## 3 Results and Discussion
Figure 3: Electrical characterization of a monolayer MoS\({}_{2}\) field-effect transistor. (**a**) \(\mathrm{I_{ds}}\)–V\({}_{\mathrm{ds}}\) output characteristics measured in a high vacuum for various gate bias values. (**b**) \(\mathrm{I_{ds}}\)–V\({}_{\mathrm{gs}}\) transfer characteristic measured in a high vacuum. (**c**) Evolution of the transfer characteristics from vacuum to atmospheric pressure of Ar or H\({}_{2}\). (**d**) Evolution of the transfer characteristics from vacuum to atmospheric pressure of O\({}_{2}\), N\({}_{2}\), and CH\({}_{4}\). To complete the characterization of the transport properties in PdSe\({}_{2}\)- (Figure 4a) and MoS\({}_{2}\)-based (Figure 4b) field-effect transistors, we also investigated the effect of electron beam irradiation. Indeed, 2D materials are necessarily exposed to electron irradiation during fabrication or imaging processes, as in electron beam lithography or simply in SEM imaging. To measure such an effect, we performed an experiment in the SEM chamber using a 10 keV-electron beam to irradiate the nanosheets at various fluences. We clarify here that electrical measurements were performed soon after each irradiation (when the beam is switched off). The first I\({}_{\text{ds}}\)-V\({}_{\text{gs}}\) transfer curve was measured in its pristine state, before the irradiation, and was compared to the curves measured for successively increasing levels of fluences up to 4160 e\({}^{-}\)/nm\({}^{2}\) for PdSe\({}_{2}\) (Figure 4c) and up to 100 e\({}^{-}\)/nm\({}^{2}\) for MoS\({}_{2}\) (Figure 4d). From the data in Figure 4c, we note that electron irradiation causes a suppression of the \(n\)-type conduction towards a \(p\)-type conduction. On the other hand, from Figure 4d, we see that \(n\)-type conduction is enhanced in the MoS\({}_{2}\) device. Comparing the two behaviors, it seems that electron irradiation acts with opposite modifications on PdSe\({}_{2}\) and in MoS\({}_{2}\) devices. Actually, it has been reported that effects on PdSe\({}_{2}\) may be irreversible [34], differing from MoS\({}_{2}\), in which vacuum annealing \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline  & **Vacuum** & **Ar** & **H\({}_{\text{2}}\)** & **O\({}_{\text{2}}\)** & **N\({}_{\text{2}}\)** & **CH\({}_{\text{4}}\)** \\ \hline \(\mathbf{|E_{ads}|}\)**[meV]** & 1 & 1 & 70 & 106 & 114 & 407 \\ \(\mathbf{H_{w}}\)**(V)** & 12.4 & 25.4 & 31 & 39.4 & 40.9 & 51.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the hysteresis width, H\({}_{\text{w}}\), extracted from the transfer curves of Figure 3c and 3(d) for the various gases, with the indication of the gas adsorption energy E\({}_{\text{ads}}\). E\({}_{\text{ads}}\), which is negative, is obtained by DFT calculations assuming that E\({}_{\text{ads}}\) = E\({}_{\text{MoS2+gas}}\)-E\({}_{\text{MoS2}}\)-E\({}_{\text{gas}}\), with E\({}_{\text{MoS2+gas}}\) the total energy of the system, E\({}_{\text{MoS2}}\) the energy of MoS\({}_{2}\) and E\({}_{\text{gs}}\) the gas phase molecules [31; 32; 33]. Figure 4: SEM image (top-view) of (**a**) PdSe\({}_{2}\) and (**b**) monolayer MoS\({}_{2}\). Field-effect transistors used to study the effect of 10 keV electron beam irradiation on the transport properties of the transistors. (c) Transfer characteristics measured for various fluences for (**c**) PdSe\({}_{2}\) and (**d**) monolayer MoS\({}_{2}\). can restore its initial state [35]. To explain the experimental observations, we need to take into account that electron irradiation can easily produce Se and S vacancies, due to the small energy (less than 10 eV) necessary for the displacement of a chalcogen atom [36]. Vacancy formation is responsible for \(p\)-type conductivity, in particular when dealing with thick nanosheets (as in the case of 15-nm-thick PdSe\({}_{2}\)), in which a larger beam energy can be adsorbed [34]. A further effect of electron irradiation is the formation of electron-hole pairs in both the SiO\({}_{2}\) oxide and the Si substrate.