Two-dimensional polymer synthesis : towards a two-dimensional replicating system for nanostructures

Abstract

The general concept of a replicating monolayer system is introduced as a new method of nanostructure synthesis. One possible implementation of a 2-D replicating system is pursued which uses a diacetylene moiety for cross-linking and amide hydrogen bonding for molecular recognition between replicates and templates. The synthesis of several monomers for amide hydrogen-bonded adlayer formation is described. The assembly and crosslinking of diacetylene monomers on an underlying amide-capped self- assembled monolayer (SAM) was studied on unpatterned thermally evaporated gold films. Raman and Fourier-transform infrared spectroscopies, as well as ellipsometry and contact angle data, indicate that amide hydrogen bonding interactions are sufficient to organize an adlayer of diacetylene-containing molecules on the underlying SAM which can be polymerized with ultraviolet light. In order to obtain gold substrates suitable for cross-linking of bis(diacetylene) monomers, new methods of producing ultraflat gold surfaces were developed.

(cont.) A solid- state bonding technique using only gold was developed, yielding ultraflat gold surfaces, with root-mean-square roughnesses of -0.5 nm, on glass slides which are free of impurities from epoxies or other bonding agents. The patterning and cross-linking of poly(diacetylene) adlayers on ultraflat gold surfaces was investigated by atomic force microscopy (AFM). Soft lithography was suitable for adlayer structures down to about 500 nm. Electron beam lithography for patterning of polymerizable adlayers was demonstrated for the first time. The polymerized adlayer patterns were significantly more difficult to remove from the gold surface than unpolymerized adlayer patterns, indicating cross-linking. Studies to remove adlayer patterns as intact 2-D polymers failed, due either to poor cross-linking or robustness of the resulting 2-D polymers. In another approach to nanostructure synthesis, the synthesis of monofunctionalized gold nanoparticles by a solid phase synthetic route was described. This represents a versatile method of producing monofunctionalized nanoparticles, which can be used to produce and study more elaborate nanoparticle structures.