AVS 45th International Symposium
    Applied Surface Science Division Wednesday Sessions
       Session AS+BI+SS-WeM

Paper AS+BI+SS-WeM11
Self-Assembling Trichloro- and Trimethoxy- silanes on TiO@sub 2@(100) Crystal

Wednesday, November 4, 1998, 11:40 am, Room 307

Session: Organized Molecular Monolayers
Presenter: R. Magnée, LISE - Facultés Universitaires Notre-Dame de la Paix, Belgium
Authors: R. Magnée, LISE - Facultés Universitaires Notre-Dame de la Paix, Belgium
J.-J. Pireaux, LISE - Facultés Universitaires Notre-Dame de la Paix, Belgium
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Trichlorosilanes (CH@sub 3@(CH@sub 2@)@sub n@SiCl@sub 3@, n = 1, 7, 17) and trimethoxysilanes (CH@sub 3@(CH@sub 2@)@sub n@Si(OCH@sub 3@)@sub 3@ , n = 2, 7, 17) SAM's were deposited by dipping a TiO@sub 2@ (100) crystal in a 10@super -3@M toluene solution for 4 hours. The titanium dioxide surface was prepared by Ar@super +@ sputtering, annealing in UHV to get a clear LEED (1x3) pattern, then exposed to atmosphere before dipping. Silane molecules need H@sub 2@O or a hydroxylated surface to react but it was not necessary to hydroxylate the TiO@sub 2@ because of the air exposure. Hydroxylation was confirmed by FT-IR and XPS. X-Ray and Ultra-violet Photoelectrons Spectroscopy (XPS, UPS) were then used for the SAM's charaterization. We expect a siloxane network to appear at the interface in addition to the Ti-O-Si bonds. XPS results show that the silane groups do indeed bind to the TiO@sub 2@ surface but that some defects are also present at the interface: for n=17 the amount of OH groups is 4 % of the total oxygen signal while this value is doubled for n=7. Probably due to the higher reactivity of chlorine atoms, trichlorosilanes present less defects than trimethoxysilanes. By comparison with theoretical calculations,@footnote 1@ UPS provides information on the alkane chain conformation: we show that longer silane molecules (n=17) are grafted in a zigzag planar conformation, while n=7 molecules seem to present chain defects. This is consistent with the self-assembling process that depends on long-range interchain interactions. For the smallest chains (n=1,2), the XPS C/Si ratios are always too high, suggesting some contamination: this is probably due to solvent incorporation in the layer. HREELS analysis (not yet performed at the date of abstract submission) may help to get more information on the order of the layers. @FootnoteText@ @footnote 1@ A.-S. Duwez, S. Di Paolo, J. Ghijsen, J. Riga, M. Deleuze, J. Delhalle, J. Phys. Chem. B, 101 (1997) 884.