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Terahertz image of graphene paves the way for optimization and industrialization

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Terahertz image of graphene paves the way for optimization and industrialization


Graphene Flagship researchers have developed a new measurement standard for the analysis of graphene and layered materials that can speed up production and optimize device fabrication. Credit: Graphene Flagship.

Graphene Flagship Researchers Develop a New Measurement Standard for Analysis graphene and multilayer materials that can speed up production and optimize device fabrication.

X-ray scans have revolutionized medical treatment by allowing us to see a person from the inside without surgery. Likewise, terahertz spectroscopy penetrates graphene films, allowing scientists to draw detailed maps of their electrical quality without damaging or contaminating the material. Graphene Flagship has brought together researchers from academia and industry to develop and refine this analytical method, and a new measurement tool is now ready to characterize graphene.

These efforts were made possible by a collaborative environment created by the European consortium Graphene Flagship, with the participation of scientists from Graphene Flagship partners, DTU, Denmark, IIT, Italy, Aalto University, Finland, AIXTRON, UK, imec, Belgium, Graphenea, Spain, University of Warsaw, Poland, and Thales R&T, France, as well as employees in China, Korea and the USA.

Graphene is often sandwiched between many different layers and materials used in electronic and photonic devices. This complicates the quality assessment process. Terahertz spectroscopy simplifies the task. It displays encapsulated materials and shows the quality of the graphene underneath, exposing flaws at critical points in the manufacturing process. It is a fast, non-destructive technology that explores the electrical properties of graphene and laminates without the need for direct contact.

The development of characterization techniques such as terahertz spectroscopy is fundamental to accelerating large-scale production as they ensure that graphene devices are produced consistently and predictably, without drawbacks. Quality control precedes trust. With other developments pioneered by Graphene Flagship, such as roll-to-roll graphene and laminates, fabrication technology is poised to take the next step. Terahertz spectroscopy allows us to ramp up graphene production without losing quality.

Terahertz image of graphene opens the way to industrialization

Terahertz spectroscopy penetrates graphene films, allowing scientists to draw detailed maps of their electrical quality without damaging or contaminating the material. Credit: Peter Baggild (Graphene Flagship / DTU)

“This is the method we need to meet the high performance production levels provided by Graphene Flagship,” explains Peter Baggild of DTU, Graphene Flagship partner. “We are confident that terahertz spectroscopy in graphene production will become as routine an X-ray scan in hospitals,” he adds. “In fact, thanks to terahertz spectroscopy, you can easily map even meter-scale samples of graphene without touching them, which is not possible with some other modern methods.” In addition, Graphene Flagship is currently exploring how to apply terahertz spectroscopy directly to graphene roll-to-roll production lines and accelerate imaging.

Collaboration was key to this achievement. Graphene Flagship researchers in academia have worked closely with leading graphene manufacturers such as Graphene Flagship partners AIXTRON, Graphenea, and IMEC. “This is the best way to ensure that our solution is relevant to our end users, companies that produce graphene and laminates on an industrial scale,” says Böggild. “Our publication is a comprehensive case study that highlights the versatility and reliability of terahertz spectroscopy for quality control and should help our colleagues apply this technique to many industrially important substrates such as silicon, sapphire, silicon carbide and polymers.” he adds.

Setting standards is an important step in the development of any new material to ensure that it is safe, authentic, and offers reliable and consistent performance. This is why Graphene Flagship has a dedicated working group dedicated to graphene standardization, measurement and analytical methods, and manufacturing processes. The newly developed terahertz spectroscopy method will soon become a standard technical specification thanks to the work of the Flagship Committee on Graphene Standardization. “This will undoubtedly accelerate the adoption of this new technology as it will show how the analysis and comparison of graphene samples can be performed in a reproducible manner,” explains Peter Jepsen of Graphene Flagship Partner DTU, co-author of the study. “Terahertz spectroscopy is another step towards increasing confidence in products containing graphene,” he concludes.

