Dresden 2014 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 43: Poster II: Organic thin films; Atomic layer deposition, Thin film characterization: Structure analysis and composition (XRD, TEM, XPS, SIMS, RBS, ...)
DS 43.28: Poster
Donnerstag, 3. April 2014, 16:00–19:00, P1
Pseudo-rotational Epitaxy of Octadecyltrichlorosilane Monolayers on Sapphire (001) — •Hans-Georg Steinrück1, Andreas Magerl1, Moshe Deutsch2, and Ben Ocko3 — 11Lehrstuhl für Kristallographie und Strukturphysik, Universität Erlangen Nürnberg, Germany — 2Bar-Ilan University, Ramat- Gan, Israel — 3Brookhaven National Laboratory, Upton NY, USA
Octadecyltrichlorosilane (OTS) self-assembled monolayers (SAMs) on the (001) sapphire surface are vertically aligned, well-packed and have hexagonal ordering like the underlying sapphire as shown by X-ray grazing incidence diffraction. The SAM lattice planes are preferentially aligned along the sapphire in-plane structure albeit with an angular rotational distribution, which is well described by a Lorentzian profile with a FWHM of 10 degrees. The hexagonal SAM lattice constant is incommensurate with the sapphire by 1.2% at room temperature, and the degree of incommensuration increases at higher temperatures. The radial correlation length of 232 Å is three times larger than for the same monolayers on a native silicon oxide surface and scales with the orientation φ of domains via ξ∼ 1/sin·φ. Our results suggest that a commensurate epitaxial arrangement is distorted by steric hindrances caused by both the packing density of the alkyl chains and the dimension and the cross-linking of the head groups. This results in a size-dependent strain within the OTS domains. We call these novel structural properties of a SAM pseudo-rotational epitaxy.