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05/19/2016 : 130379
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A New Era in Nanophotonics Is Unlocked by Tiny Polaritons
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Posted by Okachinepa on 10/31/2024 @
Courtesy of SynEvol
Credit: ICFO/ David Alcaraz Iranzo
When electromagnetic waves couple with charged particles or vibrations in a material's atomic structure, they produce polaritons, which are special excitations. Their ability to restrict light in extremely small spaces, down to nanometer-sized volumes, is essential for improving interactions between light and matter, which is why they play a significant role in nanophotonics. Polaritons can be produced very efficiently in two-dimensional materials that are only one atom thick. Compared to bulk materials, these 2D materials provide better tunability, less energy loss (increasing polariton lifetimes), and extreme light confinement.
Researchers employ nanoscale structures called nanoresonators to improve polaritonic characteristics and further refine light confinement. A nanoresonator's material and geometry shape the polaritons that oscillate and resonate at particular frequencies when light interacts with it. This creates new opportunities for sophisticated optical manipulation by enabling extremely accurate control of light at the nanoscale.
Although the application of polaritons for light confinement is well-established, techniques for exploring them can yet be improved. Optical measurements have gained popularity in recent years, but their large detectors need additional equipment. This limits the miniaturization of the detection system and the signal clarity (known as the signal-to-noise ratio) one can obtain from the measurements, which in turn hinders the application of polaritonic properties in areas where these two features are essential, such as molecular sensing.
In a recent article published in Nature Communications, researchers from the University of Ioannina, Universidade do Minho, the International Iberian Nanotechnology Laboratory, Kansas State University, the National Institute for Materials Science (Tsukuba, Japan), POLIMA (University of Southern Denmark), URCI (Institute of Materials Science and Computing, Ioannina), ICFO Dr. Sebastián Castilla, Dr. Hitesh Agarwal, Dr. David Alcaraz, Dr. Roshan Krishna Kumar, and ICREA Prof. Frank Koppens led the team.
For the first time, spectrally resolved electrical detection of 2D polaritonic nanoresonators is made possible by the integrated device, which also represents a major advancement in device shrinking.
The team applied electrical spectroscopy to a stack of three layers of 2D materials, specifically, an hBN (hexagonal boron-nitrate) layer was placed on top of graphene, which was layered on another hBN sheet. Researchers discovered a number of benefits of electrical spectroscopy over commercial optical methods during the studies. With the former, the spectral range covered is significantly broader (that is, it spans a wider range of frequencies, including the infrared and terahertz ranges), the required equipment is significantly smaller, and the measurements present higher signal-to-noise ratios.
Two key characteristics of this electro-polaritonic platform make it a breakthrough in the area. First, most optical techniques no longer require an external detector for spectroscopy. The system can be further reduced in size because a single device can function as both a polaritonic platform and a photodetector. Secondly, the integrated device effectively gets over the drawback that increasing light confinement generally degrades the quality of this confinement (e.g., reducing periods of light trapping). "Our platforms are of outstanding quality, attaining optical lateral confinement records and high-quality factors of up to 200, roughly." The photodetection efficiency is greatly increased by graphene's remarkable level of confinement and purity, according to Dr. Sebastián Castilla, the article's first co-author.
Furthermore, very tiny 2D polaritons (with lateral diameters of about 30 nanometers) can be probed using the electrical spectroscopy method. "The imposed resolution limitations made it extremely difficult to detect using traditional techniques," he continues.
Castilla now considers what new insights their new strategy might yield. This electro-polaritonic integrated platform could be useful for applications in optical spectrometry, hyperspectral imaging, and sensing. On-chip electrical detection of molecules and gasses, for example, may become feasible in the sensing situation, he says. "I am confident that our efforts will pave the way for numerous applications that have been impeded by the large size of conventional commercial platforms."
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Traditional Solar Cells Are Outperformed by New Material
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Posted by Okachinepa on 10/24/2024 @
Courtesy of SynEvol
A unique phenomenon known as the bulk photovoltaic (BPV) effect may enable some materials to outperform conventional p-n junctions in solar cells. The BPV effect in alpha-phase indium selenide (α-In2Se3) along the out-of-plane direction has just been empirically proven for the first time by Japanese researchers, which is in line with previous theoretical predictions. Their α-In2Se3 device's remarkable conversion efficiency is a major advancement for photosensors and next-generation solar cell technology.
