Aurelia Butler

Self-erasing chips developed at the University of Michigan could help stop counterfeit electronics or provide alerts if sensitive shipments are tampered with.
They rely on a new material that temporarily stores energy, changing the color of the light it emits. It self-erases in a matter of days, or it can be erased on demand with a flash of blue light.
“It’s very hard to detect whether a device has been tampered with. It may operate normally, but it may be doing more than it should, sending information to a third party,” said Parag Deotare, assistant professor of electrical engineering and computer science.
With a self-erasing bar code printed on the chip inside the device, the owner could get a hint if someone had opened it to secretly install a listening device. Or a bar code could be written and placed on integrated circuit chips or circuit boards, for instance, to prove that they hadn’t been opened or replaced on their journeys. Likewise, if the lifespan of the bar codes was extended, they could be written into devices as hardware analogues of software authorization keys.
The self-erasing chips are built from a three-atom-thick layer of semiconductor laid atop a thin film of molecules based on azobenzenes — a kind of molecule that shrinks in reaction to UV light. Those molecules tug on the semiconductor in turn, causing it to emit slightly longer wavelengths of light.
To read the message, you have to be looking at it with the right kind of light. Che-Hsuan Cheng, a doctoral student in material science and engineering in Deotare’s group and the first author on the study in Advanced Optical Materials, is most interested in its application as self-erasing invisible ink for sending secret messages.

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The stretched azobenzene naturally gives up its stored energy over the course of about seven days in the dark — a time that can be shortened with exposure to heat and light, or lengthened if stored in a cold, dark place. Whatever was written on the chip, be it an authentication bar code or a secret message, would disappear when the azobenzene stopped stretching the semiconductor. Alternatively, it can be erased all at once with a flash of blue light. Once erased, the chip can record a new message or bar code.
The semiconductor itself is a “beyond graphene” material, said Deotare, as it has many similarities with the Nobel Prize-winning nanomaterial. But it can also do something graphene can’t: It emits light in particular frequencies.
The research team included the group of Jinsang Kim, professor of material science and engineering. Da Seul Yang, a doctoral student in macromolecular science and engineering, designed and made the molecules. Cheng then floated a single layer of the molecules on water and dipped a silicon wafer into the water to coat it with the molecules.
Then, the chip went to Deotare’s lab to be layered with the semiconductor. Using the “Scotch tape” method, Cheng essentially put sticky tape on a chunk of the semiconductor, tungsten diselenide, and used it to draw off single layers of the material: a sandwich of a single layer of tungsten atoms between two layers of selenium atoms. He used a kind of stamp to transfer the semiconductor onto the azobenzene-coated chip.
Next steps for the research include extending the amount of time that the material can keep the message intact for use as an anti-counterfeit measure.
The research is funded by the Air Force Office of Scientific Research. Kim is also a professor of chemical engineering, biomedical engineering, macromolecular science and engineering, and chemistry.
The University of Michigan has applied for patent protection and is seeking commercial partners to help bring the technology to market. More

Scientists at Tokyo Institute of Technology (Tokyo Tech) have shed light on the relationship between the magnetic properties of topological insulators and their electronic band structure. Their experimental results offer new insights into recent debates regarding the evolution of the band structure with temperature in these materials, which exhibit unusual quantum phenomena and are envisioned to be crucial in next-generation electronics, spintronics, and quantum computers.
Topological insulators have the peculiar property of being electrically conductive on the surface but insulating on their interior. This seemingly simple, unique characteristic allows these materials to host of a plethora of exotic quantum phenomena that would be useful for quantum computers, spintronics, and advanced optoelectronic systems.
To unlock some of the unusual quantum properties, however, it is necessary to induce magnetism in topological insulators. In other words, some sort of ‘order’ in how electrons in the material align with respect to each other needs to be achieved. In 2017, a novel method to achieve this feat was proposed. Termed “magnetic extension,” the technique involves inserting a monolayer of a magnetic material into the topmost layer of the topological insulator, which circumvents the problems caused by other available methods like doping with magnetic impurities.
Unfortunately, the use of magnetic extension led to complex questions and conflicting answers regarding the electronic band structure of the resulting materials, which dictates the possible energy levels of electrons and ultimately determines the material’s conducting properties. Topological insulators are known to exhibit what is known as a “Dirac cone (DC)” in their electronic band structure that resembles two cones facing each other. In theory, the DC is ungapped for ordinary topological insulators, but becomes gapped by inducing magnetism. However, the scientific community has not agreed on the correlation between the gap between the two cone tips and the magnetic characteristics of the material experimentally.
In a recent effort to settle this matter, scientists from multiple universities and research institutes carried out a collaborative study led by Assoc Prof Toru Hirahara from Tokyo Tech, Japan. They fabricated magnetic topological structures by depositing Mn and Te on Bi2Te3, a well-studied topological insulator. The scientists theorized that extra Mn layers would interact more strongly with Bi2Te3 and that emerging magnetic properties could be ascribed to changes in the DC gap, as Hirahara explains: “We hoped that strong interlayer magnetic interactions would lead to a situation where the correspondence between the magnetic properties and the DC gap were clear-cut compared with previous studies.”
By examining the electronic band structures and photoemission characteristics of the samples, they demonstrated how the DC gap progressively closes as temperature increases. Additionally, they analyzed the atomic structure of their samples and found two possible configurations, MnBi2Te4/Bi2Te3 and Mn4Bi2Te7/Bi2Te3, the latter of which is responsible for the DC gap.
However, a peculiarly puzzling finding was that the temperature at which the DC gap closes is well over the critical temperature (TC), above which materials lose their permanent magnetic ordering. This is in stark contrast with previous studies that indicated that the DC gap can still be open at a temperature higher than the TC of the material without closing. On this note, Hirahara remarks: “Our results show, for the first time, that the loss of long-range magnetic order above the TC and the DC gap closing are not correlated.”
Though further efforts will be needed to clarify the relationship between the nature of the DC gap and magnetic properties, this study is a step in the right direction. Hopefully, a deeper understanding of these quantum phenomena will help us reap the power of topological insulators for next-generation electronics and quantum computing.

