Atomic oxygen generation in atmospheric pressure RF plasma jets driven by tailored voltage waveforms in mixtures of He and O₂

Abstract

Absolute atomic oxygen densities measured space resolved in the active plasma volume of a COST microplasma reference jet operated in He/O2 and driven by tailored voltage waveforms are presented. The measurements are performed for different shapes of the driving voltage waveform, oxygen admixture concentrations, and peak-to-peak voltages. Peaks- and valleys-waveforms constructed based on different numbers of consecutive harmonics, N, of the fundamental frequency f 0 = 13.56 MHz, different relative phases and amplitudes are used. The results show that the density of atomic oxygen can be controlled and optimized by voltage waveform tailoring (VWT). It is significantly enhanced by increasing the number of consecutive driving harmonics at fixed peak-to-peak voltage. The shape of the measured density profiles in the direction perpendicular to the electrodes can be controlled by VWT as well. For N > 1 and peaks-/valleys-waveforms, it exhibits a strong spatial asymmetry with a maximum at one of the electrodes due to the spatially asymmetric electron power absorption dynamics. Thus, the atomic oxygen flux can be directed primarily towards one of the electrodes. The generation of atomic oxygen can be further optimized by changing the reactive gas admixture and by tuning the peak-to-peak voltage amplitude. The obtained results are understood based on a detailed analysis of the spatio-temporal dynamics of energetic electrons revealed by phase resolved optical emission spectroscopy.

Influence of pulse modulation frequency on helium RF atmospheric pressure plasma jet characteristics

“…[ 30,41 ] Electron impact excitation of ground‐state molecular and atomic oxygen leads to the emission at 844.6 and 777.4 nm, which is predicted by the dissociative excitation, given as, and direct impact excitation mechanisms, where O * refers to the O (3p 5 P) state, which emits at 777.4 nm, and the O (3p 3 P) state, which emits at 844.6 nm. [ 48–50 ] The generation of oxygen metastable is predominantly caused by electron impact dissociation of O 2 , and electron‐induced processes dominate the generation of ground‐state atomic oxygen. The formation of such intense reactive species in helium discharge is beneficial for atmospheric pressure plasma applications, especially for biomedical treatment and plasma processing.…”

Low-Temperature Plasma for Biology, Hygiene, and Medicine: Perspective and Roadmap

“…Plasma Control: Control over plasma composition is mandatory for a targeted medical application. Tremendous progress has been made in controlling electron dynamics, e.g., through a multifrequency approach [44]. Ensuring a reproducible composition by using a tailored gas surrounding the active effluent has opened the door to several promising fundamental biomedical studies.…”

Effects of O2 Addition on the Discharge Parameters and Production of Reactive Species of a Transferred Atmospheric Pressure Plasma Jet

“…Many studies indicated that the addition of small amounts of oxygen (O 2 ) to the gas employed to produce plasma, usually argon (Ar) or helium (He), can increase the amount of atomic oxygen (O) produced in the APPJ [11][12][13][14][15][16][17]. To verify this increase in the population of O most authors have measured the light emission from excited O atoms coming from the 777 nm triplet or, in some cases, from the 844 nm triplet [13].…”