TSCM America oferă contramăsuri tehnice pentru detectarea și verificarea vulnerabilităților și a tuturor amenințărilor de interceptare activă și a dispozitivelor de telecomunicații, inclusiv a sistemelor analogice, digitale și VoIP
Pe suprafețele plane plate ale unui substrat cu diamant acoperit cu grafen, moleculele se auto-asamblează în arhitectura țintă într-un mod asemănător cu proteinele și nanotehnologia ADN-ului. Singura forță motrice provine din interacțiunile supramoleculare construite prin legături de hidrogen. Asa cum era de asteptat, reteaua moleculara produce o fotocurent atunci cand este expusa la lumina.
| Posted: Mar 02, 2016 | |
Molecular graphene architectures see the light(Nanowerk News) Organic photovoltaics bear great potential for large-scale, cost-effective solar power generation. One challenge to be surmounted is the poor ordering of the thin layers on top of the electrodes. Utilizing self-assembly on atomically flat, transparent substrates, a team of scientists at the Technical University of Munich (TUM) has engineered ordered monolayers of molecular networks with photovoltaic responses. The findings open up intriguing possibilities for the bottom-up fabrication of optoelectronic devices with molecular precision. |
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| Nature is unrivaled when it comes to the self-assembly of complex, high-performance molecular machinery for light absorption, exciton or charge separation and electron transfer. Molecular nanotechnologists have long dreamt of mimicking such extraordinary biomolecular architectures and rewiring them to produce inexpensive electricity. | |
| Now researchers from the Departments of Physics and Chemistry at the Technical University of Munich (TUM), from the Max-Planck Institute for Polymer Research (Mainz, Germany) and the Université de Strasbourg (France) have modified dye molecules in such a manner that allows them to serve as building blocks of self-assembling molecular networks (Nature Communications, „Photoresponse of supramolecular self-assembled networks on graphene-diamond interfaces”). | |
| On the atomically flat surfaces of a graphene coated diamond substrate the molecules self-assemble into the target architecture in a manner akin to proteins and DNA nanotechnology. The sole driving force stems from the engineered supramolecular interactions via hydrogen bonds. As expected, the molecular network produces a photocurrent when exposed to light. | |
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| Scanning tunneling microscopic topography of melamine linked terrylene-diimide molecules with inserted model of the molecular nertwork (Scale bar: 2nm). (Image: C. A. Palma / TUM) | |
| From art to application | |
| “For a long time engineered self-assembled molecular architectures were looked upon as arty,” says PD Dr. Friedrich Esch, a lead author of the study. “With this publication we present for the first time a serious practical implementation of this technology.” | |
| “In conventional organic photovoltaics the improvement of molecular order is still a challenge. In contrast, the nanotechnology toolbox provides us with the possibility of an atomically precise layout of the constituting components a priori,” says Dr. Carlos-Andres Palma, who co-supervised the study. “The possibility of full physicochemical control of the components gives us additional set-screws for functional optimization.” | |
| The scientists now hope to scale up the device configuration and certify the photovoltaic response under standard conditions. “Intercalating self-assembled dyes between stacks of two-dimensional electrodes like graphene, opens up the possibility of easy scale-up to efficient photovoltaic monolayer elements”, claims Dr. Palma “This will put our work on the solar cell technology map”. | |
| Perfect match of surface chemistry and physics | |
| The scientists used terrylene-diimide molecules as photoactive dyes. The network is formed when the elongated terrylene molecules link up with trivalent melamine. By choosing adequate side groups for the terrylene diimide the authors of the study determine which architectures can form. | |
| “This work is an excellent example of the interdisciplinary cooperation we seek to initiate with the institution of the Catalysis Research Center: a perfect match of chemistry and physics,” says Professor Ulrich Heiz, director of the TUM Catalysis Research Center. |
| Source: Technical University of Munich |
o echipă de cercetători de la MIT și în altă parte a constatat că, cel puțin în unele reactoare, adăugarea unei cantități mici de nanotuburi de carbon la metal poate încetini dramatic acest proces de defalcare.utilizabilă în aliajele de temperatură mai ridicată utilizate în reactoarele comerciale.
