## 3 Results and Discussion
The dependence of the potentiodynamic polarization curve for the corrosion potential (\(\mathbf{E}_{\text{corr}}\)) vs. corrosion current density (\(\mathbf{I}_{\text{corr}}\))  
Figure 3.5 Dependency of chemical composition of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface on ferric-ionic catalyst (i.e., PDTA–Fe) concentration after dipping of Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface into slurries. (**a**) Ge 2p spectra, (**b**) Sb 3d spectra, and (**c**) Te 3d spectra. on the corrosion inhibitor (i.e., PEI) concentration was observed for the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface being dipped into the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface CMP slurry using the Fenton reaction and a corrosion inhibitor (i.e., PEI), as shown in Figure 3.6 From the potentiodynamic polarization curves in Figure 6a, the dependency of \(\mathbf{E}_{\text{corr}}\) and \(\mathbf{I}_{\text{corr}}\) on the corrosion inhibitor concentration was calculated, as shown in Figure 6b. When the corrosion inhibitor (i.e., PEI) concentration increased from 0 to 0.09 wt%, \(\mathbf{E}_{\text{corr}}\) increased almost linearly from 0.28 to 0.3 V while \(\mathbf{I}_{\text{corr}}\) decreased exponentially from \(-6.15\) to \(-6.93\) A/cm\({}^{2}\). This result indicates that the addition of a corrosion inhibitor (i.e., PEI) into the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface CMP slurry clearly suppressed corrosion, and the corrosion inhibition degree was greatly enhanced with increasing PEI concentration. To understand the mechanism by which PEI suppresses corrosion on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface, the chemical composition of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after CMP using a Fenton reaction-based CMP slurry containing a corrosion inhibitor was analyzed by XPS as a function of the PEI concentration. NH\({}_{3}\)\({}^{+}\) and NH\({}_{2}\)\({}^{+}\) peak intensities adsorbed on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface were found at 401.3 and 399.1 eV, respectively, as shown in Figure 7a. Note that both peaks represent the adsorption of a corrosion inhibitor (i.e., PEI) on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface after CMP. Both peak intensities rapidly enhanced as soon as the PEI of 0.01-wt% was added in the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface CMP slurry and then very slightly increased with the PEI concentration when PEI concentration increased from 0.01 to 0.07-wt%, as shown in Figure 7b. With a further increase in the PEI concentration above 0.07-wt%, both peak intensities remarkably increased with increasing PEI concentration. In addition, the relative NH\({}_{3}\)\({}^{+}\) peak intensity is approximately two times higher than the relative NH\({}_{2}\)\({}^{+}\) peak intensity. The chemical composition analysis results evidently prove that a corrosion inhibitor (i.e., PEI) is well adsorbed on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface, since the positively charged protonated amine groups (NH\({}_{3}\)\({}^{+}\) and NH\({}_{2}\)\({}^{+}\)) of PEI are statically attractive to the negatively charged Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface at pH 2. Note that the surface zeta potential of the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface at pH 2 is \(-1.29\) mV, as shown in Figure S4. In addition, a higher concentration of the catalyst with protonated amine groups (i.e., NH\({}_{3}\)\({}^{+}\) and NH\({}_{2}\)\({}^{+}\)) in a Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface CMP slurry led to a higher adsorption of the catalyst on the Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\) film surface. To observe how the adsorption of the catalyst affects the CMP performance, both Ge\({}_{1}\)Sb\({}_{4}\)Te\({}_{5}\)- and Si\({}_{3}\)N\({}_{4}\) film polishing rates were estimated as a function of the corrosion inhibitor (i.e., PEI) concentration.