Technology

Researchers in the University of Minnesota College of Science and Engineering have developed a unique new device using the wonder material graphene that provides the first step toward ultrasensitive biosensors to detect diseases at the molecular level with near perfect efficiency.

Ultrasensitive biosensors for probing protein structures could greatly improve the depth of diagnosis for a wide variety of diseases extending to both humans and animals. These include Alzheimer’s disease, Chronic Wasting Disease, and mad cow disease—disorders related to protein misfolding. Such biosensors could also lead to improved technologies for developing new pharmaceutical compounds.

The research is published in Nature Nanotechnology, a peer-reviewed scientific journal published by Nature Publishing Group.

“In order to detect and treat many diseases we need to detect protein molecules at very small amounts and understand their structure,” said Sang-Hyun Oh, University of Minnesota electrical and computer engineering professor and lead researcher on the study. “Currently, there are many technical challenges with that process. We hope that our device using graphene and a unique manufacturing process will provide the fundamental research that can help overcome those challenges.”

Graphene, a material made of a single layer of carbon atoms, was discovered more than a decade ago. It has enthralled researchers with its range of amazing properties that have found uses in many new applications, including creating better sensors for detecting diseases.

Significant attempts have been made to improve biosensors using graphene, but the challenge exists with its remarkable single atom thickness. This means it does not interact efficiently with light when shined through it. Light absorption and conversion to local electric fields is essential for detecting small amounts of molecules when diagnosing diseases. Previous research utilizing similar graphene nanostructures has only demonstrated a light absorption rate of less than 10 percent.

In this new study, University of Minnesota researchers combined graphene with nano-sized metal ribbons of gold. Using sticky tape and a high-tech nanofabrication technique developed at the University of Minnesota, called “template stripping,” researchers were able to create an ultra-flat base layer surface for the graphene.

They then used the energy of light to generate a sloshing motion of electrons in the graphene, called plasmons, which can be thought to be like ripples or waves spreading through a “sea” of electrons. Similarly, these waves can build in intensity to giant “tidal waves” of local electric fields based on the researchers’ clever design.

By shining light on the single-atom-thick graphene layer device, they were able to create a plasmon wave with unprecedented efficiency at a near-perfect 94 percent light absorption into “tidal waves” of electric field. When they inserted protein molecules between the graphene and metal ribbons, they were able to harness enough energy to view single layers of protein molecules.

“Our computer simulations showed that this novel approach would work, but we were still a little surprised when we achieved the 94 percent light absorption in real devices,” said Oh, who holds the Sanford P. Bordeau Chair in Electrical Engineering at the University of Minnesota. “Realizing an ideal from a computer simulation has so many challenges. Everything has to be so high quality and atomically flat. The fact that we could obtain such good agreement between theory and experiment was quite surprising and exciting.”

Read more at: https://phys.org/news/2019-03-graphene-based-device-ultrasensitive-biosensors.html#jCp

For the Kerker effect to occur, particles need to have electric and magnetic polarizabilities of the same strength. This, however, is very challenging to achieve, as magnetic optical resonances in small particles are relatively weak. Researchers at Ioffe Institute, in St. Petersburg, have recently shown that a similar effect can be attained when small particles are trembling in space.

“Even though the light scattering has been understood for more than a century after the works of Rayleigh, Raman, Landsberg and Mandelstam, it remains both a fundamental and applied challenge to route light scattered at the nanoscale in the direction at will,” Alexander Poshakinskiy, one of the researchers who carried out the study, told Phys.org. “The ability to control the direction, frequency and polarization of the scattered light is essential for operation of optical circuits.”

Devices that can control the direction of scattered light could have numerous useful applications, particularly for the operation of antennas and routing of light. In the 1980s, researchers theorized that a directional scattering of light can be achieved via the so-called Kerker effect. This effect essentially exploits the interference of electric and magnetic dipole emission patterns, which have different spatial parity, yielding the suppression of forward or backward scattering when they are superposed.

