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  Pettenkofer C. ; Otto A.: Strong subthreshold photoemission from Ag(111) islands. Europhysics Letters 65 (2004), p. 692-698

Abstract:
Epitaxial silver islands of (111) orientation of 50 ¿ 100 nm diameter and multilayer thickness grow without strain on WSe2. Besides the common photoelectron emission (PE) out of the occupied Shockley surface state S1 on Ag (111) strong subthreshold PE is observed at photon energies down to 0.7 eV below the work function of Ag(111) and with final energies down to 0.7 eV below the vacuum level of Ag (111). The subthreshold PE is assigned to direct transitions into the image potential states (IM) n = 1 and n = 2,3,4 and an elastic escape from these states into the vacuum. The escape path is tentatively assigned to the area of the slopes of the islands where the local work function is reduced.