au transformat hârtia de țesut – similar cu cea a toaletei – într-un nou tip de senzor care poate detecta un puls, o clipire a ochiului și alte mișcări umane. Senzorul este ușor, flexibil și ieftin, cu aplicații potențiale în domeniul sănătății, al divertismentului și al roboticii.rată că, prin ruperea hârtiei absorbante cu nanocompozite și prin ruperea fibrelor de hârtie, hârtia acționează ca un senzor . Acesta poate detecta o batai inimii, forta degetului, miscare a degetului, miscare a ochilor si multe altele, a spus Jae-Hyun Chung, profesor asociat UW de inginerie mecanica si autor principal al cercetarii.
Posted: Feb 13, 2018
Tissue paper sensors show promise for health care, entertainment, robotics
(Nanowerk News) University of Washington engineers have turned tissue paper – similar to toilet tissue – into a new kind of wearable sensor that can detect a pulse, a blink of an eye and other human movement. The sensor is light, flexible and inexpensive, with potential applications in health care, entertainment and robotics.
The technology, described in a paper in the journal Advanced Materials Technologies („Fracture-Induced Mechanoelectrical Sensitivities of Paper-Based Nanocomposites”), shows that by tearing tissue paper that’s loaded with nanocomposites and breaking the paper’s fibers, the paper acts as a sensor. It can detect a heartbeat, finger force, finger movement, eyeball movement and more, said Jae-Hyun Chung, a UW associate professor of mechanical engineering and senior author of the research.
University of Washington graduate student, Jinyuan Zhang, demonstrates how eye movement is tracked with a tissue paper sensor.
“The major innovation is a disposable wearable sensor made with cheap tissue paper,” said Chung. “When we break the specimen, it will work as a sensor.”
These small, Band Aid-sized sensors could have a variety of applications in various fields. For example, monitoring a person’s gait or the movement of their eyes can be used to inspect brain function or a game player’s actions. The sensor could track how a special-needs child walks in a home test, sparing the child the need for hospital visits. Or the sensors could be used in occupational therapy for seniors.
“They can use these sensors and after one-time use, they can be thrown away,” said Chung.
In their research, the scientists used paper similar to toilet tissue. The paper – nothing more than conventional paper towels – is then doused with carbon nanotube-laced water. Carbon nanotubes are tiny materials that create electrical conductivity. Each piece of tissue paper has both horizontal and vertical fibers, so when the paper is torn, the direction of the tear informs the sensor of what’s happened. To trace eye movement, they’re attached to a person’s reading glasses.
For now, the work has been contained to a laboratory, and researchers are hoping to find a suitable commercial use. A provisional patent was filed in December 2017.
anunță săptămâna aceasta că au construit un film subțire stabil din fier, cobalt și mangan, care se mândrește cu literele fizice aplicate ( „momente mari în filmul subțire al aliajului FexCoyMnz din aliajele ternare” ) un moment atomic mediu cu 50% mai mare decât limita Slater-Pauling. Realizată printr-o tehnică cunoscută sub denumirea de epitaxie cu fascicule moleculare (MBE), aliajul cubic (bcc) centrat pe corp ternar prezintă o densitate de magnetizare de 3,25 magnetoni Bohr pe atom, depășind maximul considerat anterior de 2,45.
Posted: Feb 13, 2018
Three’s company: New alloy sets magnetism benchmark
(Nanowerk News) The burgeoning field of spintronics leverages electron spins – as opposed to their charge – to enhance solid-state devices like hard drives and cell phone components by prolonging battery life. Spintronic developments, however, are increasingly running up against a barrier known as the Slater-Pauling limit, the maximum for how tightly a material can pack its magnetization. Now, a new thin film is poised to break through this decades-old benchmark.
A team of researchers from Montana State University and Lawrence Berkeley National Laboratory announces this week in Applied Physics Letters („Large moments in bcc FexCoyMnz ternary alloy thin films”), that they constructed a stable thin film made from iron, cobalt and manganese that boasts an average atomic moment potentially 50 percent greater than the Slater-Pauling limit. Made with a technique known as molecular beam epitaxy (MBE), the ternary body-centered cubic (bcc) alloy features a magnetization density of 3.25 Bohr magnetons per atom, besting the previously considered maximum of 2.45.