Amaya Zurutuza, article co-author and scientific director of Graphene Flagship, a Graphenea partner, says: “At Graphenea, we are convinced that terahertz imaging can help develop quality control methods that can meet manufacturing requirements and provide relevant information on graphene quality. what is needed on our way to the successful industrialization of graphene. “

Turid Gspann, Chair of the Flagship Graphene Standardization Committee, says: “This terahertz [spectroscopy] It is expected that this technology will become widespread in industry. It does not require any special sample preparation and is a mapping method that allows you to analyze large areas with a minimum of time. “

Marco Romagnoli, Head of Electronics and Photonics Integration, Graphene Flagship, adds: “The THz Spectroscopy Instrument for wafer scale applications is a state of the art high TRL system for characterizing multilayer stacks on wafers containing CVD graphene. Works in a short time and with good accuracy, and provides the main parameters of interest such as carrier mobility, conductivity, scattering time, and carrier density. This valuable technical achievement also exemplifies the benefits of being part of a large collaborative project such as the Graphene Flagship. “

Andrea C. Ferrari, Graphene Flagship Science and Technology Officer and Chair of its Management Group, adds: “Once again, Graphene Flagship researchers are pioneering new characterization techniques to drive the development of graphene technology. This helps us move steadily along our innovation and technology roadmap and will drive the commercialization of graphene in a wide range of applications. ”

Reference: “Case Studies of the Electrical Characteristics of Graphene Using Terahertz Time Domain Spectroscopy” by Patrick R. Welan, Bingbin Zhou, Odile Bezensnet, Abhaya Shivayogimatha, Niraja Mishra, Qian Shen, Bjarke S. Jessen, Iwona Pasternak, David MA Mackenzie, G.G. , Kunzhi Sun, Pierre Seneor, Bruno Dlubak, Birong Luo, Frederic Vosterberg, Depin Huang, Haofei Shi, Da Luo, Meihui Wang, Rodney Su Ruoff, Ben R. Conran, Clifford McAlees, Cedric Huygebaert, Stephen Brems, Ilarothy J. Attack, Wlodek Strupinski, Dirch H. Petersen, Stephen Forti, Camilla Coletti, Alexander Juvre, Kenneth B.K. Theo, Alba Centeno, Amaya Zurutuza, Pierre Leganier, Peter U Jepsen and Peter Baggild, February 17, 2021, 2D materials
DOI: 10.1088 / 2053-1583 / abdbcb





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A revolutionary technique designed to dramatically reduce scattered light in space telescopes

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A revolutionary technique designed to dramatically reduce scattered light in space telescopes


Scattered light decomposition using ultrafast time-of-flight imaging. Credit: Lionel Clermont / Liege Spatial Center / University of Liege.

A team of researchers from the Center for Spatial Spaces of Liege (CSL) of the University of Liege has just developed a method for determining the sources and origin of scattered light in space telescopes. This is a major breakthrough in space technology that will aid in the acquisition of ever more accurate space imagery and the development of ever more efficient space instruments. This research has just been published in the journal. Scientific reports

Space telescopes are becoming more powerful. Technological developments in recent years have made it possible, for example, to observe objects further and further in the Universe or to measure the composition of the Earth’s atmosphere with even greater accuracy. However, there is another factor limiting the performance of these telescopes: stray light. Long known phenomenon: stray light results in light reflections (ghostly reflections between lenses, scattering, etc.), which degrade image quality and often result in blurry images. Until now, the methods for testing and characterizing this scattered light during the telescope design phase have been very limited, making it easy to know if the instrument was sensitive to the phenomenon, forcing engineers to revise all their calculations. in positive cases, leading to significant delays in the commissioning of these advanced tools.


Over time, various sources of scattered light (ghosts) appear and disappear on the detector. The arrival time is related to the length of the optical path, we can identify each participant and compare them with the theoretical model. Credit: Lionel Clermont / Liege Spatial Center / University of Liege.

