The response of palladium metal-insulator-semiconductor devices to hydrogen-oxygen mixtures: Comparisons between kinetic models and experiment

The operation of hydrogen-sensitive metal-insulator-semiconductor (MIS) devices in the presence of oxygen is described using a detailed model of the surface and interface kinetics. The solution methods developed here build on existing models by considering adsorbed oxygenated species in the interaction between atomic hydrogen at the metal-semiconductor interface and the external surface. The net effect of the adsorbed oxygenated species is to increase the amount of interfacial hydrogen predicted to exist within the structure at equilibrium. These theoretical predictions are compared to computed results from a previously existing model; furthermore, both mechanistic models are analyzed in light of new and previously published experimental response trends for MIS devices. Although the two models considered in this work are each found to be useful in understanding some aspects of the response, elementary reaction mechanisms appear to be inadequate for prediction of response curves. The results of these comparisons suggest that the kinetics for operation of MIS sensors in hydrogen-oxygen mixtures are quite complex, and may be strongly morphology-dependent. Published by Elsevier B.V

Suppression of erosion in the DIII-D divertor with detached plasmas

The ability to withstand disruptions makes carbon-based materials attractive for use as plasma-facing components in divertors. However, such materials suffer high erosion rates during attached plasma operation which, in high power long pulse machines, would give short component lifetimes and high tritium inventories. The authors present results from recent experiments in DIII-D, in which the Divertor Materials Evaluation System (DiMES) was used to examine erosion and deposition during short exposures to well defined plasma conditions. These studies show that during operation with detached plasmas, produced by gas injection, net erosion is suppressed everywhere in the divertor. Net deposition of carbon with deuterium was observed at the inner and outer strikepoints and in the private-flux region between strikepoints. For these low temperature plasmas (T{sub e} < 2eV), physical sputtering is eliminated. These results show that with detached plasmas, the location of carbon net erosion and the carbon impurity source, probably lies outside the divertor. Physical or chemical sputtering by charge-exchange neutrals or ions in the main plasma chamber is a probable source of carbon under these plasma conditions