Low-cost setup for determining the thickness of van der Waals materials*

Crystalline van der Waals materials consist of layers tied together through weak van der Waals forces. They reveal new physical and electrical properties when exfoliated into thin flakes. Depending on the number of layers (i.e. thickness), the properties of these materials can vastly differ. Here, we report a low-cost procedure to determine the thickness of the different flakes by using the optical contrast predicted by a thin-film model. Thin flakes of hexagonal Boron Nitride, graphene, and mica are exfoliated onto Silicon Oxide /Silicon wafers and illuminated perpendicularly by LEDs (450nm-650nm) via an optical microscope. The contrasts between the thin flakes and the bare areas of the substrate are determined for each wavelength and compared to the model. The resulting thickness calculations are then compared to atomic force microscope results.