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

Precise determination of the layer number (<i>N</i>) of hexagonal boron nitride (hBN) is crucial for its integration with other layered materials in applications such as ferroelectric devices and moiré potential modulation. We present a nondestructive method to accurately identify <i>N</i>, 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 <i>N</i> 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.