  How quanta of energy and charge are transported on both atomic spatial and
ultrafast time scales is at the heart of modern technology. Recent progress in
ultrafast spectroscopy has allowed us to directly study the dynamical response
of an electronic system to interaction with an electromagnetic field. Here, we
present energy-dependent photoemission delays from the noble metal surfaces
Ag(111) and Au(111). An interferometric technique based on attosecond pulse
trains is applied simultaneously in a gas phase and a solid state target to
derive surface-specific photoemission delays. Experimental delays on the order
of 100 as are in the same time range as those obtained from simulations. The
strong variation of measured delays with excitation energy in Ag(111), which
cannot be consistently explained invoking solely electron transport or initial
state localization as supposed in previous work, indicates that final state
effects play a key role in photoemission from solids.
