Autor: Liliana Decu

Filme transparente, conductive, promițătoare pentru dezvoltarea unor ecrane flexibile (Transparent, conductive films promising for developing flexible screens)

Cercetătorii au demonstrat fabricarea pe scară largă a unui nou tip de peliculă electrozică transparentă pe bază de argint nanopatternat. Ecranele tactile cu ecran tactil și televizoarele cu ecran plat utilizează electrozi transparenți pentru a detecta atingerea și pentru a comuta rapid culoarea fiecărui pixe; cercetătorii raportează fabricarea unui film subțire transmițător transparent pe discuri de sticlă cu diametrul de 10 centimetri. Pe baza estimărilor teoretice care se potrivesc îndeaproape cu măsurătorile experimentale, ele calculează că electrozii subțiri de film subțire pot funcționa semnificativ mai bine decât cei utilizați pentru afișajele flexibile existente și ecranele touch.

Posted: Jun 07, 2018

Transparent, conductive films promising for developing flexible screens

(Nanowerk News) Researchers have demonstrated large-scale fabrication of a new type of transparent conductive electrode film based on nanopatterned silver. Smartphone touch screens and flat panel televisions use transparent electrodes to detect touch and to quickly switch the color of each pixel. Because silver is less brittle and more chemically resistant than materials currently used to make these electrodes, the new films could offer a high-performance and long-lasting option for use with flexible screens and electronics. The silver-based films could also enable flexible solar cells for installation on windows, roofs and even personal devices.
In the journal Optical Materials Express („Transparent and conductive electrodes by large-scale nano-structuring of noble metal thin-films”), the researchers report fabrication of a transparent conducting thin-film on glass discs 10 centimeters in diameter. Based on theoretical estimations that matched closely with experimental measurements, they calculate that the thin-film electrodes could perform significantly better than those used for existing flexible displays and touch screens.
Nanopatterned Thin-Film Illustration
The researchers used an approach called colloidal lithography to create a silver nanopattern that conducts electricity while letting light through the holes. The new transparent electrode films could be useful for solar cells as well as flexible displays and touch screens. (Image: Jes Linnet, University of Southern Denmark)
„The approach we used for fabrication is highly reproducible and creates a chemically stable configuration with a tunable tradeoff between transparency and conductive properties,” said the paper’s first author, Jes Linnet from the University of Southern Denmark. „This means that if a device needs higher transparency but less conductivity, the film can be made to accommodate by changing the thickness of the film.”

Finding a flexible alternative
Most of today’s transparent electrodes are made of indium tin oxide (ITO), which can exhibit up to 92 percent transparency – comparable to glass. Although highly transparent, ITO thin films must be processed carefully to achieve reproducible performance and are too brittle to use with flexible electronics or displays. Researchers are seeking alternatives to ITO because of these drawbacks.
The anti-corrosive nature of noble metals such as gold, silver and platinum makes them promising ITO alternatives for creating long-lasting, chemically resistant electrodes that could be used with flexible substrates. However, until now, noble metal transparent conductive films have suffered from high surface roughness, which can degrade performance because the interface between the film and other layers isn’t flat.
Silver Thin-Film with Particles
This scanning electron microscopy image shows a thin film of silver deposited over plastic nanoparticles. Dissolving the particles leaves a precise pattern of honeycomb-like holes that allow light to pass through, producing an electrically conductive and optically transparent film. (Image: Jes Linnet, University of Southern Denmark)
Transparent conductive films can also be made using carbon nanotubes, but these films don’t currently exhibit high enough conductance for all applications and tend to also suffer from surface roughness due to the nanotubes stacking on top of each other.
In the new study, the researchers used an approach called colloidal lithography to create transparent conductive silver thin films. They first created a masking layer, or template, by coating a 10-centimeter wafer with a single layer of evenly sized, close-packed plastic nanoparticles. The researchers placed these coated wafers into a plasma oven to shrink the size of all the particles evenly. When they deposited a thin film of silver onto the masking layer, the silver entered the spaces between the particles. They then dissolved the particles, leaving a precise pattern of honeycomb-like holes that allow light to pass through, producing an electrically conductive and optically transparent film.

