Controlling the vertical transport of photocarriers to the surface

Spatial control of the vertical transport of carriers from the bulk to the surface for photochemical processes could provide improved selectivity and efficiency. Here we exploit the intensity variations in the photoexciting beam to drive competing nonlinear optical processes, and thereby allow vertical carrier tranport in only selected regions within the photoexcited spot. Using time-resolved photoemission microscopy, we make a movie of the resulting spatially inhomogeneous photocarrier dynamics. Our work provides a new pathway to control charge and current distributions in space and time within an optical spot, with implications for photovoltaics, photocatalysis and semiconductor devices.