Unoccupied band dispersion of Si(1 1 1):√3 × √3-Ag surface studied by time- and angle-resolved two-photon photoemission spectroscopy

► AR-2PPE and AR-1PPE study on Si(1 1 1):√3 × √3-Ag surface electronic states. ► The band dispersion of unoccupied surface state has been clearly observed. ► The lifetime of unoccupied surface state has been determined from TR-2PPE spectra.