(Left) Breakdownn of the printed substrate (Right) Tunneling microscope view of silicene (via PAtrick Vogt)

Graphene has been widely touted as the future replacement of silicon in electrical applications. In a turn of tables, element 14 (silicon) returns as a two dimensional allotrope known as "silicene." A collaborative effort between Berlin's Technical University and Aix-Marseille University led by Patrick Vogt were successful in creating a hexagonal sheet of silicon which is only 1 atom thick.

While graphene is an excellent superconductor in itself, it does not get along with silicon all that well due to integration/band-gap problems concerning the two materials. Whereas silicon (Si) based silicene has a honeycomb-lattice structure that allows electrons to ‘jump’ with relative ease back and forth which makes for a novel transistor on the small scale. To synthesize the silicene sheet, the scientists condensed silicon vapor onto a silver substrate. Then it was verified using a scanning tunneling microscope with an angular-resolved photoemission spectroscopy (ARPES), which is a scientific term for observing the distribution of electrons on a very, very small scale. The results showed silicene followed suit with predicted characteristics. Keep in mind, this does not mean an atom sized silicon transistor can be made. Silicon components are somewhat unpredictable smaller than 10 nano-meters.

Four other groups have claimed to accomplish the same feat using the same methods, but this team was the first to back it up with clear (albeit tiny) proof. The next step the team wants to pursue is to grow silicene on insulated substrates to measure its electrical properties which would give them better ideas as to how it could be incorporated into future electronics.

Silicene concept latice (via wikipedia)

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(Right) Professor Michael Weinert (Left) Graduate student Haihui Pu holding up a sculpture of the graphene monoxide (GMO) atomic structure

Graphene has been applied for a myriad of applications that include generators, solid state memory, and RF mixers to name a few. However, scientists from the University of Wisconsin have been successful at transforming graphene into a new substance which makes it ideal for use as a semiconductor.

The team of scientists and engineers were conducting experiments involving graphene-oxide heated inside a vacuum in order to reduce the oxygen content mixed throughout the on-atom thick material. Instead of eliminating the oxygen the team found that they created a new substance they call ‘graphene-monoxide’ (GMO). Actually, they succeeded in creating 4 new materials by varying the temperature inside the vacuum but all are collectively known as GMO. Graphene is extremely efficient when it comes to conducting electricity over gold and copper wiring, but until now the substance has only been applied as conductors and insulators.

GMO (graphene-monoxide), the team found, exhibits all three characteristics for electrical conductivity (conducting, insulating and semiconducting), which would be beneficial in making future electronics faster as we are reaching the end of how small we can go with silicon-based conductivity. The team is still exploring the exact details as to how they created this new substance and what the ideal conditions will be for its creation and destruction. Don’t expect GMO to be used as a semiconductor or implemented in near-future designs like new batteries anytime soon.

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See more about graphene:

Girl Scout cookies to graphene

155Ghz graphene transistor

Graphene transistor from Nobel Prize winner

Transparent graphene transistor material stretches beyond all others

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Graphene made cheap and green

Cutting Costs and Cooling Efficiently With Graphene

Creating graphene with the help of pond scum

Researches can grow large sheets of graphene in one step

Reduced graphene oxide (a) Optical magnification of sheet (b) increased magnification

Most of you have heard of graphene, one atom thick super-packed sheet of carbon atoms. It is little know that, depending on the process used, graphene is very difficult to produce. The materials used to make the extremely hard substance usually consist of using sodium ethoxide, magnesium or sugar as well of a host of other substances. The quantity produced using these materials is typically on the small side due to the toxic by-products (hydrazine) that come as a result of the manufacturing process (which is usually done with heat and/or chemicals).

A research team from Toyohashi Tech (Japan) headed by Yuji Tanizawa have come up with a novel way of producing graphene that significantly reduces, if not eliminates, the toxic after-birth by using micro-organisms found in ponds and rivers. Hydrazine is used to remove the oxygen from the graphene film which makes it denser and also stronger. Tanizawa and his team were able to eliminate the toxic by-product by realizing that graphene acts as a magnate to micro-organisms. These organisms, taken from a local river bank, help to reduce the oxygen left over from the chemical process used to create the graphene sheets.

GO (graphene oxide) via traditional methods in blue. Red is the bacterial reduced GO.

The team found that when sheets of graphene oxide (GO) were placed in a dish containing the pond water which was left to sit for three days produced high-quality graphene sheets. This process is not only a more environmentally friendly way of mass producing high-quality graphene, but it’s also a cheaper one. Maybe now we can actually see graphene introduced in our electronic devices' as core-technology.

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All images via Toyohashi University of Technology

Final  graphene material (left). Magnified transistor image (center).  Transistors placed onto a balloon. (right) (Via Lee, American Chemical  Society)

There appears to be legions of engineers and scientists pushing hard for stretchable electronics.  The latest comes in the form of a transparent material containing sets  of graphene transistors. Up to a 5% flex could be achieved before  degradation of the electrical qualities.

