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 An innovative high-performance material: biofibers made from green lacewing silk
20.01.2017 | Fraunhofer-Institut für Angewandte Polymerforschung IAP

nachricht Treated carbon pulls radioactive elements from water
20.01.2017 | Rice University

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Traffic jam in empty space

New success for Konstanz physicists in studying the quantum vacuum

An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...

Im Focus: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Sustainable Water use in Agriculture in Eastern Europe and Central Asia

19.01.2017 | Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

 
Latest News

Helmholtz International Fellow Award for Sarah Amalia Teichmann

20.01.2017 | Awards Funding

An innovative high-performance material: biofibers made from green lacewing silk

20.01.2017 | Materials Sciences

Ion treatments for cardiac arrhythmia — Non-invasive alternative to catheter-based surgery

20.01.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>