Nanoscale Analysis
external page Tip-enhanced Raman Spectroscopy (TERS) is a powerful analytical technique for surface molecular imaging at the nanoscale under ambient conditions. It combines high spatial resolution of scanning probe microscopy (SPM) with the high chemical sensitivity and specificity of surface-enhanced Raman spectroscopy (SERS). Our team focuses on the further development of this technique and its application in the material, chemical and biological sciences, with the aim to turn it into a versatile analytical tool for nanoscience and nanotechnology. [NOTE: this is NOT nanomaterial/nanoparticle based analytical chemistry]
Raman spectroscopy is a well-established analytical tool that provides fingerprint vibrational information from the molecules under investigation. However, Raman scattering is a relatively weak effect compared to, for e.g., fluorescence. SERS overcomes this issue using localized surface plasmon resonance and offers several orders of magnitude improvement in sensitivity via plasmonic signal enhancement. However, the (often random) heterogeneity of SERS substrates leads to a significant variation in plasmonic signal enhancement across the sample surface limiting its range of applications especially nanoscale molecular imaging. In TERS, the signal enhancing structure is reduced to a single 'SERS hotspot' created at the end of a sharp metallic tip, which can be accurately positioned in contact with a surface using either an atomic force microscope (AFM) or a scanning tunnelling microscope (STM). This approach, external page pioneered in our laboratory in 2000, provides the possibility to perform hyperspectral molecular imaging with greater than 10 nm spatial resolution by scanning the local 'SERS hot spot' over the sample surface.
A typical TERS instrument combines a confocal laser scanning Raman microscope with an AFM or STM and contains a set-up for precise alignment of a customized metallic SPM probe with the excitation laser spot. A piezo-controlled movable sample stage is used to perform hyperspectral Raman imaging of the sample surface in nm size steps. TERS systems can be based on an inverted (bottom illumination) or upright (top illumination) optical microscope (both available in our laboratory) and in most cases the same objective is used for excitation and collection of Raman signals. Figure 1 schematically shows the basic working principle of a TERS setup combining a Raman microscope with a STM in upright geometry.
The general aim of our research is to turn TERS into a versatile analytical technique for surface science, with a particular emphasis on reproducible molecular imaging at the nanoscale under ambient conditions.
Current Scientific Projects:
