Micro Cavity Discharge:
Micro-Hollow Cathode Discharge (MHCD) and Cathode Boundary Layer Discharge (CBLD)
Wei-Dong Zhu
Department of Applied Science and Technology
Saint Peter's College
2641 Kennedy Boulevard
Jersey City, NJ 07306
Micro-hollow cathode discharges (MHCDs)1,2 are discharges between a cathode with a micro-hollow
structure (usually circular) and an arbitrarily shaped anode. The MHCD can operate in two different
modes, depending on the value of the product of pressure, p, and the cathode hole diameter, D. In either
mode, the current-voltage characteristics have a distinct range with negative differential resistivity. For
low values of pD, generally on the order of 1 Torr cm or less, the effect of pendulum electrons inside the
cathode hollow determines the current-voltage characteristics3,4,5. For MHCDs operating at higher values
of pD, the negative differential resistivity can, according to modeling results6, be associated with a
transition from a glow discharge localized inside the hollow cathode to a glow discharge spreading along
the outer cathode surface7.
Cathode boundary layer (CBL) discharges are closely related to those MHCDs that operate in the high pD
mode. It is essentially high-pressure glow discharge generated between a planar cathode and a perforated
thin metal foil anode separated by a thin layer of dielectric material of a few hundred micrometers thick
and with the same size opening as the anode (The total thickness of the structure is only in the millimeter
range). The discharge is reduced to cathode fall and negative glow, with the negative glow acting as a
virtual anode, providing a current path to the anode8. Although there are no data available on the
electron energy distribution in CBL discharges yet, the electrons are expected to have energies
corresponding to the cathode fall voltage, according to Gill and Webb’s measurements of the electron
energy distribution in the cathode fall of a low-pressure helium glow discharge between parallel-plane
electrodes9. The cathode fall thickness is estimated to be around 50 m at a pressure of about 200 Torr in
rare gases10.
Studies of MHCD and CBLD operating in rare gases or rare gas mixture suggest the possibility of
generating extended lifetime, intense, large area, planar excimer sources in sealed discharge chambers
including getters.
1
A. El-Habachi and K.H. Schoenbach, Applied Physics Letters 72 (1997) 22
A. El-Habachi and K.H. Schoenbach, Applied Physics Letters 73 (1998) 885
3
D.J. Sturges and H.J. Oskam, Journal of Applied Physics 35 (1964) 2887
4
A.D. White, Journal of Applied Physics 30 (1959) 711
5
H. Helm, Zeitschrift für Naturforschung A 27A (1972) 1812
6
J.P. Boeuf, L.C. Pitchford and K.H. Schoenbach, Applied Physics Letters 86 (2005) 071501
7
M. Moselhy, W. Shi, R. H. Stark and K.H. Schoenbach, IEEE Transaction on Plasma Science 30 (2002) 198
8
K.H. Schoenbach, M. Moselhy and W. Shi, Plasma Sources Science and Technology 13 (2004) 177
9
P. Gill and C. E. Webb, Journal of Physics D: Applied Physics 10 (1977) 299
10
Yu.D. Korolev, K.H. Schoenbach, XXVIIth ICPIG, the Netherlands (2005)
2