## 5 Result and Conclusions  
To confirm the reliability of the Langmuir probe and OES, experiments were carried out at different microwave powers and different air pressures. The electron temperature was measured by the clean probe, the probe with contamination, and optical emission spectroscopy method. The electron density was measured by the clean probe, the OES(contribute the _Tev.oes_), and the probe with contamination(contribute the _Isat_). The result is shown in Figure 10.  
Figure 10 shows that the contamination attached to the probe surface leads to higher incorrect electron temperatures. The electron temperatures obtained by the probe with contamination are about 20 eV higher than the temperatures obtained by the clean probe. When the higher incorrect electron  
Figure 10: The microwave power and pressure against the electron density and temperature measured by the probe and optical emission spectrometry (OES). **(a,b)** The microwave power changes at the pressure of 80 Pa, **(c,d)** the pressure changes at the microwave power of 800 W.  
Figure 9: Liner fit for data of specified spectral lines driven by 800 W microwave at the pressure of 80 Pa.  
temperatures are used to calculate the density, the result will be significantly less than the correct electron density. Comparing the temperature obtained by OES, the clean probe, and the probe with contamination, the temperature _Tev.oes_ obtained by OES is much closer to _Tev.probe_ obtained by the clean probe than by probe with contamination. The _Tev.oes_ is slightly higher than that _Tev.probe_ obtained by the clean probe, which is maybe caused by the OES measurements only presenting the temperature of a part of electrons, especially the high-energy electrons [20]. The difference between these two electron temperatures decreases as the temperature drops. When the electron temperatures are lower than 1.5 eV, _Tev.oes_ is basically equal to _Tev.probe_. Therefore, in the low-temperature plasma, especially below 1.5 eV, the electron temperature obtained by OES is accurate. For the high-temperature plasma, the electron temperature obtained may be higher than the correct electron temperature. Moreover, when the _Tev.oes_ is brought into Equation (4), the slightly lower density is obtained in the same _Isat._ Using this electron temperature, _Tev.oes_ can obtain the approximate electron density from the I-V curve of the Langmuir probe with contamination. Figure 10 also shows that the electron density is increased with improving microwave power; meanwhile, the electron temperature does not change significantly. Variation of electron density and temperature with pressure are also presented. The results show that when the pressure increases, both the electron density and temperature are decreased. This paper reports that a simple method to solve the contamination is attached to the probe surface, as the plasma reaction progresses. The electron temperature _Tev_ and electron density \(n\) are important parameters in plasma diagnosis. The contamination on the probe surface leads to a higher electron temperature than the correct value. Then, the correct electron density cannot be obtained. The optical emission spectrometry (OES) can be used to solve this problem by obtaining the electron temperature. In addition, the electron temperature obtained by OES spectra can be used to calculate the electron density in the contaminative Langmuir probe I-V curve. The electron temperature and density in different pressure (40-80 Pa) and microwave power (400-800 W) are measured. It shows that this electron temperature and density obtained by this method are close to the clean probe. Therefore, the contaminative Langmuir probe with the OES can give the approximate electron temperature and density, and the cleaning interval of the Langmuir probe could be significantly extended. [PERSON] and [PERSON] contributed to the overall study design, analysis, and writing of the manuscript. [PERSON], [PERSON], [PERSON], and [PERSON] provided technical support and revised the manuscript.