## 3 Results and Discussion  
In this study, the ratio of oxygen to argon was 1:1000. Figure 2 shows the current density and applied-voltage wave forms in one cycle. The total current density \(j_{0}\) was determined according to the formula \(j_{0}=\frac{e_{0}}{L}\frac{dV}{dt}+\frac{1}{L}\int_{0}^{L}j_{g}dx\); the form of the conduction current density was set as \(j_{g}=e(\sum_{i}j_{i}-\sum_{n}j_{e,n})\)[29, 30, 31]. In the above equation, V is the applied voltage, and \(J\) is the particle flux. The current density curve and voltage curve are sinusoidal; the current phase angle is earlier than voltage. This is the discharge characteristic of a typical continuous RF-capacitive coupling discharge, which is similar to experimental results in radio-frequency, atmospheric-pressure Ar/O\({}_{2}\) discharges [20]. And the characteristic of the capacitive coupling discharge was also reported in experimental results for a dual-frequency, He-gas discharge plasma [32]. To further understand the basic characteristics of the Ar/O\({}_{2}\) discharge plasma at atmospheric pressure driven by a dual-radio-frequency source, we simulated changes in physical parameters, such as the electron temperature, particle density, electric field, ionization, and so forth, when the secondary electron emission (SEE) coefficient was 0.001, 0.005, and 0.01. Figure 3 shows the spatial distributions of cycle-averaged electron density, electron temperature, and electric field as the SEE coefficient is increased from 0.001 to 0.01. According to Figure 3a, we can see that the electron density increases with as the SEE coefficient  
\begin{table}
\begin{tabular}{c|c c} \hline \hline
**Boundary Conditions** & \(x=0\) & \(x=L\) \\
**Electron flux** & \(J_{e}=-k_{s}n_{e}-\gamma\left(\sum\limits_{i}J_{+,j}+J_{-}\right)\) & \(J_{e}=k_{s}n_{e}-\gamma\left(\sum\limits_{i}J_{+,j}+J_{-}\right)\) \\
**Positive ion flux** & \(J_{+,j}=\pm\mu_{i}n_{i}E\) & \(J_{+,j}=\pm\mu_{i}n_{i}E\) \\
**Negative ion density** & \(n=0\) & \(n=0\) \\
**Neutral particle density** & \(n=0\) & \(n=0\) \\
**Electron temperature** & \(T_{e}=0.5\) eV & \(T_{e}=0.5\) eV \\
**Potential** & \(V=V_{H}sin(2\pi f_{H}t)+\) & \(V=0\) \\  & \(V_{L}\)\(\mathrm{erg}\  
increases. When the SEE coefficient increases to 0.01, the electron density is roughly twice that with a SEE of 0.001. As we all know, secondary electrons are produced by the collisions of ions and electrodes. In the sheath region, extra electrons from the wall are accelerated by sheath's electric field and multiply rapidly. Thus, the electron density and the ionization rate rise in the discharge space. As the electron density increases, the electron temperature in the sheath decreases from 2.83 eV to 2.15 eV; the electron temperature in the plasma remains almost constant, as the electric field is strong in the sheath region, causing the collision frequency between electrons and argon atoms or oxygen molecules to increase; energy loss then increases, as shown in Figure 3b. The electric field intensity decreases as the SEE increases, as shown in Figure 3c. In our study, the electron density increased from approximately \(4\times 10^{11}\) cm\({}^{-3}\) to \(1.2\times 10^{12}\)cm\({}^{-3}\). This result corresponds well to the results of the experimental study of Ar/O\({}_{2}\) at atmospheric pressure [33]. In that study, the researchers used oxygen-to-argon ratios of 0.3% and 0.6%; the electron density and the electron temperature changed slightly. The electron density increased from approximately \(2.5\times 10^{11}\) cm\({}^{-3}\) to \(5.5\times 10^{11}\) cm\({}^{-3}\), and the electron temperature increased from approximately 1.37 eV to 1.43 eV.