Laser Raman spectroscopy depends on a change in the polarization of a molecule to produce Raman scattering. When a beam of photons strikes a molecule, the photons are scattered elastically (Rayleigh scattering) and inelastically (Raman scattering) generating Stoke’s and anti-Stokes lines. Because Raman spectroscopy is a scattering process, samples of any size or shape can be examined. Very small amounts of material can be studied down to microscopic levels (~1µm). Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for enhancing the inherently low Raman scattering cross-sections of molecules, enabling detection down to single molecules. The major mechanism of the SERS effect arises from electromagnetic field enhancement in the vicinity of metallic nanostructures when they are excited at their surface plasmon resonance.
Our aim is to increase the enhancement factors of the SERS technique by developing novel designs and fabrication methods as well as using different excitation wavelengths ranging from UV to NIR. The objective of the project is to design, fabricate and analyze optical properties of metallic nanostructures and to perform Raman spectroscopy experiments of biomolecules. In particular, our current focus is deep-UV surface-enhanced resonance Raman scattering on aluminum nanostructures. We have recently demonstrated that this technique is a highly useful analytical technique for ultrasensitive and label-free detection of biomolecules in real time.
Direct coupling of Raman spectroscopy with nanoindentation provides comprehensive mechanical characterization capabilities of materials at the nanoscale and its direct correlation to the localized chemical composition. The vibrational (phonon) states of molecules detected using Raman spectroscopy give a molecular fingerprint of the physical state of a matter. At the same time, a nanoindentation curve serves as a fingerprint of a material’s mechanical properties. In-situ Raman mapping performed before mechanical testing allows for precise positioning of the mechanical test based on chemical structure. Additionally, Raman maps performed after nanomechanical tests provide comprehensive information about the internal stress distribution within the material, resulting from plastic deformation during the test. Raman maps can be acquired in fully automated routines together with in-situ SPM imaging, modulus maps, or electrical conductance maps.