Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Magnetic forces may turn some nanotubes into metals

21.05.2004


Research documents first instance of band-gap shrinkage in a semiconductor



A new study, published in today’s issue of the journal Science, finds that the basic electrical properties of semiconducting carbon nanotubes change when they are placed inside a magnetic field. The phenomenon is unique among known materials, and it could cause semiconducting nanotubes to transform into metals in even stronger magnetic fields.

Scientists found that the "band gap" of semiconducting nanotubes shrank steadily in the presence of a strong magnetic force, said lead researcher Junichiro Kono, an assistant professor of electrical and computer engineering at Rice University. The research, which involved a multidisciplinary team of electrical engineers, chemists and physicists, helps confirm quantum mechanical theories offered more than four decades ago, and it sheds new light on the unique electrical properties of carbon nanotubes, tiny cylinders of carbon that measure just one-billionth of a meter in diameter.


"We know carbon nanotubes are exceptionally strong, very light and imbued with wonderful electrical properties that make them candidates for things like ’smart’ spacecraft components, ’smart’ power grids, biological sensors, improved body armor and countless other applications," said paper co-author Richard Smalley, director of Rice’s Carbon Nanotechnology Laboratory. "These findings remind us that there are still unique and wonderful properties that we have yet to uncover about nanotubes."

By their very nature, semiconductors can either conduct electricity, in the same way metals do, or they can be non-conducting, like plastics and other insulators. This simple transformation allows the transistors inside a computer to be either "on" or "off," two states that correspond to the binary bits -- the 1’s and 0’s -- of electronic computation.

Semiconducting materials like silicon and gallium arsenide are the mainstays of the computer industry, in part because they have a narrow "band gap," a low energy threshold that corresponds to how much electricity it takes to flip a transistor from "off" to "on."

"Among nanotubes with band gaps comparable to silicon and gallium arsenide, we found that the band gap shrank as we applied high magnetic fields," said physicist Sasa Zaric, whose doctoral dissertation was based upon the work. "In even stronger fields, we think the gap would disappear altogether."

Nanotubes, hollow cylinders of pure carbon that are just one atom thick, come in dozens of different varieties, each with a subtle difference in diameter or physical structure. Of these varieties roughly one third are metals and the rest are semiconductors.

In the experiments, which were performed at the National High Magnetic Field Laboratory (NHMFL) at Florida State University, Kono’s group placed solutions of nanotubes inside a chamber containing very strong magnetic fields. Lasers were shined at the samples, and conclusions were drawn based upon an analysis of the light that was emitted and absorbed by the samples.

"The behavior we observed is unique among known materials, but it is consistent with theoretical predictions, and we believe we understand what’s causing it," said Kono. "Our data show, for the first time, that the so-called Aharonov-Bohm phase can directly affect the band structure of a solid. The Aharonov-Bohm effect has been observed in other physical systems, but this is the first case where the effect interferes with another fundamental solid-state theorem, that is, the Bloch theorem. This arises from the fact that nanotubes are crystals with well-defined lattice periodicity. I wouldn’t be surprised to see a corresponding effect in other tubular crystals like boron nitride nanotubes."

Kono said the discovery could lead to novel new experiments on one-dimensional magneto-excitons, quantum pairings that are interesting to researchers studying quantum computing, nonlinear optics and quantum optics. Kono said it’s too early to predict what types of applied science might flow from the discovery.

The NHMFL experiments were conducted in fields up to 45 Tesla in strength -- the strongest continuous magnetic field in any lab in the world. Kono said he is arranging for additional tests in stronger magnetic fields. He has already met with research groups in France, Tokyo and at New Mexico’s Los Alamos National Laboratory, each of which has facilities that use brief pulses of power to create short-lived magnetic fields that are exceptionally strong.


The research was supported by the Welch Foundation, the Texas Advanced Technology Program, the National Science Foundation, the NHMFL and the State of Florida. Other co-authors included NHMFL’s Xing Wei, and Rice’s Robert Hauge, Gordana Ostojic, Jonah Shaver, Valerie Moore and Michael Strano. Rice’s team represented the Carbon Nanotechnology Laboratory, the Center for Nanoscale Science and Technology, the Center for Biological and Environmental Nanotechnology and the Rice Quantum Institute.

Jade Boyd | EurekAlert!
Further information:
http://chico.rice.edu/

More articles from Materials Sciences:

nachricht Move over, Superman! NIST method sees through concrete to detect early-stage corrosion
27.04.2017 | National Institute of Standards and Technology (NIST)

nachricht Control of molecular motion by metal-plated 3-D printed plastic pieces
27.04.2017 | Ecole Polytechnique Fédérale de Lausanne

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>