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Two-photon photoemission via image-potential states

1985; American Physical Society; Volume: 55; Issue: 3 Linguagem: Inglês

10.1103/physrevlett.55.300

1092-0145

K. Giesen, Fredrik S. Hage, F. J. Himpsel, H. J. Riess, W. Steinmann,

Advanced Chemical Physics Studies

Strong two-photon photoemission is observed from Ag(111) and Cu(111) surfaces with image-potential states as intermediates. Three processes are found: (a) resonant excitation, (b) relaxation into the intermediate state, and (c) energy pooling via collisions between excited electrons. For Ag(111) we find two image-potential states with binding energies of 0.77\ifmmode\pm\else\textpm\fi{}0.03 and 0.23\ifmmode\pm\else\textpm\fi{}0.03 eV, close to the hydrogenic values, and an unidentified state 2.57\ifmmode\pm\else\textpm\fi{}0.05 eV below the vacuum level. The work function is 4.49\ifmmode\pm\else\textpm\fi{}0.02 eV.