Liliana Decu – Pagina 74

Sistemul de cipuri nanofotonice măsoară lumina de la o singură celulă bacteriană pentru a permite detectarea chimică portabilă ( Nanophotonic chip system measures light from a single bacterial cell to enable portable chemical detection )

Noul sistem, descris în jurnalul Nano Letters ( „Nanoscale Plasmonic V-Groove Waveguides pentru interogarea celulelor bacteriene fluorescente unice” ), deschide calea pentru un sistem eficient și portabil on-chip pentru diverse aplicații de detectare pe bază de celule, cum ar fi Ca și detectarea substanțelor chimice în timp real.
construirea unei rețele de ghiduri de undă, diversificarea sistemului pentru a încorpora diferite tipuri de senzori bacterieni pentru detectarea diferitelor analitări biologice sau chimice.

Posted: Aug 30, 2017
Nanophotonic chip system measures light from a single bacterial cell to enable portable chemical detection (Nanowerk News) Researchers at the Hebrew University of Jerusalem have created a nanophotonic chip system using lasers and bacteria to observe fluorescence emitted from a single bacterial cell. To fix the bacteria in place and to route light toward individual bacterial cells, they used V-groove-shaped plasmonic waveguides, tiny aluminum-coated rods only tens of nanometers in diameter.
The novel system, described in the journal Nano Letters („Nanoscale Plasmonic V-Groove Waveguides for the Interrogation of Single Fluorescent Bacterial Cells”), paves the way for an efficient and portable on-chip system for diverse cell-based sensing applications, such as detecting chemicals in real-time.

Top: SEM image of bacteria deposited inside a V-groove waveguide. Bottom: napshot of bacterial fluorescence excitation via free space beam and the coupling of the fluorescence to the waveguide. The two nanocouplers at the end of the waveguide emit about the same intensity of light because they are roughly the same distance from the bacterium. (© ACS)
The field of on-chip photonic devices for biological and chemical sensing applications presents many powerful alternatives to conventional analytical techniques for applications ranging from “lab on a chip” to environmental monitoring. However, these sensing schemes rely mainly on off-chip detection and require a cumbersome apparatus, even when measuring only single cells.
The Hebrew University team looked for ways to integrate all system components, including light sources and detectors, on-chip at the nanoscale. This would result in a lab-on-chip system that is small, portable and can perform sensing in real-time.
To achieve this, they molecularly engineered live bacteria that emit a fluorescent signal in the presence of target compounds. They paired these on-chip with a nanoscale waveguide, which not only served the purpose of guiding light, but also allowed mechanical trapping of individual bacteria within the V-groove.
In three different illumination conditions, they experimentally demonstrated the interrogation of an individualEscherichia coli bacterial cell using a nanoscale plasmonic V-groove waveguide. First, they measured the light emitted from a bacterium flowing on top of the nanocoupler in a liquid environment by allowing the fluorescence from the bacterium to be coupled directly into the waveguide through the nanocoupler. Next, a bacterium was mechanically trapped within the V groove waveguide and was excited by laser directly either from the top or through the nanocoupler. In all cases, significant fluorescence was collected from the output nano coupler into the detector.
The system worked well both in wet environments, where the bacteria are flowing on top of the waveguide, and in dry conditions, where the bacteria are trapped within the waveguide.
The research was led by Prof. Uriel Levy, Director of The Harvey M. Krueger Family Center for Nanoscience and Nanotechnology at the Hebrew University in collaboration with Prof. Shimshon Belkin, at the Hebrew University’s Alexander Silberman Institute of Life Sciences, who genetically engineered the bacterial sensors, and Prof. Anders Kristensen from the Danish Technical University, who was in charge of fabricating the V-groove waveguides. Prof. Levy is the Eric Samson Chair in Applied Science and Technology, and Prof. Belkin is the Ministry of Labor and Social Welfare Chair in Industrial Hygiene, at the Hebrew University.
Unlike the more traditional plasmonic waveguides consisting of either silver or gold, the choice of aluminum was instrumental for being able to guide the fluorescent light emitted from the bacteria all the way to the output nanocoupler. Furthermore, the waveguide dimensions allow for efficient mechanical trapping of the bacteria and the multimode characteristics may become instrumental in gathering more information, e.g., on the specific position and orientation of the bacteria.
The results provide a clear indication of the feasibility of constructing a hybrid bioplasmonic system using live cells. Future work will include the construction of waveguide network, diversifying the system to incorporate different types of bacterial sensors for the detection of various biological or chemical analytes.

Source: Hebrew University of Jerusalem

Comutare de mare viteză pentru comutatoare și senzori electromecanici ultra-rapizi ( High-speed switching for ultrafast electromechanical switches and sensors )

Piezoelectromecanismele piezoMEMS sunt dispozitive miniaturizate care prezintă piezoelectricitate, adică apariția unei încărcături electrice sub tensiune mecanică aplicată. Aceste dispozitive au multe aplicații diverse în mașinile de recoltat energie, micropumpuri, senzori, capete de imprimantă cu jet de cerneală, întrerupătoare și așa mai departe. În materialele polarizate (feroelectrice) permanent, comutarea domeniului fero-elastic afectează în mod semnificativ proprietățile piezoelectrice, iar acest comportament poate fi exploatat pentru aplicațiile piezoMEMS.