„What we have is a potential breakthrough in one of the most important parameters of magnetic materials,” said Yves Idzerda, an author on the paper from Montana State University. „Large magnetic moments are like the strength of steel – the bigger the better.”
The Slater-Pauling curve describes magnetization density for alloys. For decades, iron-cobalt (FeCo) binary alloys have reigned supreme, posting a maximum average atomic moment of 2.45 Bohr magnetons per atom and defining the current limit for stable alloy magnetization density. Previously, researchers mixed FeCo alloys with high-magnetic-moment transition metals, like manganese. When these ternary alloys are made, however, they lose much of their bcc structure, a key component to their high magnetism.
Instead, this team turned to MBE, a meticulous technique akin to draping a substrate with beads of individual metal atoms, one layer at a time, to create a 10-20 nanometer film of Fe9Co62Mn29. Roughly 60 percent of the available compositions kept the bcc structure as a thin film, compared to only 25 percent in bulk.
To better understand the alloy’s composition and structure, the group used X-ray absorption spectroscopy and reflection high-energy-electron diffraction. The X-ray magnetic circular dichroism results showed that the new material yielded an average atomic moment of 3.25 Bohr magnetons per atom. When tested with a more standard vibrating sample magnetometry, even though this magnetization density dropped, it was still significantly above the Slater-Pauling limit – 2.72.
Idzerda said this discrepancy will provide areas of future research, adding that the interface between manganese and the substrate within the crystal might account for the gap.
„I have guarded optimism for this because the technique we used is a little bit nonstandard and we have to convince the community of this material’s performance,” Idzerda said.
Idzerda and his team will now investigate the robustness of iron-cobalt-manganese alloys, and more efficient fabrication techniques. They also plan to explore how molecular beam epitaxy might lead to other highly magnetic thin films, potentially mixing together four or more transition metals.
investighează modalitățile de a scrie modele de grafen în produsele alimentare și în alte materiale pentru a încorpora rapid etichetele și senzorii conductivi de identificare în produsele în sine.separată pe mâncare, ci pe mâncarea în sine”.
Multi pași laser cu un fascicul defocalizat au permis cercetătorilor să scrie modelele LIG în pânză, hârtie, cartofi, coji de nucă de cocos și plută, precum și toast. (Pâinea este prăjită mai întâi pentru a „carboniza” suprafața.) Procesul se întâmplă în aer la temperaturi ambiante.
„În unele cazuri, lexarea multiplă creează o reacție în două etape”, a spus Tour. In primul rand, laserul transforma fototeramatic suprafata tinta in carbon amorf. Apoi, pe trecerea ulterioara a laserului, absorbtia selectiva a luminii infrarosii transforma carbonul amorf in LIG, descoperind ca lungimea de unda are importanta.Acest lucru are aplicații pentru a pune urme conductive pe îmbrăcăminte, indiferent dacă doriți să încălziți îmbrăcămintea sau să adăugați un senzor sau un model conductiv”,
Posted: Feb 13, 2018
Graphene on toast, anyone? (w/video)
(Nanowerk News) Rice University scientists who introduced laser-induced graphene (LIG) have enhanced their technique to produce what may become a new class of edible electronics.
The Rice lab of chemist James Tour, which once turned Girl Scout cookies into graphene, is investigating ways to write graphene patterns onto food and other materials to quickly embed conductive identification tags and sensors into the products themselves.
„This is not ink,” Tour said. „This is taking the material itself and converting it into graphene.”
Laser-induced graphene is a highly conductive addition to a piece of bread. A Rice University lab is using an industrial laser to write graphene patterns on everyday objects, including food, cloth, cardboard and wood. (Image: Jeff Fitlow/Rice University)
The process is an extension of the Tour lab’s contention that anything with the proper carbon content can be turned into graphene. In recent years, the lab has developed and expanded upon its method to make graphene foam by using a commercial laser to transform the top layer of an inexpensive polymer film.
The foam consists of microscopic, cross-linked flakes of graphene, the two-dimensional form of carbon. LIG can be written into target materials in patterns and used as a supercapacitor, an electrocatalyst for fuel cells, radio-frequency identification (RFID) antennas and biological sensors, among other potential applications.
