In a paper published this week in Science, a Manchester team lead by Nobel laureates Professor Andre Geim and Professor Konstantin Novoselov has literally opened a third dimension in graphene research. Their research shows a transistor that may prove the missing link for graphene to become the next silicon.

Graphene – one atomic plane of carbon – is a remarkable material with endless unique properties, from electronic to chemical and from optical to mechanical.

One of many potential applications of graphene is its use as the basic material for computer chips instead of silicon. This potential has alerted the attention of major chip manufactures, including IBM, Samsung, Texas Instruments and Intel. Individual transistors with very high frequencies (up to 300 GHz) have already been demonstrated by several groups worldwide.

Unfortunately, those transistors cannot be packed densely in a computer chip because they leak too much current, even in the most insulating state of graphene. This electric current would cause chips to melt within a fraction of a second.

This problem has been around since 2004 when the Manchester researchers reported their Nobel-winning graphene findings and, despite a huge worldwide effort to solve it since then, no real solution has so far been offered.

The University of Manchester scientists now suggest using graphene not laterally (in plane) – as all the previous studies did – but in the vertical direction. They used graphene as an electrode from which electrons tunnelled through a dielectric into another metal. This is called a tunnelling diode.

Then they exploited a truly unique feature of graphene – that an external voltage can strongly change the energy of tunnelling electrons. As a result they got a new type of a device – vertical field-effect tunnelling transistor in which graphene is a critical ingredient.

(via Researchers move graphene electronics into 3D)

Organic polymers can be used to create materials with very distinct properties (both good and bad). For example, thermoset materials resist heat and solvents, making them extremely durable and allowing them to be used in the oven. The downside is that, once they’re made, that’s it—no recycling. Thermoplastics are stable below a set temperature, but they can be melted, allowing them to be remade into new materials. Unfortunately, they don’t hold up very well to solvents.

Now, researchers are saying they’ve created a third option, one that acts like a thermoplastic at high temperatures but can hold up to most solvents. The material’s secret? An embedded catalyst that allows chemical bonds to constantly rearrange. The material’s desired properties can be tuned based on the polymer it’s made from and how much catalyst remains. (via New, recyclable plastic lets you weld pieces together with a hairdryer)

Seeing beneath the surface at Knole

Helen Fawbert and her team at Knole have recently spent a day x-raying some of the magnificent pieces of furniture in the house…

(via Treasure Hunt)

Designer optoelectronics - quantum mechanics for new materials

European researchers have combined computer modelling of quantum mechanics and precision fabrication processes to create novel transparent conductive oxides made to order for a wide range of scientific and consumer applications.

Imagine specifying exactly how you want a new material to behave, handing those specs to an engineer, and getting back a brand-new material with exactly the qualities you need.

That’s what the EU-funded project NATCO (for Novel Advanced Transparent Conductive Oxides) set out to do. They designed and developed novel transparent conductive oxides (TCOs) to exacting specifications by applying quantum mechanics to predict a material’s optical and electronic properties, fabricating it, and checking their results experimentally.

The results? Completely new TCOs with a wide range of potential applications in sensors, solar cells, smart windows, and dozens of other scientific, commercial and consumer products.

“In the field of optoelectronics, there’s a great need to find better and less costly materials,” says Guy Garry, coordinator of the NATCO project. “The route we took was first to make calculations to find the best way to get the properties that we needed. When we fabricated these materials, we found that their properties were the same as we had calculated.”

This rational design process - using first principles to calculate the conductivity and transparency of novel materials before fabricating them - allowed the researchers to develop new TCOs with enhanced performance rapidly and efficiently.

“We were able to make these calculations very quickly, which allowed us to enhance existing properties and find new properties,” says Dr Garry.

Brand new optoelectronic material

TCOs - materials that combine transparency and conductivity, qualities that are not usually found together - have multiple applications. As sensors, photovoltaics, light emitting devices and electronically controllable films, they are found in scientific instruments, DVDs, digital cameras, mobile phones, computer displays and hundreds of other products.

Until recently, most TCOs relied on a material called ITO, an oxide of indium which is doped - slightly modified - by the addition of a small quantity of tin. ITOs have proved useful, but, Dr Garry says, suffer from two drawbacks. Their transparency is not very good, especially in the near-infrared range, and indium is in short supply and very expensive.

The NATCO team decided to explore a completely different material, strontium cuprate doped with varying amounts of barium. Copper, barium and strontium are far more abundant and much less expensive than indium.

Extensive calculations applying quantum mechanics predicted that, by doping strontium cuprate with a few percent by weight of barium, the researchers could create precisely the materials they wanted, combining good electrical conductivity and optical transparency.

Fabricating the new materials was a challenge. At first the materials were fabricated in the form of bulk ceramics and then, for actual applications, thin layers were deposited on suitable substrates.

In the end, the researchers settled on two deposition techniques - pulsed laser deposition (PLD) and metal organic chemical deposition (MOCVD). 