Read more: Piezoelectromecanismele piezoMEMS sunt dispozitive miniaturizate care prezintă piezoelectricitate, adică apariția unei încărcături electrice sub tensiune mecanică aplicată. Aceste dispozitive au multe aplicații diverse în mașinile de recoltat energie, micropumpuri, senzori, capete de imprimantă cu jet de cerneală, întrerupătoare și așa mai departe. În materialele polarizate (feroelectrice) permanent, comutarea domeniului fero-elastic afectează în mod semnificativ proprietățile piezoelectrice, iar acest comportament poate fi exploatat pentru aplicațiile piezoMEMS.

Comutarea de mare viteză observată în aceste experimente a fost limitată de echipamentele electrice actuale, dar este mai rapidă decât cea raportată în studiile anterioare. Mai mult, această comutare de mare viteză de 90 ° este reversibilă și poate fi utilizată pentru a spori răspunsul piezoelectric în dispozitivele piezoMEMS cu câteva zeci de nanosecunde. Prin urmare, această constatare are o importanță considerabilă pentru dezvoltarea continuă a comutatoarelor și senzorilor electromecanici ultra-rapizi.

Posted: Aug 29, 2017
High-speed switching for ultrafast electromechanical switches and sensors (Nanowerk News) Unlike the slow ferroelastic domain switching expected for ceramics, high-speed sub-microsecond ferroelastic domain switching and simultaneous lattice deformation are directly observed for the Pb(Zr0.4Ti0.6)O3 thin films. This exciting finding („In-situ observation of ultrafast 90° domain switching under application of an electric field in (100)/(001)-oriented tetragonal epitaxial Pb(Zr0.4Ti0.6)O3 thin films”) paves the way for high-frequency ultrafast electromechanical switches and sensors.
Piezo micro electro mechanical systems (piezoMEMS) are miniaturized devices exhibiting piezoelectricity, i.e., the appearance of an electric charge under applied mechanical stress. These devices have many diverse applications in energy harvesters, micropumps, sensors, inkjet printer heads, switches, and so on. In permanently polarized (ferroelectric) materials, ferroelastic domain switching affects the piezoelectric properties significantly, and this behavior can be exploited for piezoMEMS applications.
Pb(Zr1-xTix)O3 (PZT) thin films have excellent piezoelectric and ferroelectric properties; therefore, they are potential candidates for MEMS applications. Under an applied electric field, both lattice elongation and 90° ferroelastic domain switching are observed in tetragonal PZT thin films. In particular, non-180° ferroelastic domain switching has important implications for the future realization of high-performance piezoMEMS devices.
However, before the recent investigation, the speed of this 90° domain switching was unknown. In addition, the relationship between the speeds of the lattice deformation and ferroelastic domain switching had not been determined. To investigate these speeds, the research team led by Hiroshi Funakubo examined the switching behavior of Pb(Zr0.4Ti0.6)O3 thin films under applied rectangular electric field pulses.
To observe the changes in the lattice and the domain structure, time-resolved in situ synchrotron X-ray diffraction was carried out in synchronization with a high-speed pulse generator. These observations were performed at the BL13XU beamline at the SPring-8 synchrotron radiation facility. The electric field pulses were applied to the PZT thin films through Pt top electrodes, which were fabricated on top of the films.
Investigation of the diffraction peaks in the PZT thin films revealed elongation of the surface normal c-axis lattice parameter of the c-domain with a simultaneous decrease in the surface normal a-axis lattice parameter of the a-domain under the applied electric field. The intensities of the diffraction peaks also changed under the electric field. These observations provided direct evidence of 90° domain switching.

The (a-f) capacitance, strain, tilting angle, intensity, difference capacitance, and volume fraction of the c domain were measured as functions of time, respectively. The elastic deformation and ferroelastic domain switching were completed within 40 ns. (© NPG) (click on image to enlarge)
To determine the switching speed, the lattice elongation and domain switching behaviors were plotted as functions of time (Figure). These plots revealed that these processes were completed within 40 ns and occurred simultaneously in response to the applied electric field. The switching behavior was also shown to be perfectly repeatable.
The high-speed switching observed in these experiments was limited by the present electrical equipment, but is faster than that reported in previous studies. Further, this high-speed 90° switching is reversible and can be used to enhance the piezoelectric response in piezoMEMS devices by several tens of nanoseconds. Therefore, this finding is of considerable importance for the ongoing development of ultrafast electromechanical switches and sensors.

Source: Tokyo Institute of Technology

Echipa de cercetători aruncă comutatorul asupra feroelectricilor ( Research team flips the switch on ferroelectrics )

dezvoltă o nouă abordare a dispozitivelor avansate de senzor și de recoltare a energiei bazate pe controlul alinierii domeniului în materialele feroelectrice nanostructurate.Am creat filme de titanat de zirconat plumb pe diferite tipuri de substrat pentru a induce diferite tipuri de tulpini fizice, iar apoi selecționam selectiv părți din filme pentru a crea nanoroduri”, spune autorul principal Tomoaki Yamada. „Structura domeniului nanorodelor a fost aproape complet îndoită în comparație cu cea a filmului subțire

Read more:Am creat filme de titanat de zirconat plumb pe diferite tipuri de substrat pentru a induce diferite tipuri de tulpini fizice, iar apoi selecționam selectiv părți din filme pentru a crea nanoroduri”, spune autorul principal Tomoaki Yamada. „Structura domeniului nanorodelor a fost aproape complet îndoită în comparație cu cea a filmului subțire

Posted: Aug 28, 2017
Research team flips the switch on ferroelectrics (Nanowerk News) Nagoya University-led international collaboration develops new approach to advanced sensor and energy harvesting devices based on controlling domain alignment in nanostructured ferroelectric materials.
Many next-generation electronic and electro-mechanical device technologies hinge on the development of ferroelectric materials. The unusual crystal structures of these materials have regions in their lattice, or domains, that behave like molecular switches. The alignment of a domain can be toggled by an electric field, which changes the position of atoms in the crystal and switches the polarization direction. These crystals are typically grown on supporting substrates that help to define and organize the behavior of domains. Control over the switching of domains when making crystals of ferroelectric materials is essential for any future applications.
Now an international team by Nagoya University has developed a new way of controlling the domain structure of ferroelectric materials, which could accelerate development of future electronic and electro-mechanical devices (Scientific Reports, „Charge screening strategy for domain pattern control in nanoscale ferroelectric systems”).

