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Issue 9, 2004
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Carboxylic acid terminated monolayer formation on crystalline silicon and silicon nitride surfaces. A surface coverage determination with a fluorescent probe in solution

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Abstract

Carboxylic acid terminated (–COOH) monolayers (ML) have been covalently anchored on the surface (S) of crystalline silicon (Si) and silicon nitride (Si3N4) by using wet-chemistry methods. Their concentration has been determined adopting a stepwise procedure with a fluorescent probe in solution. First, 7-amino-4-methylcoumarin (H2N–C10H7O2, AMC) is covalently bonded to the monolayer on the surface through an amidation reaction forming an amide-terminated surface monolayer, S–(CH2)n–CO–NH–C10H7O2, then the surface is intensely washed in order to remove any physisorbed species, finally AMC is detached from the surface via hydrolysis of the –CO–NH– bond and quantified by a fluorescence analysis in water solution. The yields of both the amidation and hydrolysis reactions have been evaluated. By this method, submonolayers ≤0.1 ± 0.03 ML can be determined. It has been possible to evaluate the different extent of surface functionalization changing the substrate between Si and Si3N4 and for Si changing the monolayer formation reaction: heat- (Δ) or light- () promoted or via cathodic electrografting (CEG). It came out that submonolayers are formed in any case, Si3N4 is functionalized to a larger extent than Si on heating (0.52 vs. 0.15 ML) and Si is best functionalized via cathodic electrografting: Δ, 0.15; 0.20; CEG, 0.44 ML. Surface topography of some monolayers on Si and Si3N4 substrates was investigated by Atomic Force Microscopy (AFM). On clean Si, AFM showed topographical variations of 0.3–0.4 nm while for the clean Si3N4 the corrugation was around 3–4 nm. After functionalization the two surfaces were uniformly covered and the corrugation increased in both samples with a corrugation in topography of 1–2 nm for Si and 5–6 nm for Si3N4.

Graphical abstract: Carboxylic acid terminated monolayer formation on crystalline silicon and silicon nitride surfaces. A surface coverage determination with a fluorescent probe in solution

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Publication details

The article was received on 07 Oct 2003, accepted on 02 Feb 2004 and first published on 29 Mar 2004


Article type: Paper
DOI: 10.1039/B312273E
Citation: J. Mater. Chem., 2004,14, 1461-1468
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    Carboxylic acid terminated monolayer formation on crystalline silicon and silicon nitride surfaces. A surface coverage determination with a fluorescent probe in solution

    F. Cattaruzza, A. Cricenti, A. Flamini, M. Girasole, G. Longo, A. Mezzi and T. Prosperi, J. Mater. Chem., 2004, 14, 1461
    DOI: 10.1039/B312273E

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