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Administering neuropsychology evaluations to children online in the comfort of their own homes is feasible and delivers results comparable to tests traditionally performed in a clinic, a new study led by UT Southwestern researchers and Children’s Health indicates. The finding, published online this month in the Archives of Clinical Neuropsychology, could help expand access to specialists and reduce barriers to care, particularly as the popularity of telemedicine grows during the COVID-19 pandemic.
Patients with a variety of neurological disorders require periodic neuropsychological evaluations to track their cognition, academic skills, memory, attention, and other variables. Typically, these tests are done in clinics, often by specialists in these disorders.
However, explains Lana Harder, Ph.D., ABPP, associate professor of psychiatry and neurology at UTSW, many patients travel hundreds of miles to access specialists for their care — a major expense and inconvenience that can also cause fatigue and potentially influence the results. Harder also leads the neuropsychology service and is the neuropsychology training director at Children’s Health.
Research on adults has shown that these evaluations can be done effectively, with the examiner and patient in different rooms. However, those tests were conducted in controlled clinic or laboratory settings rather than patients’ homes, where distractions and technological glitches could confound results. Plus, none of the earlier studies involved children, a population that has its own unique challenges.
To evaluate whether teleneuropsychology evaluations could be effectively performed with children at home, Harder, along with Benjamin Greenberg, M.D., professor of neurology and pediatrics at UTSW and co-director with Harder of the Pediatric CONQUER Program at Children’s, and their colleagues recruited 58 patients primarily from the Pediatric Demyelinating Disease Program at Children’s Medical Center Dallas. This clinic treats patients with neurological autoimmune disorders that target myelin, an insulating layer on nerve cells that is critical to their function. The disorders include transverse myelitis, multiple sclerosis, acute disseminated encephalomyelitis, optic neuritis, and neuromyelitis optica. The patients ranged in age from 6 to 20 and traveled up to 2,033 miles for visits to the clinic.
Each child received the same 90-minute neuropsychology battery twice — once at home and once at the clinic — spaced apart by about 16 days. Half the group received the home test first; the other half got the clinic test first.

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For the home test, children received a packet of testing materials prior to their test date and, if they did not have a computer or tablet at home, borrowed a tablet from the researchers’ office in advance. For both tests, parents or other caregivers left the room, allowing the patient and researcher to interact one on one.
The home-based environment had unique challenges compared with the clinic, Greenberg explains: Any distraction, from a barking dog to a doorbell, or technological glitches, such as a poor internet connection, could invalidate the results. While distractions and technology problems occurred intermittently during remote sessions, these were typically fleeting and generally did not interfere with testing sessions.
When the researchers compared the results obtained from the home- and clinic-based tests, no significant differences were found.
But it’s not enough to show that the home-based testing is comparable to the clinic, Harder notes — patients and their caregivers must also be willing and interested in remote testing to make it feasible. To that end, the researchers gave each patient and their caregivers a survey to assess their level of satisfaction with the videoconference-based test. The vast majority (94 percent of caregivers and 90 percent of participants) responded that they were satisfied with home-based testing. If given a choice between remote or in-person, most indicated no preference.
Teleneuropsychology testing still needs to be evaluated over a broader age range and array of conditions and measures before it becomes a staple in the field, Harder says. But having this as an option could eventually help children avoid having to travel far distances to access specialists or avoid exposure from in-person visits — a boon during the era of COVID-19, she adds.
“This model could allow these young and often medically fragile children to stay put but still receive the care that they need,” Harder says.
Other researchers who contributed to this study include Joy Neumann, Morgan McCreary, and C. Munro Cullum, all of UTSW; Ana Hernandez of Children’s Medical Center; and Cole Hague, of Boston Children’s Hospital.
This work was supported by the National Multiple Sclerosis Society and the Children’s Trust.
Greenberg is a Distinguished Teaching Professor and a Cain Denius Scholar in Mobility Disorders. Cullum holds the Pam Blumenthal Distinguished Professorship in Clinical Psychology. More

