Jun 12, 2009
Nanoclusters upgrade SERS substrates
The decoration of ZnO nanorods with silver nanoclusters creates a hybrid metal–dielectric interface with enhanced light scattering properties. Increased light scattering and plasmonic coupling occur as the size of the silver nanoclusters increases and these properties can be exploited in ultrasensitive surface-enhanced Raman (SERS) technology.
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.
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.
About the author
The work was performed at the National University of Singapore by a team led by Prof. Kian Ping Loh. Suzi Deng is a PhD student studying chemistry at the National University of Singapore. Her research is focused on the magnetic and optical properties of hybrid ZnO nanostructures. This article is co-authored by HaiMing Fan, whose current research interest is in synthesis and characterizations of nanoscale materials. Loh Kian Ping is a professor in the Department of Chemistry at the National University of Singapore. His research interests include advanced functional materials and carbon science and technology.