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05/19/2016 : 142900
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Opening Up the Hidden Universe of Dark Excitons for Future Energy
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Posted by Okachinepa on 02/04/2025 @
Courtesy of SynEvol
Credit: University of Gottingen
How can we increase the efficiency of cutting-edge technologies like solar cells? With a novel method, a research team headed by the University of Göttingen has made significant progress in addressing this query.
Dark excitons are small, elusive energy carriers that can now be properly tracked in space and time for the first time. These hitherto invisible particles may be essential to the advancement of solar cells, LEDs, and sensors in the future. Nature Photonics published the team's results.
When an excited electron leaves behind a "hole," a bonded pair known as a "dark exciton" is created that carries energy but does not produce light. Imagine a balloon (the electron) floating away, leaving a hole in the ground to which it is still attached by an unseen force known as the Coulomb interaction. This is a helpful way to picture this.
These particle states are very important in ultra-thin, two-dimensional semiconductor materials, notwithstanding their difficulty in detection. Gaining insight into their behavior may lead to significant developments in energy-efficient equipment.
Courtesy of SynEvol
Credit: Lukas Kroll
In a previous article, the research team headed by Professor Stefan Mathias from the University of Göttingen's Faculty of Physics demonstrated how these dark excitons are produced in an unthinkably short amount of time and used quantum mechanical theory to explain their dynamics.
The team has recently created and applied a novel method called "Ultrafast Dark-field Momentum Microscopy" for the first time in the current investigation. With a precise resolution of 480 nanometers (0.00000048 meters), they were able to demonstrate the formation of dark excitons in a unique material composed of tungsten diselenide (WSe₂) and molybdenum disulfide (MoS₂) in an astoundingly short amount of time, lasting only 55 femtoseconds (0.000000000000055 seconds).
The first author, Dr. David Schmitt, who is also from Göttingen University's Faculty of Physics, says, "This method allowed us to measure the dynamics of charge carriers very precisely." The findings offer a basic understanding of how the sample's characteristics affect the charge carriers' motion. This implies that, for instance, this method can be applied in the future to precisely enhance the caliber and, consequently, the effectiveness of solar cells.
“This means that this technique can be used not only for these specially designed systems but also for research into new types of materials,” says Dr. Marcel Reutzel, Junior Research Group Leader in Mathias’ research group.
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Scientist Create Artificial Neurons That Can Simulate Human Sensations
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Posted by Okachinepa on 02/04/2025 @
Courtesy of SynEvol
Credit: Northwestern University and Georgia Tech
Because human senses rely on an adaptive network of sensory neurons that fire in response to external stimuli, artificially designed biological processes, including perception systems, continue to be a difficult target for experts in organic electronics.
By creating a high-performance organic electrochemical neuron that functions in the same frequency range as human neurons, a recent partnership between Georgia Tech and Northwestern University has made significant progress in the field. In order to enable real-time tactile signal detecting and processing, they additionally designed new organic materials and integrated their engineering neurons with artificial touch receptors and synapses, resulting in a comprehensive sensory system.
According to an article recently published in the Proceedings of the National Academy of Sciences (PNAS) journal, the findings might have a significant impact on intelligent robots and other systems that are now hindered by sensing systems that are not as powerful as human ones.
According to first author Yao Yao, an engineering professor at Northwestern, "the study highlights significant progress in organic electronics and their application in bridging the gap between biology and technology." "We developed an effective artificial neuron with exceptional neural properties and a smaller footprint. We used this ability to create a comprehensive tactile neuromorphic perception system that replicates actual biological functions.
Current artificial brain circuits have a tendency to fire within a limited frequency range, according to corresponding author Tobin J. Marks, Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences at Northwestern.
"The synthetic neuron in this study offers a range 50 times wider than existing organic electrochemical neural circuits, achieving unprecedented performance in firing frequency modulation," Marks stated. "On the other hand, our device's exceptional neuronal properties make it a cutting-edge development in organic electrochemical neurons."
In the domains of materials science, organic electronics, photovoltaics, chemical catalysis, organometallic chemistry, and nanotechnology, Marks is a global leader. In addition, he teaches Applied Physics, Chemical and Biological Engineering, and Materials Science and Engineering at Northwestern's McCormick School of Engineering. Antonio Facchetti, his co-corresponding author, is an adjunct chemistry professor at Northwestern and a professor at Georgia Tech's School of Materials Science and Engineering.
"This study integrates artificial tactile receptors and artificial synapses to present the first complete neuromorphic tactile perception system based on artificial neurons," Facchetti stated. "It exhibits the capacity to translate tactile stimuli into post-synaptic responses and to encode them into spiking neuronal signals in real-time."
With researchers specializing in organic synthesis developing cutting-edge materials that electronic device researchers then integrated into circuit design and manufacture, the team crossed departments and educational institutions.
Sensing systems are still challenging to replicate because of the vast network of 86 billion neurons in the human brain that are ready to fire. Scientists are constrained by the amount they can produce as well as the design's footprint. In order to move the research closer to accurately simulating human sense systems, the team plans to significantly lower the device's size in subsequent versions.
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Clean Energy Could Be Revoloutionized by a New Hydrogen Storing Jet Fuel
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Posted by Okachinepa on 02/03/2025 @
Courtesy of SynEvol
Credit: Washington State University
Using lignin-based jet fuel, a global team of researchers has created a technique to store and release volatile hydrogen, which could advance sustainable energy options.
Professor Bin Yang and associates from Washington State University showed that their lignin-based jet fuel can chemically link hydrogen in a stable liquid state in a recent study that was published in the International Journal of Hydrogen Energy. This innovation could make it easier to store and use hydrogen as a high-energy, emission-free fuel source, which would have a big impact on the fuel and transportation sectors.
“This new, lignin jet fuel-based technology could enable efficient, high-density hydrogen storage in an easy-to-handle sustainable aviation fuel, eliminating the need for pressurized tanks for storage and transport,” Yang said.
One of the main obstacles to using hydrogen as a fuel source was the focus of the study, which was conducted by researchers from WSU, Pacific Northwest National Laboratory, the University of New Haven, and Natural Resources Canada. Because of its low density and explosive properties, the lightest element is technically difficult, inefficient, and costly to store and transport.
The January paper describes how the study team used chemical reactions that yielded hydrogen and aromatic carbons from lignin jet fuel, an experimental fuel created by Yang's lab based on lignin, an organic polymer found in plants, to uncover the new hydrogen-storing method.
Yang stated that hydrogen is a flexible energy source that might assist the United States in achieving its goals for decarbonizing industry, integrating renewable energy sources, and achieving zero-emission mobility.
According to experiments, the sustainably produced fuel could boost engine performance and efficiency while eliminating aromatics, the pollutants present in conventional fuels. The discovery suggests new applications for the lignin jet fuel developed at WSU by Yang, who previously tested a new continuous process that produces the fuel from agricultural waste.
Yang stated, "This innovation offers promising opportunities for economic viability for scalable production and compatibility with existing infrastructure." "It could contribute to the development of a synergistic system that improves the ecological advantages, safety, and efficiency of both sustainable aviation fuel and hydrogen technologies."
Researchers from WSU will then work with experts from the University of New Haven to create an AI-powered catalyst that improves and completes the reactions, increasing their effectiveness and economy.
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Researchers Find a Revolutionary Method for Etching 3D NAND Memory
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Posted by Okachinepa on 02/02/2025 @
Courtesy of SynEvol
Credit: PPPL Communications Department
Improving the manufacturing process for digital memory has become crucial as electronic gadgets continue to get smaller while processing ever-increasing volumes of data. In order to satisfy the growing need for denser data storage, researchers in a public-private collaboration are investigating novel techniques to produce digital memory at the atomic level.
Improving the manufacturing process for 3D NAND flash memory, a technique that maximizes storage capacity by stacking data vertically, is one of the main priorities. According to a recent study that was published in the Journal of Vacuum Science & Technology A, the speed at which the deep, thin holes necessary for this memory are etched can be doubled by utilizing the proper combination of plasma and other required elements. Scientists from Lam Research, the University of Colorado Boulder, and the Princeton Plasma Physics Laboratory (PPPL) of the U.S. Department of Energy used models and experiments to carry out the study.
