Category Archives: energy

Carbon nanotubes (CNTs) in 466 colours

Caption: A color map illustrates the inherent colors of 466 types of carbon nanotubes with unique (n,m) designations based their chiral angle and diameter. Credit: Image courtesy of Kauppinen Group/Aalto University

This is, so to speak, a new angle on carbon nanotubes (CNTs). It’s also the first time I’ve seen two universities place identical news releases on EurekAlert under their individual names.

From the Dec. 14, 2020 Rice University (US) news release or the Dec. 14, 2020 Aalto University (Finland) press release on EurekAlert,

Nanomaterials researchers in Finland, the United States and China have created a color atlas for 466 unique varieties of single-walled carbon nanotubes.

The nanotube color atlas is detailed in a study in Advanced Materials about a new method to predict the specific colors of thin films made by combining any of the 466 varieties. The research was conducted by researchers from Aalto University in Finland, Rice University and Peking University in China.

“Carbon, which we see as black, can appear transparent or take on any color of the rainbow,” said Aalto physicist Esko Kauppinen, the corresponding author of the study. “The sheet appears black if light is completely absorbed by carbon nanotubes in the sheet. If less than about half of the light is absorbed in the nanotubes, the sheet looks transparent. When the atomic structure of the nanotubes causes only certain colors of light, or wavelengths, to be absorbed, the wavelengths that are not absorbed are reflected as visible colors.”

Carbon nanotubes are long, hollow carbon molecules, similar in shape to a garden hose but with sides just one atom thick and diameters about 50,000 times smaller than a human hair. The outer walls of nanotubes are made of rolled graphene. And the wrapping angle of the graphene can vary, much like the angle of a roll of holiday gift wrap paper. If the gift wrap is rolled carefully, at zero angle, the ends of the paper will align with each side of the gift wrap tube. If the paper is wound carelessly, at an angle, the paper will overhang on one end of the tube.

The atomic structure and electronic behavior of each carbon nanotube is dictated by its wrapping angle, or chirality, and its diameter. The two traits are represented in a “(n,m)” numbering system that catalogs 466 varieties of nanotubes, each with a characteristic combination of chirality and diameter. Each (n,m) type of nanotube has a characteristic color.

Kauppinen’s research group has studied carbon nanotubes and nanotube thin films for years, and it previously succeeded in mastering the fabrication of colored nanotube thin films that appeared green, brown and silver-grey.

In the new study, Kauppinen’s team examined the relationship between the spectrum of absorbed light and the visual color of various thicknesses of dry nanotube films and developed a quantitative model that can unambiguously identify the coloration mechanism for nanotube films and predict the specific colors of films that combine tubes with different inherent colors and (n,m) designations.

Rice engineer and physicist Junichiro Kono, whose lab solved the mystery of colorful armchair nanotubes in 2012, provided films made solely of (6,5) nanotubes that were used to calibrate and verify the Aalto model. Researchers from Aalto and Peking universities used the model to calculate the absorption of the Rice film and its visual color. Experiments showed that the measured color of the film corresponded quite closely to the color forecast by the model.

The Aalto model shows that the thickness of a nanotube film, as well as the color of nanotubes it contains, affects the film’s absorption of light. Aalto’s atlas of 466 colors of nanotube films comes from combining different tubes. The research showed that the thinnest and most colorful tubes affect visible light more than those with larger diameters and faded colors.

“Esko’s group did an excellent job in theoretically explaining the colors, quantitatively, which really differentiates this work from previous studies on nanotube fluorescence and coloration,” Kono said.

Since 2013, Kono’s lab has pioneered a method for making highly ordered 2D nanotube films. Kono said he had hoped to supply Kauppinen’s team with highly ordered 2D crystalline films of nanotubes of a single chirality.

“That was the original idea, but unfortunately, we did not have appropriate single-chirality aligned films at that time,” Kono said. “In the future, our collaboration plans to extend this work to study polarization-dependent colors in highly ordered 2D crystalline films.”

The experimental method the Aalto researchers used to grow nanotubes for their films was the same as in their previous studies: Nanotubes grow from carbon monoxide gas and iron catalysts in a reactor that is heated to more than 850 degrees Celsius. The growth of nanotubes with different colors and (n,m) designations is regulated with the help of carbon dioxide that is added to the reactor.

“Since the previous study, we have pondered how we might explain the emergence of the colors of the nanotubes,” said Nan Wei, an assistant research professor at Peking University who previously worked as a postdoctoral researcher at Aalto. “Of the allotropes of carbon, graphite and charcoal are black, and pure diamonds are colorless to the human eye. However, now we noticed that single-walled carbon nanotubes can take on any color: for example, red, blue, green or brown.”

Kauppinen said colored thin films of nanotubes are pliable and ductile and could be useful in colored electronics structures and in solar cells.

“The color of a screen could be modified with the help of a tactile sensor in mobile phones, other touch screens or on top of window glass, for example,” he said.

Kauppinen said the research can also provide a foundation for new kinds of environmentally friendly dyes.