The new work reported in the American Chemical Society journal ACS Nano(DOI:10.1021/acsnano.7b08539″) demonstrated that laser-induced graphene can be burned into paper, cardboard, cloth, coal and certain foods, even toast.
„Very often, we don’t see the advantage of something until we make it available,” Tour said. „Perhaps all food will have a tiny RFID tag that gives you information about where it’s been, how long it’s been stored, its country and city of origin and the path it took to get to your table.” He said LIG tags could also be sensors that detect E. coli or other microorganisms on food. „They could light up and give you a signal that you don’t want to eat this,” Tour said. „All that could be placed not on a separate tag on the food, but on the food itself.”
Multiple laser passes with a defocused beam allowed the researchers to write LIG patterns into cloth, paper, potatoes, coconut shells and cork, as well as toast. (The bread is toasted first to „carbonize” the surface.) The process happens in air at ambient temperatures.
„In some cases, multiple lasing creates a two-step reaction,” Tour said. „First, the laser photothermally converts the target surface into amorphous carbon. Then on subsequent passes of the laser, the selective absorption of infrared light turns the amorphous carbon into LIG. We discovered that the wavelength clearly matters.”
The researchers turned to multiple lasing and defocusing when they discovered that simply turning up the laser’s power didn’t make better graphene on a coconut or other organic materials. But adjusting the process allowed them to make a micro supercapacitor in the shape of a Rice „R” on their twice-lased coconut skin.
Defocusing the laser sped the process for many materials as the wider beam allowed each spot on a target to be lased many times in a single raster scan. That also allowed for fine control over the product, Tour said. Defocusing allowed them to turn previously unsuitable polyetherimide into LIG.
„We also found we could take bread or paper or cloth and add fire retardant to them to promote the formation of amorphous carbon,” said Rice graduate student Yieu Chyan, co-lead author of the paper. „Now we’re able to take all these materials and convert them directly in air without requiring a controlled atmosphere box or more complicated methods.”
The common element of all the targeted materials appears to be lignin, Tour said. An earlier study relied on lignin, a complex organic polymer that forms rigid cell walls, as a carbon precursor to burn LIG in oven-dried wood. Cork, coconut shells and potato skins have even higher lignin content, which made it easier to convert them to graphene.
Tour said flexible, wearable electronics may be an early market for the technique. „This has applications to put conductive traces on clothing, whether you want to heat the clothing or add a sensor or conductive pattern,” he said.
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Soldații în situații de luptă trebuie să-și scaneze în permanență împrejurimile pentru dispozitivele explozive improvizate (IED), o armă de semnătură a războiului modern de gherilă
Materialele bidimensionale, cum ar fi grafenul, care constau doar din unul sau mai multe straturi atomice, au fost un aspect foarte promițător al științei materialelor în ultimii ani. Acestea demonstrează proprietăți remarcabile care deschid posibilități tehnice complet noi, de la tehnologia senzorilor la celulele solare.
Cu toate acestea, există un fenomen important care nu a putut fi măsurat cu exactitate până în prezent: stresul și presiunea internă extremă pe care pot fi supuse astfel de materiale, care modifică adesea drastic proprietățile fizice ale materialului.
Posted: Feb 12, 2018
Rubber blanket at an atomic level
(Nanowerk News) Two-dimensional materials such as graphene, which consist of only one or a few atomic layers, have been a very promising aspect of materials science over recent years. They demonstrate remarkable properties that open up completely new technical possibilities, from sensor technology to solar cells.
However, there is one important phenomenon that could not be measured accurately up until now: the extreme internal stresses and strains that such materials may be subjected to, which often drastically alter the material’s physical properties. TU Wien has now successfully measured these distortions in 2D materials at microscopic level, which means it is now possible to observe precisely (point for point) how the properties of a material may be altered as a result of a simple distortion. These new measurement methods have now been published in the specialist journal Nature Communications („Optical imaging of strain in two-dimensional crystals”).
The basic idea of the measurement method: red light hits the surface – blue light is sent back. (Image: TU Vienna)
Stretching and compression
When a material is stretched or compressed, the distance between the individual atoms changes, and this distance has an influence on the electronic properties of the material. This phenomenon has been used in semiconductor technology for years: silicon crystals, for example, can be grown so that they are permanently under internal mechanical stress.
