## 3 Results and Discussion
### Plasma-Erosion Analysis  
In the long-time discharge test results of Figure 8, the PP failed even for the short-time operation of approximately 19 min; the PI withstood 30 min of the operation. However, the Si-reinforced films did not show the plasma erosion. The weakness of the polymer films against the plasma erosion might be affected by the chemical reaction to the air plasmas. It is currently unclear whether the plasma erosion ensures the structural change of the polymer chain. The etched patterns on the film surfaces, however, seem to be due to the chemical reactions with the plasma ions and radicals. To explicate the damages of the polymer film-surface, the IR spectroscopy was performed [50; 51]. Prior to the experiments, the film to be measured was completely dried. The spectra were recorded in the range from 4500-500 cm\({}^{-1}\) with the spectral resolution of 1.0 cm\({}^{-1}\). Each spectrum is the average of 16 scans with the detector gain of 1.00. Figure 8: Surface pictures of the solid plates after the extended-run operation (**a**), the flexible polymer films (**b**), and the reinforced-silicone (Si)-coating films (**c**) after the 10-h operation at the current of approximately 3 mA. The IR spectra of the PP-surface film in the absence or presence of the plasma discharge are shown in Figure 9. The new absorption bands of the damaged-PP film that are between 1720 and 1580 cm\({}^{-1}\) might be due to the C=C and C=O stretching vibrations and the CH bending vibrations. The broad band at approximately 1720 cm\({}^{-1}\) is related to the C=C and C=O stretching vibrations [51]. From these new absorption bands of the damaged-PP film compared with those of the original PP-surface film in Table 1, the structural change of the PP chain could be due to the plasma discharge on the PP film, as shown in Figure 10.  
To explicate the damages of the PI-film surface, the IR spectroscopy was performed, and the results are shown in Figure 11. The IR spectra of the PI-surface film in the absence or presence of the plasma discharge are shown. There were no new absorption bands regarding the PI-surface film with the plasma discharge compared with the original PI-surface film, as shown in Figure 11. This finding suggests that the structural change of the PI with the plasma discharge is not due to the rigid polymer back-bond structure such as the aromatic heterocyclic ring in the polymer main chain. Figure 11: Infrared (IR) spectra of the original polyimide (PI) surface (lower black line) and the PI surface with the plasma discharge (upper red line), showing no structural change after the plasma discharge. Figure 9: Infrared (IR) spectra of the original polypropylene (PP) surface (lower black line) and the PP surface with the plasma discharge (upper red line). In addition, there were no new absorption bands regarding the reinforced-Si-coating PI films with the plasma discharge compared with the original reinforced Si film, as shown in Figure 12. This finding suggests the absence of a chemical structural change of the reinforced-Si-coating PI films with the plasma discharge, due to the high chemical resistance and stability of the Si. From the IR-spectra results, the PP-chain structure was changed; however, that of the PI or the Si film was not changed. The PP was severely eroded by the surface plasma. The PI was also damaged by the plasma. The Si film, however, strongly resisted the plasma erosion. The erosion phenomena of the dielectric-film surfaces are considered according to the chemical and physical reactions of the plasma ions and radicals. In Figure 8 of the long-time discharge, the solid-plate surfaces were not damaged while the polymer-film surface showed the etched patterns. Regarding the ion-bombardment sputtering, the threshold ion energies in the range of 10-30 eV are evident for the physical sputtering [52]. These ion energies are not available since the electron and ion plasma energies of this experiment of the atmospheric-pressure discharge are in the order of 1 eV and 0.01 eV, respectively.