Lună: octombrie 2017

Adăugarea filmelor subțiri CNT la țesături ar putea suporta electronice portabile(Addition of CNT thin-films to fabrics could power portable electronics)

Aceste două tipuri de materiale – numite p-type și picioare de tip n – sunt necesare pentru a genera suficientă putere într-un dispozitiv termoelectric. Polimerii polimerici, un alt material termoelectric organic studiat, produc în mod obișnuit materiale de tip n care funcționează mult mai rău decât omologii lor de tip p.
Faptul că filmele subțiri SWCNT pot face picioare de tip p și n de tip aceleași materiale cu performanțe identice înseamnă că curentul electric din fiecare picior este echilibrat în mod inerent, ceea ce ar trebui să simplifice fabricarea unui dispozitiv. Materialele cu cele mai performante performanțe au avut valori de performanță care depășesc materialele termoelectrice din materiale polimerice polimerice semiconductoare din materiale polimerice de ultimă oră.a declarat că introducerea SWCNT în țesături ar putea servi o funcție importantă pentru electronice personale „portabile”. Prin captarea căldurii corporale și transformarea acesteia în energie electrică, semiconductorul ar putea alimenta electronice portabile sau senzori încorporați în îmbrăcăminte.

Posted: Oct 31, 2017

Addition of CNT thin-films to fabrics could power portable electronics

(Nanowerk News) Scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) reported significant advances in the thermoelectric performance of organic semiconductors based on carbon nanotube thin films that could be integrated into fabrics to convert waste heat into electricity or serve as a small power source.
The research demonstrates significant potential for semiconducting single-walled carbon nanotubes (SWCNTs) as the primary material for efficient thermoelectric generators, rather than being used as a component in a “composite” thermoelectric material containing, for example, carbon nanotubes and a polymer. The discovery is outlined in Energy & Environmental Science(„Large n- and p-type thermoelectric power factors from doped semiconducting single-walled carbon nanotube thin films”).
Two men stand in front of a screen that shows carbon nanotubes
NREL scientists Andrew Ferguson, left, and Jeffrey Blackburn stand in front of a screen displaying single-walled carbon nanotubes. (Photo by Dennis Schroeder/NREL)
“There are some inherent advantages to doing things this way,” said Jeffrey Blackburn, a senior scientist in NREL’s Chemical and Materials Science and Technology center and co-lead author of the paper with Andrew Ferguson. These advantages include the promise of solution-processed semiconductors that are lightweight and flexible and inexpensive to manufacture. Other NREL authors are Bradley MacLeod, Rachelle Ihly, Zbyslaw Owczarczyk, and Katherine Hurst. The NREL authors also teamed with collaborators from the University of Denver and partners at International Thermodyne, Inc., based in Charlotte, N.C.
Ferguson, also a senior scientist in the Chemical and Materials Science and Technology center, said the introduction of SWCNT into fabrics could serve an important function for “wearable” personal electronics. By capturing body heat and converting it into electricity, the semiconductor could power portable electronics or sensors embedded in clothing.
Blackburn and Ferguson published two papers last year on SWCNTs, and the new research builds on their earlier work. The first paper, in Nature Energy („Tailored Semiconducting Carbon Nanotube Networks with Enhanced Thermoelectric Properties”), showed the potential that SWCNTs have for thermoelectric applications, but the films prepared in this study retained a large amount of insulating polymer. The second paper, in ACS Energy Letters („Polymer-Free Carbon Nanotube Thermoelectrics with Improved Charge Carrier Transport and Power Factor”), demonstrated that removing this “sorting” polymer from an exemplary SWNCT thin film improved thermoelectric properties.
The newest paper revealed that removing polymers from all SWCNT starting materials served to boost the thermoelectric performance and lead to improvements in how charge carriers move through the semiconductor. The paper also demonstrated that the same SWCNT thin film achieved identical performance when doped with either positive or negative charge carriers.
These two types of material–called the p-type and the n-type legs, respectively–are needed to generate sufficient power in a thermoelectric device. Semiconducting polymers, another heavily studied organic thermoelectric material, typically produce n-type materials that perform much worse than their p-type counterparts.
The fact that SWCNT thin films can make p-type and n-type legs out of the same material with identical performance means that the electrical current in each leg is inherently balanced, which should simplify the fabrication of a device. The highest performing materials had performance metrics that exceed current state-of-the-art solution-processed semiconducting polymer organic thermoelectrics materials.
“We could actually fabricate the device from a single material,” Ferguson said. “In traditional thermoelectric materials you have to take one piece that’s p-type and one piece that’s n-type and then assemble those into a device.”
Source: National Renewable Energy Laboratory

