Pseudorotational epitaxy of self-assembled octadecyltrichlorosilane monolayers on sapphire (0001).
The structure of octadecyltrichlorosilane self-assembled monolayers (SAMs) on sapphire (0001) was studied by Å-resolution surface-specific x-ray scattering methods. The monolayer was found to consist of three sublayers where the outermost layer corresponds to vertically oriented, closely packed alkyl tails. Laterally, the monolayer is hexagonally packed and exhibits pseudorotational epitaxy to the sapphire, manifested by a broad scattering peak at zero relative azimuthal rotation, with long powderlike tails. The lattice mismatch of ∼ 1%-3% to the sapphire's and the different length scale introduced by the lateral Si-O-Si bonding prohibit positional epitaxy. However, the substrate induces an intriguing increase in the crystalline coherence length of the SAM's powderlike crystallites when rotationally aligned with the sapphire's lattice. The increase correlates well with the rotational dependence of the separation of corresponding substrate-monolayer lattice sites.
Crystallography and Structural Physics, University of Erlangen-Nürnberg, 91058 Erlangen, Germany.
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Steinrück
Crystallography and Structural Physics, University of Erlangen-Nürnberg, 91058 Erlangen, Germany.
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Magerl
Physics Department and Institute of Nanotechnology, Bar-Ilan University, Ramat-Gan 52900, Israel.
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Deutsch
Condensed Matter Physics and Materials Science Department, Brookhaven National Lab, Upton, New York 11973, USA.
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Ocko
D000537:Aluminum Oxide / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D014961:X-Ray Diffraction
D012821:Silanes; C061189:octadecyltrichlorosilane; D000537:Aluminum Oxide