High-pressure hollow cathode discharges

Abstract

Reducing the diameter of the cathode hole in a plane anode-hollow cathode geometry to 200 µm has allowed us to generate direct current discharges in argon at atmospheric pressure. Up to pressure times cathode hole diameter (pD) values of approximately 5 Torr cm, and at sub-mA currents, glow discharges (predischarges) are observed with a shape which is determined by the vacuum electric field. In the same pD range, but at higher currents of up to approximately 4 mA, the discharges are of the hollow cathode discharge type. At pD values exceeding 5 Torr cm the predischarges turn into surface discharges along the mica spacer between the electrodes. At currents >4 mA filamentary, pulsed discharges are observed. Qualitative information on the electron energy distribution in the microdischarges has been obtained by studying the VUV emission from ionized argon atoms and the argon excimer radiation at 130 nm. The results of the spectral measurements indicate the presence of a relatively large concentration of electrons with energies >15 eV over the entire pressure range. The fact that the current-voltage characteristic of the microdischarges has a positive slope over much of the current range where excimer radiation is emitted indicates the possibility of forming arrays of these discharges and using them in flat panel excimer lamps.

Hollow cathode sustained plasma microjets: Characterization and application to diamond deposition

“…The discharge does not fill the hole uniformly but appears to be localized near the inner surface of the tube. These observations are consistent with previous work on microdischarges 4 where increasing the pressure for a given hole size caused a shift in appearance from a columnar to a ring-shaped plasma. In our experiment, we increase the tube inner diameter thereby changing the p•d term to a value that no longer supports operation in the hollow cathode mode.…”

“…4 One major difference, however, is the flow which allows the discharge to be increased to lengths not possible with planar microdischarges. Another difference pertains to the absence of a dielectric material confining the discharge.…”

“…A single plasma microjet was used to grow diamond films employing gas mixtures consisting of H 2 and varying amounts of CH 4 . The gases were mixed in a region upstream of the microjet using a constant H 2 flow rate of 100 sccm and CH 4 flow rate between 0.1 and 1 sccm.…”

“…3 In one version, a planar electrode geometry is used consisting of a layered structure ͑ϳ200 m thick͒ of two metal plates on either side of a dielectric spacer with a hole through the structure. 4 Discharges are struck in the hole between the metal electrodes in direct current mode at voltages similar to those used for conventional low-pressure glow discharges but at much larger current density. The increased ionization is attributed to the Pendel effect 5 which describes the oscillatory motion of electrons in the radial electric field created in the hollow cathode.…”

Current status of microplasma research

“…When we classify them on the basis of the frequency of the power sources, the range spreads from DC to GHz. In DC operation, the most popularly used design is the hollow cathode (HC) type, which has been developed by Schoenbach's group recently for miniaturized structures and integrated assemblies [6,7]. They reached for a simple metal-insulator-metal sandwiched structure with a through-hole of a few tens to hundreds micrometers in diameter.…”