High-throughput optical thickness and size characterization of 2D materials
We describe a method using simple optical microscopy and image processing that simultaneously characterizes thousands of nanosheets in a sample area on the order of 1 mm2. Including data acquisition and processing, both the number of atomic layers and the lateral sizes of all sheets can be obtained within a few hours—approximately 100 times faster than with previous methods, such as atomic force microscopy. This is achieved by normalizing the optical image based on substrate brightness, which eliminates inhomogeneities usually limiting optical techniques. Ultimately, the method enables robust statistical analysis of populations of nanosheet materials. We demonstrate the utility of this method by examining fractions made from a sample of graphene oxide (GO) made using an emulsion-based method. Beyond providing the morphological composition of the samples, the reported method is sensitive enough to provide information about the oxidation level of a population of GO sheets and, correspondingly, optical constants of the material.