Growth regime diffusion controlled

Similar considerations clearly apply to the ArBs layer if the regime of its growth is diffusion controlled with regard to component A, so that... 

Stage III Nonlinear growth rate (Diffusion controlled regime)... 

Figure 6.2-12 Cyclic voltammogram of 0.1 - 1 mmol dm Geb on gold in dry [BMIMj PFg , starting at-500 mV towards cathodic (a) and anodic (b) regime. Two quasireversible (E, and E2) and two apparently irreversible (E4 and E5) diffusion-controlled processes are observed. E3 is correlated with the growth of two-dimensional islands on the surface, E4 and E5 with the electrodeposition of germanium, Ej with gold step oxidation, and E, probably with the iodine/iodide couple. Surface area 0.5 cm (picture from [59] - with permission of the Peep owner societes).

During growth of the ApBq layer in the diffusion controlled regime, the condition k0Bi k Bfx is satisfied in equations (1.6) to (1.8). In this case, the rate of growth of the layer is inversely proportional to its total thickness, x, existing at a time, t ... 

During its growth in the diffusion controlled regime with regard to component, ... 

Effect of the critical thickness of the ApBq layer with regard to components on the process of growth of the ArBs layer With further thickening the ApBq layer its growth regime becomes diffusion controlled (in the theoretical definition) not only with regard to component... 

Diffusion controlled growth of the ApBq and ArBs layers Increasing the thickness of the ArBs layer will inevitably result in a change of its growth regime from reaction to diffusion controlled with regard to... 

In the diffusion controlled regime the growth of each of two compound layers is due to one partial chemical reaction taking place at its common interface with another growing layer. In this case, only the A atoms diffuse across the ApBq layer adjacent to initial phase A, while only the B atoms diffuse across the ArBs layer adjacent to initial phase B. No partial chemical reactions proceed at the A ApBq and ArBs-B interfaces in view of the lack of appropriate diffusing atoms. 

An unambiguous criterion to distinguish between the growth regimes of any compound layer is the availability or lack of diffusing atoms of a given kind for other layers of a multiphase binary system. Under conditions of reaction (chemical) control these atoms are still available, while under conditions of diffusion control already not, and this is all that is necessary to explain the absence of some part of compound layers from the A-B reaction couple. 

It might seem that the ArBs layer could grow in the A-ApBq-ArBs-AiBn-B system by the same mechanism as in the ApBq-ArBs-B and ApBq-ArBs-A Bn systems, i.e. at the expense of the phase transformation of ApBq into ArBs under the influence of reaction diffusion of the A atoms. However, this is not the case. If the growth regime of the ApBq layer in the A -ApBq-ArBs-AiBn-B system is reaction controlled with regard to component A (x < ), then there is an excess of A atoms in comparison with the... 

Assume that with time the growth regime of the ApBq layer with regard to component A became diffusion controlled (x> x fl), while the ApBq phase was partly transformed into the ArBs one by reaction (4.6). The A atoms released as a result of this transformation cannot, however, cross the ApBq ArBs interface in the A ApBq ArB -A]Bu- B system in the same manner as in the ApBq -ArBs-B or ApBq ArBs-AiB system. Those A atoms will immediately be combined into the ApBq compound at this interface (onto the surface of the ArBs phase from the side of ApBq) by reaction (3.12) which is opposite to reaction (4.6). It is clear that the total result of these reactions is zero. 

---