Low-power RF Plasma Research Articles

Physical Properties of a Low-Power Helicon Source Operating on a High-Frequency Discharge with a Capacitive Component

The results of an experimental study of a low-power RF plasma source placed in a longitudinal magnetic field (helicon thruster), when it operates on a capacitive RF discharge and inductive RF discharges with a capacitive component, are presented. A significant dependence of the characteristics of the ion and electron fluxes of the source on the induction of a constant magnetic field is shown. The fundamental applicability of capacitive RF discharge as a working process in the studied plasma source is demonstrated. It is shown that the increase in the average energy of ions in the flow at the outlet of the source with the appearance of the capacitive component of the discharge is slight.

Hierarchical selective membranes combining carbonaceous nanoparticles and commercial permeable substrates for oil/water separation

Developing a simple and scalable method to create effective oil–water separation membranes and achieving optimal trade-off between its permeability and selectivity are current challenges in membrane technology for oil from water recovery. Herein, new highly hydrophobic/superoleophilic membranes (contact angles of ~143°/~0°) which meet these challenges have been obtained via a one-step process. Metallic meshes, polypropylene non-woven and cotton fabrics were exposed to low power RF-plasma of commercial grade acetylene at room temperature and medium vacuum. This way, plasma polymerized nanoparticles (NPs) were deposited over the substrates. The as-obtained membranes completely prevent the passage of water while allowing a maximum oil flux over 10,000 L m−2h−1 at 116 Pa, achieving an efficiency above 99% and reusability maintaining high performance. By controlling the mass surface density of the NPs deposit, it is possible to change both the membranes water breakthrough pressure and oil permeation speed. Membrane permeabilities were successfully obtained by fitting permeated oil volume vs time data with a Darcy-based model. The influence of surface density of NPs on the permeability and water pressure resistance was described with empirical equations. From the combination of these mathematical relations it is possible to design membranes with optimal trade-off between water pressure resistance and oil permeation speed according to the usage conditions.

Nanocrystalline silicon films prepared from silane plasma in RF-PECVD, using heliumdilution without hydrogen: structural and optical characterization

The effect of RF power on the nanocrystallization of a Si:Hnetwork has been studied by PECVD at a substrate temperature of200 °C and a gas pressure of 0.5 Torr, using silane as the source gas and helium as diluent, withoutusing hydrogen. Optical characterization of the films has been done by UV–vis spectroscopy.Structural characterization has been performed by infrared absorption, x-ray diffraction,micro-Raman studies and electron microscopy by HRTEM and FESEM. In general, astructural transformation from the amorphous to nanocrystalline phase accomplished bymetastable helium atoms in the plasma has been identified at a low RF power of 80 W.With an increase in the applied RF power up to 150 W, systematic improvement incrystallinity has been shown as depicted by increased crystalline volume fraction(∼77%), smaller grain size(∼7 nm) reduced bondedhydrogen content (∼8 at.%), enhanced polymerization in the network and gradual widening in the optical gap(∼1.86 eV) obtained at ahigh deposition rate (107 Å min−1), using 1 sccm of silane as the source gas and helium as the only diluent. He dilution of theSiH4 plasma is a well-proven approach to increase the growth rate. However, a nanocrystallinenetwork with high crystalline volume fraction and well-aligned crystallographic latticedistribution, attained in Si:H from a low-power RF plasma at a growth temperature as low as200 °C, and that obtained from purely He dilution, without usingH2, is being reported for the first time. The striking feature comprises that nc-Si:H films ofincreasing crystalline volume fraction, reduced bonded hydrogen content and wider opticalgap are produced with simultaneously increasing deposition rates, which deserves extensivetechnological impact.

Low-power inductive RF plasma sources for technological applications

The objective of the present paper is to develop an analytic theory of cylindrical low-power RF plasma sources operating at an industrial frequency (f=13.56 MHz, ω=8.52×107 s−1). Inductive surface exciters of electromagnetic fields (exciting antennas) are considered that are positioned either at the side surface of the cylinder or at one of its end surfaces. In the latter case, the plasma flows out of the source through the opposite end surface of the cylinder. A study is made of elongated systems in which the length L of the cylinder exceeds its diameter 2R and of planar disk-shaped systems with L<2R. Simple analytic expressions are derived for electromagnetic fields excited by the antenna in the source plasma. The equivalent plasma resistance and the equivalent RF power deposited in the plasma are calculated for systems with prescribed parameters, i.e., in a non-self-consistent model. Up to now, such sources have been investigated mainly through the numerical solution of the complicated general electrodynamic equations. In the Introduction, the problem is formulated in general terms and the geometry of the sources, as well as the characteristic parameters of the source plasma, is discussed. In Section 2, plasma sources operating without an external magnetic field are investigated. In Section 3, helicon plasma sources in a sufficiently strong external magnetic field are considered. Analytic predictions are compared with the results from solving the problem numerically without using the helicon approximation. Section 4 gives a brief discussion of an electron cyclotron resonance-based RF plasma source. In the Conclusion, the main results of the paper are summarized and the technological efficiency of the sources under consideration is estimated at a qualitative level.

