<h2>Akira Science AB, a start-up based in Stockholm, is betting on the combination of two revolutionary disciplines: tissue engineering and 3D printing.&nbsp;</h2>These two disciplines used to belong to two different stories that are now deeply interconnected. During the last fifty years scientists and surgeons have combined the concepts of life sciences, biology and biocompatible materials to construct functional tissues and open the way to innovative and less invasive techniques respect to traditional surgical transplants. They have been looking for new materials to substitute classical treatments to improve medical treatments where autograph or allograph of explanted tissues are required due to disease or trauma. In parallel to this story, 3D printing technologies also known as Additive Manufacturing (AM) were born in the 1980s and initially intended to quickly produce prototypes within industrial applications. When 3D printing technologies later met tissue engineering, a powerful combination consolidated to create structures with controlled geometry and high rate of reproducibility. Tissue engineers have been seeking for structures &ndash; scaffolds&nbsp;&ndash; that can provide structural and mechanical support to a damaged tissue while promoting its regeneration and allowing nutrients&rsquo; supply to the cells.The 3D printing market has been growing fast during the last decade releasing innovative technologies and materials, especially for the medical sector. 3D printing is transforming the way we manufacture objects from a centralized to a decentralized, customized production onsite.Akira Science is projected to have an active role in these future landscapes of smart and innovative manufacturing technologies applied to degradable materials for medical applications. The business potential arises from the ever-increasing need of patient-specific medical devices and of timely laboratory biological studies to test drugs and new clinical strategies - never so evident like in this pandemic period.&nbsp;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1590050859860-1590050859859.png" style="width: 655px;" class="fr-fic fr-dib">A cutting-edge new material and a smart scaffold design are the complementary and revolutionary points of force of Akira&rsquo;s strategy. The newly developed polymer (AKIMed-c12) has exceptional thermal stability, ensuring control of the material properties while printing, presenting a faster degradation time in the body environment than the current utilized materials (from 3-5 years to 9-10 months). Although newly formulated, AKIMed-c12 is made starting from well-established building blocks for the synthesis of approved biomedical materials, ensuring biocompatibility and non-toxicity in the physiological environment. While the printed scaffolds are not hard as the current available ones, but soft and pliable proving comfort to the patient (AKIMed-c12: 3D printed scaffolds).<iframe width="640" height="360" src="https://www.youtube.com/embed/GdgRqw2ZHjw?&wmode=opaque" frameborder="0" allowfullscreen="" class="fr-draggable"></iframe> The new material will be the workhorse for the 3D printing of degradable medical devices, while the smart design opens the way to new applications in tissue regeneration that were not possible until today utilizing the materials available on the market. Akira team is confident that such a combination has the potential to expand the scope of degradable 3D printed scaffolds from hard, for example bone, to soft tissue regeneration, such as breast reconstruction after mastectomy.Akira Science is providing both filaments for 3D printing and scaffolds with an architecture that satisfies customers&rsquo; need. Researchers and clinicians can buy the filament (AKIMed-c12: filament) and print the desired shape in their own facilities or can decide to ask Akira for printing their customized devices. Akira also provides support and consulting to collaborators and customers with material selection, design and simulation of the mechanical behavior of the desired scaffolds.The company continues to invest in open innovation through a continuous dialogue with customers and by setting new strategies to map future needs in tissue engineering and 3D printing opportunities.<hr>&Aacute;lvaro Morales and Tiziana Fuoco (AKIRA Science AB)

“The nexus between two revolutionary disciplines is inspiring us towards a future improved society”

Tissue Engineering and 3D Printing: Two Revolutionary Disciplines Now Fused Into One

Synthetic microparticles more intricate than some of the most complicated ones found in nature have been produced by a University of Michigan-led international team of scientists and engineers. They also investigated how that intricacy arises and devised a way to measure it.The findings, published in Science, pave the way for more stable fluid-and-particle mixes, such as paints, and new ways to twist light&mdash;a prerequisite for holographic projectors.The particle is composed of twisted spikes arranged into a ball a few microns, or millionths of a millimeter, across.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1586528981866-Canoe-content.jpg">If the gold-cysteine nanosheets are designed to remain flat, the result is a moderately complex design that the researchers called a &ldquo;kayak&rdquo; particle. Credit: Wenfeng Jiang, Kotov Lab, University of Michigan.&nbsp;Biology is a great creator of complexity on the nano- and microscales, with spiky structures such as plant pollen, immune cells, and some viruses. Among the most complex natural particles on the scale of the new synthetic particles are spiky coccolithophores. Also a few microns in diameter, this type of algae is known for building intricate limestone shells around themselves. To better understand the rules that govern how particles like these grow, scientists and engineers try to make them in the lab. But until now, there was no formalized way to measure the complexity of the results.&ldquo;Numbers rule the world, and being able to rigorously describe spiky shapes and put a number on complexity enables us to use new tools like artificial intelligence and machine learning in designing nanoparticles,&rdquo; said <a href="http://www.umkotov.com/" target="_blank">Nicholas Kotov</a>, the Joseph B. and Florence V. Cejka Professor of Engineering at the University of Michigan, who led the project.&nbsp;The team&mdash;which includes researchers at the Federal University of S&atilde;o Carlos and the University of S&atilde;o Paulo in Brazil, as well as the California Institute of Technology and the University of Pennsylvania in the U.S.&mdash;used the new framework to demonstrate that their particles were even more complicated than coccolithophores.The computational arm of the team, led by <a href="http://www.dq.ufscar.br/docentes/andre-farias-de-moura" target="_blank">Andr&eacute; Farias de Moura</a>, a professor of chemistry at the Federal University, investigated the quantum properties of the particles and the forces acting on the nanoscale building blocks.One of the key players in producing complexity can be chirality&mdash;in this context, the tendency to follow a clockwise or counterclockwise twist. They introduced chirality by coating nanoscale gold sulfide sheets, which served as their particle building blocks, with an amino acid called cysteine. Cysteine comes in two mirror-image forms, one driving the gold sheets to stack with a clockwise twist, and the other tending toward a counterclockwise twist. In the case of the most complex particle, a spiky ball with twisted spines, each gold sheet was coated with the same form of cysteine.&nbsp;<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1586529016691-Coccolithophore-content.jpg">The limestone shell produced by the coccolithophore Syracosphaera anthos, one of the most complex particles on this scale found in nature, is more intricate than kayak particles but less intricate than the spiky synthetic particle. Courtesy of www.mikrotax.org.&nbsp;But the team also controlled other interactions. By using flat particles, they created spikes that were flat rather than round. They also used electrically charged molecules to ensure that the nanoscale components built themselves into larger particles, bigger than a few hundred nanometers across, due to repulsion.&ldquo;These laws often conflict with each other, and the complexity emerges because these communities of particles have to satisfy all of them,&rdquo; said Kotov.And that complexity can be useful. Nanoscale spikes on particles like pollen keep them from clumping together. Similarly, the spikes on these particles made by the research team help them disperse in virtually any liquid, a property that is useful for stabilizing solid/liquid mixtures such as paints.The particles with twisted spikes also take in UV light and emit twisted&mdash;or circularly polarized&mdash;visible light in response.&ldquo;The understanding of these emissions was one of the hardest parts of the investigation,&rdquo; said de Moura.&nbsp;From the results of the experiments and simulations, it appears that UV energy was absorbed into the hearts of the particles and transformed through quantum mechanical interactions, becoming circularly polarized visible light by the time it left through the curved spikes.The researchers believe that the tactics they have uncovered can help scientists engineer particles that improve biosensors, electronics, and the efficiency of chemical reactions.&nbsp;The paper is titled, &ldquo;Emergence of Complexity in Hierarchically Organized Chiral Particles,&rdquo; and is published in the journal Science.

