## 3 Results
### Ion Mass Spectrometry  
Analysis of the ion mass spectra revealed that the main constituents of the ion flux to the substrate were Ar\({}^{+}\), Ar\({}^{2+}\), Al\({}^{+}\), O\({}^{+}\), O\({}_{2}^{+}\), O\({}^{-}\), and O\({}_{2}^{-}\). The types of spectra obtained for each of the component ions in each regime of working reactive gas (O\({}_{2}\)) flow differed in their intensities correspondingly. The spectra were indicative of good capture of all possible ions and gave a clear demarcation in their intensities. The magnitudes of each mass peak in each spectrum were collected and plotted against the oxygen flow. The results for the positively charged ions are shown in Figure 5. Note that the data have an error of \(\sim\)0.001 a. u., corresponding to the noise level of the secondary electron multiplier. Figure 4: Dependence of the deposition rate on oxygen flow measured using QCM. The arrows mark the forward and reverse curves. Figure 5: Fluxes of positively charged ions in the transition region vs. oxygen flow rate: (**a**) flow rate increasing; (**b**) flow rate decreasing. The measurements revealed a nonlinear dependence of argon, aluminum, and oxygen ion fluxes on an increase in the flow rate of reactive oxygen gas. In Figure 5, a sharp change in the behavior of the magnetron discharge can be seen at a threshold of 1.2 sccm of reactive O\({}_{2}\) flow that was found to influence the characteristics of the ion fluxes. The intensities of the ion fluxes have been plotted in log scale for a clearer understanding of the dependences. Figure 5a shows the dependences plotted with increasing reactive gas flow in the forward direction while Figure 5b demonstrates the dependences plotted with decreasing reactive gas flow in the reverse direction. Two limiting cases can be visualized here: before transition (left side of threshold, 0.9-1.2 sccm oxygen flow) and after transition (right side of threshold, 1.8 sccm oxygen flow). The left part of the graph is indicative of low fractions of oxygen, which is due to the chemisorption of supplied oxygen on the surface of the target. The oxygen molecules are trapped in the surface, forming an oxide layer on the target, hence poisoning it [51]. The remaining ion contribution parameters are generally constant and stable. As we glance through the right part of the graph, we notice a different state. There is a nonlinear pattern to the parameters measured which is due to the presence of free oxygen molecules in the deposition chamber volume. There exists a possibility of physisorption of oxygen atoms in the walls of the chamber, which explains the gradual decrease of oxygen ion contribution with the increase in flow rate. One should note the similarity in the deviation of the O\({}^{+}\) and O\({}_{2}\)\({}^{+}\) forward curves from the reverse ones observed earlier for the discharge voltage and current trends (Figure 3). At the same time, the signals of argon and aluminum ions do not exhibit such a pronounced feature. An important process worth mentioning is the fact the discharge is the most intense at the racetrack causing its sputtering. With an increase in oxygen supply, the possibility of racetrack widening might occur. It can act as a possible contributor for the reduction in oxygen ions' intensity as some of the oxygen ions can be embedded in the target metal surface where no oxidation had taken place (increase in non-reactive fraction on the target surface). Correspondingly, an increase in the metal ion contribution is seen which is due to the ease of ionization of metal atoms compared to argon gas in the transition phase (1.2-1.8 sccm O\({}_{2}\)). This is explained by the increase in current in the transition region, inducing a greater contribution of metal ions with low ionization energies. The dynamics of the formation of negative oxygen ions were studied as well. To do this, the polarity of the accelerating voltage for the mass analyzer was reversed.