Metalul cu nanotuburi de carbon uniform dispersat în interiorul „este conceput pentru a atenua daunele cauzate de radiații
| Posted: Mar 02, 2016 | |
Carbon nanotubes improve metal’s longevity under radiation(Nanowerk News) One of the main reasons for limiting the operating lifetimes of nuclear reactors is that metals exposed to the strong radiation environment near the reactor core become porous and brittle, which can lead to cracking and failure. Now, a team of researchers at MIT and elsewhere has found that, at least in some reactors, adding a tiny quantity of carbon nanotubes to the metal can dramatically slow this breakdown process. |
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| For now, the method has only proved effective for aluminum, which limits its applications to the lower-temperature environments found in research reactors. But the team says the method may also be usable in the higher-temperature alloys used in commercial reactors. | |
| The findings are described in the journal Nano Energy („Dispersion of carbon nanotubes in aluminum improves radiation resistance”), in a paper by MIT Professor Ju Li, postdocs Kang Pyo So and Mingda Li, research scientist Akihiro Kushima, and 10 others at MIT, Texas A&M University, and universities in South Korea, Chile, and Argentina. | |
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| The metal with carbon nanotubes uniformly dispersed inside “is designed to mitigate radiation damage” for long periods without degrading, Kang Pyo So says. Pictured is an example of how the researchers created aluminum with carbon nanotubes inside. (Image: Courtesy of the researchers) | |
| Aluminum is currently used in not only research reactor components but also nuclear batteries and spacecraft, and it has been proposed as material for storage containers for nuclear waste. So, improving its operating lifetime could have significant benefits, says Ju Li, who is the Battelle Energy Alliance Professor of Nuclear Science and Engineering and a professor of materials science and engineering. | |
| Long-term stability | |
| The metal with carbon nanotubes uniformly dispersed inside “is designed to mitigate radiation damage” for long periods without degrading, says Kang Pyo So. | |
| Helium from radiation transmutation takes up residence inside metals and causes the material to become riddled with tiny bubbles along grain boundaries and progressively more brittle, the researchers explain. The nanotubes, despite only making up a small fraction of the volume — less than 2 percent — can form a percolating, one-dimensional transport network, to provide pathways for the helium to leak back out instead of being trapped within the metal, where it could continue to do damage. | |
| Testing showed that after exposure to radiation, the carbon nanotubes within the metal can be chemically altered to carbides, but they still retain their slender shape, “almost like insects trapped in amber,” Ju Li says. “It’s quite amazing — you don’t see a blob; they retain their morphology. It’s still one-dimensional.” The huge total interfacial area of these 1-D nanostructures provides a way for radiation-induced point defects to recombine in the metal, alleviating a process that also leads to embrittlement. The researchers showed that the 1-D structure was able to survive up to 70 DPA of radiation damage. (DPA is a unit that refers to how many times, on average, every atom in the crystal lattice is knocked out of its site by radiation, so 70 DPA means a lot of radiation damage.) | |
| After radiation exposure, Ju Li says, “we see pores in the control sample, but no pores” in the new material, “and mechanical data shows it has much less embrittlement.” For a given amount of exposure to radiation, the tests have shown the amount of embrittlement is reduced about five to tenfold. | |
| The new material needs only tiny quantities of carbon nanotubes (CNTs) — about 1 percent by weight added to the metal — and these are inexpensive to produce and process, the team says. The composite can be manufactured at low cost by common industrial methods and is already being produced by the ton by manufacturers in Korea, for the automotive industry. | |
| Strength and resilience | |
| Even before exposure to radiation, the addition of this small amount of nanotubes improves the strength of the material by 50 percent and also improves its tensile ductility — its ability to deform without breaking — the team says. | |
| “This is a proof of principle,” says Kang Pyo So. While the material used for testing was aluminum, the team plans to run similar tests with zirconium, a metal widely used for high-temperature reactor applications such as the cladding of nuclear fuel pellets. “We think this is a generic property of metal-CNT systems,” he says. | |
| “This is a development of considerable significance for nuclear materials science, where composites — particularly oxide dispersion-strengthened steels — have long been considered promising candidate materials for applications involving high temperature and high irradiation dose,” says Sergei Dudarev, a professor of materials science at Oxford University in the U.K., who was not involved in this work. | |
| Dudarev adds that this new composite material “proves remarkably stable under prolonged irradiation, indicating that the material is able to self-recover and partially retain its original properties after exposure to high irradiation dose at room temperature. The fact that the new material can be produced at relatively low cost is also an advantage.” | |
| Sergei Kucheyev, a physicist at the Lawrence Livermore National Laboratory who also was not involved in this research, says, “These results could have important technological implications. They also point to our still-limited understanding of the physics of radiation defects at interfaces in technologically relevant regimes.” |
| Source: By David L. Chandler, MIT |
Read more: Carbon nanotubes improve metal’s longevity under radiation
Cercetătorii au elaborat un comportament cuantic în alte platforme, pe lângă domeniul solidar în care a fost descoperit inițial. Semnăturile unei astfel de fizici au fost observate în gazele atomice ultravold și în fotoni, unde lumina se deplasează în chipsuri fabricate. Hafezi și colegii au condus acuzația în domeniul fotonicii.