However, two-dimensional materials, which consist only of an ultra-thin layer, offer much greater potential: „A crystal can be stretched by perhaps one percent before it breaks. With 2D materials, deformation of ten or twenty percent is possible”, says Prof. Thomas Müller from the Photonics Institute (Faculty of Electrical Engineering and Information Technology) at TU Wien. Depending on the deformation and mechanical stresses present within the material, the electronic properties may completely change, such as the ability of the electrons to absorb incoming light.
„Up until now, if you wanted to measure stresses present in this type of material you had to rely on extremely complicated measurement methods”, explains Lukas Mennel (TU Wien), lead author of the publication. For example, you could observe the surface using a transmission electron microscope, measure the average distance between the atoms and then deduce any stretching or compression from that. At TU Wien, this process has now been made much simpler and more accurate.
Red light in, blue light out
Here, a remarkable effect called frequency doubling is used: „If you irradiate specific materials – in our case a layer of molybdenum disulphide – with a suitable laser beam, the material may reflect back light of a different colour”, explains Thomas Müller. Two photons in the incoming laser beam are combined to form one photon with double the energy, which is emitted from the material.
However, the intensity of this effect depends on the internal symmetry of the material. Usually, molybdenum disulphide has a honeycomb-like structure, i.e. hexagonal symmetry. If the material is stretched or compressed, this symmetry is slightly distorted – and this small distortion has a dramatic effect on the intensity of the light reflected back from the material.
If you place a layer of molybdenum disulphide over a microstructure, like putting a rubber blanket over a climbing frame, the result is a complex pattern of local distortions. You can now use a laser to scan the material point for point and thus obtain a detailed map of these stretches and compressions. „In doing so, not only can we measure the severity of these deformations, but we can also see the exact direction in which they run”, explains Lukas Mennel.
These imaging methods can now be used for the local, targeted adjustment of material properties. „For example, custom material deformations in solar cells could ensure that free charge carriers are diffused away in the right direction as quickly as possible”, says Thomas Müller. This research on 2D materials means that a new, powerful tool is now available.
au dezvoltat noi surse de lumină eficiente nanometrice bazate pe perovskitul halogenurilor. Nanosursele considerate sunt nanoparticule cu lungime subwave, care servesc atât ca emițători, cât și ca nanoantenne și permit intensificarea emisiilor de lumină în mod inerent, fără dispozitive suplimentare. Mai mult decât atât, perovskitul permite reglarea spectrelor de emisie într-un interval vizibil prin modificarea compoziției materialului. Acest lucru face ca noile nanoparticule să fie o platformă promițătoare pentru crearea de dispozitive optoelectronice compacte, cum ar fi chips-uri optice, diode emițătoare de lumină sau senzori.
Posted: Feb 12, 2018
Researchers invented light-emitting nanoantennas based on halide perovskites
(Nanowerk News) Young scientists from ITMO University developed new effective nanoscale light sources based on halide perovskite. The considered nanosources are subwavelength nanoparticles, which serve both as emitters and nanoantennas and allow enhancing light emission inherently without additional devices. Moreover, perovskite enables tuning emission spectra throughout a visible range by varying the composition of the material. This makes the new nanoparticles a promising platform for creating compact optoelectronic devices such as optical chips, light-emitting diodes, or sensors. The results were published in Nano Letters („Light-Emitting Halide Perovskite Nanoantennas”).
The nanoscale light sources and nanoantennas have already found a wide range of applications in several areas, such as ultra compact pixels, optical detection, or telecommunications. However, the fabrication of nanostructure-based devices is rather complicated due to the limited luminescence efficiency of the materials used typically as well as non-directional and relatively weak light emission of single quantum dots or molecules. An even more challenging task is placing a nanoscale light source precisely near a nanoantenna.
A research group from ITMO University managed to combine a nanoantenna and a light source in a single nanoparticle. It can generate, enhance and route emission via excited resonant modes coupled with excitons. „We used hybrid perovskite as a material for such nanoantennas,” says Ekaterina Tiguntseva, the first author of the publication. “Unique features of perovskite enabled us to make nanoantennas from this material. We basically synthesized perovskite films, and then transferred material particles from the film surface to another substrate by means of pulsed laser ablation technique. Compared to alternatives, our method is relatively simple and cost-effective.”
