How Blue is My Gold?
Vacuum-deposited films of gold on glass have excellent infrared shielding capability.
 The transparent 'blue gold' coatings have a pleasant hue which is compatible with that of the sky
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However, they are not commonly used in buildings. This is because of their high cost and their yellowish-colour. Oddly, the higher price for these materials is not due to the quantity of gold used in their creation (which amounts to less than $1 per m2), but rather to the high cost of the vacuum-deposition equipment required (which brings the cost up to ~$20 per m2). However, the Institute is investigating whether suitable coatings of gold can rather be applied using an aqueous process. This would not only be vastly cheaper but in addition it offers unprecedented opportunities to manipulate the structure of the coating at the nanoscale. Most interesting is the realisation that the gold can be deposited as nano-rods, nano-shells, or nanoscale grape-like gold/dielectric clusters. In these three cases the peak plasmon absorption of the coatings is shifted towards the infra-red which gives them a pleasant blue hue and increases their selectivity towards solar heat. The work is being supported by Anglogold Ashanti Australia Ltd in Perth and an ARC Linkage grant, and is being conducted by Prof. Michael Cortie together with post-graduate students Xiaoda Xu (SCI), Humayer Chowdhury (ENG) and Katia Peceros (SCI).
 Masters student Humayer Chowdhury, at work on his rig for testing radiactive heat transfer through coated glass samples
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The overall aim of the project is to develop a transparent gold-based coating system that costs no more than A$20 per m2 to apply retrospectively to glass windows, and which has a peak absorptivity in the near infra-red region. So far, the project has been very successful and blue coatings based on aggregated nano-spheres and on gold nano-rods have been applied to glass panes by X. Xu.
The performance of the coated glass panes has been tested in a rig designed by H. Chowdhury. Simultaneously, K. Peceros has been pursuing the difficult target of producing and characterising gold nano-shells, with some recent success in this area.
