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A scientific team led by the Department of Energy’s Oak Ridge National Laboratory has found a new way to take the local temperature of a material from an area about a billionth of a meter wide, or approximately 100,000 times thinner than a human hair.

This discovery, published in Physical Review Letters, promises to improve the understanding of useful yet unusual physical and chemical behaviors that arise in materials and structures at the nanoscale. The ability to take nanoscale temperatures could help advance microelectronic devices, semiconducting materials and other technologies, whose development depends on mapping the atomic-scale vibrations due to heat.

From left, Andrew Lupini and Juan Carlos Idrobo use ORNL's new monochromated, aberration-corrected scanning transmission electron microscope, a Nion HERMES to take the temperatures of materials at the nanoscale. Credit: Oak Ridge National Laboratory, US Dept. of Energy; photographer Jason Richards

From left, Andrew Lupini and Juan Carlos Idrobo use ORNL’s new monochromated, aberration-corrected scanning transmission electron microscope, a Nion HERMES to take the temperatures of materials at the nanoscale. Credit: Oak Ridge National Laboratory, US Dept. of Energy; photographer Jason Richards

The study used a technique called electron energy gain spectroscopy in a newly purchased, specialized instrument that produces images with both high spatial resolution and great spectral detail. The 13-foot-tall instrument, made by Nion Co., is named HERMES, short for High Energy Resolution Monochromated Electron energy-loss spectroscopy-Scanning transmission electron microscope.

Atoms are always shaking. The higher the temperature, the more the atoms shake. Here, the scientists used the new HERMES instrument to measure the temperature of semiconducting hexagonal boron nitride by directly observing the atomic vibrations that correspond to heat in the material. The team included partners from Nion (developer of HERMES) and Protochips (developer of a heating chip used for the experiment).

“What is most important about this ‘thermometer’ that we have developed is that temperature calibration is not needed,” said physicist Juan Carlos Idrobo of the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility at ORNL.

Other thermometers require prior calibration. To make temperature graduation marks on a mercury thermometer, for example, the manufacturer needs to know how much mercury expands as the temperature rises.

“ORNL’s HERMES instead gives a direct measurement of temperature at the nanoscale,” said Andrew Lupini of ORNL’s Materials Science and Technology Division. The experimenter needs only to know the energy and intensity of an atomic vibration in a material–both of which are measured during the experiment.

These two features are depicted as peaks, which are used to calculate a ratio between energy gain and energy loss. “From this we get a temperature,” Lupini explained. “We don’t need to know anything about the material beforehand to measure temperature.”

In 1966, also in Physical Review Letters, H. Boersch, J. Geiger and W. Stickel published a demonstration of electron energy gain spectroscopy, at a larger length scale, and pointed out that the measurement should depend upon the temperature of the sample. Based on that suggestion, the ORNL team hypothesized that it should be possible to measure a nanomaterial’s temperature using an electron microscope with an electron beam that is “monochromated” or filtered to select energies within a narrow range.

To perform electron energy gain and loss spectroscopy experiments, scientists place a sample material in the electron microscope. The microscope’s electron beam goes through the sample, with the majority of electrons barely interacting with the sample. In electron energy loss spectroscopy, the beam loses energy as it passes through the sample, whereas in energy gain spectroscopy, the electrons gain energy from interacting with the sample.

“The new HERMES lets us look at very tiny energy losses and even very small amounts of energy gain by the sample, which are even harder to observe because they are less likely to happen,” Idrobo said. “The key to our experiment is that statistical physical principles tell us that it is more likely to observe energy gain when the sample is heated. That is precisely what allowed us to measure the temperature of the boron nitride. The monochromated electron microscope enables this from nanoscale volumes. The ability to probe such exquisite physical phenomena at these tiny scales is why ORNL purchased the HERMES.”

ORNL scientists are constantly pushing the capabilities of electron microscopes to allow new ways of conducting forefront research. When Nion electron microscope developer Ondrej Krivanek asked Idrobo and Lupini, “Wouldn’t it be fun to try electron energy gain spectroscopy?” they jumped at the chance to be the first to explore this capability of their HERMES instrument.

