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2013年11月17日星期日

Spider's super-thin ribbons key to silk tech

Nov. 5, 2013 — The silk of a spider feared for its venomous bite could be the key to creating new super-sticky films and wafer-thin electronics and sensors for medical implants that are highly compatible with the human body.

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A team of scientists from Oxford University (UK) and The College of William and Mary (USA) studied the brown recluse spider [Loxosceles recluse] which produces super-thin ribbons of silk as opposed to the round fibres typically spun by spiders. The researchers report in the journal Advanced Materials how, in a world-first, they were able to reel and examine the unique properties of the brown recluse's silk ribbons.

Whilst the silk ribbons have the outstanding strength and toughness of standard spider silk their flat structure makes it possible to study the material's molecular structure in great detail and investigate what gives it its strength. The team found that the extreme thinness of the ribbons, which are up to 10 nanometres wide and only a few tens of nanometers thick, combined with its stiffness and the ability to adapt to the shapes of surfaces is what gives it its unprecedented adhesive properties. The team also found that the surface of the silk ribbons is covered with tiny, dot-like 'bumps' that the research team suspects further enhance adhesion.

'The enigmatic ribbon structure of these threads provides us with a window into spider silk in its simplest form,' said Professor Fritz Vollrath of Oxford University's Department of Zoology, an author of the study. 'All other silks are round, rope-like aggregates made up of many nano-scale filaments. This makes it virtually impossible to study in great detail the molecular structure of the silk itself, and the fundamentals for its great toughness.'

Professor Hannes Schniepp of The College of William and Mary, lead author of the report, said: 'We were able to modify an atomic force microscope to measure the rigidity of a single recluse fibre and discovered that this ribbon -- only a few molecules thick -- not only displays the great properties of other silks but allows us to probe its structure in unprecedented detail.'

This discovery is expected to have implications for the development of new super-sticky cling films and also for the manufacture of thin-film electronic devices, which might even be implanted as sensors in the human body -- where silks are highly valued for their outstanding combination of great mechanical strength and excellent biological compatibility.

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New compact atomic clock design uses cold atoms to boost precision

Described in a new paper, the heart of the prototype clock (the vacuum chamber containing the atoms) is about the size of a coffee mug, 150 cubic centimeters, set in a small table of lasers and electronics. This is about 10 times larger than NIST's chip-scale atomic clock packages -- for now. But when miniaturized and improved, NIST's new clock design has the potential to be about the same size and 1,000 times more precise and stable than chip-scale atomic clocks over crucial timespans of a day or more.

By achieving this goal, the cold-atom clock could also match the performance of commercial cesium-beam atomic clocks, common laboratory instruments, but in a smaller package.

"We're trying to push ultraportable clocks to higher performance levels," NIST physicist Elizabeth Donley says. "The aim is to make a clock that does not even need calibration."

NIST pioneered the development of chip-sized atomic clocks in 2004. Atomic clocks of similar design using atoms in a hot gas were commercialized a few years ago. For the past eight years this NIST research group has concentrated on a spin-off technology, chip-scale atomic magnetometers, but recently refocused on miniature atomic clock designs.

Chip-scale atomic clocks keep time well enough for many applications requiring timing synchronization over short periods, such as GPS receivers. But clock precision tends to drift over time spans beyond a few hours because the atoms are dispersed in high-pressure gases, which alter the atoms' resonant frequency -- the clock tick rate -- depending on temperature. The new cold-atom clock does not use these gases at all, thus eliminating this source of error. Improvements like this could extend the uses of small, low-power clocks to exacting applications such as synchronizing telecommunications networks.

NIST's cold-atom clock relies on about 1 million rubidium atoms held in a small glass vacuum chamber. The atoms are cooled with lasers and trapped with magnetic fields at very cold, microkelvin temperatures. Two near-infrared lasers excite the atoms symmetrically from above and below. Each laser generates two frequencies of light, which are tuned until the atoms oscillate between two energy states and stop absorbing light. This sets the clock ticking rate at a specific microwave frequency.

