Surface enhanced Raman scattering from molecules adsorbed on semiconductor surfaces

Abstract

We have demonstrated that adsorbed species on semiconductor surface can be detected by SERS (Surface Enhanced Raman Scattering) spectroscopy. We have observed the vibrations of adsorbed molecules on semiconductors, onto which we have evaporated a thin Ag film, using tris(bipyridine) ruthenium(II), Ru (bpy) 2+ 3, as a test molecule. We have deposited Ag island films on glass and GaAs surfaces. We are able to affirm that the observed SERS signals arise from the substrate surface and not from the Ag film since the Raman frequencies of the molecules adsorbed on the glass are different from those adsorbed on the GaAs surface. No Raman scattering could be detected from the substrate surfaces without the deposited Ag film because the Raman enhancement is due to the excitation of surface plasmon polaritons introduced by the surface roughness of the silver film on the substrate. These results prove that with the Ag overlayer method the SERS spectroscopy has a great potential for monitoring and elucidating the structures and properties of molecules adsorbed on semiconductors, providing that the surface morphology of the Ag can be accurately controlled. This suggests the possibility of utilizing the SERS effect as a new surface probe of semiconducor surface with monolayer sensitivity.