New Switch Could Improve Electronics

New Switch Could Improve Electronics

  11:15:00 PM    Science Lover

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Researchers at the University of Pittsburgh have invented a new type of electronic switch that performs electronic logic functions within a single molecule. The incorporation of such single-molecule elements could enable smaller, faster, and more energy-efficient electronics.

The switch was discovered by experimenting with the rotation
of a triangular cluster of three metal atoms held together by a
nitrogen atom, which is enclosed entirely within a cage made
up entirely of carbon atoms. (Credit: Image courtesy of
University of Pittsburgh)

The research findings, supported by a $1 million grant from the W.M. Keck Foundation, were published online in the Nov. 14 issue of Nano Letters.

"This new switch is superior to existing single-molecule concepts," said Hrvoje Petek, principal investigator and professor of physics and chemistry in the Kenneth P. Dietrich School of Arts and Sciences and codirector of the Petersen Institute for NanoScience and Engineering (PINSE) at Pitt. "We are learning how to reduce electronic circuit elements to single molecules for a new generation of enhanced and more sustainable technologies."

The switch was discovered by experimenting with the rotation of a triangular cluster of three metal atoms held together by a nitrogen atom, which is enclosed entirely within a cage made up entirely of carbon atoms. Petek and his team found that the metal clusters encapsulated within a hollow carbon cage could rotate between several structures under the stimulation of electrons. This rotation changes the molecule's ability to conduct an electric current, thereby switching among multiple logic states without changing the spherical shape of the carbon cage. Petek says this concept also protects the molecule so it can function without influence from outside chemicals.

Because of their constant spherical shape, the prototype molecular switches can be integrated as atom-like building blocks the size of one nanometer (100,000 times smaller than the diameter of a human hair) into massively parallel computing architectures.

The prototype was demonstrated using an Sc3N@C80 molecule sandwiched between two electrodes consisting of an atomically flat copper oxide substrate and an atomically sharp tungsten tip. By applying a voltage pulse, the equilateral triangle-shaped Sc3N could be rotated predictably among six logic states.

The research was led by Petek in collaboration with chemists at the Leibnitz Institute for Solid State Research in Dresden, Germany, and theoreticians at the University of Science and Technology of China in Hefei, People's Republic of China. The experiments were performed by postdoctoral researcher Tian Huang and research assistant professor Min Feng, both in Pitt's Department of Physics and Astronomy.

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Scientists find simple way to produce graphene

Scientists find simple way to produce graphene

  6:04:00 PM    Science Lover

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Scientists at Northern Illinois University say they have discovered a simple method for producing high yields of graphene, a highly touted carbon nanostructure that some believe could replace silicon as the technological fabric of the future.

Amartya Chakrabarti holds up a sample of
graphene produced via the dry-ice method.
Credit: Scott Walstrom, Northern Illinois University

The focus of intense scientific research in recent years, graphene is a two-dimensional material, comprised of a single layer of carbon atoms arranged in a hexagonal lattice. It is the strongest material ever measured and has other remarkable qualities, including high electron mobility, a property that elevates its potential for use in high-speed nano-scale devices of the future.

In a June communication to the Journal of Materials Chemistry, the NIU researchers report on a new method that converts carbon dioxide directly into few-layer graphene (less than 10 atoms in thickness) by burning pure magnesium metal in dry ice.

"It is scientifically proven that burning magnesium metal in carbon dioxide produces carbon, but the formation of this carbon with few-layer graphene as the major product has neither been identified nor proven as such until our current report," said Narayan Hosmane, a professor of chemistry and biochemistry who leads the NIU research group.

"The synthetic process can be used to potentially produce few-layer graphene in large quantities," he said. "Up until now, graphene has been synthesized by various methods utilizing hazardous chemicals and tedious techniques. This new method is simple, green and cost-effective."

Hosmane said his research group initially set out to produce single-wall carbon nanotubes. "Instead, we isolated few-layer graphene," he said. "It surprised us all."

