How electrons move together as a group inside cylindrical nanoparticles?
Scientists from the University of Exeter seems to find out the answer to this question. They even have made a breakthrough in the field of electromagnetism, with perspectives for metamaterials research.
In collaboration with the University of Strasbourg, scientists hypothesized how electrons move collectively in tiny metal nanoparticles shaped like cylinders.
Their theory could provide a new understanding of how light and matter interact at the nanoscale and has implications for the realization of future nanoscale devices exploiting nanoparticle-based metamaterials with spectacular optical properties.
Metallic nanoparticles have a positively charged ionic core, with a cloud of negatively charged electrons swirling around it. When light is shone on such a metallic object, the electronic cloud is displaced.
This displacement causes the whole group of electrons to be set into oscillation about the positive core. The group of electrons sloshing back and forth behaves like a single particle (a so-called quasiparticle), known as a “plasmon.”
The plasmon is primarily characterized by the frequency at which it oscillates, known as the plasmon resonance frequency.
Scientists addressed the way that plasmons in cylindrical nanoparticles oscillate. They used a technique based on nuclear physics to build an elegant analytic theory describing plasmons’ behavior in cylinders with an arbitrary aspect ratio.
The theory offers a complete description of cylindrical plasmonic nanoparticles, describing simply the plasmonic resonance in metallic nanoparticles from nanowires to circular nanodisks.
The two condensed matter theorists also considered the plasmonic response of a pair of coupled cylindrical nanoparticles. They found quantum mechanical corrections to their classical theory, which is relevant due to the nanoparticles’ small nanometric dimensions.
Dr. Charles Downing from the University of Exeter’s Physics and Astronomy department explains: “Quite unexpectedly, our theoretical work provides deep, analytic insight into plasmonic excitations in cylindrical nanoparticles, which can help to guide our experimental colleagues fabricating metallic nanorods in their laboratories.”
Guillaume Weick from the University of Strasbourg adds: “There is a trend for increasing reliance on heavy-duty computations to describe plasmonic systems. In our throwback work, we reveal humble pen-and-paper calculations can still explain intriguing phenomena at the forefront of metamaterials research.”
The theoretical breakthrough is of immediate utility to a swathe of scientists working with nano-objects in the cutting edge science of plasmonics. Longer-term, it is hoped that plasmonic excitations can be exploited in the next generation of ultra-compact circuitry, solar energy conversion, and data storage as our technology becomes increasingly miniaturized.
- Charles A. Downing et al. Plasmonic modes in cylindrical nanoparticles and dimers, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences (2020). DOI: 10.1098/rspa.2020.0530