UK-based Cella Energy has developed a synthetic fuel that could lead to US$1.50 per gallon gasoline. Apart from promising a future transportation fuel with a stable price regardless of oil prices, the fuel is hydrogen based and produces no carbon emissions when burned. The technology is based on complex hydrides, and has been developed over a four year top secret program at the prestigious Rutherford Appleton Laboratory near Oxford. Early indications are that the fuel can be used in existing internal combustion engined vehicles without engine modification.

According to Stephen Voller CEO at Cella Energy, the technology was developed using advanced materials science, taking high energy materials and encapsulating them using a nanostructuring technique called coaxial electrospraying.

“We have developed new micro-beads that can be used in an existing gasoline or petrol vehicle to replace oil-based fuels,” said Voller. “Early indications are that the micro-beads can be used in existing vehicles without engine modification.”

“The materials are hydrogen-based, and so when used produce no carbon emissions at the point of use, in a similar way to electric vehicles”, said Voller.

The technology has been developed over a four-year top secret programme at the prestigious Rutherford Appleton Laboratory near Oxford, UK.

The development team is led by Professor Stephen Bennington in collaboration with scientists from University College London and Oxford University.

Professor Bennington, Chief Scientific Officer at Cella Energy said, “our technology is based on materials called complex hydrides that contain hydrogen. When encapsulated using our unique patented process, they are safer to handle than regular gasoline.”

Source: GizMag

A team of physicists has taken a big step toward the development of useful graphene spintronic devices. The physicists, from the City University of Hong Kong and the University of Science and Technology of China, present their findings in the American Institute of Physics' Applied Physics Letters.

Graphene, a two-dimensional crystalline form of carbon, is being touted as a sort of "Holy Grail" of materials. It boasts properties such as a breaking strength 200 times greater than steel and, of great interest to the semiconductor and data storage industries, electric currents that can blaze through it 100 times faster than in silicon.

Spintronic devices are being hotly pursued because they promise to be smaller, more versatile, and much faster than today's electronics. "Spin" is a quantum mechanical property that arises when a particle's intrinsic rotational momentum creates a tiny magnetic field. And spin has a direction, either "up" or "down." The direction can encode data in the 0s and 1s of the binarysystem, with the key here being that spin-based data storage doesn't disappear when the electric current stops.

"There is strong research interest in spintronic devices that process information using electron spins, because these novel devices offer better performance than traditional electronic devices and will likely replace them one day," says Kwok Sum Chan, professor of physics at the City University of Hong Kong "Graphene is an important material for spintronic devices because its electron spin can maintain its direction for a long time and, as a result, information stored isn't easily lost."

It is, however, difficult to generate a spin current in graphene, which would be a key part of carrying information in a graphene spintronic device. Chan and colleagues came up with a method to do just that. It involves using spin splitting in monolayer graphene generated by ferromagnetic proximity effect and adiabatic (a process that is slow compared to the speed of the electrons in the device) quantum pumping. They can control the degree of polarization of the spin current by varying the Fermi energy (the level in the distribution of electron energies in a solid at which a quantum state is equally likely to be occupied or empty), which they say is very important for meeting various application requirements.

Source: EurekAlert

A recent study confirmed that low socioeconomic status (SES) is associated with higher risk of depressive symptoms in patients with rheumatoid arthritis (RA). Statistically significant differences in race, public versus tertiary-care hospital, disability and medications were found between depressed and non-depressed patients. Study findings are reported in the February issue of Arthritis Care & Research, a journal published by Wiley-Blackwell on behalf of the American College of Rheumatology (ACR).

Roughly 1.3 million Americans are affected by RA—a chronic autoimmune disease that can cause functional limitations and may lead to physical disability in many patients. Prior studies have shown that depression is common, occurring in 13% to 42% of RA patients and is associated with worse outcomes, including greater risk of heart attack, suicide, and death. In the U.S., socioeconomic position as measured by race, gender, age, income, education and health access has significant impact on overall health.

Mary Margaretten, M.D., from the Arthritis Research Group at the University of California, San Francisco (UCSF) and lead study author explained, "We assessed the extent to which low SES influences the relationship between disability and depression in order to better identify those patients at higher risk for depression." Researchers used data obtained from the UCSF RA cohort in which participants were enrolled from an urban county, public hospital that serves the poor and a referral, tertiary-care medical center. The data included 824 visits for 466 patients, 223 from the public hospital and 243 from the tertiary-care clinic.

