Atomic scale mapping of structural and chemical surface properties by tip-enhanced Raman spectroscopy

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Since little more than a decade, tip-enhanced spectroscopy techniques, including tip-enhanced Raman spectroscopy (TERS) provide groundbreaking progress in chemical and structural investigations down to the level of single orbitals. While the wealth of chemical and structural information through conventional Raman spectroscopy is limited to microscopic structures by the diffraction limit of light, TERS benefits from the high spatial resolution of otherwise chemically insensitive scanning probe techniques like atomic force microscopy and scanning tunneling microscopy. Our group already achieved an outstanding optical resolution of less than five nanometers on nanoelectronic devices. For this purpose, a noble metal tip is brought into proximity of the sample surface under simultaneous illumination of a laser to resonantly excite the tip's surface electrons that will create a near-field enhancement. As a result, the local laser field is amplified and confined by several orders of magnitude. While this technique has seen tremendous success, many researchers have abandoned their activities due to the complications in the fabrication of suitable noble metal tips. One pillar of our research program is therefore the systematic optimization of our existing TERS tips and the testing of alternative processes by a Master student. The second pillar is the systematic investigation of the near field effects in the proximity of the tip that determine the confinement and the enhancement. This implies direct measurements of the temperature in the near-field by Raman spectroscopy as well as polarization-dependent studies on the coupling between incoming and outgoing light. The third pillar will be the application of this technique to unsolved challenges in physics and material science on nanoelectronic systems: e.g. the direct measurement of strain along ferroelectric domain walls or dislocations and the chemical identification of extended defects in resistively switching binary and ternary oxides. The strength of TERS for the training of HQP lies in its experimental complexity. The near-field enhancement at the tip apex is an additional value generated by the concerted action of scanning probe microscopy, optical spectroscopy, and near field optics. Our HQP is and will be trained in all these domains. All these competences are searched for from industry as we can confirm through various collaborative R&D projects. The primary impact of this program will be through the training of HQP in these domains and secondly through the deployment of these highly sophisticated experimental techniques to the Canadian research community in academia and industry which will allow for non-destructive investigations of the chemistry, the local structure and even strain e.g. after fatigue with unrivalled nanoscale resolution.