## 3 Results and Discussion  
The MoS\({}_{2}\) films fabricated from the thermal decomposition process were uniform and continuous based on optical microscopy (3D laser microscope, VK-X250, Keyence, Osaka, Japan), as shown in Figure 1a. This demonstrates the feasibility of the large-scale growth of homogeneous MoS\({}_{2}\) films by thermal decomposition for practical electronic applications. The grown MoS\({}_{2}\) films were subjected to out-of-plane doping by CHF\({}_{3}\) plasma treatment using a dry-etching system (ULVAC original NLD-570). The radiofrequency power of this dry-etching system was set to 100 W and the pressure was set to 7.5 mTorr. The final thickness of the treated samples was obtained by etching for 30 s. Figure 1b shows the optical micrograph (OM) image of the selective-area MoS\({}_{2}\) films with and without CHF\({}_{3}\) plasma treatment. On the right, the untreated region exhibits a light blue color, while on the left, the plasma-treated region displays a dark blue color. Raman spectroscopy is being used widely to study 2D materials and to identify their thicknesses. Figure 1c shows the Raman spectra of the MoS\({}_{2}\) films in the untreated region and in the CHF\({}_{3}\) plasma-treated region, respectively. Figure 1c clearly shows two main Raman features which correspond to E\({}^{1}\)\({}_{2\text{g}}\) (approximately 381 cm\({}^{-1}\)) and A\({}_{1\text{g}}\) (approximately 406 cm\({}^{-1}\)) modes [20]. The intensity of the two peaks increases with an increase in MoS\({}_{2}\) film thickness. The strong, sharp peaks displayed in the Raman spectrograph of the untreated region indicate a thick layer of high crystalline MoS\({}_{2}\) film. On the other hand, the E\({}^{1}\)\({}_{2\text{g}}\) and A\({}_{1\text{g}}\) peaks of the CHF\({}_{3}\)-treated region are weaker due to a reduction in thickness during the plasma treatment. The energy difference between the two Raman peaks can be used to identify the number of MoS\({}_{2}\) layers. This energy difference value was obtained in the untreated region and equated to about 25.9 cm\({}^{-1}\), indicating a bulk-like multilayer MoS\({}_{2}\). However, in the CHF\({}_{3}\)-treated region, the energy difference equated to a smaller value of 23.2 cm\({}^{-1}\), indicating a lower thickness of MoS\({}_{2}\) film than in the untreated region. The difference in thickness between the untreated and the CHF\({}_{3}\) treated region was further indicated by the difference in the E\({}^{1}\)\({}_{2\text{g}}\) and A\({}_{1\text{g}}\) peak intensity between these two regions. Figure 1: (**a**) Optical micrograph (OM) image of the as-grown MoS\({}_{2}\) films on the SiO\({}_{2}\)/Si substrate. (**b**) OM image of the selective-area MoS\({}_{2}\) films with and without CHF\({}_{3}\) plasma treatment. (**c**) Raman spectra taken of the untreated and CHF\({}_{3}\)-treated regions. AFM (Dimension Icon, Bruker, Billerica, MA, USA) was used to examine the surface morphology and the thickness of the MoS\({}_{2}\) films. Figure 2a,b show the AFM image and the height profile of the as-grown MoS\({}_{2}\) films on the substrate, respectively. The difference in contrasts in the AFM image indicates the different heights in the image. From the height profile, the thickness of the as-grown MoS\({}_{2}\) was found to be about 10 nm, suggesting that there are 15 layers of MoS\({}_{2}\). The different contrasts in the AFM image shown in Figure 2c further indicated the thinning effect after plasma treatment. From the height profile in Figure 2d, the difference in height between the untreated and CHF\({}_{3}\)-treated MoS\({}_{2}\) film was found to be approximately 4 nm. Further doping could be applied by increasing the plasma etching time; however, that would result in poor and uncontained MoS\({}_{2}\) films due to MoS\({}_{2}\) chemical modification and the formation of defects introduced by energetic ions. XPS analysis was carried out to investigate the binding energies of Mo, S, and F in the CHF\({}_{3}\)-treated and untreated MoS\({}_{2}\) samples.