Charge screening in ferroelectric Pb(Zr,Ti)O3 nanorods was used to control their domain pattern. The c-domain fraction markedly increased with as the rod width decreased, while the a-domain formation prevailed by metallization of their sidewall. All the observed results could be explained by the depolarizing field, arising from the imperfect charge screening. This approach could be expanded to other low-dimensional nanoscale ferroelectric systems. (Image: Tomoaki Yamada)
“We grew lead zirconate titanate films on different substrate types to induce different kinds of physical strain, and then selectively etched parts of the films to create nanorods,” says lead author Tomoaki Yamada. “The domain structure of the nanorods was almost completely flipped compared with [that of] the thin film.”
Lead zirconate titanate is a common type of ferroelectric material, which switches based on the movement of trapped lead atoms between two stable positions in the crystal lattice. Parts of the film were deliberately removed to leave freestanding rods on the substrates. The team then used synchrotron X-ray radiation to probe the domain structure of individual rods.
The contact area of the rods with the substrate was greatly reduced and the domain properties were influenced more by the surrounding environment, which mixed up the domain structure. The team found that coating the rods with a metal could screen the effects of the air and they tended to recover the original domain structure, as determined by the substrate.
“There are few effective ways of manipulating the domain structure of ferroelectric materials, and this becomes more difficult when the material is nanostructured and the contact area with the substrate is small.” says collaborator Nava Setter. “We have learned that it’s possible to nanostructure these materials with control over their domains, which is an essential step towards the new functional nanoscale devices promised by these materials.”

Source: Nagoya University

Proiectarea polimerilor cu caracteristici noi( Designing polymers with novel features)

Senzori mici facuti din anticorpi, nanosfere de proteine care pot curata scurgeri toxice si geluri care ar putea fi injectate intr-o rana pentru a initia vindecarea.Se bazează pe explorarea proprietăților fizice ale unor noi tipuri de polimeri și pe folosirea acestor proprietăți pentru a proiecta materiale noi care ar putea avea multe aplicații utile.
Hibrizii de proteine-polimeri ar putea fi, de asemenea, materiale utile care să imite proprietățile nailonilor sau poliuretanelor, care sunt materiale derivate din petrol, care se găsesc în materiale plastice dure, acoperiri, izolații și multe alte produse. Acești hibrizi noi ar putea fi produsi în „biorefinerii”, utilizând surse durabile de biomasă regenerabilă și făcând un impact pozitiv asupra mediului.

Posted: Aug 28, 2017
Designing polymers with novel features (Nanowerk News) Tiny sensors made of antibodies, protein nanospheres that can clean up toxic spills, and gels that could be injected into a wound to initiate healing are just a few of the innovations emerging from Bradley Olsen’s lab at MIT.
Bradley OlsenOlsen’s research is based on exploring the physical properties of new types of polymers, and taking advantage of those properties to design novel materials that could have many useful applications. “My group is really interested in two things: designing materials to address important challenges, and understanding the fundamental science that’s necessary for materials design,” says Olsen, an associate professor who recently earned tenure in MIT’s Department of Chemical Engineering. His lab, which includes 15 to 20 students and postdocs, pursues these approaches mainly in the field of protein-polymer chemistry, a relatively new discipline that involves incorporating proteins into polymer materials. He credits those students with many of the key discoveries that have yielded these novel materials.
“It’s a group effort,” he says. “I think the talent and wisdom of the team far exceeds anything I could do individually.”
Block by block
Growing up in Minneapolis, Olsen became interested in chemistry in high school and applied to MIT in part because he was drawn to the Undergraduate Research Opportunities Program (UROP), which allows undergraduates to conduct research in the labs of MIT faculty.
While majoring in chemical engineering, Olsen spent three years working in the lab of Karen Gleason, the Alexander and I. Michael Kasser Professor of Chemical Engineering. At the time, Gleason was developing early versions of a technique known as initiated chemical vapor deposition, which allows scientists to use gases to form thin polymer coatings on a surface.
As a graduate student at the University of California at Berkeley, Olsen began working on synthesizing a special kind of polymers known as block copolymers. These materials consist of alternating blocks of two different kinds of monomers, which are the building blocks for synthetic polymers such as plastics and rubber.
When these monomers are arranged in blocks, it gives the overall material special properties. For example, the material may contain two monomers that would normally separate into layers, the way oil and water do. If those two chemically dissimilar molecules are bound together in a block copolymer, they can’t form separate layers. Instead, block copolymers assemble themselves into special structures, such as spheres, cylinders, or sheets, that help to minimize the interactions between the two chemically different blocks. Such materials are now commonly used in many products, including elastomers, adhesives, and personal care products.
As a graduate student, Olsen studied how these kinds of polymers could be used to control the nanostructure of semiconducting polymers. Then, as a postdoc at Caltech, he worked on developing injectable hydrogels, which could potentially be used for wound healing and stopping blood flow.
While at Caltech, Olsen received an offer to return to MIT as a faculty member, which he found hard to resist. “MIT certainly has very good students and very good colleagues, and I definitely had some nostalgia for the Boston area,” he says. “It’s fun to be back here.”
Useful materials
At MIT, Olsen has continued to develop block copolymers for a wide range of applications. In one area of research, he is designing materials where one block is a polymer and the other is a protein such as an enzyme or an antibody. These materials could then be formed into extremely sensitive biosensors.
“With this high-density array of proteins, you can potentially increase sensitivity by maybe a factor of 100 or 1,000, or even more,” Olsen says.
Protein-polymer hybrids also could be useful new materials that mimic the properties of nylons or polyurethanes, which are petroleum-derived materials that are found in hard plastics, coatings, insulation, and many other products. These new hybrids could potentially be produced in “biorefineries,” using sustainable sources of renewable biomass and making a positive impact on the environment.
Another potential application for block copolymers is detoxification, using spherical “nanoreactors” whose surfaces are coated with enzymes that could break down toxic chemicals from an oil spill. Olsen has also continued working on hydrogels, including the development of wound-healing materials, in collaboration with MIT’s Institute for Soldier Nanotechnologies.
“The things we work on are selected because the type of polymer-protein chemistry has a potential competitive advantage, and we try to apply our designs in that area,” he says.

