Aurelia Butler

A research team led by Professor Jang-Sik Lee of Pohang University of Science and Technology (POSTECH) has successfully developed an halide perovskite-based memory with an ultra-fast switching speed. The findings from this study were published in Nature Communications on June 10, 2021.
Resistive switching memory is a promising contender for next-generation memory device due to its advantages of simple structure and low power consumption. Various materials have been previously studied for resistive switching memory. Among them, halide perovskites are receiving much attention for use in the memory because of low operation voltage and high on/off ratio. However, halide perovskite-based memory devices have limitations of slow switching speed which hinder their practical application in memory devices.
To this, the researchers at POSTECH (Prof. Jang-Sik Lee, Prof. Donghwa Lee, Youngjun Park, and Seong Hun Kim) have successfully developed ultra-fast switching memory devices using halide perovskites by using a combined method of first-principles calculations and experimental verification. From a total of 696 compounds of halide perovskites candidates, Cs3Sb2I9 with a dimer structure was selected as the best candidate for memory application. To verify the calculation results, memory devices using the dimer-structured Cs3Sb2I9 were fabricated. They were then operated with an ultra-fast switching speed of 20 ns, which was more than 100 times faster than the memory devices that used the layer-structured Cs3Sb2I9. In addition, many of the perovskites contain lead (Pb) in the materials which has been raised as an issue. In this work, however, the use of lead-free perovskite eliminates such environmental problems.
“This study provides an important step toward the development of resistive switching memory that can be operated at an ultra-fast switching speed,” remarked Professor Lee on the significance of the research. He added, “this work offers an opportunity to design new materials for memory devices based on calculations and experimental verification.”
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Augmented reality (AR) is poised to revolutionise the way people complete essential everyday tasks, yet older adults — who have much to gain from the technology — will be excluded from using it unless more thought goes into designing software that makes sense to them.
The danger of older adults falling through the gaps has been highlighted by research carried out by scientists at the University of Bath in the UK in collaboration with designers from the Bath-based charity Designability. A paper describing their work has received an honourable mention at this year’s Human Computer Interaction Conference (CHI2021) — the world’s largest conference of its kind.
The study concludes that adults aged 50+ are more likely to be successful at completing AR-prompted tasks (such as ‘pick up the cube’ followed by ‘move the cube to the blue area’) when the steps are shown by a ‘ghosthand’ demonstrating the action rather than the more commonly used arrow or some other visual aid.
According to the research team, many manufacturers of AR software are failing to factor the needs and preferences of older people into their application designs.
“We can’t expect people to benefit from AR technology if they can’t follow the prompts shown to them,” said Dr Christof Lutteroth from the University’s Department of Computer Science.
Thomas Williams, the Doctor of Engineering student (funded by the EPSRC) who conducted the research from the university’s Centre for Digital Entertainment, said: “A lot more thought needs to go into understanding what older adults need from augmented reality, so users in this group understand the prompts they’re given straight away.”
He added: “AR technology has great potential for improving the lives of older adults but most AR designers give little or no thought to the kind of augmentations they use for this population.” More

Think about how many different pieces of technology the average household has purchased in the last decade. Phones, TVs, computers, tablets, and game consoles don’t last forever, and repairing them is difficult and often as expensive as simply buying a replacement.
Electronics are integral to modern society, but electronic waste (e-waste) presents a complex and growing challenge in the path toward a circular economy — a more sustainable economic system that focuses on recycling materials and minimizing waste. Adding to the global waste challenge is the prevalence of dishonest recycling practices by companies who claim to be recycling electronics but actually dispose of them by other means, such as in landfills or shipping the waste to other countries.
New research from the Hypothetical Materials Lab at the University of Pittsburgh Swanson School of Engineering develops a framework to understand the choices a recycler has to make and the role that digital fraud prevention could have in preventing dishonest recycling practices.
