Unusually large absolute Raman scattering cross section of hydrogen vibrations on Si(111)

Abstract

We have measured the absolute Raman scattering cross section of the terrace vibration mode of silicone-monohydride on a Si(111) surface that was prepared by chemical etching in a N${\mathrm{H}}_{4}$F solution. The measured cross section at the incident wavelength of 4880 \AA{} is $(\frac{d{\ensuremath{\sigma}}_{\mathrm{zz}}}{d\ensuremath{\Omega}})=(8.37\ifmmode\pm\else\textpm\fi{}0.32)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}28}$ ${\mathrm{cm}}^{2}$/(sr line Si-H bond). It is about 74 times the cross section of the symmetric stretching mode of the gaseous Si${\mathrm{H}}_{4}$ molecule. The measured excitation profile of the cross section in the range of ${\ensuremath{\lambda}}_{\mathrm{in}}=4579\ensuremath{-}5145$ \AA{} has a ${\ensuremath{\omega}}^{4}$ dependence indicating that there is no resonant enhancement of the cross section. We estimate that the Raman transition dipole matrix elements are about three times larger for the Si(111)/H monolayer system than for the free Si${\mathrm{H}}_{4}$ molecule.