Angle-resolved ultrafast two-photon-photoemission is used to investigate image-state-electron lifetimes on two bimetallic surfaces, $\mathrm{Ag}∕\mathrm{Pt}\left(111\right)$ and $\mathrm{Ag}∕\mathrm{Pt}\left(997\right)$. This photoemission probe measures the relative dependence of image-electron dynamics on parallel electron momentum, $k_{\Vert }$, for flat and stepped surfaces. The $n=1$ and $n=2$ image states are identified by their $k_{\Vert }$-dependent energy values on the flat surface and for directions parallel and perpendicular to the step array. A weakly dispersive feature was observed in the energy distribution curves in the direction across steps. We show that the ratio of the $n=2∕n=1$ state lifetimes on the flat surface at $k_{\Vert }=0$ is increased over its value for single-crystal Ag(111) due to the Pt substrate. The $k_{\Vert }$ dependence of scattering time of the $n=1$ state on both flat and stepped surfaces can be fitted to a function $T_1-S{k}_{\Vert }^2$; on the flat surface $S$ is equal to $205\pm 45\mathrm{fs}{\mathrm{\AA }}^2$, on the stepped surface the measured values for $S$ are $110\pm 30\mathrm{fs}{\mathrm{\AA }}^2$ and $40\pm 30\mathrm{fs}{\mathrm{\AA }}^2$ in the direction parallel and perpendicular to the step edges, respectively. These results are compared to those on flat and stepped Cu(100) surfaces.

• Received 10 August 2004

DOI:https://doi.org/10.1103/PhysRevB.71.165424