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26.06.2018 – 12:24

Technische Universität München

On the road to terahertz electronics: asymmetric plasmonic antennas deliver femtosecond pulses for fast optoelectronics

TECHNICAL UNIVERSITY OF MUNICH

Corporate Communications Center

phone: +49 89 289 10510 - e-mail: presse@tum.de - web: www.tum.de

This text on the web: https://www.tum.de/nc/en/about-tum/news/press-releases/detail/article/34767/

High-resolution images: https://mediatum.ub.tum.de/1446695

NEWS RELEASE

Closing the gap: On the road to terahertz electronics

Asymmetric plasmonic antennas deliver femtosecond pulses for fast optoelectronics

A team headed by Alexander Holleitner and Reinhard Kienberger, Physics professors at the Technical University of Munich (TUM), has succeeded for the first time in generating ultrashort electric pulses on a chip using metal antennas only a few nanometers in size, then running the signals a few millimeters above the surface and reading them in again a controlled manner. The technology enables the development of new, powerful terahertz components.

Classical electronics allows frequencies up to around 100 gigahertz. Optoelectronics uses electromagnetic phenomena starting at 10 terahertz. This range in between is referred to as the terahertz gap, since components for signal generation, conversion and detection have been extremely difficult to implement.

The TUM physicists Alexander Holleitner and Reinhard Kienberger succeeded in generating electric pulses in the frequency range up to 10 terahertz using tiny, so-called plasmonic antennas and run them over a chip. Researchers call antennas plasmonic if, because of their shape, they amplify the light intensity at the metal surfaces.

Asymmetric antennas

The shape of the antennas is important. They are asymmetrical: One side of the nanometer-sized metal structures is more pointed than the other. When a lens-focused laser pulse excites the antennas, they emit more electrons on their pointed side than on the opposite flat ones. An electric current flows between the contacts - but only as long as the antennas are excited with the laser light.

"In photoemission, the light pulse causes electrons to be emitted from the metal into the vacuum," explains Christoph Karnetzky, lead author of the Nature work. "All the lighting effects are stronger on the sharp side, including the photoemission that we use to generate a small amount of current."

Ultrashort terahertz signals

The light pulses lasted only a few femtoseconds. Correspondingly short were the electrical pulses in the antennas. Technically, the structure is particularly interesting because the nano-antennas can be integrated into terahertz circuits a mere several millimeters across.

In this way, a femtosecond laser pulse with a frequency of 200 terahertz could generate an ultra-short terahertz signal with a frequency of up to 10 terahertz in the circuits on the chip, according to Karnetzky.

The researchers used sapphire as the chip material because it cannot be stimulated optically and, thus, causes no interference. With an eye on future applications, they used 1.5-micron wavelength lasers deployed in traditional internet fiber-optic cables.

An amazing discovery

Holleitner and his colleagues made yet another amazing discovery: Both the electrical and the terahertz pulses were non-linearly dependent on the excitation power of the laser used. This indicates that the photoemission in the antennas is triggered by the absorption of multiple photons per light pulse.

"Such fast, nonlinear on-chip pulses did not exist hitherto," says Alexander Holleitner. Utilizing this effect he hopes to discover even faster tunnel emission effects in the antennas and to use them for chip applications.

Publication:

Towards femtosecond on-chip electronics based on plasmonic hot electron nano-emitters.

C. Karnetzky, P. Zimmermann, C. Trummer, C. Duque-Sierra, M. Wörle, R. Kienberger, A. Holleitner; Nature Communications June 25, 2018 - DOI: 10.1038/s41467-018-04666-y

https://www.nature.com/articles/s41467-018-04666-y

More information:

The experiments were funded by the European Research Council (ERC) as part of the "NanoREAL" project and the DFG Cluster of Excellence "Nanosystems Initiative Munich" (NIM).

Website Holleitner-group: https://www.wsi.tum.de/groups.php?group=holleitner

Website Kienberger-group: http://www.groups.ph.tum.de/e11

High-resolution images: https://mediatum.ub.tum.de/1446695

Contact:

Prof. Dr. Alexander Holleitner

Walter Schottky Institute / Department of Physics

Center for Nanotechnology and Nanomaterials

Technical University of Munich

Am Coulombwall 4a, 85748 Garching, Germany

Tel: +49 89 289 11575

E-Mail: holleitner@wsi.tum.de

Prof. Dr. Reinhard Kienberger

Department of Physics, E11

Technical University of Munich

James-Franck-Str. 1, 85748 Garching, Germany

Tel: +49 89 289 12840

E-Mail: reinhard.kienberger@tum.de

Technical University of Munich (TUM) is one of Europe's leading research
universities, with about 550 professors, around 10,000 academic and non-academic
staff, and 41,000 students. Its focus areas are the engineering sciences,
natural sciences, life sciences and medicine, combined with economic and social
sciences. TUM acts as an entrepreneurial university that promotes talents and
creates value for society. In that it profits from having strong partners in
science and industry. It is represented worldwide with a campus in Singapore as
well as offices in Beijing, Brussels, Cairo, Mumbai, San Francisco, and São
Paulo. Nobel Prize winners and inventors such as Rudolf Diesel, Carl von Linde,
and Rudolf Mößbauer have done research at TUM. In 2006 and 2012 it won
recognition as a German "Excellence University." In international 
rankings, TUM
regularly places among the best universities in Germany. www.tum.de