Surface-sensitive K-edge absorption spectroscopy on clean and hydrogen-terminated diamond (111) and (100) surfaces

We present a detailed electron yield spectroscopy study of the pre-K-edge f eatures of single-crystal diamond (100) and (111) surfaces which are induce d by optical transitions from the C ls core level into excited states. Both hydrogen-terminated and hydrogen-free surfaces were investigated. A sharp maximum at (h) over bar omega =287.2 eV in the spectra of the (111) and (10 0) surfaces is characteristic of the monohydrogenated surfaces, which is in terpreted as a strongly localized intramolecular excitation within the C-H bond of a surface atom. The clean diamond surfaces show maxima in the absor ption spectra at (h) over bar omega = 284.6 eV for the (111) surface, and a t 284.15 and 286.3 eV for the (100) surface which are interpreted as surfac e core excitons. From the polarization dependence of the intensities of the se features and by using dipole selection rules, the point-group symmetry o f the excited states involved in the optical transition is deduced. The tra nsition energies of the absorption maxima of the clean surface are discusse d in terms of pertinent band-structure calculations and excitonic effects. [S0163-1829(99)14247-4].