Balancing transparency and conductivity
The researchers demonstrated that their large-scale fabrication method can be used to create silver transparent electrodes with as much as 80 percent transmittance while keeping electrical sheet resistance below 10 ohms per square – about a tenth of what has been reported for carbon-nanotube-based films with the equivalent transparency. The lower the electrical resistance, the better the electrodes are at conducting an electrical charge.
colloidal lithography fabrication process
The researchers used colloidal lithography was used to create a thin film that was transparent and conductive thin film. (a) Schematic illustration of the fabrication process. (b) A single nanohole after the silver was deposited deposition and dissolving of the plastic particle. Scale bar: 200 nm. (c) Low magnification micrograph of deposited silver thin-film on homogenous particle monolayer, demonstrating large-scale feasibility. Scale bar: 50 microns. (d) Particle monolayer on substrate after spin-coating and a short (60 s) time in the plasma oven: Scale bar: 2 microns. (e) Particle monolayer after a long (3 min) time in the plasma oven, demonstrating that original particle positions are preserved even after significant size reduction. Scale bar: 10 microns. (Image: Jes Linnet, University of Southern Denmark) (click on image to enlarge)
„The most novel aspect of our work is that we accounted for both the transmission properties and the conductance properties of this thin film using theoretical analysis that correlated well with measured results,” said Linnet. „Fabrication problems typically make it hard to get the best theoretical performance from a new material. We decided to report what we encountered experimentally and postulate remedies so that this information could be used in the future to avoid or minimize problems that may affect performance.”
The researchers say that their findings show that colloidal lithography can be used to fabricate transparent conductive thin films that are chemically stable and could be useful for a variety of applications.
Source: The Optical Society

Tehnica neașteptată pentru a detecta agenții chimici de război (Unexpexted Technique to Detect Chemical Warfare agents)

Oferind un mijloc inovator, ieftin și rapid de detectare a agenților de amenințare, o nouă tehnologie de detectare poate oferi avantaje semnificative pentru războinicii desfășurați

Unexpected

Efectuarea materialelor compozite inteligente cu metale prețioase(Making composite material smart with precious metal)

Datorită modificării grosimii care influențează și compoziția spectrală a luminii reflectate, materialul ar putea fi folosit ca nanosenzori colorimetrici. Datorită dimensiunilor extrem de mici și posibilei cuplări cu un laser și spectrometru miniaturizat, compozitul ar putea fi aplicat în viitor în sistemele de laborator pe cip sau chiar în celula umană.

