Page 102 - Plastics News December 2019

tEChNoLogy

Creating switchable plasmons in plastics

esearchers in the Organic Photonics and Nano-optics Electronics. It is, however, not electrons that create
Rgoup at the Laboratory of Organic Electronics have plasmons in the conducting polymer, but polarons. A
developed optical nanoantennas made from a conducting polymer consists of a long chain of connected atoms and in
polymer. The antennas can be switched on and off, and the conducting polymer that the researchers have worked
will make possible a completely new type of controllable with, it is positive charges along the polymer chain that
nano-optical components. Plasmons arise when light are responsible for the electrical conductivity. Together
interacts with metallic nanoparticles. The incident light with associated chain distrorions these positive charges
sets off a collective oscillation, a unified forwards and form polarons, which start collective oscillations when
backwards motion, of the electrons in the particles. It light is incident on the nanostructure.
is this collective oscillation that is the plasmon. Metallic
nanostructures and their ability to shape light on a scale "Our organic antennas can be transparent to visible light
of nanometres are studied by many research groups while reacting to light at somewhat longer wavelengths,
around the world for use in, for example, biosensors making them interesting for applications such as smart
and energy conversion devices, and to reinforce other windows," says Magnus Jonsson. The researchers initially
optical phenomena. Other potential fields of use include carried out theoretical calculations and used simulations
miniature medical equipment and windows that control to design experiments, which they were subsequently
able to carry out. Shangzhi Chen, doctoral student
in the group, has managed to produce billions of
tiny nanometre-sized disks of the organic conducting
material on a surface. These small disks react to light
and act as tiny antennas. The researchers have shown
that both the diameter and the thickness of the disks
determine the frequency of light to which they react. It
is thus possible to control this wavelength by changing
the geometry of the disk. The thicker the disk, the
higher the frequency. They are also hoping that they
can increase the range of wavelengths to which the
nanoantennas react by changing the polymer used.
Another innovation they have explored is the ability
to switch the organic nanoantennas on and off, which
is difficult with conventional metals. The material
manufactured in the laboratory is initially in an

the amount of light and heat admitted to or emitted oxidised state, and the nanoantennas are switched on."We
from a building. In an article in Nature Nanotechnology, have shown that when we reduce the material by exposing
scientists from Linköping University present optical it to a vapour, we can switch off the conduction and in
nanoantennas, made from a conducting polymer instead this way also the antennas. If we then reoxidise it using,
of a traditional metal, such as gold or silver. In this case, for example, sulphuric acid, it regains its conductivity and
they used a variant of PEDOT, which is a widely used the nanoantennas switch on again. This is a relatively slow
polymer in many other areas, including thermoelectrics process at the moment, but we have taken the first steps
and bioelectronics. "We show that light can be converted and shown that it is possible," says Magnus Jonsson."While
to plasmons in nanostructures of the organic material," this is basic research, our results make possible a new type
says Magnus Jonsson, leader of the Organic Photonics of controllable nano-optical components that we believe
and Nano-optics group at the Laboratory of Organic can to be used for many applications."

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