Tag Archives: letter-materials-tech

Electrical signals transmitted at high frequencies lose none of their energy when passed through the ‘wonder material’ graphene, a study led by Plymouth University has shown.

Discovered in 2004, graphene – which measures just an atom in thickness and is around 100 times stronger than steel – has been identified as having a range of potential uses across the engineering and health sectors.

Now research has shown graphene out-performs any other known material, including superconductors, when carrying high-frequency electrical signals compared to direct current, essentially transmitting signals without any additional energy loss.

And since graphene lacks band-gap, which allows electrical signals to be switched on and off using silicon in digital electronics, academics say it seems most applicable for applications ranging from next generation high-speed transistors and amplifiers for mobile phones and satellite communications to ultra-sensitive biological sensors.

The study was led by Dr Shakil Awan, a Lecturer in the School of Computing, Electronics and Mathematics at Plymouth University, alongside colleagues from Cambridge and Tohoku (Japan) Universities and Nokia Technologies (Cambridge, UK).

Dr Shakil Awan, Lecturer in the School of Computing, Electronics and Mathematics and the principal investigator in the study, said: “An accurate understanding of the electromagnetic properties of graphene over a broad range of frequencies (from direct current to over 10 GHz) has been an important quest for several groups around the world. Initial measurements gave conflicting results with theory because graphene’s intrinsic properties are often masked by much larger interfering signals from the supporting substrate, metallic contacts and measurement probes. Our results for the first time not only confirm the theoretical properties of graphene but also open up many new applications of the material in high-speed electronics and bio-sensing.”

The study, published in the IOP 2D Materials Journal, was funded by the EU Graphene Flagship, EPSRC, ERC and Nokia Technologies, and the results are now being exploited in developing high-speed and efficient low noise amplifiers, mixers, radiation detectors and novel bio-sensors.

The latter is the focus of a three-year £1million project funded by the EPSRC on developing highly-sensitive graphene bio-sensors for early detection of dementia (such as Alzheimer’s disease) compared to current methods.

Graphene is ideally suited for this as its room temperature thermal noise is smaller than any other known material, enabling the sensitive detection of tiny numbers of antibody-antigen interactions to indicate the likelihood of a patient to develop dementia in the future.

Dr Alan Colli, from Nokia Technologies, said: “Graphene devices for next generation wireless technologies (up to and beyond 10 GHz) are progressing fast. Our study has unlocked the fundamental behaviour of graphene at high frequencies, which will be essential in the design and evaluation of future graphene-based wireless devices. This has only been made possible because of the multi-discipline expertise of the different groups based at Nokia, and in Plymouth, Cambridge and Tohoku universities.”

One of the main reasons for limiting the operating lifetimes of nuclear reactors is that metals exposed to the strong radiation environment near the reactor core become porous and brittle, which can lead to cracking and failure. Now, a team of researchers at MIT and elsewhere has found that, at least in some reactors, adding a tiny quantity of carbon nanotubes to the metal can dramatically slow this breakdown process.

For now, the method has only proved effective for aluminum, which limits its applications to the lower-temperature environments found in research reactors. But the team says the method may also be usable in the higher-temperature alloys used in commercial reactors.

The findings are described in the journal Nano Energy, in a paper by MIT Professor Ju Li, postdocs Kang Pyo So and Mingda Li, research scientist Akihiro Kushima, and 10 others at MIT, Texas A&M University, and universities in South Korea, Chile, and Argentina.

Aluminum is currently used in not only research reactor components but also nuclear batteries and spacecraft, and it has been proposed as material for storage containers for nuclear waste. So, improving its operating lifetime could have significant benefits, says Ju Li, who is the Battelle Energy Alliance Professor of Nuclear Science and Engineering and a professor of materials science and engineering.

Long-term stability

The metal with carbon nanotubes uniformly dispersed inside “is designed to mitigate radiation damage” for long periods without degrading, says Kang Pyo So.

Helium from radiation transmutation takes up residence inside metals and causes the material to become riddled with tiny bubbles along grain boundaries and progressively more brittle, the researchers explain. The nanotubes, despite only making up a small fraction of the volume — less than 2 percent — can form a percolating, one-dimensional transport network, to provide pathways for the helium to leak back out instead of being trapped within the metal, where it could continue to do damage.

