Enhancement of ultrafast photoluminescence from deformed graphene studied by optical localization microscopy

By using localization techniques, we demonstrated that the morphology of a 2D material in three dimensions can be optically obtained with nanometer precision in z-axis. This technique provides a convenient method to study the correlation between the optical properties and the morphology of 2D materials for the same area. We utilized optical localization microscopy to directly study the correlation between the ultrafast photoluminescence and the morphology of graphene. We observed enhancement of the ultrafast photoluminescence from the deformed graphene. In comparison to the planar graphene, the enhancement factor of ultrafast photoluminescence could be up to several times at the highly curved region. We found that the intensity of photoluminescence from the uniaxially rippled graphene depends on the polarization of excitation light. Furthermore, Raman spectroscopy was used to measure the strain distribution. Pump-probe measurements were conducted to reveal the carrier dynamics. From the experimental results, two mechanisms were confirmed to mainly account for the enhancement of ultrafast photoluminescence from the deformed graphene. One is the deformation-induced strain increases the absorption of graphene. The other is the prolonged carrier relaxation time in the curved graphene.