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A multivalued optical memory composed of 2D materials

Posted By Graphene Council, Friday, September 11, 2020
The National Institute for Materials Science (NIMS) has developed a memory device capable of storing multiple values using both optical and voltage input values. This device composed of layered two-dimensional materials is able to optically control the amount of charge stored in these layers. This technology may be used to significantly increase the capacity of memory devices and applied to the development of various optoelectronic devices. The research was published in Advanced Functional Materials ("Laser-assisted multilevel non-volatile memory device based on 2D van-der-Waals fewlayer-ReS2/h-BN/Graphene Heterostructures").

Memory devices used to store information (e.g., flash memory) play an indispensable role in today’s information society. The recording density of these devices has substantially increased in the past 20 years. In anticipation of widespread adoption of IoT technologies in the near future, it is desirable to accelerate the development of higher speed, larger capacity memory devices.

However, the current approach to increasing memory capacity and energy efficiency through silicon microfabrication is about to reach its limits. Development of memory devices with different working principles therefore has been awaited.

To meet expected technology needs, this research group has developed a transistor memory device composed of layered two-dimensional materials, including rhenium disulfide (ReS2) – a semiconductor – serving as a channel transistor, hexagonal boron nitride (h-BN) used as an insulating tunnel layer and graphene functioning as a floating gate.

This device records data by storing charge carriers in the floating gate in a manner similar to conventional flash memory. Hole-electron pairs in the ReS2 layer are prone to excitation when irradiated with light. The number of these pairs can be regulated by changing the intensity of the light.

The group succeeded in creating a mechanism that allows the amount of charge in the graphene layer to gradually decrease as the exited electrons once again couple with the holes in this layer. This success enabled the device to operate as a multivalued memory capable of efficiently controlling the amount of stored charge in stages through the combined use of light and voltage.

Moreover, this device can operate energy efficiently by minimizing electric current leakage—an achievement made possible by layering two-dimensional materials, thereby smoothening the interfaces between them at an atomic level.

This technology may be used to significantly increase the capacity and energy efficiency of memory devices. It also may be applied to the development of various optoelectronic devices, including optical logic circuits and highly sensitive photosensors capable of controlling the amount of charge stored in them through combined use of light and voltage.

This project was carried out by a research group consisting of Yutaka Wakayama (Leader of the Quantum Device Engineering Group (QDEG), International Center for Materials Nanoarchitectonics (MANA), NIMS), Bablu Mukherjee (Postdoctoral Researcher, QDEG, MANA, NIMS) and Shu Nakaharai (Principal Researcher, QDEG, MANA, NIMS).

This study was conducted in conjunction with another project entitled “Development of a ultra-sensitive photosensor using two-dimensional atomic film layers” funded by the Grant-in-Aid for JSPS Fellows.

Tags:  2D materials  Bablu Mukherjee  Graphene  International Center for Materials Nanoarchitecton  optoelectronics  Semiconductor  Sensors  Shu Nakaharai  The National Institute for Materials Science  Yutaka Wakayama 

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Superconducting Twisted Bilayer Graphene—Magic not Needed?

Posted By Graphene Council, Saturday, July 18, 2020
In 2018, researchers made the surprising discovery that when you layer two sheets of single-atom-thick graphene atop one another and rotate them by precisely 1.05 degrees with respect to one another, the resulting bilayer material takes on new properties: when the density of electrons in the material is increased through the application of a voltage on a nearby electrode, it becomes a superconductor—electrons can flow freely through the material, without resistance. However, with a slight change in electron density, the bilayer becomes an insulator and prevents the flow of electrons.

The specific twist angle at which this occurs was nicknamed the "magic angle," and its discovery jumpstarted interest in a branch of physics known as twistronics. The electron densities that turn the material into a superconductor or an insulator are very close to one another, so the central question of bilayer graphene twistronics has become to understand why these states—insulators and superconductors—are so intimately related.

Now, a team at Caltech has discovered that when twisted bilayer graphene is placed in contact with a single-atom-thick material that contains the heavy element tungsten, it can exhibit superconductivity at angles relatively far from the magic angle, and it does not change into an insulator at any electron density, breaking the pattern. Their work was published in the journal Nature on July 15.

What does it mean to have insulators and superconductors occurring at similar electron densities, and why is this important?

When studying how materials conduct electricity, physicists often talk about a phase diagram, a plot that represents resistance as a function of electrondensity (on one axis) and temperature (on the other). In this phase diagram for magic angle-twisted bilayer graphene, the superconducting phase and the insulating phase are adjacent on the electron-density axis. Both the superconductivity and insulating states in magic angle-twisted bilayers of graphene occur only at cryogenic temperatures, a fraction of a degree above absolute zero (−273.15 degrees Celsius). But back in the 1980s, a similar phase diagram was noted in so-called high-temperature superconductors that operate at a much higher temperature—one to two hundred degrees above absolute zero, which is still cold, but not as cold as was thought to be needed to generate the superconducting and insulating states in twisted graphene.

"Physicists got very excited about this discovery, thinking that if these two systems are indeed similar, then perhaps studying twisted bilayer graphene could teach us something about high-temperature superconductivity," says Stevan Nadj-Perge, corresponding author of the paper and assistant professor of applied physics and materials science at Caltech. "Our new findings, however, question that similarity."