Testing showed that after exposure to radiation, the carbon nanotubes within the metal can be chemically altered to carbides, but they still retain their slender shape, “almost like insects trapped in amber,” Ju Li says. “It’s quite amazing — you don’t see a blob; they retain their morphology. It’s still one-dimensional.” The huge total interfacial area of these 1-D nanostructures provides a way for radiation-induced point defects to recombine in the metal, alleviating a process that also leads to embrittlement. The researchers showed that the 1-D structure was able to survive up to 70 DPA of radiation damage. (DPA is a unit that refers to how many times, on average, every atom in the crystal lattice is knocked out of its site by radiation, so 70 DPA means a lot of radiation damage.)

After radiation exposure, Ju Li says, “we see pores in the control sample, but no pores” in the new material, “and mechanical data shows it has much less embrittlement.” For a given amount of exposure to radiation, the tests have shown the amount of embrittlement is reduced about five to tenfold.

The new material needs only tiny quantities of carbon nanotubes (CNTs) — about 1 percent by weight added to the metal — and these are inexpensive to produce and process, the team says. The composite can be manufactured at low cost by common industrial methods and is already being produced by the ton by manufacturers in Korea, for the automotive industry.

Strength and resilience

Even before exposure to radiation, the addition of this small amount of nanotubes improves the strength of the material by 50 percent and also improves its tensile ductility — its ability to deform without breaking — the team says.

“This is a proof of principle,” says Kang Pyo So. While the material used for testing was aluminum, the team plans to run similar tests with zirconium, a metal widely used for high-temperature reactor applications such as the cladding of nuclear fuel pellets. “We think this is a generic property of metal-CNT systems,” he says.

“This is a development of considerable significance for nuclear materials science, where composites — particularly oxide dispersion-strengthened steels — have long been considered promising candidate materials for applications involving high temperature and high irradiation dose,” says Sergei Dudarev, a professor of materials science at Oxford University in the U.K., who was not involved in this work.

Dudarev adds that this new composite material “proves remarkably stable under prolonged irradiation, indicating that the material is able to self-recover and partially retain its original properties after exposure to high irradiation dose at room temperature. The fact that the new material can be produced at relatively low cost is also an advantage.”

Stacking layers of nanometer-thin semiconducting materials at different angles is a new approach to designing the next generation of energy-efficient transistors and solar cells. The atoms in each layer are arranged in hexagonal arrays. When two layers are stacked and rotated, atoms from one layer overlap with those in the other layer and can form an infinite number of overlapping patterns, like the Moiré patterns that result when two screens are overlaid and one is rotated on top of the other. Theoretical calculations predict excellent electronic and optical properties for some stacking patterns, but practically, how can these patterns be made and characterized?

Recently a team led by researchers from the Department of Energy’s Oak Ridge National Laboratory used the vibrations between two layers to decipher their stacking patterns. The team employed a method called low-frequency Raman spectroscopy to measure how the layers vibrate with respect to each other and compared the frequencies of the measured vibrations with their theoretically predicted values. Their study provides a platform for engineering two-dimensional (2D) materials with optical and electronic properties that strongly depend on stacking configurations. The findings are published in ACS Nano, a journal of the American Chemical Society.

“Low-frequency Raman spectroscopy, in combination with first-principles modeling, offers a quick and easy approach to reveal complex stacking configurations in the twisted bilayers of a promising semiconductor, without relying on other expensive and time-consuming experimental techniques,” said co-lead author Liangbo Liang, a Wigner Fellow at ORNL. “We are the first to show that low-frequency Raman spectra can be used as fingerprints to characterize the relative layer stacking in semiconducting 2D materials.”

In Raman scattering, an optical method for probing atomic vibrations, a material scatters monochromatic light from a laser. Whereas conventional Raman spectroscopy may probe more than approximately 3 trillion atomic vibrations per second, low-frequency Raman spectroscopy detects vibrations that are an order of magnitude slower. The low-frequency technique is sensitive to weak attractive forces between layers, called van der Waals coupling. It can provide crucial insight about layer thickness and stacking–aspects that govern fundamental properties of 2D materials.

“This work combines state-of-the art synthesis and processing of 2D materials, their unique spectroscopic characterization, and data interpretation using first-principles theory,” said co-lead author Alex Puretzky. “High-resolution Raman spectroscopy that can probe low-frequency modes requires specialized instrumentation, and only a few places around the world have such a capability together with advanced synthesis and characterization tools, and theory and computational modeling expertise. The Center for Nanophase Materials Sciences at ORNL is among them.”

