## 1 Introduction
[40; 41; 42]. Specifically for 2D layered structures, laser irradiation would be a facile and versatile tool that can activate surface reactions such as atomic dissociation and substitutional doping as well as achieve structural modification from gentle thinning to sharp patterning [18; 20; 22; 32; 36; 37; 38; 39]. Further, by employing a focused-laser beam, defects can be created locally, probably relevant to miniaturized devices or sensor applications [32; 36; 37; 38]. Moreover, the detailed adjustment of laser processing parameters enables the subtle control of defect concentration minimizing the radiation and heat-induced damage [32; 36]. However, to understand the defect-related effects fully, it would be necessary to perform a chemical analysis. Since 2D structures are surface themselves, the surface chemical analysis should be employed to probe their chemical state precisely. There are many options for surface chemical analysis on 2D materials: Auger electron spectroscopy (AES), x-ray photoemission spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), etc. [17; 43; 45; 46; 47]. On a TEM, the crystal structure of 2D materials can be observed directly in atomic resolution, and elementary chemical analysis can also be carried out by energy-dispersive X-ray spectroscopy (EDS) using the electron beam as a radiation source [17; 21; 48]. In this work, nano-AES (n-AES), the high-resolution version of AES, was employed for the chemical analysis of ML-MoS2 for several advantages. As described in Figure 1a, the n-AES is equipped with a field emission gun (FEG) scanning electron microscope (SEM) as an electron beam source, which enables sub-micron lateral resolution of \(\sim\)10 nm, much higher than those of XPS and SIMS. Moreover, a sample can be measured as it is on the n-ASE system without any additional laborious and costly sample preparation process that may result in damage and contamination. In addition, since the n-AES system is equipped with the SEM imaging capability, micro-size mechanically exfoliated ML-MoS2 flakes and even their internal structures can be accessed for spectra acquisition in the accuracy of sub-micron. The chemical properties of a variety of low-dimensional materials and nanostructures were probed by n-AES previously [25; 32; 49; 50]. As displayed in Figure 1b, the Auger electrons are ejected by a two-step and three-electron process called the Auger effect. First, the core hole is created by the incidence beam of electrons (or photons for other cases). Then, an electron fills the core hole by the internal transition losing an amount of energy. If the transition energy is large enough to release another electron at the second outer shell, the electron can be ejected. The ejected electron, called the Auger electron, has the kinetic energy (\(E\)) as \(E=E_{\text{core}}-E_{1}-E_{2}\), where \(E_{\text{core}}\) is the core hole energy level and \(E_{1}\) and \(E_{2}\) are the binding energies of the first and second outer shells, respectively [45]. While the focused-laser-assisted defect engineering and relevant phenomena were studied previously by several research, the combinational approach of focused-laser irradiation (FLI) and nano-Auger probe has not been reported yet to my knowledge [32; 37; 38]. Here, the FLI was demonstrated for creating defects in ML-MoS2 locally and tuning ambient optical and electrical properties of ML-MoS2 via defect-assisted p-type doping. The Gaussian laser intensity profile could build up a temperature gradient around the irradiation spot, resulting in the spatially varying degree of S deficiency in ML-MoS2 in a few microns. As such, microscale gradations of optical and electrical properties could be realized as well. Then, the varying local S deficiency was probed across the irradiation center by performing the high-resolution n-AES successively.