Category Archives: Materials

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 “double-junction” cells are being widely researched in the scientific community, but are expensive to make. Now research teams in Neuchâtel – from EPFL’s Photovoltaics Laboratory and the CSEM PV-center – 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 Nature Materials.

This scanning electron microscopy image shows Silicon’s pyramids covered with perovskite. Credit: EPFL

Perovskite-on-silicon: a nanometric sandwich

Perovskite’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. “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,” say the study’s main authors Florent Sahli and Jérémie Werner.

However, creating an effective tandem structure by superposing the two materials is no easy task. “Silicon’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,” 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°C to crystallize a homogeneous film of perovskite on top of the silicon pyramids.

“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,” 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. “We are proposing to use equipment that is already in use, just adding a few specific stages. Manufacturers won’t be adopting a whole new solar technology, but simply updating the production lines they are already using for silicon-based cells,” explains Christophe Ballif, head of EPFL’s Photovoltaics Laboratory and CSEM’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.

WIN Semiconductors Corp (TPEx:3105), the world’’s largest pure-play compound semiconductor foundry, has expanded its gallium nitride (GaN) process capabilities to include a 0.45?m-gate technology that supports current and future 5G applications. The NP45-11 GaN-on-SiC process allows customers to design hybrid Doherty power amplifiers used in 5G applications including massive MIMO (multiple-input and multiple-output) wireless antenna systems. Similar to macro-cell applications, MIMO base stations often combine Doherty power amplifiers with linearization techniques to meet demanding linearity and efficiency specifications of today’s wireless infrastructure.

GaN devices outperform the incumbent LDMOS technology, offering superior efficiency, instantaneous bandwidth and linearity, particularly in the higher frequency bands utilized in 5G radio access networks.

Ideal for use in sub-6 GHz 5G applications including macro-cell transmitters and MIMO access points, the NP45-11 technology supports power applications from 100 MHz through 6GHz. This discrete transistor process is environmentally rugged, incorporating advanced moisture protection and meets the JEDEC JESD22-A110 biased HAST qualification at 55 volts. Combined with WIN Semiconductors’ environmentally rugged high voltage passive technology, IP3M-01, the NP45-11 technology enables hybrid power amplifiers in a low cost plastic package.

The NP45-11 technology is fabricated on 100mm silicon carbide substrates and operates at a drain bias of 50 volts. In the 2.7GHz band, this technology provides saturated output power of 7 watts/mm with 18 dB linear gain and more than 65% power added efficiency without harmonic tuning.

“5G radio access networks create several challenges to power amplifier designs used in MIMO systems. High output power and linear efficiency are primary design objectives to meet performance specifications and lower total cost of ownership. The tradeoff between output power and linearized efficiency is significant because of the high peak-to-average power ratio employed in today’s wireless modulation schemes. This tradeoff becomes more difficult in 5G applications due to greater instantaneous bandwidth requirements and higher operating frequency,” said David Danzilio, Senior Vice President of WIN Semiconductors Corp.

Entegris, Inc. (NASDAQ: ENTG), a distributor of specialty chemicals and advanced materials solutions, announced today it has entered into a definitive agreement to acquire the SAES Pure Gas business, from SAES Getters S.p.A. (“SAES Group”), an advanced functional materials company headquartered in Milan, Italy. The SAES Pure Gas business, a provider of high-capacity gas purification systems used in semiconductor manufacturing and adjacent markets is based in San Luis Obispo, California and will report into the Microcontamination Control division of Entegris. Under the agreement, Entegris will purchase the shares and assets which comprise the SAES Pure Gas business for approximately $355 million, subject to customary purchase price adjustments.

Materials purity plays an increasingly critical role in the performance and reliability of advanced semiconductors as the sensitivity to contamination approaches the parts per quadrillion level. Advanced memory devices require significantly higher gas consumption per processed wafer to support shrinking geometries and multi-layer device architectures. As a result of this heightened sensitivity to molecular contamination and increased gas consumption, semiconductor manufacturers are depending on bulk gas suppliers to deliver process gases that meet new purity requirements.

“With this acquisition, our customers will benefit from a complete portfolio of gas purifications solutions for both bulk and specialty gases,” said Bertrand Loy, president and Chief Executive Officer of Entegris. “We are excited about the value this transaction will create, as it demonstrates our strategy of augmenting our organic growth with high-value acquisitions that leverage our global business platform and broaden our technology portfolio.”