To achieve the magic angle usually requires such extreme precision in the placement of the two graphene sheets that only a few out of many samples will show the signature of superconductivity. The new approach developed at Caltech relaxes these stringent requirements. In the method, the graphene sheets are placed on top of another two-dimensional material that contains tungsten and selenide, called tungsten-diselenide (WSe2). The presence of tungsten enhances the coupling between an electron's "spin" (a property of subatomic particles that describes how they interact with magnetic fields) and its motion. The so-called spin–orbit coupling that is induced in twisted bilayer graphene may explain the stabilization of superconductivity.

When the additional WSe2 layers were used, the Caltech team found, superconductivity could exist even when insulating states were entirely absent. "This shows that superconductivity can be stabilized by tailoring the environment of the graphene layers," Nadj-Perge says.

"While we did observe signatures of spin–orbit coupling in our samples, whether this coupling is responsible for stabilization of superconductivity is still an open question. At this point, it is too early to say conclusively," Nadj-Perge says. "Our observations were quite unexpected. It implies that we only scratched the surface of graphene twistronics. These are exciting times for the field."

The paper is titled "Superconductivity in metallic twisted bilayer graphene stabilized by WSe2." Co-authors include Jason Alicea, professor of theoretical physics at Caltech; Caltech graduate students Harpreet Arora (PhD '20), Robert Polski, and Yiran Zhang (all of whom are leading authors on the paper); graduate students Youngjoon Choi and Hyunjin Kim; Alex Thomson, Sherman Fairchild Postdoctoral Scholar in Theoretical Physics at Caltech; Zhong Lin, Ilham Zaky Wilson, Xiaodong Xu, and Jiun-Haw Chu of the University of Washington, who provided WSe2 crystals; and Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Japan.

The research at Caltech was funded by the National Science Foundation, the United States Department of Energy, the Caltech-Gist memorandum of understanding program, the Kavli Nanoscience Institute, the Institute for Quantum Information and Matter at Caltech, the Walter Burke Institute for Theoretical Physics at Caltech, and the Kwanjeong Educational Foundation.

Tags:  applied physics and materials science at Caltech  Graphene  journal Nature  Kavli Nanoscience Institute  Kwanjeong Educational Foundation  National Science Foundation  Semiconductor  Stevan Nadj-Perge  United States Department of Energy 

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WIMI Hologram AR Plans To Invest In R&D in The Chip Field To Seek Technological Breakthroughs

Posted By Graphene Council, Friday, July 10, 2020
WIMI Hologram Cloud (NASDAQ:WIMI) has intensified its efforts in semiconductor business. On the one hand, the application demand of the semiconductor industry in the field of holographic 3D vision has been growing rapidly. On the other hand, it will help the company extend the holographic 3D vision software field from the application layer down to the chip field, and through the strategic direction of combining soft and hard holographic 3D vision software solution, namely, the strategic derivative upgrade to the semiconductor field. WIMI deep in the field of holographic 3 d visual software technology accumulation, with hundreds of related patents and software copyright, so in the direction of semiconductor business extends, and the future is proposed by integrating companies core technology advantages of IC design companies, or with the current chip factory set up a technology research and development with strong proxy technology joint venture company, to implement the supply chain upstream of the semiconductor research and development design, technical services, marketing, etc.

WIMI, the holographic giant that is the first part of holographic AR in the world, has created the third-generation 6D light field holographic technology products through years of original research and development, and its imitation is as high as 98%. WIMI has signed strategic alliances with relevant enterprises, and the scope of cooperation involves film and television, media, games, children’s education, animation, hardware and so on. It mainly involves the establishment of joint ventures, AR INTELLECTUAL property IP, holographic intellectual property IP and holographic entertainment content IP cooperation, as well as various commercial resource sharing and so on. WIMI will form hundreds of patent protection according to its own 295 related patents, and ensure that users can experience the latest and most advanced holographic AR high simulation digital product experience at the international level through strict patent protection means and technical confidentiality. At present, WIMI mainly focuses its business application scenarios in five professional fields, such as home entertainment, lightfield cinema, performing arts system, commercial publishing system and advertising display system.

According to introducing, WIMI cover from the holographic AI computer vision synthesis, holographic visual presentation, holographic interactive software development, holographic AR online and offline advertising, holographic ARSDK pay, 5G holographic communication software development, holographic development of face recognition, holographic AR technology such as holographic AI development in face of multiple links, holographic cloud is a comprehensive technology solutions provider.

According to a post on Samsung’s website, the company has taken a step toward the “ideal semiconductor” by discovering new semiconductor materials that will make future semiconductor chips smaller and faster. The Samsung Institute of Electronics and Technology recently said it had discovered a new material, “amorphous boron nitride (A-BN)”, in collaboration with Ulsan Institute of Technology. The discovery comes 16 years after a team at the University of Manchester in the UK found graphene to be an “ideal new material”.

