title: Nano-patterned layers of a grafted coumarinic chromophore.
abstract: We report on the grafting of coumarin chromophores on flat silicon surfaces and in regions of nanometric dimensions drawn on silicon surfaces. The coumarin derivative was grafted by using the quaternization of a tertiary amine group of the chromophore with a ((chloromethyl)phenylethyl)-dimethylchlorosilane (CMPDCS) grafted on silicon. Complete characterization of the grafted layer was performed as a function of reaction time by X-ray photoelectron spectroscopy, X-ray reflectometry, atomic force microscopy, fluorescence spectroscopy and laser-scanning confocal microscopy. The results indicate that about one chromophore molecule is grafted every second CMPDCS molecule, resulting in a surface density of coumarin of slightly more than one coumarin per nm2. A broadening of the distribution of the fluorescence lifetimes was observed, suggesting that the grafted molecules experience a larger distribution of environments in the grafted layer than in solution. Since this reaction is fully compatible with silicon processing technology, the grafting could also be performed in nano-regions of size as small as 250 nm defined by combining electron-beam lithography with silanization. In such nano-sized regions the distribution of fluorescence lifetimes was narrower, suggesting a possible influence of the confinement on the organization of the molecules.
authors.affiliation: Unité de physique et de chimie des hauts polymères, and Research Center on Micro- and Nanoscopic Materials and Electronic Devices, Université catholique de Louvain, Croix du Sud, 1, B-1348, Louvain-la-Neuve, Belgium.
authors.forename: Nadia
authors.initials: N
authors.lastname: Frederich
authors.forename: Bernard
authors.initials: B
authors.lastname: Nysten
authors.forename: Benoît
authors.initials: B
authors.lastname: Muls
authors.forename: Johan
authors.initials: J
authors.lastname: Hofkens
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Habib Jiwan
authors.forename: Alain M
authors.initials: AM
authors.lastname: Jonas
mesh_terms: D003374:Coumarins / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008854:Microscopy, Electron; D015394:Molecular Structure; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D012825:Silicon / Q000737:chemistry; D013057:Spectrum Analysis
chemical_list: D003374:Coumarins; C030123:coumarin; D012825:Silicon