Paper PS2-TuM11
Probe Geometry Induced Electron Energy Distribution Function (EEDF) Distortion
Tuesday, October 19, 2010, 11:20 am, Room Galisteo
| Session: |
Plasma Diagnostics, Sensors and Control |
| Presenter: |
A.E. El Saghir, North Carolina State University |
| Authors: |
A.E. El Saghir, North Carolina State University
E.M. Martin, North Carolina State University
S.S. Shannon, North Carolina State University
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| Correspondent: |
Click to Email |
One of the most valuable plasma characteristics that can be obtained from a Langmuir probe is the Electron Energy Distribution Function (EEDF). This is carried out by subtracting the ion contribution of the probe current, the shape of the electron current for probe potentials lower than the plasma potential is used to reconstruct the EEDF. The integral relationship for electron current in the transition region of a single probe voltage-current characteristic has been previously derived for planar probe configurations1. The Druyvesteyn relation for obtaining EEDF’s from Langmuir probes is derived based on a model that assumes that only an electron’s energy component perpendicular to the electric field generated by the biased probe determines whether an electron is collected or deflected by the probe when operating with an electron retarding potential. Cylindrical and spherical probe geometries have an additional electron retarding mechanism not accounted for in the Druyvesteyn relation. This additional mechanism comes in the form of a centrifugal retarding potential whose strength is determined by the initial angular momentum when the electrons are far away from the probe. In this work, formulations for cylindrical and spherical geometries are presented. These integral relationships are used to demonstrate the impact of ignoring probe geometry in EEDF extraction and highlights distortion of EEDF's when these geometric considerations are not taken into account. Finally, by combining the integral formulation for cylindrical and spherical probes with the analytical findings of Hoskinson for a finite cylindrical probe2, we present a study of the effect of finite length cylindrical probe geometries on EEDF solutions. 1Druyvesteyn M.J, Z. Phys.,vol. 64,1930, pp. 781-798.
2R. Hoskinson, and N. Hershkowitz, Plasma Sources Sci. Technol. vol. 15, 2006,pp. 85-90.
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This work is supported by the UNC General Assembly and a generous gift from Applied Materials