Silver nanoparticles-embedded zinc oxide microbars as SERS-active substrates

Abstract

We have successfully synthesized zinc oxide microbars (ZnO-µBs) and functionalized the same with Ag-NPs (called hereafter Ag-NPs@ZnO-µBs) through a generic synthesis route. High-resolution field emission scanning electron microscopy revealed that as-synthesized ZnO-µBs were nanocrystalline and of different lengths, with hexagonal faces at both edges. According to the JCPDS 36–1451 database, the lattice fringe spacing of 0.285 nm as revealed by high-resolution transmission electron microscopy was in good agreement with the spacing of {1 0 0} planes of the wurtzite phase of ZnO. In the case of Ag-NPs@ZnO-µBs constructs, the coexistence of Ag-NPs and ZnO-µBs was revealed by high-resolution transmission electron microscopy. The lattice fringes spacings coincided well with the spacing of {1 1 1} plane of the face-centered cube structure of Ag-NPs and with the spacing of the {1 0 0} plane of the wurtzite phase of ZnO as per the databases of JCPDS 04–0783 and JCPDS 36–1451 respectively. Strong Surface-Enhanced Raman Scattering (SERS) enhancement was observed in the presence of Ag-NPs@ZnO-µBs, whereas no Raman peaks other than those for ZnO were noticed in the presence of ZnO-µBs. For the Ag-NPs@ZnO-µBs construct, strong SERS enhancement up to 10⁶ has been attained. A plausible charge transfer mechanism has been demonstrated to support the experimental results. Such generic route to turn semiconductor nanostructures into SERS-active substrates using metal NPs is not only important to understand the SERS-process, but also to open up new strategies to devise efficient SERS-active substrates.