The colloidal diamond has been a dream of researchers since the 1990s. These structures — stable, self-assembled formations of miniscule materials — have the potential to make light waves as useful as electrons in computing, and hold promise for a host of other applications. But while the idea of colloidal diamonds was developed decades ago, no one was able to reliably produce the structures. Until now.
Researchers led by David Pine, professor of chemical and biomolecular engineering at the NYU Tandon School of Engineering and professor of physics at NYU, have devised a new process for the reliable self-assembly of colloids in a diamond formation that could lead to cheap, scalable fabrication of such structures. The discovery, detailed in “Colloidal Diamond,” appearing in the September 24 issue of Nature, could open the door to highly efficient optical circuits leading to advances in optical computers and lasers, light filters that are more reliable and cheaper to produce than ever before, and much more.
Pine and his colleagues, including lead author Mingxin He, a postdoctoral researcher in the Department of Physics at NYU, and corresponding author Stefano Sacanna, associate professor of chemistry at NYU, have been studying colloids and the possible ways they can be structured for decades. These materials, made up of spheres hundreds of times smaller than the diameter of a human hair, can be arranged in different crystalline shapes depending on how the spheres are linked to one another. Each colloid attaches to another using strands of DNA glued to surfaces of the colloids that function as a kind of molecular Velcro. When colloids collide with each other in a liquid bath, the DNA snags and the colloids are linked. Depending on where the DNA is attached to the colloid, they can spontaneously create complex structures.
This process has been used to create strings of colloids and even colloids in a cubic formation. But these structures did not produce the Holy Grail of photonics — a band gap for visible light. Much as a semiconductor filters out electrons in a circuit, a band gap filters out certain wavelengths of light. Filtering light in this way can be reliably achieved by colloids if they are arranged in a diamond formation, a process deemed too difficult and expensive to perform at commercial scale.
“There’s been a great desire among engineers to make a diamond structure,” said Pine. “Most researchers had given up on it, to tell you the truth — we may be the only group in the world who is still working on this. So I think the publication of the paper will come as something of a surprise to the community.”
The investigators, including Etienne Ducrot, a former postdoc at NYU Tandon, now at the Centre de Recherche Paul Pascal — CNRS, Pessac, France; and Gi-Ra Yi of Sungkyunkwan University, Suwon, South Korea, discovered that they could use a steric interlock mechanism that would spontaneously produce the necessary staggered bonds to make this structure possible. When these pyramidal colloids approached each other, they linked in the necessary orientation to generate a diamond formation. Rather than going through the painstaking and expensive process of building these structures through the use of nanomachines, this mechanism allows the colloids to structure themselves without the need for outside interference. Furthermore, the diamond structures are stable, even when the liquid they form in is removed.
The discovery was made because He, a graduate student at NYU Tandon at the time, noticed an unusual feature of the colloids he was synthesizing in a pyramidal formation. He and his colleagues drew out all of the ways these structures could be linked. When they happened upon a particular interlinked structure, they realized they had hit upon the proper method. “After creating all these models, we saw immediately that we had created diamonds,” said He.
“Dr. Pine’s long-sought demonstration of the first self-assembled colloidal diamond lattices will unlock new research and development opportunities for important Department of Defense technologies which could benefit from 3D photonic crystals,” said Dr. Evan Runnerstrom, program manager, Army Research Office (ARO), an element of the U.S. Army Combat Capabilities Development Command’s Army Research Laboratory.
He explained that potential future advances include applications for high-efficiency lasers with reduced weight and energy demands for precision sensors and directed energy systems; and precise control of light for 3D integrated photonic circuits or optical signature management.
“I am thrilled with this result because it wonderfully illustrates a central goal of ARO’s Materials Design Program — to support high-risk, high-reward research that unlocks bottom-up routes to creating extraordinary materials that were previously impossible to make.”
The team, which also includes John Gales, a graduate student in physics at NYU, and Zhe Gong, a postdoc at the University of Pennsylvania, formerly a graduate student in chemistry at NYU, are now focused on seeing how these colloidal diamonds can be used in a practical setting. They are already creating materials using their new structures that can filter out optical wavelengths in order to prove their usefulness in future technologies.
This research was supported by the US Army Research Office under award number W911NF-17-1-0328. Additional funding was provided by the National Science Foundation under award number DMR-1610788. More

