Figure 1

(a) Schematic representation of the wide-area cathodoluminescence (CL) measurement of monolayer hexagonal BN (mBN) epilayer grown on a highly oriented pyrolytic graphite (HOPG) substrate. The typical incident angle (\(\theta\)), acceleration voltage (\({V}_{{\text{acc}}}\)), probe current (\({I}_{{\text{p}}}\)), and diameter (\({\phi }_{{\text{EB}}}\)) of the e-beam were 60°, − 3.5 kV, 70 μA, and 750 μm, respectively. Monte Carlo simulations of the electron trajectories into a model mBN/HOPG for (b) the wide-area CL and (c) the standard spatially resolved CL (SRCL) measurements. They were calculated using the CASINO software³⁸. In the simulation, \(\theta\), \({V}_{{\text{acc}}}\), and \({\phi }_{{\text{EB}}}\) were set respectively to 60°, − 3.5 kV, and 1 μm for the wide-area CL and 0°, − 3.5 kV, and 30 nm for the standard SRCL measurements. (d) Simulated depth distributions of the total energy loss of irradiated electrons into mBN/HOPG for the wide-area CL (solid lines) and the standard SRCL (dashed lines) measurements with \({V}_{{\text{acc}}}\) = − 1.0, − 2.0, and − 3.5 kV.