Microwave plasmas sustained at atmospheric pressure, for instance by electromagnetic surface waves, can be efficiently used to abate greenhouse-effect gases such as perfluorinated compounds. As a working example, we study the destruction and removal efficiency (DRE) of SF6 at concentrations ranging from 0.1% to 2.4% of the total gas flow where N2, utilized as a purge gas, is the carrier gas. O2 is added to the mixture at a fixed ratio of 1.2–1.5 times the concentration of SF6 to ensure full oxidation of the SF6 fragments, providing thereby scrubbable by-products. Fourier-transform infrared spectroscopy has been utilized for identification of the by-products and quantification of the residual concentration of SF6. Optical emission spectroscopy was employed to determine the gas temperature of the nitrogen plasma. In terms of operating parameters, the DRE is found to increase with increasing microwave power and decrease with increasing gas flow rate and discharge tube radius. Increasing the microwave power, in the case of a surface-wave discharge, or decreasing the gas flow rate increases the residence time of the molecules to be processed, hence, the observed DRE increase. In contrast, increasing the tube radius or the gas-flow rate increases the degree of radial contraction of the discharge and, therefore, the plasma-free space close to the tube wall: this comparatively colder region favors the reformation of the fragmented SF6 molecules, and enlarging it lowers the destruction rate. DRE values higher than 95% have been achieved at a microwave power of 6 kW with 2.4% SF6 in N2 flow rates up to 30 standard l/min.

Various microwave-sustained, atmospheric-pressure plasma torches have been developed, investigated and applied over the last few decades. To avoid some of their shortcomings, we have designed a novel torch termed TIAGO (Torche à Injection Axiale sur Guide d'Ondes, in French). Its main advantages are simplicity, smooth impedance matching (low sensitivity to changes in operating conditions) and a short gas channel to prevent vapour condensation. Furthermore, it is possible to arrange TIAGOs in arrays to form a compact torch system which can be supplied, with equal distribution of power between plasma flames, from a single waveguide. This unique feature makes the new device particularly suitable when high gas throughputs or sequential processing are required. We describe the design, electrodynamic characteristics and experimental investigation of various torch arrangements based on the TIAGO principle, operated at 2.45 GHz with powers of a few hundred watts up to 2-3 kW per nozzle.

Large diameter (>10 mm) microwave discharges at atmospheric pressure are often constricted transversely and, when large gas flow rates are used, unstable as far as microwave power coupling is concerned. A group of small bore tubes can be used instead to provide the same gas throughput and ensure a higher probability of interaction of molecules to be processed with the carrier gas. The solution presented provides equal power sharing in these small diameter plasma columns and it employs preferably a single microwave field applicator, therefore enabling one to use only one power generator and yielding a compact system. This scheme is based on the properties of surface-wave sustained plasmas and it calls on basic principles of waveguide circuitry.

Interfacial degradation induced by hot-electron injection has been studied in n-channel metal oxide semiconductor transistors with channel lengths down to 0.2 μm. The devices were annealed in either H2 or D2 containing atmospheres. The channel transconductance and threshold voltage variations induced by hot-electron injection into the gate are consistent with interface state generation. Charge pumping experiments confirm this conclusion. The lifetime for a 10% reduction in the transconductance is enhanced by ∼10 times for devices annealed in D2 containing atmospheres as compared to those annealed in H2.

A self-consistent model describing a microwave discharge with radial energy input is proposed to simulate electromagnetic field, radiative transfer, photoionization processes, plasma chemical reactions, heat transfer and hydrodynamics. The model is implemented for the case of discharges in neon and argon; the relevant kinetic data for these gases are collected and supplemented. Self-consistent simulation has shown that the electromagnetic field and the plasma configuration do not correspond to the widely used surface-wave approach.