Surface-enhanced Raman scattering from molecules adsorbed on TiO 2 nanoparticles has been observed. This is attributed to the dominant contribution of the TiO 2 -to-molecule charge-transfer mechanism. The chargetransfer process is largely dependent on the intrinsic nature of the adsorbed molecules and the surface properties of the semiconductor. Both the stronger electron attracting ability of groups para-to the mercapto group bonded with TiO 2 surface and the plentiful surface states of TiO 2 nanoparticles are favorable to TiO 2 -tomolecule charge-transfer and SERS for molecules adsorbed on TiO 2 .

The phonon dispersions of monolayer and few-layer graphene (AB bilayer, ABA and ABC trilayers) are investigated using the density-functional perturbation theory (DFPT). Compared with the monolayer, the optical phonon E2g mode at Γ splits into two and three doubly degenerate branches for bilayer and trilayer graphene, respectively, due to the weak interlayer coupling. These modes are of various symmetry and exhibit different sensitivity to either Raman or infrared (IR) measurements (or both). The splitting is found to be 5 cm −1 for bilayer and 2 to 5 cm −1 for trilayer graphene. The interlayer coupling is estimated to be about 2 cm −1 . We found that the highest optical modes at K move up by about 12 cm −1 for bilayer and 18 cm −1 for trilayer relative to monolayer graphene. The atomic displacements of these optical eigenmodes are analyzed.

We have been able to observe the surface-enhanced Raman scattering (SERS) from 4-mercaptopyridine (4-Mpy) molecules adsorbed on ZnO nanocrystals, which display 10 3 enhancement factors (EFs). An excitation wavelength-dependent behavior is clearly observed. Another molecule BVPP is also observed to have surface-enhanced Raman signals. The chemical enhancement is most likely responsible for the observed enhancement, since plasmon resonances are ruled out. The research is important not only for a better understanding of the SERS mechanism, but also for extension of the application of Raman spectroscopy to a variety of adsorption problems on a semiconductor surface.