In an effort that spans 10 schools, project lead Jeong Ho Cho from Soongsil University and Jong-Hyun Ahn from Sungkyunkwan University,  both are South Korea, found a way to overcome common issues with making  transparent and flexible electronics by using a different type of  substrate. In past attempts, a slab of rubber or balloon surface was  used with limited flexibility. Jeong and his team fabricated single  layers of graphene onto copper foil. Using photolithography and etching  tricks, the transistor components (electrodes, semiconducting channels)  were forced into the graphene layers. The etched graphene was  transferred to the clear rubber. A stretchable ion-gel was used in the  final step to finish the transistor's components, gate insulators and  electrodes.

Graphene  can  be printed at low, and even at room, temperatures. This gave the  team an easy way to make and manipulate the organic graphene. At the  same time, graphene's innate stretch ability was ultimately the key to  their success. The fabricated material could bend at a maximum of 5% for  1,000 flexes. After which micro-cracks started forming dues to  imperfections in the graphene layers.

As  most researchers will say, the team vows to improve the capabilities of  their transparent flex transistors. The team sees applications in  medical biosensores that form to the human body and flex  displays. 100%  flexibility is what they need, but that final 95% is always the  hardest.

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Although  the researchers are using graphene transistors, the actual operation of  which may be in question. The band-gap ratio for graphene is around 30.  The larger the band gap, the more of an insulator the material becomes.  For comparison, the band gap of silicon is 1.11.

Process digram and professor Narayan Hosmane

In an effort to make single walled carbon nano-tubes, a team at Northern Illinois University (NIU) lead by professor Narayan Hosmane, how a simple way to produce graphene. Producing graphene before this discovery, was always a cumbersome, expensive, or hazardous process. Hosmane's method involves burning magnesium metal in solid state carbon dioxide, also known as dry ice. Their results produced large quantities of graphene up to 10 atoms thick. No word on whether this is a uniform thickness, nor the time of manufacturing.

Author of the report on the NIU process, Amartya Chakrabarti, admitted that, "It’s a very simple technique that’s been done by scientists before. But nobody actually closely examined the structure of the carbon that had been produced.”

Amartya Chakrabarti holding a sample of graphene made in the dry ice process

The research was supported by the National Science Foundation, Petroleum Research Fund administered by the American Chemical Society, the Robert A. Welch Foundation , and the Department of Energy.

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Pictures via NIU

It was impossible to see the edge-states of a graphene nano-ribbon until now. Before, only theoretical predictions could be made. Michael Crommie, of Berkeley Lab's Materials Sciences Division and UC Berkeley's Physics Division, used a scanning tunneling microscope on specially made graphene nano-ribbons and confirmed all the theoretical predications. The results of his research could lead to faster electronics, energy efficient nano-devices from these graphene nano-ribbons. More remarkable, electron charge and spin can be controlled at the edge-states. (See spintronics)

Using a special chemical process, graphene nano-tubes can be cut, un-zipped, in such a way that raised edges can be produced, also known as are-chair edges. It is at these scalloped edges that new potentials can be exploited. Crommie explains, "Two-dimensional graphene sheets are remarkable in how freely electrons move through them, including the fact that there's no band gap. Nanoribbons are different: electrons can become trapped in narrow channels along the nanoribbon edges. These edge-states are one-dimensional, but the electrons on one edge can still interact with the edge electrons on the other side, which causes an energy gap to open up...  We might also imagine spintronics applications, where using a side-gate geometry would allow control of the spin polarization of electrons at a nanoribbon's edge."

Controlling the edges is key to this discovery. The next step for Crommie and his team is to reproduce the arm-chair edges at a larger scale. As well as continuing the validation. Read more here.

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Stock image of the honeycomb graphene structure

Graphene is almost assuredly poised to replace silicon based devices in the future. From low cost, faster electron movement, to cooling effects, and now showing of a transistor that can operate at 155Ghz. IBM showed off its record breaking graphene transistor as of April 7th, 2011, defeating their previous record of 100Ghz set in February of 2010. IBM conducted the research to make a high-performance RF transistor for a DARPA project. The gate length of this new transistor in 40 nanometers, down from 550 from the 2010 demonstration.

The main issue with why graphene has taken over for silicon is the energy gap of the material. Graphene, at the moment, does not have a deep enough ratio to create and on-off digital switch.  However, the constant flow of energy makes graphene excellent at processing analog signals. According to IBM researcher, Yu-Ming Lin, "Graphene's high electron speed allows for faster processing of applications in analog electronics where such a high on-off ratio is not needed."

Our 155Ghz computers still await more research in gaphene, but IBM is definitely showing off a little glimpse at the future.

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