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).