Here’s a link to and a citation for the paper,

Colors of Single‐Wall Carbon Nanotubes by Nan Wei, Ying Tian, Yongping Liao, Natsumi Komatsu, Weilu Gao, Alina Lyuleeva‐Husemann, Qiang Zhang, Aqeel Hussain, Er‐Xiong Ding, Fengrui Yao, Janne Halme. Kaihui Liu, Junichiro Kono, Hua Jiang, Esko I. Kauppinen. Advanced Materials DOI: https://doi.org/10.1002/adma.202006395 First published: 14 December 2020

Thi8s paper is open access.

Spinach could help power fuel cells.

By Source (WP:NFCC#4), Fair use, https://en.wikipedia.org/w/index.php?curid=65303730

I was surprised to see a reference to the cartoon character, Popeye, in the headline (although it’s not carried forward into the text) for this October 5, 2020 news item on ScienceDaily about research into making fuel cells more efficient,

Spinach: Good for Popeye and the planet

“Eat your spinach,” is a common refrain from many people’s childhoods. Spinach, the hearty, green vegetable chock full of nutrients, doesn’t just provide energy in humans. It also has potential to help power fuel cells, according to a new paper by researchers in AU’s Department of Chemistry. Spinach, when converted from its leafy, edible form into carbon nanosheets, acts as a catalyst for an oxygen reduction reaction in fuel cells and metal-air batteries.

An October 5, 2020 American University news release (also on EurekAlert) by Rebecca Basu, which originated the news item, provides more detail about the research,

An oxygen reduction reaction is one of two reactions in fuel cells and metal-air batteries and is usually the slower one that limits the energy output of these devices. Researchers have long known that certain carbon materials can catalyze the reaction. But those carbon-based catalysts don’t always perform as good or better than the traditional platinum-based catalysts. The AU researchers wanted to find an inexpensive and less toxic preparation method for an efficient catalyst by using readily available natural resources. They tackled this challenge by using spinach.

“This work suggests that sustainable catalysts can be made for an oxygen reduction reaction from natural resources,” said Prof. Shouzhong Zou, chemistry professor at AU and the paper’s lead author. “The method we tested can produce highly active, carbon-based catalysts from spinach, which is a renewable biomass. In fact, we believe it outperforms commercial platinum catalysts in both activity and stability. The catalysts are potentially applicable in hydrogen fuel cells and metal-air batteries.” Zou’s former post-doctoral students Xiaojun Liu and Wenyue Li and undergraduate student Casey Culhane are the paper’s co-authors.

Catalysts accelerate an oxygen reduction reaction to produce sufficient current and create energy. Among the practical applications for the research are fuel cells and metal-air batteries, which power electric vehicles and types of military gear. Researchers are making progress in the lab and in prototypes with catalysts derived from plants or plant products such as cattail grass or rice. Zou’s work is the first demonstration using spinach as a material for preparing oxygen reduction reaction-catalysts. Spinach is a good candidate for this work because it survives in low temperatures, is abundant and easy to grow, and is rich in iron and nitrogen that are essential for this type of catalyst.

Zou and his students created and tested the catalysts, which are spinach-derived carbon nanosheets. Carbon nanosheets are like a piece of paper with the thickness on a nanometer scale, a thousand times thinner than a piece of human hair. To create the nanosheets, the researchers put the spinach through a multi-step process that included both low- and high-tech methods, including washing, juicing and freeze-drying the spinach, manually grinding it into a fine powder with a mortar and pestle, and “doping” the resulting carbon nanosheet with extra nitrogen to improve its performance. The measurements showed that the spinach-derived catalysts performed better than platinum-based catalysts that can be expensive and lose their potency over time.

The next step for the researchers is to put the catalysts from the lab simulation into prototype devices, such as hydrogen fuel cells, to see how they perform and to develop catalysts from other plants. Zou would like to also improve sustainability by reducing the energy consumption needed for the process.

Here’s a link to and a citation for the paper,

Spinach-Derived Porous Carbon Nanosheets as High-Performance Catalysts for Oxygen Reduction Reaction by Xiaojun Liu, Casey Culhane, Wenyue Li, and Shouzhong Zou. ACS Omega 2020, 5, 38, 24367–24378 DOI: https://doi.org/10.1021/acsomega.0c02673 Publication Date:September 15, 2020 Copyright © 2020 American Chemical Society

This paper appears to be open access.

Brain cell-like nanodevices

Given R. Stanley Williams’s presence on the author list, it’s a bit surprising that there’s no mention of memristors. If I read the signs rightly the interest is shifting, in some cases, from the memristor to a more comprehensive grouping of circuit elements referred to as ‘neuristors’ or, more likely, ‘nanocirucuit elements’ in the effort to achieve brainlike (neuromorphic) computing (engineering). (Williams was the leader of the HP Labs team that offered proof and more of the memristor’s existence, which I mentioned here in an April 5, 2010 posting. There are many, many postings on this topic here; try ‘memristors’ or ‘brainlike computing’ for your search terms.)

A September 24, 2020 news item on ScienceDaily announces a recent development in the field of neuromorphic engineering,

In the September [2020] issue of the journal Nature, scientists from Texas A&M University, Hewlett Packard Labs and Stanford University have described a new nanodevice that acts almost identically to a brain cell. Furthermore, they have shown that these synthetic brain cells can be joined together to form intricate networks that can then solve problems in a brain-like manner.

