This article reports the observation of surface-enhanced Raman scattering (SERS) from a chemically etched ZnSe surface using 4-mercaptopyridine (4-MPy) as probe molecules.
A thin film of ZnSe was grown by molecular beam epitaxy (MBE) and then etched using a strong acid. Protrusions of hemiellipsoidal nanoparticles were observed on the surface. Using the results of the Mie theory, researchers controlled the size of the nanoparticles to overlap significantly with maximum efficiency of near-field plasmon enhancement. In the Raman spectrum, researchers observed large enhancements of the a1, b1, and b2 modes when 4-MPy molecules were adsorbed on the surface using a 514.5 nm laser for excitation, indicating strong charge-transfer contributions. An enhancement factor of (2 × 106) was observed comparable to that of silver nanoparticles. Researchers concluded that this large enhancement factor was an indication of the coupled contribution of several resonances. They propose that some combination of surface plasmon, charge transfer, and band-gap resonances was most likely the contributing factor in the observed Raman signal enhancement, because all three of these resonances lie close to the excitation wavelength. (publisher abstract modified)