Aurelia Butler

Our current chip technology is largely based on silicon. Only in very special components a small amount of germanium is added. But there are good reasons to use higher germanium contents in the future: The compound semiconductor silicon-germanium has decisive advantages over today’s silicon technology in terms of energy efficiency and achievable clock frequencies.
The main problem here is to establish contacts between metal and semiconductor on a nanoscale in a reliable way. This is much more difficult with a high proportion of germanium than with silicon. The team at TU Wien, however, together with research teams from Linz and Thun (Switzerland), has now shown that this problem can be solved — with contacts made of crystalline aluminium of extremely high quality and a sophisticated silicon germanium layer system. This enables different interesting contact properties — especially for optoelectronic and quantum components.
The problem with oxygen
“Every semiconductor layer is automatically contaminated in conventional processes; this simply cannot be prevented at the atomic level,” says Masiar Sistani from the Institute for Solid State Electronics at TU Wien. First and foremost, it is oxygen atoms that accumulate very quickly on the surface of the materials — an oxide layer is formed.
With silicon, however, this is not a problem: silicon always forms exactly the same kind of oxide. “With germanium, however, things are much more complicated,” explains Masiar Sistani. “In this case, there is a whole range of different oxides that can form. But that means that different nanoelectronic devices can have very different surface compositions and therefore different electronic properties.”
If you now want to connect a metallic contact to these components, you have a problem: Even if you try very hard to produce all these components in exactly the same way, there are still inevitably massive differences — and that makes the material complex to handle for use in the semiconductor industry. More

Universitat Autònoma de Barcelona researchers have developed a magnetic material capable of imitating the way the brain stores information. The material makes it possible to emulate the synapses of neurons and mimic, for the first time, the learning that occurs during deep sleep.
Neuromorphic computing is a new computing paradigm in which the behavior of the brain is emulated by mimicking the main synaptic functions of neurons. Among these functions is neuronal plasticity: the ability to store information or forget it depending on the duration and repetition of the electrical impulses that stimulate neurons, a plasticity that would be linked to learning and memory.
Among the materials that mimic neuron synapses, memresistive materials, ferroelectrics, phase change memory materials, topological insulators and, more recently, magneto-ionic materials stand out. In the latter, changes in the magnetic properties are induced by the displacement of ions within the material caused by the application of an electric field. In these materials it is well known how the magnetism is modulated when applying the electric field, but the evolution of magnetic properties when voltage is stopped (that is, the evolution after the stimulus) is difficult to control. This makes it complicated to emulate some brain-inspired functions, such as maintaining the efficiency of learning that takes place even while the brain is in a state of deep sleep (i.e., without external stimulation).
This study, led by researchers from the UAB Department of Physics Jordi Sort and Enric Menéndez, in collaboration with the ALBA Synchrotron, the Catalan Institute of Nanoscience and Nanotechnology (ICN2) and the ICMAB, proposes a new way of controlling the evolution of magnetization both in the stimulated and in the post-stimulus states.
The researchers have developed a material based on a thin layer of cobalt mononitride (CoN) where, by applying an electric field, the accumulation of N ions at the interface between the layer and a liquid electrolyte in which the layer has been placed can be controlled. “The new material works with the movement of ions controlled by electrical voltage, in a manner analogous to our brain, and at speeds similar to those produced in neurons, of the order of milliseconds,” explain ICREA research professor Jordi Sort and Serra Húnter Tenure-track Professor Enric Menéndez. “We have developed an artificial synapse that in the future may be the basis of a new computing paradigm, alternative to the one used by current computers,” Sort and Menéndez point out.
By applying voltage pulses, it has been possible to emulate, in a controlled way, processes such as memory, information processing, information retrieval and, for the first time, the controlled updating of information without applied voltage. This control has been achieved by modifying the thickness of the cobalt mononitride layers (which determines the speed of the ions motion), and the frequency of the pulses. The arrangement of the material allows the magnetoionic properties to be controlled not only when the voltage is applied but also, for the first time, when the voltage is removed. Once the external voltage stimulus disappears, the magnetization of the system can be reduced or increased, depending on the thickness of the material and the protocol how the voltage has been previously applied.
