Speaker
Description
With the rising interest in using cathodoluminescence (CL) to probe exciton physics of 2D materials, the weak signal originating from scattering off a single atomic layer remains a significant challenge. In this work, we present high-resolution CL measurements of suspended single-, double, and multi- layers of transition-metal dichalcogenides (TMDCs). These require the use of slow electrons to enhance the probability of inelastic scattering. The experimental system within a scanning electron microscope (SEM) combines the SPARC CL detector by Delmic and a home-built ultra-sensitive CL detector for low-energy electrons that uses an ellipsoidal mirror and a single-photon avalanche photodiode (SPAD). To effectively capture the resulting emission without obstructing the sensitive low-voltage electron beam, our custom setup implements a bottom-collection geometry. This configuration allows for a drastically minimized working distance, enabling us to approach the sample closely and significantly enhance the spatial resolution of the optical mapping.
We explore the CL across different layer stacking of $\text{WS}_2$ and $\text{MoS}_2$ for several configurations: (a) either bare or capped by hBN, (b) single-, double-, or multi-layer, (c) find the spatial origin of the CL emission, (d) and for various electron-beam energies. Additionally, we quantify the functionality of the different acquisition and detection systems, and their functionality for low-eV electron irradiation.