Crystal Growth Studies on Microporous Zincophosphate-Faujasite Using Atomic Force Microscopy

Abstract

In this paper we report the first in situ atomic force microscopy study on the crystal growth of zincophosphate-faujasite (ZnPO-FAU). Results show that growth at low to moderate supersaturation conditions takes place by a birth-and-spread and/or spiral growth mechanism. At medium-to-high supersaturation conditions, growth starts preferentially at crystal edges and corners forming macrosteps with a height of several nanometers that advance toward the center of the crystal. This behavior may be explained by nucleation inhibition on the crystal surface due to surface reconstruction and impurity adsorption after synthesis. ZnPO-FAU crystals were found to be metastable at the experimental conditions (25 °C, 1 atm) as initial growth slowed down considerably during the duration of the experiment and was then followed by the dissolution of the crystals and the precipitation of a new phase. Linear defect formation, due to low angle dislocations, was also imaged for the first time and was found to be commonplace in the system. Defect formation was linked to the embedding of microcrystals of the same phase as growth takes place. Owing to the low angle nature of the misfit crystals were able to “heal” themselves after multiple layers have grown.