# Temporal Stability of Modified Surfaces of Insulating HV Devices Using Atmospheric Pressure Plasma
## 5 Experimental Evaluation and Results Discussion  
Based on the described measurement methodology [14,25], the measurements of surface resistance and its evaluation of time dependence are processed graphically. The processing was statistically evaluated and plotted as the mean value (AVG) and scatter (Scatter) both for tested samples (AVG) and for samples without exposure (AVG swe), and with deviations with scatter, as shown in Figures 27-32. The evaluation was divided into the group of thermoset and thermoplastic dielectrics, and the group with treatment in an  
Figure 26: Schematic showing the arrangement of the plasma chamber and the modified surface of the dielectric sample (**a**) with generator at\(f_{\text{g}}\) = 13.56 MHz and with plasma generation under an argon atmosphere and (**b**) principle sources of signals in the frequency spectrum of the detected powers. atmosphere of Ar, Ar+O\({}_{2}\) and Ar+N\({}_{2}\). The settings of the generator, gas flow, treatment time and treatment method correspond to the above description. Figure 28: The statistical evaluation of the surface resistance of thermoset dielectric samples in an Ar+O\({}_{2}\) atmosphere. Figure 29: The statistical evaluation of the surface resistance of thermoplastic dielectric samples in an Ar+N\({}_{2}\) atmosphere. The evaluation carried out in this way points to the changes achieved during the treatment of the surface by plasma discharge under atmospheric pressure, always without additions. Several insights emerge from Figures 27-32. It has been shown that the treatment of thermoplastic with a mixture of Ar+O\({}_{2}\) plumes is very effective and the increase in surface resistance is significant. Treatment with Ar+N\({}_{2}\) gases is less effective but significant. On the other hand, the surface of the thermoset-type dielectric is almost unchanged when treated with a plasma discharge in Ar+O\({}_{2}\) and Ar+N\({}_{2}\) gases. The change in surface resistance is minimal. However, when treated with plasma when applied only in the Ar atmosphere, there is a significant change in the surface resistance of the thermoset sample. Comparison of the quantitative results from Figures 27-32 with the RF record of Figures 6-13 and Table 1 reveals the correlation between the modification changes and the RF spectrum. Figure 31: The statistical evaluation of the surface resistance of thermoplastic dielectric samples in an Ar atmosphere. Figure 32: The statistical evaluation of the surface resistance of thermoset dielectric samples in an Ar atmosphere. Figures 13 and 27 show a striking dependence between a significant change in surface resistance and high-frequency activity in the \(f\) = 170-180 MHz band for a thermoplastic sample for Ar+O\({}_{2}\) gas. From the above evaluations, it is clear that the highest change in the surface resistance of the thermoplastic was achieved when applying an argon-oxygen atmosphere, as shown in Table 1. This is reflected in the evaluated spectrum from Figure 13. For quantitative evaluation, it is important to note the significant changes in the spectral image in the frequency range of 175 to 185 MHz and the changed spectrum as a whole. For the thermoset sample, the most significant changes in the surface resistance occur under an argon plasma atmosphere, as shown in Table 1. This situation is reflected in the spectrum in Figure 9. It displays typical changes characterized by a very wide frequency range and density of frequency spectrum changes. Further research will be focused on determining the dependence of the surface resistance of the dielectric with different admixtures of precursors in gas. The procedure will be based on the methodology verified above. The parameter of the optimal performance of the nozzle at the set composition of the atmosphere for the plasma discharge will also be analyzed.