| Abstract
| - The vibrational spectra of atomically flat hydrogen- and deuterium-passivated Si(111)-(1 × 1) surfaces areinvestigated using theoretical and experimental techniques. An unexpected isotopic shift is observed for theSi−H bending mode when hydrogen is replaced with deuterium, with δ(Si−H) = 626 cm-1 and δ(Si−D) =537 cm-1. The Si−H stretching mode, in contrast, behaves as expected with ν(Si−H) = 2083 cm-1 andν(Si−D) = 1516 cm-1. Density functional studies reveal that the mode observed at 537 cm-1 is mostly aphonon mode, which results from the coupling of near-surface phonons with the lower frequency bendingmode of the deuterated surface. This coupling causes a shift in the ordering of the expected vibrational modeswhen hydrogen is replaced by deuterium. We also suggest that such a mode around 535 cm-1 should be seenfor many other surfaces and is a general feature of many monovalently terminated Si(111) surfaces.
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