Researchers at the Center Spatial de Liège (CSL), in collaboration with the University of Strasbourg, have just developed a revolutionary method to solve this problem using a femtosecond pulsed laser to send light beams to illuminate the telescope. “The scattered light beams take (in a telescope) different optical paths from the beams that form the image,” explains Lionel Clermont, an expert in space optical systems and scattered light at CSL. Thanks to this and with the help of an ultra-fast detector (with a resolution of the order of 10-9 seconds, ie, one thousandth of a millionth of a second), we measure the image and various effects of scattered light at different times. In addition to this decomposition, we can identify each of the participants using their arrival time, which is directly related to the optical path, and thus know the source of the problem. “

CSL engineers demonstrated the effectiveness of this method in an article just published in the journal. Scientific reportsin which they present the first film showing ghostly reflections in a refractive telescope at different times. “We were also able to use these measurements to reverse engineer theoretical models,” says Lionel Clermont, “which will allow, for example, better imaging models in the future.”

By comparing these measurements with numerical models, scientists will now be able to pinpoint the origin of the scattered light and thus act accordingly to improve the system, both by improving equipment and developing correction algorithms.

This method, developed at CSL, is not just a scientific curiosity, it could lead to a small revolution in the field of high-performance space instruments. “We have already received a lot of interest from ESA (European Space Agency) and industrialists in the space sector,” says Marc Georges, metrology and laser expert at CSL and co-author of the study. This method solves an urgent problem that has not been solved until now. “

In the near future, CSL researchers intend to continue developing this method, raise its TRL (Technology Readiness Level) and bring it to an industrial level. Industrial applications are already planned for the FLEX (Fluorescence Explorer) Earth observation telescope, which is part of ESA’s Living Planet program. The researchers hope they can apply this to scientific instruments as well.

Ref: “Scattered Light Characterization Using Ultrafast Time-of-Flight Imaging” by L. Clermont, W. Uring and M. Georges, 12 May 2021, Scientific reports
DOI: 10.1038 / s41598-021-89324-y





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Engineers harvest energy from Wi-Fi signals to power small electronics

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Engineers harvest energy from Wi-Fi signals to power small electronics


The microcircuit contains about 50 torque oscillators. Credit: National University of Singapore.

Researchers have developed a method using torque oscillators to use wireless signals and convert them into energy to power small electronics.

With the advent of the digital age, the number of Wi-Fi sources for wirelessly transferring information between devices has grown exponentially. This leads to widespread use of the 2.4 GHz radio frequency that WiFi uses, with redundant signals available for alternative use.

To harness this underutilized energy source, a research team from the National University of Singapore (NUS) and Japan’s Tohoku University (TU) have developed technology that uses tiny smart devices known as torque oscillators (STOs) to collect and convert wireless radio frequencies into energy. to power small electronics. In their study, the researchers successfully harvested energy using Wi-Fi band signals to wirelessly power a light emitting diode (LED) without using any kind of battery.

“We are surrounded by Wi-Fi signals, but when we are not using them to access the Internet, they are inactive and this is a huge waste. Our latest result is a step towards converting the available 2.4 GHz radio waves into a clean energy source, which reduces the need for batteries to power the electronics we regularly use. Thus, small electrical devices and sensors can be powered wirelessly using radio frequency waves as part of the Internet of Things. With the advent of smart homes and cities, our work could lead to energy efficient applications in communications, computing and neuromorphic systems, ”said Professor Yang Hyunsoo of NUS’s Electrical and Computer Engineering Department, who led the project.

Yang Hyunsoo and Raghav Sharma

The research breakthrough was made by a team led by Professor Yang Hyunsoo (left). Dr. Raghav Sharma (right), the first author of the article, holds a microcircuit in which about 50 torque oscillators are built. Credit: National University of Singapore.