Chemical vapor deposition, widely employed to synthesize 2D materials like graphene, was used to make perfectly triangular crystal monolayers of molybdenum diselenide just three atoms thick. Feedstock molecules of molybdenum oxide and sulfur were reacted in a flowing gas within a high-temperature furnace to form the triangular crystals on silicon substrates.

“Numerous parameters need to be properly adjusted to synthesize large, triangular 2D crystals successfully,” Puretzky said. “Then, carefully removing the crystals and stacking them precisely in different orientations is a big challenge.”

He continued, “The precise, equilateral triangular shape of the synthesized and transferred crystals allowed us to measure the twist angles with a high precision using standard optical and atomic force microscopy images, which was a key factor in our experiments.”

Theoretical and computational aspects were challenging too. “Raman spectroscopy is heavily based on theory for interpretation and assignment of the observed Raman spectra, especially for new materials that have never before been measured,” Puretzky said.

The study revealed patterns in the stacked bilayers that strongly depend on the twist angle. Some specific twist angles, though, showed periodically repeating patches with the same stacking orientation. “These unique patterns may provide a new platform for optoelectronic applications of these materials,” Puretzky said.

The team’s findings also showed fascinating effects of the vibrations between the layers. As different stacking patterns appeared when layers were displaced, variable spacings occurred between the layers at some specific twist angles. The researchers plan further measurements and modeling for different stacking configurations to better understand how these vibrational decays might alter the thermal properties of these materials–knowledge that could affect applications in heat dissipation and thermoelectric energy conversion.

A critical milestone has been reached in cadmium telluride (CdTe) solar cell technology, helping pave the way for solar energy to directly compete with electricity generated by conventional energy sources.

Scientists at the Energy Department’s National Renewable Energy Laboratory (NREL) collaborated with researchers at Washington State University and the University of Tennessee to improve the maximum voltage available from a CdTe solar cell, which is a key factor in improving solar cell efficiency.

The research appears in the Nature Energy journal article, “CdTe solar cells with open-circuit voltage breaking the 1 V barrier,” authored by James Burst, Joel Duenow, David Albin, Eric Colegrove, Matthew Reese, Jeffery Aguiar, Chun-Sheng Jiang, Maulik Patel, Mowafak Al-Jassim, Darius Kuciauskas, Santosh Swain, Tursunjun Ablekim, Kelvin Lynn, and Wyatt Metzger.

Silicon solar cells currently represent 90% of the solar cell market, but it will be difficult to significantly reduce their manufacturing costs. CdTe solar cells offer a low-cost alternative. These cells also have the lowest carbon footprint and adapt better than silicon in real-world conditions including hot, humid weather and low light. However, CdTe solar cells have not been as efficient as multicrystalline silicon solar cells until recently.

One key area where CdTe has underperformed is in the maximum voltage available from the solar cell, a measure called open-circuit voltage. The quality of CdTe materials has prevented industry, universities, and national laboratories for the past 60 years from obtaining open-circuit voltage exceeding 900 millivolts on billions of solar cells; the vast majority have been limited to 750 to 850 millivolts.

The research team improved cell voltage by shifting away from a standard processing step using cadmium chloride. Instead, they placed a small number of phosphorus atoms on tellurium lattice sites and then carefully formed ideal interfaces between materials with different atomic spacing to complete the solar cell. This approach improved the CdTe conductivity and carrier lifetime each by orders of magnitude, thereby enabling the fabrication of CdTe solar cells with an open-circuit voltage breaking the 1-volt barrier for the first time. The innovation establishes new research paths for solar cells to become more efficient and provide electricity at lower cost.

A team of researchers, led by a group at the University of California, Riverside, have demonstrated for the first time the transmission of electrical signals through insulators in a sandwich-like structure, a development that could help create more energy efficient electronic devices.

Conventional electronic devices rely on the transport of electrons in a semiconductor such as silicon. Now, researchers are exploiting the ‘spin’ of the electron rather than its charge to create a new generation of ‘spintronic’ devices that are potentially more energy efficient and more versatile than those currently making up silicon chips and circuit elements.

The UC Riverside-led research, which was published online Wednesday (March 2) in the journal Nature Communications, is significant because it demonstrates that a tri-layer, sandwich-like, structure can serves as a scalable pure spin current device, an essential ingredient in spintronics.

