A dielectric barrier discharge (DBD) atmospheric cold plasma was evaluated as a tool to increase the extraction rate of total phenolic content (TPC) and antioxidant activity from green tea leaves. The effects of nitrogen DBD cold plasma on changes of color and surface morphology were investigated. Optimum conditions of cold plasma treatment (treatment time and generation power) were obtained by response surface methodology. After the nitrogen DBD cold plasma at 15 W of the generation power for 15 min, the TPC and antioxidant activity of green tea increased by 41.14% and 41.06%, respectively. The catechin also increased by 103.12%. The scanning electron microscopy results showed cell ablation and ruptures of the green tea leaf surface after nitrogen DBD cold plasma treatment.

The main objective of the current paper is to describe the effect of external inductance (EI) on the current discharge waveforms of HiPIMS at different pulse-on time (P on) and its relation with static deposition rate and topographical properties of deposited titanium thin films, which is investigated by scanning electron microscope and atomic force microscope. It has shown that the higher the EI, independent of the P on , the higher the peak power is. The delay time also extensively increases when an EI is implemented into the circuit. However, the rise time does not have a linear dependency with the EI and its behavior changes to some extent at different P on. By increasing the EI from zero to 30 mH at P on = 60 μs, the peak power subsequently rises from 11 to 32 kW at constant time-average power. Meanwhile, the deposition rate decreases from 8.5 to 1.5 nm/min, which is mainly attributed to the metal ions return to the target surface and nonlinear dependency of sputtering yield with applied voltage. It was also revealed that the higher peak power has no special effect on the surface roughness of titanium thin films deposited by HiPIMS.

In this paper, we present a new structure for Ar–N2 plasma jet generation where a pulsed electric field is modified with a second alternating electric field, referred to as mixed electric field. The electric field distribution through the jet tube is simulated for the conventional and newly designed plasma jet. It is demonstrated that the value of the electric field becomes stronger due to mixed electric field, particularly between the tip and ring electrodes through the tube. Not only does the length of plasma jet increase from 15 cm to 30 cm when a mixed electric field is employed, but also the temperature of the substrate surface decreases from 62 °C to 52 °C at the same power, which is favorable for industrial applications. It is shown that introducing more nitrogen into the plasma jet shortens the length of the jet, while the jet length could substantially be improved using the current design. The capability of surface treatment at different electrical power is also evaluated on deposited TiN layers by the conventional and current plasma jet. The surface treatment by the newly designed plasma jet based on mixed electric field shows no detectable damage on the TiN layer, while the conventional plasma jet degrades the surface at equal power. The hydrophilicity of the surface is also measured by the contact angle of a water droplet, which decreases from 66 to 31° after surface treatment, implying the surface becomes more hydrophilic. The temperature distribution on the substrate is also evaluated for Ar–N2 plasma jet and compared with the conventional plasma jet structure.

In this paper, the dynamics and flow behaviour of an atmospheric argon plasma jet was studied in the new nozzle structure similar to the surface dielectric barrier discharge (SDBD) using the Schlieren imaging method. The effect of plasma jet driven by repetitive high-voltage microsecond pulses with low-frequency sinusoidal bias was measured qualitatively in a single mirror Schlieren optical system. The enhancement of plasma jet length and cross-section of plasma jet with surface in this condition is due to highly turbulent flow of argon plasma jet in this structure. This study revealed the important role of SDBD structure and modulated electric field on the behaviour of plasma jet in a high diameter nozzle. In practice, this technique allows us to increase the jet length of the nozzle output to 5 cm and under these conditions, the diameter of the plasma jet cross-section is increased to 8 mm, without increasing the electrical power consumption. Eventually, the hydrophilicity of the surface is also measured by the contact angle of a water droplet that decreases from 78 • to 8 • after surface treatment, implying we were able to reach a super-hydrophilic surface with this plasma jet structure. K E Y W O R D S hydrophilicity, modulated electric field, plasma jet, Schlieren imaging, surface dielectric barrier discharge (SDBD)

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