Oriented growth of ETS-4 films using the method of secondary growth

Oriented growth of polycrystalline ETS-4 films on porous titania substrates was investigated using the method of secondary growth, utilizing synthesis mixtures with compositions of 3.6SiO ₂/1TiO ₂/5.5Na ₂O/xH ₂SO ₄/230.2H ₂O, where x = 4.4 or x = 3.6. Dense seed layers, obtained in situ by hydrothermal synthesis (x = 4.4), were partially (a, c)-out-of-plane oriented. Films were prepared in just one secondary growth step. Films developed by evolutionary, epitaxial growth of seed crystals and were highly (x = 4.4) b-out-of-plane oriented. Highly b-out-of-plane oriented ETS-4 films were also grown from dense, partially b-out-of-plane oriented seed layers on porous a-alumina substrates using identical synthesis mixtures. [Shattuck et al., Microporous Mesoporous Mater. 2006, 88, 56]. These findings suggest that the film orientation is dictated by the secondary growth conditions and is not determined by the seed layer orientation. This was attributed to the highly anisotropic growth rates of ETS-4 and the limited growth space provided by dense seed layers. Overall, these results indicate that by effectively decoupling nucleation from seed crystal growth, and by providing conditions for the fastest growth of crystals along the b-direction in a confined space, it is possible to fabricate highly b-out-of-plane oriented ETS-4 films for advanced applications.