Close-packed planar arrays of nanometer-diameter metal clusters that are covalently linked to each other by rigid, double-ended organic molecules have been self-assembled. Gold nanocrystals, each encapsulated by a monolayer of alkyl thiol molecules, were cast from a colloidal solution onto a flat substrate to form a close-packed cluster monolayer. Organic interconnects (aryl dithiols or aryl di-isonitriles) displaced the alkyl thiol molecules and covalently linked adjacent clusters in the monolayer to form a two-dimensional superlattice of metal quantum dots coupled by uniform tunnel junctions. Electrical conductance through such a superlattice of 3.7-nanometer-diameter gold clusters, deposited on a SiO 2 substrate in the gap between two gold contacts and linked by an aryl di-isonitrile [1,4-di(4-isocyanophenylethynyl)-2-ethylbenzene], exhibited nonlinear Coulomb charging behavior.

Double-ended aryl dithiols [alpha,alpha'-xylyldithiol (XYL) and 4,4'-biphenyldithiol] formed self-assembled monolayers (SAMs) on gold(111) substrates and were used to tether nanometer-sized gold clusters deposited from a cluster beam. An ultrahigh-vacuum scanning tunneling microscope was used to image these nanostructures and to measure their current-voltage characteristics as a function of the separation between the probe tip and the metal cluster. At room temperature, when the tip was positioned over a cluster bonded to the XYL SAM, the current-voltage data showed "Coulomb staircase" behavior. These data are in good agreement with semiclassical predictions for correlated single-electron tunneling and permit estimation of the electrical resistance of a single XYL molecule (approximately18 ± 12 megohms).

No abstract

No 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.