This new effect opens a whole range of opportunities for new neuromorphic computing functions. It offers a new logic function that allows, for example, the possibility of mimicking the neural learning that occurs after brain stimulation, when we sleep profoundly. This functionality cannot be emulated by any other type of existing neuromorphic materials.
“When the thickness of the cobalt mononitride layer is below 50 nanometers and with a voltage applied at a frequency greater than 100 cycles per second, we have managed to emulate an additional logic function: once the voltage is applied, the device can be programmed to learn or to forget, without the need for any additional input of energy, mimicking the synaptic functions that take place in the brain during deep sleep, when information processing can continue without applying any external signal,” highlight Jordi Sort and Enric Menendez.
The research, published in Materials Horizons, has been led by researchers from the UAB Department of Physics Jordi Sort, also a researcher at the Catalan Institute for Research and Advanced Studies (ICREA), and Enric Menéndez (Serra Húnter Tenure-track Professor). and with the participation of Zhengwei Tan, Julius de Rojas and Sofia Martins, researchers from the UAB Department of Physics; Aitor Lopeandia, from the Physics Department of the UAB and the Catalan Institute of Nanoscience and Nanotechnology (ICN2); Alberto Quintana, from the Barcelona Institute of Materials Science (ICMAB-CSIC); Javier Herrero-Martín, from the ALBA Synchrotron; José L. Costa-Krämer, from the Institute of Micro and Nanotechnology (IMN-CNM-CSIC); and researchers from CNR-SPIN in Italy, and from IMEC and Quantum Solid State Physics (KU Leuven) in Belgium. More

Quantum dots are nanoscale crystals capable of emitting light of different colors. Display devices based on quantum dots promise greater power efficiency, brightness and color purity than previous generations of displays. Of the three colors typically required to display full color images — red, green and blue — the last has proved difficult to produce. A new method based on self-organizing chemical structures offers a solution, and a cutting-edge imaging technique to visualize these novel blue quantum dots proved essential to their creation and analysis.
Peer closely at the screen of your device, and you might be able to see the individual picture elements, pixels, that make up the image. Pixels can appear almost any color, but they are not actually the smallest element on your screen as they are typically made up of subpixels which are red, green and blue. The variable intensity of these subpixels gives the individual pixels the appearance of a single color from a palette of billions. The underlying technology behind subpixels has evolved from the days of early color television, and there is now a number of possible options. But the next big leap is likely to be so-called quantum dot light emitting diodes, or QD-LEDs.
Displays based on QD-LEDs already exist, but the technology is still maturing, and current options have some drawbacks, specifically regarding the blue subpixels within them. Of the three primary colors, blue subpixels are the most important. Through a process called down-conversion, blue light is used to generate green and red light. Because of this, blue quantum dots require more tightly controlled physical parameters. This often means blue quantum dots are highly complex and costly to produce, and their quality a critical factor in any display. But now, a team of researchers led by Professor Eiichi Nakamura from the University of Tokyo’s Department of Chemistry has a solution.
“Previous design strategies for blue quantum dots were very top down, taking relatively large chemical substances and putting them through a series of processes to refine them into something that worked,” said Nakamura. “Our strategy is bottom up. We built on our team’s knowledge of self-organizing chemistry to precisely control molecules until they form the structures we want. Think of it like building a house from bricks rather than carving one from stone. It’s much easier to be precise, design the way you want, and is more efficient and cost effective too.”
But it’s not just the way Nakamura’s team produced their blue quantum dot that’s special; when exposed to ultraviolet light, it produces nearly perfect blue light, according to the international standard for measuring color accuracy, known as BT.2020. This is due to the unique chemical makeup of their dot, a hybrid mix of organic and inorganic compounds including lead perovskite, malic acid and oleylamine. And only through self-organization can these be coaxed into the form required, which is a cube of 64 lead atoms, four to a side.
“Surprisingly, one of our biggest challenges was in finding that malic acid was a key piece of our chemical puzzle. It took over a year methodically trying different things to find it,” said Nakamura. “Perhaps less surprising is that our other main challenge was to determine the structure of our blue quantum dot. At 2.4 nanometers, 190 times smaller than the wavelength of the blue light we sought to create with it, the structure of a quantum dot cannot be imaged by conventional means. So, we turned to an imaging tool pioneered by some of our team known as SMART-EM, or ‘cinematic chemistry’ as we like to call it.”
