▎ 摘　　要

An extremely long decay time of hot carriers in graphene at room temperature was observed for the first time by monitoring the photoinduced thermionic emission using a highly sensitive time-of-flight angle-resolved photo-emission spectroscopy method. The emission persisted beyond 1 ns, two orders of magnitude longer than previously reported carrier decay. The long lifetime was attributed to the excitation of image potential states at very low laser fluencies.