The design and development of solar cells is based on a thorough understanding of the photovoltaic effect, which is the process by which light can be transformed into useable electrical energy. The majority of solar cells used today use p-n junctions, which take advantage of the photovoltaic effect that happens at the interface of various materials. However, such designs are constrained by the Shockley–Queisser limit, which puts a hard cap on their theoretical maximum solar conversion efficiency and imposes a tradeoff between the voltage and current that can be produced via the photovoltaic effect.
Nonetheless, a fascinating phenomenon called the bulk photovoltaic (BPV) effect is present in some crystalline materials. Electrons stimulated by light can migrate coherently in a particular direction rather than reverting to their initial places in materials that lack internal symmetry. The BPV effect is created as a result of what are referred to as "shift currents." Alpha-phase indium selenide (α-In2Se3) has not yet been experimentally studied, despite experts' predictions that it would exhibit this feature.
A Japanese research team headed by Associate Professor Noriyuki Urakami from Shinshu University set out to investigate the BPV effect in α-In2Se3 in order to close this knowledge gap. The journal Applied Physics Letters has published their findings.
Because of its potential to produce a shift current, this material has recently gained a lot of attention in the field of condensed matter physics. This prediction has never been experimentally proven before, according to our findings," Prof. Urakami says.
Initially, a thin α-In2Se3 layer was positioned between two transparent graphite layers to create a layered device. In order to monitor any currents produced by light irradiation, these graphite layers were used as electrodes and coupled to an ammeter and a voltage source. It is noteworthy that the researchers utilized this particular layer configuration because they concentrated on the shift currents in the α-In2Se3 layer that were occurring in the out-of-plane direction.
The presence of shift currents in the out-of-plane direction was confirmed by the researchers after testing with varying external voltages and incident light frequencies, hence validating the predictions described above. The BPV effect was present across a broad spectrum of light frequencies.
Above all, the researchers measured the BPV effect's potential in α-In2Se3 and contrasted it with that of other materials. Prof. Urakami says, "Our α-In2Se3 device demonstrated a quantum efficiency that is comparable to that of low-dimensional materials with enhanced electric polarization, and several orders of magnitude higher than other ferroelectric materials." "This discovery will direct the selection of materials for the development of functional photovoltaic devices in the near future," he continues.
By advancing the field of renewable energy generation, the research team hopes that their work will eventually have a good environmental impact. One of the most important technologies for environmental energy harvesting and a promising path towards a carbon-neutral future, solar cells, could be further accelerated by our results, Prof. Urakami says with optimism.
In addition to improving the design of sensitive photodetectors, we expect that this discovery opens the door for future research aimed at utilizing the BVP effect to significantly boost solar cell performance.
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The Brilliant Mystery of Next-Gen Quantum Technology
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Posted by Okachinepa on 10/21/2024 @
Courtesy of SynEvol
Credit: University of Chicago
Due to its extreme durability, rigidity, and thermal conductivity, synthetic diamond is a material that is well suited for use in both conventional and quantum electronics. It has great qualities for these uses and is chemically stable. The main obstacle is that diamonds can only grow on other diamonds.
Because of this property, called homoepitaxy, using diamonds in technologies such as quantum computers, sensors, telephones, and other gadgets means that either the technology's full potential has to be sacrificed or it has to rely on big, costly diamond chunks.
According to UChicago Pritzker School of Molecular Engineering (PME) Associate Professor Alex High, "Diamond stands alone in terms of its material properties, both for electronics—with its wide band gap, very best thermal conductivity, and exceptional dielectric strength—and for quantum technologies—it hosts nitrogen vacancy centers that are the gold standard for quantum sensing at room temperature." "But it's actually pretty bad as a platform."
Courtesy of SynEvol
Credit: UChicago Pritzer School of Molecular Engineering
A significant challenge for researchers working with diamonds has been resolved by a paper from UChicago PME's High Lab and Argonne National Laboratory that was published on October 10 in Nature Communications. This technique creates a novel way of bonding diamonds directly to materials that integrate easily with either quantum or conventional electronics.
"We provide a surface treatment to the carrier and diamond substrates, which increases their mutual attraction. The two extremely flat surfaces will be glued together by making sure we have a pristine surface roughness," added first author Xinghan Guo, who received his PhD from UChicago PME in the spring. An annealing procedure strengthens and improves the connection. Our diamond can therefore withstand a variety of nanofabrication procedures. It sets our procedure apart from just putting a diamond on top of another substance.
Using this method, the researchers fused silicon, fused silica, sapphire, thermal oxide, and lithium niobate to diamond directly without the need of a "glue" material in between.
