Evidence for surface-enhanced Raman scattering on nonmetallic surfaces: Copper phthalocyanine molecules on GaP small particles

We have been able to observe the enhanced Raman scattering from copper phthalocyanine molecules deposited on layers of gas-evaporated GaP small particles. It is found that the enhancement factor increases as the average particle size increases; a maximum enhancement factor obtained in the size range between 400 and 1100 A&#778 is as high as 700. We show by calculating the efficiency of electric field enhancement at the surface of a GaP sphere that the electromagnetic mechanism of enhancement can operate even for a nonmetallic particle, in which surface plasmon modes are not excited.