Real-space imaging of transient carrier dynamics by nanoscale pump–probe microscopy

Smaller and faster are key concepts underlying the progress of current nanoscience and nanotechnology. The development of a method of exploring the transient carrier dynamics in organized nanostructures with pinpoint accuracy is therefore highly desirable. Here, we present a new microscopy that enables real-space measurement of the spatial variation of ultrafast dynamics. It is a pulse-laser-combined scanning tunnelling microscopy with a novel delay-time modulation method based on a pulse-picking technique. A non-equilibrium carrier distribution is generated with ultrashort laser pulses, and its relaxation processes are observed by scanning tunnelling microscopy using a pump–probe technique. We have directly analysed the recombination of excited carriers via the gap states associated with a cobalt nanoparticle/GaAs structure in real space. Through the site dependence of the decay time on the tunnelling current injection from the scanning tunnelling microscopy tip, the hole capture rate at the gap states has been imaged on the nanoscale for the first time