Creating and measuring intricacy in particles that could improve electronics and chemical reactions.

World's most complex synthetic microparticle outdoes nature's intricacy

For years, scientists have looked for ways to cool molecules down to ultracold temperatures, at which point the molecules should slow to a crawl, allowing scientists to precisely control their quantum behavior. This could enable researchers to use molecules as complex bits for quantum computing, tuning individual molecules like tiny knobs to carry out multiple streams of calculations at a time.While scientists have super-cooled atoms, doing the same for molecules, which are more complex in their behavior and structure, has proven to be a much bigger challenge.Now MIT physicists have found a way to cool molecules of sodium lithium down to 200 billionths of a Kelvin, just a hair above absolute zero. They did so by applying a technique called collisional cooling, in which they immersed molecules of cold sodium lithium in a cloud of even colder sodium atoms. The ultracold atoms acted as a refrigerant to cool the molecules even further.Collisional cooling is a standard technique used to cool down atoms using other, colder atoms. And for more than a decade, researchers have attempted to supercool a number of different molecules using collisional cooling, only to find that when molecules collided with atoms, they exchanged energy in such a way that the molecules were heated or destroyed in the process, called &ldquo;bad&rdquo; collisions.In their own experiments, the MIT researchers found that if sodium lithium molecules and sodium atoms were made to spin in the same way, they could avoid self-destructing, and instead engaged in &ldquo;good&rdquo; collisions, where the atoms took away the molecules&rsquo; energy, in the form of heat. The team used precise control of magnetic fields and an intricate system of lasers to choreograph the spin and the rotational motion of the molecules. As result, the atom-molecule mixture had a high ratio of good-to-bad collisions and was cooled down from 2 microkelvins to 220 nanokelvins.&ldquo;Collisional cooling has been the workhorse for cooling atoms,&rdquo; adds Nobel Prize laureate Wolfgang Ketterle, the John D. Arthur professor of physics at MIT.&nbsp;&ldquo;I wasn&rsquo;t convinced that our scheme would work, but since we didn&rsquo;t know for sure, we had to try it. We know now that it works for cooling sodium lithium molecules. Whether it will work for other classes of molecules remains to be seen.&rdquo;Their findings, published today in the journal Nature, mark the first time researchers have successfully used collisional cooling to cool molecules down to nanokelvin temperatures.Ketterle&rsquo;s coauthors on the paper are lead author Hyungmok Son, a graduate student in Harvard University&rsquo;s Department of Physics, along with MIT physics graduate student Juliana Park, and Alan Jamison, a professor of physics at the University of Waterloo and visiting scientist in MIT&rsquo;s Research Laboratory of Electronics.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1586440710384-MIT-Molecular-Fridge-02.jpg">A new refrigerator for molecules. Sodium atoms (yellow spheres) collide with sodium-lithium molecules (combined-yellow-red-spheres). The atom-molecule mixture is trapped in an optical trap whose effective edge is shown as a white rim. As the trap is loosened (depicted as a dimmer rim), the most energetic sodium atoms leave the trap, providing evaporative cooling. The cooling is transferred to the molecules via elastic collisions. The frost on the molecules indicates that they have reached a temperature of 200 billionths of a degree Kelvin. Figure credit: Pilsu Heo at Micropicture (South Korea)<h2>Reaching ultralow temperatures</h2>In the past, scientists found that when they tried to cool molecules down to ultracold temperatures by surrounding them with even colder atoms, the particles collided such that the atoms imparted extra energy or rotation to the molecules, sending them flying out of the trap, or self-destructing all together by chemical reactions.The MIT researchers wondered whether molecules and atoms, having the same spin, could avoid this effect, and remain ultracold and stable as a result. They looked to test their idea with sodium lithium, a &ldquo;diatomic&rdquo; molecule that Ketterle&rsquo;s group experiments with regularly, consisting of one lithium and one sodium atom.&ldquo;Sodium lithium molecules are quite different from other molecules people have tried,&rdquo; Jamison says. &ldquo;Many folks expected those differences would make cooling even less likely to work. However, we had a feeling these differences could be an advantage instead of a detriment.&rdquo;The researchers fine-tuned a system of more than 20 laser beams and various magnetic fields to trap and cool atoms of sodium and lithium in a vacuum chamber, down to about 2 microkelvins &mdash; a temperature Son says is optimal for the atoms to bond together as sodium lithium molecules.Once the researchers were able to produce enough molecules, they shone laser beams of specific frequencies and polarizations to control the quantum state of the molecules and carefully tuned microwave fields to make atoms spin in the same way as the molecules. &nbsp;&ldquo;Then we make the refrigerator colder and colder,&rdquo; says Son, referring to the sodium atoms that surround the cloud of the newly formed molecules. &ldquo;We lower the power of the trapping laser, making the optical trap looser and looser, which brings the temperature of sodium atoms down, and further cools the molecules, to 200 billionths of a kelvin.&rdquo;The group observed that the molecules were able to remain at these ultracold temperatures for up to one second. &ldquo;In our world, a second is very long,&rdquo; Ketterle says. &ldquo;What you want to do with these molecules is quantum computation and exploring new materials, which all can be done in small fractions of a second.&rdquo;If the team can get sodium lithium molecules to be about five times colder than what they have so far achieved, they will have reached a so-called quantum degenerate regime where individual molecules become indistinguishable and their collective behavior is controlled by quantum mechanics. Son and his colleagues have some ideas for how to achieve this, which will involve months of work in optimizing their setup, as well as acquiring a new laser to integrate into their setup.&nbsp;&ldquo;Our work will lead to discussion in our community why collisional cooling has worked for us but not for others,&rdquo; Son says &ldquo;Perhaps we will soon have predictions how other molecules could be cooled in this way.&rdquo;

 A new “refrigerator” super-cools molecules to nanokelvin temperatures. The technique may enable more complex, molecule-based quantum computing.  Image: José-Luis Olivares, MIT

Technique may enable molecule-based quantum computing.

