In a recent article published in Science Advances, we demonstrate scattering-type near-field optical microscopy (s-SNOM) based on low-temperature non-contact atomic force microscopy (nc-AFM). This resulted from a strong collaboration with Melanie Müller’s group in Department of Physical Chemistry and Electron Microscopy group in Department of Inorganic Chemistry. An ultralow tip-oscillation amplitude driven by a nc-AFM qPlus sensor allows for the sensitive detection of a plasmonic near-field localized in a narrow Ag-Ag gap. The nc-AFM-based s-SNOM achieves 1-nm resolution, surpassing the conventional s-SNOM resolutions.

Our letter published in Physical Review Letters demonstrates the usefulness of tip-enhanced Raman spectroscopy (TERS) in characterizing physisorption systems. Weakly adsorbbed molecules, such as hydrogen on metal surfaces, are difficult to visualize even with scanning tunneling microscopy. Nevertheless, a plasmon-enhanced molecular spectroscopy technique called TERS well detects physisorbed hydrogen at the tip-sample junction. By analizing the vibrational/rotational spectra, we can also learn about the optical properties of the local tip-sample junction. Unlike previous TERS-measurement targets, the physisorption system exhibits poor chemical enhancement. Instead, the ultraconfined electromagnetic field at the atomic-scale local junction, namely, a plasmonic picocavity, dominates the Raman signal enhancement.

I am pleased to welcome Hyeji to our group as a doctral candidate. She works on single-molecule measurements using ultrahigh-vacuum low-temperature scanning probe microscopy. I wish her success!

In an international conference, The 10th International Symposium on Surface Science (ISSS-10), Dr. Youngwook Park won Young Researcher Prize for his poster on the control of single-molecule photoswitching, and Mr. Kyungmin Kim, who visited us last year, also won Student Prize for his poster on tip-enhanced Raman spectroscopy measurements he conducted here. Their poster presentations were indeed remarkable. Congratulations, Youngwook and Kyungmin!

Our research on nano-optoelectronics has been published in Nature Communications. Plasmons, nanoscale confined light, are promising as triggers for photochemical reactions and optoelectronic devices in the single- or even sub-molecular level, but the precise control of them remains challenging. By subnanoscale positioning of a silver tip with plasmon resonance, we controlled a photoswitch of a single-anhydride-molecule/silicon-surface system where chemical bonding between molecular O atoms and surface Si atoms are ruptured and formed repeatably by the plasmons. What is the role of the silicon surface? What kind of molecules can be switched? How can we achieve a sustainable switch? We addressed these issues in the article, which should significantly contribute to future design and control of ultimately minitualized photodevices.