Grupul utilizează un cip pe bază de siliciu care este umplut cu o serie de structuri în formă de inel numite rezonatoare. Rezonatorii sunt conectați între ei prin intermediul ghidurilor de undă.
Designul cipului determină strict condițiile în care lumina poate călători de-a lungul marginilor, mai degrabă decât prin regiunile interioare. Cercetatorii masoara spectrul de transmitere, care este fractia de lumina care trece cu succes printr-o cale margine. Pentru a circula fără obstacole prin modurile protejate de margini, lumina trebuie să posede o anumită energie. Transmisia crește atunci când energia luminoasă corespunde acestui criteriu.
| Posted: Mar 02, 2016 | |
Characterizing quantum Hall light zooming around a photonic chip(Nanowerk News) When it comes to quantum physics, light and matter are not so different. Under certain circumstances, negatively charged electrons can fall into a coordinated dance that allows them to carry a current through a material laced with imperfections. That motion, which can only occur if electrons are confined to a two-dimensional plane, arises due to a phenomenon known as the quantum Hall effect. |
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| Researchers, led by Mohammad Hafezi, a JQI Fellow and assistant professor in the Department of Electrical and Computer Engineering at the University of Maryland, have made the first direct measurement that characterizes this exotic physics in a photonic platform. | |
| The research was published online Feb. 22 and featured on the cover of the March 2016 issue of Nature Photonics („Measurement of Topological Invariants in a 2D Photonic System”). These techniques may be extended to more complex systems, such as one in which strong interactions and long-range quantum correlations play a role. | |
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| Image of photonic chip and apparatus. (Image: E. Edwards/JQI) | |
| The quantum Hall effect is best understood by peering through the lens of topology. In the 1980s, physicists discovered that electrons in some materials behave strangely when subjected to large magnetic fields at extreme cryogenic temperatures. Remarkably, the electrons at the boundary of the material will flow along avenues of travel called ‘edge states’, protected against defects that are most certainly present in the material. | |
| Moreover, the conductance–a measure of the current–is quantized. This means that when the magnetic field is ramped up, then the conductance does not change smoothly. Instead it stays flat, like a plateau, and then suddenly jumps to a new value. The plateaus occur at precise values that are independent of many of the material’s properties. This hopping behavior is a form of precise quantization and is what gives the quantum Hall effect its great utility, allowing it to provide the modern standard for calibrating resistance in electronics, for instance. | |
| Researchers have engineered quantum Hall behavior in other platforms besides the solid-state realm in which it was originally discovered. Signatures of such physics have been spotted in ultracold atomic gases and photonics, where light travels in fabricated chips. Hafezi and colleagues have led the charge in the photonics field. | |
| The group uses a silicon-based chip that is filled with an array of ring-shaped structures called resonators. The resonators are connected to each other via waveguides. | |
| The chip design strictly determines the conditions under which light can travel along the edges rather than through the inner regions. The researchers measure the transmission spectrum, which is the fraction of light that successfully passes through an edge pathway. To circulate unimpeded through the protected edge modes, the light must possess a certain energy. The transmission increases when the light energy matches this criteria. | |
| For other parameters, the light will permeate the chip interior or get lost, causing the transmission signal to decrease. The compiled transmission spectrum looks like a set of bright stripes separated by darker regions (see figure). Using such a chip, this group previously collected images of light traveling in edge states, definitively demonstrating the quantum Hall physics for photons. | |
| In this new experiment Hafezi’s team modified their design to directly measure the value of the topology-related property that characterizes the photonic edge states. This measurement is analogous to characterizing the quantized conductance, which was critical to understanding the electron quantum Hall effect. In photonics, however, conductance is not relevant as it pertains to electron-like behavior. Here the significant feature is the winding number, which is related to how light circulates around the chip. Its value equals to the number of available edge states and should not change in the face of certain disruptions. | |
| To extract the winding number, the team adds 100 nanometer titanium heaters on a layer above the waveguides. Heat changes the index of refraction, namely how the light bends as it passes through the waveguides. In this manner, researchers can controllably imprint a phase shift onto the light. Phase can be thought of in terms of a time delay. For instance, when comparing two light waves, the intensity can be the same, but one wave may be shifted in time compared to the other. The two waves overlap when one wave is delayed by a full oscillation cycle—this is called a 2π phase shift. | |
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| (click on image to enlarge) | |