Graphene permite circuite electronice de mare viteză pe materiale flexibile(Graphene enables high-speed electronics on flexible materials)

Detectorul are caracteristici unice. La temperatura camerei, detectează semnale în intervalul de frecvență de la 330 la 500 gigahertzi. Este translucid și flexibil și se deschide la o varietate de aplicații. Tehnica poate fi utilizată pentru imagistică în zona terahertz (camera THz), dar și pentru identificarea diferitelor substanțe (senzor). De asemenea, poate avea un beneficiu potențial în îngrijirea sănătății, unde undele terahertz pot fi folosite pentru detectarea cancerului. Alte domenii în care detectorul poate fi utilizat sunt senzori de imagine pentru vehicule sau pentru comunicații fără fir.
Caracteristicile electronice unice ale grafenului, combinate cu natura sa flexibilă, fac din el un material promițător de integrare în plastic și țesătură, ceea ce va constitui un bloc de construcție important într-o lume viitoare interconectată. Tehnologia Graphene permite aplicații noi, printre altele, obiecte de zi cu zi, care sunt denumite în mod obișnuit Internetul Lucrurilor.
Detectorul arată posibilitățile concrete ale grafenului, un material care conduce extrem de bine curentul electric. Este o caracteristică care face ca grafenul să devină un bloc de atracție în domeniul electronicii rapide. Activitatea cercetătorilor de la Chalmers este, prin urmare, un important pas înainte pentru grafen în zona terahertz și un progres pentru performanțe ridicate și tehnologie ieftină terahertz

Posted: Oct 31, 2017

Graphene enables high-speed electronics on flexible materials

(Nanowerk News) A flexible detector for terahertz frequencies (1000 gigahertz) has been developed by Chalmers researchers using graphene transistors on plastic substrates. It is the first of its kind, and can extend the use of terahertz technology to applications that will require flexible electronics, such as wireless sensor networks and wearable technology. The results are published in the scientific journal Applied Physics Letters („A flexible graphene terahertz detector”).
flexible graphene terahertz detector
With the help of the two-dimensional material graphene, the first flexible terahertz detector has been developed by researchers at Chalmers. The opportunities are great within health and Internet of Things, and for new types of sensors. (Image: Boid – Product Design Studio, Gothenburg)
Terahertz radiation has a wide range of uses and can occur in everything from radio astronomy to medicine. The term refers to the electromagnetic waves whose frequencies range from 100 gigahertz to 10 terahertz. Demand for higher bandwidth in wireless communications and depiction for security applications has led to intensified research on systems and components intended for terahertz frequencies.
One challenge has long been to enable low weight and cheap applications. However, advances in polymer technology have promoted the development of flexible electronics and enabled the production of high frequency units on flexible substrates.
Now, Chalmers researchers Xinxin Yang, Andrei Vorobiev, Andrey Generalov, Michael A. Andersson and Jan Stake have developed the first mechanically flexible and graphene-based terahertz detector in its kind. Thus, paving the way for flexible terahertz electronics.
The detector has unique features. At room temperature, it detects signals in the frequency range 330 to 500 gigahertz. It is translucent and flexible, and opens to a variety of applications. The technique can be used for imaging in the terahertz area (THz camera), but also for identifying different substances (sensor). It may also be of potential benefit in health care, where terahertz waves can be used to detect cancer. Other areas where the detector could be used are imaging sensors for vehicles or for wireless communications.
The unique electronic features of graphene, combined with its flexible nature, make it a promising material to integrate into plastic and fabric, something that will be important building blocks in a future interconnected world. Graphene electronics enables new applications for, among other things, everyday objects, which are commonly referred to as the Internet of Things.
The detector shows the concrete possibilities of graphene, a material that conduct electric current extremely well. It is a feature that makes graphene an attractive building block in fast electronics. The Chalmers researchers’ work is therefore an important step forward for graphene in the terahertz area, and a breakthrough for high performance and cheap flexible terahertz technology.
The detector drew attention at the EU Tallinn Digital Summit recently, where several important technological innovations made possible by graphene and related materials were on display. At the summit, EU Heads of State and Government gathered to discuss digital innovation and Europe’s digital future. The flagship focus was to show what role graphene can play.
The research is also part of Xinxin Yang’s licentiate seminar, which will be presented at Chalmers on 22 November 2017.
Source: Chalmers University of Technology

De cleiuri și gaze: senzori de aderență la bară și senzori nanomecanici(Of glues and gases: Barnacle adhesion and nanomechanical sensors)

Yoshikawa va vorbi și despre cercetarea și dezvoltarea unui al doilea sistem nanomecanic care utilizează „analiza aero-termo-dinamică a masei” (AMA), pentru a caracteriza gazele prin măsurarea directă a greutății lor moleculare în condiții ambiante fără vacuum, ionizare sau instrumente voluminoase cerută de analiza spectrală în masă. Similar metodei de deformare prin care MSS detectează moleculele de gaze, AMA calculează greutatea moleculară a unei specii de gaz prin măsurarea modificării mecanice a unui obiect elastic simplu plasat sub un flux constant al gazului. Procesul poate fi realizat atât la scară nanometrică, cât și la macroscala, permițând senzorilor AMA să fie extrem de mici, portabili și capabili să fie integrați în alte dispozitive, cum ar fi telefoanele mobile.