Cinematic chemistry is an evolution of electron microscope imaging that is more akin to shooting a video than taking a still image. For capturing details of the structure of the blue quantum dot, this is essential, as the nanocrystal is actually quite dynamic, so any single image of it would only tell a small piece of its story. Unfortunately, the blue quantum dot is also quite short-lived, though this was expected, and the team is now aiming to improve its stability with the aid of industrial collaboration.
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If you hold one wire mesh on top of another one and look through it, you’ll see a larger pattern called a moiré pattern formed by the overlapping grids of the two meshes, which depends on their relative twisted angle. Scientists developing new materials are actively studying moiré patterns in overlapping atomically thin materials — they produce intriguing electronic phenomena that includes unconventional superconductivity and ferromagnetism.
Supercomputer simulations have helped scientists reveal in a bilayer moiré system a new species of an electronic phenomenon called an exciton, which is an electrically neutral quasiparticle, yet one that can carry energy and consists of an electron and electron ‘hole’ that can be created for example by light impinging certain semiconductors and other materials.
The newly discovered excitons were produced by moiré patterns from two-dimensional sheets of exotic semiconductors called transition metal dichalcogenides, with the electron bound to the hole but separated from each other by a characteristic distance in the sheet. This was named an intralayer charge-transfer exciton and was a surprise to the scientists because such excitons do not exist in the individual sheets. The research can be used in the development of new optical sensors and communication technology such as optical fibers and lasers.
Novel Exciton Discovered
“In this work we discovered a novel exciton of unforeseen intralayer charge-transfer characteristics in a moiré superlattice formed by two atomically thin layers of transition metal dichalcogenide materials,” said Steven G. Louie, a distinguished professor of physics at the University of California, Berkeley (UC Berkeley), and a senior faculty scientist at the Lawrence Berkeley National Laboratory (LBNL).
Louie is the corresponding author of research published August 2022 in the journal Nature. In it, the scientists developed computer models that go beyond the conventional parameterized models that have been used to describe moiré systems and moiré excitons. Instead, they performed ab initio calculations that only start with the identity and initial position of the 3,903 atoms of the moiré superlattice unit cell. More

X-rays can be used like a superfast, atomic-resolution camera, and if researchers shoot a pair of X-ray pulses just moments apart, they get atomic-resolution snapshots of a system at two points in time. Comparing these snapshots shows how a material fluctuates within a tiny fraction of a second, which could help scientists design future generations of super-fast computers, communications, and other technologies.
Resolving the information in these X-ray snapshots, however, is difficult and time intensive, so Joshua Turner, a lead scientist at the Department of Energy’s SLAC National Accelerator Center and Stanford University, and ten other researchers turned to artificial intelligence to automate the process. Their machine learning-aided method, published October 17 in Structural Dynamics, accelerates this X-ray probing technique, and extends it to previously inaccessible materials.
“The most exciting thing to me is that we can now access a different range of measurements, which we couldn’t before,” Turner said.
Handling the blob
When studying materials using this two-pulse technique, the X-rays scatter off a material and are usually detected one photon at a time. A detector measures these scattered photons, which are used to produce a speckle pattern — a blotchy image that represents the precise configuration of the sample at one instant in time. Researchers compare the speckle patterns from each pair of pulses to calculate fluctuations in the sample.
“However, every photon creates an explosion of electrical charge on the detector,” Turner said. “If there are too many photons, these charge clouds merge together to create an unrecognizable blob.” This cloud of noise means the researchers must collect tons of scattering data to yield a clear understanding of the speckle pattern. More

While quantum computing seems like the big-ticket item among the developing technologies based on the behaviour of matter and energy on the atomic and subatomic level, another direction promises to open a new door for scientific research itself — quantum microscopy.
With the advance of quantum technologies, new microscopy modalities are becoming possible — ones that can see electric currents, detect fluctuating magnetic fields, and even see single molecules on a surface.
A prototype of such a microscope, demonstrating high resolution sensitivity, has been developed by an Australian research team headed by Professor Igor Aharonovich of the University of Technology Sydney and Dr Jean-Philippe Tetienne of RMIT University. The team’s findings have now been published in Nature Physics.
