Optical gap between dangling-bond states of a single-domain diamond C(111)-2 x 1 by reflectance anisotropy spectroscopy

The optical gap between dangling- bond states has been measured on a single- domain diamond C( 111)- 2 x 1 surface. The experimental result is 1.47 eV. Such a large surface gap ( even larger if excitonic effects are considered) so far has not been obtained by state- of- the- art band calculations and its physical origin is still not elucidated. The experimental result suggests a strong electron- phonon interaction in this surface. The renormalization of the bare electronic transition energy by electron- phonon interaction provides a clue to solve the apparent disagreement between theory and experiment.