Characterization of molecular linkages placed between zeolite microcrystal monolayers and a substrate with X-ray reflectivity

We prepared silicalite-1 microcrystal (MC) monolayers on a Si wafer using two different types of molecular linkages, namely, through chloropropyl (CP) groups and through CP/polyethylene imine/CP groups. Whereas the scanning electron microscope images of the two MC monolayers look very much alike but hardly give any information on the nature of molecular linkage between the monolayers and the substrate, their reflectivity curves are distinctively different, despite the fact that the thicknesses of the molecular linkage layers (similar to 10-20 angstrom) are negligibly small compared to the thicknesses of MC monolayers, (similar to 3200 angstrom). On the basis of the atomic force microscopic images of the MC surfaces, a rough surface layer with the thickness of similar to 160 angstrom was introduced onto the surface of each MC to conduct a meaningful simulation of the curves with the recursive Parratt formalism. The obtained thickness, roughness, and density of each layer were reasonable, indicating that X-ray reflectivity is a very useful tool for the characterization of very thin layers of molecular linkages existing between much thicker MC monolayers and the substrate.