While studying the obtained perovskite nanoparticles, the scientists discovered that their emission can be enhanced if its spectra match with the Mie-resonant mode. „Such resonances were named in honor of Gustav Mie, an outstanding German scientist,” explains George Zograf, Engineer at the Laboratory of Hybrid Nanophotonics and Optoelectronics at ITMO University. “He developed a general theory describing how the light interacts with sphere-like objects smaller than the wavelength. Currently, scientists are particularly interested in Mie-resonances related to dielectric and semiconductor nanoparticles. Perovskites used in our work are also semiconductors with luminescence efficiency much higher than that of many other materials. Our study shows that combination of excitons with the Mie resonance in perovskite nanoparticles makes them efficient light sources at room temperature.”
In addition, the radiation spectrum of the nanoparticles can be changed by varying the anions in the composition of the material. „The structure of the material remains the same, we simply use another component in the synthesis of perovskite films. Therefore, it is not necessary to adjust the method each time. It remains the same, yet the emission color of our nanoparticles changes,” says Ekaterina.
„As far as we know, no one could get subwavelength perovskite nanoantennas with an adjustable emission spectrum before,” adds George. “When we submitted this paper our senior colleagues jokingly demanded that we bake some pastry reflecting the concept of our work in case the article is accepted. As a result, we celebrated the publication of the work with cupcakes in the colors of our nanoparticles’ emission. We adopted this nice tradition from a research group led by Prof. Jeremey Baumberg at the University of Cambridge.”
The scientists are currently continuing the research of light-emitting perovskite nanoantennas using various components for their synthesis. In addition, they are developing new designs of perovskite nanostructures which may improve ultra compact optical and transmission devices.
au reușit să dezvolte un material compozit care are astăzi cele mai bune proprietăți piezoelectrice.Piezoelectrica este unul dintre cele mai uimitoare materiale din lume.Materialele compozite bazate pe polimeri și feroelectrice clasice, care au proprietăți piezo- și piroelectrice, au un număr de avantaje în comparație cu ceramica pură: densitatea, capacitatea de a produce părți de orice dimensiune și formă, elasticitatea mecanică, stabilitatea proprietăților electrofizice și simplitatea și costul relativ scăzut al producției. În plus, compozitul sintetizat sa dovedit a fi excelent la presiuni ridicate, ceea ce îl face o bază excelentă pentru senzori de presiune „.
Piezoelectrics are one of the world`s most amazing materials. It is possible to literally squeeze electricity from them. That is, an electric charge appears at the time of the material`s compression (or stretching). This is called the piezoelectric effect. Piezoelectric materials can be applied in many fields – from pressure sensors and sensitive elements of a microphone to the controller ink pressing in ink-jet printers and quartz resonators.
Topography (a), PFM images of a pristine state (b) and after poling by +/ 60V (c). (Image: NUST MISIS)
Lead zirconate titanate is one of the most popular piezoelectric materials. However, it has several disadvantages: it is heavy and inflexible. Additionally, lead production often causes great harm to the environment. That is why scientists are constantly looking for new materials with low lead content as well as with less weight and greater flexibility. In particular, the creation of flexible piezoelectric materials (while maintaining the key properties) would greatly expand piezoelectric materials` possibilities both as acoustic membrane and as pressure sensors.
An international team of scientists from the University of Duisburg-Essen (Germany), NUST MISIS, National Research Tomsk State University and the National Research University of Electronic Technology, working with the financial support of the Russian Science Foundation (grant 16-19-10112), has managed to create such a material and analyze its properties. For this, the nanoparticles consisting of titanate-zicronate barium-lead were placed in a complex polymer consisting of vinylidene disluoride and trifluoroethylene. By diversifying the composition of the components, scientists were able to get the most ideal composite.
„The Russian-German group of scientists, including Dmitri Kiselev, a Senior Researcher at the NUST MISIS R&D Center for Materials Science & Metallurgy, has managed to create a composite material based on ceramics and organic polymer whose properties exceed today`s best piezoelectric materials. The research’s experimental part was carried out with an atomic-force microscope in the University of Duisburg-Essen (Germany). Thanks to this scientific collaboration, Dmitri Kiselev has gained skills from the world`s best scanning probe microscope, which he can later apply at NUST MISIS”, said Alevtina Chernikova, Rector of NUST MISIS.
