Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Duke chemists describe new kind of ’nanotube’ transistor

30.03.2004


Duke University researchers exploring ways to build ultrasmall electronic devices out of atom-thick carbon cylinders have incorporated one of these "carbon nanotubes" into a new kind of field effect transistor. The Duke investigators also reported new insights into their previously published technique for growing nanotubes in straight structures as long as half an inch.



Duke assistant chemistry professor Jie Liu will report on these and other nanotube developments during three talks at a national meeting of the American Chemical Society to be held March 28-April 1 in Anaheim, Calif.

Field effect transistors, among the workhorse devices of microelectronics technology, are tiny switches in which the passage of electric current between a "source" and a "drain" is controlled by an electric field in a middle component called a "gate."


Carbon nanotubes -- so named because of their billionths-of-a-meter dimensions ("nano" means billionths) -- combine exceptional strength, minuscule size and flexible electronic properties. They can behave either like conducting metals or like semiconductors, depending on how carbon atoms are arranged on their walls. As a result, they offer great promise as components in electronic devices even smaller than those available today.

The Duke research group headed by Liu is among a number that have incorporated a semiconducting nanotube as a component in an experimental field effect transistor. The nanotube is grown on a surface of silicon dioxide with metal electrodes evaporated on the nanotube’s surface serving as the device’s electron source and drain. Meanwhile, a layer of silicon fabricated under the silicon dioxide serves as the transistor’s gate, also called a "back gate."

However, other groups have found that this back gate of silicon, which is "doped" with other chemicals to fine-tune its electronic properties, is poorly coupled with the rest of the device. The result is excess power demand. "To turn the device from off to on, you need five to ten volts," Liu said in an interview.

To address this shortcoming, teams at two other universities have found they can reduce the power demand to between 0.3 and 0.5 volts by adding an additional gate made of a tiny droplet of salty water.

"That’s an order of magnitude of difference," Liu said of what he termed a "water gate." But "the disadvantage is that water is a liquid. So we looked for a way of replacing this water droplet with something that has similar properties but is a solid."

In a new paper in the research journal Nanoletters, Liu, graduate students Chenguang Lu and Qiang Fu, and research associate Shaoming Huang describe substituting an electrically conducting polymer that has been developed for dry lithium battery technology.

This substitute compound, called lithium perchlorate/polyethylene oxide (PEO), "can achieve similarly good device performance and avoid the problem of using liquid in the device," the Duke authors wrote in their paper. This PEO "polymer gate" is placed directly over the carbon nanotube.

Liu’s team found the polymer gate’s electronic properties can also be more easily fine-tuned to control the direction of the electric current by doping the underlying nanotube with other small carbon-containing molecules.

Doping silicon-based semiconductors in that way requires fabricators to precisely incorporate chemicals into those materials’ internal crystal structures. "For a nanotube, you just coat it on the surface, which is a lot easier," Liu said.

Also at the Anaheim meeting, Liu presented an update on research his group reported in the Journal of the American Chemical Society in April 2003 on growing straight and exceptionally long nanotubes that can be potentially cut into smaller lengths for splicing into electronic nanoarrays.

That 2003 journal report described how quick heating the emerging nanotubes in a continuously flowing feeding gas of carbon monoxide and hydrogen to a temperature hot enough to melt glass made the tubes grow in unusually long and true alignment. "We now have a much better understanding of why this fast heating technology performs differently," Liu said in an interview before his 2004 presentation.

In previous methods of using this chemical vapor deposition (CVD) process to grow nanotubes, the tubes extend along a surface of silicon dioxide. In the process, they encounter "physical resistance caused by the friction of bumping into other surface features," he explained. "That stops the growth of the nanotubes."

But quick-heating in the flowing gas makes the incipient nanotube lift up slightly above the surface as it begins to grow, he said. The growing nanotube follows the direction of the gas and stays slightly suspended, thus avoiding interacting with surface that is rough at molecular dimensions. "It’s like flying a kite," he added.

Monte Basgall | EurekAlert!
Further information:
http://www.dukenews.duke.edu/

More articles from Power and Electrical Engineering:

nachricht Electrical fields drive nano-machines a 100,000 times faster than previous methods
19.01.2018 | Technische Universität München

nachricht ISFH-CalTeC is “designated test centre” for the confirmation of solar cell world records
16.01.2018 | Institut für Solarenergieforschung GmbH

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

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

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Let the good tubes roll

19.01.2018 | Materials Sciences

How cancer metastasis happens: Researchers reveal a key mechanism

19.01.2018 | Health and Medicine

Meteoritic stardust unlocks timing of supernova dust formation

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>