Self-assembled thin-films of gold nanoparticles for the fabrication of electronic devices

Gold nanoparticles may be used as an element in fabricating numerous nanoelectronic devices. In this study, compact monolayers of 5nm and 10nm diameter gold particles were formed on a water surface using a convective self-assembly cell. Micro-contact printing was used to transfer monolayer films of Au MPNs to various substrates using a PDMS stamp-pad. Highly conductive lines were formed for potential use in fabricating a chemi-resistive sensing device and other electronic devices by exposing multilayer films of Au MPNs to ozone in a UVO cleaner. Alkanethiol coated Au nanoparticles when oxidized in the UVO cleaner lose their organic coating without altering their gold core and decrease the inter-core separation in the film. Formation of oxidized sulfur indicating conversion of the thiolate bond between sulfur and gold to a sulfonate or sulfonate bond was studied by XPS. Upon exposure for 15mins in the UVO cleaner, films consisting of four or six monolayers of 10nm diameter Au particles became highly conductive. The conductivity of these films is 105-106 Ω-1m-1 where the ideal bulk conductivity of gold is ∼4.5*107 Ω -1m-1. The temperature dependence of the conductivity of these films suggest that they to conduct by single-electron tunneling. AFM and TEM images of these highly conductive films show them to retain the small particle size, the close-packed structure, and the smooth surface of the original MPN films. When films of alkanethiol coated Au MPNs are oxidized for a short time (around 5mins in the UVO cleaner) the sulfur atom that bonds the alkanethiol molecules to the particles are oxidized. The organic layer encapsulating the particles may then be exchanged readily with other molecules. Molecular exchange was accomplished without altering the close-packed structure of the films in a novel exchange cell that makes use of a PDMS pad to hold the Au-nanoparticles in place. This exchange process was used to functionalize the particles with 4-pyridinethiol (4-PySH) and with 1,4-phenylenediisocyanide (1,4-PDI), which were then used to attach metalloporphyrins to the particles