The study was carried out in collaboration with the research team of Professor Guo Yong Xin, who also works with the Department of Electrical and Computer Engineering at NUS, and Professor Shunsuke Fukami and his team from the Technical University. Results published in Nature Communications May 18, 2021

Converting Wi-Fi Signals into Usable Energy

Torque generators are a class of new devices that generate microwaves and are used in wireless communication systems. However, the application of STO is difficult due to the low power output and wide line width.

While cross-synchronization of multiple STOs is a way to overcome this problem, existing circuits, such as short-range magnetic coupling between multiple STOs, have spatial limitations. On the other hand, long distance electrical synchronization using vortex generators is limited to frequency characteristics of only a few hundred MHz. Dedicated current sources are also required for individual STOs, which can complicate overall on-chip implementation.

To overcome spatial and low frequency limitations, the research team developed an array in which eight STOs are connected in series. Using this array, the 2.4 GHz electromagnetic radio waves that WiFi uses were converted into a constant voltage signal, which was then transmitted to a capacitor to light up a 1.6V LED. When the capacitor charged for five seconds, it could light up alone and with the same LED for one minute after turning off the wireless power.

In their study, the researchers also highlighted the importance of electrical topology for the design of STO systems on a chip and compared series versus parallel design. They found that the parallel configuration is more useful for wireless transmission due to better time domain stability, spectral noise characteristics, and impedance mismatch control. On the other hand, series connections have the advantage of collecting energy due to the additive effect of diode voltage from STO.

Commenting on the importance of their results, Dr. Raghav Sharma, the first author of the paper, shared: “In addition to creating an STO array for wireless transmission and energy collection, our work also demonstrated control over the timing state of coupled STOs. using injection blocking from an external RF source. These results are important for promising synchronized STO applications such as high-speed neuromorphic computing. “

Next steps

To enhance their technology’s ability to harvest energy, researchers are looking to increase the amount of STO in their array. In addition, they plan to test their energy harvesters to wirelessly charge other useful electronic devices and sensors.

The research team also hopes to work with industry partners to explore the development of embedded STOs for autonomous smart systems that could open up possibilities for wireless charging and wireless signal detection systems.

Reference: “An array of electrically coupled spin-torsion oscillators for 2.4 GHz data transmission and energy harvesting” Raghav Sharma, Rahul Mishra, Tung Ngo, Yong-Sin Guo, Shunsuke Fukami, Hideo Sato, Hideo Ono and Hyunsu Yang, 18 May 2021 Nature Communications
DOI: 10.1038 / s41467-021-23181-1





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Advances in nanotechnology allow for thinner transistors with exceptional performance

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Interface Between Semimetal and 2D Semiconductor


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At the interface between a semimetal (bismuth) and a two-dimensional semiconductor (MoS2), there is no energy barrier for the passage of electrons, which leads to an ultra-low contact resistance between them. Credit: Courtesy of the researchers

Atomically thin materials are a promising alternative to silicon transistors; researchers can now more efficiently connect them to other elements of the microcircuit.

Moore’s Law, the famous prediction that the number of transistors that can be placed on a microchip doubles every couple of years, runs into basic physical constraints. These constraints could stunt decades of progress unless new approaches are found.

One new area of ​​research is using atomically thin materials instead of silicon as the basis for new transistors, but connecting these “2D” materials to other traditional electronic components has proven difficult.

Now researchers in Massachusetts Institute of Technology, The University of California at Berkeley, a Taiwan semiconductor company, and others have found a new way to create these electrical connections that can help unlock the potential of 2D materials and promote miniaturization of components – perhaps enough to expand Moore’s Law. at least in the near future, the researchers say.

The results are described in the journal. Nature, in an article by recent MIT alumni Ping-Chun Shen, Ph.D. ’20 and Kong Su, Ph.D. ’20, postdoc Yusuan Lin, Ph.D. ’19, MIT professors Jing Kong, Thomas Palacios and Joo Li, and 17 others employees of the Massachusetts Institute of Technology, the University of California at Berkeley, and other institutions.

