EEDF measurements by gridded probes
- Univ. of Oxford (United Kingdom)
A knowledge of the plasma parameters and the energy of the electrons can greatly improve the role of plasma in applications such as plasma chemistry, processing of materials, fight production and laser technology. With the development of data acquisition techniques the calculation of the EEDF from experimentally obtained probe characteristics has become increasingly utilised. The geometry of the probe is taken in account in deriving the plasma density from the ion collection part of the I-V characteristic. The electrons are ignored taking the characteristic at high negative potentials and the curves are interpreted following the radial or the orbital motion theory. Instead when the electron distribution is the object of the investigation a linearised ion contribution is often subtracted in the part of the characteristic where the ion current curvature is highest. In order to make a quantitative estimate we refer to the numerical work of Nairn et al. who calculate the ion current in radial motion for an extended range of the ratio motion for an extended range of the ratio r{sub p}/{lambda}{sub D} (radius of the cylindrical probe over the Debye distance). Radial motion has been proved to be applicable in most of the plasmas used for processing. We can compare the derivative of the ion current with respect to the voltage with the derivative of the electron retardation current which, in the normalization used, depends on the ratio of the ion to the electron mass. Let us consider, for example, a typical probe used for EEDF measurements, with r{sub p}/{lambda}{sub D} = 1 in Argon. We can see that the ion slope is already 14% of the electron slope for a floating potential only 3.6 kT{sub e}/e negative with respect to the plasma. Lighter gases, for the same voltage, will show a greater error. This work proposes the gridded probe as a reliable method to extend the measurements of the EEDF to values well negative with respect to the floating potential.
- OSTI ID:
- 212994
- Report Number(s):
- CONF-950749-; TRN: 96:010143
- Resource Relation:
- Conference: 22. international conference on phenomena in ionized gases, Hoboken, NJ (United States), 31 Jul - 4 Aug 1995; Other Information: PBD: 1995; Related Information: Is Part Of XXII International conference on phenomena in ionized gases. Contributed papers 4; Becker, K.H.; Carr, W.E.; Kunhardt, E.E. [eds.]; PB: 256 p.
- Country of Publication:
- United States
- Language:
- English
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