Several qualitatively different structural models have been examined in a critical evaluation of spectroscopic and other data for the Si(111)-(2×1) surface. Within the one-electron theory, only a novel $\pi$-bonded chain model with a covalent surface, and not the generally accepted buckled model with an ionic surface, is consistent with the data.

• Received 16 July 1981

DOI:https://doi.org/10.1103/PhysRevLett.47.1913