Posted: Oct 30, 2017

Of glues and gases: Barnacle adhesion and nanomechanical sensors

(Nanowerk News) Among the diverse research studies being presented at this year’s 64th AVS International Symposium and Exhibition, being held Oct. 29-Nov. 2, 2017, in Tampa, Florida, are two biomaterial interfaces sessions that feature some highly unusual applications of engineering. The first describes the use of stress forces – more commonly employed to evaluate the failure mechanisms of materials and devices made from them – to discover how barnacles stick to surfaces. The second explores the development of two novel mechanical systems, both smaller than the eye can see, for use with gas molecules: one to detect them with ultra-high sensitivity and the other to precisely measure their molecular weights.
In the first presentation, biomedical engineer Manuel Figueroa of the College of New Jersey will discuss his research examining the effect of hydrophobicity (resistance to bonding with water) on the adhesive ability of the acorn barnacle, Amphibalanus amphitrite. This species is an abundant and widespread biofouler that is particularly troublesome for the marine shipping industry since a barnacle-encrusted ship hull creates drag on the vessel, reducing its performance and increasing fuel consumption.
To analyze barnacle adhesion in the laboratory, Figueroa allowed the arthropods to attach for two weeks to untreated glass slides representing hydrophilic surfaces as well as glass slides coated with hydrophobic self-assembled monolayers. He then removed the barnacles using a force gauge and calculated the critical shear stress needed to do the job for both sets. Finally, the quantity of glue remaining on the substrates was measured. What Figueroa discovered was that the critical shear stress was significantly higher for the hydrophobic surfaces as was the density of residual glue. The strong correlation, he said, suggests that hydrophobic surfaces may provide a protected environment for the barnacles to release their adhesive and that barnacle release only occurs when this cohesion fails. With further research, these findings may help shipbuilders and others design surfaces that exploit the nonadhesive characteristics.
In the second presentation, nanotechnology researcher Genki Yoshikawa of the National Institute for Materials Science in Japan will discuss the ongoing development and application of two nanometer-scale (billionth of a meter) mechanical devices for the detection and characterization of gas molecules. The first is the membrane-type surface stress sensor (MSS), that utilizes a circular membrane connected by cantileverlike “bridge spans” to a frame with embedded electrical resistors. Gas molecules are detected when they adsorb to the receptor layer coated on the membrane and deform it slightly, thereby perturbing the current flowing through the resistors. The MSS has great potential as a gas sensor, Yoshikawa said, because it is highly sensitive, can be designed to detect specific gases, and offers portability, ease of use and low cost. However, Yoshikawa said that adapting the MSS into a practical consumer mobile/”internet of things” sensor system requires “further optimization and integration of lots of components including receptor layers, hardware including electronics and sample handling, multidimensional data analysis, and precise calibration for high reproducibility.” This, Yoshikawa said, is the mission of an industry-academia-government consortium known as the MSS Alliance.
Yoshikawa also will talk about his group’s research and development of a second nanomechanical system that uses “aero-thermo-dynamic mass analysis” (AMA), to characterize gases by directly measuring their molecular weight in ambient conditions without the vacuum, ionization or bulky instrumentation required by mass spectral analysis. Similar to the deformation method by which MSS detects gas molecules, AMA calculates the molecular weight of a gas species by measuring the mechanical alteration of a simple elastic object placed under a constant flow of the gas. The process can be carried out at the nanoscale as well as the macroscale, allowing AMA sensors to be extremely tiny, portable and capable of being integrated into other devices such as cell phones.