The quantum microscope is based on atomic impurities, that following laser illumination, emit light that can be directly related to interesting physical quantities such as magnetic field, electric field or the chemical environment in proximity to the defect.
Professor Aharonovich said the ingenuity of the new approach was that, as opposed to the bulky crystals often employed for quantum sensing, the research team had utilised atomically thin layers, called hexagonal boron nitride (hBN).
“This van der Waals material — that is, made up of strongly bonded two-dimensional layers — can be made to be very thin and can conform to arbitrarily rough surfaces, thus enabling high resolution sensitivity,” Professor Aharonovich said. More

A key question in a number of court cases is whether a speaker on an audio recording is a particular known speaker, e.g., whether a speaker on a recording of an intercepted telephone call is the defendant.
In most English-speaking countries, expert testimony is only admissible in a court of law if it will potentially assist the judge or the jury to make a decision. If the judge or the jury’s speaker identification were equally accurate or more accurate than a forensic scientist’s forensic voice comparison, then the forensic-voice-comparison testimony would not be admissible.
In a research paper “Speaker identification in courtroom contexts — Part I,” recently published in the journal Forensic Science International, a multidisciplinary international team of researchers has reported the first set of results from a comprehensive study that compares the accuracy of speaker-identification by individual listeners (like judges or jury members) with the accuracy of a forensic-voice-comparison system that is based on state-of-the-art automatic-speaker-recognition technology, and that does so using recordings that reflect the conditions of an actual case.
The questioned-speaker recording was of a telephone call with background office noise, and the known-speaker recording was of a police interview conducted in echoey room with background ventilation-system noise.
The forensic-voice-comparison system performed better than all the 226 listeners who were tested.
The research team was made up of forensic data scientists, legal scholars, experimental psychologists, and phoneticians, based in the UK, Australia, and Chile.
Corresponding author Dr Geoffrey Stewart Morrison, director of the Forensic Data Science Laboratory at Aston University, said:
“A few years ago, when I was testifying in a court case, I was asked by a lawyer why the judge couldn’t just listen to the recordings and make a decision. Wouldn’t the judge do better than the forensic-voice-comparison system that I had used? That was the spark that lead to us conducting this research. I was expecting our forensic-voice-comparison system to perform better than most of the listeners, but I was surprized when it actually performed better than all of them. I’m happy that we now have such a clear answer to the question asked by the lawyer.”
Contributing author Dr Kristy A Martire, School of Psychology at the University of New South Wales, said:
“Past experiences where we have successfully recognized familiar speakers, such as family members or friends, can lead us to believe that we are better at identifying unfamiliar voices than we really are. This study shows that whatever ability a listener may have in recognizing familiar speakers, their ability to identify unfamiliar speakers is unlikely to be better than a forensic-voice-comparison system.”
Contributing author Professor Gary Edmond, School of Law at the University of New South Wales, said:
“Unequivocal scientific findings are that identification of unfamiliar speakers by listeners is unexpectedly difficult and much more error-prone than judges and others have appreciated. We should not encourage or enable nonexperts, including judges and jurors, to engage in unduly error-prone speaker identification. Instead, we should seek the services of real experts: specialist forensic scientists who employ empirically validated and demonstrably reliable forensic-voice-comparison systems.”
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Want to know if the Golden Gate Bridge is holding up well? There could be an app for that.
A new study involving MIT researchers shows that mobile phones placed in vehicles, equipped with special software, can collect useful structural integrity data while crossing bridges. In so doing, they could become a less expensive alternative to sets of sensors attached to bridges themselves.
“The core finding is that information about structural health of bridges can be extracted from smartphone-collected accelerometer data,” says Carlo Ratti, director of the MIT Sensable City Laboratory and co-author of a new paper summarizing the study’s findings.
The research was conducted, in part, on the Golden Gate Bridge itself. The study showed that mobile devices can capture the same kind of information about bridge vibrations that stationary sensors compile. The researchers also estimate that, depending on the age of a road bridge, mobile-device monitoring could add from 15 percent to 30 percent more years to the structure’s lifespan.
“These results suggest that massive and inexpensive datasets collected by smartphones could play an important role in monitoring the health of existing transportation infrastructure,” the authors write in their new paper.
The study, “Crowdsourcing Bridge Vital Signs with Smartphone Vehicle Trips,” is being published in Nature Communications Engineering. More