Cathodoluminescence enhancement and quenching in type-I van der Waals heterostructures: Cleanliness of the interfaces and defect creation

Layered materials, such as transition metal dichalcogenides, can be combined at will in van der Waals heterostructures and lead to a variety of new phenomena. To better understand the coupling between layers and the variation of electronic and optical properties, noninvasive techniques with the best possible spatial resolution are needed. Here we show that due to an enhanced interaction cross section with electrons in a type-I van der Waals heterostructure, made of single-layer molybdenum disulfide and thin boron nitride, cathodoluminescence is strongly enhanced. It can be mapped with a spatial resolution far exceeding what can be achieved in more commonly used photoluminescence experiments, thereby providing invaluable insights into the optoelectronic properties at the nanoscale. We demonstrate that the technique is noninvasive, i.e., it does not induce any defect, only if the interface between boron nitride and the molybdenum disulfide layer is pristine. In the presence of trapped species, structural defects are locally induced by the electron beam in the layer. Such defects quench the luminescence and present clear Raman signatures. We show that optimizing the heterostructure preparation techniques can lead to extended areas with clean interfaces that lead to a more homogeneous cathodoluminescence signal