China Science & Technology Forum

[JSCh]

Chinese physicist says revolutionary technique means alloys can be developed in hours instead of years

• Inspired by early colour television, method can create thousands of alloys quickly
• Leader of Beijing team says a ‘revolution in material science’ is close to hand

Stephen Chen
Published: 7:10pm, 7 May, 2019

Speedy development of alloys may accelerate programmes to explore the harsh environments of space and ocean depths. Photo: Xinhua

Chinese physicists say they have developed a method that can cut the time involved in the discovery of alloys from years to hours.

The technique has led to the creation of high performance alloys, including the world's toughest amorphous metal, or metallic glass, for use in extremely hot environments.

The search for an alloy typically takes years, but now it can be done in less than two hours, the Chinese researchers said.

Part of their findings was published in the journal Nature this month.

Inspired by the colour gun method used to create images for television sets, the Beijing team speeds up alloy discovery. Photo: Handout

In the conventional method, metals needed to be weighed, melted to an alloy and tested for performance. To find the right formula, researchers might need to test more than a thousand combinations and each test might take a day or two.

Professor Wang Weihua, researcher with the institute of physics at the Chinese Academy of Sciences in Beijing and lead scientist of the study, said his team’s research was inspired by early colour televisions, which used three electric devices known as guns that fired red, green and blue light onto the back of the screen to create real-world colours for the viewer.

Wang’s team’s alloy technology also involved three guns, but instead of electronic pulses they fired “bullets” made of different metals. These struck a silicon board simultaneously and fused to form alloys.

Sensors quickly measured the alloys’ properties and picked the most appropriate for the researchers.

This approach allowed scientists to create more than 1,000 samples, test their performance and select the most promising within a couple of hours.

“We proved it works,” Wang said. “It will increase people's confidence. There will be a revolution in material science.”

The alloy reported in the Nature paper contained iridium, nickel and tantalum. It had a distorted atomic structure similar to that of glass. Metallic glasses can be extremely strong but they usually weaken by temperatures of 400 degrees Celsius or more.

The Beijing team hopes artificial intelligence, in tandem with its technique, will start a materials revolution. Photo: Handout

The new alloy can maintain a tensile strength nearly eight times that of steel at more than 700 degrees Celsius, researchers said.

It can also remain intact for months in aqua regia, the mixture of nitric acid and hydrochloric acid that can dissolve gold and platinum.

Such properties make the alloy an ideal candidate material for manufacturing critical components for use in harsh environments such as space, ocean depths and battlefields.

“We are introducing artificial intelligence into the design and search for new amorphous metals,” Wang said. “It can further increase the speed of discoveries. In the near future, we may even be able to create material on demand.

“The potential application is almost unlimited.”



Chinese physicist says revolutionary technique means alloys can be developed in hours instead of years | South China Morning Post

Ming-Xing Li, Shao-Fan Zhao, Zhen Lu, Akihiko Hirata, Ping Wen, Hai-Yang Bai, MingWei Chen, Jan Schroers, YanHui Liu, Wei-Hua Wang. High-temperature bulk metallic glasses developed by combinatorial methods. Nature (2019). DOI: 10.1038/s41586-019-1145-z​

 

[JSCh]

China eyes earthquake warning and prediction technology
By Chen Xi Source:Global Times Published: 2019/5/12 22:13:17

A depiction of one firemen and one soldier rescuing victims from the rubble exhibited at the Wenchuan Earthquake Museum. Photo: Li Hao/GT

China's earthquake early warning system is the "fastest in the world," Chinese seismologists asserted on Sunday, crediting high-technology and artificial intelligence to a delay of 6.2 seconds.

"The average response time of the earthquake early warning system in China is 6.2 seconds now, 30 percent quicker than Japan, which is nine seconds," Wang Tun, head of the Chengdu-based Institute of Care-life, which specializes in earthquake early warnings, told the Global Times on Sunday.

This made the average response time of China's system "the fastest in the world," Wang said.

Wang's remark came on the 11th anniversary of the 8.0-magnitude Wenchuan earthquake of May 12, 2008, in which more than 69,000 people died.

Wang said if there was an early warning system at that time, perhaps there would have been 30 percent fewer deaths.

Studies suggest that a three-second early warning time can reduce casualties by 14 percent and a 10-second early warning time can reduce them by 39 percent, Wang said.

China's early warning system also covers the largest area in the world, according to a document that the public affairs department of the Institute of Care-life sent to the Global Times on Sunday.

The system includes 31 provinces and regions, 2.2 million square kilometers and 660 million people, about 90 percent of densely populated quake-prone areas.

Warning messages are dispatched via mobile phone, radio and television, government microblogs and dedicated receiving terminals.

Warnings were sent during 50 earthquakes including the 7.0-magnitude quake in Lushan, Sichuan Province in 2013 and the 6.5-magnitude quake in Ludian county, Southwest China's Yunnan Province in 2014, the document noted.

The early warning success rate came about through the introduction of cutting-edge technology, according to Wang. Artificial intelligence identifies seismic waveforms and reduces false alarms, he noted.

The warning system can still be improved, experts agree.

Electromagnetic waves travel faster than seismic waves, meaning people in areas outside the epicenter can use the time difference to protect themselves, "but it cannot play a role in reducing disasters in the hardest-hit areas," Sun Shihong, a China Earthquake Networks Center researcher, told the Global Times on Sunday.