Nanoscale resolution makes it possible to characterize the local temperature during phase transitions in materials–an impossibility with techniques that do not have the spatial resolution of HERMES spectroscopy. For example, an infrared camera is limited by the wavelength of infrared light to much larger objects.

Whereas in this experiment the scientists tested nanoscale environments at room temperature to about 1300 degrees Celsius (2372 degrees Fahrenheit), the HERMES could be useful for studying devices working across a wide range of temperatures, for example, electronics that operate under ambient conditions to vehicle catalysts that perform over 300 C/600 F.

Scientists at Rice University and the Indian Institute of Science, Bangalore, have discovered a method to make atomically flat gallium that shows promise for nanoscale electronics.

The Rice lab of materials scientist Pulickel Ajayan and colleagues in India created two-dimensional gallenene, a thin film of conductive material that is to gallium what graphene is to carbon.

Extracted into a two-dimensional form, the novel material appears to have an affinity for binding with semiconductors like silicon and could make an efficient metal contact in two-dimensional electronic devices, the researchers said.

The new material was introduced in Science Advances.

Gallium is a metal with a low melting point; unlike graphene and many other 2-D structures, it cannot yet be grown with vapor phase deposition methods. Moreover, gallium also has a tendency to oxidize quickly. And while early samples of graphene were removed from graphite with adhesive tape, the bonds between gallium layers are too strong for such a simple approach.

So the Rice team led by co-authors Vidya Kochat, a former postdoctoral researcher at Rice, and Atanu Samanta, a student at the Indian Institute of Science, used heat instead of force.

Rather than a bottom-up approach, the researchers worked their way down from bulk gallium by heating it to 29.7 degrees Celsius (about 85 degrees Fahrenheit), just below the element’s melting point. That was enough to drip gallium onto a glass slide. As a drop cooled just a bit, the researchers pressed a flat piece of silicon dioxide on top to lift just a few flat layers of gallenene.

They successfully exfoliated gallenene onto other substrates, including gallium nitride, gallium arsenide, silicone and nickel. That allowed them to confirm that particular gallenene-substrate combinations have different electronic properties and to suggest that these properties can be tuned for applications.

“The current work utilizes the weak interfaces of solids and liquids to separate thin 2-D sheets of gallium,” said Chandra Sekhar Tiwary, principal investigator on the project he completed at Rice before becoming an assistant professor at the Indian Institute of Technology in Gandhinagar, India. “The same method can be explored for other metals and compounds with low melting points.”

Gallenene’s plasmonic and other properties are being investigated, according to Ajayan. “Near 2-D metals are difficult to extract, since these are mostly high-strength, nonlayered structures, so gallenene is an exception that could bridge the need for metals in the 2-D world,” he said.

People are growing increasingly dependent on their mobile phones, tablets and other portable devices that help them navigate daily life. But these gadgets are prone to failure, often caused by small defects in their complex electronics, which can result from regular use. Now, a paper in today’s Nature Electronics details an innovation from researchers at the Advanced Science Research Center (ASRC) at The Graduate Center of The City University of New York that provides robust protection against circuitry damage that affects signal transmission.

The breakthrough was made in the lab of Andrea Alù, director of the ASRC’s Photonics Initiative. Alù and his colleagues from The City College of New York, University of Texas at Austin and Tel Aviv University were inspired by the seminal work of three British researchers who won the 2016 Noble Prize in Physics for their work, which teased out that particular properties of matter (such as electrical conductivity) can be preserved in certain materials despite continuous changes in the matter’s form or shape. This concept is associated with topology–a branch of mathematics that studies the properties of space that are preserved under continuous deformations.

“In the past few years there has been a strong interest in translating this concept of matter topology from material science to light propagation,” said Alù. “We achieved two goals with this project: First, we showed that we can use the science of topology to facilitate robust electromagnetic-wave propagation in electronics and circuit components. Second, we showed that the inherent robustness associated with these topological phenomena can be self-induced by the signal traveling in the circuit, and that we can achieve this robustness using suitably tailored nonlinearities in circuit arrays.”

