High temperature diffusion

Ceramic—metal interfaces are generally formed at high temperatures. Diffusion and chemical reaction kinetics are faster at elevated temperatures. Knowledge of the chemical reaction products and, if possible, their properties are needed. It is therefore imperative to understand the thermodynamics and kinetics of reactions such that processing can be controlled and optimum properties obtained. 

This is shown as a black circle in Fig. 19. One can draw further inferences if one is willing to apply (20) with the D+ given by the solid line in Fig. 16, i.e., the room-temperature value of Seager and Anderson (1988), interpolated toward the high-temperature diffusion coefficient of Van Wieringen... 

Similarly, at high temperatures, diffusion in a crystal of formula MX by interstitials will reflect the population of Frenkel defects present [Eqs. (2.13) and (2.14b)] as... 

Comparisons with high temperature diffusion studies... 

The activation energies calculated for Rb, Cs and Sr in the present study (Table III and Figure 8) are considerably lower than those calculated for high temperature diffusion in both crystalline and glass silicates. This discrepancy in the latter case implies that the glass matrix may be significantly different in high and low temperature diffusion studies. 

The influence of hydration on alkali metal diffusion rates appears to decrease with ionic ratio as shown by a closer correlation between high-and low-temperature diffusion data (Figure 7) and activation energies (Figure 8) for Rb relative to Cs. Measured Na diffusion coefficients in hydrated obsidian at 25°C can be accurately reproduced by extrapolation of high temperature diffusion rates for nonhydrated obsidian (3) indicating that diffusion rates of smaller ions such as sodium are not affected by the hydration process. 

While the growth of thermal oxides is dominated by high-temperature diffusion of oxygen in the oxide matrix, anodic oxide growth is dominated by field-enhanced hydroxyl diffusion at RT. These different growth mechanisms result in pronounced differences in the morphological, chemical and electrical properties of the oxide. 

Bailey A. (1971). Comparison of low-temperature with high-temperature diffusion of sodium in albite. Geochim. Cosmochim. Acta, 35 1073-1081. 

The thin-source method is also referred to as the thin-film method. One surface is cut into a plane surface and polished. A very thin layer is then sprayed or spread onto the surface. The thin layer contains the component of interest, which at high temperature diffuses into the interior of the sample from the polished surface. After the experiment, a section is cut perpendicular to the polished surface. Concentration profile is measured as a function of distance away from this surface. If the length of the concentration profile is much greater than (> 100 times) the thickness of the thin layer on the surface, the problem may be treated as a... 

Although the radioactive decay constants are independent of temperature and pressure, the retention of the radiogenic daughter in a mineral depends strongly on temperature because at high temperatures diffusivity is high, resulting in... 

At a very low temperature where an adatom jumps only occasionally, about one atomic jump in every few seconds, field ion microscope studies conclude that the surface diffusion of adatoms is consistent with a discrete nearest neighbor random walk. However, in molecular dynamic simulations of diffusion phenomena, which are carried out only for high temperature diffusions where atomic jumps are very rapid, i.e. an atomic... 

Before describing the high temperature diffusion experiments, some properties of the chemisorption layer will be discussed. Changes, including evaporation, are inappreciable below 800°K for fully or partially covered surfaces. At this temperature and above, irreversible changes occur in the... 

High-temperature diffusion-limited current mode cell. 

This problem was addressed by Van Deemter [1], who assumed a constant burning rate to obtain a solution in closed form. Later, Johnson et. al. [2] and Olson et al. [3] treated high-temperature, diffusion controlled burning, where the reaction rate depends only weakly on temperature. Both predicted the propagation of a sharply defined burn front, but neither gave any indication of what might happen at lower temperatures, where chemical reaction rate controls. This case was discussed by Ozawa [4], who showed that oxidation is slow and there is no clear burn front. 

In Section 17.3.2(i) we have indicated a range of uses for polysilicon. For all of these applications there is a need to control layer structure. In addition, careful control of doping levels is also necessary. This can be done with post-deposition doping but this requires a high temperature (typically >900°C) in order to move the dopant atoms from the surface and to drive them into the layer. This high temperature diffusion step can cause thermal damage. One solution is to use in situ doping at the normal temperature of polysilicon deposition i.e., ca. 600°C. 

To avoid reaction between the Si substrate and A1 metallizations during the manufacture of integrated circuits at high temperatures, diffusion barriers are necessary. It has been demonstrated that high crystallization-temperature glasses such as Ta Ir glasses make excellent diffusion barriers in many microelectronics applications. 

In the processes described so far, the resist is removed after etching, baring the patterned oxide that serves as a mask during subsequent high-temperature diffusion of dopants into the exposed silicon substrate. There are examples, however, where the resist material is left behind to become... 

NO in the equilibrium NO mixture at a constantly controlled high temperature diffuses toward the second half of the cavity, where it is oxidized electrochemically to NO2 by the use of an NO conversion electrode (Pt-Rh). Thus, almost pure NO2 can be obtained if the NO conversion efficiency is high. 

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