Oriented films of epitaxial MFI overgrowths

Growth of oriented films of epitaxial MFI overgrowths by the in situ method was studied by SEM, TEM and powder XRD. By using a short hydrothermal treatment, it was possible to grow well-defined, b-oriented ZSM-5 films on polished quartz substrates. It was found that these b-oriented precursor ZSM-5 films grew along the b-axis in an aluminum free silicalite-1 synthesis mixture. Simultaneously, 90° rotational intergrowths formed on top of the b-oriented crystals. Upon further growth in several short synthesis steps, the 90° rotational intergrowths formed an a-oriented silicalite-1 film on top of the first b-oriented film. Only very weak reflections representing other crystallographic planes than (h 0 0) and (0 k 0) are observed by XRD in these samples, which shows that all crystals are a- or b-oriented. Continuous crystals, extending from the support to the top surface of the film was observed by electron microscopy.