Volume 96, Issue 5, 01 September 2004
Index of content:
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
96(2004); http://dx.doi.org/10.1063/1.1768615View Description Hide Description
Chemical oxygen-iodine lasers (COIL) are attractive for diverse industrial applications because they are capable of high efficiency, high power operation, and because the wavelength can be transmitted through fiber optics and couples efficiently with most metals. Conventional COILs are pumped with that is generated by reaction of in a basic solution. Current trends in pumping COILs involve producing the in electric discharges, thereby circumventing the hazards, complexity, and weight associated with pumping and storing caustic liquids. In this work, we have investigated the scaling of yields with specific energy deposition in mixtures in flowing radio frequency (rf) discharges at pressures of a few to tens of Torr using a global plasma kinetics model. We found that yield increases nearly linearly with specific energy deposition in molecules up to a few per molecule, with yields peaking around by . Further increases in specific energy deposition serve only to increase dissociation and gas heating, thereby reducing the yield. We also found that variations in peak yields at a given specific energy deposition are caused by secondary effects resulting from dilution, pressure, and power level. We show that these secondary effects alter the yield by shifting the ratio.
96(2004); http://dx.doi.org/10.1063/1.1769602View Description Hide Description
Molecular dynamics simulations of , , and impacting siliconsurfaces reveal the spontaneous formation of segregated layers of and , formed due to ion impact and ion-induced mixing. The mechanisms of steady-state etching under these conditions involve a leading front of that fluorinates the substrate, followed by a region or zone of . The and layers move through the substrate during steady-state etching. is generally etched from the surface of the layer by an ion impact. Carbon reaction with in the zone raises the total atomic density in the layer to nearly three times the value observed in undisturbed and reduces the etch rate by limiting ion mixing. Etching stops completely if the layer becomes so impervious that ions cannot reach the front. The importance of the depth profile of ion energy deposition in sustaining etching is very clearly observed in the simulations.
96(2004); http://dx.doi.org/10.1063/1.1775301View Description Hide Description
A series of measurements carried out with a point-grid electrode system has clarified that the current-voltage characteristics of the negative corona discharge obey the Townsend relation, further, in which the coefficient is proportional to temperature and the power of the electrode gap independently, and the corona onset voltage is proportional to the product of the reciprocal of temperature and the power of the electrode gap. The empirical formula derived from their relations has estimated negative coronacurrents with an accuracy of for a given parameter set, which will allow application to ion generator design.
96(2004); http://dx.doi.org/10.1063/1.1778474View Description Hide Description
We present the development and application of a versatile finite-element method to discretize direct current and radio frequency (rf) induced plasma-sheath dynamics, using multifluid equations. For the former, argon gas is assumed, and the solution is verified by comparison with a theoretical model obtained from the literature. For rf discharges, partially ionized helium gas is considered between two electrodes coated in a dielectric material. The computed solutions for charge densities, the ion velocity and the neutral gas density and crossflow distributions show expected trends. Specifically, ion and electron number densities at the peak discharge current are compared with published numerical results. The derived electric field is utilized with a simple phenomenological model applicable to the transverse velocity in a one-dimensional situation to predict the anticipated hump in the near wall profile. The next step of extending the model, through future work, to two dimensions and for polyphase supply as implemented in realistic configurations is greatly facilitated by the generality of the chosen finite-element method.