Temperature-dependent angle-resolved photoemission study for quantum-well states in Ag nanofilms

We have performed a temperature-dependent photoemission study for quantum-well states in Ag(111) nanofilms grown on Cu(111) substrate. It is found that the linewidths of both quantum-well state and surface state broaden and their intensities decrease with increasing a temperature from 40 to 350 K. The linear temperature dependence of the linewidths of both states are explained as the temperature dependence of the phonon contribution to the photohole lifetime width, expressed as $2\pi \lambda k_{B}T.\mathrm{}$ It is found that the electron-phonon mass-enhancement parameter λ for quantum-well states is almost the same with that for surface state and an average over the bulk Fermi surface. The temperature dependence of the intensities have been discussed using the standard Debye-Waller factors. It is found that the effective Debye temperature derived from the quantum-well state is higher than that from the surface state, suggesting different properties of phonon states coupled to each electronic state.