Plasmonics in the clouds

(Nanowerk Spotlight) Optical materials composed of plasmonic nanoparticles have revolutionized the ability to control light – yet these plasmonic materials are typically limited to only a few phases of matter, either as two-dimensional (2D) solids or dilute liquids.
Researchers at the U.S. Naval Research Laboratory now have experimentally realized a plasmonic aerosol by efficiently transitioning liquid suspensions of gold nanorods into the gas phase and simultaneously measuring their optical spectra.
Reporting their findings in Physical Review B ("Plasmonic aerosols"), they experimentally establish plasmonic aerosols and demonstrate that they are optically homogeneous, thermodynamically stable, with wide wavelength tunability (by controlling the aspect ratio of the nanorods) and have extremely large sensitivities to their environment.
conceptual rendering of a plasmonic aerosol
Conceptual rendering of a plasmonic aerosol. (Image: Jake Fontana and Robert Gates)
This novel plasmonic material could potentially open the door to many interesting applications ranging from geoengineering, vacuum microelectronics, molecular diagnostics, nanomedicines, nanojet printing and nonlinear optics.
"The aerosols are very sensitive to their surrounding environment, which may be used in the laboratory to aid in probing the nanoscale mechanisms governing macroscale atmospheric processes," Jake Fontana, Ph.D., a research physicist at the U.S. Naval Research Laboratory in Washington, DC, tells Nanowerk. "Additionally, these material may also open up broad and innovative approaches to understand the underlying physics of inaccessible climatology, astronomy, petroleum and medical environments."
Today, one of the largest uncertainties to accurately predicting climate and extreme weather events is the relationship between aerosol particles and cloud systems, which is a poorly understood nonlinear process (the aerosol particles serve as nucleation sites for water molecules to condense into droplets that can then form into clouds).
For instance, as the researchers write in their paper, recent work posited that aerosol particles from the exhaust of ships enhanced the intensity and electrification of storms, showing that the density of lightning strikes doubled over shipping lanes. Moreover, ultrafine aerosol particles with diameters below 50 nm, once thought to be too small to influence cloud formation, have recently been shown to significantly intensify the convective strength of cloud systems.
"Fundamentally, we solved a decades-old problem of simultaneously aerosolizing and measuring plasmonic nanoparticles in the gas phase, thereby merging the fields of plasmonics and aerosols," Fontana points out. "Globally, we anticipate plasmonic aerosols will open up broad and innovative approaches to understand the underlying physics of inaccessible climatology, astronomy, petroleum and medical environments."
While studies on micrometer sized aerosols have been carried out for decades, this is the first demonstration of efficiently aerosolizing plasmonic nanoparticles from the liquid to the gas phase, while simultaneously optically measuring them.
The aim of this work was to develop an approach to understand the relationship between aerosol nanoparticles and cloud systems in the laboratory to potentially help in addressing current geoengineering challenges.
"To that end, we are interested in experimentally measuring the response of the aerosols in different gas environments as well as refining our bench top aerosolization and detection apparatus," concludes Fontana.
By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny. Copyright © Nanowerk

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