“As we executed our evolutionary strategy for SAES Group and considered potential acquirers for the SAES Pure Gas business, we viewed Entegris as the ideal partner given its leadership in the semiconductor industry, the complementary nature of its filtration and purification offerings, and its financial and operational strengths,” said Massimo della Porta, president of SAES Getters S.p.A.

According to a recent press release issued by SAES Group, the SAES Pure Gas business recorded revenues of €81 million, or $91.5 million, and an adjusted EBITDA of €29.3 million, or $33.1 million, for its fiscal year ended December 31, 2017 and revenues of €25.5 million, or $31 million, and an adjusted EBITDA of €7.8 million, or $9.6 million, for the first quarter of 2018. Entegris intends to fund the acquisition from its available cash and expects that the transaction will be immediately accretive.

The closing of the transaction is subject to the completion of a pre-closing restructuring of certain of SAES Group’s US legal entities and other customary closing conditions. The transaction is expected to close in the next two to four weeks.

Researchers at Oregon State University are looking at a highly durable organic pigment, used by humans in artwork for hundreds of years, as a promising possibility as a semiconductor material.

Findings suggest it could become a sustainable, low-cost, easily fabricated alternative to silicon in electronic or optoelectronic applications where the high-performance capabilities of silicon aren’t required.

Optoelectronics is technology working with the combined use of light and electronics, such as solar cells, and the pigment being studied is xylindein.

“Xylindein is pretty, but can it also be useful? How much can we squeeze out of it?” said Oregon State University physicist Oksana Ostroverkhova. “It functions as an electronic material but not a great one, but there’s optimism we can make it better.”

Xylindien is secreted by two wood-eating fungi in the Chlorociboria genus. Any wood that’s infected by the fungi is stained a blue-green color, and artisans have prized xylindein-affected wood for centuries.

The pigment is so stable that decorative products made half a millennium ago still exhibit its distinctive hue. It holds up against prolonged exposure to heat, ultraviolet light and electrical stress.

“If we can learn the secret for why those fungi-produced pigments are so stable, we could solve a problem that exists with organic electronics,” Ostroverkhova said. “Also, many organic electronic materials are too expensive to produce, so we’re looking to do something inexpensively in an ecologically friendly way that’s good for the economy.”

With current fabrication techniques, xylindein tends to form non-uniform films with a porous, irregular, “rocky” structure.

“There’s a lot of performance variation,” she said. “You can tinker with it in the lab, but you can’t really make a technologically relevant device out of it on a large scale. But we found a way to make it more easily processed and to get a decent film quality.”

Ostroverkhova and collaborators in OSU’s colleges of Science and Forestry blended xylindein with a transparent, non-conductive polymer, poly(methyl methacrylate), abbreviated to PMMA and sometimes known as acrylic glass. They drop-cast solutions both of pristine xylindein and a xlyindein-PMMA blend onto electrodes on a glass substrate for testing.

They found the non-conducting polymer greatly improved the film structure without a detrimental effect on xylindein’s electrical properties. And the blended films actually showed better photosensitivity.

“Exactly why that happened, and its potential value in solar cells, is something we’ll be investigating in future research,” Ostroverkhova said. “We’ll also look into replacing the polymer with a natural product – something sustainable made from cellulose. We could grow the pigment from the cellulose and be able to make a device that’s all ready to go.

“Xylindein will never beat silicon, but for many applications, it doesn’t need to beat silicon,” she said. “It could work well for depositing onto large, flexible substrates, like for making wearable electronics.”

This research, whose findings were recently published in MRS Advances, represents the first use of a fungus-produced material in a thin-film electrical device.

“And there are a lot more of the materials,” Ostroverkhova said. “This is just first one we’ve explored. It could be the beginning of a whole new class of organic electronic materials.”

Applied Materials, Inc. today announced a breakthrough in materials engineering that accelerates chip performance in the big data and AI era.

In the past, classic Moore’s Law scaling of a small number of easy-to-integrate materials simultaneously improved chip performance, power and area/cost (PPAC). Today, materials such as tungsten and copper are no longer scalable beyond the 10nm foundry node because their electrical performance has reached physical limits for transistor contacts and local interconnects. This has created a major bottleneck in achieving the full performance potential of FinFET transistors. Cobalt removes this bottleneck but also requires a change in process system strategy. As the industry scales structures to extreme dimensions, the materials behave differently and must be systematically engineered at the atomic scale, often under vacuum.