The article on Samsung’s official website says the key to solving the challenge of semiconductor materials is to look at two-dimensional materials. One of the challenges based on existing silicon semiconductor technology is “increasing integration”. As integration increases, more information can be processed quickly, but technical problems such as interference between electrical circuits also arise. Two-dimensional materials are becoming the key to solving the industry’s woes, so they are attracting a lot of attention. The two-dimensional material has the properties of a conductor, non-conductor or semiconductor at even the smallest atomic units of matter, and is so thin and difficult to bend that it is about 100,000th the thickness of A4 paper.

The most representative of these is graphene. For many years, The Samsung Electronics Technology Institute has been researching and developing graphene for large-scale semiconductor manufacturing applications. Based on this source technology, they have recently focused on graphene for wiring. As semiconductors become more integrated, the lines between the circuits become narrower and the impedance increases. This is due to graphene’s compact hexagonal structure, which ACTS as the thinest, hardest and resistive barrier.

Amorphous boron nitride is a derivative of white graphene. It consists of nitrogen and boron atoms, but has an amorphous molecular structure that separates it from white graphene. In addition, in order to miniaturize the semiconductor, it is regarded as one of the core elements of the medium. It is one of the key elements of the semiconductor miniaturization and can play a role in preventing electrical interference. In other words, it is the key to overcoming the problem of electromagnetic interference as semiconductors become more integrated. “In order to apply graphene to semiconductor engineering, it requires technology that can be generated directly on silicon wafers at 400°C,” said Shin Hyun Jin, a researcher at Samsung Electronics Research Institute.

The team not only ensured the lowest dielectric constant of 1.78 in the world, but also demonstrated that the material could be produced on a large scale in a semiconductor substrate at 400°C, thus taking a step towards process innovation. Amorphous boron nitride can be used in semiconductor systems including memory semiconductors (DRAM, NAND, etc.) and is expected to be used in memory semiconductors for server servers that require high performance.

A semiconductor is a substance whose conductivity is intermediate between that of a conductor and an insulator. Compared with conductors and insulators, semiconductor materials are the latest to be discovered. It was not until the 1930s, when purification techniques for materials were improved, that the existence of semiconductors was truly recognized by academia. Semiconductor is mainly composed of four parts: integrated circuit, photoelectric device, discrete device and sensor. Since integrated circuit accounts for more than 80% of the share of devices, semiconductor and integrated circuit are usually equivalent. Integrated circuits are divided into four categories according to product types: microprocessor, memory, logic devices and emulators. Usually we call them chips.

At present, many technology giant qualcomm, mediatek, nvidia and other related companies in artificial intelligence, 5G, the Internet of things, and other areas of the chain are layout, the demand for upstream suppliers is no longer a simple electronic components or products supply, to the supplier’s technical service ability, providing comprehensive solution ability, and one-stop value-added service ability are put forward higher requirements.

Holographic technology is simply through AR, let the audience can watch the holographic characters or open hole in the real scene of real reduction, simulation is as high as 98% above, immersive, micro user experience can be described with stunning beauty holographic patterns, the combination of the holographic technology and entertainment viewer can become a character in the movie/stage, involved in the film/stage pre-made environment and plot, let the viewer, as it were, feel oneself is a member of a movie/stage viewer is the main character in the movie or a part of it, and continue to interact with content to produce films/stage.

Analysts at Maxim Group, LLC have a ‘buy’ rating on WIMI with a $8 price target, meaning the stock has 200% upside. According to Maxim Group, LLC equity research on WIMI, WIMI is the leader in the augmented reality (AR) long-term growth market. Zion Research expects the global augmented reality (AR) market to grow at a compound annual rate of more than 63% by 2025. Companies are increasingly using augmented reality for a variety of purposes. Frost &; Sullivan expects the total revenue of China’s holographic AR industry to grow by 83 percent, from 3.6 billion yuan (about $5 billion) in 2017 to 455 billion yuan (about $65 billion) in 2025.

According to the annual report, WIMI business began to expand gradually in 2017, with revenues of 192 million yuan, 225 million yuan and 319 million yuan in 17-19, with growth rates of 17% and 41%, showing an accelerating momentum. In terms of net profit, it was 73 million yuan, 89 million yuan and 102 million yuan respectively in 17-19 years.

From the above data WIMI, it is not difficult to see that the business growth of WIMI is in a benign development trend. From 2017 to 2019, the financial revenue of the three years has been increasing continuously. The amount of revenue generated from this market is increasing and the market expansion is expanding.

WIMI Hologram Cloud (NASDAQ:WIMI) will invest more funds, through to the longitudinal extension in the field of semiconductor, and the future of the integration of on semiconductor assets or cooperate with chip factory, will greatly improve the WIMI strength of technical services, further enhance viscosity related to the current customers, at the same time, based on a higher added value, enhance the WIMI sales ability of the company. WIMI plans to develop semiconductor market-related businesses in the next three years, and WIMI is expected to see new growth.

Throughout the past half century, the rapid development of semiconductors has provided the basis for our technological explosion. But developments in 5G seem to point the way. Looking back on the glorious history of semiconductor development, also to a certain extent represents the history of human civilization. If the development of machines liberated human labor, the development of semiconductors liberated human computing power.

