Nanoscale crystal orientation in silicalite-1 films studied by grazing incidence X-ray diffraction

The structural evolution of nanoscale MFI type zeolite films was studied with grazing incidence diffraction using synchrotron X-ray radiation. The films were obtained via assisted adsorption of nanosize MFI seed crystals, followed by calcination and hydrothermal synthesis on top of the seed layers. The diffractograms of the multilayer adsorbed and grown zeolite films at different incident and exit angles reflect the distribution of the crystal orientation along the film thickness. The adsorbed multilayer of seed crystals has a fairly rough surface and randomly oriented crystals, compared to the thicker film obtained after additional hydrothermal growth. With increasing zeolite film thickness, the surface becomes smoother and most of the crystals show preferred orientation with the b-axis close to perpendicular to the substrate surface. The average diameter of the crystallites was estimated in both adsorbed and grown films based on the broadening of the Bragg peaks, in good agreement with electron micrographs. (C) 2001 Elsevier Science B.V. All rights reserved.