Posted: Jun 05, 2018

Making composite material smart with precious metal

(Nanowerk News) Doping polymer brushes with gold nanoparticles results in a switchable composite material which changes its thickness depending on the pH value. The research by physicists at the TU Darmstadt, published in the journal Soft Matter („Making strong polyelectrolyte brushes pH-sensitive by incorporation of gold nanoparticles”), could be used to design chemical nanosensors in diagnostics or environmental analytics.
Polymer brushes are chains of large molecules which are densely grafted on a surface. Due to electrostatic forces, the chains extend from the surface and form a fur-like layer with a thickness of several hundred nanometres.
Currently, research focuses on the design of polymer systems responding to various environmental stimuli such as pH value, temperature or specific biomarkers. Physicists at TU Darmstadt and TU Berlin have shown for the first time how the thickness of a polymer brush can be made switchable by incorporating pH-sensitive gold nanoparticles.
“The combination of polymer chains and gold nanoparticles is promising, especially in medical diagnostics or environmental analytics,” says Dikran Boyaciyan. The 30-year-old PhD student works in the “Soft Matter at Interfaces” group led by professor Regine von Klitzing.
Dikran Boyaciyan
Physicist Dikran Boyaciyan synthesizes polymer brushes in the lab. (Image: Sebastian Keuth)
„This technology is still at an early stage of development. The primary objective is how the interaction between polymer systems and nanoparticles may be tuned and calibrated in a controlled environment,” Boyaciyan explains. Smart polymer materials could be used in chemical nanosensors which report on toxins or cancer cells, monitor parameters of organs or target the release of drugs inside the human body.
Boyaciyan tested two types of pH-insensitive polymers with respect to their prospect for long-term use as sensors: the non-ionic PNIPAM and the cationic PMETAC. The former was found unsuitable because of gold particles being washed out from the brush at high pH values. In the cationic PMETAC brush, however, the gold particles adhered unaffected by pH changes.
Furthermore, Boyaciyan was able to show how to make a reversible pH-switchable composite from PMETAC by incorporating gold nanoparticles and how its complex formation works. In an acidic environment, the particles lose their charge and both particle-particle interactions and particle-brush interactions occur. This leads to a swollen brush because of its chains being less confined.
In contrast, an alkaline environment causes negative charges on the particles and interactions with the positively charged brush are preferred. The chains collapse resulting in a thinner brush layer.
Because of the thickness change also influencing the spectral composition of the reflected light, the material could be used as colorimetric nanosensors. Due to the extremely small dimensions and possible coupling with a miniaturized laser and spectrometer the composite could, in future, be applied in lab-on-a-chip systems or even within the human cell.
Source: TU Darmstadt

Pigmentul produs de ciuperci arată promisiunea ca material semiconductor(Fungi-produced pigment shows promise as semiconductor material)

reprezintă prima utilizare a unui material produs de ciuperci într-un dispozitiv electric subțire.Cercetatorii de la Universitatea de Stat din Oregon se uita la un pigment organic durabil, folosit de om in lucrari de arta de sute de ani, ca o posibilitate promitatoare ca material semiconductor.
Constatările sugerează că ar putea deveni o alternativă durabilă, ieftină și ușor fabricată la siliciu în aplicații electronice sau optoelectronice, unde nu sunt necesare capacitățile de înaltă performanță ale siliciului.
Optoelectronica este o tehnologie care lucrează cu utilizarea combinată a luminii și electronicii, cum ar fi celulele solare, iar pigmentul studiat este xylindein.

Posted: Jun 05, 2018

Fungi-produced pigment shows promise as semiconductor material

(Nanowerk News) Researchers at Oregon State University are looking at a highly durable organic pigment, used by humans in artwork for hundreds of years, as a promising possibility as a semiconductor material.
Findings suggest it could become a sustainable, low-cost, easily fabricated alternative to silicon in electronic or optoelectronic applications where the high-performance capabilities of silicon aren’t required.
Optoelectronics is technology working with the combined use of light and electronics, such as solar cells, and the pigment being studied is xylindein.
Chlorociboria Aeruginascens fungus on a tree log
Chlorociboria Aeruginascens fungus on a tree log. (Image: Oregon State University)
„Xylindein is pretty, but can it also be useful? How much can we squeeze out of it?” said Oregon State University physicist Oksana Ostroverkhova. „It functions as an electronic material but not a great one, but there’s optimism we can make it better.”
Xylindien is secreted by two wood-eating fungi in the Chlorociboria genus. Any wood that’s infected by the fungi is stained a blue-green color, and artisans have prized xylindein-affected wood for centuries.
The pigment is so stable that decorative products made half a millennium ago still exhibit its distinctive hue. It holds up against prolonged exposure to heat, ultraviolet light and electrical stress.
„If we can learn the secret for why those fungi-produced pigments are so stable, we could solve a problem that exists with organic electronics,” Ostroverkhova said. „Also, many organic electronic materials are too expensive to produce, so we’re looking to do something inexpensively in an ecologically friendly way that’s good for the economy.”
With current fabrication techniques, xylindein tends to form non-uniform films with a porous, irregular, „rocky” structure.
„There’s a lot of performance variation,” she said. „You can tinker with it in the lab, but you can’t really make a technologically relevant device out of it on a large scale. But we found a way to make it more easily processed and to get a decent film quality.”
Ostroverkhova and collaborators in OSU’s colleges of Science and Forestry blended xylindein with a transparent, non-conductive polymer, poly(methyl methacrylate), abbreviated to PMMA and sometimes known as acrylic glass. They drop-cast solutions both of pristine xylindein and a xlyindein-PMMA blend onto electrodes on a glass substrate for testing.
They found the non-conducting polymer greatly improved the film structure without a detrimental effect on xylindein’s electrical properties. And the blended films actually showed better photosensitivity.
„Exactly why that happened, and its potential value in solar cells, is something we’ll be investigating in future research,” Ostroverkhova said. „We’ll also look into replacing the polymer with a natural product – something sustainable made from cellulose. We could grow the pigment from the cellulose and be able to make a device that’s all ready to go.
„Xylindein will never beat silicon, but for many applications, it doesn’t need to beat silicon,” she said. „It could work well for depositing onto large, flexible substrates, like for making wearable electronics.”
This research, whose findings were recently published in MRS Advances („Fungi-Derived Pigments for Sustainable Organic (Opto)Electronics”), represents the first use of a fungus-produced material in a thin-film electrical device.
„And there are a lot more of the materials,” Ostroverkhova said. „This is just first one we’ve explored. It could be the beginning of a whole new class of organic electronic materials.”
Source: Oregon State University