Tags:  2D materials  amorphous boron nitride  Graphene  hexagonal  Maxim Group  Samsung Institute of Electronics and Technology  Semiconductor  Shin Hyun Jin  Ulsan Institute of Technology  University of Manchester  WIMI Hologram Cloud 

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Samsung Leads Semiconductor Paradigm Shift with New Material Discovery

Posted By Graphene Council, Wednesday, July 8, 2020
Researchers at the Samsung Advanced Institute of Technology (SAIT) have unveiled the discovery of a new material, called amorphous boron nitride (a-BN), in collaboration with Ulsan National Institute of Science and Technology (UNIST) and the University of Cambridge. Published in the journal Nature, the study has the potential to accelerate the advent of the next generation of semiconductors.

2D Materials – The Key to Overcoming Scalability Challenges

Recently, SAIT has been working on the research and development of two-dimensional (2D) materials – crystalline materials with a single layer of atoms. Specifically, the institute has been working on the research and development of graphene, and has achieved groundbreaking research outcomes in this area such as the development of a new graphene transistor as well as a novel method of producing large-area, single-crystal wafer-scale graphene. In addition to researching and developing graphene, SAIT has been working to accelerate the material’s commercialization.

“To enhance the compatibility of graphene with silicon-based semiconductor processes, wafer-scale graphene growth on semiconductor substrates should be implemented at a temperature lower than 400°C.” said Hyeon-Jin Shin, a graphene project leader and Principal Researcher at SAIT. “We are also continuously working to expand the applications of graphene beyond semiconductors.”

2D Material Transformed – Amorphous Boron Nitride

The newly discovered material, called amorphous boron nitride (a-BN), consists of boron and nitrogen atoms with an amorphous molecule structure. While amorphous boron nitride is derived from white graphene, which includes boron and nitrogen atoms arranged in a hexagonal structure, the molecular structure of a-BN in fact makes it uniquely distinctive from white graphene.

Amorphous boron nitride has a best-in-class ultra-low dielectric constant of 1.78 with strong electrical and mechanical properties, and can be used as an interconnect isolation material to minimize electrical interference. It was also demonstrated that the material can be grown on a wafer scale at a low temperature of just 400°C. Thus, amorphous boron nitride is expected to be widely applied to semiconductors such as DRAM and NAND solutions, and especially in next generation memory solutions for large-scale servers.

“Recently, interest in 2D materials and the new materials derived from them has been increasing. However, there are still many challenges in applying the materials to existing semiconductor processes.” said Seongjun Park, Vice President and Head of Inorganic Material Lab, SAIT. “We will continue to develop new materials to lead the semiconductor paradigm shift.”

Tags:  2D Materials  Graphene  Hyeon-Jin Shin  journal Nature  Samsung  Samsung Advanced Institute of Technology  Semiconductor  Ulsan National Institute of Science and Technology  University of Cambridge 

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2D Semiconductors Found to Be Close-To-Ideal Fractional Quantum Hall Platform

Posted By Graphene Council, Wednesday, July 8, 2020
Columbia University researchers report that they have observed a quantum fluid known as the fractional quantum Hall states (FQHS), one of the most delicate phases of matter, for the first time in a monolayer 2D semiconductor. Their findings demonstrate the excellent intrinsic quality of 2D semiconductors and establish them as a unique test platform for future applications in quantum computing. The study was published online today in Nature Nanotechnology.

“We were very surprised to observe this state in 2D semiconductors because it has generally been assumed that they are too dirty and disordered to host this effect,” says Cory Dean, professor of physics at Columbia University. “Moreover, the FQHS sequence in our experiment reveals unexpected and interesting new behavior that we’ve never seen before, and in fact suggests that 2D semiconductors are close-to-ideal platforms to study FQHS further.”

The fractional quantum Hall state is a collective phenomenon that comes about when researchers confine electrons to move in a thin two-dimensional plane, and subject them to large magnetic fields. First discovered in 1982, the fractional quantum Hall effect has been studied for more than 40 years, yet many fundamental questions still remain. One of the reasons for this is that the state is very fragile and appears in only the cleanest materials.

“Observation of the FQHS is therefore often viewed as a significant milestone for a 2D material—one that only the very cleanest electronic systems have reached,” notes Jim Hone, Wang Fong-Jen Professor of Mechanical Engineering at Columbia Engineering.

While graphene is the best known 2D material, a large group of similar materials have been identified over the past 10 years, all of which can be exfoliated down to a single layer thickness. One class of these materials is transition metal dichalcogenides (TMD), such as WSe2, the material used in this new study. Like graphene, they can be peeled to be atomically thin, but, unlike graphene, their properties under magnetic fields are much simpler. The challenge has been that the crystal quality of TMDs was not very good.

“Ever since TMD came on the stage, it was always thought of as a dirty material with many defects,” says Hone, whose group has made significant improvement to the quality of TMDs, pushing it to a quality near to graphene—often considered the ultimate standard of purity among 2D materials.

In addition to sample quality, studies of the semiconductor 2D materials have been hindered by the difficulties to make good electrical contact. To address this, the Columbia researchers have also been developing the capability to measure electronic properties by capacitance, rather than the conventional methods of flowing a current and measuring the resistance. A major benefit of this technique is that the measurement is less sensitive both to poor electrical contact and to impurities in the material. The measurements for this new study were performed under very large magnetic fields—which help to stabilize the FQHS—at the National High Magnetic Field Lab.

