Self-assembled Nanowires as Building Blocks for Tip Enhanced Raman Spectroscopy (TERS) Probes

Raman spectroscopy (RS) is widely used for chemical characterization of molecular species, however, the low efficiency of RS limits its applications to large samples and the spatial resolution is limited to that of optical microscopes (~ 0.5 μm). In Tip Enhanced Raman Spectroscopy (TERS) both limitations are resolved using a metallic, or metal-coated, scanning probe microscope (SPM) tip. The SPM provides large spatial resolution while the metallic termination provides large Raman enhancement (RE) resulting from localized surface plasmon resonances in the vicinity of low-dimension metals. Theoretical predictions suggest that TERS can achieve RE of 107-1012and high (<5 nm) spatial resolution, however, such capabilities are still far from being realized. The major limitation in the progress of TERS, and its wide use in non-specialized research laboratories, is the lack of reproducible tips with high enhancing factors. This project will study a new approach, namely, the use of self-assembled nanostructures as building blocks for the assembly of TERS tips. The research group has the experience to prepare a wide range of nanostructures suitable to be used for this purpose; in particular, Si, ZnO, ZnS and CdS nanowires with a reproducible and well-defined metallic tip (20 to 200 nm in diameter). The researchers will make extensive use of their recently acquired Near-field Scanning Optical Microscope (NSOM)-Raman system that provides a fully functional platform to study TERS. The ability to fabricate such tips, systematically and reproducibly, is expected to become a major contribution towards the development of reliable TERS with vast applications in many fields like semiconductor, biological, and biomedical technologies.