Surface electrons were selectively photoexcited into the normally unoccupied antibonding surface state on the cleaved Si(111) (2×1) surface by 2.8-μ m infrared laser radiation. The time decay of the antibonding-state population was then followed in real time by picosecond time-resolved uv photoemission spectroscopy. The relaxation dynamics was found to be cleavage dependent, and appears to be controlled by defects, which give rise to a unique signature in the photoemission spectra.

• Received 21 May 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.881