For advanced quantum applications, the researchers bonded crystalline membranes as thin as 100 nanometers, while preserving spin coherence, in place of bulk diamonds that are normally several hundred microns thick and are used to study quantum qubits.
Quantum researchers, as opposed to jewelers, like a diamond with a little imperfection. Researchers are able to construct robust qubits that are perfect for quantum computing, quantum sensing, and other applications by carefully designing flaws in the crystal lattice.
"Diamond has a broad bandgap. It is not active. It's really well-behaved and has excellent thermal and electrical properties, according to F. Joseph Heremans, co-author of the paper and dual employee of Argonne and UChicago PME. Its basic physical characteristics meet several requirements that are advantageous to many different fields. Simply put, integrating with different materials was exceedingly challenging up until now.
However, this required larger—though still microscopic—chunks of the material, as thin diamond membranes were previously impossible to integrate directly into devices. Fourth-year UChicago Engineering student Avery Linder, co-author of the paper, likened the process of creating sensitive quantum devices from these diamonds to attempting to manufacture a single grilled cheese sandwich out of an entire block of cheddar cheese.
Co-author of the article, UChicago PME Assistant Professor Peter Maurer, specializes in quantum biosensing and uses cutting-edge quantum techniques to detect basic biological processes more precisely and precisely at the micro- and nanoscale.
"The integration of diamond-based quantum sensors into real measurement devices, like a commercial microscope or a diagnostic device, has remained an outstanding challenge, even though we have overcome many challenges related to the interface of intact biological targets with these sensors." Maurer stated. "Many of these problems have been resolved by the new work Alex's lab is leading with diamond membrane bonding, which takes us a significant step closer to applications."
Courtesy of SynEvol
Credit: UChicago Pritzer School of Molecular Engineering
Each carbon atom in a diamond shares four electrons with four other carbon atoms. The hard, long-lasting interior structure of the gem is derived from these covalent bonds, or electron-sharing connections.
However, this results in what are known as "dangling bonds" on lone atoms searching for a mate if there isn't another carbon atom nearby to share electrons with. The scientists were able to directly link the nanometer-scale diamond wafers to other surfaces by producing a diamond surface full of these dangling bonds.
Due to its desire to adhere to another object, Linder suggested that it be compared to a sticky surface. Thus, in essence, we have created sticky surfaces and assembled them.
"This new method could have a big impact on how we manufacture quantum, and even phones or computers," Linder stated.
The development of complementary metal-oxide semiconductors (CMOS) from large individual transistors in labs in the 1940s to the potent, compact integrated circuits found in modern computers and phones is what High compares the new diamond technology to.
"We're hoping that something akin to a CMOS-style revolution for diamond-based quantum technologies can result from our ability to generate these thin films and integrate them in a scalable fashion," he stated.
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Boosting Scientific Research Using FAIR AI Models
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Posted by Okachinepa on 10/16/2024 @
Courtesy of SynEvol
Credit: Argonne Leadership Computing Facility Visualization and Data Analytics Group
The findable, accessible, interoperable, and reusable (FAIR) principles were first put forth by researchers to outline recommended practices for increasing the use of datasets by researchers and machines. These ideas have now been modified for usage with scientific datasets and research software with the goal of improving research transparency, reproducibility, and reusability while also encouraging software reuse as opposed to redevelopment.
These concepts are currently also followed by artificial intelligence (AI) models, which use different digital assets such as advanced computing, research software, and databases. A collection of useful, succinct, and quantifiable FAIR principles designed especially for AI models is presented in a recent work. It goes on to explain how scientific discovery can be greatly accelerated by combining datasets and FAIR AI models.
In this paper, the FAIR principles for AI models are precisely defined and their use in a particular kind of advanced microscopy is demonstrated. In particular, it shows how FAIR datasets and AI models may be combined to describe materials at the Advanced Photon Source at Argonne National Laboratory (ANL) twice as quickly as using conventional methods.
The paper also emphasizes how accelerating scientific discovery can be achieved by tying the Argonne Leadership Computing Facility and ANL's Advanced Photon Source together. This approach reduces hardware disparities, enables researchers to speak the same AI language, and accelerates AI-driven discoveries. The adoption of these FAIR standards for AI models is expected to stimulate new relationships between data, AI models, and high-performance computing as well as propel the development of next-generation AI technologies.
