Ultrafast time-resolved measurement of energy transport at the metal-liquid interface

The nanoscale light-matter interaction at metallic interfaces has many important applications, especially when it is crucial to enhance the surface-to-volume ratio and to achieve high spatial energy confinement. Here, we report an ultrafast time-resolved measurement to study photo-excited transport at the metal-liquid interfaces of colloidal gold nanoparticles (AuNPs). By using the transient absorption spectroscopy method together with the stimulated emission depletion of fluorescence molecules, we simultaneously measured the perturbations of energy states on both sides of the interfaces within a nanoscale distance. Our measurement results showed the evidence of ultrafast coupling between AuNPs and their surrounding solvent molecules at the picosecond time scale. This method can be extended to study the energy transfer mechanisms at the various interfaces for biology, chemistry, or optoelectronics.