DEPARTMENT OF
PHYSICAL CHEMISTRY
Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
PC Online Talk
Chair: Nikolai Paßler

Thursday, June 11, 2020, 3:00 pm
https://us02web.zoom.us/j/83447040357
Dr. Borja Cirera
FHI Department PC
Dramatic enhancement of Raman scattering and Raman thermometry in electrically-fused junctions
The ability to precisely design Å-scale plasmonic cavities has boosted the sensitivity and spatial resolution of surface- and tip-enhanced Raman scattering (SERS and TERS). In this context, low-temperature scanning probe microscopy (LT-SPM) offers great advantages to perform nanoscale vibrational spectromiscroscopy (TER-SM). Along with nanofabrication techniques of plasmonic tips, LT-SPM now allows to examine light–matter interactions in plasmonic “picocavities” down to the sub-molecular level. However, the underlying mechanisms behind the large enhancement factors present in such cavities remain unclear. We reveal how TERS evolves at vanishing tip–sample distances including the transition from a tunneling to conductive coupled regime. Upon atomic-point contact (APC) formation, a dramatic TERS enhancement is observed. In order to shed light on the mechanisms behind, we examined different model systems: an Ag tip with ultrathin ZnO films and single C60 molecules on the Au(111), Ag(111), and Cu(111) surfaces at 10 K. A pronounced electromagnetic enhancement of Raman scattering is commonly observed for a few Å gaps. The sudden increase of the TERS intensity upon APC formation is attributed to the chemical interaction between the tip and the sample which provides additional charge transfer enhancement. Furthermore, intense anti-Stokes signals can be observed, allowing us to perform Raman thermometry in electrically-fused plasmonic junctions. The results reveal pronounced non-thermal contributions, which underlines the necessity to better understand atomic-scale light–matter interactions.

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https://us02web.zoom.us/j/83447040357
Meeting ID: 834 4704 0357