This paper presents the experimental and numerical results about the influence of nitrogen (N2) and oxygen (O2) admixture on the development of a helium (He) atmospheric-pressure plasma jet (APPJ) in a long dielectric tube. The results revealed that the jet length and the propagation velocity are strongly affected by introducing N2 or O2 into the He flow. Specifically, it was observed that a higher N2/O2 admixture led to the decrease in the density of both energetic and relative low-energy electrons outside the grounded electrode, which corresponds to the shortening of the jet length. In the He/O2 mixture, the electrons are easily captured by O2/O in the region of the plasma bulk. In the He/N2 mixture, the jet propagation characteristics will change since N2 has many low-level excitation states that consumed a large number of energetic electrons. The simulation shows that the magnitude of the axial electric field in the jet head depends strongly on the amount of N2 and/or O2 in the gas flow. In both cases, the peak electric field is on the order of 5 kV/cm, which is significantly higher than that in pure helium of 3 kV/cm even if the admixture is low (less than 4% N2 or 2% O2 in this work). Positive charges of higher density in the jet head are needed to induce a stronger electric field for the jet propagating in N2(x%)/He and O2(x%)/He mixtures compared with that in pure He.

The characteristics of an atmospheric pressure plasma jet (APPJ) based on needle-to-ring dielectric barrier discharge (DBD) have been investigated experimentally. The plasma jet is driven by a sinusoidal voltage, and the working gas is argon. The jet length, the voltage-current waveforms, the optical emission spectra and the plasma evolution have been studied. Moreover, the transferred charges of the discharge pulse and the electron excitation temperature were investigated. These results reveal that there exist two or more current pulses per half-cycle as the applied voltage increases. In fact, the multiple current pulses correspond to multiple breakdowns between the electrodes. This phenomenon in DBD-APPJ is mainly attributed to the surface charges on the grounded ring electrode surface, which can induce a strong reverse electric field to counteract the applied electric field. In addition, the jet length is extended stepwise as the number of current pulses increases. The residual excited species or charges remaining from the previous discharge play an essential role in the formation of a stronger next discharge and are responsible mainly for a higher electron excitation temperature, which makes the jet develop farther (i.e., a longer jet). Finally, we obtain a preliminary control condition to switch a single current pulse into multiple pulses, which has a benefit for industrial applications.

Atmospheric pressure plasma jet has received increasing attention due to its wide potential applications such as in material processing and surface modification. This paper presents the characteristics of titanium oxide (TiO₂) thin films deposited by using atmospheric pressure corona plasma jet based on a needle-plate configuration. The influences of corona polarity and operating parameters on the properties of TiO₂ films are investigated. The characteristics of positive and negative corona discharge, the developing process and the emission spectrum of the plasma jet are tested, and the TiO₂ films prepared under different conditions are measured and analyzed. The results show that the TiO₂ film prepared by negative corona plasma has a more uniform surface, and the Ti content in TiO₂ film is higher than that by the positive corona plasma. The adhesion force is higher than 4.7 N/cm and the surface resistance of the film is less than 10¹⁰ Ω. The deposition of the TiO₂ film is closely related to the nucleation mechanism of the precursor in the plasma jet and/or the interface between jet and substrate. These results will provide useful reference for preparing uniform and functional oxide film materials by atmospheric pressure plasma jet.

Harmonic hexagonal superlattice pattern in a dielectric barrier discharge at atmospheric pressure Chinese Science Bulletin 54, 2325 (2009); Advances of atmospheric-pressure dielectric-barrier-discharge plasma jets

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