Source: By Anne Trafton, MIT

Un senzor tactil microfluidic bazat pe un design senzor de presiune al diafragmei (A microfluidic tactile sensor based on a diaphragm pressure sensor design )

cercetatorii raporteaza un senzor tactil microfluidic bazat pe un design al senzorului de presiune al diafragmei.
Dezvoltarea senzorilor de presiune flexibili are diverse aplicații potențiale în robotica moale, electronice portabile și piele artificială artificială.
Ca o dovadă a conceptului, cercetătorii au proiectat și fabricat o brățară PDMS cu un senzor de presiune cu membrană microfluidică încorporată pentru măsurarea măsurătorilor dinamice ale impulsurilor.

Posted: Aug 28, 2017
A microfluidic tactile sensor based on a diaphragm pressure sensor design (Nanowerk News) In a new paper in Advanced Materials („Wearable Microfluidic Diaphragm Pressure Sensor for Health and Tactile Touch Monitoring”), researchers report a microfluidic tactile sensor based on a diaphragm pressure sensor design.
The development of flexible pressure sensors has various potential applications in soft robotics, wearable electronics, and artificial electronic skins.

Microfluidic tactile diaphragm pressure sensor. a) Optical image of a finished microfluidic diaphragm sensor. b) Schematic layout of the diaphragm sensor and c) the equivalent circuit schematic forming an equivalent Wheatstone bridge circuit. d) Simulation of the normal stress for the radial sensing grids (?r) (along X-axis) and the normal stress for the tangential sensing grids (σt) (along Y-axis) of the sensor under 1 kPa pressure applied over a 9 mm diameter and e) a schematic diagram indicating testing conditions. (© Wiley-VCH Verlag) (click on image to enlarge)
This novel diaphragm pressure sensor design utilizing an embedded equivalent Wheatstone bridge circuit makes the most of tangential and radial strain fields, allowing the researchers to achieve a combination of high sensitivity, linearity, low limit of detection, high resolution, and temperature self-compensation.
The usage of the Wheatstone bridge design also provides built-in temperature compensation allowing for operation between 20 and 50°C without external offsets.
Due to its performance, the diaphragm pressure sensor meets the requirement of a variety of potential applications. Among many, one feasible and effective health monitoring application is heart-rate monitoring.
As a proof of concept, the researchers designed and fabricated a PDMS wristband with an embedded microfluidic diaphragm pressure sensor to measure dynamic pulse measurements.

Tactile sensing glove. a) Photograph of hand-shaking wearing the PDMS tactile sensing glove. b) Schematic of the PDMS tactile sensing glove. c) Photograph of the tactile sensing glove worn while grasping a grape. d) Real-time response recorded from the corresponding thumb and index finger sensors for gently grasping and releasing the grape. e) Photograph of the tactile sensing glove worn while gripping a bat and the corresponding output voltage map across the sensors within the glove. (© Wiley-VCH Verlag) (click on image to enlarge)
„The detection limit of our sensor has been shown to be below 100 Pa with sub-50 Pa resolution,” the authors note. „The extremely low detection limit and resolution combined with an ultrafast response time of 90 ms allows for the sensor to be used in a wide range of applications.”
As the team demonstrates, the liquid-state diaphragm pressure sensors may be utilized as either standalone devices for monitoring pressure at a specific point or into large arrays for tactile mapping in a variety of electronic skin and smart textile applications for wearables, robotics, and beyond.

By Michael Berger – Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny.

Materialele intunecate nanostructurate storc combustibilul verde din lumina soarelui (Nanostructured dark materials squeeze green fuel from sunlight )

a găsit acum un traseu mai durabil pentru producția de combustibil de hidrogen , folosind, materiale haotice lumina-capcană , care imita naturale de divizare a apei fotosintetice .Un metamaterial nanostructurat cu un aranjament asemănător floarea-soarelui poate fi scufundat în apă pentru a genera gaz hidrogen cu o eficiență superbă

Posted: Aug 28, 2017
Nanostructured dark materials squeeze green fuel from sunlight (Nanowerk News) Hydrogen gas, an important synthetic feedstock, is poised to play a key role in renewable energy technology; however, its credentials are undermined because most is currently sourced from fossil fuels, such as natural gas.
A King Abdullah University of Science and Technology (KAUST) team has now found a more sustainable route to hydrogen fuel production using chaotic, light-trapping materials that mimic natural photosynthetic water splitting (Advanced Materials, „Enhanced solar-to-hydrogen generation with broadband Epsilon-Near-Zero nanostructured photocatalysts”).