Nonvolatile storage, such as NAND flash memory, keeps data even in the event of a power outage. Since NAND flash memory is the type found in thumb drives and memory cards for digital cameras, most people are familiar with it. Mobile phones and PCs also use it. As our data storage needs increase as a result of artificial intelligence, it will become more crucial to make this kind of memory denser still so that more data can fit into the same footprint, according to Igor Kaganovich, a lead research physicist at PPPL.
Courtesy of SynEvol
Credit: PPPL Communications Department
Information is stored in digital memory in units known as cells. Each cell's state—whether it is on or off—is recorded in the data. The cells in conventional NAND flash memory are stacked one on top of the other. To store more data in a smaller space, 3D NAND flash memory stacks a lot of memory cells on top of one another. It would be like building a 10-story apartment building to house more people instead of a home.
Making holes in alternating layers of silicon oxide and silicon nitride is a crucial step in the formation of these stacks. By subjecting the layered material to chemicals in the form of plasma (partially ionized gasses), the holes can be etched. Atoms in the layered substance interact with those in the plasma, forming out of the perforations.
Researchers aim to improve the process of creating these holes so that each one has smooth sides, is deep, small, and vertical. Scientists have been experimenting with different ingredients and temperatures since it has been difficult to get the recipe precisely right.
Courtesy of SynEvol
Credit: Lam Research
"High-energy ions are obtained from plasma in these processes," stated Yuri Barsukov, a former PPPL researcher who is currently employed at Lam Research. "The simplest way to make the very small but deep, circular holes required for microelectronics is to use the charged particles found in plasma," he stated. Reactive ion etching is the technique, however it isn't entirely understood and should be made better. Maintaining the wafer, or semiconductor material sheet to be treated, at a low temperature is one recent advancement. Cryo etching is the name of this new method.
The holes are typically created by cryoetching using distinct hydrogen and fluorine gasses. The outcomes of this procedure were contrasted with those of a more sophisticated cryo-etching method that generates the plasma using hydrogen fluoride gas.
“Cryo etch with the hydrogen fluoride plasma showed a significant increase in the etching rate compared to previous cryo-etch processes, where you are using separate fluorine and hydrogen sources,” said Thorsten Lill of Lam Research. Lam Research, which has its headquarters in Fremont, California, provides chipmakers with wafer fabrication services and equipment.
When silicon oxide and silicon nitride were tested independently, the etch rate for the oxide layer and silicon nitride rose when the hydrogen fluoride plasma was used rather than the individual hydrogen and fluorine gases. Etching both materials at the same time produced the most gain, even though the effect for silicon nitride was more noticeable than for silicon oxide. The alternating silicon oxide and silicon nitride layers actually saw a more than twofold increase in etching rate, going from 310 to 640 nanometers per minute. (The breadth of a human hair is around 90,000 nanometers.)
"It appears that the etch's quality has also improved, which is noteworthy," Lill stated.
Phosphorus trifluoride, a necessary component for etching silicon dioxide to any appreciable degree, was also examined by the researchers. Despite its prior use, the researchers aimed to better comprehend and measure its effects. They discovered that whereas phosphorus trifluoride only slightly raised the silicon nitride etch rate, it doubled the etch rate for silicon dioxide.
The researchers also looked at ammonium fluorosilicate, a chemical molecule that is created when silicon nitride and hydrogen fluoride combine during the etching process. Ammonium fluorosilicate can slow down etching, however water can counteract this effect, according to the research. Barsukov's calculations showed that the ammonium fluorosilicate linkages were weakened by water. "When water is present, the salt can break down at a lower temperature, which can speed up etching," Barsukov explained.
Kaganovich said the research is also important because it shows how scientists in industry, academia, and national laboratories can work together to answer important questions in the microelectronics field. Additionally, it compiles data from theorists and experimentalists.
“We are building bridges to the greater community,” he said. “This is an essential step in gaining a better understanding of semiconductor manufacturing processes for everyone.”
Lill said he appreciates working with PPPL on semiconductor manufacturing research because PPPL research offers a range of capabilities in plasma simulation for microelectronics.