By aiming at the atoms from opposite directions simultaneously, the laser arrangement cancels a major source of measurement error -- the Doppler shift, or the change in the atoms' apparent resonant frequency as they interact and move with the laser light. The clock also has special quantum features unique to rubidium atoms that boost the signal contrast and make the detection of the clock ticks more precise.

NIST researchers are already working on the next version of the cold-atom clock. In addition to reducing its size, researchers expect to improve its performance by adding magnetic shielding and antireflection coating. The research is funded in part by the Defense Advanced Research Projects Agency.

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Inkjet-based circuits created at fraction of time and cost

The technique, called instant inkjet circuits, allows the printing of arbitrary-shaped conductors onto rigid or flexible materials and could advance the prototyping skills of non-technical enthusiasts and novice hackers.

"We believe there is an opportunity to introduce a new approach to the rapid prototyping of fully custom-printed circuits," said Gregory Abowd, Regents' Professor in the School of Interactive Computing at Georgia Tech and an investigator in the study. "Unlike existing methods for printing conductive patterns, conductivity in our technique emerges within a few seconds and without the need for special equipment."

Recent advances in chemically bonding metal particles allowed the researchers to use silver nanoparticle ink to print the circuits and avoid thermal bonding, or sintering, a time-consuming and potentially damaging technique due to the heat. Printing the circuits on resin-coated paper, PET film and glossy photo paper worked best. Researchers also made a list of materials to avoid, such as canvas cloths and magnet sheets.

"Everything we introduced in our research is available in the market and makes it possible for people to try this at home," said Yoshihiro Kawahara, associate professor at the University of Tokyo and the primary investigator who developed the methodology while in Atlanta. "The method can be used to print circuit boards, sensors and antennas with little cost, and it opens up many new opportunities."

To make the technique possible, researchers optimized commercially available tools and materials including printers, adhesive tape and the silver ink. Designing the circuit itself was accomplished with desktop drawing software, and even a photocopy of a drawing can produce a working circuit.

Once printed, the circuits can be attached to electronic components using conductive double-sided tape or silver epoxy adhesive, allowing full-scale prototyping in mere hours. The homemade circuits might allow tinkerers to quickly prototype crude calculators, thermostat controls, battery chargers or any number of electronic devices.

"Using this technology in the classroom, it would be possible to introduce students to basic electronics principles very cheaply, and they could use a range of electronic components to augment the experience," said Steve Hodges, a team member from Microsoft Research.

To show the capabilities of the new technique for capacitive touch sensing -- the interaction prominent in smartphone interfaces -- and the flexibility of the printed circuits, the researchers attached a capacitive ribbon with embedded inkjet-printed circuits into a drinking glass. The capacitive ribbon sensor formed to the contour of the glass and, when connected to a micro controller, was able to measure how much liquid was left in the glass.

The details for replicating the process were presented at the 2013 ACM International Joint Conference on Pervasive and Ubiquitous Computing (UbiComp 2013) in Zurich, Switzerland, Sept. 8-12. The research "Instant Inkjet Circuits: Lab-based Inkjet Printing to Support Rapid Prototyping of UbicComp Devices" won a best paper award at the conference and can be found here: http://dl.acm.org/citation.cfm?id=2493486.

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Wireless device converts 'lost' energy into electric power: Metamaterial cells provide electric power as efficiently as solar panels

Nov. 7, 2013 — Using inexpensive materials configured and tuned to capture microwave signals, researchers at Duke University's Pratt School of Engineering have designed a power-harvesting device with efficiency similar to that of modern solar panels.

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The device wirelessly converts the microwave signal to direct current voltage capable of recharging a cell phone battery or other small electronic device, according to a report appearing in the journal Applied Physics Letters in December 2013.

It operates on a similar principle to solar panels, which convert light energy into electrical current. But this versatile energy harvester could be tuned to harvest the signal from other energy sources, including satellite signals, sound signals or Wi-Fi signals, the researchers say.

