Passivation profiles

SOME MEASUREMENTS OF THE DEVELOPMENT OF ACCEPTOR-PASSIVATION PROFILES BENEATH HYDROGENATED... 

Figure 15 shows the time development of a typical passivation profile (Seager and Anderson, 1988). The integral, from any depth x to infinity, of the amount by which the curve for any given time falls below the asymp-... 

Fig. 16. Panorama of values in the literature for diffusion coefficients of hydrogen in silicon and for other diffusion-related descriptors. Black symbols represent what can plausibly be argued to be diffusion coefficients of a single species or of a mixture of species appropriate to intrinsic conditions. Other points are effective diffusion coefficients dependent on doping and hydrogenation conditions polygons represent values inferred from passivation profiles [i.e., similar to the Dapp = L2/t of Eq. (95) and the ensuing discussion] pluses and crosses represent other quantities that have been called diffusion coefficients. The full line is a rough estimation for H+, drawn assuming the top points to refer mainly to this species otherwise the line should be higher at this end. The dashed line is drawn parallel a factor 2 lower to illustrate a plausible order of magnitude of the difference between 2H and H.

Fig. 15. Typical time development of a passivation profile measured on a gold-silicon Schottky diode by the C-V method during the hydrogenation process (Seager and Anderson, 1988). Ordinate is the net density of fixed negative charge, i.e., B minus H+. Hydrogenation was at constant ion flux, 298 K, and with the gold film held at 3 V positive with respect to the silicon base. The lines are computer-generated fits to the model described in the text.

Fig. 3.22. Depth profile of a passivation layer on high-purity chromium. The 0 layer is on the top, the 0 layer at the interface with the metal.

Technica, 1988 Wheatley, 1988 Ziomas, 1989). Plume dispersion consists of two phases the gravityslumping and passive dispersion period. Continuous releases with any time-profile and puff releases as of short duration continuous releases are treated using the release category and th r... 

According to the depth profile of lithium passivated in LiAsF6 / dimethoxyethane (DME), the SEI has a bilayer structure containing lithium methoxide, LiOH, Li20, and LiF [21]. The oxide-hydroxide layer is close to the lithium surface and there are solvent-reduction species in the outer part of the film. The thickness of the surface film formed on lithium freshly immersed in LiAsF /DME solutions is of the order of 100 A. 

Shuman, C. A., Alley, R. B., Anandakrishnan, S. et al. (1995). Temperature and accumulation at the Greenland Summit Comparison of high-resolution isotope profiles and passive microwave brightness temperature trends. /. Geophys. Res. 100(D5), 9165-9177. 

In this book we will focus on physicochemical profiling in support of improved prediction methods for absorption, the A in ADME. Metabolism and other components of ADME will be beyond the scope of this book. Furthermore, we will focus on properties related to passive absorption, and not directly consider active transport mechanisms. The most important physicochemical parameters associated with passive absorption are acid-base character (which determines the charge state of a molecule in a solution of a particular pH), lipophilicity (which determines distribution of a molecule between the aqueous and the lipid environments), solubility (which limits the concentration that a dosage form of a molecule can present to the solution and the rate at which the molecule dissolves from... 

We have called the plot of log Co versus pH the flux factor profile, with the idea that such a plot when combined with intrinsic permeability, can be the basis of an in vitro classification scheme to predict passive oral absorption as a function of pH. This will be discussed later. 

This article presents a brief account of theory and practical aspects of rotating hemispherical electrodes. The fluid flow around the RHSE, mass transfer correlations, potential profile, and electrochemical application to the investigations of diffusivity, reaction rate constants, intermediate reaction products, passivity, and AC techniques are reviewed in the following sections. 

Figure 28 The biophysical model for passive diffusion and concurrent intracellular metabolism of a drug for a simple A-to-B reaction process. Concentration-distance profiles are depicted in the aqueous boundary layer and intracellular domain for the drug and metabolite. The bottom diagram depicts the direction of the fluxes of drug and metabolite viewed from the donor and receiver sides of the cell monolayer. Details of basic assumptions are found in the text.

The CAT model estimates not only the extent of drug absorption, but also the rate of drug absorption that makes it possible to couple the CAT model to pharmacokinetic models to estimate plasma concentration profiles. The CAT model has been used to estimate the rate of absorption for saturable and region-depen-dent drugs, such as cefatrizine [67], In this case, the model simultaneously considers passive diffusion, saturable absorption, GI degradation, and transit. The mass balance equation, Eq. (51), needs to be rewritten to include all these processes ... 

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