And earthquake prediction remains a largely experimental topic.

China in 2018 began using the world's first cloud image system based on sensory technology to release more timely and reliable warnings for earthquakes.

Wang's team uses a cloud image system that involves deep-buried sensors that can detect stress and energy dynamics 8 to 20 kilometers below the surface.

"Earthquake prediction technology, an unsolved global and technological problem, is expected to be well tested within three years," Wang said.

 

[JSCh]

NEWS RELEASE 13-MAY-2019
Just like toothpaste: fluoride radically improves the stability of perovskite solar cells
EINDHOVEN UNIVERSITY OF TECHNOLOGY

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The atomic structure of fluoride (NaF) containing metal halide perovskite (FAPbI3). Due to its high eletronegativity, fluoride stabilizes the perovskite lattice by forming strong hydrogen bonds and ionic bonds on the surface of the material. CREDIT: Eindhoven University of Technology

Solar cells made of perovskite hold much promise for the future of solar energy. The material is cheap, easy to produce and almost as efficient as silicon, the material traditionally used in solar cells. However, perovskite degrades quickly, severely limiting its efficiency and stability over time. Researchers from Eindhoven University of Technology, energy research institute DIFFER, Peking University and University of Twente have discovered that adding a small amount of fluoride to the perovskite leaves a protective layer, increasing stability of the materials and the solar cells significantly. The solar cells retain 90 percent of their efficiency after 1000 hours operation at various extreme testing conditions. The findings are published today in the leading scientific journal Nature Energy.

Because they are so cheap to make, perovskite solar cells have been at the center of much recent solar research. As a consequence, their efficiency has risen from less than 4 percent in 2009 to over 24 percent at present, which is close to traditional silicon cells. So-called tandem cells, which combine silicon and perovskite cells, achieve an efficiency of more than 28 percent.

Despite this success, perovskite has a number of defects due to the nature of the material and the way it is manufactured. Over time, vacancies in the atomic structure of the metal halide trigger the degradation of the perovskite under the influence of moisture, light and heat.

Protective layer

The researchers in Eindhoven, Twente and Beijing have experimented with a new type of perovskite, by adding a small amount of fluoride in the production process. Just like fluoride in toothpaste, the fluoride ions form a protective layer around the crystal, preventing the diffusion of the harmful defects.

"Our work has improved the stability of perovskite solar cells considerably", says Shuxia Tao, assistant professor at the Center for Computational Energy Research, a joint center of the Department of Applied Physics of TU/e and DIFFER, and co-author of the paper. "Our cells maintain 90 percent of their efficiency after 1000 hours under extreme light and heat conditions. This is many times as long as traditional perovskite compounds. We achieve an efficiency of 21.3 percent, which is a very good starting point for further efficiency gains".

Due to its high eletronegativity, fluoride stabilizes the perovskite lattice by forming strong hydrogen bonds and ionic bonds on the surface of the material.

Much of the work of the team from Eindhoven has gone into explaining why fluoride is such an effective ingredient compared to other halogens. Using computer simulations they conclude that part of its success is due to the small size and high electronegativity of fluoride ions. The higher the electronegativity of an element, the easier it attracts electrons of neighbouring elements. This helps fluoride ions to form strong bonds with the other elements in the perovskite compound, forming a stable protective layer.

Future research

The study is seen as an important step towards the successful implementation of perovskite solar cells in the future. However, much work remains to be done. The gold standard in the solar industry is a retention rate of at least 85 percent of original efficiency after ten to fifteen years, a standard which is still some way off for perovskite cells.

"We expect it will take another five to ten years for these cells to become a commercially viable product. Not only do we need to further improve their efficiency and stability, we also need to gain a better theoretical understanding of the relevant mechanisms at the atomic scale. We still don't have all the answers to why some materials are more effective than others in increasing the long-term stability of these cells", says Tao.


Just like toothpaste: fluoride radically improves the stability of perovskite solar cells | EurekAlert! Science News

Nengxu Li, Shuxia Tao, Yihua Chen, Xiuxiu Niu, Chidozie K. Onwudinanti, Chen Hu, Zhiwen Qiu, Ziqi Xu, Guanhaojie Zheng, Ligang Wang, Yu Zhang, Liang Li, Huifen Liu, Yingzhuo Lun, Jiawang Hong, Xueyun Wang, Yuquan Liu, Haipeng Xie, Yongli Gao, Yang Bai, Shihe Yang, Geert Brocks, Qi Chen, Huanping Zhou. Cation and anion immobilization through chemical bonding enhancement with fluorides for stable halide perovskite solar cells. Nature Energy (2019). DOI: 10.1038/s41560-019-0382-6​

 

[JSCh]

China cracks cheap lithium production in electric car breakthrough | South China Morning Post

• Scientific breakthrough leads to record low costs for essential battery ingredient
• US and Europe seek to break Chinese dominance in global supply chain

Stephen Chen
Published: 11:00pm, 14 May, 2019

The production of lithium – an essential ingredient in batteries for electric cars – has become easier and significantly cheaper, thanks to a technological breakthrough, just as US concerns about China’s dominance in the supply chain are on the rise.