The key to the power harvester lies in its application of metamaterials, engineered structures that can capture various forms of wave energy and tune them for useful applications.

Undergraduate engineering student Allen Hawkes, working with graduate student Alexander Katko and lead investigator Steven Cummer, professor of electrical and computer engineering, designed an electrical circuit capable of harvesting microwaves.

They used a series of five fiberglass and copper energy conductors wired together on a circuit board to convert microwaves into 7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power.

"We were aiming for the highest energy efficiency we could achieve," said Hawkes. "We had been getting energy efficiency around 6 to 10 percent, but with this design we were able to dramatically improve energy conversion to 37 percent, which is comparable to what is achieved in solar cells."

"It's possible to use this design for a lot of different frequencies and types of energy, including vibration and sound energy harvesting," Katko said. "Until now, a lot of work with metamaterials has been theoretical. We are showing that with a little work, these materials can be useful for consumer applications."

For instance, a metamaterial coating could be applied to the ceiling of a room to redirect and recover a Wi-Fi signal that would otherwise be lost, Katko said. Another application could be to improve the energy efficiency of appliances by wirelessly recovering power that is now lost during use.

"The properties of metamaterials allow for design flexibility not possible with ordinary devices like antennas," said Katko. "When traditional antennas are close to each other in space they talk to each other and interfere with each other's operation. The design process used to create our metamaterial array takes these effects into account, allowing the cells to work together."

With additional modifications, the researchers said the power-harvesting metamaterial could potentially be built into a cell phone, allowing the phone to recharge wirelessly while not in use. This feature could, in principle, allow people living in locations without ready access to a conventional power outlet to harvest energy from a nearby cell phone tower instead.

"Our work demonstrates a simple and inexpensive approach to electromagnetic power harvesting," said Cummer. "The beauty of the design is that the basic building blocks are self-contained and additive. One can simply assemble more blocks to increase the scavenged power."

For example, a series of power-harvesting blocks could be assembled to capture the signal from a known set of satellites passing overhead, the researchers explained. The small amount of energy generated from these signals might power a sensor network in a remote location such as a mountaintop or desert, allowing data collection for a long-term study that takes infrequent measurements.

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Business Top apprentice is project manager at IBM

2013/11/15

Sadie Hawkins

The 20-year-old project manager for IBM UK, Sadie Hawkins has been named EAL Advanced Apprentice of the Year.

She is in the second year of a three-year apprenticeship and is already handling a multi-million budget as an IBM project manager for a major telecoms client.

“Sadie was the stand out winner among a list of very impressive young candidates. It is testament to her hard work and dedication that she has been acknowledged in these prestigious awards,” said Julia Chippendale, managing director of EAL, the awarding organisation for industry qualifications.

Hawkins aims to develop her career with IBM and she encouraged all young persons to consider an apprenticeship as an option.

“It has given me a unique opportunity to work towards a fulfilling career. I aim to use this success to inspire others and to continue my development and desire to learn,” said Hawkins.

She received her award at the National Apprenticeship Awards in Birmingham.

Hawkins left Park House School in Newbury Berkshire with A levels in IT, English Literature and Psychology and A/S levels in History and Business Studies.

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Taking a new look at carbon nanotubes

Nov. 12, 2013 — Despite their almost incomprehensibly small size -- a diameter about one ten-thousandth the thickness of a human hair -- single-walled carbon nanotubes come in a plethora of different "species," each with its own structure and unique combination of electronic and optical properties. Characterizing the structure and properties of an individual carbon nanotube has involved a lot of guesswork -- until now.

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Researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley have developed a technique that can be used to identify the structure of an individual carbon nanotube and characterize its electronic and optical properties in a functional device.

