Bringing graphene into the undergraduate classroom

We present an undergraduate instructional laboratory experiment that introduces students to the most well-known van der Waals material, graphene. Like all van der Waals materials, graphene is a crystal that can be peeled into layers, in some cases, down to atomic thicknesses. In this experiment, students first fabricate a sample consisting of few-layer graphene flakes atop of a silicon wafer substrate using the mechanical exfoliation method. The students then use a microscope setup to acquire images of the sample under white-light and LED illumination. These images are analyzed to produce optical contrast values (a measure of the reflectance of the graphene flakes) as a function of illumination wavelength. A theoretical model for optical contrast is developed based on thin-film interference and the resulting theory and experiment are compared, yielding a value for the graphene flake's thickness. This experiment is designed for advanced instructional laboratory and upper level optics courses. It may also be simplified into a qualitative introductory physics laboratory, demonstration, or outreach workshop activity.