In PLD, a burst of laser light vaporises the material to be deposited, creating a thin film on a glass or silicon surface. It allows precise control, but can’t be used on large surfaces.

MOCVD uses organic chemistry to create gasses that deposit the desired material onto a surface. It is a more complicated procedure, but has the advantage of being able to be scaled up to coat large surfaces.

Once they had fabricated the materials, the researchers could test how well their electrical and optical properties matched the predicted values. “This was the first time that this kind of work was done on TCOs,” says Dr Garry.

Multiple applications in the works

Today, one of the most promising applications of NATCO’s new TCOs is in the area of exquisitely sensitive biosensors. These devices, with the tongue-twisting title of Elecro-Chemical Optical Waveguide Light-mode Spectroscopy Sensors, are fabricated by the Hungarian consortium partner MicroVacuum. They work by measuring how light is bent as it passes through a very thin optical wave guiding layer.

When target molecules bind to the surface of the detector, they change the TCO´s refractive index, which in turn changes how light passes through the waveguide. Applying a varying electric field through the layer provides further information about the molecules.

“We got very good results on these devices using our strontium cuprate materials,” says Dr Garry. He foresees a wide range of applications for these sensors, especially in the area of proteomics.

The project’s commercial and academic partners are pursuing other applications for NATCO’s designer TCOs, including more efficient solar cells, smart windows, novel light sources, and materials to modulate laser light.

For Dr Garry, the results of the project’s first-principles modelling and precision fabrication approach are so encouraging that he plans to apply them to more challenging problems.

“We’d like to use this route to study more complicated materials,” he says. “For example, to look at ferro-electricity to see why some materials with the same structure are ferro-electric while others are not.”

More information: NATCO project - http://www.trt.tha … co/index.htm

Provided by ICT Results (news : web)

[Source: Phys.Org]

Cornell researchers made a thin film of europium titanate ferromagnetic and ferroelectric by “stretching” it. They did it by depositing the material on an underlying substrate with a larger spacing between its atoms.

Researchers ‘stretch’ a lackluster material into a possible electronics revolution

It’s the Clark Kent of oxide compounds, and - on its own - it is pretty boring. But slice europium titanate nanometers thin and physically stretch it, and then it takes on super hero-like properties that could revolutionize electronics, according to new Cornell research. (Nature, Aug. 19, 2010.)

Researchers report that thin films of europium titanate become both ferroelectric (electrically polarized) and ferromagnetic (exhibiting a permanent magnetic field) when stretched across a substrate of dysprosium scandate, another type of oxide. The best simultaneously ferroelectric, ferromagnetic material to date pales in comparison by a factor of 1,000.

Simultaneous ferroelectricity and ferromagnetism is rare in nature and coveted by electronics visionaries. A material with this magical combination could form the basis for low-power, highly sensitive magnetic memory, magnetic sensors or highly tunable microwave devices.

The search for ferromagnetic ferroelectrics dates back to 1966, when the first such compound - a nickel boracite - was discovered. Since then, scientists have found a few additional ferromagnetic ferroelectrics, but none stronger than the nickel compound - that is, until now.

“Previous researchers were searching directly for a ferromagnetic ferroelectric - an extremely rare form of matter,” said Darrell Schlom, Cornell professor of materials science and engineering, and an author on the paper.

“Our strategy is to use first-principles theory to look among materials that are neither ferromagnetic nor ferroelectric, of which there are many, and to identify candidates that, when squeezed or stretched, will take on these properties,” said Craig Fennie, assistant professor of applied and engineering physics, and another author on the paper.

This fresh strategy, demonstrated using the europium titanate, opens the door to other ferromagnetic ferroelectrics that may work at even higher temperatures using the same materials-by-design strategy, the researchers said.

Other authors include David A. Muller, Cornell professor of applied and engineering physics; and first author June Hyuk Lee, a graduate student in Schlom’s lab.

The researchers took an ultra-thin layer of the oxide and “stretched” it by placing it on top of the disprosium compound. The crystal structure of the europium titanate became strained because of its tendency to align itself with the underlying arrangement of atoms in the substrate.

Fennie’s previous theoretical work had indicated that a different kind of material strain - more akin to squishing by compression - would also produce ferromagnetism and ferroelectricity. But the team discovered that the stretched europium compound displayed electrical properties 1,000 times better than the best-known ferroelectric/ferromagnetic material thus far, translating to thicker, higher-quality films.

This new approach to ferromagnetic ferroelectrics could prove a key step toward the development of next-generation memory storage, superb magnetic field sensors and many other applications long dreamed about. But commercial devices are a long way off; no devices have yet been made using this material. The Cornell experiment was conducted at an extremely cold temperature - about 4 degrees Kelvin (-452 Fahrenheit). The team is already working on materials that are predicted to show such properties at much higher temperatures.

Provided by Cornell University (news : web)

[Source: Phys.org]