This article reports that by chemically etching a thin film of crystalline ZnSe with acid, the authors observed a strong Raman enhancement of the surface phonon modes of ZnSe on adsorption of a molecule (4-mercaptopyridine).
The surface is composed of oblate hemi-ellipsoids, which has a large surface-to-bulk ratio. The assignment of the observed modes (at 248 and 492 cm−1) to a fundamental and first overtone of the surface optical mode is consistent with observations from high-resolution electron energy loss spectroscopy as well as calculations. (publisher abstract modified)