"Using a novel high-contrast polarization-based optical microscopy set-up, we've demonstrated video-rate imaging and in-situ spectroscopy of individual carbon nanotubes on various substrates and in functional devices," says Feng Wang, a condensed matter physicist with Berkeley Lab's Materials Sciences Division. "For the first time, we can take images and spectra of individual nanotubes in a general environment, including on substrates or in functional devices, which should be a great tool for advancing nanotube technology."

Wang, who is also a professor with UC Berkeley's Physics Department, is the corresponding author of a paper describing this research in the journal Nature Nanotechnology. Co-authors are Kaihui Liu, Xiaoping Hong, Qin Zhou, Chenhao Jin, Jinghua Li, Weiwei Zhou, Jie Liu, Enge Wang and Alex Zettl.

A single-walled carbon nanotube can be metallic or semiconducting depending on its exact structure. Semiconducting nanotubes can have very different electronic bandgaps, resulting in wildly different electronic or optical properties.

"To fully understand field-effect devices or optoelectronic devices made from single-walled carbon nanotubes, it is critical to know what species of carbon nanotube is in the device," Wang says. "In the past, such information could not be obtained and researchers had to guess as to what was going on."

The physical structure and electronic properties of each individual species of single-walled carbon nanotubes are governed by chirality, meaning their structure has a distinct left/right orientation or "handedness," which cannot be superimposed on a mirror image. As a result, achieving chirality-controlled growth of carbon nanotubes and understanding the physics behind chirality-dependent devices are two of the biggest challenges in nanotube research.

"Polarization-based optical microscopy and spectroscopy techniques are well-suited for meeting these challenges, as polarized light is extremely sensitive to optical anisotropy in a system and has long been exploited to study chirality in molecules and crystals," Wang says. "However, the small signal and unavoidable environment background has made it difficult to use polarized optical microscopy to study single carbon nanotubes."

Difficulties arise from an apparent contradiction in polarization-based optical microscopy. For any optical microscope, a large numerical aperture (NA) objective is crucial for high-spatial resolution, but polarized light passing through a large NA objective becomes strongly depolarized. With their new technique, Wang and his colleagues were able to do what has not been done before and simultaneously achieve both high polarization and high spatial resolution.

"The key to our success was the realization that light illumination and light collection can be controlled separately," Wang says. "We used a large NA objective for light collection to obtain high spatial resolution, but were able to create an effectively small NA objective for illumination to maintain high polarization purity."

In their set-up, Wang and his colleagues collected nanotube-scattered polarized light with a 0.8 NA objective but used a much more narrow incident beam to create illumination light from a supercontinuum laser with a much smaller NA. The result was polarization an order of magnitude higher than what has been achieved with conventional polarized microscopy and spatial resolution at the nanoscale. This enabled them to obtain complete chirality profiles of hundreds of as-grown carbon nanotubes, and to perform in-situ monitoring in active field-effect devices.

"We observed that high order nanotube optical resonances are dramatically broadened by electrostatic doping, an unexpected behavior that points to strong inter-band electron-electron scattering processes dominating the ultrafast dynamics of excited states in carbon nanotubes," Wang says.

In addition to individual single-walled carbon nanotubes, Wang and his colleagues say their technique can also be used to greatly enhance the optical contrast of other anisotropic nano-sized materials that are "invisible" to conventional optical microscopes, including graphene nanoribbons, semiconductor nanowires and nanorods, and nanobiomaterials such as actin filaments.

This research was supported by grants from the National Science Foundation, the Center for Integrated Nanomechanical Systems, and by DOE's Office of Science.

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New way to dissolve semiconductors holds promise for electronics industry

Richard L. Brutchey and David H. Webber note that making low-cost, semiconducting thin films on a large scale holds promise for improving a number of electronic applications, including solar cells. The problem has been finding a liquid that can dissolve semiconductors so that they can be subsequently solution-processed using inexpensive methods. Hydrazine can do the trick for many of these materials, but as a compound that is sometimes used in rocket fuel, it is explosive and highly toxic. It's also a poor option for making semiconducting thin films en masse. Brutchey and his team decided to search for a safer solution.

