Crystal growth of lepidocrocite and magnetite under Langmuir monolayers

Thin films of lepidocrocite (gamma-FeO(OH)) and magnetite (Fe3O4) formed by supplying NH3 gas to a FeCl2 solution through an appropriate Langmuir monolayer were studied by X-ray diffraction analysis and transmission electron microscopy. No crystals were deposited at the air/water interface without a monolayer. However, a (0 1 0) preferentially oriented gamma-FeO(OH) thin film was deposited under a stearyl alcohol monolayer at the beginning of the crystal growth, and later turned into a non-oriented Fe3O4 particulate film. The molecular arrangement of a stearyl alcohol monolayer and the ionic arrangement of the (0 1 0) plane of gamma-FeO(OH) match geometrically well with each other, indicating that a stearyl alcohol monolayer worked as a template for epitaxial growth of a (0 1 0) oriented gamma-FeO(OH) thin film, while the dissolution-precipitation reaction prevented the templating effect resulting in the formation of a nonoriented Fe3O4 particulate film. (C) 1998 Elsevier Science B.V. All rights reserved.