## 3 Results and Discussion
### Ambient Photoluminescence Characterization
Figure 2: Surface morphology and optical characteristics of MoS\({}_{2}\) monolayer (ML) prepared by the mechanical exfoliation method: (**a**) An optical microscopy (OM) image to show the ML and bilayer (BL) regions of MoS\({}_{2}\) flakes on 300-nm-thick SiO\({}_{2}\)/Si substrates Sub. The red dashed circle indicates the spot on the ML region treated by the focused-laser irradiation (FLI). The images of atomic force microscopy (AFM) were taken (**b**) before and (**c**) after the FLI process. The region of the red dashed rectangular (**a**) was scanned for the AFM images. (**b**,**c**) are presented in the same scales. (**d**) The AFM line profile was scanned along the green segment marked in (**a**,**c**) to confirm the irradiated MoS\({}_{2}\) flake to be ML-thick (\(\sim\)0.6 nm). (**e**) Typical ambient Raman and (**f**) photoluminescence (PL) spectra measured from the pristine ML-MoS\({}_{2}\) flake before the FLI process. The spot for spectrum acquisition is marked with the yellow cross in (**a**). In (**f**), based on the Lorentzian curve fitting, the PL spectrum can be de-convoluted to three subsidiary peaks (sub-peaks) contributed from the radiative recombination processes involved with neutral excitons (A), negatively charged excitons (also referred to as trions) (A\({}^{-}\)), and spin-orbit interactions (B), respectively. A set of PL spectra were successively measured with the interval of 0.5 \(\upmu\)m along the white dashed line in Figure 3c, moving the focused-laser spot from the origin 0 to the spot of \(d=7.0\)\(\upmu\)m across the irradiated region. In Figure 3e, the representative PL spectra indicate that the ambient PL intensity was enhanced up to \(\sim\)1500% in the vicinity of the irradiation center. The variation in the integrated PL intensities of A and A\({}^{-}\) peaks, \(I_{\rm A}\) and \(I_{\rm A^{-}}\), and their sum, \(I_{\rm A+A^{-}}\), are plotted with varying \(d\) in Figure 3f. As expected, the substantial enhancement of the ambient PL intensity by the FLI process was likely to be caused by the defect-assisted evolution of A radiation represented by the sharp increase in \(I_{\rm A}\) near the irradiated spot, consistently with a similar laser process as well as other various defect creation methods, including global annealing, irradiation with alpha particles and electrons, etc. [7; 25; 26; 32; 33; 36; 37; 38]. Further, in terms of the spectral fractions of A and A\({}^{-}\) peaks given in Figure 3f, the competitive contributions from A and A\({}^{-}\) radiations to the ambient PL could be evaluated (Figure S2). In the un-irradiated region (\(d<2.5\)\(\upmu\)m) at some  
Figure 3: Local modulation of ambient PL intensity of ML-MoS\({}_{2}\) irradiated area selectively using the focused laser beam: **(a)** An OM image of the ML-MoS\({}_{2}\) flake, including the red dashed circle, indicates the spot for the selective FLI process on the ML region. The maps of the total integrated PL intensity, \(I_{\rm Total}\), obtained from the ML-MoS\({}_{2}\) **(b)** before and **(c)** after the FLI process. **(a–c)** are presented in the same scale, and **(b,c)** are drawn in the same color scale for the integrated PL intensity. **(d)** The Raman spectra were measured before and after the FIR process at \(d=6.0\)\(\upmu\)m near the irradiation center. The parameter \(d\) is the distance from the origin 0 to a measured spot along the white dashed line in **(c)**. **(e)** A series of representative ambient PL spectra were measured by moving the focused-laser spot from the origin 0 to the spot of \(d=7.0\)\(\upmu\)m across the irradiated region. **(f)** The variation in the integrated PL intensities of A and A\({}^{-}\) peaks, \(I_{\rm A}\) and \(I_{\rm A^{-}}\), and their sum, \(I_{\rm A+A^{-}}\), with \(d\). For a comparison, **(e,f)** include the data measured from the pristine ML-MoS\({}_{2}\) before the FLI process.