Two-dimensional localization of fast electrons in p(2x2)-Cs/Cu(111)

The system p(2x2)-Cs/Cu(111) reveals a manifold of surface localized electronic states, such as image states, quantum well states, and surface resonances. We find an electronic state with a band energy above the vacuum level while strictly localized at the Cs monolayer. An electron populating this state will have a large in-surface-plane kinetic energy and, presumably, a very long lifetime. The state could be an interesting tool for control of electron induced surface reactions.