title: Ultrathin silica films: the atomic structure of two-dimensional crystals and glasses.
abstract: For the last 15 years, we have been studying the preparation and characterization of ordered silica films on metal supports. We review the efforts so far, and then discuss the specific case of a silica bilayer, which exists in a crystalline and a vitreous variety, and puts us into a position to investigate, for the first time, the real space structure (AFM/STM) of a two-dimensional glass and its properties. We show that pair correlation functions determined from the images of this two-dimensional glass are similar to those determined by X-ray and neutron scattering from three-dimensional glasses, if the appropriate sensitivity factors are taken into account. We are in a position, to verify, for the first time, a model of the vitreous silica structure proposed by William Zachariasen in 1932. Beyond this, the possibility to prepare the crystalline and the glassy structure on the same support allows us to study the crystal-glass phase transition in real space. We, finally, discuss possibilities to use silica films to start investigating related systems such as zeolites and clay films. We also mention hydroxylation of the silica films in order to adsorb metal atoms modeling heterogenized homogeneous catalysts.
authors.affiliation: Department of Chemical Physics, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin (Germany).
authors.forename: Christin
authors.initials: C
authors.lastname: Büchner
authors.forename: Leonid
authors.initials: L
authors.lastname: Lichtenstein
authors.forename: Xin
authors.initials: X
authors.lastname: Yu
authors.forename: J Anibal
authors.initials: JA
authors.lastname: Boscoboinik
authors.forename: Bing
authors.initials: B
authors.lastname: Yang
authors.forename: William E
authors.initials: WE
authors.lastname: Kaden
authors.forename: Markus
authors.initials: M
authors.lastname: Heyde
authors.forename: Shamil K
authors.initials: SK
authors.lastname: Shaikhutdinov
authors.forename: Radosław
authors.initials: R
authors.lastname: Włodarczyk
authors.forename: Marek
authors.initials: M
authors.lastname: Sierka
authors.forename: Joachim
authors.initials: J
authors.lastname: Sauer
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Freund
keywords: bilayers; silcon; surface chemistry; thin films