To achieve their goals, the team used nonlinear resonators to mold a band-diagram of the circuit array. The array was designed so that a change in signal intensity could induce a change in the band diagram’s topology. For low signal intensities, the electronic circuit was designed to support a trivial topology, and therefore provide no protection from defects. In this case, as defects were introduced into the array, the signal transmission and the functionality of the circuit were negatively affected.

As the voltage was increased beyond a specific threshold, however, the band-diagram’s topology was automatically modified, and the signal transmission was not impeded by arbitrary defects introduced across the circuit array. This provided direct evidence of a topological transition in the circuitry that translated into a self-induced robustness against defects and disorder.

“As soon as we applied the higher-voltage signal, the system reconfigured itself, inducing a topology that propagated across the entire chain of resonators allowing the signal to transmit without any problem,” said A. Khanikaev, professor at The City College of New York and co-author in the study. “Because the system is nonlinear, it’s able to undergo an unusual transition that makes signal transmission robust even when there are defects or damage to the circuitry.”

“These ideas open up exciting opportunities for inherently robust electronics and show how complex concepts in mathematics, like the one of topology, can have real-life impact on common electronic devices,” said Yakir Hadad, lead author and former postdoc in Alù’s group, currently a professor at Tel-Aviv University, Israel. “Similar ideas can be applied to nonlinear optical circuits and extended to two and three-dimensional nonlinear metamaterials.”

3-D printing has gained popularity in recent years as a means for creating a variety of functional products, from tools to clothing and medical devices. Now, the concept of multi-dimensional printing has helped a team of researchers at the Advanced Science Research Center (ASRC) at the Graduate Center of the City University of New York develop a new, potentially more efficient and cost-effective method for preparing biochips (also known as microarrays), which are used to screen for and analyze biological changes associated with disease development, bioterrorism agents, and other areas of research that involve biological components.

Biological probes are patterned into biochips using nanoscopic light-pens, allowing researchers to increase the number of probes that can be immobilized in a single chip. Credit: Advanced Science Research Center at the Graduate Center, CUNY

Biological probes are patterned into biochips using nanoscopic light-pens, allowing researchers to increase the number of probes that can be immobilized in a single chip. Credit: Advanced Science Research Center at the Graduate Center, CUNY

In a paper published today in the journal Chem, researchers with the ASRC’s Nanoscience Initiative detail how they have combined microfluidic techniques with beam-pen lithography and photochemical surface reactions to devise a new biochip printing technique. The method involves exposing a biochip’s surface to specific organic reagents, and then using a tightly focused beam of light to adhere the immobilized reagents to the chip’s surface. The process allows scientists to repeatedly expose a single chip to the same or different factors and imprint the reactions onto different sections of the biochip. The result is a biochip that can accommodate more probes than is achievable with current commercial platforms.

“This is essentially a new nanoscale printer that allows us to imprint more complexity on the surface of biochip than any of the currently available commercial technologies,” said Adam Braunschweig, lead researcher and associate professor with the ASRC’s Nanoscience Initiative. “It will help us to gain much better understanding of how cells and biological pathways work.”

An additional benefit of the new tool is that it allows researchers to reliably print on a variety of delicate materials–including glasses, metals, and lipids–on the length scale of biological interactions, and without the use of a clean room. It also allows scientists to fit more reactive probes onto a single chip. These improvements could, in theory, reduce the cost of biochip-facilitated research.

ASRC scientists are now exploring ways to fine tune their new technique for creating these biochips. “We want to be able to record even more complex surface interactions and reduce our resolution down to a single molecule,” said ASRC Research Associate Carlos Carbonell, the paper’s lead author. “This technique gives rise to a new method of microarray creation that should be useful to the entire field of biological ‘omics’ research.”

A research team led by UCLA scientists and engineers has developed a method to make new kinds of artificial “superlattices” — materials comprised of alternating layers of ultra-thin “two-dimensional” sheets, which are only one or a few atoms thick. Unlike current state-of-the art superlattices, in which alternating layers have similar atomic structures, and thus similar electronic properties, these alternating layers can have radically different structures, properties and functions, something not previously available.