According to Dmitri Kiselev, the developed material has a very distinct field of application due to its polymer component: „Composite materials based on polymer and classic ferroelectrics, which have piezo- and pyroelectric properties, have a number of advantages compared to pure ceramics: low density, the ability to manufacture parts of any size and shape, mechanical elasticity, stability of electrophysical properties, and the simplicity and relatively low cost of production. Additionally, the synthesized composite has proved to be excellent at high pressures which makes it an excellent base for pressure sensors”.
According to Kiselev, to study the composite they had to modify the standard technique which allowed them to correctly visualize the nanoparticles of ceramics in the volume of the polymer matrix: „In order to capture the electrical signal more clearly, we heated our sample in a certain way from room temperature to 60 degrees Celsius. It allowed us to measure the material’s characteristics very qualitatively and reproducibly. Our method will greatly simplify the work of our colleagues in the study of composites, so I hope that it will be in demand among our colleagues microscopists”.
Source: National University of Science and Technology MISIS
Un sistem numit Arielle combină elemente precum casca de înaltă tehnologie și armura corpului, printre alte articole de îmbrăcăminte, care pot regla temperatura corpului forțelor de luptă de mâine în timp real – ceea ce reprezintă un avantaj pentru forțele în climatul tropical înfundat
Acest material reușește majoritatea proprietăților izbitoare ale BP și, în plus, oferă o stabilitate mai bună a mediului, un cost de fabricație mult mai mic (cu metode de chimie umedă) și o absorbție mai puternică a luminii decât cele ale BP. În acest scenariu, FL-α-Te ar putea fi considerat un succesor superior al BP.
Posted: Feb 09, 2018
Few-layer tellurium as a promising successor of black phosphorus
(Nanowerk News) Two-dimensional (2D) layered materials have received considerable attention because of their potential applications in various fields since the experimental discovery of graphene.
Two-dimensional elementary semiconductors are particularly desired owing to their superior features in terms of fabrication, purification and doping.
Few-layer black phosphorus (BP) is the first 2D mono-elementary semiconductor showing high electronic carrier mobility, strong optical absorption, linear dichroism, promising figure of merit and high tunability with external fields. All the properties immediately put few-layer BP under spotlights since its discovery in 2014.
However, the flawed air-stability and difficulties in largescale fabrication were found to be two remaining issues that obscure practical applications of few-layer BP in the industry. People thus get started to question if a promising or even superior successor of BP exists. The target semiconductor is preferably an elementary one. It should also allow low-cost and large-scale synthesis and offer good environmental stability without sacrificing those striking properties offered by BP.
Professor Wei Ji has led a research group at Renmin University of China to theoretically model surfaces and interfaces of emerging electronic materials and to predict physical properties of devices comprised of these materials.
Recently, they collaborated with Prof. Yang Chai from the Hong Kong Polytechnic University to report a theoretical study of a novel chain-like 2D-material, namely few-layer α-Tellurium (FL-α-Te), and predicted this material to have extremely high carrier mobility with a layer-tunable bandgap, strong light absorption, mixing of vibrational modes, layer-dependent energy maps of valence and conduction bands and among other striking properties („Few-layer Tellurium: one-dimensional-like layered elementary semiconductor with striking physical properties”).
The FL-α-Te is a representative material of layered one-dimensional materials, which are a novel and fast developing category of 2D-materials. They first examined the stability of three likely few-layer phases using state-of-the-art density functional theory calculations.
Their calculation shows α-Tellurium is the most stable phase for bilayer and thicker layers. Given the stability unveiled, they found that a covalent-like quasi-bonding (CLQB) dominates the inter-chain interaction in both intra- and inter-layer directions. This CLQB is in analogy to the found interlayer interactions in BP, PtS2 or PtSe2, in which it shows wavefunction hybridization but does not provide extra energy gain.
They managed to correlate this bonding with the layer-dependent geometric and electronic structures and their resulting behaviors in terms of electric, optical, and vibrational properties.