They found an answer in a mixture of two compounds that could dissolve a set of important semiconducting materials called chalcogenides at room temperature and normal air pressure. The researchers state, "We believe these initial results indicate that the chemistry can be further extended to other families of chalcogenide materials and may hold promise for applications that would benefit from solution deposition of semiconductor thin films."

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Carbon nanotube field electron emitters will get space testing

Nov. 14, 2013 — A pair of carbon nanotube arrays will be flying in space by the end of the year to test technology that could provide more efficient micro-propulsion for future generations of spacecraft. Part of a Cube Satellite (CubeSat) developed by the Air Force Institute of Technology (AFIT), the arrays will support what is expected to be the first-ever space-based testing of carbon nanotubes as electron emitters.

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Researchers at the Georgia Tech Research Institute (GTRI) produced the arrays using unique technology that grows bundles of vertically-aligned nanotubes embedded in silicon chips. In future versions of electrically-powered ion thrusters, electrons emitted from the carbon nanotube tips may be used to ionize a gaseous propellant such as xenon. The ionized gas would then be ejected through a nozzle to provide thrust for moving a satellite in space.

"The mission will characterize how well these field emission electron sources operate in the space environment relative to how well they work on the ground in vacuum chamber," said Jud Ready, a GTRI principal research engineer. "Launch vibrations and exposure to a space environment that includes atomic oxygen and micrometeorites could have some unusual effects on the arrays. This mission will help us evaluate whether these carbon nanotube electron emitters could be used in ion thrusters."

Existing ion thrusters rely on thermionic cathodes, which use high temperatures generated by electrical current to produce electrons. These devices require significant amounts of electricity to generate the heat, and must consume a portion of the propellant for their operation.

If the carbon nanotube arrays can be used as electron emitters, they would operate at lower temperatures with less power -- and without using the limited on-board propellant. That could allow longer mission times for satellites, or reduce the weight of the micro-propulsion systems.

The carbon nanotube arrays are part of ALICE, a CubeSat micro-satellite developed and built by the Air Force Institute of Technology at Wright-Patterson Air Force Base in Ohio. On a mission scheduled for Dec. 5 from Vandenberg Air Force Base in California, ALICE will ride into space on an Atlas V rocket being used to launch a separate and much larger payload. Just 10 by 10 by 30 centimeters in size, ALICE will be part of an array of eight CubeSats -- so named because they fit into small modular launchers attached to the main satellite.

The work could lead to improved micro-propulsion systems useful to small spacecraft, said Jonathan Black, director of the Center for Space Research and Assurance at AFIT.

"Technology like the devices being tested on ALICE is essential to our future ability to maneuver micro satellites or change their orbits," he explained. "Being able to incorporate propulsion into microsatellites like CubeSats increases mission longevity and the types of missions they can perform. Successful demonstrations of advanced technologies like those being flown on ALICE will ultimately lead to smaller, lighter and more energy-efficient propulsion, resulting in decreased launch costs while increasing the performance of all satellites using electric propulsion."

Utilizing a multi-departmental team, AFIT engineers in the Electrical Engineering Department developed a payload to directly expose the carbon nanotube arrays to the space environment while protecting an identical control array within the satellite. The arrays, which are approximately one centimeter square, will be switched on and off and their behavior studied. The payload experiment utilizes a sensor device known as the Integrated Miniaturized Electromagnetic Analyzer (iMESA), designed by engineers at the U.S. Air Force Academy (USAFA). The data collected from the satellite will be downloaded and processed at AFIT by students and technicians in the Department of Aeronautics and Astronautics.

The carbon nanotube arrays are excellent conductors and their geometry makes them ideal electron emitters.

"We use carbon nanotubes because they have a high aspect ratio and provide a nanoscale point that emits the electrons," said Graham Sanborn, who worked on the project as part of his Ph.D. thesis in Georgia Tech's School of Materials Science and Engineering. "The electric field focuses on the tip so we are able to get electron emission at lower voltages than might be required for other materials."

