Single-molecule energetics

Abstract: 

Understanding the energetics of single molecules is essential for unraveling the fundamental quantum interactions that govern chemical reactions. Traditional ensemble-based measurements often obscure key dynamical processes, necessitating techniques that provide real-space, single-molecule insights. The scanning tunneling microscope (STM) has emerged as a versatile tool for imaging, manipulating, and exciting individual molecules on solid surfaces, offering unprecedented spatial resolution. Beyond its conventional role, STM can also serve as a localized excitation source, enabling precise control over molecular quantum states through inelastic tunneling electrons.

Building on this capability, we have developed an advanced optical STM technology that integrates STM with light irradiation and detection systems, allowing us to investigate novel chemical reactions and spectroscopy at the single-molecule level. By leveraging localized surface plasmons (LSPs)—collective oscillations of free electrons induced in metallic nanostructures—we have achieved breakthroughs in single-molecule emission and absorption spectroscopy. The interaction between LSPs and molecular electronic/vibrational states has enabled us to induce and probe exciton formation in isolated molecules. Furthermore, we visualized fluorescence resonance energy transfer between different molecules and explored the detailed mechanisms of LSP-induced single-molecule chemical dynamics.

Additionally, our research has demonstrated the application of LSPs for measuring tip-enhanced resonance Raman spectra and achieving ultrahigh-energy resolution photoluminescence spectroscopy using a tunable excitation laser. These optical setups allow real-space measurement of photocurrent pathways in single molecules, expanding our understanding of molecular-scale energy conversion. In this talk, I will share our recent findings in single-molecule energetics, highlighting our methodological advancements and their broader implications for nanoscience and molecular spectroscopy. 

(You can find what we have been doing at https://www2.riken.jp/Kimlab)

20250522_대학원 세미나_김유수 교수.pdf