TEMPERATURE-DEPENDENCE OF SURFACE-STATE LIFETIMES, DEPHASING RATES AND BINDING-ENERGIES ON CU(111) STUDIED WITH TIME-RESOLVED PHOTOEMISSION

The ultrafast electron dynamics of surface states on Cu(lll) is invest igated as a function of temperature between 25 K and 460 K employing t ime-resolved two-photon photoemission (2PPE) spectroscopy. Analysis of the thermally-induced energy shift of the unoccupied n = 1 image pote ntial state based on a multiple reflection model allows a precise dete rmination of the position of the upper edge (L6+) Of the sp-gap in the (111)-direction (EL6+(T) - E-F = 4.15 eV -(0.26 meV/K)T). We find tha t the lifetime of the n = 1 image state decreases from 22 +/- 3 fs at 25 K to 14 +/- 3 fs at 350 K. This is attributed to the increasing pen etration depth of the image state wave function into the bulk at highe r temperatures, where the image state crosses the band edge. The phono n contribution to the electronic dephasing of the n = 0 surface state and the n = 1 image state on Cu(lll) is determined from their temperat ure-dependent linewidths using three-level optical Bloch equations and is found to correlate with their wave function overlap with bulk stat es. (C) 1998 Elsevier Science B.V.