Biofilms — microbial communities that form slimy layers on surfaces — are difficult to treat and remove, often because the microbes release molecules that block the entry of antibiotics and other therapies. Now, researchers reporting in ACS Applied Materials & Interfaces have made magnetically propelled microbots derived from tea buds, which they call “T-Budbots,” that can dislodge biofilms, release an antibiotic to kill bacteria, and clean away the debris. Watch a video of the T-Budbots here.
Many hospital-acquired infections involve bacterial biofilms that form on catheters, joint prostheses, pacemakers and other implanted devices. These microbial communities, which are often resistant to antibiotics, can slow healing and cause serious medical complications. Current treatment includes repeated high doses of antibiotics, which can have side effects, or in some cases, surgical replacement of the infected device, which is painful and costly. Dipankar Bandyopadhyay and colleagues wanted to develop biocompatible microbots that could be controlled with magnets to destroy biofilms and then scrub away the mess. The team chose Camellia sinensis tea buds as the raw material for their microbots because the buds are porous, non-toxic, inexpensive and biodegradable. Tea buds also contain polyphenols, which have antimicrobial properties.
The researchers ground some tea buds and isolated porous microparticles. Then, they coated the microparticles’ surfaces with magnetite nanoparticles so that they could be controlled by a magnet. Finally, the antibiotic ciprofloxacin was embedded within the porous structures. The researchers showed that the T-Budbots released the antibiotic primarily under acidic conditions, which occur in bacterial infections. The team then added the T-Budbots to bacterial biofilms in dishes and magnetically steered them. The microbots penetrated the biofilm, killed the bacteria and cleaned the debris away, leaving a clear path in their wake. Degraded remnants of the biofilm adhered to the microbots’ surfaces. The researchers note that this was a proof-of-concept study, and further optimization is needed before the T-Budbots could be deployed to destroy biofilms in the human body.
Video: https://www.youtube.com/watch?v=-_GxUTO0qGI&pp=QAA%3D

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A BCI is an apparatus that allows an individual to control a machine or computer directly from their brain. Non-invasive means of control like electroencephalogram (EEG) readings taken through the skull are safe and convenient compared to more risky invasive methods using a brain implant, but they take longer to learn and users ultimately vary in proficiency.
He and collaborators conducted a large-scale human study enrolling subjects in a weekly 8-week course in simple, widely-practiced meditation techniques, to test their effect as a potential training tool for BCI control. A total of 76 people participated in this study, each being randomly assigned to the meditation group or the control group, which had no preparation during these 8 weeks. Up to 10 sessions of BCI study were conducted with each subject. He’s work shows that humans with just eight lessons in mindfulness-based attention and training (MBAT) demonstrated significant advantages compared to those with no prior meditation training, both in their initial ability to control BCI’s and in the time it took for them to achieve full proficiency.
After subjects in the MBAT group completed their training course they, along with a control group, were charged with learning to control a simple BCI system by navigating a cursor across a computer screen using their thought. This required them to concentrate their focus and visualize the movement of the cursor within their head. During the course of the process, He’s team monitored their performance and brain activity via EEG.
As stated prior, the team found that those with training in MBAT were more successful in controlling the BCI, both initially and over time. Interestingly, the researchers found that differences in brain activity between the two sample groups corresponded directly with their success. The meditation group showed significantly enhanced capability of modulating their alpha rhythm, the activity pattern monitored by the BCI system to mentally control the movement of a computer cursor.
His findings are very important for the process of BCI training and the overall feasibility of non-invasive BCI control via EEG. While prior work from his group has shown that long-term meditators were better able to overcome the difficulty of learning non-invasive mind control, this work shows that just a short period of MBAT training can significantly improve a subject’s skill with a BCI. This suggests that education in MBAT could provide a significant addition to BCI training. “Meditation has been widely practiced for well-being and improving health,” said He. Our work demonstrates that it can also enhance a person’s mental power for mind control, and may facilitate broad use of noninvasive brain-computer interface technology.”
It could also inform neuroscientists and clinicians working in BCI design and maintenance. A thorough understanding of the brain is crucial for creating the machine learning algorithms BCI’s use to interpret brain signals. This knowledge is especially important in BCI recalibration, which can be time-consuming and frequently necessary for non-invasive BCI’s.
The work of He and his team presents a new application for a well-known and widely practiced form of meditation, and may even offer insights into the neurological effects of meditation and how it may be adapted for better BCI training. This study offers novel information for researchers of BCI’s and presents a new tool for both understanding the brain and preparing subjects to use a BCI.