Few-layer α-Te has extremely high hole-mobility up 105 cm2/Vs exceptionally along the non-covalent-bound (CLQB) direction and 103 cm2/Vs for the covalent-bound direction, tunable bandgap from 0.31 eV (Bulk) to 1.17 eV (2L), anisotropic inter-chain (-layer) vibrational behaviors, a crossover of interlayer shear and breathing force constants, large ideal strength (over 20%) and nearly isotropic strong light absorption (up to 9% per layer) from a highly anisotropic geometry.
They also found, specifically in few-layer α-Te, that the energy surfaces of both valence and conduction bands substantially develop from bulk to bilayer, exhibiting an „M-like” line profile of the hole pocket, which was usually found in topological insulators and is ideal for thermoelectrics.
This material succeeds most of the striking properties of BP and additionally offers a better environmental stability, a much lower fabrication cost (with wet-chemistry methods) and a stronger light absorption than those of BP. In this scenario, FL-α-Te could be regarded as a superior successor of BP.
The extraordinarily high carrier mobility revealed in the CLQB direction conceptually updates the understanding of the role of non-covalent interactions in carrier mobility and may open a new avenue for seeking high carrier mobility materials.
Nanographene are grila hexagonală de carbon din grafen, dar constă doar din câteva inele de carbon cu proprietăți electronice reglabile. Una dintre problemele sale majore care împiedică aplicarea pe scară largă a dispozitivelor optoelectronice sau a biomedicinei este insolubilitatea sa. Prin urmare, pentru a suprima stivuirea și agregarea, s-a sintetizat un nou tip de nanograf cu o structură îndoită, așa-numitul nanographene deformat.
Posted: Feb 09, 2018
Water-soluble warped nanographene and its application for photo-induced cell death
(Nanowerk News) Graphene and its nano-sized little sibling, nanographene, are well known for their remarkable photoelectronic properties. However, biomedical applications are hampered by the insolubility of the materials, especially in water.
A Japanese team of scientists has now introduced substituted “warped nanographene,” which is soluble in a broad range of solvents while maintaining its photophysical properties. In their publication in Angewandte Chemie („A Water-Soluble Warped Nanographene: Synthesis and Applications for Photoinduced Cell Death”), the authors also emphasize its photodynamic potential to selectively kill cells upon irradiation.
Nanographene has the hexagonal carbon lattice of graphene but consists of only a few carbon rings with tunable electronic properties. One of its big issues hampering widespread application in optoelectronic devices or biomedicine is its insolubility. Therefore, to suppress stacking and aggregation, a new type of nanographene with a bended structure has been synthesized, the so-called warped nanographene.
Kenichiro Itami at Nagoya University, Japan, and his colleagues have now found a way to furnish the warped nanographene even further to obtain a fully soluble, amphiphilic product. The new structure was biocompatible, but upon irradiation it killed its host cell. This effective photosensitization behavior could inspire future research in photodynamic cancer therapy, the authors believe.
The poor solubility of graphene-like materials has been regarded problematic since the discovery of graphene as an intriguing one-layer carbon modification in 2004. To improve solubility, Itami and his colleagues have developed warped nanographene molecules with chemical substituents at the outer rim of the aromatic structure.
The substituents were introduced by the relatively simple and powerful strategy of borylation. Once the molecule is borylated, the boron substituent can be replaced by other substituents, in this case, by an aromatic molecule bearing highly soluble tetra(ethylene glycol) chains (TEG).
Applying this substitution–replacement strategy twice, the scientists accomplished the synthesis of a warped, i.e., bended, nanographene molecule that was stable in a broad range of solvents including water. Excited with a laser, it exhibited green fluorescence.
This fluorescence points to applications in biology, for example, as a dye in bioimaging. A further application came rather unexpected, the scientists reported. Upon excitation, the molecule, which was otherwise not harmful to the cells, killed the cell population of the human HeLa cell line to almost 100 percent.
The authors proposed: “Although the mechanism is unclear, the relatively high efficiency of the singlet oxygen generation of [the soluble warped nanographene] may contribute to its HeLa cell death.” Thus, a mechanism similar to dye sensitization and production of reactive oxygen species can be assumed.
These second-generation nanographenes combine the remarkable optoelectronic properties of graphene with biocompatibility. They may well play a future role in bioimaging, photodynamic therapy, and similar applications.
