# EBIC Imaging of Conductive Paths Formed in Graphene Oxide as a Result of Resistive Switching
## 3 Results and Discussion
Figure 3: The secondary electron images of the region shown in Figure 1 before (**a**) and after applying \(-\)15 V (**b**). The light line in the upper right corner is the edge of the Al contact. Figure 2: Typical switching characteristics of Al/GO/n-Si MIS structures showing multiple sharp transitions from HRS to LRS. As already pointed out in [11], for probing the underlying physics of the resistive switching mechanism of the conductive path, the EBIC imaging should be elucidated. For this purpose, the dependencies of the EBIC contrast associated with a conductive path on the electron beam energies \(E_{b}\) (from 10 keV to 30 keV) were first investigated. The sign of the contrast was found to be independent of the e-beam energy and corresponds to minority carriers (holes) flowing to the Al top electrode. Analysis of the induced current measured at a typical bright spot at \(E_{b}\) of 10 and 20 keV shows that its values exceed the beam current by 320 and 200 times, respectively. The induced current measured far from the bright spots is about 100 times smaller. As mentioned above, the induced current consists of a few components. To evaluate the contribution of each of these components to the measured induced current, calculation of the depth dependence of the deposited energy was carried out using the Monte Carlo method. The depth dependencies of the energy deposited by one primary electron with \(E_{b}\) of 10 and 20 keV are shown in Figure 5. According to these results, the energies deposited inside a 40 nm thick GO film are about 185 and 95 eV for 10 and 20 keV electrons, respectively. This implies that, for the GO bandgap of about 3 eV [40; 41], each primary electron generates 20 and 10 electron-hole (e-h) pairs, respectively, inside the GO film, as the electron-hole pair creation energy is about three times larger than a bandgap [42]. Thus, even if the excess carrier recombination is neglected, the current induced inside the GO film cannot exceed the beam current by more than 20 times. Owing to recombination, this value should be even lower. This estimation is in agreement with the measurements of the electron-beam-induced current in a thin isolating film, which was of the same order of magnitude as the beam current [43]. The electron emission coefficient from the grounded Al film should be lower than 1, hence the emission current should also be lower than the beam current at the beam energies used. The bright spots in EBIC mode observed in the MIM structures were previously explained by hot carrier injection from the Al electrode [11]. For the MIS structures studied in the present work, the energy deposited in an Al film is 140 and 70 eV for 10 and 20 keV electrons, respectively. Therefore, the number of hot electrons cannot exceed a few tens per one primary electron, especially considering that the escape depth of the hot electrons from Al hardly exceeds a few nm. Therefore, the hot carrier injection from the Al electrode cannot explain the increase in the induced current of a few hundred times. The escape depth of the hot electrons from Si does not exceed 3 nm [44], implying that the number of hot carriers created in this region is not higher than a few carriers per one incident electron. Additionally, such an injection contradicts the direction of the measured current. Based on the above analysis, it can be concluded that the observed  
Figure 4: The EBIC images of the selected region at 10 keV after applying negative bias of 15 V (**left**) and then positive bias of 20 V (**right**). local increase in the induced current is caused by the large number of e-h pairs generated inside Si. Indeed, for \(E_{b}\) of 10 and 20 keV, the total number of carriers generated per one incident electron in Si is estimated to be 2270 and 4850, respectively, i.e., high enough to provide the observed current values. The formation of the conductive channels results in a local decrease in the GO film resistance.