To enable the use of cobalt as a new conducting material in the transistor contact and interconnect, Applied has combined several materials engineering steps – pre-clean, PVD, ALD and CVD – on the Endura® platform. Moreover, Applied has defined an integrated cobalt suite that includes anneal on the Producer® platform, planarization on the Reflexion® LK Prime CMP platform and e-beam inspection on the PROVision™ platform. Customers can use this proven, Integrated Materials Solution to speed time-to-market and increase chip performance at the 7nm foundry node and beyond.

“Five years ago, Applied anticipated an inflection in the transistor contact and interconnect, and we began developing an alternative materials solution that could take us beyond the 10nm node,” said Dr. Prabu Raja, senior vice president of Applied’s Semiconductor Products Group. “Applied brought together its experts in chemistry, physics, engineering and data science to explore the broad portfolio of Applied’s technologies and create a breakthrough Integrated Materials Solution for the industry. As we enter the big data and AI era, there will be more of these inflections, and we are excited to be having earlier and deeper collaborations with our customers to accelerate their roadmaps and enable devices we never dreamed possible.”

While challenging to integrate, cobalt brings significant benefits to chips and chip making: lower resistance and variability at small dimensions; improved gapfill at very fine dimensions; and improved reliability. Applied’s integrated cobalt suite is now shipping to foundry/logic customers worldwide.

Applied Materials, Inc. (Nasdaq:AMAT) is a leader in materials engineering solutions used to produce virtually every new chip and advanced display in the world.

Physicists developed a way to determine the electronic properties of thin gold films after they interact with light. Nature Communications published the new method, which adds to the understanding of the fundamental laws that govern the interaction of electrons and light.

“Surprisingly, up to now there have been very limited ways of determining what exactly happens with materials after we shine light on them,” says Hayk Harutyunyan, an assistant professor of physics at Emory University and lead author of the research. “Our finding may pave the way for improvements in devices such as optical sensors and photovoltaic cells.”

From solar panels to cameras and cell phones — to seeing with our eyes — the interaction of photons of light with atoms and electrons is ubiquitous. “Optical phenomenon is such a fundamental process that we take it for granted, and yet it’s not fully understood how light interacts with materials,” Harutyunyan says.

One obstacle to understanding the details of these interactions is their complexity. When the energy of a light photon is transferred to an electron in a light-absorbing material, the photon is destroyed and the electron is excited from one level to another. But so many photons, atoms and electrons are involved — and the process happens so quickly — that laboratory modeling of the process is computationally challenging.

For the Nature Communications paper, the physicists started with a relatively simple material system — ultra-thin gold layers — and conducted experiments on it.

“We did not use brute computational power,” Harutyunyan says. “We started with experimental data and developed an analytical and theoretical model that allowed us to use pen and paper to decode the data.”

Harutyunyan and Manoj Manjare, a post-doctoral fellow in his lab, designed and conducted the experiments. Stephen Gray, Gary Wiederrecht and Tal Heipern — from the Argonne National Laboratory — came up with the mathematical tools needed. The Argonne physicists also worked on the theoretical model, along with Alexander Govorov from Ohio University.

For the experiments, the nanolayers of gold were positioned at particular angles. Light was then shined on the gold in two, sequential pulses. “These laser light pulses were very short in time — thousands of billions of times shorter than a second,” Harutyunyan says. “The first pulse was absorbed by the gold. The second pulse of light measured the results of that absorption, showing how the electrons changed from a ground to excited state.”

Typically, gold absorbs light at green frequencies, reflecting all the other colors of the spectrum, which makes the metal appear yellow. In the form of nanolayers, however, gold can absorb light at longer wave lengths, in the infrared part of the spectrum.

“At a certain excitation angle, we were able to induce electronic transitions that were not just a different frequency but a different physical process,” Harutyunyan says. “We were able to track the evolution of that process over time and demonstrate why and how those transitions happen.”

Using the method to better understand the interactions underlying light absorption by a material may lead to ways to tune and manage these interactions.

Photovoltaic solar energy cells, for instance, are currently only capable of absorbing a small percentage of the light that hits them. Optical sensors used in biomedicine and photo catalysts used in chemistry are other examples of devices that could potentially be improved by the new method.

