Measurement Of Electron Energy Distribution Function Research Articles

The measurement of electron energy distribution functions in methane-hydrogen plasmas

Abstract The electron energy distribution function (EEDF) is a key factor in the reaction kinetics of any plasma. The EEDF can, in principle, be obtained from the second derivative of the electron retarding region of a Langmuir probe characteristic. In the high frequency discharges used for the deposition of diamond-like carbon, the method is complicated by both the electric field sustaining the plasma and a tendency for the probe to exhaust the bulk of the electron distribution in the region of the plasma space potential. Experimental details of a novel, low current, asymmetric Langmuir probe, designed to circumvent these problems, are discussed, together with measurements of EEDFs made on a range of hydrogen-methane plasmas.

On electron energy distribution function measurements in microwave discharges sustained by propagating surface waves

The possibility of measuring the electron energy distribution function in microwave discharges sustained by the field of propagating surface waves via a second derivative technique is demonstrated. The influence of different measuring probe orientations (axial or radial with respect to the discharge axis) on the measured electrodynamic surface wave parameters and distribution functions is examined. The electron energy distribution functions obtained by axial and radial probe orientation show different behaviour. Significant influence of the presence of probes on the space distribution of the radial electric field component outside the discharge is observed. The results show that it is more appropriate to use a radially orientated probe for diagnostics in microwave discharges created by surface waves.

Electron energy distribution function measurements in a planar inductive oxygen radio frequency glow discharge

A tuned, cylindrical Langmuir probe was used to measure current-voltage traces in a planar, inductive oxygen, radio frequency glow discharge at several pressures ranging from 0.5 to 10 mT. The plasma potentials were determined from the zero crossings of the trace second derivatives. Positive ion densities were evaluated using orbit motion limited probe theory; electron densities were estimated by integrating the area under the unnormalized distribution function. By applying the Druyvesteyn formula to the digitized probe traces, the electron energy distribution functions were obtained. The distribution functions ranged from Maxwellian at 0.5 mT to almost Druyvesteyn-like at 10 mT.

Time-resolved optical emission and electron energy distribution function measurements in rf plasmas

Comparisons between experimentally measured time-dependent electron energy distribution functions and optical emission intensities are reported for low-frequency (100 and 400 kHz) radio-frequency driven discharges in argon. The electron energy distribution functions were measured with a time-resolved Langmuir probe system. Time-resolved optical emissions of argon resonance lines at 687.1 and 750.4 nm were determined by photon-counting methods. Known ground-state and metastable-state excitation cross sections were used along with the measured electron energy distribution functions to calculate the time dependence of the optical emission intensity. It was found that a calculation using only the ground-state cross sections gave the best agreement with the time dependence of the measured optical emission. Time-dependent electron density, electron temperature, and plasma potential measurements are also reported.

Langmuir probe measurements of the electron energy distribution function in radio-frequency plasmas

Plasma parameters, including the electron energy distribution function (EEDF), have been measured in 13.56 MHz argon and nitrogen plasmas using a tuned probe. The EEDF measured over a range of pressures in argon are approximately bi-Maxwellian, whereas the nitrogen EEDF becomes highly non-Maxwellian at high gas pressures. The EEDF measurements also demonstrate that the argon radio-frequency (rf) plasma can be sustained entirely by single step ionization, whereas in the case of nitrogen, another source of ionization is necessary to account for the plasma production rate. The low pressure EEDF display an isotropic group of ionizing electrons despite the fact that their mean free paths are greater than the chamber dimension. This persistence of rf plasmas at low pressures is also discussed.

Langmuir探針回路系におけるプラズマインピーダンスと電子エネルギー分布関数測定に対する影響

Langmuir探針回路系におけるプラズマインピーダンスと電子エネルギー分布関数測定に対する影響

Time-resolved electron energy distribution function measurements in a pulsed magnetic multipole hydrogen discharge

The time evolution of measured plasma parameters, including the electron energy distribution function (EEDF), in the discharge and post-discharge regime of a pulsed hydrogen magnetic multipole plasma is presented. The time necessary for the plasma to reach equilibrium has been established as 160 μs. The present results clarify the mechanisms which initiate the discharge. The decay rates of the charged-particle density and energy in the post-discharge have been measured. These measurements indicate that particle transport to the wall is the dominant loss mechanism for both charged-particle density and energy. The time-resolved EEDF is found to be non-Maxwellian in the discharge and Maxwellian in the late post-discharge.

Electron-energy distribution function measurements in capacitively coupled rf discharges

Measurements by Langmuir probes have been performed in a capacitively coupled, parallel- plate rf discharge of He and Ar with pressures ranging from 0.1 to 2 Torr and discharge power from 10 to 50 W at 27 MHz. The first part of this paper is devoted to a discussion of the preparation of the electrostatic probe technique, for which a rf discharge is well known to be a very hostile environment, and of its intrinsic limitations, in order to assess the reliability of the measurements. Results showing a marked non-Maxwellian character of the electron-energy distribution function are then presented and discussed in the light of the most recent theories about the sustainment of this kind of gas discharge.

Improved circuit for potential fluctuation compensation in the plasma during the electron energy distribution function measurement by a probe

An improved circuit consisting of a simple voltage follower for the measurement of electron energy distribution function in a plasma has been proposed. This circuit makes it possible to eliminate the fluctuation of plasma space potential, the deviation of dc probe voltage caused by the probe current drawing across the plasma resistance, and the attenuation of the second derivative signal during the measurement, simultaneously. Both the probe circuit considerations and the experimental results are presented.