Stable nanoclusters to impart metamaterial optical properties

A team from Rice University has developed a method to manufacture stable, 3D nanoclusters that could be used to impart metamaterial optical properties into unstructured substrates such as liquids, glasses and plastics.

The team, led by Professors Naomi Halas and Peter Nordlander, chose an Andor iKon-M NIR-enhanced CCD camera coupled to a hyperspectral imaging system to collect the dark-field scattering spectra of individual nanoclusters.

Their results reveal a very strong agreement between the experimental spectral characterisation of 3D nanoclusters with varying configurations (number, geometry, and orientation of the cluster) and the team’s theoretical calculations based on finite element analysis.

In a statement Prof Nordlander said: ‘The precise way in which the nanoparticles are arranged, rather than their composition, dictates the optical characteristics through an effect called localised surface plasmon resonance.

‘Theory suggests that the optical properties of different nanoclusters should be either remarkably sensitive to, or highly independent of, nanoparticle number and cluster geometry and our results bear this out.

‘The Andor iKon-M camera played a key role; the very low dark current due to the advanced thermoelectric cooling combined with high sensitivity over a large wavelength regime allowing us to image even very weakly-scattering nanoparticles to determine their optical properties.

‘Demonstrating an efficient assembly method for plasmonic ‘artificial molecules’ or ‘meta-atoms’ is a significant step towards a new generation of optical emitters and sensors, molecular contrast agents, nano-scale lasers and superlenses.’

Prof Halas said: ‘The universality of the fabrication method could extend the use of plasmonic nanoclusters to other regions of the spectrum, either by incorporating different materials, for example, aluminium for the UV, or spherical core/shell nanoparticles, for example, nanoshells for the IR.

‘They are also compatible with easily applied material coating methods, such as aerosols, and could lead to materials with transparency windows at specific frequencies and with constant ratios and line widths. And, they could also enable electromagnetic characteristics not yet achievable in current types of metamaterials as well as new approaches to current technological challenges, such as high-throughput chemical and biological sensing.’