Analysis showed that 37% of participants had moderate to severe depression, scoring 10 or higher on the Patient Health Questionnaire (PHQ-9). The mean Health Assessment Questionnaire (HAQ) score was 1.2 and the disease activity score (DAS28) was 4, indicating fairly high levels of functional impairment and disease activity, respectively. Researchers also found significant differences between depressed and non-depressed patients related to race, public versus university hospital, functional limitation and disease modifying anti-rheumatic drug (DMARD) treatment. Differences in depression severity were not impacted by gender, age, disease duration, steroid use and dose, or biologic therapy.

Furthermore, the team found that county hospital patients also had significantly higher depression scores (PHQ-9 of 7.3) than patients at the university medical center (PHQ-9 of 5.7). An interaction existed between socioeconomic status and disability such that the association of functional limitation with depression scores was stronger for patients at the public hospital clinic compared to those at the tertiary-care clinic.

Dr. Margaretten concluded, "For the same level of disability, patients with low SES may be more likely to experience depression. Detection and documentation of the differing effects of disability on depression between patients of different socioeconomic status can help rheumatologists improve health outcomes by initiating appropriate and timely treatment for depression."

Source: EurekAlert

Until now, scientists have thought that the process of erasing information requires energy. But a new study shows that, theoretically, information can be erased without using any energy at all. Instead, the cost of erasure can be paid in terms of another conserved quantity, such as spin angular momentum.

In the study, physicists Joan Vaccaro from Griffith University in Queensland, Australia, and Stephen Barnett from the University of Strathclyde in Glasgow, UK, have quantitatively described how information can be erased without any energy, and they also explain why the result is not as contentious as it first appears. Their paper is published in a recent issue of the Proceedings of the Royal Society A.

Traditionally, the process of erasing information requires a cost that is calculated in terms of energy – more specifically, heat dissipation. In 1961, Rolf Landauer argued that there was a minimum amount of energy required to erase one bit of information, i.e. to put a bit in the logical zero state. The energy required is positively related to the temperature of the system’s thermal reservoir, and can be thought of as the system’s thermodynamic entropy. As such, this entropy is considered to be a fundamental cost of erasing a bit of information.

However, Vaccaro and Barnett have shown that an energy cost can be fully avoided by using a reservoir based on something other than energy, such as spin angular momentum. Subatomic particles have spin angular momentum, a quantity that, like energy, must be conserved. Basically, instead of heat being exchanged between a qubit and thermal reservoir, discrete quanta of angular momentum are exchanged between a qubit and spin reservoir. The scientists described how repeated logic operations between the qubit’s spin and a secondary spin in the zero state eventually result in both spins reaching the logical zero state. Most importantly, the scientists showed that the cost of erasing the qubit’s memory is given in terms of the quantity defining the logic states, which in this case is spin angular momentum and not energy.

The scientists explained that experimentally realizing this scheme would be very difficult. Nevertheless, their results show that physical laws do not forbid information erasure with a zero energy cost, which is contrary to previous studies. The researchers noted that, in practice, it will be especially difficult to ensure the system’s energy degeneracy (that different spin states of the qubit and reservoir have the exact same energy level). But even if imperfect conditions cause some energy loss, there is no fundamental reason to assume that the cost will be as large as that predicted by Landauer’s formula.

The possibility of erasing information without using energy has implications for a variety of areas. One example is the paradox of Maxwell’s demon, which appears to offer a way of violating the second law of thermodynamics. By opening and closing a door to separate hot and cold molecules, the demon supposedly extracts work from the reservoir, converting all heat into useful mechanical energy. Bennett’s resolution of the paradox in 1982 argues that the demon’s memory has to be erased to complete the cycle, and the cost of erasure is at least as much as the liberated energy. However, Vaccaro and Barnett’s results suggest that the demon’s memory can be erased at no energy cost by using a different kind of reservoir, where the cost would be in terms of spin angular momentum. In this scheme, the demon can extract all the energy from a heat reservoir as useful energy at a cost of another resource.

As the scientists explained, this result doesn't contradict historical statements of the second law of thermodynamics, which are exclusively within the context of heat and thermal reservoirs and do not allow for a broader class of reservoirs. Moreover, even though the example with Maxwell’s demon suggests that mechanical work can be extracted at zero energy cost, this extraction is associated with an increase in the information-theoretic entropy of the overall system.

“The maximization of entropy subject to a constraint need apply not only to heat reservoirs and the conservation of energy,” Vaccaro explained to PhysOrg.com.