“Realization of the conventional Kerker effect requires the particles to have electric and magnetic polarizabilities of the same strength,” Poshakinskiy said. “However, this is challenging because magnetic response at optical frequencies is extremely weak. A possible workaround is to use large submicron-size nanoparticles hosting both electric and magnetic Mie resonances. However, optical Kerker effect for the particles smaller than the wavelength in the medium is still unfeasible. In our work, we show that even small particles, that lack magnetic response when at rest, do acquire it when they start trembling in space, enabling realization of what we call optomechanical Kerker effect.”

In the optomechanical Kerker effect, proposed by Poshakinskiy and his colleague Alexander Poddubny, the tunable directional scattering of light is attained for a particle that lacks magnetic resonances as it trembles in space. The trembling motion of the electric dipole in space leads to the appearance of a magnetic dipole, as one could expect from the Lorentz transformation.

“We show that magnetic and electric dipole induced in the trembling particle by incident light counterintuitively are of the same order when inelastic scattering is considered,” Poshakinskiy explained. “The phase difference between the electric and magnetic dipoles is governed by the frequency dependence of the particle permittivity. For a resonant particle, this enables control of the scattering direction via the detuning of light frequency from the resonance: The light is scattered preferably forward at resonance and backward away from it. “

The researchers show that in the optomechanical Kerker effect, the figure of merit that quantifies how much of the light is scattered in a particular direction compared to all other directions (i.e. directivity), can be as high as 5.25. This exceeds the directivity of 3 attained in the classical Kerker effect, due to the additional electric quadrupole momentum induced by the mechanical motion.

In their study, Poshakinskiy and Poddubny also introduced a second effect, which they refer to as ‘the optomechanical spin-Hall effect.’ In this effect, a directional inelastic scattering of light, depending on its circular polarization, is realized for a small trembling particle.

“The optomechanical spin-Hall effect can be achieved when a particle vibrates around a circular trajectory rather that a straight line,” Poshakinskiy said. “We show that the angular mechanical momentum of the particle can be transferred to the spin of light. Then the electromagnetic waves scattered by the trembling particle to the left and to the right attain opposite circular polarization.”

The findings gathered by Poshakinskiy and Poddubny suggest that the interaction between light and mechanical motion has an intrinsically multipolar nature. This quality could be exploited in a variety of systems, ranging from cold atoms to two-dimensional materials and superconducting qubits.

“We believe that the proposed optomechanical Kerker opens a new multidisciplinary field by uncovering, for the first time, to our knowledge, a highly untrivial link between optomechanics and nanophotonics,” Poshakinskiy said. “From a practical point of view, the proposed effects can be used to design non-reciprocal nanoscale optical devices.”

Optical non-reciprocity, meaning that light is transmitted forward and backward through an optical circuit differently, is crucial for optical signal processing. Most existing non-reciprocal optomechanical devices are based on optical resonators, which limit their minimal size to sub-microns. The results collected by Poshakinskiy and Poddubny show that tunable optomechanical non-reciprocity can also occur at nanoscale when using small trembling particles with resonant polarizability.

“Optical non-reciprocity is also a key ingredient for the design of photonic topological circuits,” Poshakinskiy added. “In an array of trembling particles, one can expect a disorder-robust propagation of light and sound, ensured by the time modulation of optical and mechanical properties.”

The study carried out by Poshakinskiy and Poddubny shows how the tunable directional scattering of light can be achieved at nanoscale, introducing the optomechanical Kerker and spin-Hall effects. In the future, their findings could have several interesting applications, for instance, informing the design of non-reciprocal topological circuits. The researchers are now planning to demonstrate the optomechanical Kerker effect in lab experiments.

“The proof of concept would be observation of the directional backscattering by trembling objects, which can be realized even away from material resonances,” Poshakinskiy said “We believe that this can be done in a variety of systems e.g., semiconductor quantum dots, transitional metal dichalcogenides or graphene. However, the key feature of the optomechanical Kerker effect is the possibility to switch the direction of scattering between forward and backward. This requires particles with extremely sharp resonances in their electromagnetic response. Our estimations show that such switching can be realized for cold atoms in optical traps or superconducting qubits in radio-frequency circuits.”

