Single-molecule nanospectroscopy
Microscopic understanding and molecular-level control of individual electronic quantum states of a single molecule are a long-standing challenge in spectroscopy. Imada et al. found that a narrow-line tunable laser combined with a scanning tunneling microscope was able to generate photoluminescence spectra of the electronic and vibrational states of single molecules with micro–electron volt energy resolution and submolecular spatial resolution. The authors also discovered a way to tune the energy levels through a linear Stark effect and plasmon-exciton coupling in the tunneling junction. The proposed technique paves the way to efficient exploitation of energy conversion dynamics in electronic excited states, which constitutes the bedrock principle of such systems as LEDs, photovoltaics, and photosynthetic cells.
Science, abg8790, this issue p. 95
Abstract
Ways to characterize and control excited states at the single-molecule and atomic levels are needed to exploit excitation-triggered energy-conversion processes. Here, we present a single-molecule spectroscopic method with micro–electron volt energy and submolecular-spatial resolution using laser driving of nanocavity plasmons to induce molecular luminescence in scanning tunneling microscopy. This tunable and monochromatic nanoprobe allows state-selective characterization of the energy levels and linewidths of individual electronic and vibrational quantum states of a single molecule. Moreover, we demonstrate that the energy levels of the states can be finely tuned by using the Stark effect and plasmon-exciton coupling in the tunneling junction. Our technique and findings open a route to the creation of designed energy-converting functions by using tuned energy levels of molecular systems.