“This is the first study where we have been able to emulate a neuron with just a single nanoscale device, which would otherwise need hundreds of transistors,” said Dr. R. Stanley Williams, senior author on the study and professor in the Department of Electrical and Computer Engineering. “We have also been able to successfully use networks of our artificial neurons to solve toy versions of a real-world problem that is computationally intense even for the most sophisticated digital technologies.”

In particular, the researchers have demonstrated proof of concept that their brain-inspired system can identify possible mutations in a virus, which is highly relevant for ensuring the efficacy of vaccines and medications for strains exhibiting genetic diversity.

A September 24, 2020 Texas A&M University news release (also on EurekAlert) by Vandana Suresh, which originated the news item, provides some context for the research,

Over the past decades, digital technologies have become smaller and faster largely because of the advancements in transistor technology. However, these critical circuit components are fast approaching their limit of how small they can be built, initiating a global effort to find a new type of technology that can supplement, if not replace, transistors.

In addition to this “scaling-down” problem, transistor-based digital technologies have other well-known challenges. For example, they struggle at finding optimal solutions when presented with large sets of data.

“Let’s take a familiar example of finding the shortest route from your office to your home. If you have to make a single stop, it’s a fairly easy problem to solve. But if for some reason you need to make 15 stops in between, you have 43 billion routes to choose from,” said Dr. Suhas Kumar, lead author on the study and researcher at Hewlett Packard Labs. “This is now an optimization problem, and current computers are rather inept at solving it.”

Kumar added that another arduous task for digital machines is pattern recognition, such as identifying a face as the same regardless of viewpoint or recognizing a familiar voice buried within a din of sounds.

But tasks that can send digital machines into a computational tizzy are ones at which the brain excels. In fact, brains are not just quick at recognition and optimization problems, but they also consume far less energy than digital systems. Hence, by mimicking how the brain solves these types of tasks, Williams said brain-inspired or neuromorphic systems could potentially overcome some of the computational hurdles faced by current digital technologies.

To build the fundamental building block of the brain or a neuron, the researchers assembled a synthetic nanoscale device consisting of layers of different inorganic materials, each with a unique function. However, they said the real magic happens in the thin layer made of the compound niobium dioxide.

When a small voltage is applied to this region, its temperature begins to increase. But when the temperature reaches a critical value, niobium dioxide undergoes a quick change in personality, turning from an insulator to a conductor. But as it begins to conduct electric currents, its temperature drops and niobium dioxide switches back to being an insulator.

These back-and-forth transitions enable the synthetic devices to generate a pulse of electrical current that closely resembles the profile of electrical spikes, or action potentials, produced by biological neurons. Further, by changing the voltage across their synthetic neurons, the researchers reproduced a rich range of neuronal behaviors observed in the brain, such as sustained, burst and chaotic firing of electrical spikes.

“Capturing the dynamical behavior of neurons is a key goal for brain-inspired computers,” said Kumar. “Altogether, we were able to recreate around 15 types of neuronal firing profiles, all using a single electrical component and at much lower energies compared to transistor-based circuits.”

To evaluate if their synthetic neurons [neuristor?] can solve real-world problems, the researchers first wired 24 such nanoscale devices together in a network inspired by the connections between the brain’s cortex and thalamus, a well-known neural pathway involved in pattern recognition. Next, they used this system to solve a toy version of the viral quasispecies reconstruction problem, where mutant variations of a virus are identified without a reference genome.

By means of data inputs, the researchers introduced the network to short gene fragments. Then, by programming the strength of connections between the artificial neurons within the network, they established basic rules about joining these genetic fragments. The jigsaw puzzle-like task for the network was to list mutations in the virus’ genome based on these short genetic segments.

The researchers found that within a few microseconds, their network of artificial neurons settled down in a state that was indicative of the genome for a mutant strain.

Williams and Kumar noted this result is proof of principle that their neuromorphic systems can quickly perform tasks in an energy-efficient way.

The researchers said the next steps in their research will be to expand the repertoire of the problems that their brain-like networks can solve by incorporating other firing patterns and some hallmark properties of the human brain like learning and memory. They also plan to address hardware challenges for implementing their technology on a commercial scale.

“Calculating the national debt or solving some large-scale simulation is not the type of task the human brain is good at and that’s why we have digital computers. Alternatively, we can leverage our knowledge of neuronal connections for solving problems that the brain is exceptionally good at,” said Williams. “We have demonstrated that depending on the type of problem, there are different and more efficient ways of doing computations other than the conventional methods using digital computers with transistors.”

If you look at the news release on EurekAlert, you’ll see this informative image is titled: NeuristerSchematic [sic],

Caption: Networks of artificial neurons connected together can solve toy versions the viral quasispecies reconstruction problem. Credit: Texas A&M University College of Engineering

(On the university website, the image is credited to Rachel Barton.) You can see one of the first mentions of a ‘neuristor’ here in an August 24, 2017 posting.

Here’s a link to and a citation for the paper,

Third-order nanocircuit elements for neuromorphic engineering by Suhas Kumar, R. Stanley Williams & Ziwen Wang. Nature volume 585, pages518–523(2020) DOI: https://doi.org/10.1038/s41586-020-2735-5 Published: 23 September 2020 Issue Date: 24 September 2020

This paper is behind a paywall.