A key element in this breakthrough is the material. To demonstrate the effect, the magnetic insulator needs to be truly insulating, or there will be a parasitic signal from leakage. On the other hand, a high-quality magnetic insulator grown on metal had never been demonstrated.

Using combination of sputtering (for metals) and pulsed laser deposition (for insulator), we successfully showed that the 50-100 nanometer thick magnetic insulator, such as yttrium iron garnet, is not only magnetic and insulating, but also of high quality when it is grown on 5 nanometer thick platinum.

In the structures used by the researchers, there are two metals and a magnetic insulator in between. The metals are for spin current generation and detection (conversion of spin current back to charge current) via the so-called spin Hall effect and inverse spin Hall effect.

The magnetic insulator is an electrical insulator but a good spin current conductor. The spin current flowing in the insulator does not involve mobile electrons therefore it does not dissipate energy as an electrical current does in joule heating.

The researchers have also demonstrated that the signal transmission can be switched on and off and modulated in its strength by a magnetic field. The electrical signal transmission through the magnetic insulators can be switched on and off depending on the magnetic state, or direction of the magnetization, of the magnetic insulators.

So the direction of the magnetization can be regarded as a memory state of non-volatile random access memory devices. In addition, the signal level can be modulated by changing the direction of the magnetization; therefore, it can also be used as analog devices. The sandwich structure can be made small by nanofabrication so that the devices can be scaled down.

Electrons can extend our view of microscopic objects well beyond what’s possible with visible light–all the way to the atomic scale. A popular method in electron microscopy for looking at tough, resilient materials in atomic detail is called STEM, or scanning transmission electron microscopy, but the highly-focused beam of electrons used in STEM can also easily destroy delicate samples.

This is why using electrons to image biological or other organic compounds, such as chemical mixes that include lithium–a light metal that is a popular element in next-generation battery research–requires a very low electron dose.

Scientists at the Department of Energy’sc Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new imaging technique, tested on samples of nanoscale gold and carbon, that greatly improves images of light elements using fewer electrons.

The newly demonstrated technique, dubbed MIDI-STEM, for matched illumination and detector interferometry STEM, combines STEM with an optical device called a phase plate that modifies the alternating peak-to-trough, wave-like properties (called the phase) of the electron beam.

This phase plate modifies the electron beam in a way that allows subtle changes in a material to be measured, even revealing materials that would be invisible in traditional STEM imaging.

Another electron-based method, which researchers use to determine the detailed structure of delicate, frozen biological samples, is called cryo-electron microscopy, or cryo-EM. While single-particle cryo-EM is a powerful tool–it was named as science journal Nature‘s 2015 Method of the Year –it typically requires taking an average over many identical samples to be effective. Cryo-EM is generally not useful for studying samples with a mixture of heavy elements (for example, most types of metals) and light elements like oxygen and carbon.

“The MIDI-STEM method provides hope for seeing structures with a mixture of heavy and light elements, even when they are bunched closely together,” said Colin Ophus, a project scientist at Berkeley Lab’s Molecular Foundry and lead author of a study, published Feb. 29 in Nature Communications, that details this method.

If you take a heavy-element nanoparticle and add molecules to give it a specific function, conventional techniques don’t provide an easy, clear way to see the areas where the nanoparticle and added molecules meet.

“How are they aligned? How are they oriented?” Ophus asked. “There are so many questions about these systems, and because there wasn’t a way to see them, we couldn’t directly answer them.”

While traditional STEM is effective for “hard” samples that can stand up to intense electron beams, and cryo-EM can image biological samples, “We can do both at once” with the MIDI-STEM technique, said Peter Ercius, a Berkeley Lab staff scientist at the Molecular Foundry and co-author of the study.

The phase plate in the MIDI-STEM technique allows a direct measure of the phase of electrons that are weakly scattered as they interact with light elements in the sample. These measurements are then used to construct so-called phase-contrast images of the elements. Without this phase information, the high-resolution images of these elements would not be possible.

In this study, the researchers combined phase plate technology with one of the world’s highest resolution STEMs, at Berkeley Lab’s Molecular Foundry, and a high-speed electron detector.

They produced images of samples of crystalline gold nanoparticles, which measured several nanometers across, and the super-thin film of amorphous carbon that the particles sat on. They also performed computer simulations that validated what they saw in the experiment.

The phase plate technology was developed as part of a Berkeley Lab Laboratory Directed Research and Development grant in collaboration with Ben McMorran at University of Oregon.

