High-resolution real-space imaging of individual organic molecules is a powerful tool to elucidate their diverse structures and associated functionalities. However, most investigations to date have been restricted to small, thermally-evaporable molecules. Recently, the combination of an electrospray ion-beam deposition (ES-IBD) source with scanning tunneling microscopy (STM) under ultra-high vacuum conditions has enabled the study of biologically relevant systems—such as glycans and peptides—at sub-molecular resolution. This methodological advance is particularly advantageous for probing molecules with high conformational flexibility and complexity, providing unprecedented insights into their structural details. Using this approach, we have achieved sub-nanometer resolution imaging of individual glycans, allowing us to resolve glycan connectivity and distinguish between regioisomers. Furthermore, we developed a novel strategy for identifying the sequence position of a single amino acid type incorporated within a peptide chain. This selective recognition of a single amino acid in a peptide allows for the identification of the full peptide sequence and its self-assembled structure. Additionally, we have developed a novel STM system capable of simultaneously acquiring spatially-resolved photon maps alongside with the topography. Using this setup, we achieved photon count rates of approximately six million photons per second at a tunneling current of 1 nA, resulting from the decay of plasmon-polariton excitations between an Ag(111) surface and an Ag tip. This detection efficiency (approximately 10%) surpasses all previously reported experimental setups by an order of magnitude. The high photon detection rates open up new possibilities for multidimensional measurements.