Glass-like wood windows protect against UV rays and insulate heat

Engineers at the University of Maryland designed a transparent ceiling made of wood that highlights the natural woodgrain pattern. Credit: A. James Clark School of Engineering, University of Maryland [downloaded from https://phys.org/news/2020-08-glass-like-wood-insulates-tough-blocks.html]

An August 7, 2020 news item by Martha Hell on phys.org announces the latest research (links to previous posts about this research at the end of this post) on ‘transparent’ wood from the University of Maryland,

Need light but want privacy? A new type of wood that’s transparent, tough, and beautiful could be the solution. This nature-inspired building material allows light to come through (at about 80%) to fill the room but the material itself is naturally hazy (93%), preventing others from seeing inside.

An August 16, 2020 University of Maryland news release (also on EurekAlert) describes the work in more detail,

Engineers at the A. James Clark School of Engineering at the University of Maryland (UMD) demonstrate in a new study that windows made of transparent wood could provide more even and consistent natural lighting and better energy efficiency than glass

In a paper just published [July 31, 20202] in the peer-reviewed journal Advanced Energy Materials [this seems to be an incorrectly cited journal; I believe it should be Nature Communications as indicated in the phys.org news item], the team, headed by Liangbing Hu of UMD’s Department of Materials Science and Engineering and the Energy Research Center lay out research showing that their transparent wood provides better thermal insulation and lets in nearly as much light as glass, while eliminating glare and providing uniform and consistent indoor lighting. The findings advance earlier published work on their development of transparent wood.

The transparent wood lets through just a little bit less light than glass, but a lot less heat, said Tian Li, the lead author of the new study. “It is very transparent, but still allows for a little bit of privacy because it is not completely see-through. We also learned that the channels in the wood transmit light with wavelengths around the range of the wavelengths of visible light, but that it blocks the wavelengths that carry mostly heat,” said Li.

The team’s findings were derived, in part, from tests on tiny model house with a transparent wood panel in the ceiling that the team built. The tests showed that the light was more evenly distributed around a space with a transparent wood roof than a glass roof.

The channels in the wood direct visible light straight through the material, but the cell structure that still remains bounces the light around just a little bit, a property called haze. This means the light does not shine directly into your eyes, making it more comfortable to look at. The team photographed the transparent wood’s cell structure in the University of Maryland’s Advanced Imaging and Microscopy (AIM) Lab.

Transparent wood still has all the cell structures that comprised the original piece of wood. The wood is cut against the grain, so that the channels that drew water and nutrients up from the roots lie along the shortest dimension of the window. The new transparent wood uses theses natural channels in wood to guide the sunlight through the wood.

As the sun passes over a house with glass windows, the angle at which light shines through the glass changes as the sun moves. With windows or panels made of transparent wood instead of glass, as the sun moves across the sky, the channels in the wood direct the sunlight in the same way every time.

“This means your cat would not have to get up out of its nice patch of sunlight every few minutes and move over,” Li said. “The sunlight would stay in the same place. Also, the room would be more equally lighted at all times.”

Working with transparent wood is similar to working with natural wood, the researchers said. However, their transparent wood is waterproof due to its polymer component. It also is much less breakable than glass because the cell structure inside resists shattering.

The research team has recently patented their process for making transparent wood. The process starts with bleaching from the wood all of the lignin, which is a component in the wood that makes it both brown and strong. The wood is then soaked in epoxy, which adds strength back in and also makes the wood clearer. The team has used tiny squares of linden wood about 2 cm x 2 cm, but the wood can be any size, the researchers said.

Here’s a link to and a citation for the July 31, 2020 paper,

Scalable aesthetic transparent wood for energy efficient buildings by Ruiyu Mi, Chaoji Chen, Tobias Keplinger, Yong Pei, Shuaiming He, Dapeng Liu, Jianguo Li, Jiaqi Dai, Emily Hitz, Bao Yang, Ingo Burgert & Liangbing Hu. Nature Communications volume 11, Article number: 3836 (2020) DOI: https://doi.org/10.1038/s41467-020-17513-w Published 31 July 2020

This paper is open access.

There were two previous posts about this work at the University of Maryland,

University of Maryland looks into transparent wood May 11, 2016 posting

Transparent wood more efficient than glass in windows? Sept, 8, 2016 posting

I also have this posting, which is also from 2016 but features work in Sweden,

Transparent wood instead of glass for window panes? April 1, 2016 posting

I seem to have stumbled across a number of transparent wood stories in 2016. Hmm I think I need to spend more time searching previous titles for my postings so I didn’t end up with too many that sound similar.

Spray-on coatings for cheaper smart windows

An August 6, 2020 RMIT University (Australia) press release (also on EurekAlert but published August 5, 2020) by Gosia Kaszubska announces a coating that makes windows ‘smart’,

A simple method for making clear coatings that can block heat and conduct electricity could radically cut the cost of energy-saving smart windows and heat-repelling glass [electrochromic windows?].

The spray-on coatings developed by researchers at RMIT are ultra-thin, cost-effective and rival the performance of current industry standards for transparent electrodes.

Combining the best properties of glass and metals in a single component, a transparent electrode is a highly conductive clear coating that allows visible light through.

The coatings – key components of technologies including smart windows, touchscreen displays, LED lighting and solar panels – are currently made through time-consuming processes that rely on expensive raw materials.

The new spray-on method is fast, scalable and based on cheaper materials that are readily available.