Oamenii de știință dezvoltă materiale care ar putea regenera emailul dentar(Scientists develop material that could regenerate dental enamel)

Cercetatorii de la Universitatea Queen Mary din Londra au dezvoltat un nou mod de a dezvolta materiale mineralizate care ar putea regenera tesuturile tari, cum ar fi smaltul si osul dentar.Materialele ar putea fi utilizate pentru o mare varietate de complicații dentare, cum ar fi prevenirea și tratamentul cariilor dentare sau sensibilității la dinți – cunoscută și sub numele de hipersensibilitate la dentină.

Posted: Jun 01, 2018

Scientists develop material that could regenerate dental enamel

(Nanowerk News) Researchers at Queen Mary University of London have developed a new way to grow mineralised materials which could regenerate hard tissues such as dental enamel and bone.
Enamel, located on the outer part of our teeth, is the hardest tissue in the body and enables our teeth to function for a large part of our lifetime despite biting forces, exposure to acidic foods and drinks and extreme temperatures. This remarkable performance results from its highly organised structure.
However, unlike other tissues of the body, enamel cannot regenerate once it is lost, which can lead to pain and tooth loss. These problems affect more than 50 per cent of the world’s population and so finding ways to recreate enamel has long been a major need in dentistry.
The study, published in Nature Communications („Protein disorder–order interplay to guide the growth of hierarchical mineralized structures”), shows that this new approach can create materials with remarkable precision and order that look and behave like dental enamel.
Close-up of enamel-like material
Close-up of the enamel-like material. (Image: Alvaro Mata)
The materials could be used for a wide variety of dental complications such as the prevention and treatment of tooth decay or tooth sensitivity – also known as dentin hypersensitivity.
Dr Sherif Elsharkawy, a dentist and first author of the study from Queen Mary’s School of Engineering and Materials Science, said: „This is exciting because the simplicity and versatility of the mineralisation platform opens up opportunities to treat and regenerate dental tissues. For example, we could develop acid resistant bandages that can infiltrate, mineralise, and shield exposed dentinal tubules of human teeth for the treatment of dentin hypersensitivity.”
The mechanism that has been developed is based on a specific protein material that is able to trigger and guide the growth of apatite nanocrystals at multiple scales – similarly to how these crystals grow when dental enamel develops in our body. This structural organisation is critical for the outstanding physical properties exhibited by natural dental enamel.
Lead author Professor Alvaro Mata, from Queen Mary’s School of Engineering and Materials Science, said: „A major goal in materials science is to learn from nature to develop useful materials based on the precise control of molecular building-blocks. The key discovery has been the possibility to exploit disordered proteins to control and guide the process of mineralisation at multiple scales. Through this, we have developed a technique to easily grow synthetic materials that emulate such hierarchically organised architecture over large areas and with the capacity to tune their properties.”
Enabling control of the mineralisation process opens the possibility to create materials with properties that mimic different hard tissues beyond enamel such as bone and dentin. As such, the work has the potential to be used in a variety of applications in regenerative medicine. In addition, the study also provides insights into the role of protein disorder in human physiology and pathology.
Source: Queen Mary University of London