“Electronics have huge environmental impacts across their life cycle, from mining rare raw materials to the energy-intensive manufacturing, all the way to the complicated e-waste stream,” said Christopher Wilmer, the William Kepler Whiteford Faculty Fellow and associate professor of chemical and petroleum engineering, who leads the Hypothetical Materials Lab. “A circular economy model is well-suited to mitigating each of these impacts, but less than 40 percent of e-waste is currently estimated to be reused or recycled. If our technology is going to be sustainable, it’s important that we understand the barriers to e-waste recycling.”
Some U.S. firms that have touted safe, ethical and green recycling practices never actually recycle much of what they receive; instead, their e-waste was illegally stockpiled, abandoned or exported. Between 2014 and 2016, the Basel Action Network used GPS trackers in electronics delivered to U.S. recyclers, showing that 30 percent of the products ended up overseas.
The researchers developed a model framework that analyzes dishonest end-of-life electronics management and what leads recyclers to pursue fraudulent activities. They find that the primary way to ensure an e-waste recycler will engage in honest practices with minimum supervision is to make it the more profitable option, either by decreasing the costs of recycling or increasing the penalties for fraudulent practices.
“The main barrier to honest recycling is its cost,” said lead author Daniel Salmon, a graduate student in the Department of Electrical and Computer Engineering. “One of our main findings is that if we find a way to make it more profitable for companies to recycle, we will have less dishonest recycling. Targeted subsidies, higher penalties for fraud and manufacturers ensuring their electronics are more easily recyclable are all things that could potentially solve this problem.”
The researchers also suggest the use of the blockchain as neutral, third-party supervision to avoid fraudulent recycling practices.
“Our model mentions the influence of monitoring and supervision, but self-reporting by companies enables dishonesty. On the other hand, something like the blockchain does not,” said Wilmer, who founded Ledger, the first peer-reviewed scholarly journal dedicated to blockchain and cryptocurrency. “Relying on an immutable record may be one solution to prevent fraud and align behaviors across recyclers toward a circular economy.”
The work is part of a larger NSF-funded convergence research project on the circular economy, which is led by Melissa Bilec, deputy director of the Mascaro Center, associate professor of civil and environmental engineering, and Roberta A. Luxbacher Faculty Fellow at Pitt.
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Materials provided by University of Pittsburgh. Original written by Maggie Pavlick. Note: Content may be edited for style and length. More

A commonly studied perovskite can superfluoresce at temperatures that are practical to achieve and at timescales long enough to make it potentially useful in quantum computing applications. The finding from North Carolina State University researchers also indicates that superfluorescence may be a common characteristic for this entire class of materials.
Superfluorescence is an example of quantum phase transition — when individual atoms within a material all move through the same phases in tandem, becoming a synchronized unit.
For example, when atoms in an optical material such as a perovskite are excited they can individually radiate light, create energy, and fluoresce. Each atom will start moving through these phases randomly, but given the right conditions, they can synchronize in a macroscopic quantum phase transition. That synchronized unit can then interact with external electric fields more strongly than any single atom could, creating a superfluorescent burst.
“Instances of spontaneous synchronization are universal, occurring in everything from planetary orbits to fireflies synchronizing their signals,” says Kenan Gundogdu, professor of physics at NC State and corresponding author of the research. “But in the case of solid materials, these phase transitions were thought to only happen at extremely low temperatures. This is because the atoms move out of phase too quickly for synchronization to occur unless the timing is slowed by cooling.”
Gundogdu and his team observed superfluorescence in the perovskite methyl ammonium lead iodide, or MAPbI3, while exploring its lasing properties. Perovskites are materials with a crystal structure and light-emitting properties useful in creating lasers, among other applications. They are inexpensive, relatively simple to fabricate, and are used in photovoltaics, light sources and scanners.
“When trying to figure out the dynamics behind MAPbI3’s lasing properties, we noticed that the dynamics we observed couldn’t be described simply by lasing behavior,” Gundogdu says. “Normally in lasing one excited particle will emit light, stimulate another one, and so on in a geometric amplification. But with this material we saw synchronization and a quantum phase transition, resulting in superfluorescence.”
