Interface optical phonons in spheroidal dots: Raman selection rules

The contribution of interface phonons to first-order Raman scattering in nanocrystals with nonspherical geometry is analyzed. Interface optical phonons in the spheroidal geometry are discussed and the corresponding Fr\"ohlich-like electron-phonon interaction is reported in the framework of the dielectric continuum approach. It is shown that the interface phonon modes are strongly dependent on the nanocrystal geometry, particularly on the ellipsoid's semiaxis ratio. The new Raman selection rules have revealed that solely interface phonon modes with even angular momentum are allowed to contribute to the first-order phonon-assisted scattering of light. On this basis we are able to give an explanation for the observed low-frequency ``shoulders'' present in the Raman cross section of several II-VI semiconductor nanostructures.