Excitonic excitations play an important role in the optical response of low-dimension nanoscale semi-conducting materials. During its lifetime, excitons may diffuse or migrate in particular directions, thus constituting a form of excitation information transfer on the nanoscale. The details of the spatio-temporal evolution of excitons remain unclear, because it has been challenging to directly visualize this process with nanometer spatial resolution and femtosecond temporal resolution. Here we describe pump-probe measurements at the nanoscale, using the photo-induced force microscopy (PiFM) and near-field scanning optical microscopy (NSOM) at ambient conditions. We analyze the spatial and temporal characteristics of the excitons in quasi-1D semiconductor nanowires, and provide unprecedented views of their evolution.
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