In this study, researchers generated an undeformed bi-crystal gold sample at Argonne National Laboratory's Advanced Photon Source, resulting in a FAIR experimental dataset of Bragg diffraction peaks. The Materials Data Facility published this FAIR and AI-ready dataset.
Then, using the ThetaGPU supercomputer and the open-source API PyTorch, the researchers used this dataset to train three different types of AI models at the Argonne Leadership Computing Facility (ALCF): a traditional model; an NVIDIA TensorRT version of the traditional PyTorch AI model; and a model trained on the SambaNova DataScaleTM system at the ALCF AI Testbed. These AI models include uncertainty quantification metrics that make it evident whether predictions made by the AI are reliable.
The researchers' suggested FAIR principles for AI models were then followed by the publication of these three distinct models in the Data and Learning Hub for Science. Then, using the ALCF's ThetaGPU supercomputer, they connected all of these resources, FAIR AI models, and datasets to do repeatable AI-driven inference.
Globus is used for process orchestration, whereas Globus Compute is used for workflow execution. The researchers asked their University of Illinois colleagues to independently confirm that the results could be replicated after using software to automate this task.
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Telescopes can Assist Gaining Access to Renewable Energy.
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Posted by Okachinepa on 10/11/2024 @
Courtesy of SynEvol
Constructing a renewable energy system for a telescope in the distant Atacama Desert of Chile might also provide 66% of the energy needs of a local town, raising the prospect of cooperative development around other out-of-the-way infrastructure projects.
By incorporating renewable energy sources into the AtLAST telescope's design, more environmentally friendly energy systems would be made available to the neighboring residential areas and the astronomical community on the Chajnantor plateau. By integrating renewable energy sources, this integration would lessen the local need on fossil fuels.
According to the research, installing comparable energy systems at neighboring telescopes could lower the amount of energy generated by fossil fuels by 30GWh per year, resulting in emissions reductions of 18–24 kilotonnes of carbon dioxide equivalent. Additionally, this would help the local communities have access to reasonably priced renewable energy sources.
Chile's Chajnantor plateau in the Atacama Desert is home to observatories such as the Atacama Pathfinder Experiment (APEX) and the Atacama Large Millimeter/submillimeter Array (ALMA), making it a top location for astronomy worldwide. Astronomical facilities are frequently isolated from the national energy grid as a result of their distant location, and thus depend on gas and diesel generators to operate their power-intensive operations.
Chile's Chajnantor plateau in the Atacama Desert is home to observatories such as the Atacama Pathfinder Experiment (APEX) and the Atacama Large Millimeter/submillimeter Array (ALMA), making it a top location for astronomy worldwide. Astronomical facilities are frequently isolated from the national energy grid as a result of their distant location, and thus depend on gas and diesel generators to operate their power-intensive operations.
Due to its exceptional sun radiation levels, the Atacama Desert is also a highly desirable site for solar energy projects. Atacamenʃos pay more for their electricity than those in the capital region, despite the fact that the region is home to 85% of Chile's solar energy developments.For instance, San Pedro de Atacama, one of Chile's most popular tourist sites outside of Patagonia, is 100 kilometers from the national electricity grid's end...
Up until 2022, the town and the areas around it relied only on diesel and natural gas generators, and there are often power outages. Lithium mining in the area are primarily powered by renewable energy, which is then exported to neighboring provinces.
The possibility of supplying San Pedro de Atacama with excess energy from the AtLAST telescope's energy system was determined by the researchers. "Without additional capacities in PV or battery, San Pedro de Atacama could cover 66% of its electricity demand with a solar renewable energy system sized to supply the telescope," says co-author Luis Ramirez Camargo, an assistant professor at Utrecht University's Copernicus Institute of Sustainable Development.
This concept focuses on transparent and equitable decision-making and is built on "energy communities," which are associations of public, private, and commercial organizations that collectively invest in or share energy infrastructure or offer energy services.
The researchers set up forums where locals and other impacted parties could discuss the prospects and difficulties of moving toward a more sustainable energy system in the San Pedro de Atacama region. Lead author Guillermo Valenzuela Venegas, a researcher at the University of Oslo, states that "it is essential to arrive at just, locally applicable solutions for the energy transition to allow those who are truly affected to participate in the discussion and be able to influence decision-making."
"Distributing benefits to multiple stakeholders through an energy community can lead to a more socially accepted and just energy transition," claims Ramirez Camargo. "Our research shows that astronomy can lead by example in the urgent transition to an equitable net-zero world, keeping our planet habitable and ensuring no one is left behind."
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