The cost of extracting the mineral has been slashed to a “record low” of 15,000 yuan (US$2,180) per ton by the new process, a Chinese government report said.

That compares to an international price for lithium ranging from $12,000 to $20,000 per ton – and a long-term contract price of about $17,000 – over the past year, according to some industrial estimates.

The precise production costs of lithium are a closely guarded business secret, but industry insiders interviewed by the South China Morning Postagreed that the rate quoted in the report could be considered one of, if not the lowest, around.

While China’s lithium output is still relatively low, it dominates supply of the end product, producing nearly two-thirds of the world’s lithium-ion batteries, compared with 5 per cent for the United States, and also controls most of the world’s lithium processing facilities, according to data from Benchmark Minerals Intelligence.

The US has moved to offset China’s dominance in the electric car supply chain, with draft legislation aimed at streamlining regulation and permitting requirements for the development of mines for lithium, graphite and other minerals used in the process.

Republican Senator Lisa Murkowski, who introduced the Minerals Security Act alongside Democrat Senator Joe Manchin at the beginning of May, said China’s lead in the electric car supply chain sector gave it an edge in the ongoing trade dispute.

“My greatest challenge right now is to educate other members of Congress as to why this needs to be a national priority,” she said.

“Our challenge is still a failure to understand the vulnerability we are in as a nation when it comes to reliance on others for our minerals.”

The US is not the only country playing catch-up with China. France and Germany have also asked the European Commission to support a 1.7 billion euro (US$1.9 billion) battery cell consortium, aimed at reducing China’s dominance.

The scientific breakthrough could change the amount of lithium China is able to produce in future. State-owned company Qinghai Lithium Industries – which has been taking advantage of the new process – has enjoyed an average profit margin of more than 50 per cent over the past three years, with total revenues exceeding three billion yuan, according to the Chinese government report.

Li Jian, an executive manager of the company, said the estimate on production costs was “quite accurate” but did not include tax and bank loan interest. He also predicted production costs would “likely decline further in the future with continued technical advancement”.

Lithium is extracted from brine but separating it from other elements present in the salts remains a challenge worldwide. Magnesium, in particular, is extremely difficult to separate from lithium because the two minerals have similar ionic properties.

According to the report, a 15-year research project funded by the Chinese Academy of Sciences has cracked a cost-effective way of unbinding lithium from other minerals, especially magnesium, through multiple processing stages with complex electronic and membrane filtering treatments.

Dr Ren Dongming, director of the Centre for Renewable Energy Development under China’s National Development and Reform Commission, said the attractive economic return would increase the number of lithium suppliers, helping to bring the price of batteries down and eventually benefit consumers.

“Cheaper lithium will benefit electric car makers such as Tesla,” he said.

Half to 30 per cent of the cost of an electric car currently goes on the battery, according to some industrial estimates. Lower prices, increased range and improving infrastructure such as charge stations would make zero-emission vehicles a more attractive option for car buyers, Ren said.

About four per cent of the cars on the road last year were running on electricity, according to the Centre of Automotive Management, a Germany-based research institute. The biggest stock – nearly one million cars – was registered in China, believed to be one of the world’s most lithium-rich countries.

According to a 2017 Chinese government estimate, the salt lakes on the Tibetan Plateau – where the new technology is being used – hold more than 60 per cent of the world’s lithium reserves. The US Geological Survey estimate last year was significantly lower, placing just 7 per cent of the world’s reserves in China. Meanwhile, other estimates have ranked China’s lithium reserves in second place, after Chile.

China’s lithium production remains low, however, with Chinese mines contributing just 9 per cent to global lithium production last year.

In contrast, Chinese factories are consuming more of the metal than any other country, mostly for battery production. Top lithium producers such as Australia and Chile sell most of their output to China and, in recent years, Chinese companies have been buying up mines in lithium-rich countries such as Argentina and Australia.

The buying spree has prompted suspicions that Beijing is hoarding its domestic resources while trying to control the global lithium supply.

Xu Hong, a professor at the China University of Geosciences in Beijing, said hoarding was not the main reason for China’s low rate of lithium production.

Instead, the isolation and harsh environment of the Tibetan Plateau – including high altitudes and low oxygen levels – prohibited large-scale mining at the salt lakes.

“The lithium reserves in China may be rich, but many are difficult to exploit,” she said.

The separation technology was a recent breakthrough, so adaptation of the method and construction of more factories would take time. and there were also concerns that mining activity could damage the sensitive local environment.

“These all need to be considered as costs,” Xu said.

 

[JSCh]

China Focus: New technology enables large-scale production of artemisinin for malaria
Source: Xinhua| 2019-05-13 18:36:56|Editor: Xiang Bo

BEIJING, May 13 (Xinhua) -- Chinese researchers have developed a new technology to produce artemisinin, a top malaria treatment, on a large scale.

Sweet wormwood was used in ancient Chinese therapy to treat various illnesses, including fevers typical of malaria. Nearly five decades ago, Chinese scientists identified its active ingredient, artemisinin.

In 2005, the World Health Organization recommended artemisinin-based Combination Therapies (ACTs) as the most effective malaria treatment available. Global demand for artemisinin increased, but the quality and supply have not been stable.

According to researchers from the Institute of Process Engineering (IPE), Chinese Academy of Sciences, due to its complex structure, artemisinin is currently difficult and not economically feasible to chemically synthesize.

