Effects of chloride ions on flower-like Ag-coated ZnO nanorod arrays and the Raman enhancement

Abstract

Chloride solutions are used to modify flower-like Ag-coated ZnO nanorod (Ag-ZnO-NR) arrays, leading to the formation of Ag-nanosphere decorated ZnO-NR arrays, which have a morphology with each sphere-like Ag nanoparticle independently lying at the top of ZnO-NR and thus can be used as a new kind of substrates for the study of surface-enhanced Raman spectroscopy (SERS). The chloride modification is dominated by Ag abnormal migration on ZnO NRs in the environment of chloride solution. The concentration of chloride ions for effective modification is higher than ∼1 × 10−4 M and the final morphology is nearly steady as the soaking time is longer than 10 min. On the modified SERS substrates, the thermalization of probing molecules during Raman measurement is substantially depressed. Using the SERS samples prepared by loading the probing molecules in the presence of chloride ions, the Raman signals are obviously enhanced with an extremely high signal-to-noise ratio. The Raman enhancement is evidenced to be due to the enhanced adsorption of probing molecules on Ag surface in the presence of chloride ions.