title: Surface self-diffusion of organic molecules adsorbed in porous silicon.
abstract: The pulsed field gradient nuclear magnetic resonance method has been employed to probe self-diffusion of organic guest molecules adsorbed in porous silicon with a 3.6 nm pore size. The molecular self-diffusion coefficient and intrapore adsorption were simultaneously measured as a function of the external vapor pressure. The latter was varied in a broad range to provide pore loading from less than monolayer surface coverage to full pore saturation. The measured diffusivities are found to be well-correlated with the adsorption isotherms. At low molecular concentrations in the pores, corresponding to surface coverages of less than one monolayer, the self-diffusion coefficient strongly increases with increasing concentration. This observation is attributed to the occurrence of activated diffusion on a heterogeneous surface. Additional experiments in a broad temperature range and using binary mixtures confirm this hypothesis.
authors.affiliation: Department of Molecular Physics, Kazan State University, Kazan 420008, Russia. valiulli@rz.uni-leipzig.de
authors.forename: Rustem
authors.initials: R
authors.lastname: Valiullin
authors.forename: Pavel
authors.initials: P
authors.lastname: Kortunov
authors.forename: Jörg
authors.initials: J
authors.lastname: Kärger
authors.forename: Viktor
authors.initials: V
authors.lastname: Timoshenko