| On the chip, enough heat is added to add a 2π phase shift to the light. The researchers observe an energy shift in the transmission stripes corresponding to light traveling along the edge. Notably, in this chip design, the light can circulate either clockwise (CW) or counterclockwise (CCW), and the two travel pathways do not behave the same (in contrast to an interferometer). When the phase shift is introduced, the CW traveling light hops one direction in the transmission spectrum, and the CCW goes the opposite way. The winding number is the amount that these edge-state spectral features move and is exactly equivalent to the quantized jumps in the electronic conductance. | |
| Sunil Mittal, lead author and postdoctoral researcher explains one future direction, “So far, our research has been focused on transporting classical [non-quantum] properties of light–mainly the power transmission. It is intriguing to further investigate if this topological system can also achieve robust transport of quantum information, which will have potential applications for on-chip quantum information processing.” | |
| Background: Symmetry and Topology | |
| Physicists use different approaches to classify matter; symmetry is one powerful method. For instance, the microscopic structure of a material like diamond looks the same even while shifting your gaze to a new spot in the crystal. These symmetries – the rotations and translations that leave the microscopic structure the same – predict many of the physical properties of crystals. | |
| Symmetry can actually offer a kind of protection against disruptions. Here, the word protection means that the system (e.g. a quantum state) is robust against changes that do not break the symmetry. Recently, another classification scheme based on topology has gained significant attention. Topology is a property that depends on the global arrangement of particles that make up a system rather than their microscopic details. The excitement surrounding this mathematical concept has been driven by the idea that the topology of a system can offer a stability bubble around interesting and even exotic physics, beyond that of symmetry. Physicists are interested in harnessing states protected by both symmetry and topology because quantum devices must be robust against disturbances that can interfere with their functionality. |
| Source: Joint Quantum Institute |
Read more: Characterizing quantum Hall light zooming around a photonic chip
a dezvoltat structuri de o scara nanometrica care pot fi folosite ca biosenzori pentru sectoare medicale, alimentare sau de mediu pentru a detecta boli, alergeni sau contaminanti; Sau pot fi utilizate pentru a reduce reflexia celulelor solare, pentru a crește eficiența acestora.
| Posted: Mar 02, 2016 | |
Nanostructures used as biosensors allow diseases or allergens to be detected(Nanowerk News) The industrial engineer Iñaki Cornago-Santos has developed structures on a nanometric scale that can be used as biosensors for medical, food or environmental sectors to detect diseases, allergens or contaminants; or can be used to reduce the reflection of solar cells in order to increase their efficiency. This is what he says in his PhD thesis defended at the NUP/UPNA-Public University of Navarre. |
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| Iñaki Cornago, during the fabrication process of nanostructures. | |
| “Over the years tremendous progress has been made in micro- and nano-fabrication techniques with the help of the industry of semi-conductor materials,” explained Iñaki Cornago. “The aim of these advances is to be able to fabricate increasingly smaller components that are closer to each other in line with a trend known as miniaturization.” | |
| Within the techniques used in these micro- and nano-fabrication processes, in his PhD thesis Cornago made use of what is known as laser interference lithography, which consists of applying laser radiation to a photo-sensitive material to create structures on a nanometric scale. In this case, he used glass, gold and silicon, among other materials, to which he gave shapes such as lines, holes, pillars or cones. | |
| The applications of these nanostructures can be clasified in two groups: anti-reflective surfaces and biosensors. “In the first case, they are used to create a medium that reduces the reflection caused when light hits a surface,” said Cornago. „This mechanism can be used to minimize, for example, the undesired reflections that are produced in glasses, windows or car windows and also the reflection produced on solar panels, which can increase the efficiency of these photovoltaic cells.” | |
| Optical response to a biological reaction | |
| As regards the second group of applications, nanostructures are used “to achieve a specific optical response that, together with a biological reaction, allows information to be obtained about the presence of a substance in a sample”. The thesis, supervised by Rafael Rodríguez-Trías, lecturer in the NUP/UPNA’s Department of Mechanical, Energy and Materials Engineering, and the PhD holder in Engineering Javier Bravo Larrea, presents ”a range of biosensor types that can be used in sectors, such as food, to find allergens, for example, as in the case of gluten or nuts; in the biomedical sector to detect diseases in biological samples, such as blood or urine; or in the environmental sector to spot toxins or chemical contaminants in marine waters”. |
| Source: Elhuyar Fundazioa |
Read more: Nanostructures used as biosensors allow diseases or allergens to be detected
