Oriented Molecular Sieve Films by Heteroepitaxial Growth
Hae-Kwon Jeong, John Krohn, Khristina Sujaoti and Michael Tsapatsis
Univ. of Massachussetts at Amherst, US
Keywords: Molecular Sieve, Oriented films, heteroepitaxial growth, Titanosilicate
Potential uses of crystalline molecular sieves as selective membranes, membrane reactors, chemical sensors, optical devices as well as in other new applications rely on the ability to grow them as films.1-12 The crystallinity of these materials along with being a main advantage imposes demanding challenges for film fabrication.3 It is well recognized that these challenges include the control of preferred orientation that is important for two main reasons. First, for some framework structures, preferred orientation can be reflected in the transport and other (e.g., optical, electronic) properties of the film.4 Second, as it was shown recently for the case of MFI, different orientations can result in differences of the grain boundary structure which in turn influences the overall performance of a film, especially in membrane applications.10,12 Many studies have attempted to achieve preferred orientation in molecular sieve films, in situ method 7,13 and secondary growth technique.8-18 However, the success is still limited by available shapes/sizes and deposition20 methods of seed particles and by constraints in adjusting the growth velocities of crystal planes in a given molecular sieve.
In this talk, we will demonstrate the formation of a preferentially oriented film of one molecular sieve (ETS-10) filling the space in between pre-oriented needles of another (ETS-4) by heteroepitaxial growth. This novel method is expected to extend the secondary growth method to other molecular sieve types and orientations. For example, zeolite beta (BEA) is known to grow by a similar epitaxial relation on SSZ-31 needles.19 Based on the method presented here, b-/or a- out-of-plane-oriented zeolite beta films could be grown on c-out-of-plane oriented films of SSZ-31. More interestingly, the orientation of molecular sieve membranes fabricated by heteroepitaxial growth can be adjusted by changing the orientation of the precursor layers. For example, a c-oriented ETS-10 membrane could be fabricated on an a-oriented ETS-4 precursor layer.
NSTI Nanotech 2003 Conference Technical Program Abstract