Microcontact Printing of Uniform Nanoparticle Arrays

Abstract

Uniform, close-packed monolayer and bilayer arrays of alkanethiol-coated gold nanoparticles have been used as “ink” for microcontact printing (μCP) following the technique of Xia and Whitesides (see Xia, Y.; Whitesides, G. M. Polym. Mater. Sci. Eng. 1997, 77, 596). The process is accomplished in two steps. First, a uniform monolayer of the nanoparticles is self-assembled on a water surface and is transferred intact to a patterned poly(dimethylsiloxane) (PDMS) stamp pad by the Langmuir−Schaefer (LS) method. In the case of multilayer printing, this “inking” step is repeated as many times as desired. Because multilayer arrays are assembled on the stamp pad layer-by-layer, adjacent layers may be made up of the same or different particles. The nanoparticles are transferred to a solid substrate by conformal contact of the stamp pad and the substrate. The technique has been used to print patterned monolayer and bilayer arrays on both hydrophobic and hydrophilic substrates. The quality of the transferred arrays has been verified optically and by transmission electron microscopy (TEM). This new μCP technique should be applicable to any particles that can be spread as a monolayer on a water surface and promises to be useful for nanofabrication.