## 3 Results
### Gas Sensing Properties  
There is a modest temperature range for optimal adsorption and desorption, and they are largely influenced by the operating temperature. This affects the detection response of semiconductors and metal oxide gas sensors [51; 52]. Sensors fabricated using pure In\({}_{2}\)O\({}_{3}\), Au/In\({}_{2}\)O\({}_{3}\), Pd/In\({}_{2}\)O\({}_{3}\), and Pt/In\({}_{2}\)O\({}_{3}\) nanoparticles were tested at 1, 5, 10, and 50 ppm CO gas concentrations in the 50 to 200 \({}^{\circ}\)C temperature range to find their optimum operating temperatures. Figure 10 shows that the resistance of sensors degraded, as indicated by the downward drift of the resistance over time, whose trends were especially distinct for the Pt/In\({}_{2}\)O\({}_{3}\) and Pd/ In\({}_{2}\)O\({}_{3}\) at 50 \({}^{\circ}\)C. The sensing characteristics of MOS (metal semiconductor) gas sensors depend on various parameters such as sensing material, operating temperature, humidity, and target gas type, etc. Operating temperature is an important parameter for gas sensor materials because it has a significant influence on the occurrence of surface reactions during gas detection. When the gas sensor in the measuring chamber is exposed to dry air at a fixed temperature, oxygen molecules are adsorbed on the gas sensor surface, increasing its resistance. Looking at the XPS spectrum results, the density of oxygen molecules adsorbed on the gas sensor will increase in the order of Pd/ In\({}_{2}\)O\({}_{3}\), Pt/ In\({}_{2}\)O\({}_{3}\), and Au/In\({}_{2}\)O\({}_{3}\) according to the sensing material. Even though a small amount of humidity exists in the measuring chamber, water molecules will move to the surface area of the gas sensor that lacks adsorbed oxygen ions, reducing its resistance. Therefore, because the desorption of water molecules is more difficult at lower temperatures than at higher temperatures, at lower operating temperatures, the decrease in resistance of the gas sensor over time can be greater in the order of Au/ In\({}_{2}\)O\({}_{3}\), Pt/ In\({}_{2}\)O\({}_{3}\) and Pd/ In\({}_{2}\)O\({}_{3}\). \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Gas Sensors**} & \multicolumn{2}{c}{**OI**} & \multicolumn{2}{c}{**OII**} \\  & \multicolumn{2}{c}{**(Lattice Oxygen)**} & \multicolumn{2}{c}{**(Oxygen Vacancy)**} \\ \cline{2-5}  & **Peak (eV)** & **Percentage (\%)** & **Peak (eV)** & **Percentage (\%)** \\ \hline Au/In\({}_{2}\)O\({}_{3}\) & 530.1 & 35 & 530.6 & 65 \\ Pd/In\({}_{2}\)O\({}_{3}\) & 529.9 & 51 & 530.7 & 49 \\ Pt/In\({}_{2}\)O\({}_{3}\) & 529.9 & 56 & 530.8 & 44 \\ \hline \end{tabular}
\end{table} 
Table 1: The relative percentages of lattice oxygen and oxygen vacancies for Au/In\({}_{2}\)O\({}_{3}\), Pd/In\({}_{2}\)O\({}_{3}\), and Pt/In\({}_{2}\)O\({}_{3}\) particles. Figure 11a-c shows the sensitivities of the Pt/In\({}_{2}\)O\({}_{3}\), Pd/In\({}_{2}\)O\({}_{3}\), and Au/In\({}_{2}\)O\({}_{3}\) gas sensors as a function of temperature at various CO gas concentrations (also presented in Table 2). It was clearly shown that the sensitivity continuously increases with increases in the CO gas concentration. CO poisoning, which is worse due to the easier oxidation of Pt nanoparticles than other particles, seems to have a bad influence on the detection characteristics such as the response and recovery time of the Pt/In\({}_{2}\)O\({}_{3}\) sensor, as shown in Figure 10b. However, the sensitivities of the Pd/In\({}_{2}\)O\({}_{3}\) and Au/In\({}_{2}\)O\({}_{3}\) gas sensors revealed different trends, not only monotonically increasing, but also showing their highest sensitivities at 100 \({}^{\circ}\)C, with increasing sensing temperature.