The MIDI-STEM technique could prove particularly useful for directly viewing nanoscale objects with a mixture of heavy and light materials, such as some battery and energy-harvesting materials, that are otherwise difficult to view together at atomic resolution.

It also might be useful in revealing new details about important two-dimensional proteins, called S-layer proteins, that could serve as foundations for engineered nanostructures but are challenging to study in atomic detail using other techniques.

In the future, a faster, more sensitive electron detector could allow researchers to study even more delicate samples at improved resolution by exposing them to fewer electrons per image.

“If you can lower the electron dose you can tilt beam-sensitive samples into many orientations and reconstruct the sample in 3-D, like a medical CT scan. There are also data issues that need to be addressed,” Ercius said, as faster detectors will generate huge amounts of data. Another goal is to make the technique more “plug-and-play,” so it is broadly accessible to other scientists.

 

A new one atom-thick flat material that could upstage the wonder material graphene and advance digital technology has been discovered by a physicist at the University of Kentucky working in collaboration with scientists from Daimler in Germany and the Institute for Electronic Structure and Laser (IESL) in Greece.

Reported in Physical Review B, Rapid Communication, the new material is made up of silicon, boron and nitrogen – all light, inexpensive and earth abundant elements – and is extremely stable, a property many other graphene alternatives lack.

“We used simulations to see if the bonds would break or disintegrate – it didn’t happen,” said Madhu Menon, a physicist in the UK Center for Computational Sciences. “We heated the material up to 1,000 degree Celsius and it still didn’t break.”

Using state-of-the-art theoretical computations, Menon and his collaborators Ernst Richter from Daimler and a former UK Department of Physics and Astronomy post-doctoral research associate, and Antonis Andriotis from IESL, have demonstrated that by combining the three elements, it is possible to obtain a one atom-thick, truly 2D material with properties that can be fine-tuned to suit various applications beyond what is possible with graphene.

While graphene is touted as being the world’s strongest material with many unique properties, it has one downside: it isn’t a semiconductor and therefore disappoints in the digital technology industry. Subsequent search for new 2D semiconducting materials led researchers to a new class of three-layer materials called transition-metal dichalcogenides (TMDCs). TMDCs are mostly semiconductors and can be made into digital processors with greater efficiency than anything possible with silicon. However, these are much bulkier than graphene and made of materials that are not necessarily earth abundant and inexpensive.

Searching for a better option that is light, earth abundant, inexpensive and a semiconductor, the team led by Menon studied different combinations of elements from the first and second row of the Periodic Table.

Although there are many ways to combine silicon, boron and nitrogen to form planar structures, only one specific arrangement of these elements resulted in a stable structure. The atoms in the new structure are arranged in a hexagonal pattern as in graphene, but that is where the similarity ends.

The three elements forming the new material all have different sizes; the bonds connecting the atoms are also different. As a result, the sides of the hexagons formed by these atoms are unequal, unlike in graphene. The new material is metallic, but can be made semiconducting easily by attaching other elements on top of the silicon atoms.

The presence of silicon also offers the exciting possibility of seamless integration with the current silicon-based technology, allowing the industry to slowly move away from silicon instead of eliminating it completely, all at once.

“We know that silicon-based technology is reaching its limit because we are putting more and more components together and making electronic processors more and more compact,” Menon said. “But we know that this cannot go on indefinitely; we need smarter materials.”

Furthermore, in addition to creating an electronic band gap, attachment of other elements can also be used to selectively change the band gap values – a key advantage over graphene for solar energy conversion and electronics applications.

Other graphene-like materials have been proposed but lack the strengths of the material discovered by Menon and his team. Silicene, for example, does not have a flat surface and eventually forms a 3D surface. Other materials are highly unstable, some only for a few hours at most.

The bulk of the theoretical calculations required were performed on the computers at the UK Center for Computational Sciences with collaborators Richter and Andriotis directly accessing them through fast networks. Now the team is working in close collaboration with a team led by Mahendra Sunkara of the Conn Center for Renewable Energy Research at University of Louisville to create the material in the lab. The Conn Center team has had close collaborations with Menon on a number of new materials systems where they were able to test his theory with experiments for a number of several new solar materials.

“We are very anxious for this to be made in the lab,” Menon said. “The ultimate test of any theory is experimental verification, so the sooner the better!”

Some of the properties, such as the ability to form various types of nanotubes, are discussed in the paper but Menon expects more to emerge with further study.

