## 3 Results and Discussion
(**d**) Raman spectra of the three samples. (**e**) PL spectra of the three samples. (**f**) PL spectra of MoS2/WS2 HS and WS2/MoS2 HS. To investigate the interlayer electronic coupling in the WS\({}_{2}\)/MoS\({}_{2}\) HS, the PL spectra of ML-WS\({}_{2}\), ML-MoS\({}_{2}\), and WS\({}_{2}\)/MoS\({}_{2}\) HS are depicted in Figure 2e. Fitted by the Lorenz function, the PL spectrum of WS\({}_{2}\) exhibits two peaks at 1.972 and 2.003 eV, which can be attributed to the A-excitons and negative trions of ML-WS\({}_{2}\). The PL spectrum of MoS\({}_{2}\) can also be divided into two peaks at 1.816 and 1.984 eV, corresponding to the A-excitons and B-excitons of ML-MoS\({}_{2}\). After the formation of the heterostructure, only the exciton peak from WS\({}_{2}\) can be observed, possibly due to the low emission intensity of MoS\({}_{2}\), making it indistinguishable in the overlapping region from the PL spectrum. It is worth noting that the energy from trions slightly red-shifts from 1.972 to 1.935 eV while the PL intensity maximum of the heterostructure decreases dramatically from 34,234 (for ML-WS\({}_{2}\)) to 6560. This abrupt decrease in intensity indicates the formation of a heterojunction between WS\({}_{2}\) and MoS\({}_{2}\) accompanied by interlayer charge transfer, which can suppress exciton recombination and result in a decreased PL intensity. No distinct peak of interlayer exciton is observed, which could be attributed to the reduced intensity caused by non-parallel stacking of the monolayers [55]. To study the influence of stacking order on the exciton performance, the PL spectrum of MoS\({}_{2}\)/WS\({}_{2}\) HS with MoS\({}_{2}\) in the upper layer is also conducted, as shown in Figure 2f. Interestingly, MoS\({}_{2}\)/WS\({}_{2}\) and WS\({}_{2}\)/MoS\({}_{2}\) exhibit similar exciton behavior, revealing that stacking order does not significantly affect the exciton behavior of the heterostructure. Given the absence of the peaks related to the interlayer exciton and MoS\({}_{2}\) exciton in the PL spectrum of WS\({}_{2}\)/MoS\({}_{2}\) HS, it becomes extremely challenging to analyze the excitonic properties and charge transfer in the vdW heterostructures. To gain clearer insights into the variation in the heterostructure's excitonic characteristics, it is essential to enhance the proportion of exciton emission of MoS\({}_{2}\) in the PL spectrum of the heterostructure region. A feasible approach is to reduce the PL intensity of WS\({}_{2}\) without affecting the exciton emission of MoS\({}_{2}\). Considering that WS\({}_{2}\) is the upper layer of the heterostructure, we propose a method for the upper WS\({}_{2}\) layer in the heterojunction to contact the tip of the AFM probe and divert the excited electrons in the conduction band of WS\({}_{2}\) using the high work function of the Si probe, thus inhibiting the emission caused by exciton recombination in WS\({}_{2}\). The experimental setup is illustrated in Figure 3a, which integrates a homemade LSCPRS and an AFM. To study the influence of the probe contact on the exciton properties, the PL spectra of ML-WS\({}_{2}\), ML-MoS\({}_{2}\), and WS\({}_{2}\)/MoS\({}_{2}\) HS are measured with and without Si probe contact (Figure 3b). To better compare the energy and shape of the emission peaks, the PL intensities of ML-WS\({}_{2}\) and WS\({}_{2}\)/MoS\({}_{2}\) HS without Si probe contact are multiplied by a shrinkage factor of 0.02. It is shown that upon contact with the Si probe, the PL shapes of ML-WS\({}_{2}\) and ML-MoS\({}_{2}\) remain basically unchanged. The PL intensities slightly decrease because the Si probe inhibits exciton recombination by guiding the escape pathway of the electrons. The peak positions exhibit a blue shift, which can be attributed to the local electric field generated by the contacted Si probe, thereby influencing the band structure and exciton binding energy of WS\({}_{2}\) and MoS\({}_{2}\)[56]. Excitingly, with Si probe contact, the PL spectrum  
Figure 3: (**a**) Illustration of the measurement.