dezvolta funcționalitatea complementară a materialului semiconductor compus (III-V CMOS), care susține atât funcționalitatea analogică, cât și cea digitală în domeniul frecvențelor undei milimetrice. Nivelele III-V vor fi folosite pentru a menține controlul electrostatic, deoarece lungimea porții este redusă pentru nodurile tehnologice viitoare. Secțiunea transversală mică a nanofirelor facilitează în continuare integrarea pe substraturile cu ajutorul nanotehnologie
| Posted: Mar 02, 2016 | |
Meeting the increasing performance demands at millimetre-wave frequencies(Nanowerk News) Future radar imaging systems and 5G communication systems will generate improved resolution and provide higher data-transmission rates when operated at higher frequencies, but at the cost of increased power consumption. To reduce power consumption, increase performance, and lower costs, the European project INSIGHT (Integration of III-V Nanowire Semiconductors for Next Generation High Performance CMOS SOC Technologies) is aiming at developing III-V CMOS (complementary metal-oxide-semiconductor) technology. The six partners, including universities, research institutes and one company, are committed to establishing a manufacturable III-V CMOS technology on Si substrates, to reduce costs and to save scarce materials. |
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| The INSIGHT mission is to develop complementary functionality in compound semiconductor material (III-V CMOS), supporting both analogue and digital functionality in the millimetre-wave frequency domain. III-V nanowires will be used to maintain electrostatic control, as the gate length is scaled for future technology nodes. The small nanowire cross-section further facilitates the integration onto Si substrates using nanotechnology. | |
| “The fabrication of high-performance III-V components on large Si substrates using CMOS compatible technologies opens a path for cost reduction of millimetre-wave key components with minimized usage of critical materials” says Lars-Erik Wernersson, Professor at Lund University and coordinator for INSIGHT. Lund University is coordinating this new European Horizon 2020 research project that has been funded with 4.3 million Euros over 36 months. | |
| Professor Lars-Erik Wernersson from Lund University, introducing the INSIGHT project. | |
| IBM foresees a growing need to push the limits of chip technology to meet the emerging demands of cognitive computers, Internet of Things and Cloud platforms, due to the enormous amount of data they are handling – 90% of which is unstructured. The new technology developed in INSIGHT offers a potential solution to scale chip technology beyond the 10 nm node as well as opening up a range of new application areas. Integrating III-V materials into Si CMOS can enable better logic circuits with a lower power consumption, and in addition can enable the realization of System-on-Chip (SoC) products taking full advantage of III-V’s state-of-the-art RF/Analog metrics. | |
| There is a growing need for performance enhancements of key components in the millimetre-wave frequency range and new consumer applications are demanding low costs. The new technology offers a potential solution, as it may provide both high-performance analogue and digital functionality on the same platform where the improved manufacturability allows production on larger wafers. The INSIGHT consortium addresses the technology need with the ambition to demonstrate circuits and systems by optimizing both material and device properties. | |
| The introduction of III-V materials on silicon substrates by using nanowires is one of the most innovative heterogeneous integration approaches today. Fraunhofer | |
| IAF will bring in their III-V process and circuit design experience, and is interested in transferring the results and findings to next generation III-V device technologies. | |
| The LETI participation in the INSIGHT project involves both the Silicon Component division and the Integrated Circuit & Embedded System division, ranging from materials to the circuit demonstration. The technology expands the LETI platform for smart devices and Internet of Things with the potential to squeeze multiple functions into a single die. | |
| III-V CMOS technology may be particularly suited for millimetre-wave front-ends where it will be used to detect and generate signals for communication, radar and imaging. It is the goal of the INSIGHT consortium to develop key technologies for both the receivers and transmitters, while exploring the limits of the transistor geometry and layout. | |
| Besides Fraunhofer IAF (Germany) and LETI (France), the consortium consists of Lund University (Sweden), University of Glasgow (UK), Tyndall National Institute (Ireland) and IBM (Switzerland). The expertise of the partners spans the complete spectrum from materials, through devices, all the way to circuits and systems, allowing the consortium to take this promising technology further along the path to commercial products. INSIGHT is funded under the Horizon 2020 Programme for Research and Development of the European Union (Grant agreement number 688784). |
| Source: Project INSIGHT |
Read more: Meeting the increasing performance demands at millimetre-wave frequencies
Folosind o combinație de pulverizare (pentru metale) și depunere pulsată cu laser (pentru izolator), am arătat cu succes că izolatorul magnetic cu grosimea de 50-100 nanometri, cum ar fi granat de fier de ytriu, nu este numai magnetic și izolator, Este cultivată pe platină de 5 nanometri grosime.
