Conventional and non-conventional diagnostics of a stable atmospheric pressure DC normal glow microplasma discharge intended for in situ TEM studies

Abstract

A simple setup utilizing parallel flat electrodes with a 50-150 µm interelectrode distance divided by a Kapton spacer with a 1 mm diameter whole as discharge region intended for in situ TEM studies is presented. The rather small setup operated in Ar or He results in an atmospheric pressure DC normal glow discharge and is investigated using various diagnostics. I-V characteristics show a glow-like behavior of the microplasma. Significant differences due to the working gas, electrode material and electrode distance have been observed. Currents in the range of 0.5-3 mA resulted in electrode potentials of 140-190 V for most experimental conditions. Optical emission spectroscopy and imaging revealed stable plasma operation and enabled the determination of current densities (approx. 16 mA/mm2 for He, or 28 mA/mm2 for Ar) independent of the input current as the discharge channel grows in diameter. Sheath thicknesses in the range of a few μm have been calculated by the collision-dominated Child-Langmuir law and trends are confirmed by the optical imaging. Energy flux measurements revealed a pronounced effect of ions on the measurement process and resulted in high energy fluxes locally up to 275 W/cm2. Effective secondary electron emission coefficients ranging from 1 to 1.6 depending on the discharge conditions have been determined based on the energy balance at the cathode.

Microplasma characteristics of direct-current atmospheric pressure glow discharge in dependence of gap distance and discharge current

“…Meanwhile, the generation of large-area microplasma at atmospheric pressure can be realized by the microelectrode arrays, which is hardly realized in large gap [8][9][10]. Therefore, microplasma at atmospheric pressure is very popular in the microsystems and portable devices, especially in the field of the medical treatment [7], surface modifications [11,12], sensing application [13,14], nanomaterials synthesis [15], CO 2 reduction [9,16], etc, because of the reduced dimensions, the absence of heat damage, a highly reactive environment and an implementable large-area discharges.…”

On the plasma permeability of highly porous ceramic framework materials using polymers as marker materials

“…[ 19–24 ] Thus, usage of the large surface‐to‐volume ratio of t‐ZnO as electrode material could enhance plasma properties, especially, for microplasmas, where the surface‐to‐volume ratio is already quite large. [ 25–27 ]…”