The method could simplify the fabrication of smart windows, which can be both energy-saving and dimmable, as well as low-emissivity glass, where a conventional glass panel is coated with a special layer to minimise ultraviolet and infrared light.

Lead investigator Dr Enrico Della Gaspera said the pioneering approach could be used to substantially bring down the cost of energy-saving windows and potentially make them a standard part of new builds and retrofits.

“Smart windows and low-E glass can help regulate temperatures inside a building, delivering major environmental benefits and financial savings, but they remain expensive and challenging to manufacture,” said Della Gaspera, a senior lecturer and Australian Research Council DECRA Fellow at RMIT.

“We’re keen to collaborate with industry to further develop this innovative type of coating.

“The ultimate aim is to make smart windows much more widely accessible, cutting energy costs and reducing the carbon footprint of new and retrofitted buildings.”

The new method can also be precisely optimised to produce coatings tailored to the transparency and conductivity requirements of the many different applications of transparent electrodes.

Global demand for smart glazing

The global market size for smart glass and smart windows is expected to reach $6.9 billion by 2022, while the global low-E glass market is set to reach an estimated $39.4 billion by 2024.

New York’s Empire State Building reported energy savings of $US2.4 million and cut carbon emissions by 4,000 metric tonnes after installing smart glass windows.

Eureka Tower in Melbourne features a dramatic use of smart glass in its “Edge” tourist attraction, a glass cube that projects 3m out of the building and suspends visitors 300m over the city. The glass is opaque as the cube moves out over the edge of the building and becomes clear once fully extended.

First author Jaewon Kim, a PhD researcher in Applied Chemistry at RMIT,  said the next steps in the research were developing precursors that will decompose at lower temperatures, allowing the coatings to be deposited on plastics and used in flexible electronics, as well as producing larger prototypes by scaling up the deposition.

“The spray coater we use can be automatically controlled and programmed, so fabricating bigger proof-of-concept panels will be relatively simple,” he said.

Caption: The ultra-thin clear coatings are made with a new spray-on method that is fast, cost-effective and scalable. Credit: RMIT University

That is an impressive level of transparency. As per usual, here’s a link to and a citation for the paper (should you wish to explore further),

Ultrasonic Spray Pyrolysis of Antimony‐Doped Tin Oxide Transparent Conductive Coatings by Jaewon Kim, Billy J. Murdoch, James G. Partridge, Kaijian Xing, Dong‐Chen Qi, Josh Lipton‐Duffin, Christopher F. McConville, Joel van Embden, Enrico Della Gaspera. Advanced Materials Interfaces DOI: https://doi.org/10.1002/admi.202000655 First published: 05 August 2020

This paper is behind a paywall.

Converting carbon dioxide into fuel with blinking nanocrystals

A July 16, 2020 news item on Nanowerk announces some work from Rutgers University (New Jersey, US) where carbon dioxide could one day be converted into fuel or perhaps be used in quantum computers,

Imagine tiny crystals that “blink” like fireflies and can convert carbon dioxide, a key cause of climate change, into fuels.

A Rutgers-led team has created ultra-small titanium dioxide crystals that exhibit unusual “blinking” behavior and may help to produce methane and other fuels, according to a study in the journal Angewandte Chemie (“A Blinking Mesoporous TiO2-x Composed of Nanosized Anatase with Unusually Long-Lived Trapped Charge Carriers”).

The crystals, also known as nanoparticles, stay charged for a long time and could benefit efforts to develop quantum computers.

I don’t think I have the imagination necessary for this image, which illustrates the work according to the researchers,

The arrows point to titanium dioxide nanocrystals lighting up and blinking (left) and then fading (right). Images: Tewodros Asefa and Eliska Mikmekova

A July 16, 2020 Rutgers University news release (also on EurekAlert), which originated the news item, delves further into the topic,

“Our findings are quite important and intriguing in a number of ways, and more research is needed to understand how these exotic crystals work and to fulfill their potential,” said senior author Tewodros (Teddy) Asefa, a professor in the Department of Chemistry and Chemical Biology in the School of Arts and Sciences at Rutgers University-New Brunswick [in New Jersey]. He’s also a professor in the Department of Chemical and Biochemical Engineering in the School of Engineering.

More than 10 million metric tons of titanium dioxide are produced annually, making it one of the most widely used materials, the study notes. It is used in sunscreens, paints, cosmetics and varnishes, for example. It’s also used in the paper and pulp, plastic, fiber, rubber, food, glass and ceramic industries.

The team of scientists and engineers discovered a new way to make extremely small titanium dioxide crystals. While it’s still unclear why the engineered crystals blink and research is ongoing, the “blinking” is believed to arise from single electrons trapped on titanium dioxide nanoparticles. At room temperature, electrons – surprisingly – stay trapped on nanoparticles for tens of seconds before escaping and then become trapped again and again in a continuous cycle.

The crystals, which blink when exposed to a beam of electrons, could be useful for environmental cleanups, sensors, electronic devices and solar cells, and the research team will further explore their capabilities.

Here’s a link to and a citation for the paper,

A Blinking Mesoporous TiO2−x Composed of Nanosized Anatase with Unusually Long‐Lived Trapped Charge Carriers by Dr. Tao Zhang, Dr. Jingxiang Low, Prof. Jiaguo Yu, Dr. Alexei M. Tyryshkin, Dr. Eliška Mikmeková, Prof. Tewodros Asefa. Angewandte Chemie DOI: https://doi.org/10.1002/anie.202005143 First published [online]: 22 May 2020

This paper is behind a paywall.