Single layer semiconductor transistor

Single layer semiconductor transistor illustration. Credit: Courtesy of the researchers

“We’ve solved one of the biggest challenges of miniaturizing semiconductor devices — the contact resistance between a metal electrode and a single-layer semiconductor material,” says Su, who now works at the University of California, Berkeley. The solution turned out to be simple: using a semimetal, an element of bismuth, to replace conventional metals to bond with a single layer material.

Such ultra-thin single-layer materials, in this case molybdenum disulfide, are seen as a major contender for breaking the miniaturization limits currently faced by silicon transistor technology. But creating an efficient, highly conductive interface between such materials and metal conductors to connect them to each other, as well as to other devices and power supplies, has been a challenge holding back progress towards such solutions, Su says.

At the interface between metals and semiconductor materials (including these single-layer semiconductors), a phenomenon called a metal-induced gap state occurs, which results in the formation of a Schottky barrier, a phenomenon that prevents the flow of charge carriers. The use of a semi-metal whose electronic properties are between metals and semiconductors, combined with proper energy equalization between the two materials, solved the problem.

Lin explains that the rapid pace of miniaturization of transistors that make up computer processors and memory chips stalled earlier, around 2000, until a new development that allowed 3D semiconductor-on-chip architecture broke the congestion in 2007. and rapid progress resumed. But now, he said, “we think we are on the edge of another bottleneck.”

Miniature transistors with exceptional performance

With this technology, miniature transistors with exceptional performance are demonstrated to meet the requirements of the technology roadmap for future transistors and microchips. Credit: Courtesy of the researchers

The so-called two-dimensional materials, thin sheets only one or a few atoms thick, meet all the requirements for a further leap in the miniaturization of transistors, potentially reducing several times the key parameter called channel length – from about 5 to 10 nanometers in modern chips with subnanometer scale. Many such materials are under extensive research, including a whole family of compounds known as transition metal dichalcogenides. The molybdenum disulfide used in the new experiments belongs to this family.

The problem of achieving metal-to-metal contact with such low resistance materials has also impeded fundamental research into the physics of these new single-layer materials. Because existing connection methods have such high resistance, the tiny signals needed to track the behavior of electrons in a material are too weak to pass through. “There are many examples from physics that require low contact resistance between metal and semiconductor. So this is a huge problem for the world of physics as well, ”says Su.

It can take some time and further development to understand how to scale and integrate such systems commercially. But for such applications of physics, the researchers say, the impact of new discoveries can be felt quickly. “I think that in physics, many experiments can immediately benefit from this technology,” says Su.

Meanwhile, the researchers continue their research as they continue to shrink their devices and look for other pairs of materials that could improve electrical contacts with another type of charge carrier known as holes. They solved the problem for the so-called N-type transistor, but if they can find a combination of channel material and electrical contact to create an efficient single-layer P-type transistor, it will open up many new possibilities for the next generation. They say chips.

Reference: “Ultra-low contact resistance between semi-metal and single-layer semiconductors” Ping-Chun Sheng, Kong Su, Yuxuan Lin, Ang-Sheng Chou, Chao-Ching Cheng, Ji-Hong Park, Min-Hui Chiu, Ang-Yu Lu, Hao. -Ling Tan, Mohammad Mahdi Tavakoli, Gregory Pitner, Xiang Ji, Zhengyang Kai, Nannan Mao, Jiangtao Wang, Vincent Tung, Joo Lee, Jeffrey Bokor, Alex Zettl, Chi-Yi Wu, Thomas Palacios, Line-Jong Li and Jing May 12, 2021 Nature
DOI: 10.1038 / s41586-021-03472-9

In addition to the Massachusetts Institute of Technology and UC Berkeley, the team included researchers from Lawrence Berkeley National Laboratory, Taiwan Semiconductor Manufacturing Company, National Taiwan University and King Abdullah University of Science and Technology in Saudi Arabia. This work was supported by the National Science Foundation, the US Army Research Office, the Office of Naval Research, and the US Department of Energy.





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