Efficient cathodoluminescence of monolayer transitional metal dichalcogenides in a van der Waals heterostructure

摘要

Monolayer two-dimensional transitional metal dichalcogenides, such as MoS2,WS2 and WSe2, are direct band gap semiconductors with large exciton bindingenergy. They attract growing attentions for opto-electronic applicationsincluding solar cells, photo-detectors, light-emitting diodes andphoto-transistors, capacitive energy storage, photodynamic cancer therapy andsensing on flexible platforms. While light-induced luminescence has been widelystudied, luminescence induced by injection of free electrons could promiseanother important applications of these new materials. However,cathodoluminescence is inefficient due to the low cross-section of theelectron-hole creating process in the monolayers. Here for the first time weshow that cathodoluminescence of monolayer chalcogenide semiconductors can beevidently observed in a van der Waals heterostructure when the monolayersemiconductor is sandwiched between layers of hexagonal boron nitride (hBN)with higher energy gap. The emission intensity shows a strong dependence on thethicknesses of surrounding layers and the enhancement factor is more than 1000folds. Strain-induced exciton peak shift in the suspended heterostructure isalso investigated by the cathodoluminescence spectroscopy. Our resultsdemonstrate that MoS2, WS2 and WSe2 could be promising cathodoluminescentmaterials for applications in single-photon emitters, high-energy particledetectors, transmission electron microscope displays, surface-conductionelectron-emitter and field emission display technologies.