Retarding Field Analyzer

 

The figure shows the principle of a Retarding Field Analyzer.

A hole grid system of two grids (plasma grid and extraction grid) extracts particles from the plasma. The extraction grid can have a positive potential (measuring electron energy distribution) or a negative one (measuring ion energy distribution.

The collector measures the particle current in dependence on the retarding voltage. In order to find the energy distribution of the extracted particles, one has to differentiate the curve with respect to the retading voltage.

 

With a retarding field analyzer with a hole array it is possible to extract particles from an area of about some cm2, because of the larger current. The retarding field analyzer is made of a laser cutted hole grid system with holes 0.5 mm diameter and 0.25 mm grid distance. Therefore two limits arise:

  • Gas pressure has to be smaller than 10-1 mbar (mean free path has to be larger than free flight lenght in the analyzer of about 1mm),
  • Plasma charge density has to be in maximum up to 1011 cm-3 (Debye-Lentgh hast ot be bigger than hole diameter of 0.5 mm).
  Retarding Field Analyzer
with a 15 x 15 mm hole raster screen
(hole diameter 0.5mm)
Examples of an electron energy distribution (EED - left) and an ion energy distribution (IED-right), measured by a Cold Cathod Plasma JENION ACC 30 x 125 PS  

 
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