Read more at: https://phys.org/news/2019-03-optomechanical-kerker-effect-vibrating-nanoparticles.html#jCp

Physicists from the University of Sheffield have discovered that when two atomically thin graphene-like materials are placed on top of each other their properties change, and a material with novel hybrid properties emerges, paving the way for design of new materials and nano-devices.

This happens without physically mixing the two atomic layers, nor through a chemical reaction, but by attaching the layers to each other via a weak so called van der Waals interaction—similar to how a sticky tape attaches to a flat surface.

In the ground-breaking study published in Nature, scientists have also found that the properties of the new hybrid material can be precisely controlled by twisting the two stacked atomic layers, opening the way for the use of this unique degree of freedom for the nano-scale control of composite materials and nano-devices in future technologies.

The idea to stack layers of different materials to make so-called heterostructures goes back to the 1960s, when semiconductor gallium arsenide was researched for making miniature lasers—which are now widely used.

Today, heterostructures are common and are used very broadly in semiconductor industry as a tool to design and control electronic and optical properties in devices.

More recently in the era of atomically thin two-dimensional (2-D) crystals, such as graphene, new types of heterostructures have emerged, where atomically thin layers are held together by relatively weak van der Waals forces.

The new structures nicknamed ‘van der Waals heterostructures’ open a huge potential to create numerous ‘meta’-materials and novel devices by stacking together any number of atomically thin layers. Hundreds of combinations become possible otherwise inaccessible in traditional three-dimensional materials, potentially giving access to new unexplored optoelectronic device functionality or unusual material properties.

In the study researchers used van der Waals heterostructures made out of so-called transition metal dichalcogenides (TMDs), a broad family of layered materials. In their three-dimensional bulk form they are somewhat similar to graphite—the material used in pencil leads—from where graphene was extracted as a single 2-D atomic layer of carbon.

The researchers found that when two atomically thin semiconducting TMDs are combined in a single structure their properties hybridise.

Professor Alexander Tartakovskii, from the Department of Physics and Astronomy at the University of Sheffield, said: “The materials influence each other and change each other’s properties, and have to be considered as a whole new ‘meta’-material with unique properties—so one plus one doesn’t make two.

“We also find that the degree of such hybridisation is strongly dependent on the twist between the individual atomic lattices of each layer.

“We find that when twisting the layers, the new supra-atomic periodicity arises in the heterostructure—called a moiré superlattice.

“The moiré superlattice, with the period dependent on the twist angle governs how the properties of the two semiconductors hybridise.”

In other studies, similar effects have been discovered and studied mostly in graphene, the ‘founding’ member of the 2-D materials family. The latest study shows that other materials, in particular semiconductors such as TMDs, show strong hybridisation, that in addition can be controlled by the twist angle.

Scientists believe the study shows huge potential for the creation of new types of materials and devices.

Professor Tartakovskii added: “The more complex picture of interaction between atomically thin materials within van der Waals heterostructures emerges. This is exciting, as it gives the opportunity to access an even broader range of material properties such as unusual and twist-tunable electrical conductivity and optical response, magnetism etc. This could and will be employed as new degrees of freedom when designing new 2-D-based devices.”

Researchers would like to do further studies to explore more material combinations to see what the capabilities of the new method are.

Read more at: https://phys.org/news/2019-03-equal-graphene-like-d-materials.html#jCp

Siemens is to team up with three US energy labs to test new technologies to bolster electricity supply, options and resiliency.

Siemens Corporate Technology, the company’s central research and development unit located in Princeton, New Jersey, has signed a memorandum of understanding with three US Department of Energy R&D facilities: The National Renewable Energy Laboratory in Golden, Colorado; the Oak Ridge National Laboratory in Oak Ridge, Tennessee; and the Pacific Northwest National Laboratory in Richland, Washington.

The memorandum established the framework for research scientists to share information and resources. They could collaborate on technologies to help integrate innovative power electronic devices with the electric grid, including smart inverters for solar panels, batteries, and electrical vehicles that are capable of supporting the nation’s power system.

The MOU may also lead to jointly-led scientific workshops, lectures, and symposia, as well as co-written publications and journal articles.