This is an artist's concept of two kinds of monolayer atomic crystal molecular superlattices. On the left, molybdenum disulfide with layers of ammonium molecules, on the right, black phosphorus with layers of ammonium molecules. Credit: UCLA Samueli Engineering

This is an artist’s concept of two kinds of monolayer atomic crystal molecular superlattices. On the left, molybdenum disulfide with layers of ammonium molecules, on the right, black phosphorus with layers of ammonium molecules. Credit: UCLA Samueli Engineering

For example, while one layer of this new kind of superlattice can allow a fast flow of electrons through it, the other type of layer can act as an insulator. This design confines the electronic and optical properties to single active layers, and prevents them from interfering with other insulating layers.

Such superlattices can form the basis for improved and new classes of electronic and optoelectronic devices. Applications include superfast and ultra-efficient semiconductors for transistors in computers and smart devices, and advanced LEDs and lasers.

Compared with the conventional layer-by-layer assembly or growth approach currently used to create 2D superlattices, the new UCLA-led process to manufacture superlattices from 2D materials is much faster and more efficient. Most importantly, the new method easily yields superlattices with tens, hundreds or even thousands of alternating layers, which is not yet possible with other approaches.

This new class of superlattices alternates 2D atomic crystal sheets that are interspaced with molecules of varying shapes and sizes. In effect, this molecular layer becomes the second “sheet” because it is held in place by “van der Waals” forces, weak electrostatic forces to keep otherwise neutral molecules “attached” to each other. These new superlattices are called “monolayer atomic crystal molecular superlattices.”

The study, published in Nature, was led by Xiangfeng Duan, UCLA professor of chemistry and biochemistry, and Yu Huang, UCLA professor of materials science and engineering at the UCLA Samueli School of Engineering.

“Traditional semiconductor superlattices can usually only be made from materials with highly similar lattice symmetry, normally with rather similar electronic structures,” Huang said. “For the first time, we have created stable superlattice structures with radically different layers, yet nearly perfect atomic-molecular arrangements within each layer. This new class of superlattice structures has tailorable electronic properties for potential technological applications and further scientific studies.”

One current method to build a superlattice is to manually stack the ultrathin layers one on top of the other. But this is labor-intensive. In addition, since the flake-like sheets are fragile, it takes a long time to build because many sheets will break during the placement process. The other method is to grow one new layer on top of the other, using a process called “chemical vapor deposition.” But since that means different conditions, such as heat, pressure or chemical environments, are needed to grow each layer, the process could result in altering or breaking the layer underneath. This method is also labor-intensive with low yield rates.

The new method to create monolayer atomic crystal molecular superlattices uses a process called “electrochemical intercalation,” in which a negative voltage is applied. This injects negatively charged electrons into the 2D material. Then, this attracts positively charged ammonium molecules into the spaces between the atomic layers. Those ammonium molecules automatically assemble into new layers in the ordered crystal structure, creating a superlattice.

“Think of a two-dimensional material as a stack of playing cards,” Duan said. “Then imagine that we can cause a large pile of nearby plastic beads to insert themselves, in perfect order, sandwiching between each card. That’s the analogous idea, but with a crystal of 2D material and ammonium molecules.”

The researchers first demonstrated the new technique using black phosphorus as a base 2D atomic crystal material. Using the negative voltage, positively charged ammonium ions were attracted into the base material, and inserted themselves between the layered atomic phosphorous sheets.”

Following that success, the team inserted different types of ammonium molecules with various sizes and symmetries into a series of 2D materials to create a broad class of superlattices. They found that they could tailor the structures of the resulting monolayer atomic crystal molecular superlattices, which had a diverse range of desirable electronic and optical properties.”The resulting materials could be useful for making faster transistors that consume less power, or for creating efficient light-emitting devices,” Duan said.

Samsung Electronics Co., Ltd. today announced that it has achieved the industry’s highest light efficacies for its fillet-enhanced chip-scale package (FEC) LED lineup – LM101B, LH181B and LH231B.