References
Presentation BI-MoM1, “Characterization of Adult Barnacle Adhesion Upon Reattachment to Hydrophobic Surfaces” by Manuel Figueroa, is at 8:20 a.m. EDT Oct. 30, 2017, in Room 12 in the Tampa Convention Center, Tampa, Florida.
Presentation MN+BI_NS-MoM-3, “Nanomechanical Sensors (MSS, AMA) Toward IoT Olfactory Sensor System” by Genki Yoshikawa, is at 9:00 a.m. EDT Oct. 30, 2017, in Room 24 in the Tampa Convention Center, Tampa, Florida.
Source: AVS

Studiile noi privind catodii dezordonați pot furniza baterii de litiu foarte necesare(New studies on disordered cathodes may provide much-needed jolt to lithium batteries)

„Materialele catodice noi reprezintă direcția cea mai fierbinte în bateriile Li-ion”, a spus Ceder. „Câmpul este un pic blocat.Pentru a obține mai multe îmbunătățiri în stocarea de energie există doar câteva direcții de a merge.Una este baterii solid-state, iar cealaltă este de a continua să îmbunătățească densitatea de energie a materialelor electrod.Două nu sunt reciproc exclusiv această linie de cercetare nu este încă epuizată. „

Posted: Oct 30, 2017

New studies on disordered cathodes may provide much-needed jolt to lithium batteries

(Nanowerk News) Today’s lithium-ion battery was invented so long ago, there are not many more efficiencies to wring out of it. Now researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) report major progress in cathodes made with so-called „disordered” materials, a promising new type of lithium battery.
In a pair of papers published this month in Nature Communications („Mitigating oxygen loss to improve the cycling performance of high capacity cation-disordered cathode materials”) and Physical Review Letters („Electronic-Structure Origin of Cation Disorder in Transition-Metal Oxides”), a team of scientists led by Gerbrand Ceder has come up with a set of rules for making new disordered materials, a process that had previously been driven by trial-and-error. They also found a way to incorporate fluorine, which makes the material both more stable and have higher capacity.
„This really seems to be an interesting new direction for making high energy density cathodes,” said Ceder, a Senior Faculty Scientist at Berkeley Lab who also has an appointment at UC Berkeley’s Department of Materials Science and Engineering. „It’s remarkable that all the disordered rock salts people have come up with so far have very high battery capacity. In the PRL paper we give a guideline for how to more systematically make these materials.”
Gerbrand Ceder
A team of scientists led by Gerbrand Ceder reported major progress in cathodes made with so-called „disordered” materials, a promising new type of lithium battery. (Image: Berkeley Lab)

The benefits of disorder
The cathode material in lithium batteries is typically „ordered,” meaning the lithium and transition metal atoms are arranged in neat layers, allowing lithium to move in and out of the layers. A few years ago, Ceder’s group discovered that certain types of disordered material could store even more lithium, giving batteries higher capacity.
The lead author of the PRL paper is Alexander Urban, a Berkeley Lab postdoctoral fellow.
„Despite their attractive properties, discovering new disordered materials has been mostly driven by trial-and-error and by relying on human intuition,” Urban said. „Now we have for the first time identified a simple design criterion to predict novel disordered compositions. The new understanding establishes a relationship between the chemical species, local distortions of the crystal structure, and the tendency to form disordered phases.”
The other advantage of using disordered materials is the ability to avoid the use of cobalt, a limited resource, with more than half the world’s supply existing in politically unstable countries. By moving to disordered rock salts, battery designers could be free to use a wider range of chemistries. For example, disordered materials have been made using chromium, titanium, and molybdenum.
„We want the ability to have more compositional freedom, so we can tune other parameters,” Ceder said. „There are so many properties to optimize – the voltage, the long-term stability, whether it’s easy to synthesize – there’s so much that goes into taking a battery material to a commercial stage. Now we have a recipe for how to make these materials.”

How and why to fluorinate batteries
Another major advance in lithium-ion batteries is reported in the Nature Communications paper, which shows that disordered materials can be fluorinated, unlike other battery materials. Fluorination confers two advantages: it allows more capacity and makes the material more stable. In a battery, the increased stability would translate into a device with long cycle life and that is less likely to catch fire.
The lead author of the paper, Jinhyuk Lee, formerly a Berkeley Lab researcher, worked with scientists at Berkeley Lab’s Advanced Light Source (ALS), a source of X-ray beams for scientific research, to conduct in situ experiments. „The ALS was really important to understand the mechanism by which we get higher capacity,” Ceder said. „What’s really cool is you can look at the battery while it’s operating, and look at the electronic structure of the cathodes. So you learn how it charges and discharges, where the electrons go, which is a crucial aspect of charge storage.”
ALS scientists Shawn Sallis and Wanli Yang are co-authors, as is Bryan McCloskey of Berkeley Lab. „His group was crucial in showing these materials are more stable and don’t lose oxygen,” Ceder said.
Now that they have demonstrated the concept, Ceder plans to follow up by trying to add even more fluorine to the materials.
„New cathode materials is the hottest direction in Li-ion batteries,” Ceder said. „The field is a bit stuck. To get more improvements in energy storage there are only a few directions to go. One is solid-state batteries, and the other is to keep improving the energy density of electrode materials. The two are not mutually exclusive. This research line is definitely not exhausted yet.”
Source: Lawrence Berkeley National Laboratory