GTRI uses a series of deposition and etching steps to fabricate the arrays in clean rooms at Georgia Tech. Each one-centimeter square array contains as many as 50,000 nanotube bundles, and each bundle is grown from a five-micron pit etched into the silicon.

"The design has specific geometry to prevent electrical shorting between electrodes that are very close together," explained Sanborn.

Spacecraft are launched using chemical rockets that provide large amounts of thrust. Once in orbit, however, the vehicles can use electrically-powered thrusters to change orbits or make other maneuvers.

"Ion thrusters provide very low amounts of thrust," Sanborn said. "They are just pushing out gas molecules, but they operate very efficiently. Ion thrusters can operate for thousands of hours at a time. Cumulatively, you can achieve a significant velocity change."

The ALICE acronym is composed of several other acronyms. The "A" represents AFIT, while the "L" is for LEO -- the low Earth orbit where the satellite will operate. The "I" represents the iMESA system; the "C" is for the carbon nanotubes, while the "E" represents "Experiment."

The satellite, the first for AFIT, was designed, tested and integrated by a multi-departmental team of professors, students and technicians. The partnership with GTRI and USAFA provided students in each institution an opportunity to participate in ground-breaking research with the potential to impact numerous future satellites employing electric propulsion.

Other potential applications for Georgia Tech's CNT-based electron emitters include displays, electrodynamic tethers, vacuum electronics and traveling wave tubes.

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Viewpoints Engineering graduates must get market savvy

2013/11/15

David Wicks managing director at European Recruitment

Graduates need to learn how to sell themselves, writes David Wicks, managing director at European Recruitment in his latest viewpoint on the technology recruitment sector

In my last column I argued that businesses should hire graduates and not simply poach talent with 2-5 years experience. This week I balance this argument with my assessment of the graduate market.

On a recent visit, one of my clients (graphics world leader) illustrated an example that highlights the difficulty in hiring graduates. The graduate interviewed possessed a superb 1st class Engineering BSc from a top university, but an hour into the interview, there was no evidence of passion or engagement with his degree, and he certainly didn’t come across as someone worth investing in.

Just as my client was kicking him out the door, he made a final effort to find out something interesting that he’d done, disregarding his CV. The grad thought for a moment and said “I guess, in my spare time, I made a 3D printer…”.

Turns out this graduate had made the whole thing from scratch including all the hardware and software. He was hired on the spot.

This story is one example of the naivety of graduates and their ability to sell themselves. As recruiters we still experience this with experienced mid to senior level professionals. How many companies miss out on excellent hires, graduate or otherwise, because of this?

Do universities need to be preparing STEM (science, technology, engineering and mathematics) graduates much better with other pragmatic skills that will help them navigate the job market? If not, whose job is this?

Could it simply be a numbers game? Apparently we are not producing many engineering grads in the first place.

When researching this article I came across the following written only last week by James Dyson, inventor and founder of the Dyson company: “…it’s hardly a surprise when Britain produces only 12,000 graduate engineers from its universities each year – France produces nearly four times that number…the French value their engineers… As a result there is a generation of young French students, gagging to study engineering at university.”

Dyson goes on to say: “They should remove the immigration cap for the brightest and best, and make a special science and engineering visa. The problem is that we are fast approaching a point where 80% of postgraduate engineering positions at British universities are taken by students from outside the UK.”

And Dyson adds: “Our peculiar visa system means that these bright engineers and scientists, given a world class education in our universities, can’t stay here when they finish their studies. We are training them up, only to send them packing – to compete with us. It’s madness.”

It speaks for itself, particularly when businesses are not as engaged with universities in the UK to iron out these business, communication and emotional intelligence deficiencies early on. This would then increase the overall value of a STEM graduate.

I’d recommend to the government that the Oxbridge and Russell Group STEM departments need to be expanded dramatically to allow more students to enter these vigorous programmes – even if this is to the detriment of the 50th to 109th ranked Universities, so that the overall cost and risk is brought down in these subjects.

