## 4 Conclusions  
In conclusion, the impact on the glow discharge of the ammonia gas introduced into the TMS-O\({}_{2}\) gas mixture was studied using the in situ OES observation. The glow discharge using only the TMS and oxygen gas mixture was characterized by the transition lines of oxygen atoms/molecules (O and O\({}^{2+}\) lines) with the species of SiO and OH radicals, whereas the emissions associated with the nitrogen- and hydrogen-related lines and CN\({}^{*}\)/CH lines are predominated over the OES spectra obtained from the glow discharge incorporated with the ammonia gas. This revealed that the incorporation of the ammonia gas in the glow discharge facilitated suppressing energetic oxygen-related radicals, thereby slowing down the deposition rates of the synthesized films. Based on the measurements of the chemical bond configurations and elemental compositions, the films synthesized from the TMS-O\({}_{2}\)-NH\({}_{3}\) gas mixture were basically constructed from Si-O-Si networks with a slight decrease in the oxygen content and the limited incorporation of nitrogen and carbon atoms. The small amounts of the nitrogen and carbon atoms incorporated into the deposited film resulted in a flat surface with a decrease in the protrusions originating from the structural voids. The lowest surface roughness (\(\sim\)0.48 nm) with the near-absence of protrusions was obtained from the film synthesized from the TMS-O\({}_{2}\)-NH\({}_{3}\) gas mixture at a gas flow ratio of 0.5. However, as the introduced ammonia gas in the glow discharge increased to a gas flow ratio of 0.75, C-H/C-C and species of Si(CH\({}_{3}\))\({}_{x}\) bonds apparently appeared in the deposited film as a consequence of the apparent increase in the carbon content. A significant reduction in the atomic ratio of O/Si, which showed dominating C-H/C-C and Si-CH\({}_{2}\)-Si bonds in the FTIR spectrum, was then obtained from the film synthesized from the TMS-NH\({}_{3}\) gas mixture. The surface roughness of the film that contained considerable C-H and Si-CH bonds was apparently increased to 1.34 nm. The formation of the protrusion structures was found to be deeply correlated with the degree of the internal stress residing in the deposited film. The lower the residual compressive stress, the fewer the protrusions and the lower the surface roughness measured. Accordingly, the WVTR of the PET substrate coated with the film synthesized from the TMS-O\({}_{2}\) gas mixture (\(\sim\)1.65 g/m\({}^{2}\)/day) apparently decreased to 0.06 g/m\({}^{2}\)/day as the substrate was coated with the film synthesized from the glow discharge incorporated with ammonia gas at a gas flow ratio of 0.5. The enhancement of the deposited film as a barrier to water vapor permeation was attributed to the improvement in the Si-O-Si networks originating from the prevention of void formation due to the limited incorporation of nitrogen atoms, and thereby it possessed the lowest residual compressive stress and exhibited the smoothest surface roughness.  
This work was supported by the Ministry of Science and Technology under Ministry of Science and Technology (MOST) 105-2622-E-150-004-CC2 and Industrial Technology Research Institute (ITRI)/ITRI under A200-105 BA2.  
[PERSON] organized and designed the experiment procedures; [PERSON] and [PERSON] supported the measurement results and wrote this paper; [PERSON], [PERSON], and [PERSON] executed the film depositions and resulting materials analysis. All authors read and approved the final version of the manuscript to be submitted.  
The authors declare no conflict of interest.