The presence of a solvent

The attachment energy must be corrected by quantity AEfK to account for the influence of the solvent that can be more or less adsorbed on the crystal [TER 01].

Morphological importance and cleavage

Frequently (but this is not an absolute rule), the depth of the minimum interaction potential between two molecules is a decreasing function of the distance separating the two molecules when this minimum is reached. Figure 2.3 is a schematic of this.

Aspect of the minimum potential according to the intermolecular distance

Figure 2.3. Aspect of the minimum potential according to the intermolecular distance

In other words:

We can apply the same logic to write out:

This is to say that, if the interplanar distance dhkl corresponding to the direction of Miller’s indices h, k, l decreases, then the attachment energy increases.

Of course, the easy cleavage planes are those for which Efix is weak, that is for which dhkl is high.

Indeed, we have seen that (see section 2.2.1):

If Efix increases, then the growth rate R increases.

However, according to relationship [2.1]:

If dhkl decreases, then R increases

Moreover, inversely:

If dhkl increases, then R decreases and the morphological importance MI increases.

The morphological importance of a face is consequently an increasing function of the interplanar distance. However, we have seen that the greater the value of dhki, the easier the occurrence of cleavage.

In conclusion, planes of high morphological importance are planes of easy cleavage [BRA 66].

Energy aspect and kinetic perspective

The attachment energy calculation for a layer is performed at the atomic level only by highly specialized research departments. Moreover, Hartmann and Bennema’s theory [HAR 80] only concerns crystallization obtained from a low-pressure vapor. For this reason, we will now consider the kinetic growth theories that provide analytical explanations for growth R and whose parameters can be readily adapted according to experimental results.

< Prev   CONTENTS   Source   Next >