Constricted Plasma Source

The constricted plasma source (CPS) utilizes a special form of a dc glow discharge, the little-known constricted glow discharge. It is characterized by the presence of a small orifice (or constriction) placed in the discharge path between cathode and anode. If flowing gas is used, both electric current and gas have to go trough the constriction. As a result, an electric double layers forms upstream the constriction with a voltage drop which can exceed the first ionization potential of the gas in use. Ionization processes occur in the vicinity of the constriction, and the ionized gas (plasma) is "blown" through the constriction by the pressure gradient.

The Figure below shows one version of our Constricted Plasma Sources, operating with oxygen. The source is used for the growth of GaN thin films as well as optical films on glass and plastics.

The Constricted Plasma Source has a number of advantages:

operation in a wide range of pressure is possible
no heated parts (such as filaments) are present, thus the source is compatible with oxygen and other reactive gases
ion energy is low (less than 20 eV, i.e., lower than most other ion or plasma sources
simple, robust construction.

The development of the CPS was honored by a R&D 100 Award (1997) of the R&D Magazine.

References:

A. Anders and S. Anders, The working principle of the hollow-anode plasma source, Plasma Sources Science & Technology, vol. 4 (1995) 571-575.
A. Anders, N. Newman, M. Rubin, M. Dickinson, E. Jones, P. Phatak, and A. Gassmann, Hollow-anode plasma source for molecular beam epitaxy of gallium nitride, Rev. Sci. Instrum., vol. 67 (1996) 905-907.