Towards an optimal antenna for helicon waves excitation

Helicon sources are known to produce high-density plasmas and have found many applications. Different types of antenna have been used for helicon excitation but none of them generate a radio-frequency (rf) field that matches the helicon wave field determined by the dispersion equation. We show that this match can be obtained to a very good approximation by using a birdcage type antenna. Our plasma experiments show that a helicon regime with electron densities up to 5x10(12) cm(-3) is obtained for very low rf power injection (typically 200 W), and at an unusual operating pressure up to 25 Pa

Plasma generation by inductive coupling with a planar resonant RF network antenna

A planar antenna operating at 13.56MHz is presented for potential applications in plasma processing. It consists of interconnected elementary resonant meshes composed of inductive and capacitive elements. Due to its structure, the antenna exhibits a set of resonant modes associated with peaks of the real input impedance. Each mode is defined by its particular distribution of current and voltage oscillating at the frequency of the mode. A rectangular antenna of 0.55m x 0.20m has been built and first results obtained with argon plasmas are presented. Efficient plasma generation is shown by plasma densities above 3 x 10(17) m(-3) at 2000 W with reasonable uniformity over the antenna area. The plasma couples inductively with the resonating currents flowing in the antenna above a threshold power of about 60 W. The real input impedance at antenna resonance avoids the problem of strong reactive currents and voltages in the matching box and RF power connections associated with conventional large-area plasma sources. Resonant RF networks have a strong potential interest for various designs of plasma sources

Current-induced magnetization switching in pseudo spin-valves

The spin transfer torque model applied in the context of a Fokker-Planck analysis (Li and Zhang 2004 Phys. Rev. B 69 134416) is shown to account for a complete set of statistical data for switching times obtained with pseudo spin-valves (Fabian et al 2003 Phys. Rev. Lett. 91 257209). Current densities of the order of 10(7) A cm(-2) injected in Co/Cu/Co bilayers electrodeposited in nanoporous membranes gave rise to magnetization switching. Statistics could be accumulated on one single nanowire at a time: the field at which the average residence times in parallel and antiparallel configurations were equal, these times as a function of current, and the ratio of the times as a function of current and field

RF bias to suppress post-oxidation of mu c-Si:H films deposited by inductively-coupled plasma using a planar RF resonant antenna

One challenge for microcrystalline silicon (mu c-Si:H) deposition is to achieve high deposition rates while maintaining high quality films. In this work, an inductively-coupled plasma (ICP) is used to deposit mu c-Si:H on glass substrates by means of a novel planar resonant antenna at 13.56 MHz. No particle formation occurs in the low pressure (5 Pa) plasma, but the films suffer post-oxidation. By embedding a 5 MHz RF-biased substrate, films deposited simultaneously with and without RF bias are compared. It is shown that large area, low pressure (5 Pa), particle-free ICP deposition at 1 nm/s of mu c-Si:H films can be obtained without post-oxidation by means of a planar resonant antenna, provided that RF substrate bias is included for independent control of the ion energy. (C) 2017 Elsevier Ltd. All rights reserved

Laser-aided plasma diagnostics of a helicon plasma source for fusion neutral beams

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