## 3 Results and Discussion  
### Ambient Photoluminescence Characterization  
As shown in the optical microscopy (OM) image of Figure 2a, several MoS\({}_{2}\) flakes were prepared on a SiO\({}_{\text{x}}\)/Si substrate by the mechanical exfoliation method, and one of the MoS\({}_{2}\) flakes was chosen for the FLI process. By comparing the contact mode, AFM images scanned from the region of the MoS\({}_{2}\) flake, including the irradiation spot before and after the FLI process, as shown in Figure 2b,c, respectively, the surface of the MoS\({}_{2}\) flake was found to be not damaged without any sign of significant decomposition of MoS\({}_{2}\). Previously, [PERSON] et al. demonstrated that the MoS\({}_{2}\) films could be thinned by FLI [18]. In this work, by the gentle FLI process, only the contaminant residue along the edges of the flakes was observed to be removed, probably along with the creation of defects that is discussed later. In Figure 2d, the line profile across the MoS\({}_{2}\)/SiO\({}_{\text{x}}\) boundary extracted from the AFM image in Figure 2c shows that the MoS\({}_{2}\) flake is \(\sim\)0.6 nm thick and, therefore, ML-thick [2]. In Figure 2e, the representative Raman spectrum measured from the pristine ML-MoS\({}_{2}\) flake before the FLI process shows the typical Raman aspect of ML-MoS\({}_{2}\), validating the crystal structure quality. Moreover, in Figure 2f, the PL spectra measured from the pristine ML-MoS\({}_{2}\) flake in the ambient conditions showed a strong PL peak with a peak position of \(\sim\)1.84 eV, representing the direct bandgap feature of the ML-MoS\({}_{2}\) not shown from thicker MoS\({}_{2}\) sheets. As described in Figure 2f, the Lorentzian curve fitting resolves the PL peak into three subsidiary peaks which originate with the radiative recombination processes of A (\(\sim\)1.89 eV), A\({}^{-}\) (\(\sim\)1.84 eV), and spin-orbit interactions (B) (\(\sim\)2.01 eV), respectively. First, the area-selective modulation of ambient PL by the FLI process and relevant mechanisms is discussed. Figure 3b,c show the maps of the total integrated PL intensity, \(I_{\text{Total}}\), acquired from the MoS\({}_{2}\) flakes shown in Figure 3a before and after the FLI process in ambient conditions. The area-selective enhancement of ambient PL intensity is clearly observed around the laser-focused irradiation spot on the ML-MoS\({}_{2}\) flake. The shape of the PL-enhanced area is shown to be irregular, probably because the laser-driven heat was not transferred uniformly in all directions from the irradiation spot due to structural imperfections, surface adsorbates, interfacial contaminants, etc. Moreover, the flake edges could be heated more intensively than the flake interior due to the difficulty in heat dissipation, as observed from the strong PL signal along the edge near the irradiation center in Figure 3c. The well-shaped PL-enhanced area was found in the other sample and will be discussed later. Figure 3d includes the Raman spectra measured before and after the FIR process at \(d=6.0\) um near the irradiation center, where \(d\) is defined as the distance from the origin 0 to a measured spot along the white dashed line in Figure 3c. In Figure 3d, as observed from the electron-irradiated free-standing ML-MoS\({}_{2}\) by [PERSON] et al. and explained by their first-principles density function theory calculations, the red shift of the E\({}_{2g}\) peak by \(\sim\)1.61 cm\({}^{-1}\) indicates probably the partial absence of S including the formation of S vacancies, while the A\({}_{1g}\) peak does not show any obvious shift [33]. [PERSON] et al. reported a similar red shift of the E\({}_{2g}\) peak of ML-MoS\({}_{2}\) by FLI; however, theyalso observed that the A\({}_{1g}\) peak was blue-shifted clearly [36]. This discrepancy may be due to the fact that the peak shifts are also affected by other factors, including the change in the mechanical strain induced by substrates and the removal of surface and interface contaminants by FLI [10].