Monolayer-Controlled Deposition of Silicon Oxide Films on Gold, Silicon, and Mica Substrates by Room-Temperature Adsorption and Oxidation of Alkylsiloxane Monolayers

Abstract

Ultrathin SiO 2 films with thicknesses between 0.3 and 8 nm were grown on native silicon (Si/SiO 2 ), muscovite mica and polycrystalline gold substrates via repeated application of a binary reaction sequence, which involved the formation of a self-assembled alkylsiloxane monolayer (step A) and UV-ozone oxidation of the hydrocarbon groups (step B). Using octadecyltrichlorosilane as a precursor, SiO 2 films could be grown in a strictly linear, layer-by-layer mode on each of the three substrates with a growth rate of 3.0 ( 0.3 Å per deposition cycle, which corresponds to a monolayer of SiO 2 . The properties of these oxide films (composition, structure, packing density) were found to be essentially identical and independent of the substrate, as evidenced by ellipsometry, infrared reflection, and X-ray photoelectron spectroscopy. Furthermore, the quality of the oxide layers was investigated as a function of the hydrocarbon chain length of the alkylsiloxane monolayer formed in step A, using four different alkyltrichlorosilanes, R-SiCl 3 (R ) C 18 H 37 , C 11 H 23 , C 4 H 9 , CH 3 ), as precursors. For each compound, a linear increase of the SiO 2 film thickness with the number of applied deposition cycles was again observed, but the growth rate increased noticeably from 2.8 Å/cycle for the C 18 and the C 11 compound to 3.2 Å/cycle and 6.5 Å/cycle for the C 4 and the C 1 compound, respectively, concomitant with an increase of the surface roughness in atomic force microscopy images of the oxide films. The packing density of the Si atoms in these films remains essentially constant for longer-chain precursors (R g C 4 ), although the structure of the hydrocarbon layer changes drastically from a highly-ordered, perpendicular alignment on the surface (R ) C 18 ) to a random, isotropic arrangement (R e C 11 ). For films prepared from shorter precursors (R < C 4 ), however, multilayer formation sets in and results in film growth rates clearly beyond the monolayer level. A minimum chain length of about four C atoms is therefore required to restrict the alkylsiloxane film formation (step A) to the monolayer level and to provide reproducible and precise control of the oxide film thickness in this deposition process.

In situ loading of palladium nanoparticles on mica and their catalytic applications

“…Development of mica-containing functional materials has attracted considerable attention in recent years. For instance, mica can be used as a substrate for conducting mica composites [22][23][24], as colored pigments [25][26][27][28], biosensors [29][30][31][32], potential catalysts containing gold or palladium nanoparticles [33,34], and so on. Ferrero et al immobilized nanometer sized gold particles on mica by atom deposition, however, they did not study the catalytic property of the resultant material [33].…”

Interface-directed sol-gel: direct fabrication of the covalently attached ultraflat inorganic oxide pattern on functionalized plastics

“…Accordingly, a variety of specially optimized methods have been designed to address the above-mentioned deposition problems on plastics, which mainly include organic/photochemical reactions [42][43][44][45][46][47][48][49][50][51][52][53][54], plasma-enhanced deposition [55][56][57][58][59], atomic layer deposition [30,51,52], vacuum UV-enhanced vapor deposition [46][47][48][49][50][51][52][53][54], liquid phase deposition [43,44,60] and sol-gel [61][62][63]. Among these methods, sol-gel stands out because it is a very useful and well-established method to fabricate high quality pure or hybrid films on various substrates without the need of complicated vacuum facilities and high temperature [61][62][63].…”

“…We consider that the precise tailoring of chemical structures on substrate surfaces is especially important, because it has been demonstrated that functionalized surface often plays a key role in determining the surface morphology [46][47][48][49][50][51][52][53][54], pattern formation [41] and adhesion strength [42][43][44][45] of inorganic coating. Recently, our lab successfully achieved precise tailoring of chemical structures on a polymer surface at molecular level by an extremely simple "confined photocatalytic oxidation" (CPO) reaction [77].…”

Surface treatment and characterization: Perspectives to electrophoresis and lab‐on‐chips

“…The growth of the multilayer is strictly linear, and involves three repeated grafting cycles. Vallant et al [111] have reported the fabrication of multilayers by repeated binary reactions, consisting of the growth of an alkylsiloxane monolayer followed by UV/ ozone oxidation of the alkyl chains. The possibility to obtain a strictly linear layer-by-layer (LbL) organization over more than 20 cycles was demonstrated.…”