The traditional industrial method to produce artemisinin is to treat sweet wormwood leaves with organic solvents like petroleum ether.

The extraction process is long, energy consumption is high and productivity is low.

In the study, the IPE researchers proposed enhancing contact between the solvent and the leaves by reflux to speed up the artemisinin extraction. The extraction time was reduced from seven hours to four and a half.

After treating sweet wormwood leaves with solvents, they optimized the evaporation process with a thin film evaporator, an apparatus that provides a continuous evaporation process, especially for heat-sensitive products, to retrieve the solvents.

Compared to the traditional process, the time it takes to produce the artemisinin concentrate is reduced by 87.5 percent.

Meanwhile, the purity of the final product is increased to more than 99 percent, and energy consumption is also reduced.

The new technology puts the recovery of the solvents at 99.9 percent, while energy consumption per ton of artemisinin drops by 43 percent and the product purity rises to higher than 99 percent, said Wang Hui from the IPE.

"This technology solves the main shortcomings in the traditional artemisinin production process and could also provide ideas for other natural products production," said Zhang Suojiang, IPE director.

The new technology has been deployed at a plant of Tianyuan Biotechnology in Yuzhou in Henan province.

Jiang Hongge, manager of the company, said that the production line using the new technology had been in stable operation for a year at the plant with an annual production of 60 tons of artemisinin.

Sixty tons of artemisinin corresponds to about 150 million treatment courses of ACT.

The WHO says an estimated 409 million treatment courses of ACT were procured by countries in 2016.

Artemisinin produced at the plant has been sold to India, Sudan and other developing countries. The company also plans to build artemisinin production lines in Ghana.

 

[JSCh]

Researchers Build a Self-Driving Parallel Testing System
May 13, 2019

Realizing autonomous driving is one of the most challenging tasks in Artificial Intelligence research. The solution lies in building a new Turing test system, which is able to test and verify the autonomous vehicle's capability in understanding complex traffic scenario and making driving decision, and thus stimulate the development of autonomous driving technology.

How to test the system intelligence is a vital research issue in Artificial Intelligence. Based on Turing, safe and reliable AI systems can be achieved if and only if the tests have clear definitions of tasks and efficient methods to generate abundant data for tests.

Recently, researchers from the Institute of Automation of the Chinese Academy of Sciences (CASIA), Tsinghua University, and Xi'an Jiaotong University built a new self-driven closed-loop parallel testing system. The system focuses on implementing more challenging tests to accelerate the building and testing of autonomous vehicles.

They constructed an intelligent closed-loop parallel testing system with an recognition mechanism to realize self-upgrading under human experts' guidance.

This system contains three parts. The first part establishes a set of semantic definitions to characterize the tasks that should be finished by autonomous vehicles. The second part implements the tests for specified task instances. The field test and simulation test are tightly integrated into a parallel testing system which keeps collecting new field data to update the simulation system. The third part evaluates both vehicle performances and task difficulties to seek the most challenging new tasks.

Specially, an adversarial learning model was designed to automatically generate new task instances that may be harder than existing task instances based on the past testing results, aiming to push the autonomous vehicles to improve its capability in adjusting to complex environment. It is believed that the system can effectively accelerate the progress of autonomous driving technology.

The study, published in Science Robotics, was supported by the National Natural Science Foundation of China.

System overview flowchart. (Image by CASIA)
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Researchers Build a Self-Driving Parallel Testing System---Chinese Academy of Sciences

 

[JSCh]

3D Quantum Hall effect confirmed by experiment - In the Focus - Southern University of Science and Technology
May 9, 2019
Research News

Recently, Associate Professor Zhang Liyuan from the Department of Physics at Southern University of Science and Technology worked with Professor Qiao Zhenhua of the University of Science and Technology of China (USTC), and Associate Professor Shengyuan Yang of Singapore University of Technology and Design (SUTD). The three of them have proved, through experimentation, the 3D quantum Hall effect from the ZrTe5 crystal. The research was published in the top academic journal Nature, in a paper entitled “Three-dimensional quantum Hall effect and metal–insulator transition in ZrTe5.”

In the 1980s, scientists discovered the quantum Hall effect (QHE) in two-dimensional electronic systems, making the topology play a central role in condensed matter physics. For decades, there have been theoretical predictions about the possibility of extending QHE to a three-dimensional electronic system, but it has never been proven experimentally.

The researchers measured the low-temperature electrical transmission of bulk ZrTe5 crystals under magnetic field and calculated the quantum limit at a relatively low magnetic field. The researchers observed a non-dissipative longitudinal resistivity, close to zero, proportional to half of the Fermi wavelength along the field in the Hall resistivity platform. This response has a 3D QHE characteristic that strongly suggests that Fermi surface instability is driven by enhanced interaction effects at extreme quantum limits.

By further increasing the magnetic field, both the longitudinal and Hall resistivity increase significantly and exhibit a metal-insulator transition behavior, indicating another quantum phase transition driven by the magnetic field.

The results of this study provide reliable experimental evidence for 3D QHE, providing a useful platform for further exploration of singular quantum phases and transitions in 3D systems.

