Enhancement Factors in Tip-Enhanced Raman Spectroscopy with Atomically-Precise Systems
Tip-enhanced Raman spectroscopy (TERS) in plasmonic nanocavities has achieved sub-nanometer resolution, proving to be a valuable complement to traditional scanning probe microscopy (SPM) techniques for studying the local physico-chemical properties of low-dimensional materials. In the theoretical framework of TERS, the significant enhancement of the Raman signal is attributed to two key mechanisms: (1) electromagnetic (EM) enhancement, where atomically-confined electromagnetic fields amplify the signal, and (2) chemical enhancement (CHEM), where the interaction of the adsorbate with its environment or the excitation source further boosts the signal. This work explores how these enhancement mechanisms can be studied using a precisely controlled SPM junction and atomically defined systems. I demonstrate that molecular or atomic point contact formation usually results in a pronounced chemical enhancement of the Raman signal, which remains effective even on weakly plasmonic or non-plasmonic substrates. These results open up new possibilities for probing the optoelectronic properties of adsorbates on catalytically relevant surfaces and a broad range of semiconductors with atomic precision.