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NT/ A nanoscale view of bubble formation

Nanotechnology & nanomaterials biweekly vol.36, 15th November — 28th November

TL;DR

  • A nanoscale view of bubble formation: Using computer simulation, a research team succeeded in modeling the behavior of molecules at the liquid — gas interface at the nanometer scale, enabling them to describe the boiling process with extreme precision. The findings could be applied to future cooling systems for microprocessors, or to the production of carbon-neutral hydrogen, known as green hydrogen.
  • Scientists have developed a new way to guide the self-assembly of a wide range of novel nanoscale structures using simple layered block copolymers as starting materials. The work could help guide the design of custom surface coatings with tailored optical, electronic, and mechanical properties for use in sensors, batteries, filters, and more.
  • Researchers have discovered new properties of tiny magnetic whirlpools called skyrmions. Their pivotal discovery could lead to a new generation of microelectronics for memory storage with vastly improved energy efficiency.
  • Using a unique combination technology, a team of researchers from Nagoya University in Japan has analyzed the mechanisms of the light-matter interaction in nanomaterials at the smallest and fastest levels.
  • Scientists have discovered new waves with picometer-scale spatial variations of electromagnetic fields which can propagate in semiconductors like silicon.
  • To design better rechargeable ion batteries, engineers and chemists have collaborated to combine a powerful new electron microscopy technique and data mining to visually pinpoint areas of chemical and physical alteration within ion batteries.
  • Researchers have developed a static prevention technology using a triboelectric nanogenerator. The findings of this study facilitate improved and more efficient static prevention with commercialization potential by expanding the application range of triboelectric nanogenerators.
  • The challenge of fabricating nanowires directly on silicon substrates for the creation of the next generation of electronics has finally been solved. Next-generation spintronics will lead to better memory storage mechanisms in computers, making them faster and more efficient.
  • Researchers have published a new theory for making batches of carbon nanotubes with a single, desired chirality. Their method could simplify the purification of nanotubes that are all metallic or all semiconductors.
  • First insights into engineering crystal growth by atomically precise metal nanoclusters have been achieved in a new study.
  • And more!

Nanotech Market

Nanotechnology deals with the ability to see, understand, measure, predict, produce or control matter at the nanoscale (below 100 nanometers). The realm of nanotechnology lies between 0.1 and 100 nanometers, wherein a nanometer is defined as one-thousandth of a micron. As a versatile technology with widespread applications in a wide range of end-use sectors, nanotechnology is currently facing a mixed bag of challenges and opportunities as the COVID-19 pandemic continues to spread across the globe. With the world fighting its biggest public health crisis in history, nanotechnology healthcare applications are storming into the spotlight led by the focus on nano intervention in terms of designing effective ways to identify, diagnose, treat and eliminate the spread of COVID-19 infections. Their role as nanocarriers has the potential to design risk-free and effective immunization strategies. In the post-COVID-19 period, the use of nanotechnology solutions in the production of a multitude of devices & products will continue to grow.

Amid the COVID-19 crisis, the global market for Nanotechnology estimated at US$42.2 Billion in the year 2020, is projected to reach a revised size of US$70.7 Billion by 2026, growing at a CAGR of 9.2% over the analysis period. Nanocomposites, one of the segments analyzed in the report, is projected to record a 8.7% CAGR and reach US$35.4 Billion by the end of the analysis period. After a thorough analysis of the business implications of the pandemic and its induced economic crisis, growth in the Nanomaterials segment is readjusted to a revised 10.1% CAGR for the next 7-year period.

Global nanotechnology market to reach US $126.8 billion by the year 2027. Amid the COVID-19 crisis, the global market for Nanotechnology is estimated at US $54.2 billion in the year 2020, and is projected to reach a revised size of US $126 billion.

Latest News & Research

Microscopic liquid–gas interface effect on liquid wetting

by Jinming Zhang, Wei Ding, Zuankai Wang, Hao Wang, Uwe Hampel in Journal of Colloid and Interface Science

When a liquid boils in a vessel, tiny vapor bubbles form at the bottom and rise, transferring heat in the process. How these small bubbles grow and eventually detach was previously not known in any great detail. A German-Chinese research team under the leadership of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) has now managed to fundamentally expand this understanding.

Using computer simulation, the experts succeeded in modeling the behavior of molecules at the liquid-gas interface at the nanometer scale, enabling them to describe the boiling process with extreme precision. The findings could be applied to future cooling systems for microprocessors, or to the production of carbon-neutral hydrogen, known as green hydrogen, as the team reported in the Journal of Colloid and Interface Science.

How droplets or vapor bubbles wet a surface depends on the type and nature of the surface material. For example, spherical drops form on hydrophobic materials, with minimum contact area to the base. With hydrophilic materials, however, the liquid tends to create flat deposits — the solid-liquid interface is then much larger. Such processes can be described theoretically by the Young-Laplace equation. This equation yields a contact angle that characterizes droplet behavior on the surface: large angles indicate poor wetting, whereas small angles indicate good wetting.