Punctele cuantice vizualizează rezonanțele vibraționale minuscule(Quantum dots visualize tiny vibrational resonances)

lumină.
O aplicație posibilă a acestei descoperiri, potrivit lui Sam Carter de la Naval Research Lab, unul dintre autorii lucrării, este de a detecta forțe subtile produse de obiecte dense din apropiere. „Materialele nucleare ascunse ar putea fi detectabile”, a spus el, „din moment ce materiale dense cum ar fi plumbul sunt folosite pentru a proteja dispozitivele.”
Ecranul foarte dens necesar pentru materialele nucleare cauzează mici anomalii gravitaționale și mișcări minore care ar putea fi detectabile de un dispozitiv bazat pe principiul descoperit aici. Cercetătorii intenționează să-și continue activitatea făcând abstracție de spinul electronic. Se speră că tehnicile de măsurare a efectului pe spin vor crește sensibilitatea dispozitivelor.

Posted: Oct 30, 2017

Quantum dots visualize tiny vibrational resonances

(Nanowerk News) In the late 18th century, Ernst Chladni, a scientist and musician, discovered that the vibrations of a rigid plate could be visualized by covering it with a thin layer of sand and drawing a bow across its edge. With the bow movement, the sand bounces and shifts, collecting along the nodal lines of the vibration. Chladni’s discovery of these patterns earned him the nickname, „father of acoustics.” His discovery is still used in the design and construction of acoustic instruments, such as guitars and violins.
Recently, investigators have discovered a similar effect with much smaller vibrating objects excited by light waves. When laser light is used to drive the motion of a thin, rigid membrane, it plays the role of the bow in Chladni’s original experiment and the membrane vibrates in resonance with the light. The resulting patterns can be visualized through an array of quantum dots (QDs), where these tiny structures emit light at a frequency that responds to movement. The advance is reported this week in a cover article of Applied Physics Letters („Sensing flexural motion of a photonic crystal membrane with InGaAs quantum dots”).
Image of a Chladni Plate'S Mode of Vibration Visualized By Grains of Sand Collected at the Nodes
Background: Image of a Chladni plate’s mode of vibration visualized by grains of sand collected at the nodes. Left-top: Cross-sectional scanning tunneling microscopy image of an indium arsenide quantum dot. Left-bottom: Variation of quantum dot emission line frequencies as a function of time due to vibrations of the photonic crystal membrane. Right: Scanning electron micrograph of a photonic crystal membrane, displaced according to one of the vibrational modes, with red and blue representing positive and negative displacement, respectively. (Image: Sam Carter and co-authors)
In addition to being a modern take on an old phenomenon, the new discovery could lead to the development of sensing devices as well as methods for controlling the emission characteristics of QDs. Since the light frequency emitted by the QDs is correlated with the movement of the underlying membrane, new devices for sensing motion, such as accelerometers, can be envisioned. A reverse application is also possible since the motion of the underlying membrane can be used to control the frequency of light emitted by the QDs.
The tiny devices in the work reported here consist of a 180-nanometer thick slice of semiconductor, suspended like a trampoline above a solid substrate. An array of QDs, analogous to the sand in the acoustic example, are embedded in the slice, whose thickness is less than one-tenth of one percent that of a human hair.
A second probe laser is used to visualize the resulting resonances. The QDs absorb the probe light and emit a second light pulse in response, which is picked up by a detector and routed to a display. The resulting patterns are remarkably like those visualized in Chladni’s original acoustic experiment, even though the new device is driven entirely by light.
One possible application of this discovery, according to Sam Carter of the Naval Research Lab who is one of the paper’s authors, is to sense subtle forces produced by nearby dense objects. „Concealed nuclear materials could be detectable,” he said, „since dense materials like lead are used to shield the devices.”
The highly dense shielding needed for nuclear materials causes small gravitational anomalies and tiny movements that might be detectable by a device based on the principle discovered here. The investigators plan to continue their work by looking at electronic spin. It is hoped that techniques to measure the effect on spin will increase the sensitivity of the devices.
Source: American Institute of Physics

Tactical Assault Light Operator Suit (TALOS) + FlyBoard Air Ducted-Fan Hoverboard = Flying Super Solidiers: Forțele militare de forțe speciale de operații (SOF) Assaulters / Operatorii să se arunce la țintă în exo-Armor ‘Iron Man'(Tactical Assault Light Operator Suit (TALOS)+FlyBoard Air Ducted-Fan Hoverboard=Flying Super Solidiers:Future Military Special Operations Forces(SOF) Assaulters/Operators to Fly Themselves to the Target in Exo-Armor ‘Iron Man’ -Type Combat Suits?)