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Materials provided by College of Engineering, Carnegie Mellon University. Original written by Dan Carroll. Note: Content may be edited for style and length. More

Physicists at Chalmers University of Technology in Sweden, together with colleagues in Russia and Poland, have managed to achieve ultrastrong coupling between light and matter at room temperature. The discovery is of importance for fundamental research and might pave the way for advances within, for example, light sources, nanomachinery, and quantum technology.
A set of two coupled oscillators is one of the most fundamental and abundant systems in physics. It is a very general toy model that describes a plethora of systems ranging from guitar strings, acoustic resonators, and the physics of children’s swings, to molecules and chemical reactions, from gravitationally bound systems to quantum cavity electrodynamics.
The degree of coupling between the two oscillators is an important parameter that mostly determines the behaviour of the coupled system. However, the question is rarely asked about the upper limit by which two pendula can couple to each other — and what consequences such coupling can have.
The newly presented results, published in Nature Communications, offer a glimpse into the domain of the so called ultrastrong coupling, wherein the coupling strength becomes comparable to the resonant frequency of the oscillators. The coupling in this work is realised through interaction between light and electrons in a tiny system consisting of two gold mirrors separated by a small distance and plasmonic gold nanorods. On a surface that is a hundred times smaller than the end of a human hair, the researchers have shown that it is possible to create controllable ultrastrong interaction between light and matter at ambient conditions — that is, at room temperature and atmospheric pressure.
“We are not the first ones to realise ultrastrong coupling. But generally, strong magnetic fields, high vacuum and extremely low temperatures are required to achieve such a degree of coupling. When you can perform it in an ordinary lab, it enables more researchers to work in this field and it provides valuable knowledge in the borderland between nanotechnology and quantum optics,” says Denis Baranov, a researcher at Chalmers University of Technology and the first author of the scientific paper.
To understand the system the authors have realised, one can imagine a resonator, in this case represented by two gold mirrors separated by a few hundred nanometers, as a single tone in music. The nanorods fabricated between the mirrors affect how light moves between the mirrors and change their resonance frequency. Instead of just sounding like a single tone, in the coupled system the tone splits into two: a lower pitch, and a higher pitch.
The energy separation between the two new pitches represents the strength of interaction. Specifically, in the ultrastrong coupling case, the strength of interaction is so large that it becomes comparable to the frequency of the original resonator. This leads to a unique duet, where light and matter intermix into a common object, forming quasi-particles called polaritons. The hybrid character of polaritons provides a set of intriguing optical and electronic properties.
The number of gold nanorods sandwiched between the mirrors controls how strong the interaction is. But at the same time, it controls the so-called zero-point energy of the system. By increasing or decreasing the number of rods, it is possible to supply or remove energy from the ground state of the system and thereby increase or decrease the energy stored in the resonator box.
What makes this work particularly interesting is that the authors managed to indirectly measure how the number of nanorods changes the vacuum energy by “listening” to the tones of the coupled system (that is, looking at the light transmission spectra through the mirrors with the nanorods) and performing simple mathematics. The resulting values turned out to be comparable to the thermal energy, which may lead to observable phenomena in the future.
“A concept for creating controllable ultrastrong coupling at room temperature in relatively simple systems can offer a testbed for fundamental physics. The fact that this ultrastrong coupling “costs” energy could lead to observable effects, for example it could modify the reactivity of chemicals or tailor van der Waals interactions. Ultrastrong coupling enables a variety of intriguing physical phenomena,” says Timur Shegai, Associate Professor at Chalmers and the last author of the scientific article.
In other words, this discovery allows researchers to play with the laws of nature and to test the limits of coupling.
“As the topic is quite fundamental, potential applications may range. Our system allows for reaching even stronger levels of coupling, something known as deep strong coupling. We are still not entirely sure what is the limit of coupling in our system, but it is clearly much higher than we see now. Importantly, the platform that allows studying ultrastrong coupling is now accessible at room temperature,” says Timur Shegai.

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Materials provided by Chalmers University of Technology. Original written by Mia Halleröd Palmgren. Note: Content may be edited for style and length. More