Brookhaven National Laboratory, Florida Strong Magnetic Field Laboratory, Massachusetts Institute of Technology, Singapore University of Technology and Design and Renmin University of China are participating units. Associate Professor Zhang Liyuan, Professor Qiao Zhenhua (USTC), and SUTD Associate Professor Shengyuan a. Yang are co-authors.

This work has been strongly supported by the Guangdong Innovation and Entrepreneurship Team, the Shenzhen Peacock Team, and the Basic Research-Disciplinary Layout Project.

Paper link: https://www.nature.com/articles/s41586-019-1180-9

Source: Department of Physics
Translated and Adapted: Chris Edwards​

 

[JSCh]

The Chinese Academy of Science announce that recently, the Institute of Physics and Chemistry of the Chinese Academy of Sciences has successfully developed a 500W@2K cold compressor prototype, with various performance indicators meeting the predetermined requirements. It is used for superfluid helium cooling technology and is the key technology to ensure the stable operation of the next generation of higher energy superconducting accelerators.

 

[JSCh]

Focus: Longer Movies at Four Trillion Frames per Second
May 17, 2019• Physics 12, 55

A new technique produces long-lasting movies of nonluminous objects with just a few hundred femtoseconds between frames.

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Y. Lu et al., Phys. Rev. Lett. (2019)
Movie short. Images of the letter A written in dye, acquired at eight distinct wavelengths and at four different time delays: 0, 4, 8, and 12 picoseconds (ps). Each of the four columns comes from a single laser pulse. The technique captures both spatial and spectral information on the picosecond timescale. (See video below.)

Generating images at a rate of more than a trillion per second, today's fastest cameras can catch molecules as they react with one another. But despite this high rate, when observing nonluminous objects, they can only produce a handful of images in a single sequence. Engineers have now demonstrated a rate of nearly four trillion frames per second, capturing as many as 60 consecutive images. The technique should allow video analysis of ultrafast processes such as the interaction of light with eye tissue in laser surgery.

High-quality, fast cameras use semiconductor structures called CCD arrays to rapidly store image data before moving them off to longer-term storage. At the highest speeds, these cameras can only produce a handful of consecutive frames, mainly because of the limited CCD space. The images must be stored in nonoverlapping subregions of the CCD, so increasing the number of images leads to a reduction in image resolution. To overcome this limitation, researchers led by photonics specialist Feng Chen of the Xi’an Jiaotong University in China have now exploited a technique called compressive sampling, which allows the storage of images in overlapping CCD regions.

...

--> Physics - Focus: Longer Movies at Four Trillion Frames per Second

Compressed Ultrafast Spectral-Temporal Photography
Yu Lu, Terence T. W. Wong, Feng Chen, and Lidai Wang
Phys. Rev. Lett. 122, 193904 (2019)

Published May 17, 2019​

 

[JSCh]

NEWS RELEASE 20-MAY-2019
Thinking outside the box: 'Seeing' clearer and deeper into live organs
Scientists using a unique approach have developed a new biomedical imaging contrast agent

UNIVERSITY OF TECHNOLOGY SYDNEY

Scientists using a unique approach have developed a new biomedical imaging contrast agent. They say the breakthrough overcomes a major challenge to "seeing" deeper into live tissue, and opens the way for significant improvements in optical imaging technology.

The development, a result of international collaboration between Fudan University in China and the University of Technology Sydney (UTS), has the potential to take bio-imaging resolution beyond what is currently possible with CT and PET imaging technology. The research is published in Nature Photonics.

Professor Dayong Jin, a senior author on the study and Director of the UTS Institute for Biomedical Materials & Devices (IBMD), said "this outcome is a great example that shows how we transform advances in photonics and material sciences into revolutionary biotechnologies at IBMD".

Optical contrast agents are used primarily to improve the visualisation and differentiation in tissue and blood vessels in both clinical and research settings.

To optimize the brightness of a contrast agent, and to efficiently illuminate single cells and biomolecules, the challenge lies in overcoming a limitation in physics, called "concentration quenching". This is caused by the cross relaxation of energy between emitters when they are too close to each other, so that having too many emitters leads to a quenching of the overall brightness.

"The new approach in this research was to unlock the concentration quenching effect by using the pure rare earth element ytterbium that only has a single excited state to avoid inter-system cross relaxation", explained by Professor Jin, "so that a network of over 5,000 pure ytterbium emitters can be tightly condensed within a space of 10 nm in diameter, a thousand times smaller than a cell".

At this emitter density all possible atomic doping sites are occupied by ytterbium within the crystal lattice structure, and once properly passivated (made unreactive), by a thin layer of biocompatible calcium fluoride, the material is free of concentration quenching.

"This enables the efficiency of photonics conversion to approach the theoretical limit of 100%. This not only benchmarks a new record in photonics and material sciences, but also opens up a lot of potential applications", Professor Jin said.

Lead author on the paper, Mr Yuyang Gu, a PhD student at Fudan University, said "using this new contrast agent in a mouse model allowed us to see through whole mice".

The fundamental physics of the fluorescent probes used in optical imaging means there is only a narrowly defined near infrared (NIR) "window" [optical transparency window] beyond which visible light cannot penetrate tissue. To design a contrast agent that both absorbs and emits in the NIR without losing the energy is difficult.

