Graphene news

Charged impurities proven to be the source of low electron mobility in graphene

posted Mar 15, 2012, 6:03 AM by Hatef Sadeghi

Researchers from Vanderbilt say they now understand for certain why graphene is so sensitive to its electrical environment. Solving this issue will allow to have better electron mobility in graphene at room-temperature, and come close to graphene's theoretical (but not practical) high electron mobility.
The problem is charged impurities on the surface of graphene. This was suspected before, but is now confirmed. Now the challenge will be to make graphene without those charged impurities.

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Graphene membranes sealed everything but water, can be used to distill alcohol

posted Jan 27, 2012, 5:57 AM by Hatef Sadeghi

A team of researchers led by Professor Sir Andre Geim demonstrated a graphene-Oxide based membrane that is impermeable to all gases and liquids (i.e. it's vacuum-tight) - but water can evaporate though it as if there's no membrane at all.
The researchers explain: "Graphene oxide sheets arrange in such a way that between them there is room for exactly one layer of water molecules. They arrange themselves in one molecule thick sheets of ice which slide along the graphene surface with practically no friction. If another atom or molecule tries the same trick, it finds that graphene capillaries either shrink in low humidity or get clogged with water molecules."
This membrane can be used to remove water from a mixture or container. The team sealed a bottle of Vodka with such a membrane and this resulted in water evaporating - and the drink became stronger with time.

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Researchers discover new graphene nanomaterials With tunable functionality in electronics

posted Jan 8, 2012, 5:10 AM by Hatef Sadeghi

Researchers from the Rensselaer Polytechnic Institute have discovered new graphene based materials that can be customized to produce specific band gap and magnetic properties (i.e. have tunable functionality in electronics). The materials may be used to enable new nanoelectronics, optics, and spintronics devices.
The researchers found out that graphitic nanoribbons can be segmented into several different surface structures called nanowiggles. Each of these structures produces highly different magnetic and conductive properties. This means that you can basically create a new graphene nanostructure that is customized for a specific task or device.

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Carbon Nanotube-Enabled Flexible Backplanes Promise Smart Device Ubiquity

posted Dec 20, 2011, 8:20 AM by Hatef Sadeghi   [ updated Dec 20, 2011, 8:26 AM ]

Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a material that uses carbon nanotubes to create a flexible backplane for an artificial electronic skin (e-skin).
Curiously the researchers bemoan the general problem that has existed in this are of flexible electronics of not being able to attain a pure single-walled carbon nanotube (SWNT) solution to create your flexible electronic devices. I say curious because Zhenan Bao—the same researcher at Stanford who developed the artificial skin—also developed in cooperation with researchers from the University of California Davis a method by which to come up with the exact mix of SWNTs you want.
In the Berkeley Lab press release it is made clear that the researchers used “a SWNT solution enriched to be 99-percent semiconductor tubes”, but it doesn’t indicate how they were able to get that level of purity. Maybe they can give Bao a shout out and try and use her method.
In any case, it will be interesting to see if the two research groups can move this initial work that uses  artificial skin as a demonstration of the methods into broader uses for furthering the development of flexible electronics.

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IBM produced RF ICs on an 8" graphene wafer

posted Dec 11, 2011, 6:48 PM by Hatef Sadeghi

IBM has managed to produce RF integrated circuits on an 8" graphene wafer. IBM says that this demonstration is a "major step in transitioning this promising material from a scientific curiosity into a real technology". The graphene was grown on copper foil from high-temperature vapor and later coated with the polymer PMMA.
These are RF devices - as it's still difficult to create logic using graphene (it has no natural bandgap), although some researchers are working towards methods to fix this issue.

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Graphene-based transistor array that can record electrical signals generated by biological cells

posted Dec 11, 2011, 6:46 PM by Hatef Sadeghi

Researchers from the Juelich Research Center and the Technische Universitaet Muenchen developed a graphene-based transistor array that can record electrical signals generated by biological cells.
The team demonstrated an array of 16 graphene solution-gated field-effect transistors (G-SGFETs) - produced over a copper foil using standard photolithographic and etching and chemical vapor deposition processes. A biological cell layer analogous to the heart muscle was deposited directly over this array. The transistor array detected and recorded single cells' action potentials at high resolution.

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Graphene oxide spun into several meters long fibers

posted Dec 11, 2011, 6:44 PM by Hatef Sadeghi

Researchers from China's Zhejiang University in Hangzhou demonstrated meter long graphene fibers - made from nano-sized flakes of graphene oxide. These fibers are strong and flexible and can be tied in knots or woven into conductive "mats".
The researchers use web spinning to turn a graphene oxide solution into long (tens of meters!) fibers. They then treated those fibers with chemical reduction to turn them back in strings of graphene. The next stage for their research is to improve the fiber's strength - which currently cannot compete with carbon fibers.

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Graphene used as a transparent conducting layer for UV LEDs

posted Nov 10, 2011, 8:57 AM by Hatef Sadeghi

Researchers from Korea and the USA developed a Ultraviolet nitride (UV) LED that uses a few layers of graphene as a transparent conducting layer. They say that Graphene may prove better than the currently-used ITO as it performs better in terms of cost, transparency, and, heat and current spreading. Graphene also sports improved transmission in the ultraviolet.
Graphene however suffers from reliability and degradation issues that must be further investigated.

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Dramatic optical limiting effect in graphene demonstrated

posted Nov 8, 2011, 2:36 AM by Hatef Sadeghi

Researchers from Singapore and the UK demonstrated a dramatic optical limiting effect in graphene using dispersed sub-oxidized graphene. While transparency in graphene is useful, having non-transparent (or light limiting) graphene also has its applications.
The optical-limiting effect achieved using suspensions of carbon nanotubes or carbon black occurs through a 'damage' mechanism involving the development of microbubbles or microplasmas at high light fluence, which increases light scattering and breaks the optical transparency.

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Korean researchers fabricated a stretchable, transparent graphene-based transistor

posted Oct 28, 2011, 1:55 AM by Hatef Sadeghi

Korean researchers fabricated a stretchable, transparent graphene-based transistor. They say that the new to transistor overcomes some of the problems faced by transistors made of conventional semiconductor materials - which simply cannot be made stretchable and transparent on substrates such as rubber slabs or balloons.
To make the transistor, the researchers synthesized single layers of graphene and then stacked them layer by layer on copper foil. Using photolithography and etching techniques, the researchers patterned some of the transistor’s essential elements, including the electrodes and semiconducting channel, onto the graphene. After transferring these components onto a stretchable rubber substrate, the researchers printed the remaining components – gate insulators and gate electrodes – onto the device using stretchable ion gel.
The graphene based transistors could be stretched up to 5% for 1,000 times and still maintain their good electrical properties. In one experiment, the researchers fabricated the graphene transistors on a rubber balloon and measured its electrical properties as they inflated the balloon. When stretched more than 5%, the electrical properties began to degrade, due partly to microcracks and other defects in the graphene films.

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