When a vapor bubble forms on a wall in a boiling liquid, a very thin film of liquid — invisible to the eye — remains beneath it. This film determines how the bubble grows and how it detaches from the wall. The contact angle also plays a key role in this respect.

The underlying theory is based on a relatively simple approach. “It takes into account both the pressure exerted externally by the liquid and the vapor pressure inside the bubble,” explained Professor Uwe Hampel, Head of Experimental Thermal Fluid Dynamics at the HZDR. “Then there is capillary pressure, which is created by the curvature of the bubble surface.”

Recently, however, a range of experiments using laser measurement have demonstrated that this established theory fails for very small droplets and bubbles: on the nanoscale, the measured contact angles deviated significantly in some cases from the theoretical predictions.

To solve this problem, the German-Chinese research team set about revising the theory. To do this, they took a closer look at the processes that occur when a liquid boils.

“We considered in detail the interfacial behavior of molecules,” explained HZDR researcher Dr. Wei Ding. “Then we used a computer to simulate the interaction between these molecules.”

In doing so, the research group discovered a significant difference from previous approaches: the forces acting between the molecules do not simply add up linearly. Instead, the interaction is much more complex, resulting in distinct nonlinear effects. These are precisely the effects that the experts consider in their new, expanded theory.

“Our hypothesis provides a good explanation for the results obtained in recent experiments,” stated Ding with delight. “We now have a far more precise understanding of the behavior of tiny droplets and vapor bubbles.”

Besides completing our understanding of the theoretical basis, the findings also hold the promise of progress in several areas of technology, such as microelectronics. In this area, processors are now so powerful that they give off increasing amounts of heat, which must then be dissipated by cooling systems.

“There are ideas to remove this heat by boiling a liquid,” remarked Uwe Hampel. “With our new theory, we should be able to determine the conditions under which rising vapor bubbles can dissipate heat energy most efficiently.” The equations could also help to cool fuel elements in a nuclear reactor more effectively than in the past.

The electrolysis of water to produce carbon-neutral hydrogen, referred to as green hydrogen, is another potential application. Countless gas bubbles form on the membrane surfaces of an electrolyzer during water splitting. With this new theory, it seems conceivable that these bubbles can be influenced more specifically than before, enabling more efficient electrolysis in the future. The key to all these potential applications lies in the selection and structuring of appropriate materials.

“Adding nanogrooves to a surface, for example, can significantly accelerate the detachment of gas bubbles during boiling,” explained Wei Ding. “With our new theory, such structuring can now be more finely tailored — a project on which we are already working.”

Priming self-assembly pathways by stacking block copolymers

by Sebastian T. Russell, Suwon Bae, Ashwanth Subramanian, Nikhil Tiwale, Gregory Doerk, Chang-Yong Nam, Masafumi Fukuto, Kevin G. Yager in Nature Communications

Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have developed a new way to guide the self-assembly of a wide range of novel nanoscale structures using simple polymers as starting materials. Under the electron microscope, these nanometer-scale structures look like tiny Lego building blocks, including parapets for miniature medieval castles and Roman aqueducts. But rather than building fanciful microscopic fiefdoms, scientists are exploring how these novel shapes might affect a material’s functions.

The team from Brookhaven Lab’s Center for Functional Nanomaterials (CFN) describes their novel approach to control self-assembly in a paper just published in Nature Communications. A preliminary analysis shows that different shapes have dramatically different electrical conductivity. The work could help guide the design of custom surface coatings with tailored optical, electronic, and mechanical properties for use in sensors, batteries, filters, and more.

“This work opens the door to a wide range of possible applications and opportunities for scientists from academia and industry to partner with experts at CFN,” said Kevin Yager, leader of the project and CFN’s Electronic Nanomaterials group. “Scientists interested in studying optical coatings, or electrodes for batteries, or solar cell designs could tell us what properties they need, and we can select just the right structure from our library of exotic shaped materials to meet their needs.”

To make the exotic materials, the team relied on two areas of longstanding expertise at CFN. First is the self-assembly of materials called block copolymers — including how various forms of processing affect the organization and rearrangement of these molecules. Second is a method called infiltration synthesis, which replaces rearranged polymer molecules with metals or other materials to make the shapes functional — and easy to visualize in three dimensions using a scanning electron microscope.

“Self-assembly is a really beautiful way to make structures,” Yager said. “You design the molecules, and the molecules spontaneously organize into the desired structure.”

In its simplest form, the process starts by depositing thin films of long chainlike molecules called block copolymers onto a substrate. The two ends of these block copolymers are chemically distinct and want to separate from each other, like oil and water. When you heat these films through a process called annealing, the copolymer’s two ends rearrange to move as far apart as possible while still being connected. This spontaneous reorganization of chains thus creates a new structure with two chemically distinct domains. Scientists then infuse one of the domains with a metal or other substance to make a replica of its shape, and completely burn away the original material. The result: a shaped piece of metal or oxide with dimensions measuring mere billionths of a meter that could be useful for semiconductors, transistors, or sensors.