  care este posibil un adevărat schimbător de jocuri pentru militari;o soluție modulară de protecție a capului balistic și o posibilă tehnologie modulară pentru tehnologie TALSO

49Stim

Ghidarea laserului aleatoriu(Guiding the random laser)

Cercetătorii sunt capabili să obțină aceste rezultate prin fabricarea și utilizarea unei fibre optice din fibră optică Anderson. Fibra este fabricată dintr-un „cuart satinos”, un geam artizan extrem de poros, utilizat în mod obișnuit doar pentru calibrarea mașinilor care atrag fibră optică. Când este tras în bucle lungi, materialul poros formează zeci de canale microscopice de aer în fiecare fibră.Echipa de cercetare a fabricat un nou tip de fibră optică care este capabilă să controleze aceste lasere aleatorii.

Posted: Oct 27, 2017

Guiding the random laser

(Nanowerk News) At its most basic level, a random laser is precisely what its name implies; random. It’s random in the spectrum of light it produces and in the way that light is emitted, making what could be an extremely versatile laser source, nearly useless for most practical applications.
So, how do you control some of the randomness to make useful devices? It’s a question that’s led a team of researchers at The University of New Mexico to a discovery that’s taking laser technology to the next level.
„It’s been incredible to see how this project has progressed,” said Behnam Abaie, a Ph.D. student at UNM’s Center for High Technology Materials (CHTM). „When I first came to work with Professor [Arash] Mafi, I knew this project had the potential to be very successful but I never expected this.”
Abaie is the first-author on a paper recently published in Nature’s Light: Science & Applications („Random lasing in an Anderson localizing optical fiber”). The article provides a technical analysis of how the research team, led by CHTM Interim Director Arash Mafi, is able to reliably control these extremely powerful, but previously uncontrollable, lasers.
Glass Anderson Localized Optical Fiber
The research team fabricated a new type of optical fiber that is capable of controlling these random lasers. (Image: University of New Mexico)
„Our success in being able to control these random lasers addresses decade-old issues that have prevented these lasers from becoming mainstream devices,” said Mafi, who is also an associate professor in UNM’s Dept. of Physics & Astronomy. „It’s a very exciting contribution.”
Traditional lasers consist of three main components: an energy source, gain medium and optical cavity. The energy source is provided through a process called ‘pumping’ and can be supplied through an electrical current or another light source. That energy then passes through the gain medium which contains properties that amplify the light. The optical cavity ­- a pair of mirrors on either side of the gain medium – bounce the light back and forth through the medium, amplifying it each time. The result is a directed, intense beam of light called a laser.
Random lasers, by comparison, perform using a pump, a highly-disordered gain medium but no optical cavity. They are extremely useful due to their simplicity and broad spectral features, meaning a single random laser can produce a beam of light containing multiple spectra, a very beneficial property for certain applications like biomedical imaging. However, given their nature, random lasers are difficult to reliably control due to their multi-directional output and chaotic fluctuation.
The UNM team, in collaboration with researchers at Clemson University and the University of California San Diego, has been able to overcome these obstacles in an efficient way – a victory they hope will continue to push the use of random lasers forward.
„Our device has all the great qualities of a random laser, plus spectral stability and it is highly directional,” said Mafi. „It’s a wonderful development.”
Researchers are able to achieve these results through the fabrication and use of a unique glass Anderson localizing optical fiber. The fiber is made of a ‘satin quartz’, an extremely porous artisan glass that is typically only used to calibrate the machinery that draws fiber optics. When pulled into long rods, the porous material forms dozens of microscopic air channels in each fiber.
„The glass that we’re using for these fiber optics is actually material that we would typically throw away because it is very porous,” said Abaie. „But, it’s those holes in the glass that are actually creating the channels that control the laser.”
Once filled with a gain medium and pumped using a single-colored green laser, the random laser becomes less random and highly controllable, thanks to a phenomenon known as Anderson Localization.
„There is still a lot to learn about Anderson Localization but it’s exciting for us to be part of this development,” said Mafi. „To be able to actually make devices that utilize this phenomenon, it’s taking the science to yet another level.”
Mafi and his research team are some of the leading experts in Anderson Localization. In 2014, they published an article on a different device capable of transmitting images using the phenomenon. That research was named one of Physics World’s Top Ten Breakthroughs of the year.
Moving forward, Mafi says they hope to broaden the spectrum of this new device and make it more efficient, creating a broad spectrum illumination source that can be utilized around the world.
Source: University of New Mexico

Dispozitivele fabricate din materiale 2D separă sărurile din apa de mare(Devices made from 2D materials separate salts in seawater)

Frezele sunt realizate din grafen, nitrură de bor hexagonală (hBN) și disulfură de molibden (MoS 2 ) și, în mod surprinzător, permit ionilor cu diametre mai mari decât dimensiunea fantei să treacă prin. Studiile de excludere a dimensiunilor permit o mai bună înțelegere a modului în care funcționează filtre biologice similare la scară largă, cum ar fi aquaporins, și astfel vor contribui la dezvoltarea unor filtre cu flux înalt pentru desalinizarea apei și a tehnologiilor aferente.