"Although ytterbium has a 'pure energy' level that helps protect photons absorbed in the NIR band before being emitted, with negligible loss of energy, the simple excited state only permits emissions in the very similar band of NIR, which makes it impractical to use the conventional colour filters to discriminate the emissions from the highly scattering environment of laser excitation", Professor Jin said.

"The research needed 'new physics'. We really had to think outside the box."

Instead of spectrally "filtering" the signal emissions, the researchers further employed a time-resolved technique that paused the excitation light, and took advantage of the "photon storage" property of ytterbium emitters, slowing down the emission of light, long enough to allow a clearer separation between the excitation and emission of light in the time domain. Professor Jin likens this phenomena to the scenario when, after powering off a TV, the long-lived fluorescence of a "ghost" image is seen as an afterglow in the darkness.

For the past five years, Professor Jin and his team have developed a library of Super Dots, ?-Dots, Hyper Dots and Thermal Dots as multiphoton luminescent probes for sensing and imaging applications.

"This outcome is another quantum leap, bringing us a new set of research capacities towards the development of more efficient and functional nanoscale sensors and biomolecular probes" Professor Jin added.

Fudan University Chief Investigator, Professor Fuyou Li said "This is a 'new' luminescent process with high efficiency. We hope to find more suitable applications based on the fine tuning of the decay process of such kind of probes."

The combined use of high density of ytterbium emitters and time-resolved approach meant it was possible to maximise the number of emitters, the light conversion efficiency and the overall brightness of the contrast agent, and thereby significantly improving detection sensitivity, resolution and depth.

Professor Jin said that it was another example of how breakthroughs in physics can lead to the development of new and improved medical technologies citing the evolution, and revolution, in diagnostic methods such as X-rays, CT and PET imaging.


Thinking outside the box: 'Seeing' clearer and deeper into live organs | EurekAlert! Science News

Yuyang Gu, Zhiyong Guo, Wei Yuan, Mengya Kong, Yulai Liu, Yongtao Liu, Yilin Gao, Wei Feng, Fan Wang, Jiajia Zhou, Dayong Jin, Fuyou Li. High-sensitivity imaging of time-domain near-infrared light transducer. Nature Photonics (2019). DOI: 10.1038/s41566-019-0437-z​

 

[JSCh]

NEWS RELEASE 22-MAY-2019
How to enlarge 2D materials as single crystals?
Turn it around and find the right symmetric code

INSTITUTE FOR BASIC SCIENCE

(a-c), schematic of edge-coupling-guided hBN growth on a Cu (110) vicinal surface with atomic step edges along the <211> direction. (b) shows the top view and (c) shows a side view. CREDIT: IBS

What makes something a crystal? A transparent and glittery gemstone? Not necessarily in the microscopic world. When all of its atoms are arranged in accordance with specific mathematical rules, we call the material a single crystal. Like the natural world has its unique symmetry just as snowflakes or honeycombs,, the atomic world of crystals is designed by its own structure and symmetry. This material structure has a profound effect on its physical properties as well. Specifically, single crystals play an important role in inducing material's intrinsic properties to its full extent. Faced with the coming end of the miniaturization process that the silicon-based integrated circuit has allowed up to this point, huge efforts have been dedicated to find a single crystalline replacement for silicon.

In search for the transistor of the future, two-dimensional (2D) materials, especially graphene have been the subject of intense research around the world. Being thin and flexible as a result of being only a single layer of atoms, this 2D version of carbon even features unprecedented electricity and heat conductivity. However, the last decade's efforts for graphene transistors have been held up by physical restraints graphene allows no control over electricity flow due to the lack of band gap. Then, what about other 2D materials? A number of interesting 2D materials have been reported to have similar or even superior properties. Still, the lack of understanding in creating ideal experimental conditions for large-area 2D materials has limited their maximum size to just a few mm 2.

Scientists at the Center for Multidimensional Carbon Material (CMCM) within the Institute for Basic Science (IBS) (located in the Ulsan National Institute of Science and Technology (UNIST)) have presented a novel approach to synthesize large-scale of silicon wafer size, single crystalline 2D materials. Prof. Feng Ding and Ms. Leining Zhang in collaboration with their colleagues in Peking University, China and other institutes have found a substrate with a lower order of symmetry than that of a 2D material that facilitates the synthesis of single crystalline 2D materials in a large area. "It was critical to find the right balance of rotational symmetries between a substrate and a 2D material," notes Prof. Feng Ding, one of corresponding authors of this study. The researchers successfully synthesized hBN single crystals of 10*10 cm2 by using a new substrate: a surface nearby Cu (110) that has a lower symmetry of (1) than hBN with (3).

Then, why does symmetry matters? Symmetry, in particular rotational symmetry, describes how many times a certain shape fits on to itself during a full rotation of 360 degrees. The most efficient method to synthesize large-area and single crystals of 2D materials is to arrange layers over layers of small single crystals and grow them upon a substrate. In this epitaxial growth, it is quite challenging to ensure all of the single crystals are aligned in a single direction. Orientation of the crystals is often affected by the underlying substrate. By theoretical analysis, the IBS scientists found that an hBN island (or a group of hBN atoms forming a single triangle shape) has two equivalent alignments on the Cu(111) surface that has a very high symmetry of (6). "It was a common view that a substrate with high symmetry may lead to the growth of materials with a high symmetry. It seemed to make sense intuitively, but this study found it is incorrect," says Ms. Leining Zhang, the first author of the study.