| Posted: Mar 02, 2016 | |
Spinning better electronic devices(Nanowerk News) A team of researchers, led by a group at the University of California, Riverside, have demonstrated for the first time the transmission of electrical signals through insulators in a sandwich-like structure, a development that could help create more energy efficient electronic devices. |
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 Jing Shi, a professor of physics.Conventional electronic devices rely on the transport of electrons in a semiconductor such as silicon. Now, researchers are exploiting the ‘spin’ of the electron rather than its charge to create a new generation of ‘spintronic’ devices that are potentially more energy efficient and more versatile than those currently making up silicon chips and circuit elements.The UC Riverside-led research, which was published online Wednesday (March 2) in the journal Nature Communications („Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta)trilayers”), is significant because it demonstrates that a tri-layer, sandwich-like, structure can serves as a scalable pure spin current device, an essential ingredient in spintronics. A key element in this breakthrough is the material. To demonstrate the effect, the magnetic insulator needs to be truly insulating, or there will be a parasitic signal from leakage. On the other hand, a high-quality magnetic insulator grown on metal had never been demonstrated. |
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| Using combination of sputtering (for metals) and pulsed laser deposition (for insulator), we successfully showed that the 50-100 nanometer thick magnetic insulator, such as yttrium iron garnet, is not only magnetic and insulating, but also of high quality when it is grown on 5 nanometer thick platinum. | |
| In the structures used by the researchers, there are two metals and a magnetic insulator in between. The metals are for spin current generation and detection (conversion of spin current back to charge current) via the so-called spin Hall effect and inverse spin Hall effect. | |
| The magnetic insulator is an electrical insulator but a good spin current conductor. The spin current flowing in the insulator does not involve mobile electrons therefore it does not dissipate energy as an electrical current does in joule heating. | |
| The researchers have also demonstrated that the signal transmission can be switched on and off and modulated in its strength by a magnetic field. The electrical signal transmission through the magnetic insulators can be switched on and off depending on the magnetic state, or direction of the magnetization, of the magnetic insulators. | |
| So the direction of the magnetization can be regarded as a memory state of non-volatile random access memory devices. In addition, the signal level can be modulated by changing the direction of the magnetization; therefore, it can also be used as analog devices. The sandwich structure can be made small by nanofabrication so that the devices can be scaled down. |
| Source: University of California – Riverside | |
Read more: Spinning better electronic devices
Studiul lor oferă o platformă pentru ingineria materialelor bidimensionale (2D) cu proprietăți optice și electronice care depind puternic de configurațiile de stivuire. Constatările sunt publicate în ACS Nano („Twisted MoSe2 Bilayers cu stivuire variabilă locală și cuplaj interlayer dezvăluit de spectrometrie Raman de joasă frecvență”).
