Electronic applications of gold nanoclusters

Jia Liu, Purdue University

Abstract

The goal of this research is to fabricate high-density nanostructures for electronic and chemical sensing applications using metal nanoclusters. Chemical self-assembly is a technique for achieving ordered nano-/micro-scale structures at low cost and high throughput. We have developed a simplified Langmuir-Blodgett technique which enables the self-assembly of highly ordered, hexagonal close-packed monolayer arrays of dodecanethiol encapsulated gold clusters with 4–5 nm diameters, spanning over 1 cm in diameter on a water surface. Such a monolayer can be transferred onto a flat substrate by touching the film with the substrate. Multilayer films can be deposited by multiple transfers. We have employed a “solvent vapor annealing” technique to further improve the long-range ordering of the cluster array on a water surface. We have attempted to link monolayer cluster arrays with conjugated organic molecules. However, it has proven to be difficult to accomplish this for large-area arrays. Bilayer arrays may be easily linked, however, utilizing the z-direction mobility of clusters in the second layer. Electronic conduction through monolayer and bilayer cluster films deposited across interdigitated electrodes on SiO2 substrates has been measured. Unlinked monolayer films are highly resistive and unstable. Linked bilayer films exhibit substantially improved stability and conductivity (about two orders of magnitude increase in conductance). In an attempt to fabricate a nanoscale electronic device structure using nanoclusters and molecules, we have synthesized a hybrid structure consisting of a nanocluster layer, a molecular layer, and a semiconductor substrate. A anoscale ohmic contact to GaAs with performance comparable to that of conventional large-area ohmic contacts can be fabricated by depositing Au nanoclusters onto a Low-Temperature-Grown GaAs (LTG:GaAs) substrate, using a self-assembled monolayer of xylyl dithiol as a molecular tether for the clusters. For the purpose of fabricating complex electronic devices/circuits that require a selective deposition of ordered cluster arrays in a pre-defined pattern, we have developed a directed selfassembly technique utilizing “micro-contact printing” to impose the desired pattern of xylyl dithiol tether layer on a LTG:GaAs substrate. Micro-patterned monolayer cluster arrays can be deposited on the substrate and strong electronic coupling between the clusters and the semiconductor substrate has been achieved.

Degree

Ph.D.

Advisors

Andres, Purdue University.

Subject Area

Chemical engineering

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