Previously, various substrates such as Cu(111) have been used to synthesize single crystalline hBN in a large area, but none of them were successful. Every effort ended with hBN islands aligning along in several different directions on the surfaces. Convinced by the fact that the key to achieve unidirectional alignment is to reduce the symmetry of the substrate, the researchers made tremendous efforts to obtain vicinal surfaces of a Cu(110) orientation; a surface obtained by cutting a Cu(110) with a small tilt angle. It is like forming physical steps on Cu. As a hBN island tends to place in parallel to the edge of each step, it gets only one preferred alignment. The small tilt angle lowers the symmetry of the surface as well.

They eventually found that a class of vicinal surfaces of Cu (110) can be used to support the growth of hBN with perfect alignment. On a carefully selected substrate with the lowest symmetry or the surface will repeat itself only after a 360degree rotation, hBN has only one preferred direction of alignment. The research team of Prof. Kaihui Liu in Peking University, has developed a unique method to anneal a large Cu foil, up to 10*10 cm2, into a single crystal with the vicinal Cu (110) surface and, with it, they have achieved the synthesis of hBN single crystals of same size.

Besides flexibility and ultrathin thickness, emerging 2D materials can present extraordinary properties when they get enlarged as single crystals. "This study provides a general guideline for the experimental synthesis of various 2D materials. Besides the hBN, many other 2D materials could be synthesized with the large area single crystalline substrates with low symmetry," says Prof. Feng Ding. Notably, hBN is the most representative 2D insulator, which is different from the conductive 2D materials, such as graphene, and 2D semiconductors, such as molybdenum disulfide (MoS2). The vertical stacking of various types of 2D materials, such as hBN, graphene and MoS2, would lead to a large number of new materials with exceptional properties and can be used for numerous applications, such as high-performance electronics, sensors, or wearable electronics."


How to enlarge 2D materials as single crystals? | EurekAlert! Science News

Li Wang, Xiaozhi Xu, Leining Zhang, Ruixi Qiao, Muhong Wu, Zhichang Wang, Shuai Zhang, Jing Liang, Zhihong Zhang, Zhibin Zhang, Wang Chen, Xuedong Xie, Junyu Zong, Yuwei Shan, Yi Guo, Marc Willinger, Hui Wu, Qunyang Li, Wenlong Wang, Peng Gao, Shiwei Wu, Yi Zhang, Ying Jiang, Dapeng Yu, Enge Wang, Xuedong Bai, Zhu-Jun Wang, Feng Ding, Kaihui Liu. Epitaxial growth of a 100-square-centimetre single-crystal hexagonal boron nitride monolayer on copper. Nature (2019). DOI: 10.1038/s41586-019-1226-z​

 

[JSCh]

China-developed 3D mapping camera ready for commercial use
Source: Xinhua| 2019-05-23 21:10:26|Editor: Li Xia

CHANGCHUN, May 23 (Xinhua) -- A Chinese science academy has come up with an independently-developed camera for capturing three dimensional (3D) photographs for geographic mapping.

The research was done by scientists of the Changchun Institute of Optics, Fine Mechanics and Physics, affiliated to the Chinese Academy of Sciences.

Ding Yalin, the chief scientist of the project, said the resolution of the camera developed by the team can reach 0.08 meters when taking photos from the height of 2,000 meters, which is almost twice as high as that of the most advanced products of the same kind abroad.

The camera has wide application potential for geographic mapping, general surveying of agriculture and forestry, natural resource exploration and island mapping, Ding said.

The team has achieved a number of scientific breakthroughs in the development of optical lenses, which include large aspheric surface design and processing and high-precision flexible lens adjusting technology.

It has developed a software system for automatic processing of data captured by the camera.

Ding said the camera's application has been tested in a number of surveying and mapping projects under a variety of geographic conditions. The photos are evaluated to have a high resolution and mapping accuracy.

The team is working on the commercialization of the camera.

 

[JSCh]

Scientists Propose to Advance Material Sustainability Through Plainification---Chinese Academy of Sciences
May 24, 2019

Extensive alloying makes material development more resource-dependent. Alloyed materials with complicated compositions become more difficult to synthesis and to recycle. With increasing alloying, material cost continues to spiral while property enhancements level off. The sustainability of materials, especially metals, has gained more and more attentions.

In a study published in Science, Prof. LI Xiuyan and Prof. LU Ke from Shenyang National Laboratory for Materials Science (SYNL), Institute of Metal Research of the Chinese Academy of Sciences proposed to advance material properties by plainification, which means tailoring stable interfaces at different length scales instead of alloying.

The newly proposed strategy intends to lower materials cost and increase their resource-independence and recyclability, therefore advancing material sustainability.

Plainification of materials aims to reduce alloying in material development. Although with sound principle, plainification of metals is facing challenges due to the intrinsic instability of microstructures at the nanometer scale where property variations are dramatically elevated.

Previous studies from Prof. LI Xiuyan and Prof. LU Ke, published respectively in Science in 2018 and Phys. Rev. Lett. in 2019, revealed that nano-sized grains in pure copper and nickel produced from plastic deformation exhibit notable thermal and mechanical stability against coarsening below a critical grain size, thanks to an autonomous grain boundary relaxation to low-energy states.

