Junction diffusion

The possibility of measuring a nonequilibrium liquid junction (diffusion) potential by using voltaic cells has been checked also ... 

It will be noted that liquid junction diffusion potentials can be eliminated almost completely by ensuring that the bulk of the current is carried by cations and anions possessing equal mobilities, e.g. KCl or NHiNOg. Thus by inserting a saturated solution of B.s,o. 16... 

Figure 18.1—Electrochemical measurement string using an ion selective (or specific) electrode (ISEJ. The membrane potential varies with the concentration of the specific ion in solution. Other potentials are fixed by the construction of the electrode. The junction (diffusion) potential Ej has a low value and is generally constant. Measurement is typically conducted with an ionometer. Manufacturers also supply combined electrodes that include both electrodes (external and ion selective) in the same device. Commonly employed pH electrodes are of this type. The schematics of combined electrodes are much less clear due to the proximity of the membrane to other electrode components.

The hydrated layer has finite thickness, therefore the exchanging ions can diffuse inside this layer, although their mobility is quite low compared to that in water (n 10-11cm2s-1 V-1). As we have seen in the liquid junction, diffusion of ions with different velocities results in charge separation and formation of the potential. In this case, the potential is called the diffusion potential and it is synonymous with the junction potential discussed earlier. It can be described by the equation developed for the linear diffusion gradient, that is, by the Henderson equation (6.24). Because we are dealing with uni-univalent electrolytes, the multiplier cancels out and this diffusion potential can be written as... 

The gap-junctional diffusion rate constant of Ca and IP3 are denoted respectively by 7c and jp. The subscripts 1 and 2 indicate the concentrations in the first and second cell respectively. The symmetric expression is used for the second cell. 

The influence of triple-junctions upon experimental Ge diffusion profiles (850 to lOOOC) in nanocrystalline Si was investigated using three-dimensional finite element simulations. It was found that triple-junction diffusion was not negligible in nanocrystalline Si made of 40nm wide grains. Ge triple-junction diffusion coefficient could be described by ... 

See also flowing junction, diffusion potential, Luggin probe, Macinnes. 

The liquid junction (diffusion) potential should always be a concern until a cell without transfer is tested. Note that the terms liquid junction potential and diffusion potential are used interchangeably in the literature. Measurement, calculation, and minimization of the liquid junction potential formed at the interface of two solutions are some of the topics to be addressed in this chapter. 

Most of the electrochemical cells have liquid junction (diffusion) potential. The electrochemical cells without transfer are free of it. The example of the electrochemical cell without transfer is the famous Harned cell. 

A.A. Fedorov, M.Y. Gutkin, LA. Ovid ko, Triple junction diffusion and plastic flow in finegrained materials. Scr. Mater. 47(1), 51-55 (2002)... 

Heating is used to alloy the deposited material with the substrate surface. Post-deposition diffusion and reaction can form a more extensive interfacial region and induce compound formation in semiconductor metallization (Figure 9.3). Post-deposition heating and diffusion can be used to completely convert the deposited material to interfacial material. For example, a platinum film on silicon can be heated to form a platinum silicide layer. The diffusion at the interface can be studied by the motion of markers. Post-deposition interdiffusion can result in the failure of a metallized semiconductor device by diffusion and shorting of the junctions. Diffusion can be hmited by using diffusion barriers. Heating plus isostatic pressure may be used to remove voids in semiconductor metallization. 

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