A nanostructured metamaterial with a sunflower-like arrangement can be immersed in water to generate hydrogen gas with superb efficiency. (© WILEY-VCH Verlag)
The complex enzymes inside plants are impractical to manufacture, so researchers have developed photocatalysts that employ high-energy, hot electrons to cleave water molecules into hydrogen and oxygen gas. Recently, nanostructured metals that convert solar electrons into intense, wave-like plasmon resonances have attracted interest for hydrogen production. The high-speed metal plasmons help transfer carriers to catalytic sites before they relax and reduce catalytic efficiency.
Getting metal nanoparticles to respond to the entire broadband spectrum of visible light is challenging. “Plasmonic systems have specific geometries that trap light only at characteristic frequencies,” explains Andrea Fratalocchi, who led the research. “Some approaches try to combine multiple nanostructures to soak up more colors, but these absorptions take place at different spatial locations so the sun’s energy is not harvested very efficiently.”
Fratalocchi and his team devised a new strategy using metal nanostructures known as epsilon-near-zero (ENZ) metamaterials that grow with random, fractal needles similar to a tiny pine tree. Inside the cavities formed by the protruding metal branches, the propagation of light slows to a near standstill. This enables the ENZ substance to squeeze all visible light colors to the same nanometer-scale locations.
However, optimizing the ENZ material for hydrogen generation proved a protracted process of months. Not every needle-like structure works the same way, which meant the team had to fine tune all fabrication parameters to find the correct disorder for efficient reactions. Then, choosing semiconducting titanium dioxide as a substrate to collect hot electrons required crystals with extremely high purity. Finally, the concentration and position of platinum nanoparticles used to catalytically split water molecules needed to be precisely controlled, depositions that are difficult with ENZ’s complex geometry.
The result was worth the perseverance: experiments revealed the ENZ photocatalyst used broadband light to generate hot carriers within a narrow 10-nm interfacial region for an overall 300% gain in efficiency.
“Due to the possibility of controlling their absorption, the ENZ nanostructures are ideal candidates for solar-energy harvesting,” says Fratalocchi. “We recently engineered an industrial prototype with impressive efficiency, which makes us very optimistic about the future possibilities of this technology.”

Source: King Abdullah University of Science and Technology

Celulele solare perovskite sunt monocristaline (Perovskite solar cells go single crystal )

Celulele hibride emergente organice-anorganice solare bazate pe CH perovskit 3 NH 3 PbI 3 , pe de altă parte, nu sunt ieftine numai pentru a procesa , dar și flexibilă, și astfel sunt larg urmărite ca fiind una dintre cele mai promițătoare tehnologii de ultimă generație de conversie fotovoltaice.Prin optimizarea continuă a materialelor și dispozitivelor, ei cred că celulele solare perovskite singulare cristaline vor rivaliza omologii lor policristali în viitorul apropiat.

Posted: Aug 28, 2017
Perovskite solar cells go single crystal (Nanowerk News) Photovoltaic conversion is regarded as the ultimate solution to the mankind’s ever growing demand for energy, yet the traditional silicon-based solar cells are expensive to produce, and the production itself involves intensive energy consumption.
The emerging hybrid organic-inorganic solar cells based on perovskite CH3NH3PbI3, on the other hand, are not only inexpensive to process but also flexible, and thus are widely pursued as one of the most promising next generation photovoltaic conversion technologies.
Since its first report in 2009, the photovoltaic conversion efficiency of perovskite solar cells has increased spectacularly from 3.81% to 22.1% in just 7 years, and such unprecedented rise has fueled worldwide pursuit for its efficiency record.
Nevertheless, in the last two years, the pace in perovskite solar cell efficiency increase has slowed down considerably despite that it is still far away from the projected theoretical limit of 31%. Therefore, researchers are exploring new strategies to further enhance the perovskite solar cell performance.
The current perovskite solar cells are based on polycrystalline CH3NH3PbI3 films, and thus inevitably have many defects in grains and grain boundaries that affect the device performance.

Single crystalline CH3NH3PbI3 self-grown on FTO/TiO2 substrate. (a) Schematic self-growth via temperature gradient and capillary effect; (b) cross-sectional SEM image of CH3NH3PbI3 on FTO/TiO2; (c) high resolution TEM image of single crystalline CH3NH3PbI3. (© Science China Press)
Efforts have been made to produce bulk CH3NH3PbI3 crystals that exhibit exceptional photovoltaic properties such as long diffusion length and lifetime of photo-generated charge carriers, though the integration of bulk crystal into perovskite solar cell device architecture proves rather challenging.
Now a team of Chinese and US scientists from Shenzhen Institute of Technology, Shijiazhuang Tiedao University, Peking University, Argonne National Laboratory, Institute of Metal Research, and University of Washington, led by Profs. Jiangyu Li and Jinjin Zhao, has successfully grown single crystalline film of CH3NH3PbI3 directly on electron-collecting FTO/TiO2 substrate, as shown in Fig. 1 („Single crystalline CH3NH3PbI3 self-grown on FTO/TiO2 substrate for high efficiency perovskite solar cells”).
They took advantage of temperature gradient and capillary effect during the growth process, enabling them to produce high quality single crystalline film tightly integrated on FTO/TiO2. This proves critical, as FTO/TiO2 is the most widely used electron-collecting substrate for perovskite solar cells, making the subsequent device fabrication straightforward.
Indeed, the single crystalline CH3NH3PbI3 film shows excellent photovoltaic properties. Measured directly on FTO glass substrate with poor electron extraction, the time-resolved photoluminescence shows much longer carrier lifetime in single crystalline CH3NH3PbI3 film compared to polycrystalline one, as seen in Fig. 2(a).

