Ultrafast diffusion transport dynamics of photoexcited carriers in graphene is a key process which determines the performance of graphene-based optoelectronic devices. However, it was studied rarely, especially one of the graphene grown by chemical vapor deposition (CVD) method, due to the lack of effective experimental techniques. Here an imaging transmission-grating-modulated pump-probe spectroscopy is developed and is non-destructive to graphene samples. It is used to study ultrafast diffusion transport dynamics of mono-, few- and multi-layer graphene. A big diffusion coefficient for monolayer graphene, over 10,000 cm2/s, is observed. However, the diffusion coefficient decreases sharply for bilayer graphene, and then decreases slowly with increase of layer number of graphene. We attribute the big diffusion coefficient of monolayer and the sharp fall of diffusion coefficient of bilayer graphenes to unique Dirac cone band structure in monolayer and destruction of Dirac cone band structure in bilayer graphene, respectively.

© 2016 Optical Society of America

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