Keep your building cool with super paint

As temperatures rise and the Arctic melts, scientists are searching for ways to keep us and our buildings cool without adding unduly to our current problems. A July 8, 2020 University of California at Los Angeles news release (also on EurekAlert) announces a new paint,

A research team led by UCLA materials scientists has demonstrated ways to make super white paint that reflects as much as 98% of incoming heat from the sun. The advance shows practical pathways for designing paints that, if used on rooftops and other parts of a building, could significantly reduce cooling costs, beyond what standard white ‘cool-roof’ paints can achieve.

The findings, published online in Joule, are a major and practical step towards keeping buildings cooler by passive daytime radiative cooling — a spontaneous process in which a surface reflects sunlight and radiates heat into space, cooling down to potentially sub-ambient temperatures. This can lower indoor temperatures and help cut down on air conditioner use and associated carbon dioxide emissions.

“When you wear a white T-shirt on a hot sunny day, you feel cooler than if you wore one that’s darker in color — that’s because the white shirt reflects more sunlight and it’s the same concept for buildings,” said Aaswath Raman, an assistant professor of materials science and engineering at UCLA Samueli School of Engineering, and the principal investigator on the study. “A roof painted white will be cooler inside than one in a darker shade. But those paints also do something else: they reject heat at infrared wavelengths, which we humans cannot see with our eyes. This could allow buildings to cool down even more by radiative cooling.”

The best performing white paints currently available typically reflect around 85% of incoming solar radiation. The remainder is absorbed by the chemical makeup of the paint. The researchers showed that simple modifications in a paint’s ingredients could offer a significant jump, reflecting as much as 98% of incoming radiation.

Current white paints with high solar reflectance use titanium oxide. While the compound is very reflective of most visible and near-infrared light, it also absorbs ultraviolet and violet light. The compound’s UV absorption qualities make it useful in sunscreen lotions, but they also lead to heating under sunlight – which gets in the way of keeping a building as cool as possible.

The researchers examined replacing titanium oxide with inexpensive and readily available ingredients such as barite, which is an artist’s pigment, and pow[d]ered polytetrafluoroethylene, better known as Teflon. These ingredients help paints reflect UV light. The team also made further refinements to the paint’s formula, including reducing the concentration of polymer binders, which also absorb heat.

“The potential cooling benefits this can yield may be realized in the near future because the modifications we propose are within the capabilities of the paint and coatings industry,” said UCLA postdoctoral scholar Jyotirmoy Mandal, a Schmidt Science Fellow working in Raman’s research group and the co-corresponding author on the research.

Beyond the advance, the authors suggested several long-term implications for further study, including mapping where such paints could make a difference, studying the effect of pollution on radiative cooling technologies, and on a global scale, if they could make a dent on the earth’s own ability to reflect heat from the sun.

The researchers also noted that many municipalities and governments, including the state of California and New York City, have started to encourage cool-roof technologies for new buildings.

“We hope that the work will spur future initiatives in super-white coatings for not only energy savings in buildings, but also mitigating the heat island effects of cities, and perhaps even showing a practical way that, if applied on a massive, global scale could affect climate change,” said Mandal, who has studied cooling paint technologies for several years. “This would require a collaboration among experts in diverse fields like optics, materials science and meteorology, and experts from the industry and policy sectors.”

Here’s a link (also in the news release) to and a citation for the paper,

Paints as a Scalable and Effective Radiative Cooling Technology for Buildings by Jyotirmoy Mandal, Yuan Yang, Nanfang Yu, Aaswath P. Raman. Joule DOI: https://doi.org/10.1016/j.joule.2020.04.010 Published: May 29, 2020

This paper is behind a paywall.

New capacitor for better wearable electronics?

Supercapacitors are a predictable source of scientific interest and excitement. The latest entry in the ‘supercapacitor stakes’ is from a Russian/Finnish/US team according to a June 11, 2020 Skoltech (Skolkovo Institute of Science and Technology) press release (also on EurekAlert),

Researchers from Skoltech [Russia], Aalto University [Finland] and Massachusetts Institute of Technology [MIT; US] have designed a high-performance, low-cost, environmentally friendly, and stretchable supercapacitor that can potentially be used in wearable electronics. The paper was published in the Journal of Energy Storage.

Supercapacitors, with their high power density, fast charge-discharge rates, long cycle life, and cost-effectiveness, are a promising power source for everything from mobile and wearable electronics to electric vehicles. However, combining high energy density, safety, and eco-friendliness in one supercapacitor suitable for small devices has been rather challenging.

“Usually, organic solvents are used to increase the energy density. These are hazardous, not environmentally friendly, and they reduce the power density compared to aqueous electrolytes with higher conductivity,” says Professor Tanja Kallio from Aalto University, a co-author of the paper.

The researchers proposed a new design for a “green” and simple-to-fabricate supercapacitor. It consists of a solid-state material based on nitrogen-doped graphene flake electrodes distributed in the NaCl-containing hydrogel electrolyte. This structure is sandwiched between two single-walled carbon nanotube film current collectors, which provides stretchability. Hydrogel in the supercapacitor design enables compact packing and high energy density and allows them to use the environmentally friendly electrolyte.

