Dephasing and population decay of the Cu (100) and (111) image potential states induced by scattering on low coverage alkali adsorbates

Image states at surfaces are very sensitive to the presence of impurities on the surface. A theoretical study of the effect of alkali adsorbates on the image state dynamics is performed for the Cs/Cu(1 0 0) and Na/Cu(1 1 1) systems using a wave-packet propagation approach. Scattering of the image state electron by an alkali adsorbate is shown to induce large inter-band and intra-band transitions leading respectively to the population decay and to the dephasing of the image state. Even very low alkali coverage in the 10(-3) monolayer range can effectively affect the image states, reducing their lifetime and broadening their photoemission peaks. The present theoretical results are discussed and compared with available experimental results on the perturbation of image states by various adsorbates. (C) 2002 Elsevier Science B.V. All rights reserved.