Crystal growth of analcime studied by AFM and atomistic simulation

A combined atomic force microscopy (AFM) and atomistic simulation approach affords a high-resolution picture of the structure and surface termination of synthetic analcime and provides insight into the atomic-scale mechanism of crystal growth. AFM measurement reveals a repeated step height of ∼0.6 nm on the {2 1 1} crystal face corresponding to the interlayer separation for the {2 1 1} rather than higher index surfaces, as is observed in, e.g., zeolite A. Analysis of the possible terminating structures for the {2 1 1} face from surface energy evaluations indicates that a unique terminating structure is favoured implying a step height of ∼0.6 nm in accord with the experimental measurement. Analysis of intermediate stages of growth using classical simulation approaches suggests that the mechanism may be mediated purely by monomeric rather than oligomeric species, which contrasts with the presumed secondary building unit mechanism for many zeolitic materials.