“The unique properties of these exotic particles could be used to design quantum computers that are protected from many sources of errors.”



"The fractional numbers that characterize the FQHS we observed—the ratios of the particle to magnetic flux number—follow a very simple sequence," says Qianhui Shi, the paper's first author and a postdoctoral researcher at the Columbia Nano Initiative. “The simple sequence is consistent with generic theoretical expectations, but all previous systems show more complex and irregular behavior. This tells us that we finally have a nearly ideal platform for the study of FQHS, where experiments can be directly compared to simple models.”

Among the fractional numbers, one of them has an even denominator. “Observing the fractional quantum Hall effect was itself surprising, seeing the even-denominator state in these devices was truly astonishing, since previously this state has only been observed in the very best of the best devices,” says Dean.

Fractional states with even denominators have received special attention since their first discovery in the late 1980s, since they are thought to represent a new kind of particle, one with quantum properties different from any other known particle in the universe. “The unique properties of these exotic particles,” notes Zlatko Papic, associate professor in theoretical physics at the University of Leeds, “could be used to design quantum computers that are protected from many sources of errors.”

So far, experimental efforts to both understand and exploit the even denominator states have been limited by their extreme sensitivity and the extremely small number of materials in which this state could be found. “This makes the discovery of the even denominator state in a new—and different—material platform, really very exciting,” Dean adds.

The two Columbia University laboratories—the Dean Lab and the Hone Group—worked in collaboration with the NIMS Japan, which supplied some of the materials, and Papic, whose group performed computational modelling of the experiments. Both Columbia labs are part of the university’s Material Research Science and Engineering Center. This project also used clean room facilities at both the Columbia Nano Initiative and City College. Measurements at large magnetic fields were made at the National High Magnetic Field Laboratory, a user facility funded by the National Science Foundation and headquartered at Florida State University in Tallahassee, Fl.

Now that the researchers have very clean 2D semiconductors as well as an effective probe, they are exploring other interesting states that emerge from these 2D platforms.

Tags:  2D materials  Columbia Nano Initiative  Columbia University  Cory Dean  Graphene  Jim Hone  Nature Nanotechnology  Qianhui Shi  Semiconductor  transition metal dichalcogenides  Wang Fong-Jen 

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Production-scale nanocharacterization of graphene within reach

Posted By Graphene Council, Friday, May 15, 2020
European project “Real time nano CHAracterization reLatEd techNoloGiES” (CHALLENGES) aims to adapt nanoscale metrology for the manufacturing industry, scaling up high resolution imaging for CMOS electronics, silicon photovoltaics, and 2D materials.

The project, having kicked off with an online meeting on April 23rd, started April 1st and will last for three years under the “Research and innovation actions” (RIA) programme. With a total budget of nearly 4.7 million EUR, the project is run by a consortium of 14 partners from 7 countries.

CHALLENGES is coordinated by a large silicon foundry company and it is strongly driven by industrial and applicative needs. The Consortium includes renowned EU research labs with top-class facilities and capacities, industry leading enterprises and innovative SMEs with a worldwide collaboration network that will boost the international dimension and impact of the project.

The overarching goal is to apply unconventional plasmonic materials in unconventional spectrum ranges, coupled with tip-enhanced local probing spectroscopy, to develop a revolutionary spectroscopic system for real time nanotechnology characterization compatible with semiconductor production. The end goal is a fully automated AFM-based tool not requiring human intervention in routine operations. The solution will lean on current advances in machine learning for automatic detection of relevant sites on large samples to be probed with high resolution.

The large number of SME’s involved in the project will benefit from the development milestones such as novel plasmonic tips, machine learning algorithms optimized for imaging, cleanroom-ready AFM system, industrial in-line quality control methods for production lines of graphene, CIS, nanowires, epitaxial silicon, TMD wafers, and thin silicon solar cells and modules.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 861857.

Tags:  2D materials  CHALLENGES  CMOS  Graphene  Nanoscale  Nanotechnology  Semiconductor 

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People in Graphene - David Graves to Head New Research at PPPL for Plasma Applications in Industry and Quantum Information Science

Posted By Graphene Council, Monday, May 11, 2020
Updated: Tuesday, May 12, 2020

David Graves, an internationally-known chemical engineer, has been named to lead a new research enterprise that will explore plasma applications in nanotechnology for everything from semiconductor manufacturing to the next generation of super-fast quantum computers.

Graves, a professor at the University of California, Berkeley, since 1986, is an expert in plasma applications in semiconductor manufacturing. He will become the Princeton Plasma Physics Laboratory’s (PPPL) first associate laboratory director for Low-Temperature Plasma Surface Interactions, effective June 1. He will likely begin his new position from his home in Lafayette, California, in the East Bay region of San Francisco.

He will lead a collaborative research effort to not only understand and measure how plasma is used in the manufacture of computer chips, but also to explore how plasma could be used to help fabricate powerful quantum computing devices over the next decade.

