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Two-dimensional image-potential-induced electron band.

Image states represent a simple type of surface state which is very useful for studying the two-dimensional (2D) electron gas. In liquid helium an instability of the 2D electron gas develops when the density is increased. In metals the intraband and interband energy half-widths of the state are comparable (a few meV), thus preventing a steady-state population of these states. Insulators could provide a good compromise between these two extreme cases. The lifetime of electrons in a 2D electron band at a vacuum-insulator interface is studied in this paper.