| Posted: Mar 02, 2016 | |
Researchers stack the odds for novel optoelectronic 2-D materials(Nanowerk News) Stacking layers of nanometer-thin semiconducting materials at different angles is a new approach to designing the next generation of energy-efficient transistors and solar cells. The atoms in each layer are arranged in hexagonal arrays. When two layers are stacked and rotated, atoms from one layer overlap with those in the other layer and can form an infinite number of overlapping patterns, like the Moiré patterns that result when two screens are overlaid and one is rotated on top of the other. Theoretical calculations predict excellent electronic and optical properties for some stacking patterns, but practically, how can these patterns be made and characterized? |
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| Recently a team led by researchers from the Department of Energy’s Oak Ridge National Laboratory used the vibrations between two layers to decipher their stacking patterns. The team employed a method called low-frequency Raman spectroscopy to measure how the layers vibrate with respect to each other and compared the frequencies of the measured vibrations with their theoretically predicted values. Their study provides a platform for engineering two-dimensional (2D) materials with optical and electronic properties that strongly depend on stacking configurations. The findings are published in ACS Nano („Twisted MoSe2 Bilayers with Variable Local Stacking and Interlayer Coupling Revealed by Low-Frequency Raman Spectroscopy”). | |
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| Mutual rotation of two monolayers of a semiconducting material creates a variety of bilayer stacking patterns, depending on the twist angle. Fast and efficient characterization of these stacking patterns may aid exploration of potential applications in electronics and optoelectronics. (Image: ORNL) | |
| „Low-frequency Raman spectroscopy, in combination with first-principles modeling, offers a quick and easy approach to reveal complex stacking configurations in the twisted bilayers of a promising semiconductor, without relying on other expensive and time-consuming experimental techniques,” said co-lead author Liangbo Liang, a Wigner Fellow at ORNL. „We are the first to show that low-frequency Raman spectra can be used as fingerprints to characterize the relative layer stacking in semiconducting 2D materials.” | |
| In Raman scattering, an optical method for probing atomic vibrations, a material scatters monochromatic light from a laser. Whereas conventional Raman spectroscopy may probe more than approximately 3 trillion atomic vibrations per second, low-frequency Raman spectroscopy detects vibrations that are an order of magnitude slower. The low-frequency technique is sensitive to weak attractive forces between layers, called van der Waals coupling. It can provide crucial insight about layer thickness and stacking–aspects that govern fundamental properties of 2D materials. | |
| „This work combines state-of-the art synthesis and processing of 2D materials, their unique spectroscopic characterization, and data interpretation using first-principles theory,” said co-lead author Alex Puretzky. „High-resolution Raman spectroscopy that can probe low-frequency modes requires specialized instrumentation, and only a few places around the world have such a capability together with advanced synthesis and characterization tools, and theory and computational modeling expertise. The Center for Nanophase Materials Sciences at ORNL is among them.” | |
| Chemical vapor deposition, widely employed to synthesize 2D materials like graphene, was used to make perfectly triangular crystal monolayers of molybdenum diselenide just three atoms thick. Feedstock molecules of molybdenum oxide and sulfur were reacted in a flowing gas within a high-temperature furnace to form the triangular crystals on silicon substrates. | |
| „Numerous parameters need to be properly adjusted to synthesize large, triangular 2D crystals successfully,” Puretzky said. „Then, carefully removing the crystals and stacking them precisely in different orientations is a big challenge.” | |
| He continued, „The precise, equilateral triangular shape of the synthesized and transferred crystals allowed us to measure the twist angles with a high precision using standard optical and atomic force microscopy images, which was a key factor in our experiments.” | |
| Theoretical and computational aspects were challenging too. „Raman spectroscopy is heavily based on theory for interpretation and assignment of the observed Raman spectra, especially for new materials that have never before been measured,” Puretzky said. | |
| The study revealed patterns in the stacked bilayers that strongly depend on the twist angle. Some specific twist angles, though, showed periodically repeating patches with the same stacking orientation. „These unique patterns may provide a new platform for optoelectronic applications of these materials,” Puretzky said. | |
| The team’s findings also showed fascinating effects of the vibrations between the layers. As different stacking patterns appeared when layers were displaced, variable spacings occurred between the layers at some specific twist angles. The researchers plan further measurements and modeling for different stacking configurations to better understand how these vibrational decays might alter the thermal properties of these materials–knowledge that could affect applications in heat dissipation and thermoelectric energy conversion. |
| Source: Oak Ridge National Laboratory |
Read more: Researchers stack the odds for novel optoelectronic 2-D materials
cercetatorii cred ca manipularea transferului de masa folosind metamaterialele ar putea ajuta la reducerea energiei necesare pentru anumite procese chimice si biomoleculare. Tehnica propusă ar folosi materiale polimerice cu model special pentru a direcționa fluxul atomilor prin folosirea proprietăților lor fizice specifice.