"It's a very simple technique that's been done by scientists before," added Amartya Chakrabarti, first author of the communication to the Journal of Materials Chemistry and an NIU post-doctoral research associate in chemistry and biochemistry. "But nobody actually closely examined the structure of the carbon that had been produced."


Provided by Northern Illinois University

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Graphene Gets a Teflon Makeover

Graphene Gets a Teflon Makeover

  1:31:00 AM    Science Lover

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University of Manchester scientists have created a new material which could replace or compete with Teflon in thousands of everyday applications.

Graphane crystal. This novel two-dimensional material is 
obtained from graphene (a monolayer of carbon atoms) 
by attaching hydrogen atoms (red) to each carbon atoms 
(blue) in the crystal. (Credit: Mesoscopic Physics Group, 
Prof. Geim - University of Manchester)

Professor Andre Geim, who along with his colleague Professor Kostya Novoselov won the 2010 Nobel Prize for graphene -- the world's thinnest material, has now modified it to make fluorographene -- a one-molecule-thick material chemically similar to Teflon.

Fluorographene is fully-fluorinated graphene and is basically a two-dimensional version of Teflon, showing similar properties including chemical inertness and thermal stability.

The results are reported in the advanced online issue of the journal Small. The work is a large international effort and involved research groups from China, the Netherlands, Poland and Russia.

The team hope that fluorographene -- a flat, crystal version of Teflon and is mechanically as strong as graphene -- could be used as a thinner, lighter version of Teflon, and also find applications in electronics, such as for new types of LED devices.

Graphene, a one-atom-thick material that demonstrates a huge range of unusual and unique properties, has been at the centre of attention since groundbreaking research carried out at The University of Manchester six years ago.

Its potential is almost endless -- from ultrafast transistors just one atom thick to sensors that can detect just a single molecule of a toxic gas and even to replace carbon fibres in high performance materials that are used to build aircraft.

Professor Geim and his team have exploited a new perspective on graphene by considering it as a gigantic molecule that, like any other molecule, can be modified in chemical reactions.

Teflon is a fully-fluorinated chain of carbon atoms. These long molecules bound together make the polymer material that is used in a variety of applications including non-sticky cooking pans.

The Manchester team managed to attach fluorine to each carbon atom of graphene..

To get fluorographene, the Manchester researchers first obtained graphene as individual crystals and then fluorinated it by using atomic fluorine.

To demonstrate that it is possible to obtain fluorographene in industrial quantities, the researchers also fluorinated graphene powder and obtained fluorographene paper.

Fluorographene turned out to be a high-quality insulator which does not react with other chemicals and can sustain high temperatures even in air.

One of the most intense directions in graphene research has been to open a gap in graphene's electronic spectrum, that is, to make a semiconductor out of metallic graphene. This should allow many applications in electronics. Fluorographene is found to be a wide gap semiconductor and is optically transparent for visible light, unlike graphene that is a semimetal.

Professor Geim said: "Electronic quality of fluorographene has to be improved before speaking about applications in electronics but other applications are there up for grabs."

Rahul Nair, who led this research for the last two years and is a PhD student working with Professor Geim, added: "Properties of fluorographene are remarkably similar to those of Teflon but this is not a plastic.

"It is essentially a perfect one-molecule-thick crystal and, similar to its parent, fluorographene is also mechanically strong. This makes a big difference for possible applications.

"We plan to use fluorographene an ultra-thin tunnel barrier for development of light-emitting devices and diodes.

"More mundane uses can be everywhere Teflon is currently used, as an ultra-thin protective coating, or as a filler for composite materials if one needs to retain the mechanical strength of graphene but avoid any electrical conductivity or optical opacity of a composite."

Industrial scale production of fluorographene is not seen as a problem as it would involve following the same steps as mass production of graphene.

The Manchester researchers believe that the next important step is to make proof-of-concept devices and demonstrate various applications of fluorographene.

Professor Geim added: "There is no point in using it just as a substitute for Teflon. The mix of the incredible properties of graphene and Teflon is so inviting that you do not need to stretch your imagination to think of applications for the two-dimensional Teflon. The challenge is to exploit this uniqueness."

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