“This discovery opens a new chapter in material science by offering new opportunities for researchers to explore functional flexibility and new properties for new applications,” he said. “We can expect some surprises.”

EPFL researchers have developed conductive tracks that can be bent and stretched up to 4 times their original length; they could be used in artificial skin, connected clothing and on­-body sensors.

Conductive tracks are usually hard printed on a board. But those recently developed at EPFL are altogether different: they are almost as flexible as rubber and can be stretched up to four times their original length and in all directions. And they can be stretched a million times without cracking or interrupting their conductivity. The invention is described in an article published today in the journal Advanced Materials.

Both solid and flexible, this new metallic and partially liquid film offers a wide range of possible applications. It could be used to make circuits that can be twisted and stretched – ideal for artificial skin on prosthetics or robotic machines. It could also be integrated into fabric and used in connected clothing. And because it follows the shape and movements of the human body, it could be used for sensors designed to monitor particular biological functions.

“We can come up with all sorts of uses, in forms that are complex, moving or that change over time,” said Hadrien Michaud, a PhD student at the Laboratory for Soft Bioelectronic Interfaces (LSBI) and one of the study authors.

Extensive research has gone into developing an elastic electronic circuit. It is a real challenge, as the components traditionally used to make circuits are rigid. Applying liquid metal to a thin film in polymer supports with elastic properties naturally seems like a promising approach.

Thin and reliable

Owing to the high surface tension of some of these liquid metals, experiments conducted so far have only produced relatively thick structures. “Using the deposition and structuring methods that we developed, it’s possible to make tracks that are very narrow – several hundredths of a nanometer thick – and very reliable,” said Stéphanie Lacour, who runs the lab.

Apart from their unique fabrication technique, the researchers’ secret lies in the choice of ingredients, an alloy of gold and gallium. “Not only does gallium possess good electrical properties, but it also has a low melting point, around 30o,” said Arthur Hirsch, a PhD student at LSBI and co-author of the study. “So it melts in your hand, and, thanks to the process known as supercooling, it remains liquid at room temperature, even lower.” The layer of gold ensures the gallium remains homogeneous, preventing it from separating into droplets when it comes into contact with the polymer, which would ruin its conductivity.

Chemists and polymer scientists collaborating at the University of Massachusetts Amherst reported this week that they have for the first time identified an unexpected property in an organic semiconductor molecule that could lead to more efficient and cost-effective materials for use in cell phone and laptop displays, for example, and in opto-electronic devices such as lasers, light-emitting diodes and fiber optic communications.

Physical chemist Michael Barnes and polymer scientist Alejandro Briseño, with doctoral students Sarah Marques, Hilary Thompson, Nicholas Colella and postdoctoral researcher Joelle Labastide, discovered the property, directional intrinsic charge separation, in crystalline nanowires of an organic semiconductor known as 7,8,15,16-tetraazaterrylene (TAT).

A new paper from UMass Amherst describes a structure that will make it easier to use a certain molecule for new applications, for example in devices that use polarized light input for optical switching, by exploiting its directionality. Inset shows a structural schematic of the TAT crystal packing geometry and direction of charge separation. Credit: UMass Amherst/Mike Barnes

A new paper from UMass Amherst describes a structure that will make it easier to use a certain molecule for new applications, for example in devices that use polarized light input for optical switching, by exploiting its directionality. Inset shows a structural schematic of the TAT crystal packing geometry and direction of charge separation. Credit: UMass Amherst/Mike Barnes

The researchers saw not only efficient separation of charges in TAT, but a very specific directionality that Barnes says “is quite useful. It adds control, so we’re not at the mercy of random movement, which is inefficient. Our paper describes an aspect of the nanoscopic physics within individual crystals, a structure that will make it easier to use this molecule for new applications such as in devices that use polarized light input for optical switching. We and others will immediately exploit this directionality.”

He adds, “Observing the intrinsic charge separation doesn’t happen in polymers, so far as we know it only happens in this family of small organic molecule crystalline assemblies or nanowires. In terms of application we are now exploring ways to arrange the crystals in a uniform pattern and from there we can turn things on or off depending on optical polarization, for example.”

However, the UMass Amherst team believes the property is not an oddity unique to this material, but that several materials potentially share it, making the discoveries in TAT interesting to a wide variety of researchers, Barnes says. Similar kinds of observations have been noted in pentacene crystals, he notes, which show something similar but without directionality. In this work supported by the U.S. Department of Energy and UMass Amherst’s Center for Hierarchical Manufacturing, they propose that the effect comes from a charge-transfer interaction in the molecule’s charge-conducing nanowires that can be programmed.

