Growth models in microporous materials

Crystallisation pathways in framework materials, such as zeolites, have been monitored using a combination of atomic force microscopy, high-resolution electron microscopy and modelling. The principle conclusions of this study is that many open-framework crystals grow via a layer growth mechanism. The layers have a thickness which is related to the unit cell parameter in the direction of growth. The development of each layer can be sub-divided into a number of individual growth processes including nucleation of a new layer (or terrace), growth at edge sites and kink sites. Modelling of atomic force micrographs yields relative probabilities for these individual growth processes and reveals that growth at kink sites is favoured with nucleation of new terraces the slowest process. The layer mechanisms proposed explain the incorporation of defects in framework structures and further elucidate the role of structure directing agents. (C) 2001 Elsevier Science BN. All rights reserved.