The scientists managed to improve the volumetric capacitive performance, high energy density and power density for the prototype over analogous supercapacitors described in previous research. “We fabricated a prototype with unchanged performance under the 50% strain after a thousand stretching cycles. To ensure lower cost and better environmental performance, we used a NaCl-based electrolyte. Still the fabrication cost can be lowered down by implementation of 3D printing or other advanced fabrication techniques,” concluded Skoltech professor Albert Nasibulin.

Here’s a link to and a citation for the paper,

Superior environmentally friendly stretchable supercapacitor based on nitrogen-doped graphene/hydrogel and single-walled carbon nanotubes by Evgeniia Gilshtein, Cristina Flox, Farhan S.M. Ali, Bahareh Mehrabimatin, Fedor S.Fedorov, Shaoting Lin, Xuanhe Zhao, Albert G. Nasibulin, Tanja Kallio. Journal of Energy Storage Volume 30, August 2020, 101505 DOI: https://doi.org/10.1016/j.est.2020.101505

This paper is behind a paywall.

I’m trying to remember if I’ve ever before seen a material that combines graphene and single-walled carbon nanotubes (SWCNTs). Anyway, here’s an image the researchers are using illustrate their work,

Caption: This is an outline of the new supercapacitor. Credit: Pavel Odinev / Skoltech

Energy-efficient artificial synapse

This is the second neuromorphic computing chip story from MIT this summer in what has turned out to be a bumper crop of research announcements in this field. The first MIT synapse story was featured in a June 16, 2020 posting. Now, there’s a second and completely different team announcing results for their artificial brain synapse work in a June 19, 2020 news item on Nanowerk (Note: A link has been removed),

Teams around the world are building ever more sophisticated artificial intelligence systems of a type called neural networks, designed in some ways to mimic the wiring of the brain, for carrying out tasks such as computer vision and natural language processing.

Using state-of-the-art semiconductor circuits to simulate neural networks requires large amounts of memory and high power consumption. Now, an MIT [Massachusetts Institute of Technology] team has made strides toward an alternative system, which uses physical, analog devices that can much more efficiently mimic brain processes.

The findings are described in the journal Nature Communications (“Protonic solid-state electrochemical synapse for physical neural networks”), in a paper by MIT professors Bilge Yildiz, Ju Li, and Jesús del Alamo, and nine others at MIT and Brookhaven National Laboratory. The first author of the paper is Xiahui Yao, a former MIT postdoc now working on energy storage at GRU Energy Lab.

That description of the work is one pretty much every team working on developing memristive (neuromorphic) chips could use.

On other fronts, the team has produced a very attractive illustration accompanying this research (aside: Is it my imagination or has there been a serious investment in the colour pink and other pastels for science illustrations?),

A new system developed at MIT and Brookhaven National Lab could provide a faster, more reliable and much more energy efficient approach to physical neural networks, by using analog ionic-electronic devices to mimic synapses.. Courtesy of the researchers

A June 19, 2020 MIT news release, which originated the news item, provides more insight into this specific piece of research (hint: it’s about energy use and repeatability),

Neural networks attempt to simulate the way learning takes place in the brain, which is based on the gradual strengthening or weakening of the connections between neurons, known as synapses. The core component of this physical neural network is the resistive switch, whose electronic conductance can be controlled electrically. This control, or modulation, emulates the strengthening and weakening of synapses in the brain.

In neural networks using conventional silicon microchip technology, the simulation of these synapses is a very energy-intensive process. To improve efficiency and enable more ambitious neural network goals, researchers in recent years have been exploring a number of physical devices that could more directly mimic the way synapses gradually strengthen and weaken during learning and forgetting.

Most candidate analog resistive devices so far for such simulated synapses have either been very inefficient, in terms of energy use, or performed inconsistently from one device to another or one cycle to the next. The new system, the researchers say, overcomes both of these challenges. “We’re addressing not only the energy challenge, but also the repeatability-related challenge that is pervasive in some of the existing concepts out there,” says Yildiz, who is a professor of nuclear science and engineering and of materials science and engineering.

“I think the bottleneck today for building [neural network] applications is energy efficiency. It just takes too much energy to train these systems, particularly for applications on the edge, like autonomous cars,” says del Alamo, who is the Donner Professor in the Department of Electrical Engineering and Computer Science. Many such demanding applications are simply not feasible with today’s technology, he adds.

The resistive switch in this work is an electrochemical device, which is made of tungsten trioxide (WO3) and works in a way similar to the charging and discharging of batteries. Ions, in this case protons, can migrate into or out of the crystalline lattice of the material,  explains Yildiz, depending on the polarity and strength of an applied voltage. These changes remain in place until altered by a reverse applied voltage — just as the strengthening or weakening of synapses does.

The mechanism is similar to the doping of semiconductors,” says Li, who is also a professor of nuclear science and engineering and of materials science and engineering. In that process, the conductivity of silicon can be changed by many orders of magnitude by introducing foreign ions into the silicon lattice. “Traditionally those ions were implanted at the factory,” he says, but with the new device, the ions are pumped in and out of the lattice in a dynamic, ongoing process. The researchers can control how much of the “dopant” ions go in or out by controlling the voltage, and “we’ve demonstrated a very good repeatability and energy efficiency,” he says.

