Received February 19, 2001

Abstract:

We report here on the two-dimensional patterns formed by supramolecular materials deposited from solution on oxidized silicon substrates. The supramolecular materials studied are composed of mushroom-shaped nanostructures measuring 2-5 nm in cross-section and approximately 7-8 nm in height. Two different materials were studied, one containing nanostructures with a hydrophilic phenolic base surface and the other containing a hydrophobic one with trifluoromethyl groups. The substrates were exposed to solutions of these materials for a set induction time at a series of concentrations using a motorized dipping apparatus. Samples were characterized by contact-angle measurements and tapping-mode atomic force microscopy. We observed distinct patterns as a function of concentration in phenolic supramolecular materials that interact favorably with the oxidized silicon surface. At low concentrations (0.01 wt %), the nanostructures form islands with uniform size of approximately 0.02 m, which have the height of a single nanostructure (7.2 nm). As concentration increases, a string-like morphology with uniform width is observed first, followed by a percolating texture. At yet higher concentrations, the film transforms to a honeycomb morphology, but its height still remains equal to that of a single nanostructure. When interactions between the nanostructure and the surface are not favorable (i.e., between trifluoromethyl end groups and oxidized silicon), uniform height patterns are not observed. The distinct geometries are possibly the result of strong material-substrate interactions balanced by a repulsive force that could have electrostatic origin. The extremely uniform thickness of the two-dimensional patterns may originate in the hydrophobic and hydrophilic nature of opposite poles of the nanostructures, thus suppressing vertical growth of the film.

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