## 2 Materials and Methods
### SiC Sensors: Tecnology Features
#### 2.1.2 Monte Carlo Simulations of the SiC Response  
The SiC detector shown in Figure 1, has been simulated using the Monte Carlo Geant4 toolkit [24; 25; 26] to study the performance of the sensors in terms of energy deposited within the active layer and the produced charge. The use of SiC detectors with very high energy electron (VHEE) beams, i.e., with energy exceeding 100 MeV, has recently become attractive for the treatment of deep tumours with the electron FLASH radiotherapy; it is relevant to investigate the configuration of such sensors in terms of thickness and size suitable for the detection of high energy electrons. As an example, Figure 2a,b shows the results obtained with the simulations of SiC sensors having a thickness of 2 \(\upmu\)m, 5 \(\upmu\)m, 10 \(\upmu\)m, 15 \(\upmu\)m and 20 \(\upmu\)m. The energy deposited by 7 MeV, 9 MeV, 100 MeV and 200 MeV electrons in the SiC sensor has been recorded in the simulations to finally calculate the produced charge within the sensor. To have a good compromise between low statistical uncertainties and reasonable computation time, 1 M histories were simulated. To reproduce a realistic case of a dose-to-water deposition of, for instance, 2 Gy, a normalization factor for the total number of histories was retrieved, considering the ratio between the dose deposited for 1 M histories and 2 Gy. This normalization factor is then multiplied for each single energy deposition event for the several configurations of sensor thickness and area used. Afterwards, the total deposited energy  
Figure 1: Schematic overview (**a**) and picture (**b**) of a SiC detector developed by the SenSiC company. As an example, a SiC sensor with 20 \(\upmu\)m active thickness and the 370 \(\upmu\)m substrate is shown along with the possible “free standing membrane” configuration where the substrate is removed. for each single configuration was converted to produce a charge through the electron-hole pair production energy, considering their ratio. As shown in Figure 2a, for the case of 9 MeV and 10 \(\upmu\)m thick and 1 \(\times\) 1 cm\({}^{2}\) SiC detector, i.e., corresponding to the configuration experimentally investigated and reported in the manuscript, a total produced charge around 600 nC is produced. For higher energies, i.e., 100 MeV and 200 MeV, in order to have the same signal as the produced charge in the detector active layer, a thickness of at least 20 \(\upmu\)m needs to be used. Reducing the detector area down to 2 \(\times\) 2 mm\({}^{2}\) (Figure 2b), a charge signal of about 25 nC is predicted for the configuration studied in the paper (10 \(\upmu\)m thickness, 9 MeV), while for the 100 MeV and 200 MeV electron beams, we can see a produced charge ranging from few nC up to 20 nC for a thickness from 2 \(\upmu\)m up to 20 \(\upmu\)m, respectively. As an example, Figure 3a reports the simulated distributions of the energy deposited in the 2 \(\upmu\)m, 5 \(\upmu\)m, 10 \(\upmu\)m, 15 \(\upmu\)m and 20 \(\upmu\)m active thicknesses in the case of 9 MeV mono-energetic beam impinging on the detector surface in vacuum. As expected, the widely obtained energy loss distributions have been fitted using a Gaussian function, as shown in Figure 3a. The resulted values for the centroids and the FWHM are, respectively, 0.62, 1.67, 3.51, 5.4 and 7.4 KeV and 0.73, 1.27, 2.11, 2.97 and 4.00 KeV for the 2 \(\upmu\)m, 5 \(\upmu\)m, 10 \(\upmu\)m, 15 \(\upmu\)m and 20 \(\upmu\)m active thicknesses. Monte Carlo simulations have also been used to evaluate the effect of the presence of the substrate behind the active layer with the prospect of using such detectors for the monitoring of the beam. One of the main characteristics and requirements for the beam monitoring is, in fact, the capability of the detector to be \"transparent\", avoiding a significant perturbation of the beam in terms of final energy and angular spread.