“This is the apex of our thrust into becoming a multipurpose lab,” said Steve Cowley, PPPL director, who recruited Graves. “Working with Princeton University, and with industry and the U.S. Department of Energy (DOE), we are going to make a big push to do research that will help us understand how you can manufacture at the scale of a nanometer.” A nanometer, one-billionth of a meter, is about ten thousand times less than the width of a human hair.

The new initiative  will draw on PPPL’s expertise in low temperature plasmas, diagnostics, and modeling. At the same time, it will work closely with plasma semiconductor equipment industries and will collaborate with Princeton University experts in various departments, including chemical and biological engineering, electrical engineering, materials science, and physics.  In particular, collaborations with PRISM (the Princeton Institute for the Science and Technology of Materials) are planned, Cowley said. “I want to see us more tightly bound to the University in some areas because that way we get cross-fertilization,” he said.
Graves will also have an appointment as professor in the Princeton University Department of Chemical and Biological Engineering, starting July 1. He is retiring from his position at Berkeley at the end of this semester. He is currently writing a book (“Plasma Biology”) on plasma applications in biology and medicine. He said he changed his retirement plans to take the position at PPPL and Princeton University. “This seemed like a great opportunity,” Graves said. “There’s a lot we can do at a national laboratory where there’s bigger scale, world-class colleagues, powerful computers and other world-class facilities.”

“Exciting new direction for the Lab”

Graves is already working with Jon Menard, PPPL deputy director for research, on the strategic plan for the new research initiative  over the next five years. “It’s a really exciting new direction for the Lab that will build upon our unique expertise in diagnosing and simulating low-temperature plasmas,” Menard said. “It also brings us much closer to the university and industry, which is great for everyone.”

The staff will grow over the next five years and PPPL is recruiting for an expert in nano-fabrication and quantum devices. The first planned research would use converted PPPL laboratory space fitted with equipment provided by industry. Subsequent work  would use laboratory space at PRISM on Princeton University’s campus.  In the longer term, researchers in the growing group  would have brand new laboratory and office space as a central part the Princeton Plasma Innovation Center (PPIC), a new building planned at PPPL.

Physicists Yevgeny Raitses, principal investigator for the Princeton Collaborative Low Temperature Plasma Research Facility (PCRF) and head of the Laboratory for Plasma Nanosynthesis, and Igor Kavanovich, co-principal investigator of PCRF, are both internationally-known experts in low temperature plasmas who have forged recent partnerships between PPPL and various industry partners. The new initiative builds on their work, Cowley said.

A priority research area
Research aimed at developing quantum information science (QIS) is a priority for the DOE. Quantum computers could be very powerful in solving complex scientific problems, including simulating quantum behavior in material or chemical systems. QIS could also have applications in quantum communication, especially in encryption, and quantum sensing. It could potentially have an impact in areas such as national security. “A key question is whether plasma-based fabrication tools commonly used today will play a role in fabricating quantum devices in the future,” Menard said. “There are huge implications in that area,” Menard said. “We want to be part of that.”

Graves is an expert on applying molecular dynamics simulations to low temperature plasma-surface interactions. These simulations are used to understand how plasma-generated ions, atoms and molecules interact with various surfaces. He has extensive research experience in academia and industry in plasma-related semiconductor manufacturing. That expertise will be useful for understanding how to make “very fine structures and circuits” at the nanometer, sub-nanometer and even atom-by-atom level, Menard said. “David’s going to bring a lot of modeling and fundamental understanding to that process. That, paired with our expertise and measurement capabilities, should make us unique in the U.S. in terms of what we can do in this area.”

Tags:  David Graves  Graphene  quantum materials  Semiconductor  Steve Cowley  University of California 

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Crystal with a Twist: Researchers Grow Spiraling New Material

Posted By Graphene Council, Monday, February 17, 2020

With a simple twist of the fingers, one can create a beautiful spiral from a deck of cards. In the same way, scientists have created new inorganic crystals made of stacks of atomically thin sheets. These stacks unexpectedly spiral like a nanoscale card deck. Their surprising structures may yield unique optical, electronic and thermal properties. These properties may even include superconductivity, the ability to conduct electricity without loss. These crystals in the shape of a helix are made of stacked layers of germanium sulfide. This is a semiconductor material that, like graphene, readily forms sheets that are only a few atoms thick. Such “nanosheets” are also called “2D materials.”

This is the first time that scientists have made 2D materials that form a continuously twisting shape in a structure that is thousands layers thick. The spiral structures could hold unique properties that aren’t observed in regularly stacked materials. Scientists could likely use this technique to grow layers of other materials that form atomically thin layers.


To create the twisted structures, the team took advantage of a crystal defect called a screw dislocation, a “mistake” in the orderly crystal structure that gives it a bit of a twisting force. This “Eshelby Twist”, named after scientist John D. Eshelby, has been used by others to create nanowires that spiral like pine trees. But this study is the first time the Eshelby Twist has been used to make crystals built of stacked 2D layers of an atomically thin semiconductor.

In a major discovery last year, scientists reported that graphene becomes superconductive when two atomically thin sheets of the material are stacked and twisted at what’s called a “magic angle.” While other researchers have since succeeded at stacking two layers at a time, this new work provides a recipe for synthesizing stacked structures that are hundreds of thousands or even millions of layers thick in a continuously twisting fashion.