The results could also apply to hypothetical Carnot heat engines, which operate at maximum efficiency. If these engines use angular momentum reservoirs instead of thermal reservoirs, they could generate angular momentum effort instead of mechanical work.

As for demonstrating the concept of erasing information at zero energy cost, the scientists said that it would take more research and time.

“We are currently looking at an idea to perform information erasure in atomic and optical systems, but it needs much more development to see if it would actually work in practice,” Vaccaro said.

She added that the result is of fundamental significance, and it’s not likely to have practical applications for memory devices.

“We don't see this as having a direct impact in terms of practical applications, because the current energy cost of information erasure is nowhere near Landauer's theoretical bound,” she said. “It's more a case of what it says about fundamental concepts. For example, Landauer said that information is physical because it takes energy to erase it. We are saying that the reason it is physical has a broader context than that.”

Source: PhysOrg

The Double Chooz collaboration recently completed its neutrino detector which will see anti-neutrinos coming from the Chooz nuclear power plant in the French Ardennes. The experiment is now ready to start collecting data in order to measure fundamental neutrino properties with important consequences for particle and astro-particle physics.

Neutrinos are electrically neutral elementary particles, three of a kind plus their antiparticles. Though already postulated in 1930 their first experimental observation was made in 1956. Because of their weak interaction with other particles, matter is almost completely transparent to neutrinos and large sensitive detectors are needed to capture them.

Neutrino oscillations were a major discovery in the late 1990s with the corresponding experiments being included in the 2002 Nobel Prize. Oscillations describe in-flight transformations of different neutrino species into each other and the observation of this effect implies that neutrinos do have mass. The oscillations depend on three mixing parameters, of which two are large and have already been measured. The third one is called theta13 and is known to be smaller with an upper limit coming from a previous experiment at Chooz. The new Double Chooz detector is the first of a new generation of reactor neutrino experiments with the aim of measuring this fundamental parameter in neutrino physics which is a key area of particle physics research. The results will also have important consequences for the feasibility of future neutrino facilities which will aim for even more precise measurements.

Double Chooz consists of two identical detectors. The first one, at a distance of about 1km from the reactor cores, has now been filled and started to collect data. The number of neutrinos measured compared to the expected flux from the reactors will allow considerably improvement in the sensitivity for theta13 already in 2011. The second detector, located at a distance of 400 metres, will start operating in 2012. At this distance no significant transformation into another neutrino species is expected. By comparing the results from both detectors, theta13 can be determined with even higher precision.

Both detectors use an organic liquid scintillator, which was developed specifically for this experiment. The neutrino target in the core of the detector consists of 10 cubic metres of Gadolinium doped scintillator which can be used to tag neutrons from inverse beta decays which are induced by anti-neutrinos emitted by the reactors. The target is surrounded by three layers of other liquids in order to protect against other particles and to dampen environmental radioactivity. These liquids are contained in very thin vessels so as to minimize inactive volumes inside the detector. The target is observed by 390 immersed photomultipliers which convert the interactions into electrical signals. These signals are processed in a data acquisition system which can collect data over the next five years. The new detectors will ensure that neutrino physics will stay one the most fruitful areas of particle physics, as it has been for the past 50 years.

An essential contribution to the project was the development of the gadolinium-doped liquid scintillator by the researchers at the Max Planck Institute for Nuclear Physics in Heidelberg. Their task was to find, test, produce and purify a gadolinium compound which is solvable in an organic liquid and chemically stable for many years. In collaboration with their colleagues from Japan they checked the photomultipliers in a specially built test-bed. These central contributions will also play a crucial role for the interpretation and data analysis. Universities and research institutes from Brazil, England, France, Germany, Japan, Russia, Spain and USA comprise the Double Chooz collaboration.

Source: PhysOrg

Many trees disperse their seeds by releasing "helicopters," those single-winged seeds that are also called "samaras." As these seeds fall to the ground, their wing causes them to swirl and spin in a process called autorotation, similar to man-made helicopters. In a new study, researchers have designed and built a mechanical samara whose dynamics are very similar to those of nature’s samaras. After testing the mechanical samara, the researchers then built a variety of remote-controlled robotic samaras with onboard power sources.
The researchers, Evan Ulrich, Darryll Pines, and Sean Humbert from the University of Maryland, have published their study on the robotic samaras in a recent issue of Bioinspiration & Biomimetics. The idea for building a flying robotic device based on samaras originated several years ago, after researchers attempted to scale down full-size helicopters.