This finding offers new possibilities for developing stable nanostructured metals and alloys with novel properties, foundation of the material plainification strategy. Stabilization of nanoscale grains in metals takes advantage of their ability to suppress dislocation nucleation, providing a strengthening mechanism that is distinct from the conventional way of resisting dislocation slip.

The strengthening mechanism highlights new opportunities of plainification for greatly advancing material properties by tailoring stable interfaces at different length scales with fewer or no alloying elements.

As the chief scientist, Prof. LI Xiuyan leads the Key R&D Project on “Plainification of materials with low-energy interfaces” which is financially supported by Ministry of Science and Technology (MOST) starting in 2018.

The performance of materials is often improved by stabilizing interfaces between grains by alloying with other elements. Plainifield materials accomplish this goal by tailoring stable interfaces with fewer or no alloying elements, which can improve resource sustainability. (Image by SYNL)

 

[JSCh]

Chinese researchers discover 300,000-year-old ancient human fossils
Source: Xinhua| 2019-05-24 17:59:19|Editor: Li Xia

HEFEI, May 24 (Xinhua) -- Chinese paleontologists have discovered more than 30 ancient human fossils that dated back to about 300,000 years, at an excavation site in Dongzhi County in east China's Anhui Province.

They have also found more than 100 stone artifacts used by ancient humans as well as mammalian fossils of over 40 species. The discoveries are expected to shed new light on how ancient humans in the East Asia continent had evolved, according to the paleontologists.

The fossils and artifacts were discovered during archaeological excavations over the past 15 years at the site, which experts believe to be a collapsed cave, said Wu Xiujie, a member of the research team and a professor with the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences.

"In the cave, we not only have discovered a large number of ancient human fossils, but also found a variety of evidences of ancient human behaviors, which could shed light on scenarios of their life," Wu said.

The fossils include a human skull of the Middle Pleistocene period (from 781,000 to 126,000 years ago) that contains a largely complete facial structure, most of the brain cranium, and one side of the mandible.

The site was first discovered in 2004, when mammalian fossils were accidentally found when a local farmer was building a sheep-holding pen. The first excavation of the site was conducted in the summer of 2006, which yielded a partial human frontal bone, a molar, and stone artifacts.

 

[Grandy]

Science
Chinese scientists develop transistors about the width of a human DNA strand

• Beijing team believes it has solved problem of powering tens of billions of nanometre-sized transistors without burning out the chip

Stephen Chen

Published: 12:00am, 27 May, 2019

Chinese scientists have created 3nm transistors with “high potential for real, serious applications”. Photo: Shutterstock

Chinese scientists say they have created a transistor that will increase the performance of microchips exponentially and dramatically reduce their energy use.

The most advanced computer chips on the market today use seven-nanometre transistors. Professor Yin Huaxiang said his team had developed 3nm transistors – about the width of a human DNA strand – and that tens of billions of them could fit on a fingernail-size chip.

The smaller transistors become, the more can be fitted onto chips, increasing the performance of a processor exponentially, said Yin, deputy director of microelectronics device and integrated technology at the Institute of Microelectronics, the Chinese Academy of Sciences in Beijing.

Transistors are the building blocks of processors. Those built with 3nm transistors would increase computing speed and cut energy consumption, Yin said. So, a smartphone user, for instance, could play games that demanded lots of computing power all day without the need to recharge batteries.

Chip developers at the Institute of Microelectronics believe their breakthroughs in transistors and microchips will propel Chinese technology into a serious rivalry with companies such as Samsung. Photo: AP

The Chinese team, whose research was published in part in peer-reviewed journal IEEE Electron Device Letters this month, had to overcome major obstacles, Yin said. One was the Boltzmann Tyranny, 19th century Austrian physicist Ludwig Boltzmann’s description of a problem involving the distribution of electrons in a space.

For chip developers, this meant that as more and smaller transistors went into microchips, the heat generated by the electricity the transistors needed would burn the chip.

Physicists have proposed solutions to this problem. Yin’s team, using a method known as negative capacitance, was able to power transistors by using half the theoretical minimum amount of electricity required, he said.
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Commercialisation could take a few years as the team worked on materials and quality control.

“This is the most exciting part of our work. It is not just another new finding in a laboratory. It has a high potential for real, serious applications,” Yin said. “And we have the patent.”

The breakthrough would put China into a “head-on competition with the world’s top players at the very front line of chip development”, Yin said.

“In the past, we were watching others fight. Now we are fighting the others.”

While scientists develop a new generation of transistors, the groundbreaking commercial potential of the technology is some time away, they say. Photo: Reuters

In Beijing, a Tsinghua University professor who studied future chip technology said China’s development was rapidly catching up with Western countries as a result of the trade tariffs war being fought out by Beijing and Washington.

“A gap remains, [and] it is unlikely to close overnight with a single breakthrough,” said the academic who declined to be named because of the sensitivity of the work.

While there are transistors about the size of an atom – half a nanometre – in development in China, other countries have joined the race to bring 3nm transistors to market.

Samsung in South Korea said it planned to complete the development of a 3nm transistor by the first half of next year.

Compared to 7-nm technology, Samsung said a processor built with its 3-nm transistors would use half as much power to achieve a 35 per cent higher performance.

The company did not say when it expected those chips to enter production.