09 December 2019

Researchers at the Laboratory of Organic Electronics have developed optical nanoantennas made from a conducting polymer. The antennas can be switched on and off, and will make possible a completely new type of controllable nano-optical components.

Shangzhi Chen, doctoral student and Magnus Jonsson, leader of the Organic Photonics and Nano-optics group at the Laboratory of Organic Electronics.
Shangzhi Chen, doctoral student and Magnus Jonsson, leader of the Organic Photonics and Nano-optics group at the Laboratory of Organic Electronics. Photographer: THOR BALKHED
Plasmons arise when light interacts with metallic nanoparticles. The incident light sets off a collective oscillation, a unified forwards and backwards motion, of the electrons in the particles. It is this collective oscillation that is the plasmon. Metallic nanostructures and their ability to shape light on a scale of nanometres are studied by many research groups around the world for use in, for example, biosensors and energy conversion devices, and to reinforce other optical phenomena. Other potential fields of use include miniature medical equipment and windows that control the amount of light and heat admitted to or emitted from a building.

Nature Nanotechnology

In an article in Nature Nanotechnology, scientists from Linköping University present optical nanoantennas, made from a conducting polymer instead of a traditional metal, such as gold or silver. In this case, they used a variant of PEDOT, which is a widely used polymer in many other areas, including thermoelectrics and bioelectronics.

Around billions of nanodisks deposited onto area of 1 cm2. Each one of them reacts to the incident light and creates plasmons. Around billions of nanodisks deposited onto area of 1 cm2. Each one of them reacts to the incident light and creates plasmons. Photo credit Illustration: Conceptualized“We show that light can be converted to plasmons in nanostructures of the organic material”, says Magnus Jonsson, leader of the Organic Photonics and Nano-optics group at the Laboratory of Organic Electronics.

It is, however, not electrons that create plasmons in the conducting polymer, but polarons. A polymer consists of a long chain of connected atoms and in the conducting polymer that the researchers have worked with, it is positive charges along the polymer chain that are responsible for the electrical conductivity. Together with associated chain distrorions these positive charges form polarons, which start collective oscillations when light is incident on the nanostructure.
“Our organic antennas can be transparent to visible light while reacting to light at somewhat longer wavelengths, making them interesting for applications such as smart windows”, says Magnus Jonsson.

Billions of tiny disks

The researchers initially carried out theoretical calculations and used simulations 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 oxidised state, and the nanoantennas are switched on.

“We have shown that when we reduce the material by exposing it to a vapour, we can switch off the conduction and in this Plasmons in plasticsPlasmons in plastics. Photo credit THOR BALKHEDway also the antennas. If we then reoxidise it using, for example, sulphuric acid, it regains its conductivity and the nanoantennas switch on again. This is a relatively slow process at the moment, but we have taken the first steps and shown that it is possible”, says Magnus Jonsson.

“While this is basic research, our results make possible a new type of controllable nano-optical components that we believe can to be used for many applications.”

The study was performed in collaboration between several researchers from the Laboratory of Organic Electronics and the Terahertz Materials Analysis Center at Linköping University. Financial support includes for example funding from the Swedish Research Council and the Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University.

Conductive polymer nanoantennas for dynamic organic plasmonics, Shangzhi Chen, Evan S. H. Kang, Mina S. Chaharsoughi, Vallery Stanishev, Philipp Kühne, Hengda Sun, Chuanfei Wang, Mats Fahlman, Simone Fabiano, Vanya Darakchieva and Magnus P. Jonsson, Nature Nanotechnology 2019, doi 10.1038/s41565-019-0583-y

Plasmons in plasticsSwitching on and off the antennas is a relatively slow process at the moment. Photo credit THOR BALKHED

Plasmons in medieval glass

It is plasmons that create the beautiful glowing colours in the stained-glass windows of medieval churches and mosques. The colours of the glass arise from metal particles embedded in it. But at the time, the craftsmen didn’t know that the metals give rise to plasmons. An early example of plasmons is the Lycurgus Cup at British Museum, London.

Translated by George Farrants

Contact

More news from the Laboratory of Organic Electronics

Iontronic pump in thin blood vessels.

More effective cancer treatment with iontronic pump

When low doses of cancer drugs are administered continuously near malignant brain tumours using so-called iontronic technology, cancer cell growth drastically decreases. This is demonstrated in experiments with bird embryos.

Sheet of glass with droplet.

Next-generation sustainable electronics are doped with air

Researchers at LiU have developed a new method where organic semiconductors can become more conductive with the help of air as a dopant. The study is a significant step towards future sustainable organic semiconductors.

Battery om fingertip.

Eco-friendly and affordable battery for low-income countries

A battery made from zinc and lignin that can be used over 8000 times. This has been developed by researchers at LiU with a vision to provide a cheap and sustainable battery solution for countries where access to electricity is limited.

More news

Research

Latest news from LiU

Nathalie Hallin and Hajdi Moche in conversation.

Religious people are not more generous – with one exception

Believers are no more generous than atheists – at least as long as they don’t know what the recipient believes in. This is the conclusion of a study carried out at LiU

Two persons in a room full och wires and optical instruments.

Quantum theory and information theory connected

With the help of a new experiment, researchers at LiU, have succeeded in confirming a ten-year-old theoretical study, which connects the complementarity principle with information theory.

happy young woman works on computer with books next to her, she has a sweater with math coach online symbols

Maths Coach Online – university students help with maths

“Mattecoach på nätet”, the online maths coach, has helped close to 70,000 students with maths. This collaboration between KTH, Linköping University and Chalmers has now spread internationally.