Initially chip-scale package (CSP) LEDs had not been widely used in mainstream LED lighting markets due to relatively lower efficacy levels compared to conventional LED packages. However, the newly upgraded, efficacy-leading FECs can be applied to most mainstream LED lighting environments, including ambient, downlight, spotlight, high bay, canopy and street lighting applications.

“Since introducing CSP technology to the industry in 2014, we have put extensive effort into advancing the performance levels and design flexibility of every one of our CSP LEDs,” said Yoonjoon Choi, Vice President of the LED Business Team at Samsung Electronics. “Samsung will continue to bolster its competitive edge in CSP technology, enabling the widest variety of luminaire designs with exceptional performance, reliability and cost benefits for lighting manufacturers worldwide.”

The enhanced FEC LEDs are based on Samsung’s most up-to-date CSP technology which builds TiO2 (Titanium dioxide) walls around the side surfaces of the chip to direct light output upwards. The technology provides considerably higher light efficacy than conventional CSP LEDs while offering greater flexibility for luminaire designers. Moreover, dramatically reduced cross-talk between neighboring packages allows each package to be placed in close proximity to one another.

Building on these advancements, the revamped FEC LED packages achieve the industry’s highest light efficacy levels, to suit an even wider range of lighting applications. The mid-power CSP, LM101B, features an increased efficacy of 205 lm/W (65mA, CRI 80+, 5000K), which is the highest among 1W-class, mid-power CSP LEDs. The 3W-class LH181B provides the highest light efficacy in its class with 190lm/W (350mA, CRI 70+, 5000K), which represents a more than 10-percent enhancement over the previous version. The 5W-class LH231B package continues to offer 170lm/W (700mA, CRI 70+, 5000K), the industry’s highest efficacy for the 5W class.

With Samsung FEC’s small form factor and reduced cross-talk, the LM101B is particularly well suited for spotlighting applications where packages can be densely placed within a small light-emitting surface area. Samsung also made the LM101B much simpler to mount compared to other mid-power CSP LEDs, by modifying the electrode pad.

In addition, the LH181B operates at a maximum current of 1.4A (Amps), making it an ideal component for high-power LED luminaires requiring superior lumen density.

The Samsung FEC lineup, now in mass production, is available in a full range of color temperature (CCT) and color rendering index (CRI) options.

Synopsys, Inc. (Nasdaq: SNPS) today announced a collaboration with Samsung Foundry to develop DesignWare Foundation IP for Samsung’s 8 nanometer (nm) Low Power Plus (8LPP) FinFET process technology. Providing DesignWare Logic Library and Embedded Memory IP on Samsung’s latest process technology enables designers to take advantage of a reduction in power and area compared to Samsung’s 10LPP process. The DesignWare Foundation IP will be developed to meet strict automotive-grade requirements, enabling designers to accelerate ISO 26262 and AEC-Q100 qualifications of their advanced driver assistance system (ADAS) and infotainment system-on-chips (SoCs). The DesignWare Logic Library and Embedded Memory IP will be available from Synopsys through the Foundry-Sponsored IP Program for the Samsung 8LPP process, enabling qualified customers to license the IP at no cost. The collaboration extends Synopsys’ and Samsung’s long history of working together to provide silicon-proven IP that helps designers meet their performance, power, and area requirements for a wide range of applications including mobile, automotive, and cloud computing.

“Samsung’s collaboration with Synopsys over the last decade has enabled first-pass silicon success for billions of ICs in mobile and consumer applications,” said Jongwook Kye, vice president of Design Enablement at Samsung Electronics. “As designs get more complex and migrate to smaller FinFET processes, Samsung’s advanced 8LPP process with Synopsys’ high-quality Foundation IP solutions will enable designers to differentiate their products for mobile, cryptocurrency and network/server applications, accelerate project schedules, and quickly ramp into volume production.”