“Full-scale helicopters have a high aerodynamic efficiency,” Ulrich, a PhD candidate, told PhysOrg.com. “But the aerodynamic efficiency is disproportionate, so a scaled-down helicopter has stability issues and is unfeasible. Dr. Pines, my advisor, realized that the simplest system in nature that achieves vertical flight and can autorotate like a helicopter is the samara, which is a naturally stable system.”

After further investigating the samara in order to better understand its flight dynamics, the researchers found that the winged seed is also one of nature’s most efficient fliers. The samara is a monocopter, meaning it has a single wing. For this reason, the samara has no stationary frame of reference, unlike a two-winged helicopter, and appears to fall in a complex way. However, through free-fall testing, the researchers could quantitatively measure the samara’s flight dynamics and use this information to control the samara’s autorotation and flight path.

After designing and building a mechanical samara, the researchers measured its flight dynamics in free-fall by dropping it from a height of 12 meters. Then the scientists used this data to develop three different designs of powered robotic samaras, ranging in size from 7.5 cm to 0.5 m. In flight tests, they demonstrated that the carbon fiber-based robotic samaras could be remotely steered to a desired location by altering the wing pitch, which changes the radius at which the vehicles turn. The robotic samaras could also hover, climb, and translate.

The researchers noted that the concept of a single-wing rotating aircraft is not new, with the first such vehicle being flown in 1952 by Charles McCutchen near Lake Placid, New York. Since then, several other single-winged rotating aircraft have been developed, but none of these designs has used autorotation or been based on the samara.
The samara-inspired autorotation process has several advantages compared to other small-scale aircraft that perform vertical take-off and landing. For instance, the robotic samaras are extremely damage-tolerant. If they lose power while flying, they can autorotate down and land without sustaining any damage due to their flexible structure that deflects upon impact. The robotic samaras are also passively stable, inexpensive, mechanically simple, and have a high payload capacity. Flight time is around 30 minutes, but depends on the battery size.

In the future, Ulrich plans to start a company to license and develop the technology for commercialization. In addition to developing the robotic samara into a toy, he said that the device could also have applications in satellite communications and 3D mapping.

“We want to take advantage of the autorotation mode since it doesn’t require power for flight,” he said. “If we can find a vertical column of air, it can stay aloft indefinitely. One possibility is using it as an autorotating communications platform to carry small components for satellites, without the requirement of a huge launch cost.”
In addition, since the device is continuously spinning, an onboard camera could be used to take 360° images and build a 3D map. The robotic samara spins about 15 times per second and can navigate through small areas and avoid obstacles, giving it advantages over larger vehicles such as helicopters and airplanes.

Source: PhysOrg

There are very few urban design solutions that address housing the tide of displaced people that could arise as oceans swell under global warming. Certainly few are as spectacular as this one.

The Lilypad, by Vincent Callebaut, is a concept for a completely self-sufficient floating city intended to provide shelter for future climate change refugees. The intent of the concept itself is laudable, but it is Callebaut’s phenomenal design that has captured our imagination.

Biomimicry was clearly the inspiration behind the design. The Lilypad, which was designed to look like a waterlily, is intended to be a zero emission city afloat in the ocean. Through a number of technologies (solar, wind, tidal, biomass), it is envisioned that the project would be able to not only produce it’s own energy, but be able to process CO2 in the atmosphere and absorb it into its titanium dioxide skin.

Each of these floating cities are designed to hold approximately around 50,000 people. A mixed terrain man-made landscape, provided by an artificial lagoon and three ridges, create a diverse environment for the inhabitants. Each Lilypad is intended to be either near a coast, or floating around in the ocean, traveling from the equator to the northern seas, according to where the gulf stream takes it.

The project isn’t even close to happening anytime soon, but there is value in future forward designs like the Lilypad. They inspire creative solutions, which at some point, may actually provide a real solutions to various problems.

The oceans take up roughly 70% of the earth's surface. That being said, the land left to live on is scattered through mountains, desserts and ice caps. This has prevented humans from settling at many places. The oceans however, are flat and full of life, space & energy. These factors could provide us with all the necessities for a future life at at sea...

Source: inhabitat

Excessive packaging is responsible for a lot of waste.

Because of this we were really inspired by this flat cardboard sheet that is capable of conforming to the shape of any object, saving a bundle on wasteful filler. Designed by Patrick Sung, the packaging design concept features triangulated perforations that allow it to bend around odd forms. This could also save on fuel for shipping, since all of that wasted box filler is eliminated.