But the most striking aspects of the superfluorescence were that it occurred at 78 Kelvin and had a phase lifetime of 10 to 30 picoseconds.
“Generally superfluorescence happens at extremely cold temperatures that are difficult and expensive to achieve, and it only lasts for femtoseconds,” Gundogdu says. “But 78 K is about the temperature of dry ice or liquid nitrogen, and the phase lifetime is two to three orders of magnitude longer. This means that we have macroscopic units that last long enough to be manipulated.”
The researchers think that this property may be more widespread in perovskites generally, which could prove useful in quantum applications such as computer processing or storage.
“Observation of superfluorescence in solid state materials is always a big deal because we’ve only seen it in five or six materials thus far,” Gundogdu says. “Being able to observe it at higher temperatures and longer timescales opens the door to many exciting possibilities.”
The work appears in Nature Photonics and is supported by the National Science Foundation (grant 1729383). NC State graduate students Gamze Findik and Melike Biliroglu are co-first authors. Franky So, Walter and Ida Freeman Distinguished Professor of Materials Science and Engineering, is co-author.
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Materials provided by North Carolina State University. Original written by Tracey Peake. Note: Content may be edited for style and length. More

One vision that is currently driving material scientists is to combine organic molecules (and their diverse functionalities) with the technological possibilities offered by extremely sophisticated semiconductor electronics. Thanks to modern methods of micro- and nanotechnology, the latter designs ever more efficient electronic components for a wide variety of applications. However, it is also increasingly reaching its physical limits: Ever smaller structures for functionalizing semiconductor materials such as silicon cannot be produced using the approaches of classical technology. Scientists have now presented a new approach in the journal Nature Chemistry: They show that stable and yet very well-ordered molecular single layers can be produced on silicon surfaces — by self-assembly. To do this, they use N-heterocyclic carbenes. These are small reactive organic ring molecules whose structure and properties vary in many ways and can be tailored by different “functional” groups.
Researchers led by Prof. Dr. Mario Dähne (TU Berlin, Germany), Prof. Dr. Norbert Esser (TU Berlin and Leibniz Institute for Analytical Sciences, Germany), Prof. Dr. Frank Glorius (University of Münster, Germany), Dr. Conor Hogan (Institute of Structure of Matter, National Research Council of Italy, Rome, Italy) and Prof. Dr. Wolf Gero Schmidt (University of Paderborn, Germany) were involved in the study.
Technological miniaturization reaches its limits
“Instead of trying to artificially produce smaller and smaller structures with increasing effort, it is obvious to learn from molecular structures and processes in nature and to merge their functionality with semiconductor technology,” says chemist Frank Glorius. “This would make an interface, so to speak, between molecular function and the electronic user interface for technical applications.” The prerequisite is that the ultra-small molecules with variable structure and functionality would have to be physically incorporated with the semiconductor devices, and they would have to be reproducible, stable and as simple as possible.
Harnessing the self-organization of molecules
The self-organization of molecules on a surface, as an interface to the device, can perform this task very well. Molecules with a defined structure can be adsorbed on surfaces in large numbers and arrange themselves into a desired structure that is predetermined by the molecular properties. “This works quite well on surfaces of metals, for example, but unfortunately not at all satisfactorily for semiconductor materials so far,” explains physicist Norbert Esser. This is because in order to be able to arrange themselves, the molecules must be mobile (diffuse) on the surface. But molecules on semiconductor surfaces do not do that. Rather, they are so strongly bound to the surface that they stick wherever they hit the surface.
N-Heterocyclic carbenes as a solution
Being simultaneously mobile and yet stably bonded to the surface is the crucial problem and at the same time the key to potential applications. And it is precisely here that the researchers now have a possible solution at hand: N-heterocyclic carbenes. Their use for surface functionalization has attracted a lot of interest over the past decade. On surfaces of metals such as gold, silver and copper, for example, they have proven to be very effective surface ligands, often outperforming other molecules. However, their interaction with semiconductor surfaces has remained virtually unexplored.
