Mobile Computing: flexible

Wednesday, 19 December 2012

Photonics: Graphene's flexible future

Dec. 10, 2012 — Theoretical calculations show graphene's potential for controlling nanoscale light propagation on a chip.

Semiconductors have revolutionized computing because of their efficient control over the flow of electrical currents on a single chip, which has led to devices such as the transistor. Working towards a similar tunable functionality for light, researchers from the A*STAR Institute of High Performance Computing (IHPC), Singapore, have shown how graphene could be used to control light at the nanometer scale, advancing the concept of photonic circuits on chips1.

Graphene, which is made from a single layer of carbon atoms, has excellent electronic properties; some of these are also useful in photonic applications. Usually, only metals are able to confine light to the order of a few nanometers, which is much smaller than the wavelength of the light. At the surface of metals, collective oscillations of electrons, so-called 'surface plasmons', act as powerful antennae that confine light to very small spaces. Graphene, with its high electrical conductivity, shows similar behavior to metals so can also be used for plasmon-based applications, explains Choon How Gan of IHPC, who led the research.

Gan and co-workers studied theoretically and computationally how surface plasmons travel along sheets of graphene. Even though graphene is a poorer conductor than a metal, so plasmon propagation losses are higher, it has several key advantages, says team member Hong Son Chu. "The key advantage that makes graphene an excellent platform for plasmonic devices is its large tunability that cannot be seen in the usual noble metals," he explains. "This tunability can be achieved in different ways, using electric or magnetic fields, optical triggers and temperature."

The team's calculations indicated that surface plasmons propagating along a sheet of graphene would be much more confined to a small space than they would traveling along a gold surface (see image). However, the team also showed that surface plasmons would travel far better between two sheets of graphene brought into close contact. Furthermore, by adjusting design parameters such as the separation between the sheets, as well as their electrical conductivity, much better control over surface plasmon properties is possible.

In the future, Gan and his co-workers plan to investigate these properties for applications. "We will explore the potential of graphene plasmonic devices also for the terahertz and mid-infrared regime," he explains. "In this spectral range, graphene plasmonic structures could be promising for applications such as molecular sensing, as photodetectors, or for optical devices that can switch and modulate light."

The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing

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The above story is reprinted from materials provided by The Agency for Science, Technology and Research (A*STAR).
Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Choon How Gan, Hong Son Chu, Er Ping Li. Synthesis of highly confined surface plasmon modes with doped graphene sheets in the midinfrared and terahertz frequencies. Physical Review B, 2012; 85 (12) DOI: 10.1103/PhysRevB.85.125431

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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Developing power sources for flexible, stretchable electronics

Dec. 14, 2012 — Electronic devices become smaller, lighter, faster and more powerful with each passing year. Currently, however, electronics such as cell phones, tablets, laptops, etc., are rigid. But what if they could be made bendable or stretchy?

According to the University of Delaware's Bingqing Wei, stretchable electronics are the future of mobile electronics, leading giants such as IBM, Sony and Nokia to incorporate the technology into their products.

Beyond traditional electronics, potential stretchable applications include biomedical, wearable, portable and sensory devices, such as cyber skin for robotic devices and implantable electronics.

"Advances in soft and stretchable substrates and elastomeric materials have given rise to an entirely new field," says Wei, a mechanical engineering professor at UD.

But even if scientists can engineer stretchable electronics -- what about their energy source?

"Rechargeable and stretchable energy storage devices, also known as supercapacitors, are urgently needed to complement advances currently being made in flexible electronics," explains Wei.

Wei's research group at the University is making significant progress in developing scalable, stretchable power sources for this type of application using carbon nanotube macrofilms, polyurethane membranes and organic electrolytes.

This, he says, requires new thinking about materials processing and device manufacturing to maximize energy storage without compromising energy resources.

To reveal a stretchable supercapacitator's true performance, the Wei group examined the system's electrochemical behavior using buckled single-wall nanotube (SWNT) electrodes and an elastomeric separator.

According to Wei, the supercapacitor developed in his lab achieved excellent stability in testing and the results will provide important guidelines for future design and testing of this leading-edge energy storage device.

As they work to refine the technology, Wei has filed a provisional patent to protect his team's research. The work was recently published in Nano Letters, a journal of the American Chemical Society.