New "refrigerator" super-cools molecules to nanokelvin temperatures

The human body is held together by an intricate cable system of tendons and muscles, engineered by nature to be tough and highly stretchable. An injury to any of these tissues, particularly in a major joint like the shoulder or knee, can require surgical repairs and weeks of limited mobility to fully heal.Now MIT engineers have come up with a tissue engineering design that may enable flexible range of motion in injured tendons and muscles during healing.The team has engineered small coils lined with living cells, that they say could act as stretchy scaffolds for repairing damaged muscles and tendons. The coils are made from hundreds of thousands of biocompatible nanofibers, tightly twisted into coils resembling miniature nautical rope, or yarn.The researchers coated the yarn with living cells, including muscle and mesenchymal stem cells, which naturally grow and align along the yarn, into patterns similar to muscle tissue. The researchers found the yarn&rsquo;s coiled configuration helps to keep cells alive and growing, even as the team stretched and bent the yarn multiple times.In the future, the researchers envision doctors could line patients&rsquo; damaged tendons and muscles with this new flexible material, which would be coated with the same cells that make up the injured tissue. The &ldquo;yarn&rsquo;s&rdquo; stretchiness could help maintain a patient&rsquo;s range of motion while new cells continue to grow to replace the injured tissue.&ldquo;When you repair muscle or tendon, you really have to fix their movement for a period of time, by wearing a boot, for example,&rdquo; says Ming Guo, assistant professor of mechanical engineering at MIT. &ldquo;With this nanofiber yarn, the hope is, you won&rsquo;t have to wearing anything like that.&rdquo;Guo and his colleagues published their results this week in the&nbsp;Proceedings of the National Academy of Sciences.&nbsp;His MIT co-authors are Yiwei Li, Yukun Hao, Satish Gupta, and Jiliang Hu. The team also includes Fengyun Guo, Yaqiong Wang, N&uuml; Wang, and Yong Zhao, of Beihang University.<h2>Stuck on gum</h2>The new nanofiber yarn was inspired in part by the group&rsquo;s&nbsp;<a href="http://news.mit.edu/2019/lobster-underbelly-tough-industrial-rubber-0219" target="_blank">previous work</a> on lobster membranes, where they found the crustacean&rsquo;s tough yet stretchy underbelly is due to a layered, plywood-like structure. Each microscopic layer contains hundreds of thousands of nanofibers, all aligned in the same direction, at an angle that is slightly offset from the layer just above and below.The nanofibers&rsquo; precise alignment makes each individual layer highly stretchable in the direction in which the fibers are arranged. Guo, whose work focuses on biomechanics, saw the lobster&rsquo;s natural stretchy patterning as an inspiration for designing artificial tissues, particularly for high-stretch regions of the body such as the shoulder and knee.Guo says biomedical engineers have embedded muscle cells in other stretchy materials such as hydrogels, in attempts to fashion flexible artificial tissues. However, while the hydrogels themselves are stretchy and tough, the embedded cells tend to snap when stretched, like tissue paper stuck on a piece of gum.&ldquo;When you largely deform a material like hydrogel, it will be stretched just fine, but the cells can&rsquo;t take it,&rdquo; Guo says. &ldquo;A living cell is sensitive, and when you stretch them, they die.&rdquo;<h2>Shelter in a slinky</h2>The researchers realized that simply considering the stretchability of a material would not be enough to design an artificial tissue. That material would also have to be able to protect cells from the severe strains produced when the material is stretched.The team looked to actual muscles and tendons for further inspiration, and observed that the tissues are made from strands of aligned protein fibers, coiled together to form microscopic helices, along which muscle cells grow. It turns out that, when the protein coils stretch out, the muscle cells simply rotate, like tiny pieces of tissue paper stuck on a slinky.Guo looked to replicate this natural, stretchy, cell-protecting structure as an artificial tissue material. To do so, the team first created hundreds of thousands of aligned nanofibers, using electrospinning, a technique that uses electric force to spin ultrathin fibers out from a solution of polymer or other materials. In this case, he generated nanofibers made from biocompatible materials such as cellulose.The team then bundled aligned fibers together and twisted them slowly to form first a spiral, and then an even tighter coil, ultimately resembling yarn and measuring about half a millimeter wide. Finally, they seeded live cells along each coil, including muscle cells, mesenchymal stem cells, and human breast cancer cells.The researchers then repeatedly stretched each coil up to six times its original length, and found that the majority of cells on each coil remained alive and continued to grow as the coils were stretched. Interestingly, when they seeded cells on looser, spiral-shaped structures made from the same materials, they found cells were less likely to remain alive. Guo says the structure of the tighter coils seems to &ldquo;shelter&rdquo; cells from damage.Going forward, the group plans to fabricate similar coils from other biocompatible materials such as silk, which could ultimately be injected into an injured tissue. The coils could provide a temporary, flexible scaffold for new cells to grow. Once the cells successfully repair an injury, the scaffold can dissolve away.&ldquo;We may be able to one day embed these structures under the skin, and the [coil] material would eventually be digested, while the new cells stay put,&rdquo; Guo says. &ldquo;The nice thing about this method is, it&rsquo;s really general, and we can try different materials. This may push the limit of tissue engineering a lot.&rdquo;

MIT engineers have designed coiled “nanoyarn,” shown as an artist’s interpretation here. The twisted fibers are lined with living cells and may be used to repair injured muscles and tendons while maintaining their flexibility.  Image: Felice Frankel

Twisted fibers coated with living cells could assist healing of injured muscles and tendons.

"Nanofiber yarn" makes for stretchy, protective artificial tissue

Plastic substrates for flexible displays are well known for their mechanical benefits such as thinness, lightness and flexibility, but their optical advantages are less cited. This blog post aims to shed light on the optical advantages of using plastic substrates as an alternative to glass for LCD.<h2>Plastic LCD vs glass LCD</h2>Before I describe the optical advantages of plastic substrates, I should briefly explain the structure of a glass LCD and that of a plastic LCD and how they compare in terms of thinness and lightness.Glass LCDs consist of a glass backplane containing the thin-film transistors (TFTs) and a glass frontplane containing the colour filter. In between these sheets of glass is the liquid crystal (LC) cell &ndash; the optical switch that shutters the light from passing through to the viewer.The thickness of these glass sheets can vary depending on the size and performance of the display and is often in the range of 400-700 microns (&mu;m) for each glass sheet, during processing. For some high-end ultra-slim LCDs the 400&mu;m glass can be further thinned in post-processing down to 200&mu;m &ndash; allowing for thinner notebooks and tablets, for example.<a href="https://www.flexenable.com/technology/flexible-olcd/" target="_blank" title="Organic LCDs">Organic LCDs</a> (OLCD) consist of organic TFTs built directly onto a plastic film and commonly use a plastic called tri-acetyl cellulose (TAC) film for the substrate which is typically just 40&mu;m thick. For a 13&rdquo; notebook screen, for example, moving from glass to TAC can reduce thickness and weight by at least 0.5mm and 100g respectively.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1583824528145-143334-olcdandlcdstructure.png" style="width: 1114px;" class="fr-fic fr-dib"><h2>Optical advantages of plastic LCD</h2>The mechanical advantages of plastic OLCD over glass LCD are further enhanced by the technology&rsquo;s excellent optical performance, much of which originates from the extreme thinness of plastic TAC substrates compared to glass.<h2>Improved image quality</h2>There&rsquo;s a common optical effect in displays that reduces image quality, called sparkle. You may not have heard of it, but you&rsquo;re probably familiar with it. Have you ever seen the little coloured pixels on your smartphone screen when a drop of water lands on the surface? This happens as a result of refraction, causing the viewer to perceive the pixels in a different location to their actual positon. The same effect occurs in a more subtle way with a dry screen because of surface imperfections on the front of the display, such as scratches or other roughness, causing the perceived location of the pixel beneath the glass to be changed.A similar effect can be seen when you are standing in a swimming pool trying look down at your feet - the apparent location appears to move around as a result of the surface ripples on the water. However, in much shallower water the effect is significantly reduced. For the same reason, moving to thinner plastic substrates in displays naturally reduces the degree of sparkle that is seen &ndash; meaning a crisper uniform image on the display compared to glass-based displays.<h2>High contrast TVs and monitors</h2>Over the past decade LCD display contrast, particularly in TVs has continued to improve. LCD displays work by having a bright light source (backlight) sitting under the liquid crystal display pixels. Each pixel (cell) is like a window with a pair of curtains that can be opened and closed to let the backlight through - making that pixel bright or dark. However, with LCD displays, even when the curtains are completely closed, a very small amount of light still gets through, which limits how black the display can appear.Nevertheless, LCD has continued to improve its ability to show black. In recent years this has been achieved with more sophisticated backlights that contain local dimming &ndash; allowing the brightness of the light to reduce in areas of the display where the curtains all needed to be closed (fully or partially). This is achieved by having an array of LEDs across the backlight that can be individually controlled in brightness.The ideal scenario would be to introduce &lsquo;pixel-level dimming&rsquo; &ndash; where every pixel (or every few pixels), has a controllable LED light source behind it. However, this is extremely expensive to do and would require several million LEDs in each TV.An alternative to this is the so called &ldquo;dual cell&rdquo; structure where one display pixel (cell) is placed on top of a second display pixel. This is equivalent to having two pairs of curtains in your window &ndash; akin to a blackout blind. This means a simple, low-cost backlight can be used, and excellent blacks can be achieved. These sorts of dual cell structures have been built on glass for some time. However, combining two conventional cells requires four sheets of glass &ndash; making the TV thicker, more costly, and causing other performance limitations.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1583824551649-143410-dualcell.png" style="width: 1114px;" class="fr-fic fr-dib">For an OLCD that uses 40&mu;m TAC film this means that ultra-high contrast dual cells can be built and still be thinner than today&rsquo;s &lsquo;single cell&rsquo; glass LCDs, and can be manufactured in a simpler way at lower cost with higher optical performance.