“Samsung and Synopsys share a long and successful history of providing designers with silicon-proven DesignWare IP on Samsung’s processes ranging from 180 to 10 nanometer,” said John Koeter, vice president of marketing for IP at Synopsys. “As the leading provider of physical IP with more than 100 test chip tapeouts on FinFET processes, Synopsys continues to make significant investments in developing IP to help designers take advantage of Samsung’s latest process technologies, reduce risk and speed development of their SoCs.”

Brown University engineers have devised a new method of measuring the stickiness of micro-scale surfaces. The technique, described in Proceedings of the Royal Society A, could be useful in designing and building micro-electro-mechanical systems (MEMS), devices with microscopic moving parts.

With slight modifications, an atomic force microscope could be used to measure adheasion in micro-materials. Credit: Kesari Lab/Brown University. Credit: Kesari Lab/Brown University

With slight modifications, an atomic force microscope could be used to measure adheasion in micro-materials. Credit: Kesari Lab/Brown University. Credit: Kesari Lab/Brown University

At the scale of bridges or buildings, the most important force that engineered structures need to deal with is gravity. But at the scale of MEMS — devices like the tiny accelerometers used in smartphones and Fitbits — the relative importance of gravity decreases, and adhesive forces become more important.

“The main thing that matters at the microscale is what sticks to what,” said Haneesh Kesari, an assistant professor in Brown’s School of Engineering and coauthor of the new research. “If you have parts of your device sticking together that shouldn’t be, it’s not going to work. So in order to design MEMS devices, it helps to have a good way of measuring adhesion in the materials we use.”

That’s what Kesari and two Brown graduate students, Wenqiang Fang and Joyce Mok, looked to accomplish with this new research. Specifically, they wanted to measure a quantity known as “work of adhesion,” which roughly translates into the amount of energy required to separate a unit area of two adhered surfaces.

The key theoretical insight developed in the new study is that thermal vibrations of a microbeam can be used to calculate work of adhesion. That insight suggests a method in which a slightly modified atomic force microscopy (AFM) system can be used to probe adhesive properties.

Standard AFM works a bit like a record player. A cantilever with a sharp needle moves across a target material. A laser shown on the cantilever measures the tiny undulations it makes as it moves along the material’s contours. Those undulations can then be used to map out the material’s surface properties.

Adapting the method to measure adhesion would require simply removing the metal tip from the cantilever, leaving a flat microbeam. That beam can then be lowered onto a target material, where it will adhere. When the cantilever is raised slightly, some portion of the beam will become unstuck, while the rest remains stuck. The unstuck portion of the beam will vibrate ever so slightly. The authors found a way to use the extent of that vibration, which can be measured by an AFM laser, to calculate the length of the unstuck portion, which can in turn be used to calculate the target material’s work of adhesion.

With slight modifications, an atomic force microscope could be used to measure adheasion in micro-materials. Credit: Kesari Lab/Brown University Fang says the technique could be useful in assessing new material coatings or surface textures aimed at alleviating the failure of MEMS devices through sticking.

“Once you have a robust technique for measuring the material’s work of adhesion, then you have a systematic way of evaluating these methods to get the level of adhesion needed for a particular application,” Fang said. “The main advantage to this method is that you don’t need to change a standard AFM setup very much in order to do this.”

The approach is also much simpler than other techniques, according to Mok.

“Previous methods based on interferometry are labor intensive and may require many data points to be taken,” she said. “Our theoretical framework would give a value for the work of adhesion from a single measurement.”

Having demonstrated the technique numerically, Kesari says the next step is to build the system and start collecting some experimental data. He’s hopeful that such a system will aid in pushing the MEMS field forward.

“We have MEMS accelerometers and gyroscopes, but I don’t think the field has quite lived up to its promise yet,” Kesari said. “Part of the reason for that is that people haven’t completely understood adhesion at the small scale. We think that a more robust way of measuring adhesion is the first step towards gaining such an understanding.”

