## 3 Results and Discussion  
The structure of picolinic acid and the schematic illustration of picolinic acid adsorption is shown in Figure 1a,b, respectively. The lone pair electrons in the nitrogen of the pyridine functional group of picolinic acid as active sites, which leads to the formation of complexes by covalent coordination bonding (i.e., \(\sigma\)-bonding) with tungsten oxide. Such complexes form a passivation layer on the metal surface, preventing corrosion reactions by blocking the water adsorption [14; 16; 17]. An adsorption isotherm test was carried out to identify the detailed adsorption behavior of picolinic acid on tungsten oxide. Figure 1 c,d shows the adsorption isotherm of picolinic acid on tungsten oxide as a function of picolinic acid concentrations. The adsorption data were analyzed using the Langmuir and Freundlich models [18; 19]. Figure 1: (**a**) Molecular structure of picolinic acid. (**b**) Schematic illustration of picolinic acid adsorption onto the tungsten films. Adsorption isotherms of tungsten oxide as a function of picolinic acid concentration analyzed using (**c**) [PERSON] and (**d**) Freundlich equations. The Langmuir model can be described with the equation:  
\[\frac{C_{e}}{Q_{m}}+\frac{1}{bQ_{m}}=\frac{C_{e}}{Q_{e}} \tag{2}\]  
and the Freundlich model can be expressed as:  
\[Q_{e}=K_{F}\cdot{C_{e}}^{\
icefrac{{1}}{{n}}} \tag{3}\]  
where \(Q_{e}\) is the concentration of adsorbed picolinic acid on the surface of tungsten oxide (mg/m\({}^{2}\)), \(Q_{m}\) is the maximum concentration of adsorbed picolinic acid (mg/m\({}^{2}\)), \(C_{e}\) is the concentration of picolinic acid in slurry solution (mg/L), and \(b\) is the Langmuir constant (L/mg) [18]. The Freundlich constant \(K_{F}\) is related to the adsorption capacity, and \(\
icefrac{{1}}{{n}}\) is correlated the adsorption intensity [19]. The constants calculated from adsorption models are shown in Table 1. The higher R\({}^{2}\) value of the Langmuir model compared to that of the Freundlich model indicates that the picolinic acid was homogeneously adsorbed on tungsten oxide [18,19], meaning that the picolinic acid forms a monolayer on the surface of tungsten oxide [18]. Both [PERSON] et al. and [PERSON] et al. experimentally demonstrated that the strong Lewis acid sites and Bronsted acid sites on the surface of metal oxide films could be active sites for the adsorption of pyridine functional groups [11,20,21]. From this point of view, the coordinated covalent bonding between the pyridine group of picolinic acid and the acidic sites of tungsten oxide resulted in monolayer adsorption on the surface of tungsten oxide [12,13,20,21]. Based on adsorption isotherm results, the saturated concentration of picolinic acid was determined to be 1.5 wt%. Thus, we selected four picolinic acid concentrations (0, 0.5, 1.5, and 5.0 wt% per solution weight) for subsequent experiments to determine its effect on tungsten dissolution. To verify the dispersion stability of the silica nanoparticles with picolinic acid as a CMP slurry, we measured the hydrodynamic diameters and zeta potentials of the slurries as a function of the picolinic acid concentration, as shown in Figure S1 and Table S2. As the concentration of picolinic acid increased, the measured hydrodynamic diameters was maintained at the level of 64 nm and did not change. Similarly, the zeta potentials of the slurries also constantly remained at the level of \(-\)20 mV as the concentration of picolinic acid increased. These results confirm that the dispersion stability of the silica-based slurry is not influenced by the addition of picolinic acid. After the dipping test, the topography was analyzed by AFM and SEM, as seen in Figure 2. The average roughness (R\({}_{\text{a}}\)) of each sample was calculated to quantitatively compare their topographies. In the absence of picolinic acid, the grains of tungsten were severely damaged due to the high dissolution rate of tungsten. Similar results were obtained with 0.5 wt% picolinic acid, but a few more grains were observed.