Plastic substrates for flexible displays are well known for their mechanical benefits such as thinness, lightness and flexibility, but their optical advantages are less cited.

Why certain plastic substrates are an ideal alternative to glass for LCD

The next generation of feature-filled and energy-efficient electronics will require computer chips just a few atoms thick. For all its positive attributes, trusty silicon can&rsquo;t take us to these ultrathin extremes.Now, electrical engineers at Stanford have identified two semiconductors &ndash; hafnium diselenide and zirconium diselenide &ndash; that share or even exceed some of silicon&rsquo;s desirable traits, starting with the fact that all three materials can &ldquo;rust.&rdquo;&ldquo;It&rsquo;s a bit like rust, but a very desirable rust,&rdquo; said <a href="https://profiles.stanford.edu/eric-pop" target="_blank">Eric Pop</a>, an associate professor of electrical engineering, who co-authored with post-doctoral scholar Michal Mleczko a paper that appears in the journal <a href="http://advances.sciencemag.org/content/3/8/e1700481" rel="nofollow" target="_blank">Science Advances</a>.The new materials can also be shrunk to functional circuits just three atoms thick and they require less energy than silicon circuits. Although still experimental, the researchers said the materials could be a step toward the kinds of thinner, more energy-efficient chips demanded by devices of the future.<h2>Silicon&rsquo;s strengths</h2>Silicon has several qualities that have led it to become the bedrock of electronics, Pop explained. One is that it is blessed with a very good &ldquo;native&rdquo; insulator, silicon dioxide or, in plain English, silicon rust.Exposing silicon to oxygen during manufacturing gives chip-makers an easy way to isolate their circuitry. Other semiconductors do not &ldquo;rust&rdquo; into good insulators when exposed to oxygen, so they must be layered with additional insulators, a step that introduces engineering challenges. Both of the diselenides the Stanford group tested formed this elusive, yet high-quality insulating rust layer when exposed to oxygen.Not only do both ultrathin semiconductors rust, they do so in a way that is even more desirable than silicon. They form what are called &ldquo;high-K&rdquo; insulators, which enable lower power operation than is possible with silicon and its silicon oxide insulator.As the Stanford researchers started shrinking the diselenides to atomic thinness, they realized that these ultrathin semiconductors share another of silicon&rsquo;s secret advantages: the energy needed to switch transistors on &ndash; a critical step in computing, called the band gap &ndash; is in a just-right range. Too low and the circuits leak and become unreliable. Too high and the chip takes too much energy to operate and becomes inefficient. Both materials were in the same optimal range as silicon.All this and the diselenides can also be fashioned into circuits just three atoms thick, or about two-thirds of a nanometer, something silicon cannot do.&ldquo;Engineers have been unable to make silicon transistors thinner than about five nanometers, before the material properties begin to change in undesirable ways,&rdquo; Pop said.The combination of thinner circuits and desirable high-K insulation means that these ultrathin semiconductors could be made into transistors 10 times smaller than anything possible with silicon today.&ldquo;Silicon won&rsquo;t go away. But for consumers this could mean much longer battery life and much more complex functionality if these semiconductors can be integrated with silicon,&rdquo; Pop said.<h2>More work to do</h2>There is much work ahead. First, Mleczko and Pop must refine the electrical contacts between transistors on their ultrathin diselenide circuits. &ldquo;These connections have always proved a challenge for any new semiconductor, and the difficulty becomes greater as we shrink circuits to the atomic scale,&rdquo; Mleczko said.They are also working to better control the oxidized insulators to ensure they remain as thin and stable as possible. Last, but not least, only when these things are in order will they begin to integrate with other materials and then to scale up to working wafers, complex circuits and, eventually, complete systems.&ldquo;There&rsquo;s more research to do, but a new path to thinner, smaller circuits &ndash; and more energy-efficient electronics &ndash; is within reach,&rdquo; Pop said.

Chip makers use "rust" to insulate silicon chip circuits. Two new semiconductor materials share that and other useful traits. | iStock / vladimirovic

Among other virtues, silicon “rusts” in a way that insulates a chip's circuitry. Two new ultrathin materials share that trait and others vital to the future of electronics.

New semiconductor materials exceed some of silicon's 'secret' powers

Yoel Fink stands under an unassuming LED ceiling lamp wearing what appears to be just an ordinary baseball cap. &ldquo;Do you hear it?&rdquo; he asks. Semiconductor technology within the fibers of the hat is converting the audio encoded in light pulses to electrical pulses, he explains, and those pulses are then converted to sound. &ldquo;This is one of the first examples of an advanced fabric. It looks like an ordinary hat but it&rsquo;s really a sophisticated optical communication system.&rdquo;Fink and his team are shaping a new destiny for fabrics. Clothing as a communications system: A hat that picks up light transmissions and converts them to sound can hold life-saving potential. &ldquo;Think about pedestrian safety and self-driving cars. Tremendous investments are going into cars. How about the pedestrians? Do we as pedestrians or bikers get to know if the car has detected us?&rdquo; Fink asks. &ldquo;With fabric optical communications your baseball cap can not only alert a car to your presence but importantly let you know if the car detected you. Fabrics for the self-driving future.&rdquo;This is just one example, Fink says, of how the next generation of fabrics could change how we think about all of them. An MIT professor of materials science and electrical engineering and CEO of Advanced Functional Fabrics of America (AFFOA), a $300 million institute on the edge of campus, Fink is eager to share his enthusiasm for fabrics with the MIT community. &ldquo;While all of this originated in basic science and engineering, we are focusing our efforts on transition to manufacturing and product,&rdquo; he says. &ldquo;We would not be here today if not for MIT&rsquo;s focus on the importance of transitioning technology to the marketplace.&rdquo;Fink is a high-energy ideas person. He walks quickly and talks even faster during a tour of the AFFOA facility. He and his staff lean toward the same casual clothing &ndash; t-shirts and jeans (his are typically black, &ldquo;the fastest way to lose two pounds&rdquo; he quips), and there is a pronounced clarity of purpose as he darts through the building, highlighting the rapid prototyping space and describing AFFOA&rsquo;s national advanced fabric prototyping network and the dozens of fabric ventures it&rsquo;s helping to get started.The overarching plan is to increase the value of fabrics to society, transforming them from something you buy-use-throw away to a platform for experiences and services such as communications and design-on-demand. Transforming fabrics requires new types of fiber technologies that encompass communications, energy storage, color change, physiological monitoring, and more. &ldquo;We are proposing a &lsquo;Moore&rsquo;s Law&rsquo; analog for fibers,&rdquo; Fink says. Just as the capabilities of microchips have grown exponentially over the last several decades, the capabilities of fibers are about to take off.To enable a transformation of this magnitude one needs partners, AFFOA has assembled 130 organizations into a national advanced fabric prototyping network. Many from industry are involved in dozens of projects aimed at getting &ldquo;Moore&rsquo;s law fibers&rdquo; into their products and processes. To rapidly engage industry and academia AFFOA has launched an innovative MicroAward program that is 12 weeks in duration and involves rapid iterations between AFFOA and a member seeking to address challenges in getting advanced fibers into fabrics and product. &ldquo;At AFFOA our year is 90 days long. We call it shot-clock innovation,&rdquo; says Fink.These new &ldquo;advanced fabrics&rdquo; incorporate high-speed semiconductor devices, including light-emitting diodes and diode photodetectors, into soft fabric materials. &ldquo;A lot of groups in the world today talk about &lsquo;smart fabrics&rsquo; but in fact end up just inserting conductive materials into fabrics,&rdquo; Fink says. &ldquo;Metals on their own cannot do very complex operations. You can&rsquo;t compute with a piece of metal,&rdquo; Fink says. &ldquo;To get sophisticated functionality into anything, you better involve the basic ingredient of modern technology &ndash; a semiconductor, which is what we are focusing on. We like to think about fabrics as the new software, capturing the opportunities to create new experiences and services through fabrics much in the same way that software has done over the past decade. For that we need not only technology but importantly entrepreneurs and investors to achieve that transformation and industry to make the product and help inform consumer preferences.&rdquo;Fink traces the root of his success to MIT&rsquo;s meritocratic culture, it&rsquo;s entrepreneurial spirit, the presence of mentors, and embrace of game-changing ideas. As an MIT student, Fink developed the confidence to ask a group of professors a question that led him to the basis for the discovery of a new type of mirror that has since been commercialized and used to treat hundreds and thousands of patients as part of a life-saving medical device. It also laid the groundwork for the creation of AFFOA. &ldquo;I think there is a lot of respect for students built into the system at MIT. People realize that ideas come from different directions and from all levels, that student sitting in front of you may eventually discover a cure for a disease, discover a fundamental law or form a great company so you are always listening. I found my calling at MIT and that led to where I am today,&rdquo; he says.