Phonons, which are packets of vibrational waves that propagate in solids, play a key role in condensed matter and are involved in various physical properties of materials. In nanotechnology, for example, they affect light emission and charge transport of nanodevices. As the main source of energy dissipation in solid-state systems, phonons are the ultimate bottleneck that limits the operation of functional nanomaterials.In an article recently published in Nature Communications, an INRS team of researchers led by Professor Luca Razzari and their European collaborators show that it is possible to modify the phonon response of a nanomaterial by exploiting the zero-point energy (i.e., the lowest possible – “vacuum” – energy in a quantum system) of a terahertz nano-cavity. The researchers were able to reshape the nanomaterial phonon response by generating new light-matter hybrid states. They did this by inserting some tens of semiconducting (specifically, cadmium sulfide) nanocrystals inside plasmonic nanocavities specifically designed to resonate at terahertz frequencies, i.e., in correspondence of the phonon modes of the nanocrystals.

“We have thus provided clear evidence of the creation of a new hybrid nanosystem with phonon properties that no longer belong to the original nanomaterial,” the authors said.

This discovery holds promise for applications in nanophotonics and nanoelectronics, opening up new possibilities for engineering the optical phonon response of functional nanomaterials. It also offers an innovative platform for the realization of a new generation of quantum transducers and terahertz light sources.

2D materials, which consist of a few layers of atoms, may well be the future of nanotechnology. They offer potential new applications and could be used in small, higher-performance and more energy-efficient devices. 2D materials were first discovered almost 15 years ago, but only a few dozen of them have been synthesized so far. Now, thanks to an approach developed by researchers from EPFL’s Theory and Simulation of Materials Laboratory (THEOS) and from NCCR-MARVEL for Computational Design and Discovey of Novel Materials, many more promising 2D materials may now be identified. Their work was recently published in the journal Nature Nanotechnology, and even got a mention on the cover page.

The first 2D material to be isolated was graphene, in 2004, earning the researchers who discovered it a Nobel Prize in 2010. This marked the start of a whole new era in electronics, as graphene is light, transparent and resilient and, above all, a good conductor of electricity. It paved the way to new applications in numerous fields such as photovoltaics and optoelectronics.

“To find other materials with similar properties, we focused on the feasibility of exfoliation,” explains Nicolas Mounet, a researcher in the THEOS lab and lead author of the study. “But instead of placing adhesive strips on graphite to see if the layers peeled off, like the Nobel Prize winners did, we used a digital method.”

More than 100,000 materials analyzed

The researchers developed an algorithm to review and carefully analyze the structure of more than 100,000 3D materials recorded in external databases. From this, they created a database of around 5,600 potential 2D materials, including more than 1,000 with particularly promising properties. In other words, they’ve created a treasure trove for nanotechnology experts.

To build their database, the researchers used a step-by-step process of elimination. First, they identified all of the materials that are made up of separate layers. “We then studied the chemistry of these materials in greater detail and calculated the energy that would be needed to separate the layers, focusing primarily on materials where interactions between atoms of different layers are weak, something known as Van der Waals bonding,” says Marco Gibertini, a researcher at THEOS and the second author of the study.

A plethora of 2D candidates

Of the 5,600 materials initially identified, the researchers singled out 1,800 structures that could potentially be exfoliated, including 1,036 that looked especially easy to exfoliate. This represents a considerable increase in the number of possible 2D materials known today. They then selected the 258 most promising materials, categorizing them according to their magnetic, electronic, mechanical, thermal and topological properties.

“Our study demonstrates that digital techniques can really boost discoveries of new materials,” says Nicola Marzari, the director of NCCR-MARVEL and a professor at THEOS. “In the past, chemists had to start from scratch and just keep trying different things, which required hours of lab work and a certain amount of luck. With our approach, we can avoid this long, frustrating process because we have a tool that can single out the materials that are worth studying further, allowing us to conduct more focused research.”

It is also possible to reproduce the researchers’ calculations thanks to their software AiiDA, which describes the calculation process for each material discovered in the form of workflows and stores the full provenance of each stage of the calculation. “Without AiiDA, it would have been very difficult to combine and process different types of data,” explains Giovanni Pizzi, a senior researcher at THEOS and co-author of the study. “Our workflows are available to the public, so anyone in the world can reproduce our calculations and apply them to any material to find out if it can be exfoliated.”