Photo-carrier properties and photovoltaic performance of single crystalline and polycrystalline CH3NH3PbI3. (a) time-resolved photoluminescence shows longer charge lifetime in single crystalline film and efficient charge collection at the interface with FTO/TiO2 substrate; and (b) current density-voltage curve shows a photovoltaic efficiency of 8.78 percent. (© Science China Press)
When a TiO2 electron collecting layer is added on top of FTO glass, then the charge carrier lifetime drops substantially, thanks to the efficient electron extraction at the TiO2/perovskite interface. As a result, the device exhibits photovoltaic conversion efficiency of 8.78%, the highest reported to date for a single crystalline perovskite solar cells.
The team pointed out that the system has much room for further improvement, and with continuous optimization of materials and devices, they believe that the single crystalline perovskite solar cells will rival their polycrystalline counterparts in the foreseeable future.

Source: Science China Press

Uleiul și apa se pot combina dacă condițiile sunt corecte ( Oil and water may combine if conditions are right )

Aceasta este prima data cand metanul sa dovedit a se amesteca cu apa. Substanțele de respingere se comportă sub presiuni ridicate, cum ar fi cele găsite la podeaua oceanică sau în interiorul planetelor, care ar putea avea o gamă largă de aplicații, de la înlocuirea solvenților industriali periculoși și periculoși pentru mediu la modelarea corpurilor planetare,

Posted: Aug 28, 2017
Oil and water may combine if conditions are right (Nanowerk News) They say that oil and water do not mix … but now scientists have discovered that – under certain circumstances – it may be possible.
A new study suggests that some oily molecules – which normally repel water – can be forced to dissolve in water when the two substances are squeezed together under extreme pressure.
Researchers applied high pressure to tiny containers filled with water and methane, creating conditions similar to the intense pressure found on the ocean floor or inside the planets Uranus and Neptune.
By compressing water and methane together, scientists have been able to gain insights into how the chemicals interact. Methane is often used in experiments to study the properties of substances like oil that repel water – called hydrophobic molecules.
The new findings suggest it may be possible to mix other hydrophobic molecules with water in a similar way.
The study, published in the journal Science Advances („When immiscible becomes miscible – Methane in water at high pressures”), was carried out by researchers at the University of Edinburgh.
The team squeezed methane and water molecules between two ultra-sharp diamonds and compressed them by bringing the two anvil points together. The diamond anvil was used to apply pressures of up to 20,000 Bars – 20 times greater than the pressure at the bottom of the Mariana trench, the deepest part of the world’s oceans.
Under a microscope, methane – much like oil – appears as large droplets in water at normal pressure, demonstrating that the substances do not mix. However, the team found the droplets disappeared at high pressures, indicating that the methane had dissolved.
Researchers think this happens because methane molecules shrink as pressure is increased, while water molecules stay largely the same. This could allow compacted methane molecules to fit between the much larger water molecules, enabling them to mix, the team says.
Understanding the mixing properties of water and methane could help researchers find ways of replacing expensive and hazardous solvents used in industry. It could also help provide new insights into conditions at the bottom of the ocean or in the outer solar system.
The study was supported by the Engineering and Physical Sciences Research Council and European Research Council.
Dr John Loveday, of the University of Edinburgh’s Centre for Science at Extreme Conditions in the School of Physics and Astronomy, said: „This is the first time that methane has been shown to mix with water. These exciting findings shed light on how water-repelling substances behave under high pressures, such as those found at the ocean floor or inside planets. This could have a huge range of applications, from replacing expensive and environmentally hazardous industrial solvents to modelling planetary bodies like Saturn’s largest moon, Titan.”

Source: University of Edinburgh

Noua tehnologie cu membrană lichid-metal poate contribui la viabilitatea vehiculelor pe bază de hidrogen cu celule de combustibil (New liquid-metal membrane technology may help make hydrogen fuel cell vehicles viable)

Conștient de faptul că tensiunea superficială a metalelor lichide s-ar putea schimba ca răspuns la variațiile de temperatură și compoziția gazelor la care au fost expuse, potențial producând scurgeri, au hotărât să introducă metalul între două straturi de material suport pentru a crea un lichid întins – membrana metalică sau SLiMM. O membrană constând dintr-un strat subțire (două zecimi dintr-un milimetru) de galiu lichid între un strat de carbură de siliciu și un strat de grafit a fost construită în laborator și testată pentru stabilitate și permeabilitate la hidrogen.
Membrana a fost expusă la o atmosferă de hidrogen timp de două săptămâni la temperaturi cuprinse între 480 și 550 ° C. Rezultatele au arătat că pelicula de galiu lichid a fost de până la 35 de ori mai permeabilă la hidrogen decât un strat comparabil de paladiu și că difuzia de hidrogen Membrana sandwich a fost considerabil mai mare decât pentru o membrană tipică de paladiu. De asemenea, testul a arătat că membranele au fost selective, permițând doar trecerea hidrogenului

