It is demonstrated that the reason of SERS on dielectric and semiconductor substrates is the enhancement of the electric field in the regions of the tops of the surface roughness with very small radius, or a very large curvature. The enhancement depends on the dielectric constant of the substrate and is stronger for a larger dielectric constant. It is indicated that the enhancement on dielectrics and semiconductors is weaker than on metals with the same modulus of the dielectric constant. The result obtained is confirmed by experimental data on the enhancement coefficients obtained for various semiconductor and dielectric substrates.
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