## 3 Results and Discussion
When the pressure increases to 100 nN, the intensity of WS\({}_{2}\) trions is already quenched to a level smaller than that of the WS\({}_{2}\) A-excitons. This is because the WS\({}_{2}\) trions, composed of two electrons and one hole, are more significantly affected as the electrons transitioning to the conduction band decrease due to pressure-induced band change. In contrast, the WS\({}_{2}\) A-excitons, composed of one electron and one hole, are less affected. Furthermore, the energy of WS\({}_{2}\) trions in the heterostructure also exhibits an anomalous behavior (Figure 5f). Compared to the stability of the A-excitons of WS\({}_{2}\) and MoS\({}_{2}\), the trion energy increases at a rate of 0.1 meV nN\({}^{-1}\) with increasing pressure. This blue-shift is attributed to the anticrossing effect of the electronic states under pressure, a phenomenon observed in III-V and II-VI semiconductor families [63, 64, 65, 66, 67, 68]. The more pronounced change in WS\({}_{2}\) trions compared to A-excitons is understood as the combined modulation of the electronic structure in the heterostructure region by interlayer coupling and strain induced by pressure. To investigate the reversibility of pressure modulation on the WS\({}_{2}\)/MoS\({}_{2}\) HS, the applied pressure is gradually decreased from 140 to 0 nN, as shown in Figure 6. All the emission intensities of the three peaks increase with weakening pressure. The emission intensity of the WS\({}_{2}\) A excitons exhibits the fastest increasing rate. The emission peak  
Figure 5: The peak intensity and photo energy fitted from PL spectra of (**a**,**b**) ML-WS\({}_{2}\), (**c**,**d**) ML-MoS\({}_{2}\), and (**e**,**f**) WS\({}_{2}\)/MoS\({}_{2}\) HS. positions of the A excitons from both WS2 and MoS2 remain almost unchanged, while the emission energy of the WS2 trions gradually shifts towards lower energies. Once the pressure weakens to 0 N, the peak shape and intensity of the PL spectrum almost recover to their initial states. These variation trends are opposite to the case of increasing pressure, demonstrating the good reversibility of pressure modulation on the excitonic behavior of the WS2/MoS2 HS. A possible mechanism is proposed in Figure 7. Figure 7a shows the band structure of WS2/MoS2 HS calculated using the DFT method. At the K-point, both the conduction band and valence band of WS2 are higher than those of MoS2, indicating the formation of a type-II heterostructure. It is worth noting that the energy gap of the K-\(\Gamma\) transition is smaller than that of the K-\(\Gamma\) transition, suggesting the presence of an indirect bandgap, which may lead to a significant enhancement of non-radiative transitions. Figure 7b illustrates the charge transfer in the heterostructure after contact with the Si probe. Prior to contact, the excited electrons flow from the WS2 conduction band to the MoS2, while the holes flow in the opposite direction. The spatial separation of electrons and holes leads to the dissociation of excitons, suppressing exciton recombination emission. After contact with the probe, a large number of excited electrons flow from the WS2 conduction band to the Si probe, thereby reducing the fluorescence intensity of WS2 to a similar level as MoS2. This can be attributed to the fact that, when the Si probe contacts the upper WS2 in the heterostructure region, the excited electrons in WS2 will migrate to the Si probe due to the difference in the work function, resulting in a significant dissociation of the exciton species in WS2 and a decrease in PL intensity. However, the lower MoS2 layer is not in contact with the Si probe, and the influence on the PL intensity is minimal. When the excitonic recombination efficiency in WS2 is lowered to be comparable to that in MoS2, the contribution of MoS2 in the heterostructure's PL spectrum becomes prominent. When pressure is applied to the heterostructure, it causes changes in the coupling strength of the  
Figure 6: The PL spectra of WS2/MoS2 HS under applied pressure gradually decreasing from 140 to 0 nN.