Researchers from the University of New Mexico note that reducing the density of nanoparticles in ordered arrays leads to extraordinary field enhancements.
The control of the interactions between light and matter has long been a concern of the scientists The aim is to develop and develop numerous technologies that are of fundamental importance to society. With the boom of nanotechnology in recent years, the nanoscale manipulation of light is both a promising way to continue this progress and a unique challenge due to new behaviors that occur when the dimensions of structures are comparable to the wavelength of light  Scientists from the Group for Theoretical Nanophotonics at the Department of Physics and Astronomy at the University of New Mexico have dedicated to this end in a pioneering research effort entitled "Analysis of the Borders of Nanoparticle-Generated Near-Field Arrays," recently in the journal ACS Nano a top magazine in the field of nanotechnology, published.
The group, led by assistant professor Alejandro Manjavacas, studied the optical response of periodic metal arrays Nanostructures can be manipulated to create strong electric fields in their vicinity.
The arrays studied consist of silver nanoparticles, silver balls that are hundreds of times smaller than the thickness of a human hair and arranged in a repeating pattern, although their results also apply to nanostructures of other materials. Due to the strong interaction between the individual nanospheres, these systems can be used for a variety of applications, from vibrant, high-resolution color printing to biosensors that could revolutionize healthcare.
"This new work will help advance the many applications of nanostructure arrays by providing fundamental insights into their behavior," says Manjavacas. "The near-field improvements we predict could be critical for technologies such as ultrasensitive biosensors."
Manjavacas and his team, consisting of Lauren Zundel and Stephen Sanders, both graduate students of the Faculty of Physics and Astronomy, modeled the optics response of these arrays to find exciting new results. When periodic arrays of nanostructures are illuminated with light, each of the particles generates a strong response, which in turn leads to tremendous collective behavior when all the particles can interact with each other. This happens at certain wavelengths of incident light, as determined by the particle spacing of the array, and can result in electric fields that are thousands or even tens of thousands times larger than that of the light incident on the array.
The strength of this field enhancement depends on the geometric properties of the array, such as the distance between the nanospheres and the size of the spheres themselves. On the contrary, Manjavacas and his group found that reducing the density of nanoparticles in the array, either by increasing the distance between them or by reducing their size, causes field enhancements that are not only larger, but move farther away from the array.
"It was really exciting to find that the key to these tremendous field enhancements is to keep the particles smaller and farther apart," explains Zundel.
"The reason for this is the interactions The bond between the nanoparticles and thus the collective reaction is strengthened," says Sanders.
The research was sponsored in part by the National Science Foundation (NSF) and used the high-performance computation resources provided by the UNM Center for Advanced Research Computing.
Reference: "Analysis of the Borders of the Near Field Generated by Nanoparticle Arrays" by Alejandro Manjavacas, Lunds Zundel and Stephen Sanders, September 5, 2019, ACS Nano .
DOI: 10.1021 / acsnano.9b05031