Raman scattering enhancement of a single ZnO nanorod decorated with Ag nanoparticles: synergies of defects and plasmons

Surface-enhanced Raman scattering (SERS) of a single ZnO nanorod (NR) is demonstrated by coating with Ag nanoparticles (NPs). An enhancement factor of 1.2×103 and 4.4×102 has been obtained for E2 (high) mode (437 cm-1) and A1 (TO) mode (378 cm-1), respectively. Electron paramagnetic resonance measurements reveal an unintentional donor state in ZnO NRs. The enhancement of deep-level emission and micro-absorption mapping of a single ZnO NR further confirms the presence of the donor state. The SERS is believed to result from the charge transfer between ZnO NRs and Ag NPs, which can be enhanced by the empty donor state in ZnO. Finally, single ZnO NRs coated with Ag can be used as good SERS substrates for small molecule detection. This Letter highlights the interaction between point defects and the SERS effect down to a single semiconductor NR.