Time-resolved electrostatic force microscopy using tip-synchronized charge generation with pulsed laser excitation

Nanoscale observation of charge distribution and electric polarization is crucial for understanding and controlling functional materials and devices. In particular, the importance of charge dynamics is well recognized, and direct methods to observe charge generation, transfer, and recombination processes are required. Here, we describe tip-synchronized time-resolved electrostatic force microscopy. Numerical modeling clarifies that the tip-synchronized method provides temporal resolution with the timescale of the cantilever oscillation cycle. This method enables us to resolve sub-microsecond charge migration on the surface. The recombination of photo-excited carriers in a bilayer organic photovoltaic thin film is observed as a movie with a 0.3 mu s frame step time resolution. Analysis of the images shows that the carrier lifetime is 2.3 mu s near the donor/acceptor interface. The tip-synchronized method increases the range of time-resolved electrostatic force microscopy, paving the way for studies of nanoscale charge dynamics.