With an enthusiastic team, Yoel Fink, a professor of materials science and electrical engineering and CEO of Advanced Functional Fabrics of America (AFFOA), a $300 million institute on the edge of campus, is shaping a new destiny for fabrics.  Photo: Lillie Paquette/School of Engineering

Professor Yoel Fink is helping MIT lead the way in transforming the fabric materials in our lives.

Fabrics are the future

Engineers looking to create high-performance metallic alloys that are resistant to corrosion, fatigue and wear while remaining strong often use a trial-and-error method to find the right combination of elements. Now, engineers at Washington University in St. Louis plan to use computational methods and additive manufacturing to find the best combinations, saving significant time and money.Katharine Flores, professor of mechanical engineering &amp; materials science in the School of Engineering &amp; Applied Science, will build on some foundational work in high-entropy alloys &mdash; single-phase substances of five or more metallic elements in relatively equal parts &mdash; to find new alloys for structural, load-bearing applications, such as in aircraft, power generators and energy storage devices. Instead of the time-consuming trial-and-error method, Flores will work with Rohan Mishra, assistant professor of mechanical engineering &amp; materials science, who will use quantum-mechanical computation to identify combinations of elements that have the most promise. Once identified, Flores will synthesize the alloys using a laser-aided metal-on-metal&nbsp;deposition technique to create a library of potential alloys for further testing.With a three-year, $496,077 grant from the National Science Foundation, Flores and Mishra will use these methods to look for high-entropy alloys that can withstand high temperatures. Mishra will perform the computational calculations on some of the most powerful supercomputers to identify promising candidates from a large composition space. Then Flores will use her lab&#39;s technique to create a 2-D library, a one-inch square piece of metal on which about 100 tiny dots of individual candidate alloys can be fabricated. Flores&#39; laser-deposition technique creates the library in about 30 minutes with just a few grams of material.The additive manufacturing technique is similar to polymer 3-D printing where the machine draws the material onto a surface layer by layer. However, Flores uses a laser to melt a small region of a base material, then adds up to four different powders to the melt.<blockquote>&quot;What we&#39;re doing with this research is changing the composition of the powders as we raster the laser across the surface, and there are a few ways we can do that,&quot; Flores said.</blockquote>&quot;We can change the composition of the powder continuously to produce a gradient, or we can make individual dots with different compositions.&quot;While Flores has been doing similar work in bulk metallic glasses for several years, the high-entropy alloys are a new class of materials generating significant interest, she said. One particular attribute that is appealing is that the materials don&#39;t undergo phase separation, or become less homogenous at different temperatures as other metals do.&quot;On the calculation side, Rohan is going to identify combinations of elements that produce a single phase or produce an interesting combination of other phases,&quot; said Flores, who also is director of the university&#39;s Institute of Materials Science &amp; Engineering. &quot;He will tell us what combinations to try, then we will deposit those elements and do the microstructural characterization and mechanical property measurements to test the strength and stiffness and map out those properties.&quot;Once Flores&#39; lab has the measurements, she will provide them to Mishra, who can feed them back into his computational model to improve his predictions. In addition, Mishra&#39;s team will use one of the world&#39;s most powerful microscopes at Oak Ridge National Laboratory to look at the structure of the materials at the atomic scale.In addition to accelerating the development of new alloys, the work will contribute to the growing field of additive manufacturing, which could be used to make complicated parts in a single manufacturing process.&quot;When making a part for an airplane that has 20 different pieces that need to go together, if you can make it in one piece, you eliminate all of the fasteners, which means less weight, improved fuel efficiency and reduced manufacturing and maintenance time,&quot; she said.Previously, Flores&#39; lab created 21 alloys with aluminum, cobalt, chromium, iron&nbsp;and&nbsp;nickel and tested them using X-ray diffraction, microscopy and nanoindentation, a method used to test the hardness and stiffness of materials. In research recently published in&nbsp;Intermetallics, the team found that the laser-deposition technique created alloys consistent with those created with traditional methods, showing that the technique is a highly efficient method that can speed up the process of identifying and refining the most promising compositions prior to creating larger quantities.

Research using quantum-mechanical computation will be used to identify combinations of elements that have the most promise for load-bearing applications

Materials scientists combine supercomputers, 3-D printers to create strong metallic alloys

