Atomic excitations in ion induced sputtering of a Rh(100) single crystal

Recently, we have measured the energy and angular distributions for ground- and excited-state Rh atoms emitted from a clean, oxygen- and cesium-covered Rh(100) surface. The results show that the excitation probability in all cases varies as exp(-A/av⊥) at high velocities but is nearly constant at low velocities. The parameter A/a is found to be dependent on the state of the surface and on the azimuthal and the polar angles of ejection. A comparison between the experimental results and the molecular dynamics computer simulations indicates that the independence of the excitation probability on velocity at low velocities is caused by the effect of the surface binding energy and the existence of collisional excitations taking place above the surface. Both oxygen and cesium adsorption are found to enhance the relative emission of excited-state atoms. However, the magnitude of this enhancement is quite different for these two overlayers. The results are discussed in terms of the induced changes in the Fermi level and the creation of additional excitation channels.