Surface microtopography Tracht and Habitus

Since dislocations are linear strain fields, if a crystal is treated in an appropriate atmosphere, impurity ions selectively precipitate along the dislocation. These can be detected by infra-red microscopes, and so the method was used to prove the presence of dislocations during the early period of dislocation studies. If a dislocation is decorated by metallic elements, the dislocations act as a resistance against etching, and only the portion apart from dislocations is etched, and decorated dislocations remain as protrusions. The resulting protrusions are etch hillocks. 

Since the edge free energies, y, are different for the vapor and solution phases, and particularly for solute-solvent interaction energies, the same crystal species will exhibit different Tracht and Habitus in different ambient phases and different solvents. If impurities are present in the system, this affects y and the advancing rates of steps. There are two opposite cases in impurity effects, and, depending on the interface state, some will promote growth, whereas others will suppress growth. 

The driving force, Ap,/ cT, affects the advancement rate of steps, as well as the state of the interface. Growth temperature (and pressure) may modify the morphology of growth spiral layers and may affect Tracht and Habitus through the modification of the interface state, but the effect will appear through A/ajkT. 

Crystal Growth andDislocations, London, Butterworths, 1953 

Dekeyser and S.Amefinckx,IesDislocations etIoCroissancedesCristaux, Paris, Masson et Cie,1955 

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