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A New Era of Faster, Smarter Memory Chips Is Unlocked by Terahertz Light
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Posted by Okachinepa on 01/28/2025 @
Courtesy of SynEvol
Credit: Sampson Wilcox, Research Laboratory of Electronics at MIT
The scientists were able to directly activate the material's atoms by employing a terahertz laser, which oscillates more than a trillion times per second. By precisely adjusting the laser's frequency to the atoms' inherent vibrations, they were able to cause an incredibly quick change in the atomic structure and force the substance into a new magnetic state. Their discoveries, which were just published in Nature, demonstrate how light can be used to manipulate magnetism in novel ways.
A powerful overall magnetic field is produced when the atoms in common magnets, such as those on your refrigerator, align their magnetic moments in the same direction. These substances, referred to as ferromagnets, work well but are readily affected by outside magnetic fields.
Antiferromagnets, on the other hand, have a distinct structure because their atomic spins alternate up-down, canceling each other out and leaving the system without any overall magnetization. They are therefore extremely resistant to external magnetic interference, which may be helpful in creating memory chips that are more stable and impervious to interference. Finding a trustworthy method to change their magnetic states, however, has proven to be a significant obstacle to their usefulness in practical applications.
Researchers from MIT and the Max Planck Institute for the Structure and Dynamics of Matter recently controlled and switched an antiferromagnet into a new magnetic state using terahertz light in a work that was published in the journal Nature. The potential of antiferromagnetic materials for future memory circuits that might process and store more data while using less energy and taking up less space is demonstrated by this accomplishment.
According to Angel Rubio, Director of the Theory Department at the MPSD, and Nuh Gedik, Donner Professor of Physics at MIT, who co-led the study, "such antiferromagnetic materials are generally not easy to control, but now we've found some knobs to tune and tweak them."
FePS3, a substance that changes into an antiferromagnetic phase at about 118 Kelvin (-115°C), was the material the team worked with. They postulated that by tuning into its atomic vibrations, or phonons, its magnetic state might be manipulated. “You can picture any solid as a set of atoms periodically arranged, connected by tiny springs,” explains Alexander von Hoegen, a postdoctoral researcher in Gedik’s group. "A single atom vibrates at a distinctive frequency, usually in the terahertz range, when you pull it."
The team reasoned that by exciting these phonons with a terahertz laser tuned to their natural frequency, they could nudge the atoms’ spins out of their perfectly balanced alignment. This imbalance would create a preferred orientation, shifting the material into a new state with finite magnetization.
According to Emil Viñas Boström, a postdoctoral researcher in Rubio's lab, "the idea is that you excite the atoms' terahertz vibrations, which also couple to the spins."
According to Batyr Ilyas, a PhD student in Gedik's lab, "observing a change in the material's optical properties tells us that it is no longer the original antiferromagnet, and that we are inducing a new magnetic state, essentially by using terahertz light to shake the atoms."
Several tests demonstrated that the antiferromagnet could be effectively switched into this new magnetic state by a terahertz pulse. After the laser was switched off, this state lasted for a few milliseconds. The researchers created a model explaining the interaction between spins and phonons in order to comprehend the process underlying this persistent magnetization. They discovered a particular phonon mode, which is an oscillation pattern inside the crystal lattice, that facilitated a connection between the ferromagnetic and antiferromagnetic states of the material.
According to Rubio, "this is a very uncommon scenario where the shift in magnetic fluctuations results in a new type of magnetic order." "In this case, fluctuations have a positive effect, but normally they destroy magnetic order."
Simulations showed that the sluggish dynamics of the antiferromagnetic order, referred to as critical slowing down, influenced the lifetime of the induced magnetization, close to the transition temperature. According to Viñas Boström, "it's like time slows down within the antiferromagnet and the spins begin to move very slowly close to the ordering temperature." By linking the magnetization to the antiferromagnetic fluctuations and delaying its relaxation, the phonons function as a "glue."
Because of its longer duration, scientists can see the transient magnetic state before it turns back into antiferromagnetism. Gaining insight into these dynamics may pave the way for better antiferromagnet control and application in next-generation memory storage systems.
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