Smart shirts capable of tracking heart rate, skin-like sensors to measure recovery after a stroke, and tattoo-like devices to monitor glucose levels in people with diabetes &mdash; these are some of the flexible electronics that engineers hope one day to design.To facilitate this need for flexibility, Stanford researchers are reinventing wires, circuits and transistors that can stretch and bend the way our bodies do.&nbsp;Some of the strategies for designing such body-hugging circuitry are based in part on the use of carbon nanotubes and silver nanowires that have been engineered for flexibility. But there&rsquo;s a catch: Experiments have shown that when flexible nanowires are stretched, these materials lose some of their conductance, which impedes their ability to transmit electricity and robs systems of the predictable performance that is the prerequisite for designing reliable products. More puzzling yet, when the stretch is released, conductance remains in a lowered state. This unpredictability has made flexible nanowires difficult to work with because engineers want to know in advance precisely how components will behave when they are used.&ldquo;This phenomenon had been reported before, but nobody had found an explanation for it,&rdquo; said <a href="https://profiles.stanford.edu/wei-cai" target="_blank">Wei Cai</a>, associate professor of mechanical engineering, senior author in a Stanford team that has not only discovered why conductivity changes but has developed a way to predict the performance of bendable nanowires.&ldquo;Instead of a big question mark or a lot of trial and error, we provide a model on which people can base their designs,&rdquo; said Cai.He <a href="http://www.pnas.org/content/early/2018/02/09/1717217115" rel="nofollow" target="_blank">published these findings</a> in Proceedings of the National Academy of Sciences along with six co-authors. By creating this predictive framework, they have laid the groundwork for engineers to not merely imagine but design, prototype and, one day, produce electronics that stretch and bend in useful ways.<h2>When nanowires stretch</h2>Our current conception of a wire is akin to a rope, which can only be tugged so far. Recognizing the need for a new paradigm to define what constitutes a wire, flexible circuit designers have turned to carbon nanotubes, conductive materials that might be imagined as infinitesimal bits of hair scattered on a barbershop floor. In a delicate process, engineers spray a network of these overlapping electron highways onto rectangles of a rubbery substance to form a stretchy sheet of circuit film. Electrons zip from one end of the carbon film to the other, moving along the tubes and, when necessary, jumping from tube to tube.How fast electrons move through the film depends on the inherent conductivity of the carbon nanotube, the length of the individual tubes, the length of the rectangle and the ease with which electrons can transfer from one tube to another.When experimentalists have stretched these rubber rectangles up to twice their original dimensions, the conductivity of the nanotube networks goes down and the resistance goes up. That makes basic electronic sense. The longer the rectangle, the further the electrons must travel.But when the rubber circuits were allowed to snap back to their original size, resistance remained high and conductivity low. Researchers didn&rsquo;t understand why until the Stanford team figured it out.Imagine a tangled web of rubber jump ropes loosely attached to an elastic tarp. When you stretch the tarp, the ropes will slide against each other and get longer. But when you release the tarp, the ropes don&rsquo;t snap back to their preliminary positions. They buckle and curl into each other, and that&rsquo;s what happens with the carbon nanotubes. They end up with a wavier shape, said Lihua Jin, a former postdoctoral candidate at Stanford, now an assistant professor in mechanical and aerospace engineering at UCLA, and the first author on the paper.The team saw this pattern emerge in their simulations and then reproduced those results in experiments. Using this data, they figured out how to account mathematically for this wavy transformation. &ldquo;Each tube is still conducting, but when you stretch it and then it comes back to the original shape, the tubes have a different arrangement,&rdquo; said Cai. &ldquo;That gives you a different conductivity.&rdquo;Essentially, the Stanford formula is based on the interim length between the end points of each tube. After a tube is stretched and released, it curls into itself, resembling the letter &ldquo;S.&rdquo; The Stanford engineers take the &ldquo;S&rdquo; shape and draw a straight line between the two end points. That line becomes the hypotenuse of a right triangle. The remaining two sides of the triangle give researchers two distances: one that follows the stretching direction and one that is perpendicular to the stretching direction.&ldquo;If you have a tube that lies mostly along the stretching direction, then it does not contribute to conductance in the perpendicular direction,&rdquo; said Jin. Basically, the researchers need to know the average conductivity in the stretching direction as well as the perpendicular direction.Researchers average together all the stretching distances and then all the perpendicular distances. The next step is to create a ratio between those mean lengths and the length of the rubber circuit. When that ratio changes, so do the electronic characteristics of the rubber circuit. If you stretch a film 60 percent, for example, the resistance always doubles. That&rsquo;s true no matter the starting size.&ldquo;We have stumbled upon a general behavior,&rdquo; said Cai. &ldquo;It&rsquo;s not like you need carbon nanotubes from a particular vendor and with this diameter and length; as long as you have a lot of thin wires on a film, you see this principle.&rdquo;<h2>&ldquo;Closer to reality&rdquo;</h2>Their work provides circuit designers with certainty, guidelines and predictions for making these flexible material systems. The process is no longer a shot in the dark. After the first stretch, the conductivity remains constant. So, manufacturers will one day be able to pre-stretch one of these flexible nanowire constructs and, as long as they don&rsquo;t overstretch it past the pre-engineered point, be confident in its conductive stability and ultimate usefulness as a product.This knowledge could also be useful for making sensors. For example, a patient recovering from a hand injury is working on making a fist. With a sensor placed on the knuckle, each time the conductivity changes, the doctor would know that the patient has stretched a little bit more.The next step for Cai and his team at Stanford is to tackle the same question for using nanotubes as semiconductors, which involves discovering how the electrical properties of stretchable transistors change with the deformation that occurs when they are bent.&ldquo;These flexible systems are becoming closer and closer to reality,&rdquo; Cai said.

To make ‘smart clothing’ with built-in sensors, engineers need to design stretchable wire arrays.  |  Image courtesy of Wei Cai and Lihua Jin

Stretchable wires move us closer to electronics that mold to your skin

Holographic displays need twisted light. Twisted semiconductors assembled with the help of amino acids may enable them.

Twisted semiconductors for future moving holograms

One day soon we may live in smart houses that cater to our habits and needs, or ride in autonomous cars that rely on embedded sensors to provide safety and convenience. But today&rsquo;s electronic devices may not be able handle the deluge of data such applications portend because of limitations in their materials and design, according to the authors of a Stanford-led experiment recently published in&nbsp;Nature.To begin with, silicon transistors are no longer improving at their historic rate, which threatens to end the promise of smaller, faster computing known as Moore&rsquo;s Law. A second and related reason is computer design, say senior authors and Stanford professors&nbsp;Subhasish Mitra&nbsp;and&nbsp;H.-S. Philip Wong. Today&rsquo;s computers rely on separate logic and memory chips. These are laid out in two dimensions, like houses in a suburb, and connected by tiny wires, or interconnects, that become bottlenecked with data traffic.Now, the Stanford team has created a chip that breaks this bottleneck in two ways: first, by using nanomaterials not based on silicon for both logic and memory, and second, by stacking these computation and storage layers vertically, like floors in a high-rise, with a plethora of elevator-like interconnects between the &ldquo;floors&rdquo; to eliminate delays. &ldquo;This is the largest and most complex nanoelectronic system that has so far been made using the materials and nanotechnologies that are emerging to leapfrog silicon,&rdquo; said Mitra.The team, whose other Stanford members include professors&nbsp;Roger Howe&nbsp;and&nbsp;Krishna Saraswat, integrated over 2 million non-silicon transistors and 1 million memory cells, in addition to on-chip sensors for detecting gases &ndash; a proof of principle for other tasks yet to be devised. &ldquo;Electronic devices of these materials and three-dimensional design could ultimately give us computational systems 1,000 times more energy-efficient than anything we can build of silicon,&rdquo; Wong said.First author Max Shulaker, who performed this work while a PhD candidate at Stanford, is now an assistant professor at MIT and core member of its Microsystems Technology Laboratories. He explained in a single word why the team had to use emerging nanotechnologies and not conventional silicon technologies to achieve the high-rise design: heat. &ldquo;Building silicon transistors involves temperatures of over 1,000 degrees Celsius,&rdquo; Shulaker said. &ldquo;If you try to build a second layer on top of the first, you&rsquo;ll damage the bottom layer. This is why chips today have a single layer of circuitry.&rdquo;<h2>The magic of the materials</h2>The new prototype chip is a radical change from today&rsquo;s chips because it uses multiple nanotechnologies that can be fabricated at relatively low heat, Shulaker explained. Instead of relying on silicon-based transistors, the new chip uses carbon nanotubes, or CNTs, to perform computations. CNTs are sheets of 2-D carbon formed into nanocylinders. The new&nbsp;Naturepaper incorporates prior ground-breaking work by this team in developing the world&rsquo;s&nbsp;first all-CNT computer.The memory component of the new chip also relied on new processes and materials&nbsp;improved upon by this team. Called resistive random-access memory (RRAM), this is a type of nonvolatile memory &mdash; meaning that it doesn&rsquo;t lose data when the power is turned off &ndash; that operates by changing the resistance of a solid dielectric material.The key in this work is that CNT circuits and RRAM memory can be fabricated at temperatures below 200 Celsius. &ldquo;This means they can be built up in layers without harming the circuits beneath,&rdquo; Shulaker says. &ldquo;This truly is a remarkable feat of engineering,&rdquo; says Barbara De Salvo, scientific director at CEA-LETI, France, an international expert not connected with this project.The RRAM and carbon nanotubes are built vertically over one another, making a new, dense 3-D computer architecture with interleaving layers of logic and memory. By inserting a plethora of wires between these layers, this 3-D architecture promises to address the communication bottleneck. &ldquo;In addition to improved devices, 3-D integration can address another key consideration in systems: the interconnects within and between chips,&rdquo; Saraswat said.To demonstrate the potential of the technology, the researchers placed over a million carbon nanotube-based sensors on the surface of the chip, which they used to detect and classify ambient gases.Due to the layering of sensing, data storage and computing, the chip was able to measure each of the sensors in parallel and then write directly into its memory, generating huge bandwidth without risk of hitting a bottleneck, because the 3-D design made it unnecessary to move data between chips. In fact, even though Shulaker built the chip using the limited capabilities of an academic fabrication facility, the peak bandwidth between vertical layers of the chip could potentially approach and exceed the peak memory bandwidth of the most sophisticated silicon-based technologies available today.<h2>System benefits</h2>This provides several simultaneous benefits for future computing systems.&ldquo;The new 3-D computer architecture provides dense and fine-grained integration of computing and data storage, drastically overcoming the bottleneck from moving data between chips,&rdquo; Mitra says.&ldquo;As a result, the chip is able to store massive amounts of data and perform on-chip processing to transform a data deluge into useful information,&rdquo; Mitra says.Energy efficiency is another benefit. &ldquo;Logic made from carbon nanotubes will be ten times more energy efficient as today&rsquo;s logic made from silicon,&rdquo; Wong said. &ldquo;RRAM can also be denser, faster and more energy-efficient than the memory we use today.&rdquo;Thanks to the ground-breaking approach embodied by the Nature paper, the work is getting attention from leading scientists who are not directly connected with the research. Jan Rabaey, a professor of electrical engineering and computer sciences at the University of California, Berkeley, said 3-D chip architecture is such a fundamentally different approach that it may have other, more futuristic benefits to the advance of computing. &ldquo;These [3-D] structures may be particularly suited for alternative learning-based computational paradigms such as brain-inspired systems and deep neural nets,&rdquo; Rabaey said, adding, &ldquo;The approach presented by the authors is definitely a great first step in that direction.&rdquo;

Instead of relying on silicon-based devices, a new chip uses carbon nanotubes and resistive random-access memory (RRAM) cells. | Courtesy

Silicon chips are single story, but using new semiconductor materials, engineers can stack computer logic and memory like floors in a building to bust data traffic jams.

A new 'high rise' chip breaks computing's data bottleneck in two ways

Wenfeng Jiang demonstrates the process of growing the zinc oxide nanopillars and layering the polymer over them. Credit: Evan Dougherty, Michigan Engineering Communications & Marketing.

Tooth enamel has changed very little over millions of years -- and it is remarkably resistant to shock and wear.

Synthetic tooth enamel may lead to more resilient structures

In the field of photovoltaic technologies, silicon-based solar cells make up 90% of the market. In terms of cost, stability and efficiency (20-22% for a typical solar cell on the market), they are well ahead of the competition.However, after decades of research and investment, silicon-based solar cells are now close to their maximum theoretical efficiency. As a result, new concepts are required to achieve a long-term reduction in solar electricity prices and allow photovoltaic technology to become a more widely adopted way of generating power.One solution is to place two different types of solar cells on top of each other to maximize the conversion of light rays into electrical power. These &ldquo;double-junction&rdquo; cells are being widely researched in the scientific community, but are expensive to make. Now research teams in Neuch&acirc;tel &ndash; from EPFL&rsquo;s Photovoltaics Laboratory and the CSEM PV-center &ndash; have developed an economically competitive solution. They have integrated a perovskite cell directly on top of a standard silicon-based cell, obtaining a record efficiency of 25.2%. Their production method is promising, because it would add only a few extra steps to the current silicon-cell production process, and the cost would be reasonable. Their research has been published in&nbsp;Nature Materials.Perovskite-on-silicon: a nanometric sandwich Perovskite&rsquo;s unique properties have prompted a great deal of research into its use in solar cells over the last few years. In the space of nine years, the efficiency of these cells has risen by a factor of six. Perovskite allows high conversion efficiency to be achieved at a potentially limited production cost.In tandem cells, perovskite complements silicon: it converts blue and green light more efficiently, while silicon is better at converting red and infra-red light. &ldquo;By combining the two materials, we can maximize the use of the solar spectrum and increase the amount of power generated. The calculations and work we have done show that a 30% efficiency should soon be possible,&rdquo; say the study&rsquo;s main authors Florent Sahli and J&eacute;r&eacute;mie Werner. However, creating an effective tandem structure by superposing the two materials is no easy task. &ldquo;Silicon&rsquo;s surface consists of a series of pyramids measuring around 5 microns, which trap light and prevent it from being reflected. However, the surface texture makes it hard to deposit a homogeneous film of perovskite,&rdquo; explains Quentin Jeangros, who co-authored the paper.When the perovskite is deposited in liquid form, as it usually is, it accumulates in the valleys between the pyramids while leaving the peaks uncovered, leading to short circuits.A key layer ensuring an optimal microstructure Scientists at EPFL and CSEM have gotten around that problem by using evaporation methods to form an inorganic base layer that fully covers the pyramids. That layer is porous, enabling it to retain the liquid organic solution that is then added using a thin-film deposition technique called spin-coating. The researchers subsequently heat the substrate to a relatively low temperature of 150&deg;C to crystallize a homogeneous film of perovskite on top of the silicon pyramids.&ldquo;Until now, the standard approach for making a perovskite/silicon tandem cell was to level off the pyramids of the silicon cell, which decreased its optical properties and therefore its performance, before depositing the perovskite cell on top of it. It also added steps to the manufacturing process,&rdquo; says Florent Sahli.Updating existing technologies The new type of tandem cell is highly efficient and directly compatible with monocrystalline silicon-based technologies, which benefit from long-standing industrial expertise and are already being produced profitably. &ldquo;We are proposing to use equipment that is already in use, just adding a few specific stages. Manufacturers won&rsquo;t be adopting a whole new solar technology, but simply updating the production lines they are already using for silicon-based cells,&rdquo; explains Christophe Ballif, head of EPFL&rsquo;s Photovoltaics Laboratory and CSEM&rsquo;s PV-Center.At the moment, research is continuing in order to increase efficiency further and give the perovskite film more long-term stability. Although the team has made a breakthrough, there is still work to be done before their technology can be adopted commercially.

In Neuchâtel (Switzerland), researchers from EPFL and CSEM have combined silicon- and perovskite-based solar cells. The resulting efficiency of 25.2% is a record for this type of tandem cell. Their innovative yet simple manufacturing technique could be directly integrated into existing production lines, and efficiency could eventually rise above 30%.

In the field of photovoltaic technologies, silicon-based solar cells make up 90% of the market. In terms of cost, stability and efficiency (20-22% for a typical solar cell on the market), they are well ahead of the competition.

Silicon-perovskite solar cells achieve record efficiency of 25,2 percent

Nanokirigami has taken off as a field of research in the last few years; the approach is based on the ancient arts of origami (making 3-D shapes by folding paper) and kirigami (which allows cutting as well as folding) but applied to flat materials at the nanoscale, measured in billionths of a meter.Now, researchers at MIT and in China have for the first time applied this approach to the creation of nanodevices to manipulate light, potentially opening up new possibilities for research and, ultimately, the creation of new light-based communications, detection, or computational devices.The findings are described today in the journal Science Advances, in a paper by MIT professor of mechanical engineering Nicholas X Fang and five others. Using methods based on standard microchip manufacturing technology, Fang and his team used a focused ion beam to make a precise pattern of slits in a metal foil just a few tens of nanometers thick. The process causes the foil to bend and twist itself into a complex three-dimensional shape capable of selectively filtering out light with a particular polarization.<iframe src="https://www.youtube.com/embed/VDm8_lfpXGk?&wmode=opaque" frameborder="0" allowfullscreen="" class="fr-draggable" style="width: 767px; height: 434px;"></iframe>Previous attempts to create functional kirigami devices have used more complicated fabrication methods that require a series of folding steps and have been primarily aimed at mechanical rather than optical functions, Fang says. The new nanodevices, by contrast, can be formed in a single folding step and could be used to perform a number of different optical functions.For these initial proof-of-concept devices, the team produced a nanomechanical equivalent of specialized dichroic filters that can filter out circularly polarized light that is either &ldquo;right-handed&rdquo; or &ldquo;left-handed.&rdquo; To do so, they created a pattern just a few hundred nanometers across in the thin metal foil; the result resembles pinwheel blades, with a twist in one direction that selects the corresponding twist of light.The twisting and bending of the foil happens because of stresses introduced by the same ion beam that slices through the metal. When using ion beams with low dosages, many vacancies are created, and some of the ions end up lodged in the crystal lattice of the metal, pushing the lattice out of shape and creating strong stresses that induce the bending.&ldquo;We cut the material with an ion beam instead of scissors, by writing the focused ion beam across this metal sheet with a prescribed pattern,&rdquo; Fang says. &ldquo;So you end up with this metal ribbon that is wrinkling up&rdquo; in the precisely planned pattern.&ldquo;It&rsquo;s a very nice connection of the two fields, mechanics and optics,&rdquo; Fang says. The team used helical patterns to separate out the clockwise and counterclockwise polarized portions of a light beam, which may represent &ldquo;a brand new direction&rdquo; for nanokirigami research, he says.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1571292635166-nano-kirigami-1.gif" style="width: 766px;" class="fr-fic fr-dib">The technique is straightforward enough that, with the equations the team developed, researchers should now be able to calculate backward from a desired set of optical characteristics and produce the needed pattern of slits and folds to produce just that effect, Fang says.&ldquo;It allows a prediction based on optical functionalities&rdquo; to create patterns that achieve the desired result, he adds. &ldquo;Previously, people were always trying to cut by intuition&rdquo; to create kirigami patterns for a particular desired outcome.The research is still at an early stage, Fang points out, so more research will be needed on possible applications. But these devices are orders of magnitude smaller than conventional counterparts that perform the same optical functions, so these advances could lead to more complex optical chips for sensing, computation, or communications systems or biomedical devices, the team says.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1571292689254-nano-kirigami-2.gif" style="width: 766px;" class="fr-fic fr-dib">For example, Fang says, devices to measure glucose levels often use measurements of light polarity, because glucose molecules exist in both right- and left-handed forms which interact differently with light. &nbsp;&ldquo;When you pass light through the solution, you can see the concentration of one version of the molecule, as opposed to the mixture of both,&rdquo; Fang explains, and this method could allow for much smaller, more efficient detectors.Circular polarization is also a method used to allow multiple laser beams to travel through a fiber-optic cable without interfering with each other. &ldquo;People have been looking for such a system for laser optical communications systems&rdquo; to separate the beams in devices called optical isolaters, Fang says. &ldquo;We have shown that it&rsquo;s possible to make them in nanometer sizes.&rdquo;

At left, different patterns of slices through a thin metal foil, are made by a focused ion beam. These patterns cause the metal to fold up into predetermined shapes, which can be used for such purposes as modifying a beam of light.

Folding and cutting thin metal films could enable microchip-based 3-D optical devices.

Kirigami-inspired technique manipulates light at the nanoscale

The way that ordinary materials undergo a phase change, such as melting or freezing, has been studied in great detail. Now, a team of researchers has observed that when they trigger a phase change by using intense pulses of laser light, instead of by changing the temperature, the process occurs very differently.Scientists had long suspected that this may be the case, but the process has not been observed and confirmed until now. With this new understanding, researchers may be able to harness the mechanism for use in new kinds of optoelectronic devices.The unusual findings are reported today in the journal&nbsp;Nature Physics. The team was led by Nuh Gedik, a professor of physics at MIT, with graduate student Alfred Zong, postdoc Anshul Kogar, and 16 others at MIT, Stanford University, and Skolkovo Institute of Science and Technology (Skoltech) in Russia.For this study, instead of using an actual crystal such as ice, the team used an electronic analog called a charge density wave &mdash; a frozen electron density modulation within a solid &mdash; that closely mimics the characteristics of a crystalline solid.While typical melting behavior in a material like ice proceeds in a relatively uniform way through the material, when the melting is induced in the charge density wave by ultrafast laser pulses, the process worked quite differently. The researchers found that during the optically induced melting, the phase change proceeds by generating many singularities in the material, known as topological defects, and these in turn affect the ensuing dynamics of electrons and lattice atoms in the material.These topological defects, Gedik explains, are analogous to tiny vortices, or eddies, that arise in liquids such as water. The key to observing this unique melting process was the use of a set of extremely high-speed and accurate measurement techniques to catch the process in action.The fast laser pulse, less than a picoseond long (trillionths of a second), simulates the kind of rapid phase changes that occur. One example of a fast phase transition is quenching &mdash; such as suddenly plunging a piece of semimolten red-hot iron into water to cool it off almost instantly. This process differs from the way materials change through gradual heating or cooling, where they have enough time to reach equilibrium &mdash; that is, to reach a uniform temperature throughout &mdash; at each stage of the temperature change.While these optically induced phase changes have been observed before, the exact mechanism through which they proceed was not known, Gedik says.The team used a combination of three techniques, known as ultrafast electron diffraction, transient reflectivity, and time- and angle-resolved photoemission spectroscopy, to simultaneously observe the response to the laser pulse. For their study, they used a compound of lanthanum and tellurium, LaTe3, which is known to host charge density waves. Together, these instruments make it possible to track the motions of electrons and atoms within the material as they change and respond to the pulse.<img src="https://s3-us-west-1.amazonaws.com/wevolver-project-images/froala%2F1571291637570-media2.gif" style="width: 766px;" class="fr-fic fr-dib">Video above shows electron diffraction from the sample being studied. The smaller white spots close on either side of the central dot show the charge density wave, which is analogous to a crystal structure, as it &quot;melts&quot; when hit with an ultrafast laser pulse, and then &quot;refreezes.&quot;&nbsp;In the experiments, Gedik says, &ldquo;we can watch, and make a movie of, the electrons and the atoms as the charge density wave is melting,&rdquo; and then continue watching as the orderly structure then resolidifies. The researchers were able to clearly observe and confirm the existence of these vortex-like topological defects.They also found that the time for resolidifying, which involves the dissolution of these defects, is not uniform, but takes place on multiple timescales. The intensity, or amplitude, of the charge density wave recovers much more rapidly than does the orderliness of the lattice. This observation was only possible with the suite of time-resolved techniques used in the study, with each providing a unique perspective.Zong says that a next step in the research will be to try to determine how they can &ldquo;engineer these defects in a controlled way.&rdquo; Potentially, that could be used as a data-storage system, &ldquo;using these light pulses to write defects into the system, and then another pulse to erase them.&rdquo;Peter Baum, a professor of physics at the University of Konstanz in Germany, who was not connected to this research, says &ldquo;This is great work. One awesome aspect is that three almost entirely different, complicated methodologies have been combined to solve a critical question in ultrafast physics, by looking from multiple perspectives.&rdquo;Baum adds that &ldquo;the results are important for condensed-matter physics and their quest for novel materials, even if they are laser-excited and exist only for a fraction of a second.&rdquo;

To study phase changes in materials, such as freezing and thawing, researchers used charge density waves — electronic ripples that are analogous to the crystal structure of a solid. They found that when phase change is triggered by a pulse of laser light, instead of by a temperature change, it unfolds very differently, starting with a collection of whirlpool-like distortions called topological defects. This illustration depicts one such defect disrupting the orderly pattern of parallel ripples.

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