Manipulating Optical Emission from Hexagonal Boron Nitride Using Cathodoluminescence Spectroscopy with High Spatial Resolution

Controlling light emission from materials is the basis in optoelectronics and photonics. With its wide band gap and single photon emissions across a broad spectral range, hexagonal boron nitride (hBN) has emerged as a highly promising material platform for these applications. However, there are challenges in investigating hBN using only laser excitation: analyzing band-edge emission of hBN is challenging due to the need for high energy deep ultraviolet (DUV) excitation, and sub-band gap localized emissions are difficult to study because of the diffraction limit.
Here, we use cathodoluminescence (CL) spectroscopy within an electron microscope (both STEM and SEM) to overcome those challenges. This method allows analysis of both band-edge in DUV and sub-band gap emission in visible region at the same time, providing more precise exciton dynamics. High spatial resolution optical emission studies offer deeper understanding and precise control of localized emitters. Moreover, the electron microscopy images that are obtained alongside the optical spectral map enable accurate understanding of structure-property relationships. We will demonstrate multiple strategies for manipulating hBN’s optical emission by (i) tuning the twist angle and (ii) applying local strain. First, we will show how the intensity and wavelength of emissions can be continuously tuned by varying twist angles between two hBN layers. The twist angles in heterostructures are analyzed using diffraction patterns and atomic-resolved STEM images. Second, we will demonstrate that applying strain locally induces new sub-band gap emissions due to carbon doping, which is promising for single photon emission.
This presentation will highlight cathodoluminescence as a powerful complement to photoluminescence, overcoming its limitations, and propose novel strategies to control optical properties of hBN. These insights offer exciting potential for quantum information technologies and optoelectronic applications.