While the Nature Communications paper offers proof of concept, the researchers plan to continue to refine the method’s use with gold while also experimenting with a range of other materials.

“Ultimately, we want to demonstrate that this is a broad method that could be applied to many useful materials,” Harutyunyan says.

Exagan, an innovator of gallium nitride (GaN) semiconductor technology enabling smaller and more efficient electrical converters, is accelerating the transition to greater power efficiency by launching its safe, powerful G-FET™ power transistors and G-DRIVE™ intelligent fast-switching solution, featuring an integrated driver and transistor in a single package. These GaN-based devices are easy to design into electronic products, paving the way for fast chargers that comply with the USB power delivery (PD) 3.0 type C standard while providing exceptional power performance and integration.

At this week’s PCIM Europe conference in Nuremberg, Exagan is showcasing the use of its high-power-density GaN-on-silicon semiconductors to create ultra-fast, efficient and smaller 45- to 65-watt chargers. The company’s exhibit demonstrates its electrical-converter expertise and how both G-FET and G-DRIVE can benefit new converter product designs and their applications.

“The market potential for our products is enormous including all portable electronic devices as well as homes, restaurants, hotels, airports, automobiles and more,” said Frédéric Dupont, president and CEO of Exagan. “In the near future, users will be able to quickly charge their smart phones, tablets, laptops and other devices simply by plugging a standard USB cable into a small, generic mobile charger.”

The ability of USB type C ports to serve as universal connections for the simultaneous transfer of electrical power, data and video is leading to tremendous growth. The number of devices with at least one USB type C port is forecasted to multiply from 300 million units in 2016 to nearly five billion by 2021, according to market research firm IHS Markit.

Exagan is working to accelerate the adoption of cost-effective GaN-based solutions for the charger market. The company uses 200-mm GaN-on-silicon wafers in its fabrication process, achieving highly cost efficient high-volume manufacturing.  Exagan is now sampling its fast, energy-efficient devices to key customers while ramping up production to begin volume shipments of G-FET and G-DRIVE products.

A new way of enhancing the interactions between light and matter, developed by researchers at MIT and Israel’s Technion, could someday lead to more efficient solar cells that collect a wider range of light wavelengths, and new kinds of lasers and light-emitting diodes (LEDs) that could have fully tunable color emissions.

The fundamental principle behind the new approach is a way to get the momentum of light particles, called photons, to more closely match that of electrons, which is normally many orders of magnitude greater. Because of the huge disparity in momentum, these particles usually interact very weakly; bringing their momenta closer together enables much greater control over their interactions, which could enable new kinds of basic research on these processes as well as a host of new applications, the researchers say.

The new findings, based on a theoretical study, are being published today in the journal Nature Photonics in a paper by Yaniv Kurman of Technion (the Israel Institute of Technology, in Haifa); MIT graduate student Nicholas Rivera; MIT postdoc Thomas Christensen; John Joannopoulos, the Francis Wright Davis Professor of Physics at MIT; Marin Soljacic, professor of physics at MIT; Ido Kaminer, a professor of physics at Technion and former MIT postdoc; and Shai Tsesses and Meir Orenstein at Technion.

While silicon is a hugely important substance as the basis for most present-day electronics, it is not well-suited for applications that involve light, such as LEDs and solar cells — even though it is currently the principal material used for solar cells despite its low efficiency, Kaminer says. Improving the interactions of light with an important electronics material such as silicon could be an important milestone toward integrating photonics — devices based on manipulation of light waves — with electronic semiconductor chips.

Most people looking into this problem have focused on the silicon itself, Kaminer says, but “this approach is very different — we’re trying to change the light instead of changing the silicon.” Kurman adds that “people design the matter in light-matter interactions, but they don’t think about designing the light side.”

One way to do that is by slowing down, or shrinking, the light enough to drastically lower the momentum of its individual photons, to get them closer to that of the electrons. In their theoretical study, the researchers showed that light could be slowed by a factor of a thousand by passing it through a kind of multilayered thin-film material overlaid with a layer of graphene. The layered material, made of gallium arsenide and indium gallium arsenide layers, alters the behavior of photons passing through it in a highly controllable way. This enables the researchers to control the frequency of emissions from the material by as much as 20 to 30 percent, says Kurman, who is the paper’s lead author.