Puzzle cu graphene foto excitat rezolvat(Photoexcited graphene puzzle solved)

Folosirea grafenului ca material sensibil la lumină pentru detectoarele de lumină poate oferi îmbunătățiri semnificative în ceea ce privește materialele folosite în zilele noastre.
De exemplu, grafenul poate detecta lumina de aproape orice culoare și dă un răspuns electronic extrem de rapid, într-o singură milionime dintr-o milionă de secundă. Astfel, pentru a proiecta corect detectorii de lumină pe bază de grafen, este esențial să înțelegem procesele care au loc în interiorul grafenului după ce absoarbe lumina.

Posted: Jun 01, 2018

Photoexcited graphene puzzle solved

(Nanowerk News) Light detection and control lies at the heart of many modern device applications, such as smartphone cameras. Using graphene as a light-sensitive material for light detectors can offer significant improvements with respect to materials being used nowadays.
For example, graphene can detect light of almost any color, and it gives an extremely fast electronic response within one millionth of a millionth of a second. Thus, in order to properly design graphene-based light detectors it is crucial to understand the processes that take place inside the graphene after it absorbs light.
The Mainz-based researchers Dr. Hai Wang, Professor Dmitry Turchinovich, Professor Mathias Kläui, and Professor Mischa Bonn, in collaboration with scientists from various European labs, have now succeeded in understanding these processes. The project was led by Dr. Klaas-Jan Tielrooij from ICFO in Spain, who was recently elected visiting professor at the Materials Science in Mainz (MAINZ) Graduate School of Excellence.
ultrafast optical pump
Schematic representation of the ultrafast optical pump – terahertz probe experiment, where the optical pump induces electron heating and the terahertz pulse is sensitive to the conductivity of graphene directly after this heating process. (Image: Fabien Vialla)
Published recently in Science Advances („The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies”), their work gives a thorough explanation of why the graphene conductivity in some cases increases after light absorption while it decreases in others.
The researchers were able to show that this behavior correlates with the way in which the energy from the absorbed light flows to the graphene electrons: After light is absorbed by the graphene, the processes through which graphene electrons heat up happen extremely fast and with a very high efficiency.
For highly doped graphene with many free electrons present, ultrafast electron heating leads to carriers with elevated energy, so-called hot carriers. This, in turn, leads to a decrease in conductivity. Interestingly enough, for weakly doped graphene with less free electrons, electron heating leads to the creation of additional free electrons and, thus, an increase in conductivity. These additional carriers are the direct result of the gapless nature of graphene. In gapped materials, electron heating does not lead to additional free carriers.
This simple scenario of light-induced electron heating in graphene can explain many observed effects. Aside from describing the conductive properties of the material after light absorption, it can explain carrier multiplication, where under specific conditions one absorbed light particle, i.e., a photon, can indirectly generate more than one additional free electron and thus create an efficient photo response within a device.
The results of the paper and, in particular, understanding electron heating processes accurately, will definitely mean a great boost in the design and development of graphene-based light detection technology.
Source: Johannes Gutenberg University Mainz

Elon Musk spune că nanotehnologia este „BS” – iată cum schimbă deja lumea(Elon Musk says nanotechnology is ‘BS’ – here’s how it’s already changing the world)

Nu poți să spui nanotech fără să creezi grafen. A fost numit un material de minune datorită rezistenței sale, conductivității și elasticității. Făcată din matrice bidimensionale de atomi de carbon aranjate într-un model de tip fagure, foile de grafen se pot întinde doar cu câteva atomi, dar cu o suprafață totală mai aproape de dimensiunea unui poster.
Când este amestecat cu rășini și materiale plastice, materialul rezultat va fi incredibil de puternic și ușor. Materialele compozite pe bază de grafen sunt deja utilizate pentru o gamă largă de aplicații, inclusiv echipamente sportive și panouri de caroserie. Între timp, proprietățile electrice ale grafenului înseamnă că pot îmbunătăți și tehnologiile bateriei.

