Abstract
Mechanism of MFI film growth from seed crystals and evolution of defects during the film growth were investigated. The hydrothermal growth of colloidal silicalite-1 crystals of 50nm on silicon substrate was used to reveal the MFI film formation mechanism at different time intervals using high resolution-transmission electron microscopy (HR-TEM) and extreme high resolution-scanning electron microscopy (XHR-SEM). It was found that the MFI seeds started to grow in the early stages of hydrothermal treatment from 50nm to 75nm in size and connect to the crystals in the vicinity, showing the onset of film formation. The film growth mechanism was led by the sub-colloidal particles in the synthesis solution arriving at the crystal surfaces contributing to the film growth. A continuous film with a thickness of 100nm was formed after 12h of hydrothermal treatment containing pinhole defects. Pinhole defects disappeared after 24h of hydrothermal treatment with a film thickness of 200nm and grain boundaries thickness of 2nm were formed. Furthermore, mesoporous defects were found in the grains of the film, which appeared due to the film growth by sub-colloidal particles of synthesis solution. The growth rate of the MFI film was calculated to 0.007 (μm/h) and compared with the crystal growth inside the synthesis solution.
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