To get the applicants, a hearts and minds campaign to educate UK society into the value of STEM would also really help. The visa situation is such an easy win, I’m not sure even the most anti-immigration voter could argue against post-graduate experts being of value to the country.

If we can bring up the number and quality of graduates and instil in them the value of marketing themselves then perhaps businesses will be more willing to hire those straight out of university. Graduates have a lot to offer, even if they themselves sometimes don’t realise it.

David Wicks, Managing Director at European Recruitment

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Large graphene crystals with exceptional electrical properties created

The team used surface oxygen to grow centimeter-size single graphene crystals on copper. The crystals were about 10,000 times as large as the largest crystals from only four years ago. Very large single crystals have exceptional electrical properties.

"The game we play is that we want nucleation (the growth of tiny 'crystal seeds') to occur, but we also want to harness and control how many of these tiny nuclei there are, and which will grow larger," said Rodney S. Ruoff, professor in the Cockrell School of Engineering. "Oxygen at the right surface concentration means only a few nuclei grow, and winners can grow into very large crystals."

The team -- led by postdoctoral fellow Yufeng Hao and Ruoff of the Department of Mechanical Engineering and the Materials Science and Engineering Program, along with Luigi Colombo, a material scientist with Texas Instruments -- worked for three years on the graphene growth method. The team's paper, "The Role of Surface Oxygen in the Growth of Large Single-Crystal Graphene on Copper," is featured on the cover of the Nov. 8, 2013, issue of Science.

One of the world's strongest materials, graphene is flexible and has high electrical and thermal conductivity that makes it a promising material for flexible electronics, solar cells, batteries and high-speed transistors. The team's understanding of how graphene growth is influenced by differing amounts of surface oxygen is a major step toward improved high-quality graphene films at industrial scale.

The team's method "is a fundamental breakthrough, which will lead to growth of high-quality and large area graphene film," said Sanjay Banerjee, who heads the Cockrell School's South West Academy of Nanoelectronics (SWAN). "By increasing the single-crystal domain sizes, the electronic transport properties will be dramatically improved and lead to new applications in flexible electronics."

Graphene has always been grown in a polycrystalline form, that is, it is composed of many crystals that are joined together with irregular chemical bonding at the boundaries between crystals ("grain boundaries"), something like a patch-work quilt. Large single-crystal graphene is of great interest because the grain boundaries in polycrystalline material have defects, and eliminating such defects makes for a better material.

By controlling the concentration of surface oxygen, the researchers could increase the crystal size from a millimeter to a centimeter. Rather than hexagon-shaped and smaller crystals, the addition of the right amount of surface oxygen produced much larger single crystals with multibranched edges, similar to a snowflake.

"In the long run it might be possible to achieve meter-length single crystals," Ruoff said. "This has been possible with other materials, such as silicon and quartz. Even a centimeter crystal size -- if the grain boundaries are not too defective -- is extremely significant."

"We can start to think of this material's potential use in airplanes and in other structural applications -- if it proves to be exceptionally strong at length scales like parts of an airplane wing, and so on," he said.

Another major finding by the team was that the "carrier mobility" of electrons (how fast the electrons move) in graphene films grown in the presence of surface oxygen is exceptionally high. This is important because the speed at which the charge carriers move is important for many electronic devices -- the higher the speed, the faster the device can perform.

Yufeng Hao says he thinks the knowledge gained in this study could prove useful to industry.

"The high quality of the graphene grown by our method will likely be developed further by industry, and that will eventually allow devices to be faster and more efficient," Hao said.

Single-crystal films can also be used for the evaluation and development of new types of devices that call for a larger scale than could be achieved before, added Colombo.

"At this time, there are no other reported techniques that can provide high quality transferrable films," Colombo said. "The material we were able to grow will be much more uniform in its properties than a polycrystalline film."

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