Navigation Links
Magnets trump metallics
Date:7/8/2010

Metallic carbon nanotubes show great promise for applications from microelectronics to power lines because of their ballistic transmission of electrons. But who knew magnets could stop those electrons in their tracks?

Rice physicist Junichiro Kono and his team have been studying the Aharonov-Bohm effect -- the interaction between electrically charged particles and magnetic fields -- and how it relates to carbon nanotubes. While doing so, they came to the unexpected conclusion that magnetic fields can turn highly conductive nanotubes into semiconductors.

Their findings are published online this month in Physical Review Letters.

"When you apply a magnetic field, a band gap opens up and it becomes an insulator," said Kono, a Rice professor in electrical and computer engineering and in physics and astronomy. "You are changing a conductor into a semiconductor, and you can switch between the two. So this experiment explores both an important aspect of the results of the Aharonov-Bohm effect and the novel magnetic properties of carbon nanotubes."

Kono, graduate student Thomas Searles and their colleagues at the National Institute of Standards and Technology (NIST) and in Japan successfully measured the magnetic susceptibility of a variety of nanotubes for the first time; they confirmed that metallics are far more susceptible to magnetic fields than semiconducting nanotubes, depending upon the orientation and strength of the field.

Single-walled nanotubes (SWNTs) -- rolled-up sheets of graphene -- would all look the same to the naked eye if one could see them. But a closer look reveals nanotubes come in many forms, or chiralities, depending on how they're rolled. Some are semiconducting; some are highly conductive metallics. The gold standard for conductivity is the armchair nanotube, so-called because the open ends form a pattern that looks like armchairs.

Not just any magnet would do for their experiments. Kono and Searles traveled to the Tsukuba Magnet Laboratory at the National Institute for Materials Science (NIMS) in Japan, where the world's second-largest electromagnet was used to tease a refined ensemble of 10 chiralities of SWNTs, some metallic and some semiconducting, into giving up their secrets.

By ramping the big magnet up to 35 tesla, they found that the nanotubes would begin to align themselves in parallel and that the metallics reacted far more strongly than the semiconductors. (For comparison, the average MRI machine for medical imaging has electromagnets rated at 0.5 to 3 tesla.) Spectroscopic analysis confirmed the metallics, particularly armchair nanotubes, were two to four times more susceptible to the magnetic field than semiconductors and that each chirality reacted differently.

The nanotubes were all about 0.7 to 0.8 nanometers (or billionths of a meter) wide and 500 nanometers long, so variations in size were not a factor in results by Searles. He spent a week last fall running experiments at the Tsukuba facility's "hybrid," a large-bore superconducting magnet that contains a water-cooled resistive magnet.

Kono said the work would continue on purified batches of nanotubes produced by ultracentrifugation at Rice. That should yield more specific information about their susceptibility to magnetic fields, though he suspects the effect should be even stronger in longer metallics. "This work clearly shows that metallic tubes and semiconducting tubes are different, but now that we have metallic-enriched samples, we can compare different chiralities within the metallic family," he said.


'/>"/>

Contact: David Ruth
druth@rice.edu
713-348-6327
Rice University
Source:Eurekalert

Related biology technology :

1. Sophisticated nano-structures assembled with magnets
2. Nanomagnets guide stem cells to damaged tissue
3. Let there be light: Teaching magnets to do more than just stick around
4. UD wins $4.4 million to develop next-generation magnets
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:6/23/2016)... , June 23, 2016  Blueprint Bio, a company ... to the medical community, has closed its Series A ... Nunez . "We have received a commitment ... capital we need to meet our current goals," stated ... us the runway to complete validation on the current ...
(Date:6/23/2016)... Francisco, CA (PRWEB) , ... June 23, 2016 ... ... (EDC) software, is exhibiting at the Pennsylvania Convention Center and will showcase its ... Annual conference. ClinCapture will also be presenting a scientific poster on Disrupting Clinical ...
(Date:6/23/2016)... , June 22, 2016  Amgen (NASDAQ: ... of the QB3@953 life sciences incubator to ... health. The shared laboratory space at QB3@953 was created ... a key obstacle for many early stage organizations - ... of the sponsorship, Amgen launched two "Amgen Golden Ticket" ...
(Date:6/22/2016)... 22, 2016 Research and Markets has announced ... report to their offering. ... from $29.3 billion in 2013. The market is expected to grow ... 2015 to 2020, increasing from $50.6 billion in 2015 to $96.6 ... during the forecast period (2015 to 2020) are discussed. As well, ...
Breaking Biology Technology:
(Date:5/20/2016)... , May 20, 2016  VoiceIt is ... partnership with VoicePass. By working together, ... experience.  Because VoiceIt and VoicePass take slightly different ... engines increases both security and usability. ... excitement about this new partnership. "This ...
(Date:5/12/2016)... 2016 WearablesResearch.com , a brand of ... results from the Q1 wave of its quarterly wearables ... consumers, receptivity to a program where they would receive ... insurance company. "We were surprised to see ... Michael LaColla , CEO of Troubadour Research, "primarily because ...
(Date:5/3/2016)...  Neurotechnology, a provider of high-precision biometric identification ... Identification System (ABIS) , a complete system for ... can process multiple complex biometric transactions with high ... face or iris biometrics. It leverages the core ... MegaMatcher Accelerator , which have been used in ...
Breaking Biology News(10 mins):