Lawrence Berkeley National Laboratory

The ultrafast dynamics of electronic excitations of the surface dangling bond states of Si(111) 7x7 has been investigated by second harmonic generation as a probe of transient spectral hole burning. Spectral holes induced by a 100 fs pump at \simeq 1.5 eV and their decay are interpreted in terms of electronic dephasing times as short as 15 fs. This fast time scale together with the strong excitation-induced dephasing observed is interpreted in terms of carrier-carrier scattering. In addition, strong coupling of the electronic excitation to surface optical phonons is observed and attributed to the localization at adatom sites of a surface electronic excitation and a surface phonon mode.