## 3 Results and Discussion
For the film synthesized from the TMS-O\({}_{2}\) gas mixture, the stretching and bending modes of the Si-O bonds could be determined at the peaks of 1066 and 817 cm\({}^{-1}\), respectively, while the signals related to the hydroxyl (O-H at around 2800-3700 cm\({}^{-1}\)) and silanol (Si-OH at 940 cm\({}^{-1}\)) were almost absent in the FTIR spectrum [27; 28; 29]. When the film was synthesized from the TMS-O\({}_{2}\)-NH\({}_{3}\) gas mixture at the gas flow ratios of 0.25 and 0.5, the Si-O bond was still the dominant signal over the FTIR spectra without the absorbance signal from the N-H bond at around 3200-3600 cm\({}^{-1}\)[27; 29]. However, as the introduced ammonia gas reached a gas flow ratio of 0.75, the FTIR spectrum of the resulting film exhibited an obvious reduction in the relative intensity of the Si-O bond with a satellite peak at about 1101 cm\({}^{-1}\). Furthermore, two separated peaks at 1037 and 1103 cm\({}^{-1}\), respectively, were observed from the FTIR spectrum of the film prepared using the TMS-NH\({}_{3}\) gas mixture. Figure 3b highlights the wavenumbers ranging from 700 to 1300 cm\({}^{-1}\) shown  
Figure 1: Optical emission spectra (OES) recorded from the glow discharge of the TMS-O\({}_{2}\)-NH\({}_{3}\) gas mixture at an ammonia gas flow ratio of (**a**) 0 and (**b**) 0.5, respectively. Figure 2: Deposition rates of the films as a function of the ammonia gas flow ratio in the glow discharge. in Figure 3a for further investigating the shifts and evolutions of the main Si-O peak for the films affected by the ammonia gas introduced into the gas mixture. The Si-O signal of the films synthesized from the TMS-O\({}_{2}\)-NH\({}_{3}\) gas mixture at the flow ratios of 0, 0.25, and 0.5 showed almost the same shape with a tail extending to the higher wavenumbers. As quoted from the previous reports, the appearance of this tail was attributed to the signals overlapping from the second asymmetric stretching modes of the longitudinal-optic (LO\({}_{4}\)) and transverse-optic (TO\({}_{4}\)) vibration pairs in the Si-O cage/ring structures which correlated with the structural disorder and film's porosity in the Si-O-Si networks [9; 30; 31]. The main absorbance peak of the Si-O signal at 1066 cm\({}^{-1}\) which appeared in the film synthesized from the TMS-O\({}_{2}\) gas mixture gradually shifted to a low wavenumber of 1060 cm\({}^{-1}\), as the film was prepared using the ammonia gas at a gas flow ratio of 0.5. The shift in the peak of the Si-O signal was demonstrated as the reduction of the oxygen content (O/Si) in the deposited films according to the previous reports [32; 33; 34; 35]. When the ammonia gas in the gas flow ratio reached 0.75, the intensity of the Si-O signal was markedly decreased and its peak apparently shifted to 1051 cm\({}^{-1}\) with a satellite peak related to the signals overlapped by the C-H/C-C bonds at about 1101 cm\({}^{-1}\)[29]. Such organic C-H/C-C bonds (\(\sim\)1105 cm\({}^{-1}\)) and the organosilicon (Si-CH\({}_{2}\)-Si) bond absorbed at approximately of 1037 cm\({}^{-1}\) became the dominating signals of the FTIR spectrum for the film synthesized from the TMS-NH\({}_{3}\) gas mixture [16; 20; 29; 36]. In addition, the introduced ammonia gas in the glow discharge also resulted in the films exhibiting two weak signals at about 910 and 736 cm\({}^{-1}\) which were assigned to the Si-N and Si-C bonds, respectively [13; 20; 29; 37]. Figure 4a shows the atomic concentration of the films synthesized from various gas flow ratios measured by XPS. All these films were mainly composed of the elemental Si and O. The elemental N and C in the deposited films were both increased as the gas flow ratio of NH\({}_{3}\) increased. Moreover, an apparent increase in the carbon content (\(\sim\)11.2%) was measured from the film synthesized from the gas mixture without the oxygen incorporated (i.e., the TMS-NH\({}_{3}\) gas mixture).