By adjusting the material synthesis conditions and length, the researchers could change the angle between the layers, creating a twisted structure that is tight, like a spring, or loose, like an uncoiled Slinky.

Scientists performed X-ray analyses for the study at the Advanced Light Source and measured the crystal’s twist angles at the Molecular Foundry, both DOE Office of Science user facilities.

Y.L. and J.Y. are supported by the Samsung Advanced Institute of Technology. Work at the Molecular Foundry and the Advanced Light Source was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy. H.S. and D.C.C. are supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering. within the Electronic Materials Program (KC1201). This work was performed, in part, at the Center for Nanoscale Materials, a US Department of Energy Office of Science User Facility. We thank C. So, C. Song, X. Wang, S. Yan, K. Bustillo and C. V. Stan for help with the experiments.

Tags:  2D materials  Electronics  Graphene  Samsung Advanced Institute of Technology  Semiconductor 

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Engineers mix and match materials to make new stretchy electronics

Posted By Graphene Council, Saturday, February 8, 2020
At the heart of any electronic device is a cold, hard computer chip, covered in a miniature city of transistors and other semiconducting elements. Because computer chips are rigid, the electronic devices that they power, such as our smartphones, laptops, watches, and televisions, are similarly inflexible.

Now a process developed by MIT engineers may be the key to manufacturing flexible electronics with multiple functionalities in a cost-effective way.

The process is called  “remote epitaxy” and involves growing thin films of semiconducting material on a large, thick wafer of the same material, which is covered in an intermediate layer of graphene. Once the researchers grow a semiconducting film, they can peel it away from the graphene-covered wafer and then reuse the wafer, which itself can be expensive depending on the type of material it’s made from. In this way, the team can copy and peel away any number of thin, flexible semiconducting films, using the same underlying wafer.

In a paper published today in the journal Nature, the researchers demonstrate that they can use remote epitaxy to produce freestanding films of any functional material. More importantly, they can stack films made from these different materials, to produce flexible, multifunctional electronic devices.

The researchers expect that the process could be used to produce stretchy electronic films for a wide variety of uses, including virtual reality-enabled contact lenses, solar-powered skins that mold to the contours of your car, electronic fabrics that respond to the weather, and other flexible electronics that seemed until now to be the stuff of Marvel movies.

“You can use this technique to mix and match any semiconducting material to have new device functionality, in one flexible chip,” says Jeehwan Kim, an associate professor of mechanical engineering at MIT. “You can make electronics in any shape.”

Buying time

Kim and his colleagues reported their first results using remote epitaxy in 2017. Then, they were able to produce thin, flexible films of semiconducting material by first placing a layer of graphene on a thick, expensive wafer made from a combination of exotic metals. They flowed atoms of each metal over the graphene-covered wafer and found the atoms formed a film on top of the graphene, in the same crystal pattern as the underlying wafer. The graphene provided a nonstick surface from which the researchers could peel away the new film, leaving the graphene-covered wafer, which they could reuse. 

In 2018, the team showed that they could use remote epitaxy to make semiconducting materials from metals in groups 3 and 5 of the periodic table, but not from group 4. The reason, they found, boiled down to polarity, or the respective charges between the atoms flowing over graphene and the atoms in the underlying wafer.

Since this realization, Kim and his colleagues have tried a number of increasingly exotic semiconducting combinations. As reported in this new paper, the team used remote epitaxy to make flexible semiconducting films from complex oxides — chemical compounds made from oxygen and at least two other elements. Complex oxides are known to have a wide range of electrical and magnetic properties, and some combinations can generate a current when physically stretched or exposed to a magnetic field.

Kim says the ability to manufacture flexible films of complex oxides could open the door to new energy-havesting devices, such as sheets or coverings that stretch in response to vibrations and produce electricity as a result. Until now, complex oxide materials have only been manufactured on rigid, millimeter-thick wafers, with limited flexibility and therefore limited energy-generating potential.

The researchers did have to tweak their process to make complex oxide films. They initially found that when they tried to make a complex oxide such as strontium titanate (a compound of strontium, titanium, and three oxygen atoms), the oxygen atoms that they flowed over the graphene tended to bind with the graphene’s carbon atoms, etching away bits of graphene instead of following the underlying wafer’s pattern and binding with strontium and titanium. As a surprisingly simple fix, the researchers added a second layer of graphene.

“We saw that by the time the first layer of graphene is etched off, oxide compounds have already formed, so elemental oxygen, once it forms these desired compounds, does not interact as heavily with graphene,” Kim explains. “So two layers of graphene buys some time for this compound to form.”

Peel and stack

The team used their newly tweaked process to make films from multiple complex oxide materials, peeling off each 100-nanometer-thin layer as it was made. They were also able to stack together layers of different complex oxide materials and effectively glue them together by heating them slightly, producing a flexible, multifunctional device.

“This is the first demonstration of stacking multiple nanometers-thin membranes like LEGO blocks, which has been impossible because all functional electronic materials exist in a thick wafer form,” Kim says.

