(July 29, 2015) The
term “plasmons” might sound like something from the soon-to-be-released new
Star Wars movie, but the effects of plasmons have been known about for
centuries. Plasmons are collective oscillations of conduction electrons (those
loosely attached to molecules and atoms) that roll across the surfaces of
metals while interacting with photons. For example, plasmons from nanoparticles
of gold, silver and other metals interact with visible light photons to
generate the vibrant colors displayed by stained glass, a technology that dates
back more than 1,000 years. But plasmons have high-technology applications as
well. In fact, there’s even an emerging technology named for them – plasmonics
– that holds great promise for superfast computers and optical microscopy.
At the heart of the high-technology applications of plasmons
is their unique ability to confine the energy of a photon into a spatial
dimension smaller than the photon’s wavelength. Now, a team of researchers with
Berkeley Lab’s Materials Sciences Division, working at the Advanced Light
Source (ALS), has generated and detected plasmons that boast one of the
strongest confinement factors ever: the plasmon wavelength is only one
hundredth of the free-space photon wavelength.
By focusing infrared light onto the tip of an Atomic Force
Microscope, the researchers were able to observe what are called
“Luttinger-liquid” plasmons in metallic single-walled nanotubes. A
Luttinger-liquid is the theory that describes the flow of electrons through
one-dimensional objects, such as a single-walled nanotube (SWNT), much as the
Fermi-liquid theory describes the flow of electrons through most two- and
three-dimensional metals.