Optical and electrical characterization of an atmospheric pressure microplasma jet for Ar∕CH4 and Ar∕C2H2 mixtures

Abstract

Characterization of the behavior of chemically reactive species in a nonequilibrium inductively coupled argonhydrogen thermal plasma under pulse-modulated operation A rf microplasma jet working at atmospheric pressure has been characterized for Ar, He, and Ar/ CH 4 and Ar/ C 2 H 2 mixtures. The microdischarge has a coaxial configuration, with a gap between the inner and outer electrodes of 250 m. The main flow runs through the gap of the coaxial structure, while the reactive gases are inserted through a capillary as inner electrode. The discharge is excited using a rf of 13.56 MHz, and rms voltages around 200-250 V and rms currents of 0.4-0.6 A are obtained. Electron densities around 8 ϫ 10 20 m −3 and gas temperatures lower than 400 K have been measured using optical emission spectroscopy for main flows of 3 slm and inner capillary flows of 160 SCCM. By adjusting the flows, the flow pattern prevents the mixing of the reactive species with the ambient air in the discharge region, so that no traces of air are found even when the microplasma is operated in an open atmosphere. This is shown in Ar/ CH 4 and Ar/ C 2 H 2 plasmas, where no CO and CN species are present and the optical emission spectroscopy spectra are mainly dominated by CH and C 2 bands. The ratio of these two species follows different trends with the amount of precursor for Ar/ CH 4 and Ar/ C 2 H 2 mixtures, showing the presence of distinct chemistries in each of them. In Ar/ C 2 H 2 plasmas, CH x species are produced mainly by electron impact dissociation of C 2 H 2 molecules, and the CH x /C 2 H x ratio is independent of the precursor amount. In Ar/ CH 4 mixtures, C 2 H x species are formed mainly by recombination of CH x species through three-body reactions, so that the CH x /C 2 H x ratio depends on the amount of CH 4 present in the mixture. All these properties make our microplasma design of great interest for applications such as thin film growth or surface treatment.

Optical Diagnostics of Micro Discharge Jets

“…Quantities accessible from the detected radiation are e.g. the gas temperature from rotational bands of molecular components or for high enough levels of ionisation the electron density from the Stark broadening of atomic lines [18]. Here, we present measurements of the ultraviolet (UV) and vacuum ultraviolet (VUV) emission of the APPJ in search for an energy transport mechanism providing the energy for excited atomic oxygen far outside the discharge.…”

Power dissipation, gas temperatures and electron densities of cold atmospheric pressure helium and argon RF plasma jets

“…It has a hole with a diameter of 5 mm through which the plasma can penetrate. This electrode simulates a two-electrode system used by other research groups with a concentric electrode around the tube [11,19,20], while allowing access for laser spectroscopy of the active region between the two electrodes. The plasma jet is a so-called linear field plasma jet, since the electrical field and the gas flow have the same direction [21].…”

“…Voltage and current probes can be directly connected to the electrodes, allowing us to calculate the power dissipation of the plasma [10,11]. In the case of APPJs, however, the capacity of the probes is in the same order of magnitude as the capacity of the source.…”

Nonlinear frequency coupling in dual radio-frequency driven atmospheric pressure plasmas

“…The nonlinear character of the plasma boundary sheath inherently generates higher harmonics, which are experimentally observed in the current rather than the applied voltage. 21 This requires setting a sinusoidal voltage signal rather than the current and selfconsistently solving the generated higher harmonics in the current. Unique solutions are obtained by fixing the power coupled into the plasma.…”