IONIC OSMOTIC EFFECTS INCREASE FLUID FLOW DURING PERMEATION TESTS

Fluid flow is essential for the transport of metabolites to, from and within the intervertebral disc (IVD). By applying quadriphasic mixture theory experimentally, this study relates fluid flow within the bovine nucleus pulposus (NP) to the applied fluid pressure gradients and fixed charge and mobile ion concentration gradients. 24 plugs of NP tissue (diameter 10 mm, height 1020 ± 122 μm (mean ± SD)), orientated in the axial direction, were harvested from bovine tail discs. The plugs were permeated with either; 0 M NaCl , 0.15 M NaCl or 3 M NaCl solutions by subjecting them to 30, 45 and 60 kPa fluid pressure gradients applied in a random sequence. The hypertonic solution was assumed to render all non-fluid pressure gradients negligible, whilst the hypotonic solution was assumed to render the mobile ion concentration gradient negligible. The effects of these gradients on fluid flow were expressed as a percentage of the applied fluid pressure. Fluid velocity was significantly increased through the tissue in the isotonic case compared to the hypertonic case by up to 55% of the applied fluid pressure. The fixed charges accounted for between 26% and 43% and the mobile ion gradient responsible for 12–26% of this increased fluid flow. These results highlight the importance of using a constitutive equation for permeability that includes mobile ions and fixed charges as separate phases when modeling cartilaginous tissue in order to better describe fluid flow, and thus convective transfer of metabolites, within the tissue.

Gate Oxide Damage in Dry Photoresist Stripping Environments

ABSTRACTThe effect of oxygen plasma stripping environments on the electrical properties of thin oxides has been studied. A barrel, parallel plate and downstream stripper are compared. Damage, measured by shifts in flatband voltage (Δ Vfb), increases in the density of interface traps (Dit), and degradation in minority carrier lifetimes, was observed in all plasma processed samples. Plasma treated wafers had 10–100 fold increases in Dit but recovered to nearly control levels after a 450 °C anneal. ΔVfb and lifetimes did not recover in all cases. Mobile ion contamination dominated in the high temperature (≥ 250 °C) downstream stripping tool. The mobile ion concentration was halved by decreasing the process temperature in the downstream etcher. Ion bombardment-induced damage appears to be most important in the parallel plate configuration. Lifetime results were poor for wafers etched in an unshielded barrel reactor and did not recover after anneal. Use of an etch tunnel improved results to control levels. Degradation of minority carrier lifetimes measured using the photoconductivity technique correlated well with changes in Vfb and Dit. This measurement provides a simple method for evaluating plasma-induced damage.