The interaction of a photon with a pair of oppositely charged particles — such as an electron and its corresponding “hole” — produces a quasiparticle called a plasmon, or a plasmon-polariton, which is a kind of oscillation that takes place in an exotic material such as the two-dimensional layered devices used in this research. Such materials “support elastic oscillations on its surface, really tightly confined” within the material, Rivera says. This process effectively shrinks the wavelengths of light by orders of magnitude, he says, bringing it down “almost to the atomic scale.”

Because of that shrinkage, the light can then be absorbed by the semiconductor, or emitted by it, he says. In the graphene-based material, these properties can actually be controlled directly by simply varying a voltage applied to the graphene layer. In that way, “we can totally control the properties of the light, not just measure it,” Kurman says.

Although the work is still at an early and theoretical stage, the researchers say that in principle this approach could lead to new kinds of solar cells capable of absorbing a wider range of light wavelengths, which would make the devices more efficient at converting sunlight to electricity. It could also lead to light-producing devices, such as lasers and LEDs, that could be tuned electronically to produce a wide range of colors. “This has a measure of tunability that’s beyond what is currently available,” Kaminer says.

“The work is very general,” Kurman says, so the results should apply to many more cases than the specific ones used in this study. “We could use several other semiconductor materials, and some other light-matter polaritons.” While this work was not done with silicon, it should be possible to apply the same principles to silicon-based devices, the team says. “By closing the momentum gap, we could introduce silicon into this world” of plasmon-based devices, Kurman says.

Because the findings are so new, Rivera says, it “should enable a lot of functionality we don’t even know about yet.”

At this week’s 2018 IEEE International Interconnect Technology Conference (IITC 2018), imec will present 11 papers on advanced interconnects, ranging from extending Cu and Co damascene metallization, all the way to evaluating new alternatives such as Ru and graphene. After careful evaluation of the resistance and reliability behavior, imec takes first steps towards extending conventional metallization into to the 3nm technology node.

For almost two decades, Cu-based dual damascene has been the workhorse industrial process flow for building reliable interconnects. But when downscaling logic device technology towards the 5nm and 3nm technology nodes, meeting resistance and reliability requirements for the tightly pitched Cu lines has become increasingly challenging. The industry is however in favor of extending the current damascene technology as long as possible, and therefore, different solutions have emerged.

To set the limits of scaling, imec has benchmarked the resistance of Cu with respect to Co and Ru in a damascene vehicle with scaled dimensions, demonstrating that Cu still outperforms Co for wire cross sections down to 300nm2 (or linewidths of 12nm), which corresponds to the 3nm technology node. To meet reliability requirements, one option is to use Cu in combination with thin diffusion barriers such as tantalum nitride (TaN)) and liners such as Co or Ru. It was found that the TaN diffusion barrier can be scaled to below 2nm while maintaining excellent Cu diffusion barrier properties.

For Cu linewidths down to 15–12nm, imec also modeled the impact of the interconnect line-edge roughness on the system-level performance. Line-edge roughness is caused by the lithographic and patterning steps of interconnect wires, resulting in small variations in wire width and spacing. At small pitches, these can affect the Cu interconnect resistance and variability. Although there is a significant impact of line-edge roughness on the resistance distribution for short Cu wires, the effect largely averages out at the system level.

An alternative solution to extend the traditional damascene flow is replacing Cu by Co. Today Co requires a diffusion barrier – an option that recently gained industrial acceptance. A next possible step is to enable barrierless Co or at least sub-nm barrier thickness with careful interface engineering. Co has the clear advantage of having a lower resistance for smaller wire cross-secions and smaller vias. Based on electromigration and thermal storage experiments, imec presents a detailed study of the mechanisms that impact Co via reliability, showing the abscence of voids in barrierless Co vias, demonstrating a better scalability of Co towards smaller nodes.

The research is performed in cooperation with imec’s key nano interconnect program partners including GlobalFoundries, Huawei, Intel, Micron, Qualcomm, Samsung, SK Hynix, SanDisk/Western Digital, Sony Semiconductor Solutions, TOSHIBA Memory and TSMC.

Researchers working at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) coupled graphene, a monolayer form of carbon, with thin layers of magnetic materials like cobalt and nickel to produce exotic behavior in electrons that could be useful for next-generation computing applications.