Formation of a regular molecular structure
Certain properties of the carbenes are decisive for the fact that it has now been possible for the first time to produce molecular single layers on silicon surfaces: N-heterocyclic carbenes, like other molecules, form very strong covalent bonds with silicon and are thus stably bound. However, side groups of the molecule simultaneously keep them “at a distance” from the surface. Thus, they can still move about on the surface. Although they do not travel very far — only a few atomic distances — this is sufficient to form an almost equally regular molecular structure on the surface of the regularly structured silicon crystal.
Interdisciplinary collaboration
Using a complementary multi-method approach of organic chemical synthesis, scanning probe microscopy, photoelectron spectroscopy and comprehensive material simulations, the researchers clarified the principle of this novel chemical interaction in their interdisciplinary collaboration. They also demonstrated the formation of regular molecular structures in several examples. “This opens a new chapter for the functionalization of semiconductor materials, such as silicon in this case,” emphasizes physicist Dr. Martin Franz, first author of the study.
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Although quantum technology has proven valuable for highly precise timekeeping, making these technologies practical for use in a variety of environments is still a key challenge. In an important step toward portable quantum devices, researchers have developed a new high-flux and compact cold-atom source with low power consumption that can be a key component of many quantum technologies.
“The use of quantum technologies based on laser-cooled atoms has already led to the development of atomic clocks that are used for timekeeping on a national level,” said research team leader Christopher Foot from Oxford University in the U.K. “Precise clocks have many applications in the synchronization of electronic communications and navigation systems such as GPS. Compact atomic clocks that can be deployed more widely, including in space, provide resilience in communications networks because local clocks can maintain accurate timekeeping even if there is a network disruption.”
In The Optical Society (OSA) journal Optics Express, S. Ravenhall, B. Yuen and Foot describe work carried out in Oxford, U.K. to demonstrate a completely new design for a cold atom source. The new device is suitable for a wide range of cold-atom technologies.
“In this project we took a design we made for research purposes and developed it into a compact device,” said Foot. “In addition to timekeeping applications, compact cold-atom devices can also be used for instruments for gravity mapping, inertial navigation and communications and to study physical phenomena in research applications such as dark matter and gravitational waves.”
Cooling atoms with light
Although it may seem counterintuitive, laser light can be used to cool atoms to extremely low temperatures by exerting a force that slows the atoms down. This process can be used to create a cold-atom source that generates a beam of laser-cooled atoms directed toward a region where precision measurements for timekeeping or detecting gravitational waves, for example, are carried out.
Laser cooling usually requires a complicated arrangement of mirrors to shine light onto atoms in a vacuum from all directions. In the new work, the researchers created a completely different design that uses just four mirrors. These mirrors are arranged like a pyramid and placed in a way that allows them to slide past each other like the petals of a flower to create a hole at the top of the pyramid through which the cold atoms are pushed out. The size of this hole can be adjusted to optimize the flow of cold atoms for various applications. The pyramid arrangement reflects the light from a single incoming laser beam that enters the vacuum chamber through a single viewport, thus greatly simplifying the optics.
The mirrors, which are located inside the vacuum region of the cold-atom source, were created by polishing metal and applying a dielectric coating. “The adjustability of this design is an entirely new feature,” said Foot. “Creating a pyramid from four identical polished metal blocks simplifies the assembly, and it can be used without the adjustment mechanism.”
Better measurements with more atoms
To test their new cold-atom source design, the researchers constructed laboratory equipment to fully characterize the flux of atoms emitted through a hole at the apex of the pyramid.
“We demonstrated an exceptionally high flux of rubidium atoms,” said Foot. “Most cold-atom devices take measurements that improve with the number of atoms used. Sources with a higher flux can thus be used to improve measurement accuracy, boost the signal-to-noise ratio or help achieve larger measurement bandwidths.”
The researchers say that the new source is suitable for commercial application. Because it features a small number of components and few assembly steps, scaling up production to produce multiple copies would be straightforward.
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