# EBIC Imaging of Conductive Paths Formed in Graphene Oxide as a Result of Resistive Switching
## 3 Results and Discussion  
The EBIC image of the virgin graphene-oxide-based MIS structure at zero bias is shown in Figure 1a. The dark and featureless image across the entire contact area can be explained by a high resistance (more than 1 GOhm) of the pristine GO film. The collected current flowing through this highly resistive film is less than 1 nA. After electron beam irradiation at the beam current of \(10^{-10}\) A for a few tens of minutes, the EBIC images showed no changes, thus indicating a negligible impact on the measured induced current. This is an important feature of the GO film, as it is known that the resistance of the graphene oxide films can be modified during electron beam irradiation [39]. The current-voltage (I-V) characteristics presented in Figure 2 demonstrate the typical switching behavior of GO-based MIS structures. The current-voltage characteristics obtained at both voltage polarities are similar to the earlier observed ones [21, 32]. The essential feature of these characteristics is multiple transitions from a high resistance state (HRS) to a low resistance state (LRS) occurring under both polarities of the applied voltage (shown with arrows). After applying a negative voltage to the top electrode (Set step), which resulted in multiple HRS to LRS transitions, the EBIC measurements revealed several bright spots (Figure 1b). Performing Set with a progressively increasing voltage results in an increase in the number of bright spots (Figure 1c). The images of the same area obtained in the secondary electron (SE) mode before and after multiple switching events (Figure 3) clearly indicate that the bright spots are not associated with the appearance of surface defects and/or surface morphology variation. As the current through the MIS structure increased after performing Set with a progressively increased voltage, an increase in the number of bright spots allows to assume their link to the conductive paths formed in GO. During the positive voltage sweep, the GO resistance first smoothly decreased, revealed some tendency to increase at about +5 V, and then continued to decrease, demonstrating several sharp transitions to LRS (Figure 2, magenta curve). The trace-back curve revealed higher current values as compared with the curve obtained during the Set step. Thus, although the Reset process was about to take place, the resulting transition to LRS dominated and the current increased further. Figure 1: The EBIC images of the selected region at \(E_{b}=10\) keV obtained before (**a**) and after applying \(-8\) (**b**) and \(-15\) V (**c**). The EBIC images obtained after the Reset step demonstrated that the brightness of some of the conductive channels was notably reduced, while some of the conductive paths completely disappeared. A decreased number of bright spots after a Reset step at 20 V is clearly seen in Figure 4. This provides additional evidence of a direct link between conductive channels formed as a result of resistive switching and the bright spots revealed by EBIC. At the same time, Figure 4 demonstrates the appearance of new conductive channels after Reset, one of which has a very large size and substantially higher brightness. The formation of this additional conductive channel during Reset can explain the resulting increase in the LRS current shown in Figure 2. Thus, it can be concluded that the EBIC method not only is in line with the changes observed in the current-voltage characteristics, but also is able to show that a real scenario of resistive switching in GO is more complex than it can be concluded based on the current-voltage switching characteristics. Thus, it can provide more detailed information on the formation and disappearance of local conductive paths, especially at the Reset step. The difficulty in revealing such behavior from I-V measurements is caused by the cumulative impact of the multiple conductive paths in the GO film under an applied bias, whereas in EBIC mode, each conductive channel contributing to the total current is individually observed.