UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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Conference: Bucharest University Faculty of Physics 2002 Meeting


Section: Optics, Spectroscopy, Plasma and Lasers


Title:
THE SMOOTHING AND THE DIGITAL PROCESSING OF LANGMUIR PROBE CHARACTERISTIC


Authors:
H. Andrei, V. Covlea, V. V. Covlea and E. Barna


Affiliation:
The University of Bucharest, Faculty of Physics


E-mail


Keywords:


Abstract:
One of the most important parameter of a plasma source is the electron energy distribution function (EEDF), as it contains all the information about electron temperature and electron number density. It also contains information about resonant processes taking place inside the plasma. The EEDF is linked to the external parameters of the plasma source (geometrical dimensions, gas pressure and flow, dissipated power etc.). Those external parameters can eventually be used as guiding parameters in plasma processing of materials. As Druyvesteyn [1] showed in 1930, the EEDF can easily be computed from the second derivative of the voltage-current characteristic of a Langmuir probe. More recently, various methods of numerical processing of experimental data were used for this purpose. The method devised by Savitzky and Golay [2] is the one of the most widely used [3-5]. For a given point of the experimental set, the second derivative is assumed to be the second derivative of a function that fits a section of the experimental set, section centered on the given point. In this paper we analyze how the number of experimental points used in order to compute the second derivative for a given point distorts the result. References: [1]. M. Druyvesteyn - Zeitschrift für Physik, 64, (1930), p. 781 [2]. A. Savitzky, M.J.E. Golay - Analytical Chemistry, 36, (1964), p. 1627 [3]. F. Fujita, H. Yamazaki - Japanese Journal of Applied Physics, 29, (1990), p. 2139 [4]. C. A. Anderson and W. G. Graham - Plasma Sources Science and Technology, 4, (1995) p. 561 [5]. V. Covlea, H. Andrei, Diagnosticarea plasmei - lucrari de laborator, Editura Universitatii din Bucuresti, (2001), p. 55