O explicație detaliată a modului în care tehnica ar putea fi utilizată pentru a separa un amestec de azot și oxigen – prin mascarea azotului și concentrarea oxigenului
| Posted: Mar 02, 2016 | |
Metamaterial separation proposed for chemical, biomolecular uses(Nanowerk News) The unique properties of metamaterials have been used to cloak objects from light, and to hide them from vibration, pressure waves and heat. Now, a Georgia Institute of Technology researcher wants to add another use for metamaterials: creating a new directional separation technique that cloaks one compound while concentrating the other. Though the idea must still be proven experimentally, the researchers believe that manipulating mass transfer using metamaterials could help reduce the energy required for certain chemical and biomolecular processes. The proposed technique would use specially-patterned polymeric materials to direct the flow of atoms by taking advantage of their specific physical properties. |
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| A detailed explanation for how the technique could be used to separate a mixture of nitrogen and oxygen – by cloaking the nitrogen and concentrating the oxygen – was reported February 25 in the journal Scientific Reports („Mass Separation by Metamaterials”). The research was supported by a seed grant from the American Chemical Society. | |
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| Concentration profiles for concentrated compound B at different times and steady-state. (a–e) background, (f–j) anisotropic homogeneous concentrator, (k–o) multilayer concentrator. (Credit: Martin Maldovan and Juan Manuel Restrepo-Flórez, Georgia Tech) | |
| „We will control how the atoms cross the metamaterial, in which direction they will go,” said Martin Maldovan, an assistant professor in Georgia Tech’s School of Chemical & Biomolecular Engineering and School of Physics. „By designing the diffusivity of the metamaterials, we can make the atoms of one compound go one way, and the atoms of another compound go a different way. We are manipulating the physical properties to control the direction the atoms take through the metamaterial shell.” | |
| Maldovan and Graduate Research Assistant Juan Manuel Restrepo-Flórez have evaluated their metamaterial using computational techniques, and plan to build a prototype separation device this summer. The work could have applications in such areas as chemical manufacturing, crystal growth of semiconductors, waste recovery of biological solutes or chemicals, and production of artificial kidneys. | |
| The metamaterial technique could supplement traditional membranes, which control the passage of chemicals by varying solubility and diffusivity. Similar in principle to other metamaterials, the mass transfer technique can either direct chemicals around the shell, or concentrate them within the shell. | |
| „Inside the metamaterial shell, you can tell one atom to do one thing, and another atom to do something else,” Maldovan said. „Our metamaterials will control the flow because they are anisotropic – certain directions are favored by the structure. We are controlling where the atoms go.” | |
| Maldovan’s plan for the mass transfer metamaterials uses four different types of polymers, two with high diffusivity and two with low diffusivity. The size and patterning of blocks made from each material is determined by mathematical algorithms. | |
| „With this metamaterial, we can control the direction the atoms can go using the trick of anisotropy,” he explained. „This would be in addition to separation based on solubility and diffusivity. We have added an important parameter to the toolbox of chemical engineers: where to send the atoms.” | |
| In addition to separating atoms, the ability of the metamaterials to concentrate atoms could allow sensors to detect more dilute quantities, essentially amplifying the available chemical signal. | |
| In their paper, the researchers show how to separate a 50-50 mixture of nitrogen and oxygen using available polymers that have the necessary properties. Each type of separation will require polymers with different properties, not all of which are available in existing materials, meaning not all chemical or biomolecular mixtures will be amenable to separation with the new technique. | |
| The new separation process won’t replace traditional distillation and membrane separation processes, but could supplement them, Maldovan said. | |
| „Distillation and evaporation are very energy intensive, but they are the workhorses of the chemical industry,” he said. „Membrane processes have been developed to reduce energy use. Our goal is to provide a technique that uses even less energy. This could lead to better and more efficient membranes that would provide better separation.” | |
| The metamaterials will ultimately have to be fabricated at the micron scale to be effective. But Maldovan says prototypes can be made using larger structures – at the centimeter scale – to demonstrate the process. | |
| „We need first to fabricate them, then optimize the design,” he said. „We know what needs to be fabricated, so future efforts will combine design, fabrication, and optimization.” |
| Source: Georgia Institute of Technology |
Read more: Metamaterial separation proposed for chemical, biomolecular uses
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