FROM MONOLAYERS TO NANOSTRUCTURED MATERIALS - AN ORGANIC CHEMISTS VIEW OF SELF-ASSEMBLY

Simple methods are described for the production of gold nanoparticles with narrow size distributions by reduction of tetrachloroaurate solut ions in the presence of thiol-containing organic compounds which self- assemble on the gold surface. Stable solutions of somewhat larger part icles can be produced if the thiol is absent. The thiol-derivatized ma terials are stable in air over long periods and can be handled in much the same way as simple organic compounds. Using dithiols as the deriv atizing spacer units, ways have been developed for the preparation of materials in three dimensional form and as thin films attached to a so lid substrate. Such materials show conductivities that mimic the behav iour of semiconductors and that depend markedly on the structure of th e dithiol used to link the gold particles together. The increase in co nductivity with increasing temperature probably involves activated ele ctron hopping from particle to particle. Surfaces treated with a coati ng of the materials show electroreflectance changes with applied poten tial that also differ according to the structure of the dithiol spacer . Unusual effects have been observed on heterogeneous electron transfe r from electrode surfaces treated with layers of the gold nanoparticle s and dithiol spacers. Applications for these nanostructured materials can be envisaged, which range from submicroelectronic devices and cir cuitry to electrical modification of the reflectance of glass. Such ap plications will require a multidisciplinary approach with a substantia l organic chemical research input.