Posted: Aug 28, 2017
New liquid-metal membrane technology may help make hydrogen fuel cell vehicles viable (Nanowerk News) While cars powered by hydrogen fuel cells offer clear advantages over the electric vehicles that are growing in popularity (including their longer range, their lower overall environmental impact, and the fact that they can be refueled in minutes, versus hours of charging time), they have yet to take off with consumers. One reason is the high cost and complexity of producing, distributing, and storing the pure hydrogen needed to power them, which has hindered the roll-out of hydrogen refueling stations.
Engineers have long recognized the power – and limitless availability – of hydrogen, the most abundant element in the universe. Hydrogen occurs naturally in the environment, but it is almost always chemically bound to other elements–to oxygen in water (H2O), for example, or to carbon in methane (CH4). To obtain pure hydrogen, it must be separated from one of these molecules. Virtually all of the hydrogen produced in the United States is obtained from hydrocarbon fuels, primarily natural gas, through steam reforming, a multi-step process in which the hydrocarbons react with high-temperature steam in the presence of a catalyst to produce carbon monoxide, carbon dioxide, and molecular hydrogen (H2).
The hydrogen can then be separated from the other gases through a cumbersome, multi-step chemical process, but the cost and complexity of hydrogen production can be reduced by using a membrane to do the separation. Most of the hydrogen separation membranes currently being developed use the precious metal palladium, which has unusually high hydrogen solubility and permeance (which means that hydrogen easily dissolves in and travels through the metal, while other gases are excluded). But palladium is expensive (it currently sells for about $900 per ounce) and fragile.
For these reasons, chemical engineers have long searched for alternatives to palladium for use in hydrogen separation membranes, but so far, no suitable candidates have emerged. A pioneering study led by Ravindra Datta, professor of chemical engineering at Worcester Polytechnic Institute (WPI), may have identified the long-elusive palladium alternative: liquid metals.
A host of metals and alloys are liquid at the standard operating temperatures found in steam reforming systems (around 500 degrees C), and most of these are far less expensive than palladium. In addition, a membrane made with a film of liquid metal should not be prone to the defects and cracks that can render a palladium membrane unusable.
The WPI study, published in the Journal of the American Institute of Chemical Engineers („Sandwiched liquid metal membrane (SLiMM) for hydrogen purification”), is the first to demonstrate that in addition to these advantages, liquid-metal membranes also appear to be significantly more effective than palladium at separating pure hydrogen from other gases, suggesting that they may provide a practical and effective solution to the challenge of supplying affordable hydrogen for fuel-cell vehicles. „The recent shift to electric cars is irreversible,” said Datta. The next step after electric vehicles, he and others believe, is hydrogen-fuel vehicles – if the hydrogen supply puzzle is solved.

Researchers at Worcester Polytechnic Institute (WPI) tested a prototype sandwiched liquid-metal membrane with this laboratory set-up. The membrane, a thin layer of gallium sandwiched between porous ceramic supports, selectively separated hydrogen from a mixed-gas stream more efficiently than a comparable palladium membrane. (Image: Worcester Polytechnic Institute (WPI)/Curtis Sayers (click on image to enlarge)
Like battery-powered electric cars, fuel-cell vehicles have electric motors. The motors are powered by electricity generated inside the fuel cell when hydrogen and oxygen combine in the presence of a catalyst (the only „waste” product is water). While they can pull oxygen from the air, the cars must carry a supply of pure hydrogen.
Many researchers have focused on bringing the cost of that hydrogen down by making better and thinner palladium membranes. Some of the most advanced membranes were produced by retired WPI chemical engineering professor Yi Hua „Ed” Ma, who, with considerable funding from industry and the U.S. Department of Energy, pioneered a process for binding palladium to a porous steel tube, resulting in palladium layers as thin as 5 to 10 microns.
Making the palladium layer thin increases the membrane’s flux, or the rate at which pure hydrogen moves through it. „But if a membrane is too thin,” Datta said, „it becomes fragile or it develops defects. And the membranes need to be defect-free. If they develop even a hairline crack or a micropore, you have to start over.”
Six years ago, Datta and his students began to wonder whether liquid metals might overcome some of palladium’s limitations – particularly its cost and fragility–while also, potentially, offering superior hydrogen solubility and permeance. „Besides chemical affinity, permeance depends on how open a metallic crystal structure is,” he said. „Liquid metals have more space between atoms than solid metals, so their solubility and diffusability should be higher.”
After a literature review revealed no previous research on this topic, Datta successfully applied for a $1 million award from the U.S. Department of Energy to study the feasibility of using liquid metals for hydrogen separation. he and his team, graduate students Pei-Shan Yen and Nicholas Deveau (Yen earned her PhD in 2016; Deveau received his in May), decided to begin their exploration with gallium, a nontoxic metal that is liquid at room temperature.
They conducted fundamental work that revealed that gallium was an excellent candidate, as it demonstrated significantly higher hydrogen permeance than palladium at elevated temperatures. In fact, laboratory studies and theoretical modeling conducted by the team showed that a number of metals that are liquid at higher temperatures may have better hydrogen permeance than palladium.
While liquid gallium showed great promise as a material for hydrogen separation, creating a functioning membrane with the metal proved challenging, Datta said. „It turns out that liquid metals are very reactive,” he said. „You cannot place gallium on a porous metal support, as Professor Ma did with palladium, since at higher temperatures it quickly forms intermetallic compounds that kill the permeability.” The team discovered that the metal will also react with a number of ceramic materials commonly used as supports in palladium membranes.
Through modelling and experimentation, they compiled a list of materials, including carbon-based materials like graphite and silicon carbide, that do not chemically react with liquid gallium but that are also wettable by the liquid metal, meaning that the metal will spread out to form a thin film on the support material.
Aware that the surface tension of liquid metals was likely to change in response to variations in temperature and the composition of the gases they were exposed to, potentially producing leaks, they decided to insert the metal between two layers of support material to create a sandwiched liquid-metal membrane or SLiMM. A membrane consisting of a thin (two-tenths of a millimeter) layer of liquid gallium between a layer of silicon carbide and a layer of graphite, was constructed in the lab and tested for stability and hydrogen permeance.
The membrane was exposed to a hydrogen atmosphere for two weeks at temperatures ranging from 480 to 550 degrees C. The results showed that the liquid gallium film was up to 35 times more permeable to hydrogen than a comparable layer of palladium and that diffusion of hydrogen through the sandwiched membrane was considerably higher than for a typical palladium membrane. The test also showed that the membranes were selective, allowing just hydrogen to pass through.
„These tests confirmed our hypotheses that liquid metals may be suitable candidate for hydrogen separation membranes,” Datta said, „suggesting that these materials could be the long-sought substitute for palladium. There are a host of questions that still need to be answered, including whether the small membranes we constructed in the laboratory can be scaled up and whether the membranes will be resistant to substances present in reformed gases (including carbon monoxide and sulfur) that are known to poison palladium membranes.
„But by demonstrating the feasibility of sandwiched liquid-metal membranes, we have opened the door to a highly promising new area of hydrogen energy research,” Datta added, „for there are many other metals and alloys, beyond gallium, that are liquid at 500 degrees C. It is a vast open field, in terms of what materials you might use. Also, it poses a host of interesting scientific questions.”

