Interactions between small things have been very much in the news lately with the discovery of signs of the Higgs boson and extensive discussion about how the most elemental particles interact to give the universe its form. The Rice team studies nanoparticles that are orders of magnitude larger – though still so small that they can only be seen with an electron microscope – with the goal of understanding how the more elemental electromagnetic particles within behave.

This is important to electronics engineers perpetually looking for ways to shrink the size of computer chips and other devices through ever-smaller components like waveguides. The ability of nanoparticles to pass waves that can be interpreted as signals may open the door to new methods for optical computing. The work may also contribute to more finely tuned antennae and sensors.

Specifically, the researchers looked for the ways plasmons influence each other across tiny gaps – as small as one nanometer – between gold nanoparticles. Lead author Liane Slaughter, a Rice graduate student, and her colleagues engineered chains of 50-nanometer particles in single and double rows that mimicked the repeating molecular patterns of polymers. They then looked into the standing super-radiant and subradiant signals collectively sustained by the individual assemblies of nanoparticles. The composition of the chain in terms of nanoparticle sizes, shapes and positions determines the frequencies of light they can characteristically interact with.

This basic structure change from a single row to a double row led to pronounced differences demonstrated by additional subradiant modes and a lower energy super-radiant mode.

Two additional interesting effects seemed to be universal among the team’s plasmonic polymers. One was that the energy of the super-radiant mode, which results from the interaction over the most repeat units, would characteristically decrease with the addition of nanoparticles along the length, up to about 10 particles, and then level off. The other was that disorder among the repeat units – the nanoparticles – only seems to matter at the small scale.

This story is reprinted from material from
Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.