Computers Math

Researchers at MIT have developed a technique for precisely controlling the arrangement and placement of nanoparticles on a material, like the silicon used for computer chips, in a way that does not damage or contaminate the surface of the material.
The technique, which combines chemistry and directed assembly processes with conventional fabrication techniques, enables the efficient formation of high-resolution, nanoscale features integrated with nanoparticles for devices like sensors, lasers, and LEDs, which could boost their performance.
Transistors and other nanoscale devices are typically fabricated from the top down — materials are etched away to reach the desired arrangement of nanostructures. But creating the smallest nanostructures, which can enable the highest performance and new functionalities, requires expensive equipment and remains difficult to do at scale and with the desired resolution.
A more precise way to assemble nanoscale devices is from the bottom up. In one scheme, engineers have used chemistry to “grow” nanoparticles in solution, drop that solution onto a template, arrange the nanoparticles, and then transfer them to a surface. However, this technique also involves steep challenges. First, thousands of nanoparticles must be arranged on the template efficiently. And transferring them to a surface typically requires a chemical glue, large pressure, or high temperatures, which could damage the surfaces and the resulting device.
The MIT researchers developed a new approach to overcome these limitations. They used the powerful forces that exist at the nanoscale to efficiently arrange particles in a desired pattern and then transfer them to a surface without any chemicals or high pressures, and at lower temperatures. Because the surface material remains pristine, these nanoscale structures can be incorporated into components for electronic and optical devices, where even minuscule imperfections can hamper performance.
“This approach allows you, through engineering of forces, to place the nanoparticles, despite their very small size, in deterministic arrangements with single-particle resolution and on diverse surfaces, to create libraries of nanoscale building blocks that can have very unique properties, whether it is their light-matter interactions, electronic properties, mechanical performance, etc.,” says Farnaz Niroui, the EE Landsman Career Development Assistant Professor of Electrical Engineering and Computer Science (EECS) at MIT, a member of the MIT Research Laboratory of Electronics, and senior author on a new paper describing the work. “By integrating these building blocks with other nanostructures and materials we can then achieve devices with unique functionalities that would not be readily feasible to make if we were to use the conventional top-down fabrication strategies alone.”
The research is published in Science Advances. Niroui’s co-authors are lead author Weikun “Spencer” Zhu, a graduate student in the Department of Chemical Engineering, as well as EECS graduate students Peter F. Satterthwaite, Patricia Jastrzebska-Perfect, and Roberto Brenes. More

Until recently, it was widely believed among physicists that it was impossible to compress light below the so-called diffraction limit, except when using metal nanoparticles, which unfortunately also absorb light. It therefore seemed impossible to compress light strongly in dielectric materials such as silicon, which are key materials in information technologies and come with the important advantage that they do not absorb light. Interestingly, it was shown theoretically already in 2006 that the diffraction limit also does not apply to dielectrics. Still, no one has succeeded in showing this in the real world, simply because it requires such advanced nanotechnology that no one has been able to build the necessary dielectric nanostructures until now.
A research team from DTU has successfully designed and built a structure, a so-called dielectric nanocavity, which concentrates light in a volume 12 times below the diffraction limit. The result is ground-breaking in optical research and has just been published in Nature Communications.
“Although computer calculations show that you can concentrate light at an infinitely small point, this only applies in theory. The actual results are limited by how small details can be made, for example, on a microchip,” says Marcus Albrechtsen, PhD-student at DTU Electro and first author of the new article.
“We programmed our knowledge of real photonic nanotechnology and its current limitations into a computer. Then we asked the computer to find a pattern that collects the photons in an unprecedentedly small area — in an optical nanocavity — which we were also able to build in the laboratory.”
Optical nanocavities are structures specially designed to retain light so that it does not propagate as we are used to but is thrown back and forth as if you put two mirrors facing each other. The closer you place the mirrors to each other, the more intense the light between the mirrors becomes. For this experiment, the researchers have designed a so-called bowtie structure, which is particularly effective at squeezing the photons together due to its special shape.
Interdisciplinary efforts and excellent methods
The nanocavity is made of silicon, the dielectric material on which most advanced modern technology is based. The material for the nanocavity was developed in cleanroom laboratories at DTU, and the patterns on which the cavity is based are optimized and designed using a unique method for topology optimization developed at DTU. Initially developed to design bridges and aircraft wings, it is now also used for nanophotonic structures. More

