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Berlin 2012 – scientific programme

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DS: Fachverband Dünne Schichten

DS 31: Organic thin films I

DS 31.6: Talk

Thursday, March 29, 2012, 12:30–12:45, H 0111

Structures of Chlorosilanes Self-Assembled on Oxide Surfaces — •Hans-Georg Steinrück, Michael Klimczak, Stefan Gerth, and Andreas Magerl — Lehrstuhl für Kristallographie und Strukturphysik, Staudtstr. 3, D-91058 Erlangen

The topic of our recent research was to further investigate the bonding process of trichlorosilanes to oxide surfaces.

As a starting point octadecyltrichlorosilane (OTS, C17H37Cl3Si) adsorbed on the amorphous native oxide of a silicon wafer was chosen. Using X-ray reflectivity measurements a densely packed uniform OTS self-assembled monolayer with thickness of ≈26 Å was found. This agrees well with several publications.

Starting from this observation, the substrate was systematically varied, by choosing (100) oriented single crystalline quartz (SiO2) and (100) oriented single crystalline (Al2O3). Due to their crystal specific lattice parameters, a different surface coverage was expected.

To gather further insight, especially on the surface coverage and on the thickness of the monolayer, X-ray reflectivity measurements were performed for these two systems. It was found that the surface coverage on quartz is about 24% and on sapphire about 40% smaller than on the amorphous silicon dioxide. This leads to a tilt of the molecules of 30 and 45 respectively, away from the surface normal. This result can be attributed to the different distances of the bonding sites on the three substrates, which lead to unfavorable conditions for a densely packed monolayer on the crystalline substrates. Note that compared to the amorphous oxide possible bonding sites rectangular lattice of 5.17 Å×4.54 Å (SiO2) and 4.76 Å×12.99 Å (Al2O3).

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