Yildiz adds that this process is “very similar to how the synapses of the biological brain work. There, we’re not working with protons, but with other ions such as calcium, potassium, magnesium, etc., and by moving those ions you actually change the resistance of the synapses, and that is an element of learning.” The process taking place in the tungsten trioxide in their device is similar to the resistance modulation taking place in biological synapses, she says.

“What we have demonstrated here,” Yildiz says, “even though it’s not an optimized device, gets to the order of energy consumption per unit area per unit change in conductance that’s close to that in the brain.” Trying to accomplish the same task with conventional CMOS type semiconductors would take a million times more energy, she says.

The materials used in the demonstration of the new device were chosen for their compatibility with present semiconductor manufacturing systems, according to Li. But they include a polymer material that limits the device’s tolerance for heat, so the team is still searching for other variations of the device’s proton-conducting membrane and better ways of encapsulating its hydrogen source for long-term operations.

“There’s a lot of fundamental research to be done at the materials level for this device,” Yildiz says. Ongoing research will include “work on how to integrate these devices with existing CMOS transistors” adds del Alamo. “All that takes time,” he says, “and it presents tremendous opportunities for innovation, great opportunities for our students to launch their careers.”

Coincidentally or not a University of Massachusetts at Amherst team announced memristor voltage use comparable to human brain voltage use (see my June 15, 2020 posting), plus, there’s a team at Stanford University touting their low-energy biohybrid synapse in a XXX posting. (June 2020 has been a particularly busy month here for ‘artificial brain’ or ‘memristor’ stories.)

Getting back to this latest MIT research, here’s a link to and a citation for the paper,

Protonic solid-state electrochemical synapse for physical neural networks by Xiahui Yao, Konstantin Klyukin, Wenjie Lu, Murat Onen, Seungchan Ryu, Dongha Kim, Nicolas Emond, Iradwikanari Waluyo, Adrian Hunt, Jesús A. del Alamo, Ju Li & Bilge Yildiz. Nature Communications volume 11, Article number: 3134 (2020) DOI: https://doi.org/10.1038/s41467-020-16866-6 Published: 19 June 2020

This paper is open access.

Nanocellulose films made with liquid-phase fabrication method

I always appreciate a reference to Star Trek and three-dimensional chess was one of my favourite concepts. You’ll find that and more in a May 19, 2020 news item on Nanowerk,

Researchers at The Institute of Scientific and Industrial Research at Osaka University [Japan] introduced a new liquid-phase fabrication method for producing nanocellulose films with multiple axes of alignment. Using 3D-printing methods for increased control, this work may lead to cheaper and more environmentally friendly optical and thermal devices.

Ever since appearing on the original Star Trek TV show in the 1960s, the game of “three-dimensional chess” has been used as a metaphor for sophisticated thinking. Now, researchers at Osaka University can say that they have added their own version, with potential applications in advanced optics and inexpensive smartphone displays.

It’s not exactly three-dimensional chess but this nanocellulose film was produced by 3D printing methods,

Caption: Developed multiaxis nanocellulose-oriented film. Credit: Osaka University

A May 20, 2020 Osaka University press release (also on EurekAlert but dated May 19, 2020), which originated the news item, provides more detail,

Many existing optical devices, including liquid-crystal displays (LCDs) found in older flat-screen televisions, rely on long needle-shaped molecules aligned in the same direction. However, getting fibers to line up in multiple directions on the same device is much more difficult. Having a method that can reliably and cheaply produce optical fibers would accelerate the manufacture of low-cost displays or even “paper electronics”–computers that could be printed from biodegradable materials on demand.

Cellulose, the primary component of cotton and wood, is an abundant renewable resource made of long molecules. Nanocelluloses are nanofibers made of uniaxially aligned cellulose molecular chains that have different optical and heat conduction properties along one direction compared to the another.

In newly published research from the Institute of Scientific and Industrial Research at Osaka University, nanocellulose was harvested from sea pineapples, a kind of sea squirt. They then used liquid-phase 3D-pattering, which combined the wet spinning of nanofibers with the precision of 3D-printing. A custom-made triaxial robot dispensed a nanocellulose aqueous suspension into an acetone coagulation bath.

“We developed this liquid-phase three-dimensional patterning technique to allow for nanocellulose alignment along any preferred axis,” says first author Kojiro Uetani. The direction of the patterns could be programmed so that it formed an alternating checkerboard pattern of vertically- and horizontally-aligned fibers.

To demonstrate the method, a film was sandwiched between two orthogonal polarizing films. Under the proper viewing conditions, a birefringent checkerboard pattern appeared. They also measured the thermal transfer and optical retardation properties.

“Our findings could aid in the development of next-generation optical materials and paper electronics,” says senior author Masaya Nogi. “This could be the start of bottom-up techniques for building sophisticated and energy-efficient optical and thermal materials.”

Here’s a link to and a citation for the paper,

Checkered Films of Multiaxis Oriented Nanocelluloses by Liquid-Phase Three-Dimensional Patterning by Kojiro Uetani, Hirotaka Koga and Masaya Nogi. Nanomaterials 2020, 10(5), 958; DOI: https://doi.org/10.3390/nano10050958 Published: 18 May 2020

This is an open access paper.