Optical control of single-atom dynamics in plasmonic nanogaps.

Observing and controlling dynamics of single atoms in ambient conditions is challenging when using conventional atomic-scale techniques due to their invasive character. Here, such control is achieved optically, by confining pulses of visible light within extreme plasmonic nanogaps, where they rapidly create ("write") an adatom on one facet surface. Such adatoms are shown to be storable in ambient conditions for at least a week in the dark and are observed ("read") using low-intensity surface-enhanced Raman spectroscopy (SERS). Writing at higher optical intensities stabilizes the atomic protrusion through light-induced local restructuring, which imposes a higher energy barrier for its return into the metal surface. Fluctuations in these "picocavity" SERS spectra show that while adatom movement is significantly slower under low light intensities, ambient thermal energy still enables them to explore the surrounding energetic landscape. Optical control over single metal atom dynamics opens promising avenues for next-generation microelectronics, atomic-scale imaging, and catalysis.