Probing patterned defects on graphene using differential interference contrast observation

We present here a simple optical-imaging technique for observing patterned defects on graphene. Photolithography was performed to limit areas on graphene that would be exposed to an oxygen plasma when it was introduced to generate defects on the graphene. The patterned defects were systematically characterized using conventional Nomarski differential interference contrast (DIC) observations with a nematic liquid crystal in conjunction with micro-Raman spectroscopy, which showed that the defects on graphene increased with increasing durations of oxygen-plasma treatment. Distinct differences in reflected-light Nomarski DIC were observed in the regions with defects. The combination of the DIC imaging and micro-Raman spectroscopy provides a fast, direct, and scalable method to evaluate the defects on graphene.