Monolayer K-films on Ni(100) — II. Electronic excitations

Abstract

Electronic excitations in a K layer adsorbed on Ni(100) have been observed by means of electron energy loss spectroscopy. The observed excitation energy depends on the density of K atoms in the layer. In the low density range the loss energy decreases from 3.5 to 1.5 eV as the density increases from 6.10 13 to 3.10 14 K atoms per cm 2. This loss is interpreted to be due to an excitation from below the Fermi level to the shifted K valence level Increasing the density further from 3.10 14 to 6.10 14 K atoms per cm 2 yields a loss peak that increases in energy from 1.5 to 2.3 eV. This loss peak merges into the surface-bulk plasmon complex for a thick K film and the energy vs density dependence is compatible with a plasmon excitation in the K layer.