Xiaoda Xu

Spectrally-selective gold nanorod coatings for window glass

The unique optical properties of gold nanorods, which exhibit tuneable absorption as a function of their aspect ratio, suggest that they might have potential applications in coatings for solar control on windows. Here we explore the properties of coatings produced by attaching gold nanorods to the surface of glass. Such coatings can attenuate solar radiation effectively, even at very low gold contents, but the figure-of-merit,Tvis/Tsol, of our experimental coatings was close to unity, indicating that they are not spectrally selective, However, calculations are presented to show how coatings comprised of a blend of rods with aspect ratios of greater than 3 can produce coatings withTvis/Tsol of up to at least 1.4. The maximum value possible for perfectly spectrally-selective coating in sunlight is 2.08. Unfortunately, the practical realization of such coatings requires the further development of reliable methods to scale up the production of gold nanorods of longer aspect ratios.

Radiative Heat Transfer Across Glass Coated With Gold Nano-Particles

Solar glazing based on reflective or absorptive coatings of noble metals or dielectric compounds respectively is well-known. However, the use of gold nano-particles in an absorptive role has hardly been considered. The performance of such coatings was assessed using an array of incandescent lamps as radiation source, and the results ranked against commercial glazing systems. The nanoparticle coatings attenuated the radiation by 40%. An additional 15% of the incoming energy was convected off the inside surface of the glass. The neutral color and simple manufacture of the coatings suggests that they might have applications on architectural glass.

The versatile colour gamut of coatings of plasmonic metal nanoparticles.

We have investigated the colour gamut of coatings produced by the growth of plasmonically-active coatings of cap-shaped Au or Ag nanoparticles on a transparent substrate. The control of colour and spectral selectivity that can be obtained by the manipulation of the rates of nucleation and growth were explored using a combination of experiment and calculation. In our experimental work the Au nanoparticles were grown in situ using a wet chemical electroless plating technique while the Ag nanoparticles were produced by physical vapour deposition. The optical properties were numerically simulated using the discrete dipole approximation. The resulting measured or calculated transmission spectra were mapped to the CIE L-a -b colour space. The aspect ratio of the nanoparticles was the primary factor in determining the colours in both cases. However, increasing the nucleation rate of the particles resulted in them becoming more closely packed, which also red-shifted the optical extinction peak of the structure due to interactions of their near-fields. This caused an enhancement in the blue component of the transmitted light. Coatings of Ag particles had a significantly wider and brighter colour gamut than those of Au.

Control of Plasmon Resonance in Coatings of Gold Nanorods

Gold nanorods manifest a tunable plasmon resonance with light in the visible to near-infrared regions of the spectrum, and have been proposed for use in spectrally selective coatings on glass. However, details of shape and packing density have a significant effect on the optical properties of these nanoparticle coatings. Here the paper shows how these effects can be controlled and exploited to produce a flexible spectral response.