Identification of image-potential surface states on metals

Rydberg-like surface states are identified at Au(100) and Cu(100) surfaces by use of inverse photoemission with tunable photon energy. The binding energy (0.6 eV below vacuum) and width (0.3 eV full width at half maximum) of the n=1 state agree well with previous calculations. Theory yields the expectation that these states represent a widespread phenomenon at surfaces. © 1984 The American Physical Society.