Plasmons, which are density waves of electrons, are of great interest to pure and applied scientists because of their novel properties, and because of their application to sensing and photonic technologies.
Figure 1: A micrograph of a completed gold double-nanopillar array. Copyright : 2011 American Chemical Society
These applications are possible because plasmons are sensitive to surface properties, and allow for the concentration of electric fields into small volumes. Fabricating the intricate nanostructures necessary to support plasmons, however, has proved a challenge. Now a straightforward fabrication technique, capable of generating plasmon-supporting nanogap structures over large areas, has been demonstrated by Wakana Kubo and Shigenori Fujikawa from the RIKEN Innovation Center, Wako, and the Japan Science and Technology Agency.
The researchers fabricated many copies of a structure consisting of two nested vertical gold cylinders, with the cylinders spaced apart by tens of nanometers. This structure, called a ‘double nanopillar’, was designed to support a highly concentrated electric field in the gap between the cylinders, in response to illumination with light. When the gap was filled with a liquid or gas, the optical properties of the double nanopillar changed, making it a useful sensor.
Typically, closely gapped structures such as the double nanopillar are fabricated individually by carving a polymer resist with an electron beam, but this process is slow and can pattern only small areas. Fujikawa and colleagues used a template-based coating process instead. They etched a silicon wafer to make a mold of periodically spaced holes, and applied the mold to a soft polymer film, resulting in an array of polymer pillars. They then coated these pillars with a gold layer, followed by a spacer, and a second gold layer. Finally, they removed the polymer film and spacer layers, leaving a double nanopillar array. Using this process, the researchers could make a patterned area as large as the original template, and adapt it to include different spacer materials with finely controlled thicknesses.
Kubo and Fujikawa tested the double nanopillars as sensors of refractive index, which showed sensitivities that were greater than sensors that had equivalent metal surface areas, but which did not have a nanoscale gap. This comparison demonstrated that the electric field in the double nanopillars was indeed highly concentrated. The new fabrication process marks just the beginning of an extended research program, says Fujikawa. “We do not fully understand the optical behavior of these nanostructures,” he explains. “We will seek out collaborations with other researchers to investigate them further, and will try including magnetic, electric and organic materials into our process.”
The corresponding author for this highlight is based at the Interfacial Nanostructure Research Laboratory, RIKEN Innovation Center
 Kubo, W. & Fujikawa, S. Au double nanopillars with nanogap for plasmonic sensor. Nano Letters 11, 8–15 (2011)
Researchers identify potentially druggable mutant p53 proteins that promote cancer growth
09.12.2016 | Cold Spring Harbor Laboratory
Plant-based substance boosts eyelash growth
09.12.2016 | Fraunhofer-Institut für Angewandte Polymerforschung IAP
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine