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UC Berkeley Extension announces three online integrated circuit (IC) semiconductor technology programs to meet the training needs of the surging worldwide semiconductor industry; the industry is predicted to reach $345 billion in sales this year, according to the most recent World Semiconductor Trade Statistics semiconductor market forecast. Extension’s new programs offer comprehensive curricula for professionals in varying stages of their technology careers.

Designed for technical professionals new to the field, the Professional Sequence in Semiconductor Technology Fundamentals explores microelectronics and microelectronic circuit theory, as well as IC design, semiconductor devices and computer-circuit simulation tools.

By contrast, the Certificate Program in Semiconductor IC Design is intended for professionals who have basic familiarity with the semiconductor field. This certificate combines theory and practice to provide a balanced mix of marketable skills and powerful tools to design, develop and deploy semiconductor ICs in many applications.

The Professional Sequence in Innovation Leadership for Technical Professionals demonstrates how highly successful leaders inspire people and achieve greatness, with particular focus on managing in a technical environment. Topics include basic financial management skills and their importance in decision making, planning and control.

“This is a versatile group of programs that can help technical professionals expand their skills in integrated circuit technology and technology management, depending on where they are in their careers—from newcomers to managers,” says Sean Butcher, UC Berkeley Extension program director for Technology and Engineering. “The fact that you can start these online courses at any time and proceed at your own pace makes them ideal for working professionals in this field.”

Today, we’re surrounded by a variety of electronic devices that are moving increasingly closer to us – we can attach and wear them, or even implant electronics inside our bodies.

Many types of smart devices are readily available and convenient to use. The goal now is to make wearable electronics that are flexible, sustainable and powered by ambient renewable energy.

This last goal inspired a group of Korea Advanced Institute of Science and Technology (KAIST) researchers to explore how the attractive physical features of zinc oxide (ZnO) materials could be more effectively used to tap into abundant mechanical energy sources to power micro devices. They discovered that inserting aluminum nitride insulating layers into ZnO-based energy harvesting devices led to a significant improvement of the devices’ performance. The researchers report their findings in the journal Applied Physics Letters, from AIP Publishing.

“Mechanical energy exists everywhere, all the time, and in a variety of forms – including movement, sound and vibration. The conversion from mechanical energy to electrical energy is a reliable approach to obtain electricity for powering the sustainable, wireless and flexible devices – free of environmental limitations,” explained Giwan Yoon, a professor in the Department of Electrical Engineering at KAIST.

Piezoelectric materials such as ZnO, as well as several others, have the ability to convert mechanical energy to electrical energy, and vice versa. “ZnO nanostructures are particularly suitable as nanogenerator functional elements, thanks to their numerous virtues including transparency, lead-free biocompatibility, nanostructural formability, chemical stability, and coupled piezoelectric and semiconductor properties,” noted Yoon.

The key concept behind the group’s work? Flexible ZnO-based micro energy harvesting devices, aka “nanogenerators,” can essentially be comprised of piezoelectric ZnO nanorod or nanowire arrays sandwiched between two electrodes formed on the flexible substrates. In brief, the working mechanisms involved can be explained as a transient flow of electrons driven by the piezoelectric potential.

“When flexible devices can be easily mechanically deformed by various external excitations, strained ZnO nanorods or nanowires tend to generate polarized charges, which, in turn, generate piezoelectronic fields,” said Yoon. “This allows charges to accumulate on electrodes and it generates an external current flow, which leads to electronic signals. Either we can use the electrical output signals directly or store them in energy storage devices.”

Other researchers have reported that the use of insulating materials can help provide an extremely large potential barrier. “This makes it critically important that insulating materials are carefully selected and designed – taking both the material properties and the device operation mechanism into consideration,” said Eunju Lee, a postdoctoral researcher in Yoon’s group.

To date, however, there have been few efforts made to develop new insulating materials and assess their applicability to nanogenerator devices or determine their effects on the device output performance.

The KAIST researchers proposed, for the first time, new piezoelectric ZnO/aluminum nitride (AlN) stacked layers for use in nanogenerators.

“We discovered that inserting AlN insulating layers into ZnO-based harvesting devices led to a significant improvement of their performance – regardless of the layer thickness and/or layer position in the devices,” said Lee. “Also, the output voltage performance and polarity seem to depend on the relative position and thickness of the stacked ZnO and AlN layers, but this needs to be explored further.”

The group’s findings are expected to provide an effective approach for realizing highly energy-efficient ZnO-based micro energy harvesting devices. “This is particularly useful for self-powered electronic systems that require both ubiquity and sustainability – portable communication devices, healthcare monitoring devices, environmental monitoring devices and implantable medical devices,” pointed out Yoon. And there are potentially many other applications.

Next up, Yoon and colleagues plan to pursue a more in-depth study to gain a much more precise and comprehensive understanding of device operation mechanisms. “We’ll also explore the optimum device configurations and dimensions based on the operation mechanism analysis work,” he added.

Squeezing light into tiny circuits and controlling its flow electrically is a holy grail that has become a realistic scenario thanks to the discovery of graphene. This tantalizing achievement is realized by exploiting so-called plasmons, in which electrons and light move together as one coherent wave. Plasmons guided by graphene -a two-dimensional sheet of carbon atoms – are remarkable as they can be confined to length scales of nanometers, up to two hundred times below the wavelength of light. An important hurdle until now has been the rapid loss of energy that these plasmons experience, limiting the range over which they could travel.

This problem has now been solved, as shown by researchers from ICFO (Barcelona), in a collaboration with CIC nanoGUNE (San Sebastian), and CNR/Scuola Normale Superiore (Pisa) ,all members of the EU Graphene Flagship, and Columbia University (New York).

Since the discovery of graphene, many other two-dimensional materials have been isolated in the laboratory. One example is boron nitride, a very good insulator. A combination of these two unique two-dimensional materials has provided the solution to the quest for controlling light in tiny circuits and suppression of losses. When graphene is encapsulated in boron nitride, electrons can move ballistically for long distances without scattering, even at room temperature. This research now shows that the graphene/boron nitride material system is also an excellent host for extremely strongly confined light and suppression of plasmon losses.

ICFO Prof Frank Koppens comments that “it is remarkable that we make light move more than 150 times slower than the speed of light, and at lengthscales more than 150 times smaller than the wavelength of light. In combination with the all-electrical capability to control nanoscale optical circuits, one can envision very exciting opportunities for applications.”

The research, carried out by PhD students Achim Woessner (ICFO) and Yuando Gao (Columbia) and postdoctoral fellow Mark Lundeberg (ICFO), is just the beginning of a series of discoveries on nano-optoelectronic properties of new heterostructures based on combining different kinds of two-dimensional materials. The material heterostructure was first discovered by the researchers at Columbia University. Prof. James Hone comments: “Boron nitride has proven to be the ideal ‘partner’ for graphene, and this amazing combination of materials continues to surprise us with its outstanding performance in many areas”.

Prof. Rainer Hillenbrand from CIC nanoGUNE comments: “Now we can squeeze light and at the same time make it propagate over significant distances through nanoscale materials. In the future, low-loss graphene plasmons could make signal processing and computing much faster, and optical sensing more efficient.”

The research team also performed theoretical studies. Marco Polini, from CNR/Scuola Normale Superiore (Pisa) and the IIT Graphene Labs (Genova), laid down a theory and performed calculations together with his collaborators. He explains that “according to theory, the interactions between light, electrons and the material system are now very well understood, even at a fully microscopic level. It is very rare to find a material that is so clean and in which this level of understanding is possible”.

These findings pave the way for extremely miniaturized optical circuits and devices that could be useful for optical and/or biological sensing, information processing or data communications.

Silicon Space Technology announced today the company has partnered with GLOBALFOUNDRIES to build commercial-ready products for extreme environments and applications.

Silicon Space Technology’s patented HARDSIL technology is tested and proven to operate in high-temperature environments — at 250C for more than 1,250 hours, and in high-radiation environments — with a TID performance of > 300 Krads. This is the first time any CMOS process has met these unique and extreme characteristics. This technology advancement also represents a huge milestone in extending reliability, performance and operating lifetimes, while simultaneously simplifying design complexity and reducing Size, Weight and Power (SWaP).

“We have been collaborating with GLOBALFOUNDRIES since 2012,” said Wes Morris, president and chief executive officer of SST. “The result is that Silicon Space Technology and GLOBALFOUNDRIES have a qualified CMOS process that Silicon Space Technology is already using to develop a family of ARM-based System-on-Chip (SoC) processors and memories which represent a paradigm shift for the high-temp and rad-hard markets.”

“Our partnership with Silicon Space Technology will enable us to produce a disruptive technology in the marketplace for ruggedized applications,” said Gregg Bartlett, senior vice president of the Product Management Group at GLOBALFOUNDRIES. “Now that HARDSIL is implemented and qualified in our foundry, we believe opportunities exist for it to be adopted across a wide-range of high-temp and rad-hard products and market segments.”

Silicon Space Technology is a privately held, fabless semiconductor company based in Austin, TX that provides integrated radiation-hardened (>300 Krads, latchup immune) and temperature-hardened (125C – 250C) solutions for extreme applications in the oil & gas, space, automotive, aerospace, industrial, medical and food & health industries.

Scientists at UCL, in collaboration with groups at the University of Bath and the Daresbury Laboratory, have uncovered the mystery of why blue light-emitting diodes (LEDs) are so difficult to make, by revealing the complex properties of their main component – gallium nitride – using sophisticated computer simulations.

Blue LEDs were first commercialised two decades ago and have been instrumental in the development of new forms of energy saving lighting, earning their inventors the 2014 Nobel Prize in Physics. Light emitting diodes are made of two layers of semiconducting materials (insulating materials which can be made conduct electricity in special circumstances). One has mobile negative charges, or electrons, available for conduction, and the other positive charges, or holes. When a voltage is applied, an electron and a hole can meet at the junction between the two, and a photon (light particle) is emitted.

The desired properties of a semiconductor layer are achieved by growing a crystalline film of a particular material and adding small quantities of an ‘impurity’ element, which has more or fewer electrons taking part in the chemical bonding (a process known as ‘doping’). Depending on the number of electrons, these impurities donate an extra positive or negative mobile charge to the material.

The key ingredient for blue LEDs is gallium nitride, a robust material with a large energy separation, or ‘gap’, between electrons and holes – this gap is crucial in tuning the energy of the emitted photons to produce blue light. But while doping to donate mobile negative charges in the substance proved to be easy, donating positive charges failed completely. The breakthrough, which won the Nobel Prize, required doping it with surprisingly large amounts of magnesium.

“While blue LEDs have now been manufactured for over a decade,” says John Buckeridge (UCL Chemistry), lead author of the study, “there has always been a gap in our understanding of how they actually work, and this is where our study comes in. Naïvely, based on what is seen in other common semiconductors such as silicon, you would expect each magnesium atom added to the crystal to donate one hole. But in fact, to donate a single mobile hole in gallium nitride, at least a hundred atoms of magnesium have to be added. It’s technically extremely difficult to manufacture gallium nitride crystals with so much magnesium in them, not to mention that it’s been frustrating for scientists not to understand what the problem was.”

The team’s study, published today in the journal Physical Review Letters, unveils the root of the problem by examining the unusual behaviour of doped gallium nitride at the atomic level using highly sophisticated computer simulations.

“To make an accurate simulation of a defect in a semiconductor such as an impurity, we need the accuracy you get from a quantum mechanical model,” explains David Scanlon (UCL Chemistry), a co-author of the paper. “Such models have been widely applied to the study of perfect crystals, where a small group of atoms form a repeating pattern. Introducing a defect that breaks the pattern presents a conundrum, which required the UK’s largest supercomputer to solve. Indeed, calculations on very large numbers of atoms were therefore necessary but would be prohibitively expensive to treat the system on a purely quantum-mechanical level.”

The team’s solution was to apply an approach pioneered in another piece of Nobel Prize winning research: hybrid quantum and molecular modelling, the subject of 2013’s Nobel Prize in Chemistry. In these models, different parts of a complex chemical system are simulated with different levels of theory.

“The simulation tells us that when you add a magnesium atom, it replaces a gallium atom but does not donate the positive charge to the material, instead keeping it to itself,” says Richard Catlow (UCL Chemistry), one of the study’s co-authors. “In fact, to provide enough energy to release the charge will require heating the material beyond its melting point. Even if it were released, it would knock an atom of nitrogen out of the crystal, and get trapped anyway in the resulting vacancy. Our simulation shows that the behaviour of the semiconductor is much more complex than previously imagined, and finally explains why we need so much magnesium to make blue LEDs successfully.”

The simulations crucially fit a complete set of previously unexplained experimental results involving the behaviour of gallium nitride. Aron Walsh (Bath Chemistry) says “We are now looking forward to the investigations into heavily defective GaN, and alternative doping strategies to improve the efficiency of solid-state lighting”.

A Northwestern University-led team recently found the answer to a mysterious question that has puzzled the materials science community for years–and it came in the form of some surprisingly basic chemistry.

Like many scientists, Jiaxing Huang did not understand why graphene oxide (GO) films were highly stable in water. When submerged, the individual GO sheets become negatively charged and repel each other, which should cause membrane to disintegrate. But earlier papers noted that instead of disintegrating, the films stabilized.

“It doesn’t make any sense,” said Huang, associate professor of materials science and engineering at the McCormick School of Engineering. “Many scientists have been very puzzled by this.”

Graphene oxide, a product of graphite oxidation, is often used to make graphene, a single-atom-layer thick sheet of carbon that is remarkably strong, lightweight, and has high potential in electronics and energy storage. Within the past three years, however, more scientists have become interested in GO itself, partially because of its potential for molecular separation applications.

After studying the material for many years, Huang realized that the secret of GO’s mysterious insolubility was the unintentional introduction of a common contaminant. To make a GO film, many scientists pass the acidic dispersion of individual sheets through porous anodized aluminum oxide filter discs, which are popularly used for preparing membranes of many nanomaterials. Huang’s team found that during filtration, the aluminum filter discs corrode in acidic water to release a significant number of aluminum ions, Al3+. The positively charged ion bonds with the negatively charged GO sheets to stabilize the resulting membranes.

“We have solved the puzzle using essentially freshman-level inorganic chemistry,” Huang said. “Now we know that graphene oxide films are indeed soluble in water. It’s just a matter of sample purity.”

Other multivalent metal ions, such as manganese, which is a byproduct from the synthesis of GO, can also crosslink the sheets.

Huang’s research is described in “On the origin of stability of graphene-oxide membranes in water,” published in Nature Chemistry on January 5. Other authors of the paper include graduate student Che-Ning Yeh, postdoc Kalyan Raidongia, former visiting graduate student Jiaojing Shao, and Shao’s former adviser Quan-Hong Yang from Tianjin University in China. The National Science Foundation and Office of Naval Research funded different parts described in the paper.

Huang’s finding also indicated that GO films are not as strong as researchers once thought. The aluminum ions make the film much stiffer. Without the ions, GO is three to four times weaker.

“This is a wake-up call for anyone using aluminum oxide filter discs,” he said. “People have used it for sample preparation in many areas of materials science and biology. Now we know it’s not as clean as we think.”

Chinese IC manufacturer Shanghai Huali Microelectronics Corporation gave a presentation on its outlook for the Internet of Things (IoT) market and the wide application of its specialty technology at the 2014 China Semiconductor Industry Association IC Design Branch Annual Conference (“ICCAD”), which was recently held at Hong Kong Science Park.

As a keynote speaker at the event, Henry Liu, senior director of marketing at HLMC, said, “With the development of smart automotive, smart grid, smart home and smart medical services, among other sectors, coupled with the pursuit among the general population of a simpler lifestyle and more efficient management of one’s day to day affairs, IoT has become the new hot topic of the market. The development of the market is set to further promote the prosperity of the semiconductor industry as semiconductor components are the basic core and data gateway of IoT equipment.”

According to Cisco IBSG, IoT connections worldwide are expected to reach 50 billion units, a milestone that is expected to have a profound impact on both consumers and vendors around the world. Currently, many of the world’s leading IC producers are accelerating expansion into the IoT sector in preparation for building their own ecosystem.

As one of the most advanced 12-inch wafer foundries in mainland China, HLMC’s technology starts from 55nm technology node and mainly covers 55nm LP, 40nm LP and 28nm LP as well as 55nm HV, 55nm eFlash and specialty technology. HLMC provides customers with low-cost wafer foundry solutions.  During the annual event, Chris Shao, senior director of Technology Development Division 1 at HLMC, shared features of the 55nm embedded flash technology with attendees. The 55nm embedded flash technology, one of the company’s core process platforms, provides the following advantages:

  • Core device: 1.2V; IO device: 2.5V or 5V; low working voltage and power consumption
  • Embedded SONOS technology based on standard COMS process without any need to change features and model of standard device
  • Complete retention of 55nm low power logic process-based IP bank
  • Only three additional layers of photomask are required for application of SONOS technology based on standard CMOS process, compared with 9-12 layers when using others processes, lowering manufacturing costs
  • Continuous downscaling to more advanced process nodes

Looking back the year of 2014, the IC manufacturing industry has made several great achievements: the industry’s sub-sector wafer foundry is on track to having a record year in terms of output value, as a result of the introduction of new mobile communication products and demands for special manufacturing processes used for IoT devices. The semiconductor facilities benefitting from IoT are expected to grow more rapidly than the overall semiconductor industry. Cisco IBSG estimates that 50 billion IoT products will be in existence by 2020, generating an output value of USD 14.4 trillion. Henry Liu stressed that HLMC is optimistic about the future of IoT and expressed confidence that the Company’s excellent manufacturing abilities and reliable quality management will serve to assure that it will be able to provide Chinese IC designers as well as customers worldwide with low-cost wafer foundry solutions for the IoT applications sector, including smartphones, tablets, smart TVs, set-top boxes, banking cards and automotive electronics.

In a sub-basement deep below the Laboratory for Integrated Science and Engineering at Harvard University, Mikhail Kats gets dressed. Mesh shoe covers, a face mask, a hair net, a pale gray jumpsuit, knee-high fabric boots, vinyl gloves, safety goggles, and a hood with clasps at the collar–these are not to protect him, Kats explains, but to protect the delicate equipment and materials inside the cleanroom.

While earning his Ph.D. in applied physics at the Harvard School of Engineering and Applied Sciences, Kats has spent countless hours in this cutting-edge facility. With his adviser, Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering, Kats has contributed to some stunning advances.

One is a metamaterial that absorbs 99.75 percent of infrared light–very useful for thermal imaging devices. Another is an ultrathin, flat lens that focuses light without imparting the distortions of conventional lenses. And the team has produced vortex beams, light beams that resemble a corkscrew, that could help communications companies transmit more data over limited bandwidth.

Certainly the most colorful advance to emerge from the Capasso lab, however, is a technique that coats a metallic object with an extremely thin layer of semiconductor, just a few nanometers thick. Although the semiconductor is a steely gray color, the object ends up shining in vibrant hues. That’s because the coating exploits interference effects in the thin films; Kats compares it to the iridescent rainbows that are visible when oil floats on water. Carefully tuned in the laboratory, these coatings can produce a bright, solid pink–or, say, a vivid blue–using the same two metals, applied with only a few atoms’ difference in thickness.

Capasso’s research group announced the finding in 2012, but at that time, they had only demonstrated the coating on relatively smooth, flat surfaces like silicon. This fall, the group published a second paper, in the journal Applied Physics Letters, taking the work much further.

“I cut a piece of paper out of my notebook and deposited gold and germanium on it,” Kats says, “and it worked just the same.”

That finding, deceptively simple given the physics involved, now suggests that the ultrathin coatings could be applied to essentially any rough or flexible material, from wearable fabrics to stretchable electronics.

“This can be viewed as a way of coloring almost any object while using just a tiny amount of material,” Capasso says.

It was not obvious that the same color effects would be visible on rough substrates, because interference effects are usually highly sensitive to the angle of light. And on a sheet of paper, Kats explains, “There are hills and valleys and fibers and little things sticking out–that’s why you can’t see your reflection in it. The light scatters.”

On the other hand, the applied films are so extremely thin that they interact with light almost instantaneously, so looking at the coating straight on or from the side–or, as it turns out, looking at those rough imperfections in the paper–doesn’t make much difference to the color. And the paper remains flexible, as usual.

Demonstrating the technique in the cleanroom at the Center for Nanoscale Systems, a National Science Foundation-supported research facility at Harvard, Kats uses a machine called an electron beam evaporator to apply the gold and germanium coating. He seals the paper sample inside the machine’s chamber, and a pump sucks out the air until the pressure drops to a staggering 10^-6 Torr (a billionth of an atmosphere). A stream of electrons strikes a piece of gold held in a carbon crucible, and the metal vaporizes, traveling upward through the vacuum until it hits the paper. Repeating the process, Kats adds the second layer. A little more or a little less germanium makes the difference between indigo and crimson.

This particular lab technique, Kats points out, is unidirectional, so to the naked eye very subtle differences in the color are visible at different angles, where slightly less of the metal has landed on the sides of the paper’s ridges and valleys. “You can imagine decorative applications where you might want something that has a little bit of this pearlescent look, where you look from different angles and see a different shade,” he notes. “But if we were to go next door and use a reactive sputterer instead of this e-beam evaporator, we could easily get a coating that conforms to the surface, and you wouldn’t see any differences.”

Many different pairings of metal are possible, too. “Germanium’s cheap. Gold is more expensive, of course, but in practice we’re not using much of it,” Kats explains. Capasso’s team has also demonstrated the technique using aluminum.

“This is a way of coloring something with a very thin layer of material, so in principle, if it’s a metal to begin with, you can just use 10 nanometers to color it, and if it’s not, you can deposit a metal that’s 30 nm thick and then another 10nm. That’s a lot thinner than a conventional paint coating that might be between a micron and 10 microns thick.”

In those occasional situations where the weight of the paint matters, this could be very significant. Capasso remembers, for example, that the external fuel tank of NASA’s space shuttle used to be painted white. After the first two missions, engineers stopped painting it and saved 600 pounds of weight.

Because the metal coatings absorb a lot of light, reflecting only a narrow set of wavelengths, Capasso suggests that they could also be incorporated into optoelectronic devices like photodetectors and solar cells.

“The fact that these can be deposited on flexible substrates has implications for flexible and maybe even stretchable optoelectronics that could be part of your clothing or could be rolled up or folded,” Capasso says.

Harvard’s Office of Technology Development continues to pursue commercial opportunities for the new color coating technology and welcomes contact from interested parties.

Kats, who concludes his year-long postdoctoral research position at SEAS this month, will become an assistant professor at the University of Wisconsin, Madison, in January. He credits those many hours spent in Harvard’s state-of-the-art laboratory facilities for much of his success in applied physics.

“You learn so much while you’re doing it,” Kats says. “You can be creative, discover something along the way, apply something new to your research. It’s marvelous that we have students and postdocs down here making things.”

A door has been opened to low-power off/on switches in micro-electro-mechanical systems (MEMS) and nanoelectronic devices, as well as ultrasensitive bio-sensors, with the first observation of piezoelectricity in a free standing two-dimensional semiconductor by a team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab).

Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division and an international authority on nanoscale engineering, led a study in which piezoelectricity – the conversion of mechanical energy into electricity or vice versa – was demonstrated in a free standing single layer of molybdenum disulfide, a 2D semiconductor that is a potential successor to silicon for faster electronic devices in the future.

“Piezoelectricity is a well-known effect in bulk crystals, but this is the first quantitative measurement of the piezoelectric effect in a single layer of molecules that has intrinsic in-plane dipoles,” Zhang says. “The discovery of piezoelectricity at the molecular level not only is fundamentally interesting, but also could lead to tunable piezo-materials and devices for extremely small force generation and sensing.”

Zhang, who holds the Ernest S. Kuh Endowed Chair at the University of California (UC) Berkeley and is a member of the Kavli Energy NanoSciences Institute at Berkeley, is the corresponding author of a paper in Nature Nanotechnology describing this research. The paper is titled “Observation of Piezoelectricity in Free-standing Monolayer MoS2.” The co-lead authors are Hanyu Zhu and Yuan Wang, both members of Zhang’s UC Berkeley research group. (See below for a complete list of co-authors.)

Since its discovery in 1880, the piezoelectric effect has found wide application in bulk materials, including actuators, sensors and energy harvesters. There is rising interest in using nanoscale piezoelectric materials to provide the lowest possible power consumption for on/off switches in MEMS and other types of electronic computing systems. However, when material thickness approaches a single molecular layer, the large surface energy can cause piezoelectric structures to be thermodynamically unstable.

Over the past couple of years, Zhang and his group have been carrying out detailed studies of molybdenum disulfide, a 2D semiconductor that features high electrical conductance comparable to that of graphene, but, unlike graphene, has natural energy band-gaps, which means its conductance can be switched off.

“Transition metal dichalcogenides such as molybdenum disulfide can retain their atomic structures down to the single layer limit without lattice reconstruction, even in ambient conditions,” Zhang says. “Recent calculations predicted the existence of piezoelectricity in these 2D crystals due to their broken inversion symmetry. To test this, we combined a laterally applied electric field with nano-indentation in an atomic force microscope for the measurement of piezoelectrically-generated membrane stress.”

Zhang and his group used a free-standing molybdenum disulfide single layer crystal to avoid any substrate effects, such as doping and parasitic charge, in their measurements of the intrinsic piezoelectricity. They recorded a piezoelectric coefficient of 2.9×10-10 C/m, which is comparable to many widely used materials such as zinc oxide and aluminum nitride.

“Knowing the piezoelectric coefficient is important for designing atomically thin devices and estimating their performance,” says Nature paper co-lead author Zhu. “The piezoelectric coefficient we found in molybdenum disulfide is sufficient for use in low-power logic switches and biological sensors that are sensitive to molecular mass limits.”

Zhang, Zhu and their co-authors also discovered that if several single layers of molybdenum disulfide crystal were stacked on top of one another, piezoelectricity was only present in the odd number of layers (1,3,5, etc.)

“This discovery is interesting from a physics perspective since no other material has shown similar layer-number sensitivity,” Zhu says. “The phenomenon might also prove useful for applications in which we want devices consisting of as few as possible material types, where some areas of the device need to be non-piezoelectric.”

In addition to logic switches and biological sensors, piezoelectricity in molybdenum disulfide crystals might also find use in the potential new route to quantum computing and ultrafast data-processing called “valleytronics.” In valleytronics, information is encoded in the spin and momentum of an electron moving through a crystal lattice as a wave with energy peaks and valleys.

“Some types of valleytronic devices depend on absolute crystal orientation, and piezoelectric anisotropy can be employed to determine this,’ says Nature paper co-lead author Wang. “We are also investigating the possibility of using piezoelectricity to directly control valleytronic properties such as circular dichroism in molybdenum disulfide.”

Researchers in Spain have discovered that if lead atoms are intercalated on a graphene sheet, a powerful magnetic field is generated by the interaction of the electrons’ spin with their orbital movement. This property could have implications in spintronics, an emerging technology promoted by the European Union to create advanced computational systems.

Graphene is considered the material of the future due to its extraordinary optical and electronic mechanical properties, especially because it conducts electrons very quickly. However, it does not have magnetic properties, and thus no method has been found to manipulate these electrons or any of their properties to use it in new magnetoelectronic devices, although Spanish scientists have come upon a key.

Researchers from IMDEA Nanoscience, the Autonomous University of Madrid, the Madrid Institute of Materials Science (CSIC) and the University of the Basque Country describe in the journal Nature Physics this week how to create a powerful magnetic field using this new material.

The secret is to intercalate atoms or Pb islands below the sea of hexagons of carbon that make up graphene. This produces an enormous interaction between two electron characteristics: their spin – a small ‘magnet’ linked to their rotation – and their orbit, the movement they follow around the nucleus.

“This spin-orbit interaction is a million times more intense than that inherent to graphene, which is why we obtain revolutions that could have important uses, for example in data storage,” explains Rodolfo Miranda, Director of IMDEA Nanoscience and head of the study.

To obtain this effect, the scientists laid a layer of lead on another of graphene, in turn grown over an iridium crystal. In this configuration the lead forms “islands” below the graphene and the electrons of this two-dimensional material behave as if in the presence of a colossal 80-tesla magnetic field, which facilitates the selective control of the flow of spins.

Traffic control with two lanes

“And, what is most important, under these conditions certain electronic states are topologically protected; in other words, they are immune to defects, impurities or geometric disturbances,” continues Miranda, who gives this example: “If we compare it to traffic, in a traditional spintronic material cars circulate along a single-lane road, which make collisions more likely, whilst with this new material we have traffic control with two spatially separate lanes, preventing crashes.”

Spintronics is a new technology that uses electrons’ magnetic spin to store information bits. It arose with the discovery of giant magnetoresistance, a finding which won Peter Grümberg and Albert Fert the Nobel Prize in Physics in 2007. It is an effect that causes great changes to the electric resistance of fine multi-layer materials and has led to the development of components as varied as the reader heads on hard disks or the sensors in airbags.

The first generation of spintronic or magnetoresistant devices was based on the effect magnetic materials have on electron spin. But a second generation is already up and running, and encompasses this new study, in which electrons’ own spin-orbit interaction acts on them as if there were a real external magnetic field, even if there is not.

The use of graphene as an active component in spintronics is one of the fundamental aims of the large European Union project “Graphene Flagship.” The scientists’ final objective is to wilfully control the type of spin the electrons in this new material have in order to apply it to the electronic devices of the future.