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Two-dimensional (2D) materials and heterostructures have recently gained wideattention due to potential applications in optoelectronic devices. However, theoptical properties of the heterojunction have not been properly characterizeddue to the limited spatial resolution, requiring nano-optical characterizationbeyond the diffraction limit. Here, we investigate the lateral monolayerMoS2-WS2 heterostructure using tip-enhanced photoluminescence (TEPL)spectroscopy on a non-metallic substrate with picoscale tip-sample distancecontrol. By placing a plasmonic Au-coated Ag tip at the heterojunction, weobserved more than three orders of magnitude photoluminescence (PL) enhancementdue to the classical near-field mechanism and charge transfer across thejunction. The picoscale precision of the distance-dependent TEPL measurementsallowed for investigating the classical and quantum tunneling regimes above andbelow the ~320 pm tip-sample distance, respectively. Quantum plasmonic effectsusually limit the maximum signal enhancement due to the near-field depletion atthe tip. We demonstrate a more complex behavior at the 2D lateralheterojunction, where hot electron tunneling leads to the quenching of the PLof MoS2, while simultaneously increasing the PL of WS2. Our simulations showagreement with the experiments, revealing the range of parameters andenhancement factors corresponding to various regimes. The controllablephotoresponse of the lateral junction can be used in novel nanodevices.

Picoscale control of quantum plasmonic photoluminescence enhancement at 2D lateral heterojunction