Posted: Oct 26, 2017

Devices made from 2D materials separate salts in seawater

(Nanowerk News) Researchers at the National Graphene Institute (NGI) at The University of Manchester have succeeded in fabricating tiny slits in a new membrane that are just several angstroms (0.1nm) in size. This has allowed the study of how various ions pass through these tiny holes.
The slits are made from graphene, hexagonal boron nitride (hBN) and molybdenum disulphide (MoS2) and, surprisingly, allow ions with diameters larger than the size of the slit to permeate through. The size-exclusion studies allow for a better understanding of how similar scale biological filters such as aquaporins work and so will help in the development of high-flux filters for water desalination and related technologies.
2D materials have been successfully assembled into devices with the smallest possible man made holes for water desalination
2D materials have been successfully assembled into devices with the smallest possible man made holes for water desalination. (University of Manchester)
For scientists interested in the behaviour of fluids and their filtration, it has been an ultimate but seemingly distant goal to controllably fabricate capillaries with dimensions approaching the size of small ions and individual water molecules.
Researchers have been trying to mimic naturally-occurring ion transport systems, but this has proved to be no easy task. Channels fabricated with standard techniques and conventional materials have unfortunately been limited in size by the intrinsic roughness of a material’s surface, which is usually at least ten times bigger than the hydrated diameter of small ions.
Earlier this year graphene-oxide based membranes developed at the NGI attracted considerable attention as promising candidates for new filtration technologies. This research utilising the new toolkit of 2D materials demonstrates the real-world potential of providing clean drinking water from salt water.
To better understand the fundamental mechanisms behind ion transport, a team led by Sir Andre Geim of The University of Manchester made atomically flat slits measuring just several angstroms in size. These channels are chemically inert with smooth walls on the angstrom scale.
The researchers made their slit devices from two 100-nm thick crystal slabs of graphite measuring several microns across that they obtained by shaving off bulk graphite crystals. They then placed rectangular-shaped pieces of 2D atomic crystals of bilayer graphene and monolayer MoS2 at each edge of one of the graphite crystal slabs before placing another slab on top of the first. This produces a gap between the slabs that has a height equal to the spacers’ thickness.
“It’s like taking a book, placing two matchsticks on each of its edges and then putting another book on top.” explains Geim. “This creates a gap between the books’ surfaces with the height of the gap being equal to the matches’ thickness. In our case, the books are the atomically flat graphite crystals and the matchsticks the graphene or MoS2 monolayers.”
The assembly is held together by van der Waals forces and the slits are roughly the same size as the diameter of aquaporins, which are vital for living organisms. The slits are the smallest size possible since slits with thinner spacers are unstable and collapse because of attraction between opposite walls.
Ions flow through the slits if a voltage is applied across them when they are immersed in an ionic solution, and this ion flow constitutes an electric current. The team measured the ionic conductivity as they passed through chloride solutions via the slits and found that ions could move through them as expected under an applied electric field.
“When we looked more carefully, we found that bigger ions moved through more slowly than smaller ones like potassium chloride” explains Dr Gopi Kalon, a postdoctoral researcher who led the experimental effort.
Dr Ali Esfandiar, who is the first author of the paper, adds “The classical viewpoint is that ions with a diameter larger than the slit size cannot permeate, but our results show that this explanation is too simplistic. Ions in fact behave like soft tennis balls rather than hard billiard ones, and large ions can still pass – either by distorting their water shells or maybe shedding them altogether.
The new research as published in Science, shows that these newly observed mechanisms plays a key role for desalination using the size exclusion and is a key step to creating high-flux water desalination membranes.
Source: University of Manchester

Hidrogele pentru senzori chimici(Hydrogels for Chimical Sensors)

descriem microsensorii chimici piezorezistenți pentru o caracterizare cuprinzătoare a soluțiilor, care ar putea fi încorporate în sistemele fluidice pentru monitorizarea în timp real a contaminanților organici și anorganici

Hidrogel pentru senzori chimici

Cercetătorii detectează detectarea gazului la temperatura camerei(Researchers greenlight gas detection at room temperature)