The LiDAR sensor, which recognizes objects by projecting light onto them, functions as eyes for autonomous vehicles by helping to identify the distance to surrounding objects and speed or direction of the vehicle. To detect unpredictable conditions on the road and nimbly respond, the sensor must perceive the sides and rear as well as the front of the vehicle. However, it has been impossible to observe the front and rear of the vehicle simultaneously because a rotating LiDAR sensor was used.
To overcome this issue, a research team led by Professor Junsuk Rho (Department of Mechanical Engineering and Department of Chemical Engineering) and Ph.D. candidates Gyeongtae Kim, Yeseul Kim, and Jooyeong Yun (Department of Mechanical Engineering) from POSTECH has developed a fixed LiDAR sensor that has 360° view, in collaboration with Professor Inki Kim (Department of Biophysics) from Sungkyunkwan University.
This new sensor is drawing attention as an original technology that can enable an ultra-small LiDAR sensor since it is made from the metasurface, which is an ultra-thin flat optical device that is only one-thousandth the thickness of a human hair strand.
Using the metasurface can greatly expand the viewing angle of the LiDAR to recognize objects three-dimensionally. The research team succeeded in extending the viewing angle of the LiDAR sensor to 360° by modifying the design and periodically arranging the nanostructures that make up the metasurface.
It is possible to extract three-dimensional information of objects in 360° regions by scattering more than 10,000 dot array (light) from the metasurface to objects and photographing the irradiated point pattern with a camera.
This type of LiDAR sensor is used for the iPhone face recognition function (Face ID). The iPhone uses a dot projector device to create the point sets but has several limitations; the uniformity and viewing angle of the point pattern are limited, and the size of the device is large.
The study is significant in that the technology that allows cell phones, augmented and virtual reality (AR/VR) glasses, and unmanned robots to recognize the 3D information of the surrounding environment is fabricated with nano-optical elements. By utilizing nanoimprint technology, it is easy to print the new device on various curved surfaces, such as glasses or flexible substrates, which enables applications to AR glasses, known as the core technology of future displays.
Professor Junsuk Rho explained, “We have proved that we can control the propagation of light in all angles by developing a technology more advanced than the conventional metasurface devices.” He added, “This will be an original technology that will enable an ultra-small and full-space 3D imaging sensor platform.”
Recently published in Nature Communications, this study was conducted with the support from the Samsung Research Funding & Incubation Center.
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Materials provided by Pohang University of Science & Technology (POSTECH). Note: Content may be edited for style and length. More

Biomedical and electrical engineers at UNSW Sydney have developed a new way to measure neural activity using light — rather than electricity — which could lead to a complete reimagining of medical technologies like nerve-operated prosthetics and brain-machine interfaces.
Professor François Ladouceur, with UNSW’s School of Electrical Engineering and Telecommunications, says the multi-disciplinary team has just demonstrated in the lab what it proved theoretically shortly before the pandemic: that sensors built using liquid crystal and integrated optics technologies — dubbed ‘optrodes’ — can register nerve impulses in a living animal body.
Not only do these optrodes perform just as well as conventional electrodes — that use electricity to detect a nerve impulse — but they also address “very thorny issues that competing technologies cannot address,” says Prof. Ladouceur.
“Firstly, it’s very difficult to shrink the size of the interface using conventional electrodes so that thousands of them can connect to thousands of nerves within a very small area.
“One of the problems as you shrink thousands of electrodes and put them ever closer together to connect to the biological tissues is that their individual resistance increases, which degrades the signal-to-noise ratio so we have a problem reading the signal. We call this ‘impedance mismatch’.
“Another problem is what we call ‘crosstalk’ — when you shrink these electrodes and bring them closer together, they start to talk to, or affect each other because of their proximity.”
But because optrodes use light and not electricity to detect neural signals, the problems of impedance mismatch is redundant and crosstalk minimised. More

Remember iron-on decals? All you had to do was print something out on special paper with a home printer, then transfer it onto a T-shirt using an iron. Now, scientists have developed a very similar scheme, but instead of family photos or logos, it prints circuitry. The method, reported in ACS Applied Materials & Interfaces, can print functional circuits onto items ranging from ukuleles to teacups.
As electronics continue to evolve, so too do the circuit boards that control them. Most boards used today are rigid, built on solid fiberglass backings. As electronic systems are integrated into floppy and pliable items, such as clothing and soft robots, electronics need to be flexible too. This has led to increased interest in liquid metal circuits, which often include a special alloy of gallium metal that is a liquid at room temperature. One way to make these devices is to print them out with a modified inkjet or 3D printer. But these methods require complicated steps and sophisticated equipment, making the resulting devices expensive and unsuitable for large-scale manufacturing. To make the fabrication process quicker, easier and cheaper, Xian Huang and colleagues wanted to develop a method of creating liquid metal circuitry using a desktop laser printer that could place the electronics onto many types of surfaces.
To create the circuits, the researchers printed out a connected design onto heat-transferrable thermal paper with an ordinary laser printer. The printer laid down a carbon-based toner, which was transferred to a pane of glass by heating it. These toner patterns roughened the surface and created a hydrophobic gap of air between the carbon and the liquid metal. This prevented the metal from sticking when brushed on top, so the electronic ink-based pattern only adhered on the exposed parts of the surface.
This circuit could then be stuck directly to a smooth surface, such as a plastic soda bottle. If the surface was too uneven, like the bumpy skin of an orange, the device was first placed on a piece of flexible plastic, then onto the rougher surface. Regardless of how they were attached, however, the simple electronics all functioned as intended on their various substrates — from displaying images, to RFID tagging, to sensing temperature and sound. The researchers say that this protocol should greatly expand the applications of liquid metal circuits.
The authors acknowledge funding from the Key Research and Development Program of Zhejiang Province and the National Natural Science Foundation of China.
Video: https://youtu.be/HQattovte08
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Materials provided by American Chemical Society. Note: Content may be edited for style and length. More

