In order to extend the operating range of the GEC RF Reference Cell, we developed an inductively coupled plasma source that replaced the standard parallel-plate upper-electrode assembly. Voltage and current probes, Langmuir probes, and an 80 GHz interferometer provided information on plasmas formed in argon, chlorine, and nitrogen at pressures from 0.1 Pa to 3 Pa. For powers deposited in the plasma from 20 W to 300 W, the source produced peak electron densities between 1010/cm3 and 1012/cm3 and electron temperatures near 4 eV. The electron density peaked on axis with typical full-width at half maximum of 7 cm to 9 cm. Discharges in chlorine and nitrogen had bimodal operation that was clearly evident from optical emission intensity. A dim mode occurred at low power and a bright mode at high power. The transition between modes had hysteresis. After many hours of high-power operation, films formed on electrodes and walls of one Cell. These deposits affected the dim-to-bright mode transition, and also apparently caused generation of hot electrons and increased the plasma potential.
A "reference cell" for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.
Electron densities were measured in continuous and pulse-modulated, 13.56-MHz, helium and argon discharges. These measurements were made in a symmetrically driven Gaseous Electronics Conference Reference Cell. Pulse modulation of the applied potential allowed observation of the time required for the electron density to achieve steady state. In general, helium discharges reached steady state in approximately 1.5 ms, taking three to ten times longer than argon discharges under similar operating conditions. As much as a threefold increase of the electron density was observed in the afterglow of a pulse-modulated helium discharge, indicative of large metastable densities. Absorption spectroscopy was used to measure the helium singlet and triplet metastable densities throughout the volume of the discharge. For a 1.0-Torr discharge, helium triplet metastable densities at the center of the discharge were as large as 2.5×1011 cm−3 while the peak singlet density was 3.0×1010 cm−3. The steady-state electron density varied from 3.8×1010 cm−3 at 50 V to 2.3×1011 cm−3 at 200 V for the 1.0-Torr helium discharge.
A method for measuring the interactions of dust particles within a two-dimensional (2D) layer in a plasma is presented, along with the use of dust as a probe for determining plasma presheath electric fields. Particle interactions were directly determined from the lateral compression of two-dimensional plasma dust crystals confined in a parabolic potential well. The shape of the parabolic potential well was confirmed by observing trajectories of single particles falling within the well. Particle trajectories were in good agreement with values calculated using gas temperatures derived from laser-induced-fluorescence measurements of the argon metastable velocity distributions and assuming diffusive gas scattering. Measured particle separations combined with an equation of state for the crystal were used to derive values for the plasma screening length and the charge on the particles. Screening lengths and charges were measured for a range of plasma power, pressure, and particle diameter (mass). Analysis of the particle heights and charge were used to derive the time-averaged electric fields at the edge of the rf driven plasma sheath. Measured electric fields were between 5 and 22 V/cm. For smaller particle diameters, the ion wind force was comparable to the force of gravity. These measurements showed that the particles are confined to the bulk-plasma side of the classical Bohm point.
Laser excitation of helium singlet Rydberg states results in fluorescence emanating from many other states including those in the triplet system. By monitoring this fluorescence, it is possible to observe the Stark broadening of the Rydberg states in the presence of an electric field. This technique can be used to measure electric fields in 13.56 MHz parallel-plate discharges with a high degree of spatial and temporal resolution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.