We could see how the concept would not be the most practical for all applications, but it could be really great for mailing a surprise gift to a friend! Soft items like clothing or shoes, or even products that are rigid, like a funky reusable water bottle, could be perfect for this packaging. Not to mention that the perforated lines give the package an interesting graphic pattern style. There is something to be said about the efficiency of boxes that stack, which is why it is great that the sheet can also be folded into standard 6-sided boxes.

Sung has branded his concept the UPACKS (Universal Packaging System).

Source: Inhabitat

Any city will find that a logistics system that effectively supports flow of goods from one point to another is a crucial point in keeping things running. Fleets of vehicles currently travel around the country delivering food, clothing and other stock, but at the cost of heavy emissions. While there are plans to increase the use of rail freight, inner-city deliveries are still plagued with carbon heavy emissions. So what’s the solution? Enter the eStar Electric Vehicle, a green delivery vehicle that boasts an impressive 4,000 pound payload and can travel 100 miles on a single charge.

Designed by green vehicles specialist Navistar, the eStar aims to press companies to re-evaluate how they outfit their fleets. Navistar says of their ‘peppy’ little vehicle that it is “designed from the ground up to be electric, eStar is more efficient and effective than typical electric conversions.”

It is also easy to charge as the eStar offers a simple 220 volt split phase electrical charging process that’s quick and efficient. This means that the eStar can recharge overnight in approximately 8 hours and be ready for work in the morning.

Spec-wise the eStar runs on a 80kWhr Li-ion cassette battery providing 102 horsepower and 70kw of power. With a top speed of 50 mph and zero emissions, the eStar is ideal for inner-city work. The vehicle’s size also gives it room to move. Its 36-foot turning diameter helps in navigating small spaces, while the open view from the cab gives the driver a clear 180 degree view.

If you run a business in a big city, be it flower deliveries or catering, and are looking to green up your fleet, this could provide the answer.

Beyond the transport of passengers, to ensure that we are reducing our carbon footprint, we need to consider clean automotive in all applications, even in the local delivery of goods.

Source: Inhabitat

Solar cells are made from semiconductors whose ability to respond to light is determined by their band gaps (energy gaps). Different colors have different energies, and no single semiconductor has a band gap that can respond to sunlight's full range, from low-energy infrared through visible light to high-energy ultraviolet.

Although full-spectrum solar cells have been made, none yet have been suitable for manufacture at a consumer-friendly price. Now Wladek Walukiewicz, who leads the Solar Energy Materials Research Group in the Materials Sciences Division (MSD) at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), and his colleagues have demonstrated a solar cell that not only responds to virtually the entire solar spectrum, it can also readily be made using one of the semiconductor industry's most common manufacturing techniques.

The new design promises highly efficient solar cells that are practical to produce. The results are reported in a recent issue of Physical Review Letters.

How to make a full-spectrum solar cell

"Since no one material is sensitive to all wavelengths, the underlying principle of a successful full-spectrum solar cell is to combine different semiconductors with different energy gaps," says Walukiewicz.

One way to combine different band gaps is to stack layers of different semiconductors and wire them in series. This is the principle of current high-efficiency solar cell technology that uses three different semiconductor alloys with different energy gaps. In 2002, Walukiewicz and Kin Man Yu of Berkeley Lab's MSD found that by adjusting the amounts of indium and gallium in the same alloy, indium gallium nitride, each different mixture in effect became a different kind of semiconductor that responded to different wavelengths. By stacking several of the crystalline layers, all closely matched but with different indium content, they made a photovoltaic device that was sensitive to the full solar spectrum.

However, says Walukiewicz, "Even when the different layers are well matched, these structures are still complex -- and so is the process of manufacturing them. Another way to make a full-spectrum cell is to make a single alloy with more than one band gap."

In 2004 Walukiewicz and Yu made an alloy of highly mismatched semiconductors based on a common alloy, zinc (plus manganese) and tellurium. By doping this alloy with oxygen, they added a third distinct energy band between the existing two -- thus creating three different band gaps that spanned the solar spectrum. Unfortunately, says Walukiewicz, "to manufacture this alloy is complex and time-consuming, and these solar cells are also expensive to produce in quantity."

The new solar cell material from Walukiewicz and Yu and their colleagues in Berkeley Lab's MSD and RoseStreet Labs Energy, working with Sumika Electronics Materials in Phoenix, Arizona, is another multiband semiconductor made from a highly mismatched alloy. In this case the alloy is gallium arsenide nitride, similar in composition to one of the most familiar semiconductors, gallium arsenide. By replacing some of the arsenic atoms with nitrogen, a third, intermediate energy band is created. The good news is that the alloy can be made by metalorganic chemical vapor deposition (MOCVD), one of the most common methods of fabricating compound semiconductors.

