35eV. The results are interpreted to arise from three ESD channels for Cs atoms associated with excitations of Cs, Ge, and W core levels, respectively.The electron-stimulated desorption (ESD) yields and energy distributions for Cs atoms from a cesium layer adsorbed on germanium monolayer-covered tungsten surfaces have been measured as a function of electron energy, cesium coverage Θ, and substrate temperature. Cs is adsorbed at low temperature, 160K. The measurements have been carried out using a time-of-flight method and surface ionization detector. The Cs atom appearance threshold is about 24eV at Θ 0.15 ML which can be associated with the Ge 3d level excitation energy; a resonantlike peak with a maximum at Ee about 38eV that can be associated with the W 5p3∕2 level excitation energy also appears. This peak is seen only at Θ 0.3 and at Ee about 50eV. A third resonantlike peak is observed at Θ>0.5 ML, at Ee about 80eV. The positions of th...