## 4 Discussion  
As confirmed by SEM/EDX analysis, the atmospheric pressure DCSBD plasmas generated in ambient air, pure nitrogen, pure hydrogen and in mixtures of nitrogen with hydrogen is capable of etching of PMMA polymer layers on polymer-metal mesh substrates. However, a strong degradation of the polymer substrate and also the significant damages to the metal wires were observed. On the other hand, it was found that using a short, 1 s exposure of the polymer surface to the pure hydrogen plasma it is possible to etch selectively the surface polymer layer and to uncover the metal wires without damaging them. As a consequence, we conclude that the pure hydrogen DCSBD plasma can be used for the fast, selective etching of the polymer film surface without any destruction of the metal wires. We observed that the etching mechanism strongly depends on the parameters such as treatment  
Figure 11: SEM micrographs of metal wires after 3 s plasma etching in pure H\({}_{2}\) plasma at distance H = 0.6 mm for single 3 s plasma exposure (**a**) and the multiple very short exposures (12 \(\times\) 0.25 s) (**b**). Top row—SE image; bottom row—BSE image.  
Figure 10: SEM micrographs of free metal wires treated for (**a**) 1 s (**b**), 2 s (**c**) and 3 s at distance H = 0.3 mm. Top row—SE image; bottom row—BSE image.  
time and the distance of the sample from discharge. Therefore, the effect of these parameters was discussed in more details.  
The application of pure hydrogen plasma raises the questions about the safety of the process. As in any other activity/process, it is necessary to find a trade-off between the safety, the process performance, and the product requirements. The presented plasma modification method might be improved by localized feeding of working gas just into the very narrow region where the plasma is generated. Such technical solution would enable to decrease the working gas consumption and together with smaller volume of (dangerous) working gas presented in the reactor chamber this would lead to higher safety of the entire process and whole device.  
In comparison to standard mechanical abrasion and low-pressure plasma etching of studied flexible polymer-metal mesh substrate, the presented method utilizing atmospheric DCSBD plasma is easily scalable and compatible with roll-to-roll processing of large-area substrates. To sum up, we conclude that the DCSBD plasma sources can be used for fast, large-area, roll-to-roll, selective plasma etching of complex materials like flexible transparent conductive substrates which can be applied e.g., for flexible photovoltaic applications and other emerging technologies.  
Conceptualization, M.C. and D.K.; investigation, R.K., J.J., M.Z. and J.K.; writing--original draft preparation, R.K.; writing--review and editing, R.K., D.K. and M.C. All authors have read and agreed to the published version of the manuscript.  
This research was supported by project LM2018097 funded by the Ministry of Education, Youth and Sports of the Czech Republic and project TJ01000327 funded by the Technology Agency of the Czech Republic.  
The authors thank to [PERSON] and SEFAR AG (Switzerland) for providing the polymer mesh substrate. Thanks belongs also to [PERSON] and [PERSON] both from CEPLANT, MU Brno for carrying out the trial experiments on selective etching of small polymer mesh samples providing by SEFAR AG.  
The authors declare no conflict of interest.