The potential collaboration is expected to leverage Siemens experience commercializing innovative power system technologies by supplying its Software Defined Inverter (SDI) technology, which would be tested and validated at specialized grid facilities at the three national laboratories. This promising new technology, once validated, could be incorporated into new technologies to strengthen and modernize the nation’s electric grid, including microgrids and distributed energy resources such as energy storage.

“Siemens is committed to developing innovative technologies needed to ensure that the power grid of the future is more resilient, secure, and capable of supporting distributed and low-carbon power generation assets,” said Ulrich Muenz, Siemens Corporate Technology research group head. “Collaborating with the Department of Energy’s U.S. National Laboratories and co-creating with the nation’s energy community is crucial to modernizing and enhancing America’s energy infrastructure.”

The MOU covers a five-year period with provisions to renew or extend it.

Sodium sulfur (NAS) batteries produced by Japan’s NGK Insulators are being put into use on a massive scale in Abu Dhabi, the capital of the United Arab Emirates.

The company’s battery systems have been deployed across 10 locations – 15 systems in total – adding up to 108MW / 648MWh in total, with each system able to store energy for six hours. The total undertaking includes 12 x 4MW systems and three 20MW systems. The official government Emirates News Agency described the project as the “world’s largest Virtual Battery Plant” as it opened earlier this month.

A representative at NGK’s power business division told Energy-Storage.news the ‘virtual’ description is correct in the sense that the 15 systems in 10 locations “can be controlled as a single plant. While of course they can still be controlled individually when local support to the grid is needed”.

Critical to this aggregation of the systems is the CISC (Centralised Integrated System Controller) which will be located at a control room in Mussafah, an industrial district in Abu Dhabi’s southwest where some of the battery systems are also located, with the rest in nearby Sila. CISC and the NAS systems are “ready to be operated by the TSO (transmission system operator)”, the NGK representative said.

Operational parameters increased from original scope
Awaidha Al Marar, chairman of Abu Dhabi’s Department of Energy, attended an inauguration event on 17 January, as a number of events including Abu Dhabi Sustainability Week and World Future Energy Summit (WFES) took place in the region.

The NGK CISC 648MWh project will help the city load balance across its networks during the daytime, as well as providing up to six hours backup in the case of grid outages. As with many energy storage system projects, it is primarily about reducing the strain on the grid at times of peak demand.

According to the NGK representative, the project was originally planned as thermal generation investment deferral, to reduce the cost of network operations and maintenance (O&M) and to increase total system efficiency, “as well securing that diesel will not be used anymore for peak load”. However, as the project was mapped out and development began, other services were added: frequency control, operating reserve and voltage control.

Why sodium sulfur over lithium-ion

While many grid-scale battery projects around the world are currently being executed with lithium-ion batteries, in this instance, the use of sodium sulfur, allowing for six hours of storage, is “mandatory for thermal generation investment deferral”, the NGK spokesman said, with the peak demand period being shifted itself lasting around six hours.

“[Deploying] 1MW of battery energy storage systems allows avoiding the investment in about 1.1MW of combined cycle (gas and steam) thermal power plants,” by increasing availability by about 10%, while O&M costs for battery systems “are much lower” than equivalent costs for thermal generation plants.

Energy-Storage.news asked what made the NAS battery particularly suitable for the Abu Dhabi project. The NGK representative said that the six hours of storage in each battery cell reduces total system cost versus lithium batteries. Lithium-ion systems tend to combine several one-hour duration battery cells, “which increases the integration costs”. NAS battery systems are also less sensitive to external temperature conditions. There is no need for air-conditioning to keep cells at the right operating temperature – unlike lithium batteries, NAS batteries are insulated and operate at about 300 degrees centigrade. Due to the insulation, it is still safe to touch the exterior of the module with bare hands. The NGK representative explained further that the rugged nature of the batteries and the ways they can be used provide further compelling reasons to use them in the Middle East.

NAS batteries are robust for the kind of heavy use – charging and discharging the battery each day in a full cycle from 100% state-of-charge to 0% i.e. a full 100% depth of discharge (DOD), which make generation investment deferral possible. The batteries are expected to last “15 years without degradation at system level”.