Posted: Jun 01, 2018

Elon Musk says nanotechnology is ‘BS’ – here’s how it’s already changing the world

(Nanowerk News) You might expect Elon Musk, the business magnate, engineer and serial entrepreneur would be a fan of all things techy. After all, his radical enterprises are built on pushing science to its limit. He’s behind a raft of visionary projects ranging from Tesla’s driverless electric cars and SpaceX’s self-landing reusable rockets to plans for 1,000kph “hyperloop” trains. But it appears there is a size limit to Musk’s technophilia. He recently tweeted that he thinks nanotechnology is “BS”.
So is nanotech just a buzzword used to jazz up some otherwise dull research? Or is it a real branch of scientific discovery that’s actually making a difference to the world?
Nano means small, really small. One nanometre is just one billionth of metre. At this scale we’re dealing with individual molecules and atoms (a carbon atom is about 0.3 nanometres across). So nanotech is about arranging matter that’s between one nanometre and 100 nanometres across in at least one dimension, to create usable medicines, electronics and materials.
The idea of deliberately doing science and engineering at this scale may well have started back in 1959, with a talk entitled There’s Plenty of Room at the Bottom by the great physicist Richard Feynman. But, in fact, people in ancient times used nanotechnology to create stunning works of art, without realising the scales at which they were manipulating matter.

Quantum dots
Today we’ve purposefully harnessed nanotechnology to do some incredible things. Take quantum dots. They may sound like the name of a Belgian indie band but, in fact, these real and incredibly versatile nanomaterials are being used in medical imaging, display technologies and photovoltaic solar cells.
A quantum dot is a particle of semiconducting material just a few nanometres in diameter. Due to their miniscule size, they have electronic properties that sit between what you would expect for a single molecule and a larger bulk material. One of the most useful outcomes of this is that the dots fluoresce (glow) with a colour that depends on the size of the particle. This means that by tweaking the size of the dot you can tune the colours they give off. And that property makes them an ideal candidate for use in your next flat screen TV.

Nanobiotechnology
Nature has a jump on us when it comes to nanotech. The protein molecules that replicate your DNA, digest your food and fight off infections are all nano-sized machines perfectly evolved to do a specific job in your bodies. This makes them ideal places to look for inspiration when trying to engineer something on the nanoscale.
A great example of this in action is a technique known as nanopore DNA sequencing. This technology involves proteins called porins that are normally used by bacteria to allow materials to enter and leave the cells. The porins are placed in a membrane to create channels or pores through it, and an electrical field is then applied. When DNA is forced through the pores the electrical current changes in response to the part of the DNA molecule (the base) that is in the pore.
By measuring the current as the molecule passes through the pore you can work out what the bases that comprise it are and sequence the DNA. This can be done at breakneck speed – up to 450 bases a second – using a tiny desktop device.

Graphene
You can’t mention nanotech without graphene cropping up. It’s been dubbed a wonder material due to its strength, conductivity and elasticity. Made up of two-dimensional arrays of carbon atoms arranged in a honeycomb pattern, graphene sheets can be just a few atoms thick but with a total area nearer the size of a poster.
When mixed with resins and plastics, the resulting material will be incredibly strong and lightweight. Graphene-based composite materials are already being used for a range of applications including sporting equipment and vehicle body panels. Meanwhile graphene’s electrical properties mean it can also enhance battery technologies.
Doesn’t that sound like something an electric car manufacturer might want to look into?
Source: By Mark Lorch, Professor of Science Communication and Chemistry, University of Hull