Low-power RF plasma sources for technological applications: II. plasma sources under anomalous skin effect conditions

A theory of a planar disk-shaped RF plasma source under anomalous skin effect conditions is developed. In the absence of an external magnetic field, such conditions are satisfied for transverse electromagnetic waves with phase velocities below the electron thermal velocity, and, in the presence of this field, they are satisfied for electron cyclotron waves with frequencies corresponding to the resonant absorption line. For each of these cases, the RF field power deposited in a plasma with given parameters is determined and the equivalent plasma resistance is calculated.

Low-Power RF plasma sources for technological applications: III. helicon plasma sources

The third part of the paper is devoted to an investigation of the so-called helicon plasma sources. These are RF devices operating with a relatively weak external magnetic field, which is, at the same time, strong enough for the resonant electron gyrofrequency to be much higher than the industrial frequency (ω=8.52×107 s−1). As in [1, 2], a study is made of elongated cylindrical plasma sources in a longitudinal (directed along the cylinder axis) magnetic field and planar disk-shaped plasma sources in a transverse (perpendicular to the plane of the disk) magnetic field. A comparison of the present results with the results that were obtained in [3] without using the helicon approximation leads to the conclusion that elongated helicon sources hold great promise for plasma technologies.

Low-power rf plasma sources for technological applications: I. Plasma sources without a magnetic field

A general analytical theory is developed and numerical simulations are carried out of cylindrical plasma sources operating at an industrial frequency of f=13.56 MHz ω=8.52×107 s−1). Purely inductive surface exciters of electromagnetic fields (exciting antennas) are considered; the exciters are positioned either at the side surface of the cylinder or at one of its end surfaces. In the latter case, the plasma flows out of the source through the opposite end of the cylinder. A study is made of both elongated systems in which the length L of the cylinder exceeds its diameter 2R and planar disk-shaped systems with L<2R. The electromagnetic fields excited by the antenna in the plasma of the source are determined, and the equivalent plasma resistance, as well as the equivalent rf power deposited in the plasma, is calculated.

Plasma ignition schemes for the Spallation Neutron Source radio-frequency driven H− source

The H− ion source for the Spallation Neutron Source (SNS) is a cesiated, radio-frequency driven multicusp volume source which operates at a duty cycle of 6%. In pulsed rf driven plasma sources, ignition of the plasma affects the stability of source operation and the antenna lifetime. We report on ignition schemes, based on secondary electron generation by UV light, a hot filament, a low power rf plasma (cw, 13.56 MHz), as well as source operation solely with the high power 2 MHz rf. We find that the dual frequency, single antenna scheme is most attractive for the operating conditions of the SNS H− source.

Evaluation of a radio frequency plasma for oxygen‐selective detection in capillary gas chromatography

AbstractA radio frequency plasma detector for capillary GC has been modified for oxygen‐selective detection. Purification of the plasma gas and purging of both ends of the discharge region with helium were crucial to minimizing oxygen background emission from impurities in the plasma. With a pure helium plasma, eluting hydrocarbons released oxygen from the discharge region resulting in interfering signals on the oxygen channel. These interfering signals were efficiently reduced by using a methane‐doped (0. 15%) low power RF plasma (15 W) sustained in a high make‐up flow (150 mL/min). With this plasma, a 103:1 oxygen‐to‐carbon selectivity and a 100 pg oxygen/s detection limit were obtained. The detector was linear over three orders of magnitude. The detection system has been used to screen for oxygenated compounds in two environmental samples.

Effect of plasma exposure on the performance of indium tin oxide/InP solar cells prepared by radio-frequency and ion-beam sputtering

Previous work has shown that the performance of p-type single crystal/n-type thin film indium tin oxide (ITO) solar cells, can be enhanced by exposing the substrates (InP) to a very low power rf plasma prior to deposition of the ITO and by depositing the ITO very slowly. The mechanism underlying this enhancement is the subject of this experimental investigation. The principal variables studied were the duration of the low power plasma exposure (LPPE), the doping density of the substrate, and the methods of depositing the ITO. Comparison of the cells has been made on the basis of their current/voltage characteristics and their quantum efficiency. The analysis is consistent with there being a thin n-type layer at the interface between the InP and the ITO. For the ion-beam deposited ITO, the n-type layer is vanishingly small but for the rf deposited cells it is 70–100 Å thick; the thickness reducing with longer LPPE. The thickness of this layer appears to control the device performance; the cells with thicker layers have much larger open-circuit voltage and somewhat lower currents, whereas the reverse is true for thinner layers.