Water exclusion at the nanometer scale provides long-term passivation of silicon (111) grafted with alkyl monolayers.
This work is a quantitative study of the conditions required for a long-term passivation of the interface silicon-alkyl monolayers prepared by thermal hydrosilyation of neat 1-alkenes on well-defined H-Si(111) surfaces. We present electrochemical capacitance measurements (C-U) in combination with ex situ atomic force microscopy (AFM) observations and X-ray photoelectron spectroscopy (XPS) measurements. Capacitance measurements as a function of the reaction time and XPS data reveal close correlations between the chemical composition at the interface and its electronic properties. A very low density of states is found if suboxide formation is carefully prevented. The monitoring of C-U plots and AFM imaging upon exposure of the sample in diverse conditions indicate that the initial electronic properties and structure of the interface are long-lasting only when the monolayer surface coverage is theta > 0.42. A model demonstrates that this threshold value corresponds to a monolayer with intermolecular channels narrower than approximately 2.82 A, which is equal to the diameter of a water molecule. Water exclusion from the monolayer promotes long-term passivation of the silicon surface against oxidation in air and water as well as perfect corrosion inhibition in 20% NH(4)F. We provide two criteria to assess when a sample is optimized: The first one is an effective dielectric constant <2.5, and the second one is a very characteristic energy diagram at open circuit potential.
Laboratoire de Physique de la Matière Condensée, UMR 7643 CNRS, Ecole Polytechnique, Route de Saclay, F-91128 Palaiseau, France.
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Gorostiza
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Henry de Villeneuve
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Sun
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Sanz
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Wallart
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Boukherroub
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Allongue
D000475:Alkenes / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D004563:Electrochemistry; D006859:Hydrogen / Q000737:chemistry*; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force; D036103:Nanotechnology; D017646:Organosilicon Compounds / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*; D013057:Spectrum Analysis; D013499:Surface Properties; D014867:Water / Q000737:chemistry*; D014965:X-Rays
D000475:Alkenes; D008567:Membranes, Artificial; D017646:Organosilicon Compounds; D014867:Water; D002244:Carbon; D006859:Hydrogen; D012825:Silicon