Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

The dispute about the origins of terahertz photoresponse in graphene results in a draw

25.04.2018

Physicists at MIPT and their British and Russian colleagues revealed the mechanisms leading to photocurrent in graphene under terahertz radiation. The paper published in Applied Physics Letters not only puts a period to a long-lasting debate about the origins of direct current in graphene illuminated by high-frequency radiation but also sets the stage for the development of high-sensitivity terahertz detectors. Such detectors are highly demanded in medical diagnostics, wireless communications and security systems.

In 2005 MIPT alumni Andre Geim and Konstantin Novoselov experimentally studied the behavior of electrons in graphene, a flat honeycomb lattice of carbon atoms. They found that electrons in graphene respond to electromagnetic radiation with an energy of quantum, whereas the common semiconductors have an energy threshold below which the material does not respond to light at all.


Photoresponse in graphene.

Credit: Lion_on_helium, MIPT press office

However, the direction of electron motion in graphene exposed to radiation has long remained a point of controversy, as there is a plenty of factors pulling it in different directions. The controversy was especially stark in the case of the photocurrent caused by terahertz radiation.

What sets terahertz radiation apart is its unique set of properties. As an example, it easily passes through many dielectrics without ionizing them: this is of particular value to medical diagnostic or security systems.

A terahertz camera can "see" the weapons concealed under a person's clothes, and a medical scanner can detect skin diseases at early stages by the spectral lines ("fingerprints") of characteristic biomolecules in the terahertz range.

Finally, raising the carrier frequency of Wi-Fi devices from several to hundreds of gigahertz (into the sub-terahertz range) will proportionally increase the bandwidth. But all these applications need a sensitive and low-noise terahertz detector which is simple in fabrication.

A terahertz detector designed by researchers at MIPT, MSPU and the University of Manchester (the place where graphene was first discovered) is a graphene sheet (colored green in figures 1 and 2) sandwiched between dielectric layers of boron nitride and electrically coupled to a terahertz antenna--a metal spiral about a millimeter in size.

As radiation impinges on the antenna, it rocks electrons on one side of the graphene sheet, while the resulting direct current is measured on the other side. It is the "packing" of graphene into boron nitride that enables record-high electric characteristics, giving the detector a sensitivity that is a cut above the earlier designs. However, the main result of the research is not a better-performing instrument; it is the insight into the physical phenomena responsible for the photocurrent.

There are three main effects leading to the electric current flowing in graphene exposed to terahertz radiation. The first one, the photothermoelectric effect, is due to the temperature difference between the antenna terminal and the sensing terminal. This sends electrons from the hot terminal to the cold one, like air rising up from a warm radiator up to cold ceiling.

The second effect is the rectification of current at the terminals: it turns out that the edges of graphene let through only the high-frequency signal of a certain polarity. The third and most interesting effect is called plasma wave rectification. We can think of the antenna terminal as stirring up "waves in the electronic sea" of the graphene strip, while the sensing terminal registers the average current associated with these waves.

"Earlier attempts to explain the photocurrent in such detectors used only one of these mechanisms and excluded all the others," says Dmitry Svintsov, head of the Laboratory of 2d Materials' Optoelectronics at MIPT.

"In reality, all three of them are at play, and our study found which effect dominates at which conditions. Thermoelectric effects dominate at low temperatures, while plasmonic rectification prevails at high temperatures and in longer-channel instruments. And the main thing is that we figured out how to make a detector in which the different photoresponse mechanisms will not cancel each other, but rather reinforce each other"

These experiments will help choose the best design for terahertz detectors and bring us closer to remote detection of dangerous substances, safe medical diagnostics, and high-speed wireless communications.

###

The work was supported by the Russian Science Foundation, the Ministry of Education and Science of the Russian Federation, the Leverhulme Trust (Great Britain) and the Russian Foundation for Basic Research.

Media Contact

Ilyana Zolotareva
shaibakova@phystech.edu
977-771-4699

 @phystech_en

https://mipt.ru/english/

Ilyana Zolotareva | EurekAlert!

More articles from Physics and Astronomy:

nachricht The cascade to criticality
02.06.2020 | ETH Zurich Department of Physics

nachricht K-State study reveals asymmetry in spin directions of galaxies
02.06.2020 | Kansas State University

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: New measurement exacerbates old problem

Two prominent X-ray emission lines of highly charged iron have puzzled astrophysicists for decades: their measured and calculated brightness ratios always disagree. This hinders good determinations of plasma temperatures and densities. New, careful high-precision measurements, together with top-level calculations now exclude all hitherto proposed explanations for this discrepancy, and thus deepen the problem.

Hot astrophysical plasmas fill the intergalactic space, and brightly shine in stellar coronae, active galactic nuclei, and supernova remnants. They contain...

Im Focus: Biotechnology: Triggered by light, a novel way to switch on an enzyme

In living cells, enzymes drive biochemical metabolic processes enabling reactions to take place efficiently. It is this very ability which allows them to be used as catalysts in biotechnology, for example to create chemical products such as pharmaceutics. Researchers now identified an enzyme that, when illuminated with blue light, becomes catalytically active and initiates a reaction that was previously unknown in enzymatics. The study was published in "Nature Communications".

Enzymes: they are the central drivers for biochemical metabolic processes in every living cell, enabling reactions to take place efficiently. It is this very...

Im Focus: New double-contrast technique picks up small tumors on MRI

Early detection of tumors is extremely important in treating cancer. A new technique developed by researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from normal tissue. The work is published May 25 in the journal Nature Nanotechnology.

researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from...

Im Focus: I-call - When microimplants communicate with each other / Innovation driver digitization - "Smart Health“

Microelectronics as a key technology enables numerous innovations in the field of intelligent medical technology. The Fraunhofer Institute for Biomedical Engineering IBMT coordinates the BMBF cooperative project "I-call" realizing the first electronic system for ultrasound-based, safe and interference-resistant data transmission between implants in the human body.

When microelectronic systems are used for medical applications, they have to meet high requirements in terms of biocompatibility, reliability, energy...

Im Focus: When predictions of theoretical chemists become reality

Thomas Heine, Professor of Theoretical Chemistry at TU Dresden, together with his team, first predicted a topological 2D polymer in 2019. Only one year later, an international team led by Italian researchers was able to synthesize these materials and experimentally prove their topological properties. For the renowned journal Nature Materials, this was the occasion to invite Thomas Heine to a News and Views article, which was published this week. Under the title "Making 2D Topological Polymers a reality" Prof. Heine describes how his theory became a reality.

Ultrathin materials are extremely interesting as building blocks for next generation nano electronic devices, as it is much easier to make circuits and other...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Dresden Nexus Conference 2020: Same Time, Virtual Format, Registration Opened

19.05.2020 | Event News

Aachen Machine Tool Colloquium AWK'21 will take place on June 10 and 11, 2021

07.04.2020 | Event News

International Coral Reef Symposium in Bremen Postponed by a Year

06.04.2020 | Event News

 
Latest News

Perfect optics through light scattering

02.06.2020 | Power and Electrical Engineering

The digital construction site: A smarter way of building with mobile robots

02.06.2020 | Architecture and Construction

Process behind the organ-specific elimination of chromosomes in plants unveiled

02.06.2020 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>