Crystal nucleation is a fundamental process relevant to materials synthesis, biomineralization, and environmental geochemistry. The growth of gibbsite [Al(OH)<sub>3</sub>] films on the basal surface of muscovite mica is an excellent model system for probing crystal nucleation questions. Nagy et al. (1999) observed preferred orientation of gibbsite crystals grown on muscovite using Tapping Mode AFM and powder diffraction. Using specular crystal truncation rod (CTR) analysis of muscovite surfaces reacted with AlCl<sub>3</sub> aqueous solutions, Lee et al. (2016, 2019) observed the growth of thin films and deduced they were gibbsite-like in nature based on atomic layer spacing, the structural similarity of gibbsite and muscovite octahedral Al sheets, and the close match of the a and blattice parameters of the two minerals. Legg et al. (2018) have recently shown the nucleation and growth of such films can be directly imaged using high-speed, sub-nanometer resolution atomic force microscopy (AFM). However, neither AFM nor specular CTR can identify epitaxy between film and substrate or the three-dimensional, atomic scale structure of the films. Using off-specular CTR, we have investigated the structures of these films in three dimensions. Monolayer-thick sheets of gibbsite cover up to 60% of the muscovite surface, and are laterally registered to the substrate in three distinct structural domains. Additional atomic layers observed with specular CTR suggest populations of gibbsite-like particles that are laterally-unregistered with respect to bulk muscovite and that cover an additional 10% of the surface.

Epitaxial growth of gibbsite sheets on the basal surface of muscovite mica

2019 Fall National Meeting

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