Characterization of hollow cathode and parallel plate microplasmas: scaling and breakdown

Abstract

We present an experimental comparison of parallel plate and hollow cathode microplasma structures, operated at high pressure with narrow anode-cathode gaps. A moveable anode arrangement with ±12 µm spatial resolution was used to vary the electrode separation to cover the pd range between 0.01 and 4 Torr cm for both structures. The hollow cathode discharge was operated with pressure-diameter (pD) product values between 1.8 and 7.2 Torr cm and an aspect ratio of ∼5. Analysis of V -I characteristics shows j/p 2 and j 2 p scaling for low and high current modes, respectively. Electron temperature estimates between 2 and 3 eV were obtained by solving a numerical collisional-radiative model based on transitions from 4p argon levels. The hollow cathode sheath thickness for both ionizing and non-ionizing sheath conditions was determined analytically and the diffusion equation was solved numerically to estimate the plasma density profile for the ionizing sheath case.

Generation of microdischarges in diamond substrates

“…It can be seen that while the discharge is centred in the hole, the plasma on the cathode side of the device spills out over the electrode surface to a much greater extent than for the anode side. This behaviour is consistent with observations reported for comparable microdischarges in devices based on alumina and mica insulators [1][2][3][4][5] and is due to the plasma region expanding over the cathode while the discharge is in a normal glow regime. Similar behaviour was observed for the device with metal electrodes.…”

“…Research into microdischarges, defined as discharges in which at least one dimension is less than 1 mm, has expanded considerably in recent years and the last decade has seen these devices developed for many different applications [1,2]. Recent research has seen the investigation of different operating modes, with some authors focusing on device scaling, especially ignition processes [3,4], while others have investigated operating regimes associated with reproducible instabilities [5][6][7][8]. Much of this research has focused on the gas-phase processes that occur in the micro-volumes inside these devices but the role of the surface processes and plasmasurface interactions is gaining increasing attention [9].…”

Axial light emission and Ar metastable densities in a parallel plate dc microdischarge in the steady state and transient regimes

“…Different kinds of microplasma sources have been proposed: micro atmospheric pressure plasma jet (µ-APPJ) [2], micro hollow cathode [3], and large arrays of micro discharges with dielectric barrier [4] are some of the most popular. However, very few studies of parallel plate micro discharges exist at all [5,6,7]. Due to their simple geometry the parallel plate micro discharges can be used as an ideal benchmark for different plasma models and for testing the similarities between large scale low pressure discharges and micro discharges.…”

The use of hollow cathodes in deposition processes: A critical review

“…The upper p.d limit is also dependent on the type of gas used [134]. Furthermore, for a given value of p.d and discharge current, the operating voltage has been shown to be lower for smaller values of d [18,140,179]. However, this cannot be explained in terms of a constant current density, since when the area of the cathode was decreased by a factor of four the operating voltage decreased by between 20 -30%, depending on the length of the hollow cathode.…”