SERS incurs an intense Raman signal when the plasmon frequency of the silver nanoclusters is in resonance with the radiation and gives an enhanced electromagnetic field at the surface. The size, shape, assembly and dielectric properties of the surrounding nanostructures play important roles in the enhancement of SERS. Recently, scientists in Singapore and Taiwan have demonstrated that silver nanoclusters deposited on ZnO nanowire arrays can be used as model systems to study the plasmonic coupling between the silver nanoclusters supported on a nanowire scaffold.

The hybrid SERS substrates were prepared either by nanocluster beam deposition of ~10 nm silver nanoclusters on ZnO nanowires or by annealing sputtered silver on ZnO nanowires to form ~150 nm silver nanoclusters.

Test results

When excited by a 532 nm light source, the hybrid silver NC–ZnO NW arrays were seen to offer morphology-dependent electromagnetic scattering SERS enhancement factors of 30–50 times for a 150 nm NC–ZnO NW array relative to a 10 nm NC–ZnO NW array. This difference in performance is attributed to the increased light scattering and lateral plasmon coupling between the 150 nm silver nanoclusters on neighboring wires compared with the 10 nm silver nanoclusters, which significantly enhances the local electromagnetic field at the dielectric surface.

By decorating ZnO nanowire arrays with silver nanoclusters of different sizes, the interwire plasmon coupling can be controlled. This rational tunability of SERS can be exploited for the sensitive detection and identification of trace molecular species.

The researchers presented their results in Nanotechnology.