In November, Energy-Storage.news reported on the inauguration of a 20MWh NGK NAS battery project in Niedersachsen, Germany, combined with 7.5MW / 2.5MWh of lithium-ion batteries from Hitachi Chemical. That will be a three-year demonstration, developed through Japan’s NEDO (New Energy and Industrial Technology Development Organisation) and Niedersachsen’s Ministry for Economics, Labour and Transport, as well as authorities in the City of Varel where the demonstration project is located.

Seeds of energy storage’s future

The 648MWh project marks the second announced deployment of NGK NAS batteries in the Emirates, with Dubai Electricity and Water Authority (DEWA) announcing in August last year that it will test a 1.2MW / 7.2MWh NGK sodium sulfur battery system at Mohammed bin Rashid Al Maktoum Solar Park.

Also during January, a Smart Grid Station (SGS) was inaugurated in Al Ruwayyah, Dubai by Dubai Supreme Council of Energy chairman Sheikh Ahmed bin Saeed Al Maktoum. Again, a DEWA project, the SGS was deployed in partnership with South Korea’s state-owned Korea Electric Power Corporation (KEPCO).

DEWA and KEPCO have been exchanging experiences and best practises knowledge with each other on smart city and smart grid topics, including standardisation. The Internet-of-things technology-backed SGS combines a 200kW PV system with 9kW of wind energy and a 500kWh battery energy storage system. It also uses a large thermal energy storage system which provides cooling and a smart chiller system integrated into the SGS’ building management system. The DWA-KEPCO project has been in the making since November 2015.

Developing a perfectly energy-efficient building is relatively easy to do—if you don’t give the building’s occupants any control over their environment. Since nobody wants that kind of building, Professor Christoph Reinhart has focused his career on finding ways to make buildings more energy-efficient while keeping user needs in mind.

“At this point in designing buildings, the biggest uncertainty comes from user behavior,” says Reinhart, who heads the Sustainable Design Lab in MIT’s Department of Architecture. “Once you understand heat flow, it’s a very exact science to see how much heat to add or take from a space.”

Trained in physics, Reinhart made the move to architecture because he wanted to apply the scientific concepts he’d learned to make buildings more comfortable and energy-efficient. Today, he is internationally known for his work in what architects call “daylighting”—the use of natural light to illuminate building interiors—and urban-level environmental building performance analysis. The design tools that emerged from his lab are used by architects and urban planners in more than 90 countries.

The Sustainable Design Lab’s work has also produced two spinoff companies: Mapdwell, which provides individualized cost-benefit analyses for installing solar panels; and Solemma, which provides environmental analysis tools such as DIVA-for-Rhino, a highly optimized daylighting and energy modeling software component. Reinhart is a co-founder and strategic development advisor at Mapdwell, and he is CEO of Solemma.

Through it all, physics has remained a central underpinning. “Everything our lab develops is based on physics first,” says Reinhart, who earned master’s degrees in physics from Albert Ludwigs Universität in Freiburg, Germany, and Simon Fraser University in Vancouver, Canada.

Informing design

A lifelong environmentalist, Reinhart says he was inspired to study architecture in part by the work of the Fraunhofer Institute for Solar Energy Systems, which built a completely self-sufficient solar house in Freiburg in the early 1990s.

While finishing his master’s thesis, Reinhart says, he also read an article that suggested that features such as color can be more important than performance to architects choosing a solar system—an idea that drove him to find ways to empower architects to consider aesthetics and the environmental performance of their designs at the same time. He began this effort by investigating daylighting at the Technical University of Karlsruhe, Germany.

Light is incredibly important from a design standpoint—architects talk of “painting with light”—but there are also significant technical challenges involved in lighting, such as how to manage heat and glare, Reinhart says.

“You need good sky models and you need good rendering tools to model the light. You also need computer science to make it faster—but that’s just the basics,” Reinhart says, noting that the next step is to consider how people perceive and use natural light. “This really nuanced way of thinking is what makes daylighting so fun and interesting.”

For example, designers typically render buildings with all the blinds open. If they learn that people will keep the blinds down 90 percent of the time with a given design, they are likely to rethink it, Reinhart says, because “nobody wants that.”