In one experiment, the team stacked together films of two different complex oxides: cobalt ferrite, known to expand in the presence of a magnetic field, and PMN-PT, a material that generates voltage when stretched. When the researchers exposed the multilayer film to a magnetic field, the two layers worked together to both expand and produce a small electric current. 

The results demonstrate that remote epitaxy can be used to make flexible electronics from a combination of materials with different functionalities, which previously were difficult to combine into one device. In the case of cobalt ferrite and PMN-PT, each material has a different crystalline pattern. Kim says that traditional epitaxy techniques, which grow materials at high temperatures on one wafer, can only combine materials if their crystalline patterns match. He says that with remote epitaxy, researchers can make any number of different films, using different, reusable wafers, and then stack them together, regardless of their crystalline pattern.

“The big picture of this work is, you can combine totally different materials in one place together,” Kim says. “Now you can imagine a thin, flexible device made from layers that include a sensor, computing system, a battery, a solar cell, so you could have a flexible, self-powering, internet-of-things stacked chip.”

The team is exploring various combinations of semiconducting films and is working on developing prototype devices, such as something Kim is calling an “electronic tattoo” — a flexible, transparent chip that can attach and conform to a person’s body to sense and wirelessly relay vital signs such as temperature and pulse. “We can now make thin, flexible, wearable electronics with the highest functionality,” Kim says. “Just peel off and stack up.”

Tags:  Electronics  Graphene  Jeehwan Kim  MIT  Semiconductor 

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Crystal-stacking process can produce new materials for high-tech devices

Posted By Graphene Council, Saturday, February 8, 2020
The magnetic, conductive and optical properties of complex oxides make them key to components of next-generation electronics used for data storage, sensing, energy technologies, biomedical devices and many other applications.

Stacking ultrathin complex oxide single-crystal layers -- those composed of geometrically arranged atoms -- allows researchers to create new structures with hybrid properties and multiple functions. Now, using a new platform developed by engineers at the University of Wisconsin-Madison and the Massachusetts Institute of Technology, researchers will be able to make these stacked-crystal materials in virtually unlimited combinations.

Epitaxy is the process for depositing one material on top of another in an orderly way. The researchers' new layering method overcomes a major challenge in conventional epitaxy -- that each new complex oxide layer must be closely compatible with the atomic structure of the underlying layer. It's sort of like stacking Lego blocks: The holes on the bottom of one block must align with the raised dots atop the other. If there's a mismatch, the blocks won't fit together properly.

"The advantage of the conventional method is that you can grow a perfect single crystal on top of a substrate, but you have a limitation," says Chang-Beom Eom, a UW-Madison professor of materials science and engineering and physics. "When you grow the next material, your structure has to be the same and your atomic spacing must be similar. That's a constraint, and beyond that constraint, it doesn't grow well."

A couple of years ago, a team of MIT researchers developed an alternate approach. Led by Jeehwan Kim, an associate professor in mechanical engineering and materials science and engineering at MIT, the group added an ultrathin intermediate layer of a unique carbon material called graphene, then used epitaxy to grow a thin semiconducting material layer atop that. Just one molecule thick, the graphene acts like a peel-away backing due to its weak bonding. The researchers could remove the semiconductor layer from the graphene. What remained was a freestanding ultrathin sheet of semiconducting material.

Eom, an expert in complex oxide materials, says they are intriguing because they have a wide range of tunable properties -- including multiple properties in one material -- that many other materials do not. So, it made sense to apply the peel-away technique to complex oxides, which are much more challenging to grow and integrate.

"If you have this kind of cut-and-paste growth and removal, combined with the different functionality of putting single-crystal oxide materials together, you have a tremendous possibility for making devices and doing science," says Eom, who connected with mechanical engineers at MIT during a sabbatical there in 2014.

The Eom and Kim research groups combined their expertise to create ultrathin complex oxide single-crystal layers, again using graphene as the peel-away intermediate. More importantly, however, they conquered a previously insurmountable obstacle -- the difference in crystal structure -- in integrating different complex oxide materials.

"Magnetic materials have one crystal structure, while piezoelectric materials have another," says Eom. "So you cannot grow them on top of each other. When you try to grow them, it just becomes messy. Now we can grow the layers separately, peel them off, and integrate them."

In its research, the team demonstrated the efficacy of the technique using materials such as perovskite, spinel and garnet, among several others. They also can stack single complex oxide materials and semiconductors.

"This opens up the possibility for the study of new science, which has never been possible in the past because we could not grow it," says Eom. "Stacking these was impossible, but now it is possible to imagine infinite combinations of materials. Now we can put them together."

The advance also opens doors to new materials with functionalities that drive future technologies. "This advance, which would have been impossible using conventional thin film growth techniques, clears the way for nearly limitless possibilities in materials design," says Evan Runnerstrom, program manager in materials design in the Army Research Office, which funded part of the research. "The ability to create perfect interfaces while coupling disparate classes of complex materials may enable entirely new behaviors and tunable properties, which could potentially be leveraged for new Army capabilities in communications, reconfigurable sensors, low power electronics, and quantum information science."

Tags:  Chang-Beom Eom  Evan Runnerstrom  Graphene  Jeehwan Kim  Massachusetts Institute of Technology  Semiconductor  U.S. Army Research Office  University of Wisconsin-Madison 

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