Andreas Schmid, left, and Gong Chen are pictured here with the spin-polarized low-energy electron microscopy (SPLEEM) instrument at Berkeley Lab. The instrument was integral to measurements of ultrathin samples that included graphene and magnetic materials. Credit: Roy Kaltschmidt/Berkeley Lab

The work was performed in collaboration with French scientists including Nobel Laureate Albert Fert, an emeritus professor at Paris-Sud University and scientific director for a research laboratory in France. The team performed key measurements at Berkeley Lab’s Molecular Foundry, a DOE Office of Science User Facility focused on nanoscience research.

Fert shared the Nobel Prize in Physics in 2007 for his work in understanding a magnetic effect in multilayer materials that led to new technology for reading data in hard drives, for example, and gave rise to a new field studying how to exploit and control a fundamental property known as “spin” in electrons to drive a new type of low-energy, high-speed computer memory and logic technology known as spintronics.

In this latest work, published online Monday in the journal Nature Materials, the research team showed how that spin property – analogous to a compass needle that can be tuned to face either north or south – is affected by the interaction of graphene with the magnetic layers.

The researchers found that the material’s electronic and magnetic properties create tiny swirling patterns where the layers meet, and this effect gives scientists hope for controlling the direction of these swirls and tapping this effect for a form of spintronics applications known as “spin-orbitronics” in ultrathin materials. The ultimate goal is to quickly and efficiently store and manipulate data at very small scales, and without the heat buildup that is a common hiccup for miniaturizing computing devices.

Typically, researchers working to produce this behavior for electrons in materials have coupled heavy and expensive metals like platinum and tantalum with magnetic materials to achieve such effects, but graphene offers a potentially revolutionary alternative since it is ultrathin, lightweight, has very high electrical conductivity, and can also serve as a protective layer for corrosion-prone magnetic materials.

“You could think about replacing computer hard disks with all solid state devices – no moving parts – using electrical signals alone,” said Andreas Schmid, a staff scientist at the Molecular Foundry who participated in the research. “Part of the goal is to get lower power-consumption and non-volatile data storage.”

The latest research represents an early step toward this goal, Schmid noted, and a next step is to control nanoscale magnetic features, called skyrmions, which can exhibit a property known as chirality that makes them swirl in either a clockwise or counterclockwise direction.

In more conventional layered materials, electrons traveling through the materials can act like an “electron wind” that changes magnetic structures like a pile of leaves blown by a strong wind, Schmid said.

But with the new graphene-layered material, its strong electron spin effects can drive magnetic textures of opposite chirality in different directions as a result of the “spin Hall effect,” which explains how electrical currents can affect spin and vice versa. If that chirality can be universally aligned across a material and flipped in a controlled way, researchers could use it to process data.

“Calculations by other team members show that if you take different magnetic materials and graphene and build a multilayer stack of many repeating structures, then this phenomenon and effect could possibly be very powerfully amplified,” Schmid said.

To measure the layered material, scientists applied spin-polarized low-energy electron microscopy (SPLEEM) using an instrument at the Molecular Foundry’s National Center for Electron Microscopy. It is one of just a handful of specialized devices around the world that allow scientists to combine different images to essentially map the orientations of a sample’s 3-D magnetization profile (or vector), revealing a its “spin textures.”

The research team also created the samples using the same SPLEEM instrument through a precise process known as molecular beam epitaxy, and separately studied the samples using other forms of electron-beam probing techniques.

Gong Chen, a co-lead author who participated in the study as a postdoctoral researcher at the Molecular Foundry and is now an assistant project scientist in the UC Davis Physics Department, said the collaboration sprang out of a discussion with French scientists at a conference in 2016 – both groups had independently been working on similar research and realized the synergy of working together.

While the effects that researchers have now observed in the latest experiments had been discussed decades ago in previous journal articles, Chen noted that the concept of using an atomically thin material like graphene in place of heavy elements to generate those effects was a new concept.

“It has only recently become a hot topic,” Chen said. “This effect in thin films had been ignored for a long time. This type of multilayer stacking is really stable and robust.”

Using skyrmions could be revolutionary for data processing, he said, because information can potentially be stored at much higher densities than is possible with conventional technologies, and with much lower power usage.

Molecular Foundry researchers are now working to form the graphene-magnetic multilayer material on an insulator or semiconductor to bring it closer to potential applications, Schmid said.