Fig. 6

a (i) Schematic representation of the exciton transfer process occurring in a monolayer WS\(_2\)/MoS\(_2\) heterostructure transferred onto an Ag plate. (ii) PL image of the lateral heterostructure. Excitons in the WS\(_2\) monolayer (depicted as red dots) were coupled to SPP through a non-radiative decay process. Subsequently, SPPs induced excitons in the MoS\(_2\) monolayer at the interface (depicted as blue dots). (iii) Optical microscopy images of the WS\(_2\)/MoS\(_2\) TMD lateral heterostructure. Excitons were generated in the WS\(_2\) monolayer at the laser spot (indicated by a red star). PL spectra were collected from regions on the SiO\(_2\) nanoparticle (marked as an orange dot) and groove on the silver plate (indicated by a blue slit). (iv) PL spectra collected at the launching point and interface as shown in (ii). (v) PL spectra collected in the SiO\(_2\) nanoparticle and groove in the MoS\(_2\) region as shown in (iii). (vi) Variation of PL intensity observed during the exciton–SPP–exciton conversion process as a function of propagation. b (i) Schematic illustration demonstrating the propagation of exciton-coupled SPPs. MoS\(_2\) excitons were generated by a 514 nm wavelength laser at the overlapping region where the nanowire intersected the MoS\(_2\) monolayer. (ii) Top :  Optical micrograph depicting the Ag nanowire and MoS\(_2\) flake with the incident laser spot. Bottom :  PL image showing the end of the Ag nanowire and the MoS\(_2\) monolayer. (iii) PL spectra collected at the end of the nanowire, with variations in excitation positions. (iv) SPP propagation lengths determined from PL spectra in relation to photon energy. Inset :  Peak of PL intensity as a function of transport length x. c (i) Schematic of an Ag nanowire positioned on a partially stacked MoSe\(_2\)/MoS\(_2\) bilayer with laser illuminations at four terminals. Output signals are collected at the right end of the Ag nanowire. (ii) Four combinations of excitation positions on the MoSe\(_2\)/MoS\(_2\) monolayer. (iii) Collected PL spectra corresponding to the different combinations of light illuminations at the input terminals. (iv) Implementation of an optical 4-to-2 binary encoder through plotting the measured intensity as a function of the four different input states. a Reproduced with permission [78]. Copyright [2017] Springer Nature. b Reproduced with permission [79]. Copyright [2015] John Wiley and Sons. c Reproduced with permission [80]. Copyright [2019] Springer Nature