Total pressure

About: Total pressure is a research topic. Over the lifetime, 5199 publications have been published within this topic receiving 66658 citations.

Kinetics of Thermal Growth of Ultra‐Thin Layers of SiO2 on Silicon I . Experiment

Abstract: The rate of formation of very thin films thermally grown on [111] and [100] oriented silicon wafers was studied using ellipsometry to measure oxide thickness. Film thicknesses from 10–300Aa were obtained by varying oxidation time, oxidation temperature (700°–1000°C), and oxygen concentration in O2‐N2 mixtures at 1 atm total pressure. The applicability of ellipsometry for such a study is discussed. Reproducibility of oxide films grown to thicknesses of 20–30Aa was approx. ±1.0Aa. Under otherwise equal conditions the oxide thickness grown differs for [100] and [111] oriented wafers. The pressure and temperature dependence of the linear rate constant, klin, show that the growth reaction is more complicated than was suggested earlier. In particular, a different pressure dependence for the two substrate orientations used indicates that several oxygen species participate in the rate determining steps.

Dynamic pressure method for kla measurement in large-scale bioreactors.

Abstract: A dynamic method is proposed for kla measurement in aerated and agitated reactors, in which a change in the total pressure in the reactor by approximately 20% leads to a simultaneous change in the oxygen concentration in all the bubbles in the dispersion. This procedure suppresses the influence of nonideal mixing of the gas phase on the kla value. Other dynamic methods so far used do not possess this advantage. They are based on a step change in oxygen concentration in the entering gas, where the interfacial nitrogen transport and the finite rate of the concentration change propagation into the individual bubbles in the dispersion can cause an error in the reported kla values of more than hundreds of percent. The reliability of the pressure method is tested by comparison both with the standard dynamic method, in which pure oxygen is absorbed in a liquid from which all other gas components were previously removed, and with the steady-state sulphite method. The signal of the oxygen probe used in the experiments must be independent of the pressure. A test for this in dependence is described. The pressure method is also suitable for large-scale reactors since the necessary pressure changes are sufficiently small and, morever, air can be used.

Blast waves with cosmic-ray pressure

Abstract: The effects of cosmic-ray pressure on the dynamics of self-similar, spherical blast waves and driven waves are investigated on the assumptions that the ratio of relativistic cosmic-ray pressure to total pressure at the shock front is a constant w and the the cosmic rays and thermal gas evolve as independent adiabatic fluids in the postshock flow. For blast waves from a point explosion in a uniform medium, the cosmic rays dominate the pressure near r = 0 if w>0. The solutions show that, if w is small, the ratio of cosmic-ray energy to total energy in the blast wave is several times w. The solutions are used to make specific predictions of the pion-decay ..gamma..-ray flux from a blast wave as a function of w. If w is large, the predicted fluxes from supernova remnants are close to the current observational limits. It is also noted that cosmic rays may limit the compression in the radiative shock waves of supernova remnants. The addition of cosmic pressure does not change the geneal nature of the driven wave self-similar solutions. The solutions are used to predict the pion-decay ..gamma..-ray flux from a young Type II supernova interacting with circumstellar material. Observations thesemore » ..gamma..-rays from extragalactic supernovae are not promising, but a galactic supernova could be very bright in ..gamma..-rays.« less

A Mathematical Model of the Hydrodynamics and Gas‐Phase Reactions in Silicon LPCVD in a Single‐Wafer Reactor

Abstract: A mathematical model has been developed for the fluid dynamics and the chemical reactions in silicon low pressure chemical vapor deposition (LPCVD) from silane in a cold-wall single-wafer reactor. The fluid dynamics model includes the mass, momentum, heat, and species balance equations and equations for multicomponent (thermal) diffusion. The chemical model includes five reversible homogeneous reactions and five heterogeneous deposition reactions. The equations are solved numerically using a control volume based finite difference method. The mathematical model has been used to simulate silicon growth on large (0.24 m) wafers, at varying pressures, wafer temperatures, and silane concentrations in different carrier gases. It was found that both the fluid dynamics and the chemical kinetics have a large influence on the predicted growth rates. At conventional LPCVD process conditions gas-phase reactions are negligible, and deposition is very uniform, but the growth rate is low. An increase in the wafer temperature leads to an increased growth rate, whereas uniformity is still very good. Increasing the total pressure or the silane partial pressure leads to an increased importance of gas-phase reactions and highly deteriorated uniformity. The model predictions were found to be relatively insensitive to most of the model parameters.