Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Terahertz spectroscopy enters the single-molecule regime

04.09.2018

The interaction of light with matter is the basis of spectroscopy, a set of techniques lying at the heart of physics and chemistry. From infrared light to X-rays, a broad sweep of wavelengths is used to stimulate vibrations, electron transitions, and other processes, thus probing the world of atoms and molecules.

However, one lesser-used form of light is the terahertz (THz) region. Lying on the electromagnetic spectrum between infrared and microwaves, THz radiation does have the right frequency (around 10^12 Hz) to excite molecular vibrations.


This is an illustration of a Single molecule transistor (SMT) with a bowtie antenna structure. S, D, and G denote the source, drain, and gate electrodes of the SMT, respectively. A single molecule is captured in the created nanogap.

Credit: 2018 Kazuhiko Hirakawa, Institute of Industrial Science, The University of Tokyo

Unfortunately, its long wavelength (hundreds of micrometers) is around 100,000 times a typical molecular size, making it impossible to focus THz beams onto a single molecule by conventional optics. Only large ensembles of molecules can be studied.

Recently, a team led by The University of Tokyo's Institute of Industrial Science (IIS) found a way around this problem. In a study in Nature Photonics, they showed that THz radiation can indeed detect the motion of individual molecules, overcoming the classical diffraction limit for focusing light beams. In fact, the method was sensitive enough to measure the tunneling of a single electron.

The IIS team showcased a nanoscale design known as a single-molecule transistor. Two adjacent metal electrodes, the source and the drain of the transistor, are placed on a thin silicon wafer in a "bowtie" shape. Then, single molecules--in this case C60, aka fullerene--are deposited in the sub-nanometer gaps between the source and drain. The electrodes act as antennas to tightly focus the THz beam onto the isolated fullerenes.

"The fullerenes absorb the focused THz radiation, making them oscillate around their center-of-mass," explains study first-author Shaoqing Du. "The ultrafast molecular oscillation raises the electric current in the transistor, on top of its inherent conductivity."

Although this current change is minuscule--on the order of femto-amps (fA)--it can be precisely measured with the same electrodes used to trap the molecules. In this way, two vibrational peaks at around 0.5 and 1 THz were plotted.

In fact, the measurement is sensitive enough to measure a slight splitting of the absorption peaks, caused by adding or subtracting only one electron. When C60 oscillates on a metal surface, its vibrational quantum (vibron) can be absorbed by an electron in the metal electrode.

Thus stimulated, the electron tunnels into the C60 molecule. The resulting negatively charged C60? molecule vibrates at a slightly lower frequency than neutral C60, thus absorbing a different frequency of THz radiation.

Apart from providing a glimpse of tunneling, the study demonstrates a practical method to obtain electronic and vibronic information on molecules that only weakly absorb THz photons. This could open up the wider use of THz spectroscopy, an under-developed method that is complementary to visible-light and X-ray spectroscopy, and highly relevant to nanoelectronics and quantum computing.

###

The article, "Terahertz dynamics of electron-vibron coupling in single molecules with tunable electrostatic potential," was published in Nature Photonics at DOI: 10.1038/s41566-018-0241-1.

About Institute of Industrial Science (IIS), the University of Tokyo

Institute of Industrial Science (IIS), the University of Tokyo is one of the largest university-attached research institutes in Japan.

More than 120 research laboratories, each headed by a faculty member, comprise IIS, with more than 1,000 members including approximately 300 staff and 700 students actively engaged in education and research. Our activities cover almost all the areas of engineering disciplines. Since its foundation in 1949, IIS has worked to bridge the huge gaps that exist between academic disciplines and real-world applications.

Media Contact

Kazuhiko Hirakawa
hirakawa@iis.u-tokyo.ac.jp
81-354-526-260

https://www.iis.u-tokyo.ac.jp/en/ 

Kazuhiko Hirakawa | EurekAlert!
Further information:
https://www.iis.u-tokyo.ac.jp/en/news/2955/
http://dx.doi.org/10.1038/s41566-018-0241-1

More articles from Physics and Astronomy:

nachricht Astrophysicists measure precise rotation pattern of sun-like stars for the first time
21.09.2018 | NYU Abu Dhabi

nachricht Halfway mark for NOEMA, the super-telescope under construction
20.09.2018 | Max-Planck-Institut für Radioastronomie

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: Scientists present new observations to understand the phase transition in quantum chromodynamics

The building blocks of matter in our universe were formed in the first 10 microseconds of its existence, according to the currently accepted scientific picture. After the Big Bang about 13.7 billion years ago, matter consisted mainly of quarks and gluons, two types of elementary particles whose interactions are governed by quantum chromodynamics (QCD), the theory of strong interaction. In the early universe, these particles moved (nearly) freely in a quark-gluon plasma.

This is a joint press release of University Muenster and Heidelberg as well as the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt.

Then, in a phase transition, they combined and formed hadrons, among them the building blocks of atomic nuclei, protons and neutrons. In the current issue of...

Im Focus: Patented nanostructure for solar cells: Rough optics, smooth surface

Thin-film solar cells made of crystalline silicon are inexpensive and achieve efficiencies of a good 14 percent. However, they could do even better if their shiny surfaces reflected less light. A team led by Prof. Christiane Becker from the Helmholtz-Zentrum Berlin (HZB) has now patented a sophisticated new solution to this problem.

"It is not enough simply to bring more light into the cell," says Christiane Becker. Such surface structures can even ultimately reduce the efficiency by...

Im Focus: New soft coral species discovered in Panama

A study in the journal Bulletin of Marine Science describes a new, blood-red species of octocoral found in Panama. The species in the genus Thesea was discovered in the threatened low-light reef environment on Hannibal Bank, 60 kilometers off mainland Pacific Panama, by researchers at the Smithsonian Tropical Research Institute in Panama (STRI) and the Centro de Investigación en Ciencias del Mar y Limnología (CIMAR) at the University of Costa Rica.

Scientists established the new species, Thesea dalioi, by comparing its physical traits, such as branch thickness and the bright red colony color, with the...

Im Focus: New devices based on rust could reduce excess heat in computers

Physicists explore long-distance information transmission in antiferromagnetic iron oxide

Scientists have succeeded in observing the first long-distance transfer of information in a magnetic group of materials known as antiferromagnets.

Im Focus: Finding Nemo's genes

An international team of researchers has mapped Nemo's genome

An international team of researchers has mapped Nemo's genome, providing the research community with an invaluable resource to decode the response of fish to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

"Boston calling": TU Berlin and the Weizenbaum Institute organize a conference in USA

21.09.2018 | Event News

One of the world’s most prominent strategic forums for global health held in Berlin in October 2018

03.09.2018 | Event News

4th Intelligent Materials - European Symposium on Intelligent Materials

27.08.2018 | Event News

 
Latest News

Astrophysicists measure precise rotation pattern of sun-like stars for the first time

21.09.2018 | Physics and Astronomy

Brought to light – chromobodies reveal changes in endogenous protein concentration in living cells

21.09.2018 | Life Sciences

"Boston calling": TU Berlin and the Weizenbaum Institute organize a conference in USA

21.09.2018 | Event News

VideoLinks
Science & Research
Overview of more VideoLinks >>>