For students learning a second or foreign language, text is often simplified to ensure that they can comprehend it well enough to understand the core message. Usually, complicated text in a foreign language is simplified manually by teachers or material designers. However, with the advent of artificial intelligence (AI)-based software, automatic simplification of text is now a reality. One such tool is the automatic text simplification (ATS) software, which simplifies text in second and foreign languages for L2 learners. Currently, there is limited data on the effectiveness of an ATS software in an educational setting.
To address this, Professor Dennis Murphy Odo from the Department of English Education at Pusan National University conducted a study, published in Applied Linguistics, to assess how L2 learners comprehend English language text simplified by an ATS tool. For this purpose, he recruited 61 native Korean speakers who had been studying English for the past 10 years, with reading proficiencies ranging from low to high.
These L2 learners were divided into low and high L2 reading proficiency groups and assigned to read either authentic English text derived from the Scientific American website, or automatically simplified version of that same text using a ‘Yet Another Text Simplifier’ (YATS) ATS tool. Following this, the L2 learners from both groups took a free recall test and a multiple-choice (MC) comprehension test, that tested their ability to recall and comprehend the text.
The key finding, derived from an analysis of the free recall test scores was that L2 learners with a higher reading proficiency found automatically simplified text more comprehensible, as compared to L2 learners with a lower reading proficiency.
While discussing this finding Prof. Odo remarks, “Although online automated text simplification tools can prove to be highly useful in making authentic materials more comprehensible for L2 learners beyond a certain level of foreign language reading proficiency, they may not do so for learners with a lower level of reading proficiency.”
Hence, ATS software can help L2 students with a high reading proficiency understand complicated text, and support teachers in simplifying challenging text for their students.
However, there is a need for ATS tools to be developed further, in order to make text comprehensible enough for L2 learners with low reading proficiencies. “On the positive side, software developers will continue to develop AI-enhanced tools that will make challenging texts more and more comprehensible to foreign language learners with different reading proficiencies,” says Prof. Odo in conclusion.
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Materials provided by Pusan National University. Note: Content may be edited for style and length. More

In a study that confirms its promise as the next-generation semiconductor material, UC Santa Barbara researchers have directly visualized the photocarrier transport properties of cubic boron arsenide single crystals.
“We were able to visualize how the charge moves in our sample,” said Bolin Liao, an assistant professor of mechanical engineering in the College of Engineering. Using the only scanning ultrafast electron microscopy (SUEM) setup in operation at a U.S. university, he and his team were able to make “movies” of the generation and transport processes of a photoexcited charge in this relatively little-studied III-V semiconductor material, which has recently been recognized as having extraordinary electrical and thermal properties. In the process, they found another, beneficial property that adds to the material’s potential as the next great semiconductor.
Their research, conducted in collaboration with physics professor Zhifeng Ren’s group at the University of Houston, who specialize in fabricating high-quality single crystals of cubic boron arsenide, appears in the journal Matter.
‘Ringing the Bell’
Boron arsenide is being eyed as a potential candidate to replace silicon, the computer world’s staple semiconductor material, due to its promising performance. For one thing, with an improved charge mobility over silicon, it easily conducts current (electrons and their positively charged counterpart, “holes”). However, unlike silicon, it also conducts heat with ease.
“This material actually has 10 times higher thermal conductivity than silicon,” Liao said. This heat conducting — and releasing — ability is particularly important as electronic components become smaller and more densely packed, and pooled heat threatens the devices’ performance, he explained. More

Using a simple set of magnets, MIT researchers have come up with a sophisticated way to monitor muscle movements, which they hope will make it easier for people with amputations to control their prosthetic limbs.
In a new pair of papers, the researchers demonstrated the accuracy and safety of their magnet-based system, which can track the length of muscles during movement. The studies, performed in animals, offer hope that this strategy could be used to help people with prosthetic devices control them in a way that more closely mimics natural limb movement.
“These recent results demonstrate that this tool can be used outside the lab to track muscle movement during natural activity, and they also suggest that the magnetic implants are stable and biocompatible and that they don’t cause discomfort,” says Cameron Taylor, an MIT research scientist and co-lead author of both papers.
In one of the studies, the researchers showed that they could accurately measure the lengths of turkeys’ calf muscles as the birds ran, jumped, and performed other natural movements. In the other study, they showed that the small magnetic beads used for the measurements do not cause inflammation or other adverse effects when implanted in muscle.
“I am very excited for the clinical potential of this new technology to improve the control and efficacy of bionic limbs for persons with limb-loss,” says Hugh Herr, a professor of media arts and sciences, co-director of the K. Lisa Yang Center for Bionics at MIT, and an associate member of MIT’s McGovern Institute for Brain Research.
Herr is a senior author of both papers, which appear today in the journal Frontiers in Bioengineering and Biotechnology. Thomas Roberts, a professor of ecology, evolution, and organismal biology at Brown University, is a senior author of the measurement study. More