UC Riverside

While Raman is a powerful tool that can be used to identify chemicals in a mixed environment, two of the major issues with the conventional Raman are weak signal intensity and low spatial resolution. To resolve these issues, surface and tip-enhanced Raman spectroscopy have been developed that surface-enhanced Raman spectroscopy (SERS) mainly focuses on solving the problem of weak Raman signal, while tip-enhanced Raman spectroscopy (TERS) can improve the spatial resolution overcoming the diffraction limit while enhancing Raman signal. In this work, we report a one-pot synthesis method for monodispersed silver nanocubes with tunable sizes ranging from 60 to 180 nm and investigate the size effect of silver nanocubes when monolayer close-packed silver nanocubes are used as SERS substrate. With the tunable size of silver nanocubes, the size-dependent of SERS substrate was demonstrated. TERS combines traditional Raman spectroscopy and near-field scanning optical microscopy that overcomes the diffraction limit, enabling to obtain of Raman spectroscopy and topological image simultaneously at the nanoscale. Chemically synthesized silver nanowires (AgNWs) have been reported to be used as scanning probes. Specifically, AgNW with sharp tips can significantly improve the Raman signals and spatial resolution. Here a two-step polyol synthetic method was developed to promote oxidative etching selectively to the ends of AgNWs, which eventually produced sharp-tip AgNWs with over 96% selectivity and an average tip radius of 7.87 nm. Among atomic force microscope (AFM) probes fabricated by mounting silver nanowires with different tip sharpness onto commercial AFM cantilevers, the probe based on ultra-sharp AgNW showed significant improvement in spatial resolution in topographic scanning and enhancement factor of TERS tests over the same carbon nanotube sample compared to the probes based on AgNWs with pentagonal pyramid or rounded ends. To broaden the application of TERS in the catalysis field, a second noble metal (Pd, Pt) was grown onto ultra-sharp AgNWs creating a uniform core-shell structure with tunable shell thickness. The resulting nanowires show minimal light scattering and strong tip emission when mounted onto optical fiber under excitation light of 532 nm and 650 nm wavelength suggesting feasibility as TERS probes.