Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Duke chemists describe new kind of ’nanotube’ transistor


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:

More articles from Power and Electrical Engineering:

nachricht 'Super yeast' has the power to improve economics of biofuels
18.10.2016 | University of Wisconsin-Madison

nachricht Engineers reveal fabrication process for revolutionary transparent sensors
14.10.2016 | University of Wisconsin-Madison

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: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>