## 4 Conclusions  
In summary, the focused-laser-assisted defect engineering in ML-MoS\({}_{2}\) was demonstrated, and its effects on the optical, chemical, and electrical properties of ML-MoS\({}_{2}\) were investigated systematically. The gradations of ambient PL were created by the non-uniform distribution of irradiation intensity. The enhancement of ambient PL intensity along with the exciton-trion transitions was observed as the irradiation center was approached. These area-selective and controllable p-type doping effects are likely to be caused by the defect modification assisted by the focused laser beam. These defect-related doping phenomena were analyzed by probing the local elemental deficiency of ML-MoS\({}_{2}\) flakes using the n-ASE technique, and their mechanisms were also corroborated by the cryogenic PL experiments and FET device characterization. Moreover, the augmentation of air gas sensibility was also achieved by activating the interactions between S vacancies and air molecules by this method.  
In addition, large-area synthesis of various 2D materials has been researched actively [59]. In the case of the 2D TMDC group, including 2D MoS\({}_{2}\), chemical vapor deposition (CVD) enables even wafer-scale epitaxial monolayer film growth [60]. The size and shape-related issues during focused-laser irradiation, such as overheating along flake edges and irregular heat transfer, are expected to be avoided on the continuous large-scale TMDC monolayer films. Therefore, applying this approach to CVD-grown 2D films would lead to performing more accurate and systematic defect studies as well as developing more practical device and sensor applications [59; 60; 61]. Further, beyond 2D materials, this approach based on the unique combination of experimental characterization techniques would be of high usefulness for exploring fundamental defect-related phenomena in reduced-dimension material structures as well as optimizing defect chemistry for the relevant applications.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app13010304/s1](https://www.mdpi.com/article/10.3390/app13010304/s1)]([https://www.mdpi.com/article/10.3390/app13010304/s1](https://www.mdpi.com/article/10.3390/app13010304/s1)): Figure S1: Scanning electron microscopy (SEM) imaging for nano-Auger electron spectroscopy (n-AES); Figure S2: The spectral fractions of the ambient photoluminescence (PL) peaks contributed from the radiations of exciton (A) and negatively charged exciton (A\({}^{-}\)), also referred to as trion; Figure S3: The Gaussian profile of the ambient PL emission profile; Figure S4. Vacuum annealing effects on the field-effect transistor (FET) devices based on the pristine and FLI-treated ML-MoS\({}_{2}\) channels; Table S1. Electronic characteristics of the pristine and irradiated ML-MoS\({}_{2}\)-based FET channels in vacuum and in air.  
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (NRF-2020R1C1C1008100).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** Nano-Auger experiments at the Molecular Foundry were supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05 CH11231. The author gratefully acknowledges [PERSON], [PERSON], and [PERSON] for technical assistance and useful discussion.  
**Conflicts of Interest:** The author declares no conflict of interest.