Accurate Layer-Number Determination of Hexagonal Boron Nitride Using Optical Characterization

Precise determination of the layer number (N) of hexagonal boron nitride (hBN) is crucial for its integration with other layered materials in applications such as ferroelectric devices and moire potential modulation. We present a nondestructive method to accurately identify N, combining optical contrast analysis with second harmonic generation (SHG) measurements. By studying the flakes on 90 nm thick SiO2/Si substrates, we demonstrate that red-filtered optical images provide a clear contrast step in N with an uncertainty of +/- 1 layer, while SHG measurements further reduce the error by distinguishing even and odd layers. We also introduce a real-time detection technique to identify monolayer and few-layer hBN, improving flake identification efficiency. Given the growing interest in twisted hBN interfaces and their integration in van der Waals heterostructures, this method offers a practical approach for future studies.