Source: Worcester Polytechnic Institute

NATO pregătește pentru războiul urban(NATO Preparing for Urban Warfare)

NATO cere contractorilor externi să adopte concepte privind operațiunile militare din zonele urbane, recunoscând că forțele sale nu sunt pregătite pentru războiul urban în marile orașe

NATO

Fotovoltaii perovskiți își schimbă forma atunci când sunt expuși la lumină (Photosensitive perovskites change shape when exposed to light )

Un material cristalin care schimba forma ca raspuns la lumina ar putea forma inima noilor dispozitive activate de lumina. Cristale perowskite au primit o mulțime de atenție pentru eficiența lor la transformarea luminii solare în energie electrică
Materialele fotostrictive organice oferă cea mai mare schimbare a formei raportate până acum ca răspuns la lumină – un parametru cunoscut sub numele de coeficientul lor fotostrictiv

Posted: Aug 27, 2017
Photosensitive perovskites change shape when exposed to light (Nanowerk News) A crystalline material that changes shape in response to light could form the heart of novel light-activated devices. Perovskite crystals have received a lot of attention for their efficiency at converting sunlight into electricity, but new work by scientists at King Abdullah University of Science and Technology (KAUST) shows their potential uses extend far beyond the light-harvesting layer of solar panels (Advanced Materials, „Photostriction of CH3NH3PbBr3 perovskite crystals”).
Photostriction is the property of certain materials to undergo a change in internal strain, and therefore shape, with exposure to light. Organic photostrictive materials offer the greatest shape change so far reported in response to light—a parameter known as their photostrictive coefficient—but their response is slow and unstable under ambient conditions.
KAUST electrical engineer Jr-Hau He and his colleagues have looked for photostriction in a new family of materials, the perovskites. “Perovskites are one of the hottest optical materials,” says He. His work now shows there’s more to their interesting optical properties than solar energy harvesting. The researchers tested a perovskite called MAPbBr3 and revealed it had strong and robust photostriction behavior.
To extensively test the material’s photostriction capabilities, the team developed a new method. They used Raman spectroscopy, which probes the molecular vibrations within the structure. When bathed in light, photostriction alters the internal strain in the material, which then shifts the internal pattern of vibrations. By measuring the shift in the Raman signal when the material was placed under mechanical pressure, the team could calibrate the technique and so use it to quantify the effect of photostriction.
“We demonstrated that in situ Raman spectroscopy with confocal microscopy is a powerful characterization tool for conveniently measuring intrinsic photoinduced lattice deformation,” says Tzu-Chiao Wei, a member of the team. “The same approach could be applied to measure photostriction in other materials,” he adds.
The perovskite material proved to have a significant photostriction coefficient of 1.25%. The researchers also showed that the perovskite’s photostriction was partly due to the photovoltaic effect—the phenomenon at the heart of most solar cell operation. The spontaneous generation of positive and negative charges when the perovskite is bathed in light polarizes the material, which induces a movement in the ions the material is made from.
The robust and stable photostriction of perovskite makes it useful for a range of possible devices, says Wei. “We will use this material to fabricate next-generation optoelectronic devices, including wireless remote switchable devices and other light-controlled applications,” he says.

Source: King Abdullah University of Science and Technology

Nanophotonic chip system measures light from a single bacterial cell to enable portable chemical detection

High-speed switching for ultrafast electromechanical switches and sensors

Research team flips the switch on ferroelectrics

Designing polymers with novel features

Block by block

Useful materials

A microfluidic tactile sensor based on a diaphragm pressure sensor design

Nanostructured dark materials squeeze green fuel from sunlight

Perovskite solar cells go single crystal

Oil and water may combine if conditions are right

New liquid-metal membrane technology may help make hydrogen fuel cell vehicles viable

Photosensitive perovskites change shape when exposed to light