Cercetatorii rusi au dezvoltat un mecanism pentru detectarea hidrogenului molecular folosind lumina verde pentru iluminarea unui senzor compozit nanocristalin bazat pe oxizi de zinc si indiu. Pentru prima dată, acest lucru permite un senzor de gaz care funcționează la temperatura camerei.Astfel de senzori pot fi utilizați pentru a analiza calitatea aerului în aer liber și în spații închise

Posted: Oct 25, 2017

Researchers greenlight gas detection at room temperature

(Nanowerk News) Russian researchers have developed a mechanism for detecting molecular hydrogen using green light to illuminate a nanocrystalline composite sensor based on zinc and indium oxides. For the first time, this enables a gas sensor operating at room temperature. The paper was published in the journal Scientific Reports („Green light activated hydrogen sensing of nanocrystalline composite ZnO-In2O3 films at room temperature”).
Multisensor arrays for determining gas mixture composition are currently being developed. These are monitoring systems incorporating multiple sensors that target individual gases. Such sensors can be used to analyze air quality both outdoors and in closed spaces. Tracking atmospheric pollution remains a vital concern for many developed countries. Because residential communities tend to cluster around industrial areas, it is necessary to have a mechanism in place for controlling harmful emissions from plants and factories.
Besides that, air composition measurements are required at nuclear power plants, on submarines and space stations, and at other facilities where access to fresh air is not immediately available: If the concentration of carbon dioxide increases or a toxic substance leaks into the ventilation system, this might put the lives of personnel at risk.
Commercial gas mixtures such as gas fuels also need precise composition monitoring. Among them is hydrogen. Used as gas fuel, it could conceivably replace hydrocarbons. It is a clean fuel that releases nothing but water vapor when burnt. In addition, the efficiency of burning hydrogen is 10 to 20 percent higher than that of hydrocarbons. Some car manufacturers have already started phasing in hydrogen seeing it as a fuel of the future. And yet the Hindenburg airship disaster is a sad reminder of how dangerous hydrogen can be.
Until recently, gas sensors based on nanocrystalline metal oxides had operating temperatures between 300 and 500 degrees Celsius. This made them unsafe for the detection of explosive or combustible substances. Moreover, to maintain these high temperatures, a lot of power is required, making it impossible to embed such gas sensors into the circuit boards of portable devices.
To solve this problem, Professor Leonid Trakhtenberg of MIPT; Pavel Kashkarov, director of the Institute of Nano-, Bio-, Information, Cognitive and Socio-Humanistic Science and Technology; Alexander Ilin and Pavel Forsh from Lomonosov Moscow State University; and their colleagues from Semenov Institute of Chemical Physics proposed sensors capable of operating at room temperature. Their new nanocomposite sensors are based on zinc and indium oxides, and their efficiency is maximized by green light illumination. The proposed device could be used to detect combustible, explosive, or poisonous substances in the atmosphere even at low concentrations.
“The mechanism consists in the light-induced transition of the nanocrystalline sensor components into a nonequilibrium state and the resulting change in the photoconductivity of the sensor interacting with molecular hydrogen. This effect is linked with the dependence of photoconductivity on the nonequilibrium charge carrier recombination rate,” explains Maria Ikim, a doctoral student at the Laboratory of Functional Nanocomposites of Semenov Institute of Chemical Physics of the Russian Academy of Sciences.
photoconductivity (curve 1) and electrical conductivity (curve 2) of a composite film made of zinc and indium oxides
Photoconductivity (curve 1) and electrical conductivity (curve 2) of a composite film made of zinc and indium oxides in a 1-to-9 ratio by weight under periodic exposure to air containing hydrogen. Orange marks the scope of sensor response.
“The detectors that we have developed differ from the conventional semiconductor sensors in that they operate at room temperature. This eliminates the danger of combustion or explosion, when flammable or explosive substances are involved,” says Leonid Trakhtenberg of the Department of Chemical Physics, MIPT, who holds an ScD in physics and mathematics. “Most papers on sensor photoactivation discuss the effects of ultraviolet light on sensors and focus on the detection of oxidizing gases. But the efficiency of ultraviolet light diodes is low, while their cost is far greater than that of their counterparts emitting in the visible part of the spectrum. By working with hydrogen, we explore the possibilities of the detection of reducing gases.”
The paper reported in this story proposes a novel mechanism of sensor response photoactivation, which is illustrated by the image above. It accounts for the transition of charge carriers into a nonequilibrium state. The process involved is universal: It can be used to interpret sensing results in both oxidizing and reducing gases.
The sensors proposed by the authors could be used to monitor atmospheric air composition and analyze the chemical makeup of gases used in industrial processes. Although the study focuses on gases, the same sensors could be modified to target liquids.
Source: Moscow Institute of Physics and Technology