The daylighting analysis software developed by Reinhart’s team in 1998 provides just this kind of information. Known as DAYSIM, it is now used all over the world to model annual daylight availability in and around buildings.

Reinhart has also published textbooks on daylighting: “Daylighting Handbook I: Fundamentals and Designing with the Sun” was published in in 2014, and a second volume, “Daylighting Handbook II: Daylight Simulations and Dynamic Facades,” was released last October.

“Daylighting was really my first way into architecture,” Reinhart says, noting that he thinks it’s wonderful that the field combines “rock solid science” like sky modeling with more subjective questions related to the users’ experience, such as: “When is sunlight a liability?” and “When does it add visual interest?”

Teaching and advising

After earning his doctorate in architecture from Technical University in 2001, Reinhart taught briefly at McGill University in Canada before being named an associate professor of architecture at Harvard University’s Graduate School of Design. In 2009, the student forum there named him faculty member of the year.

In 2012, he joined the faculty at MIT, where he typically supervises seven or eight graduate students, including about three working on their Ph.D.s. Often, he also has students working in his lab through the Undergraduate Research Opportunities Program. Several students majoring in computer science have proved particularly helpful, he says.

“It’s amazing what MIT students can implement,” he says.

Reinhart is also an instructor, of course, notably teaching 4.401/4.464 (Environmental Technologies in Buildings), which focuses on how to assess the energy efficiency of buildings.

“There’s nothing more fun—especially at an institution like MIT—than to teach these concepts,” he says.

The MIT Energy Initiative (MITEI) is now working to make that subject available online via MITx, and the class is expected to be part of a planned graduate certificate in energy, according to Antje Danielson, MITEI’s director of education.

City-scale modeling

Meanwhile, Reinhart has scaled his own research up to modeling energy use at the city level. In 2016, he and colleagues unveiled an energy model for Boston that estimates the gas and electricity demands of every building in the city—and his team has since assessed other urban areas.

This work has underscored for him how significant user behavior is to calculating energy use.

“For an individual building you can get a sense of the user behavior, but if you want to model a whole city, that problem explodes on you,” Reinhart says, noting that his team uses statistical methods such as Bayesian calibration to determine likely behaviors.

Essentially, they collect data on energy use and train the computer to recognize different scenarios, such as the energy used by different numbers of people and appliances.

“We throw 800 user behaviors at a sample of buildings, and since we know how much energy these buildings actually use, we only keep those behavioral patterns that give us the right energy use,” Reinhart says, explaining that repeating the process produces a curve that indicates the buildings’ most likely uses. “We don’t know exactly where people are, but at the urban level, we get it right.”

Determining how energy is being used at this broad scale provides critical information for addressing the needs of the energy system as a whole, Reinhart says. That’s why Reinhart is currently working with Exelon Corporation, a major national energy provider, to assess energy use in Chicago. “We can say, let’s foster these kinds of upgrades and pretty much guarantee that this is how the energy load throughout a neighborhood or for particular substations will change—which is just what utilities want to know,” he says.

The food-energy-water nexus

Recently, Reinhart has also begun investigating ways to make food production more energy-efficient and sustainable. His lab is developing a software component that can estimate food yields, associated use of energy and water, and the carbon emissions that result for different types of urban farms.

For example, hydroponic container farming—a system of growing food without soil inside something like a shipping container—is now being promoted by companies in some cities, including Boston. This system typically uses more electricity than conventional farming does, but that energy use can be more than offset by the reduced need for transportation, Reinhart says. Already, Reinhart’s team has shown that rooftop and container farming on available land in Lisbon, Portugal, could theoretically meet the city’s total vegetable demand.

This work exploring the nexus between food, energy, and water is just the next level of complexity for Reinhart in a career dedicated to moving the needle on sustainability. Fortunately, he’s not alone in his work; he has sent a host of young academics out into the world to work on similar concerns.

Reinhart’s former graduate students now work at universities including Cornell, Harvard, Syracuse, and the University of Toronto, and he continues to collaborate with them on projects.

It’s like having a growing family, says Reinhart, a father of two. “Students never leave. It’s like kids.”