How band gaps work

Band gaps arise because semiconductors are insulators at a temperature of absolute zero but inch closer to conductivity as they warm up. To conduct electricity, some of the electrons normally bound to atoms (those in the valence band) must gain enough energy to flow freely -- that is, move into the conduction band. The band gap is the energy needed to do this.

When an electron moves into the conduction band it leaves behind a "hole" in the valence band, which also carries charge, just as the electrons in the conduction band; holes are positive instead of negative.

A large band gap means high energy, and thus a wide-band-gap material responds only to the more energetic segments of the solar spectrum, such as ultraviolet light. By introducing a third band, intermediate between the valence band and the conduction band, the same basic semiconductor can respond to lower and middle-energy wavelengths as well.

This is because in a multiband semiconductor, there is a narrow band gap that responds to low energies between the valence band and the intermediate band. Between the intermediate band and the conduction band is another relatively narrow band gap, one that responds to intermediate energies. And finally, the original wide band gap is still there to take care of high energies.

"The major issue in creating a full-spectrum solar cell is finding the right material," says Kin Man Yu. "The challenge is to balance the proper composition with the proper doping."

In solar cells made of some highly mismatched alloys, a third band of electronic states can be created inside the band gap of the host material by replacing atoms of one component with a small amount of oxygen or nitrogen. In so -- called II-VI semiconductors (which combine elements from these two groups of Mendeleev's original periodic table), replacing some group VI atoms with oxygen produces an intermediate band whose width and location can be controlled by varying the amount of oxygen. Walukiewicz and Yu's original multiband solar cell was a II-VI compound that replaced group VI tellurium atoms with oxygen atoms. Their current solar cell material is a III-V alloy. The intermediate third band is made by replacing some of the group V component's atoms -- arsenic, in this case -- with nitrogen atoms.

Finding the right combination of alloys, and determining the right doping levels to put an intermediate band right where it's needed, is mostly based on theory, using the band anticrossing model developed at Berkeley Lab over the past 10 years.

"We knew that two-percent nitrogen ought to do the job," says Yu. "We knew where the intermediate band ought to be and what to expect. The challenge was designing the actual device."

Passing the test

Using their new multiband material as the core of a test cell, the researchers illuminated it with the full spectrum of sunlight to measure how much current was produced by different colors of light. The key to making a multiband cell work is to make sure the intermediate band is isolated from the contacts where current is collected.

"The intermediate band must absorb light, but it acts only as a stepping stone and must not be allowed to conduct charge, or else it basically shorts out the device," Walukiewicz explains.

The test device had negatively doped semiconductor contacts on the substrate to collect electrons from the conduction band, and positively doped semiconductor contacts on the surface to collect holes from the valence band. Current from the intermediate band was blocked by additional layers on top and bottom.

For comparison purposes, the researchers built a cell that was almost identical but not blocked at the bottom, allowing current to flow directly from the intermediate band to the substrate.

The results of the test showed that light penetrating the blocked device efficiently yielded current from all three energy bands -- valence to intermediate, intermediate to conduction, and valence to conduction -- and responded strongly to all parts of the spectrum, from infrared with an energy of about 1.1 electron volts (1.1 eV), to over 3.2 eV, well into the ultraviolet.

By comparison, the unblocked device responded well only in the near infrared, declining sharply in the visible part of the spectrum and missing the highest-energy sunlight. Because it was unblocked, the intermediate band had essentially usurped the conduction band, intercepting low-energy electrons from the valence band and shuttling them directly to the contact layer.

Further support for the success of the multiband device and its method of operation came from tests "in reverse" -- operating the device as a light emitting diode (LED). At low voltage, the device emitted four peaks in the infrared and visible light regions of the spectrum. Primarily intended as a solar cell material, this performance as an LED may suggest additional possibilities for gallium arsenide nitride, since it is a dilute nitride very similar to the dilute nitride, indium gallium arsenide nitride, used in commercial "vertical cavity surface-emitting lasers" (VCSELs), which have found wide use because of their many advantages over other semiconductor lasers.

With the new, multiband photovoltaic device based on gallium arsenide nitride, the research team has demonstrated a simple solar cell that responds to virtually the entire solar spectrum -- and can readily be made using one of the semiconductor industry's most common manufacturing techniques. The results promise highly efficient solar cells that are practical to produce.

Source: ScienceDaily