Graphene grain boundaries (GBs) and other nanodefects can deteriorate electronic properties. Here, using transient absorption (TA) microscopy we directly visualized GBs by TA intensity increase due to change in density of state. We also observed a faster decay due to defect-accelerated carrier relaxation in the GB area. By line-illumination and parallel detection, we increased the TA intensity imaging speed to 1000 frames per second, which is 6 orders of magnitude faster than Raman microscopy. Combined with a resonant optical delay tuner which scans a 5.3 ps temporal delay within 92 μs, our system enabled spectroscopic TA imaging, at a speed of 50 stacks per second, to probe and characterize graphene nanodefects based on the TA decay rate. Finally, we demonstrate real-time nondestructive characterization of graphene at a rolling speed of 0.3 m/min, which matches the fastest roll-to-roll manufacturing process reported.
Keywords: Graphene; grain boundary; transient absorption microscopy; ultrahigh-speed microscopy.