In the conventional view of harvesting solar energy with organic or carbon-based organic materials, the chemist explains, scientists understood that the organic active layers at work in devices absorb light, which leads to an excited state known as an exciton. In this mechanism, the exciton migrates to an interface boundary where it separates into a positive and negative charge, freeing the voltage to be used as power. “In this view, you hope that the light is well absorbed so the transfer is efficient,” he says.

In earlier work, Barnes, Briseño and others at UMass Amherst worked to control the domain size of materials to match what was believed to be the distance an exciton can travel in the time it takes to radiate, he adds. “All of this premised on idea that the mechanism for charge separation is extrinsic, that an external driving force separates the charges,” he notes. The goal had been to remove the need for that interface.”

Most recently, Briseño and colleagues reached a point in synthesizing crystals where their polymer-based devices were not performing the way they wanted, he relates. Briseño asked Barnes and colleagues to use their special measurement instrumentation to investigate. Barnes and colleagues found a structural defect that Briseño could fix. “We provided some diagnostics to him to improve their crystal growth,” Barnes says.

“From this, we noticed clues that there were some very interesting things going on, which led us to the discovery,” Barnes adds. “It’s fun when science works that way. It was a very nice mutually beneficial relationship.”

“What Nature brought us was something really much richer and more interesting than anything we could have anticipated. We thought it was going to be qualitatively similar to previous observations, perhaps different in quantitative particulars, but the real story is far more interesting. In this material, they found the way it packs crystals gives rise to its own separation, an intrinsic property of the crystalline material.”

Soitec (Euronext), a manufacturer of semiconductor materials and a supplier of wafers for radio-frequency silicon-on-insulator (RF-SOI) applications, has begun mass production of 300mm RF-SOI substrates for mobile communications. The 300mm version of Soitec’s RFeSI90 substrate is made possible by the company’s proprietary technologies, long-time experience with 200mm RF-SOI and 300mm high-volume manufacturing expertise. These advanced wafers open the door for new enhancements that enable more highly integrated ICs for 4G/LTE-Advanced communications and the next generation of wireless technologies, including 5G.

This announcement comes at the same time as Soitec reports cumulative sales of one million 200mm RF-SOI wafers since 2009, hitting a milestone that underscores the pivotal role of RF-SOI in the booming wireless communications market. The one million RF-SOI wafers manufactured and shipped by Soitec have yielded approximately 20 billion ICs for front-end modules (FEMs). Soitec’s RF-SOI substrates are now integral in manufacturing antenna switches, antenna tuners, some power amplifiers and WiFi circuits, meeting the demanding requirements of leading-edge smart phone ICs. They have been widely adopted by leading RF semiconductor companies to address cost, performance and integration needs for the 3G and 4G/LTE mobile wireless markets.

“The widespread use of Soitec’s materials technology in existing 3G and 4G portable communications demonstrates the important role of RF-SOI in high-volume, cost-sensitive applications such as cellular phones, tablets and other fast-growing markets involving mobile internet devices,” said Bernard Aspar, senior vice president of Soitec’s Communication & Power Business Unit. “Now the high-volume availability of our newest 300mm RF-SOI offering enables our customers and their customers to continue to deliver higher performance while giving them access to foundries’ larger global production capacities and more manufacturing flexibility.”

While Soitec has been shipping large volumes of 200mm RF-SOI wafers for many years and continuing to increase its 200mm production capacity, the company has been delivering over the past 18 months.

300mm RFeSI90 wafer samples for product qualification. Key partnerships with fabless semiconductor companies and foundries have been instrumental in achieving the production milestones and performance levels of Soitec’s new 300mm RF-SOI product. The large supply of 300mm wafers allows Soitec’s customers to expand their production capacities for RF-SOI devices and produce more highly integrated ICs.

The new wafers – based on a more advanced SOI process – offer higher levels of performance such as better uniformity, a key parameter in achieving greater control of transistor matching for analog semiconductor designs and allowing designs with thinner transistors and additional process options to improve RonCoff performance, the figure of merit that is used to rate the performance of an RF switch.

Soitec continues to work on future generations of RF-SOI substrates with a product roadmap to further enable more innovation and cost effectiveness for future mobile communication markets.