“It’s a powerful and scalable technique. You can easily cover large areas with these materials,” Yager said. “But the disadvantage is that this process tends to form only simple shapes — flat sheetlike layers called lamellae or nanoscale cylinders.”

Traditional self-assembly vs. pathway priming. a In traditional BCP thin-film processing, disordered, homogenous films cast from solution are annealed for long times at high temperatures to achieve conventional equilibrium morphologies (e.g., cylinders or lamellae). b Non-trivial layered initial configurations (a1 and c1) are used to initiate self-assembly pathways that pass through non-equilibrium transient states (a2 and c2) and progress towards final morphologies after long annealing times (a3 and c3). These pathways are distinct from the corresponding non-layered blend (b1 to b3). Scale bars are 100 nm.

Scientists have tried different strategies to go beyond those simple arrangements. Some have experimented with more complex branching polymers. Others have used microfabrication methods to create a substrate with tiny posts or channels that guide where the polymers can go. But making more complex materials and the tools and templates for guiding nano-assembly can be both labor-intensive and expensive.

“What we’re trying to show is that there’s an alternative where you can still use simple, cheap starting materials, but get really interesting, exotic structures,” Yager said.

The CFN method relies on depositing block copolymer thin films in layers.

“We take two of the materials that naturally want to form very different structures and literally put them on top of one another,” Yager said.

By varying the order and thickness of the layers, their chemical composition, and a range of other variables including annealing times and temperatures, the scientists generated more than a dozen exotic nanoscale structures that haven’t been seen before.

“We discovered that the two materials don’t really want to be stratified. As they anneal, they want to mix,” Yager said. “The mixing is causing more interesting new structures to form.”

If annealing is allowed to progress to completion, the layers will eventually evolve to form a stable structure. But by stopping the annealing process at various times and cooling the material rapidly, quenching it, “you can pull out transient structures and get some other interesting shapes,” Yager said.

Scanning electron microscope images revealed that some structures, like the “parapets” and “aqueducts,” have composite features derived from the order and reconfiguration preferences of the stacked copolymers. Others have crisscross patterns or lamellae with a patchwork of holes that are unlike either of the starting materials’ preferred configurations — or any other self-assembled materials.

Through detailed studies exploring imaginative combinations of existing materials and investigating their “processing history,” the CFN scientists generated a set of design principles that explain and predict what structure is going to form under a certain set of conditions. They used computer-based molecular dynamics simulations to get a deeper understanding of how the molecules behave.

“These simulations let us see where the individual polymer chains are going as they rearrange,” Yager said.

And, of course, the scientists are thinking about how these unique materials might be useful. A material with holes might work as a membrane for filtration or catalysis; one with parapet-like pillars on top could potentially be a sensor because of its large surface area and electronic connectivity, Yager suggested.

The first tests, included in the Nature Communications paper, focused on electrical conductivity. After forming an array of newly shaped polymers, the team used infiltration synthesis to replace one of the newly shaped domains with zinc oxide. When they measured the electrical conductivity of differently shaped zinc oxide nanostructures, they found huge differences.

“It’s the same starting molecules, and we’re converting them all into zinc oxide. The only difference between one and the other is how they’re locally connected to each other at the nanoscale,” Yager said. “And that turns out to make a huge difference in the final material’s electrical properties. In a sensor or an electrode for a battery, that would be very important.”

Scientists are now exploring the different shapes’ mechanical properties.

“The next frontier is multifunctionality,” Yager said. “Now that we have access to these nice structures, how can we choose one that maximizes one property and minimizes another — or maximizes both or minimizes both, if that’s what we want.”

“With this approach, we have a lot of control,” Yager said. “We can control what the structure is (using this newly developed method), and also what material it is made of (using our infiltration synthesis expertise). We look forward to working with CFN users on where this approach can lead.”

Thermal Hysteresis and Ordering Behavior of Magnetic Skyrmion Lattices

by Arthur R. C. McCray, Yue Li, Rabindra Basnet, Krishna Pandey, Jin Hu, Daniel P. Phelan, Xuedan Ma, Amanda K. Petford-Long, Charudatta Phatak in Nano Letters

Tiny magnetic whirlpools could transform memory storage in high performance computers.

Magnets generate invisible fields that attract certain materials. A common example is fridge magnets. Far more important to our everyday lives, magnets also can store data in computers. Exploiting the direction of the magnetic field (say, up or down), microscopic bar magnets each can store one bit of memory as a zero or a one — the language of computers.

Scientists at the U.S. Department of Energy’s (DOE) Argonne National Laboratory want to replace the bar magnets with tiny magnetic vortices. As tiny as billionths of a meter, these vortices are called skyrmions, which form in certain magnetic materials. They could one day usher in a new generation of microelectronics for memory storage in high-performance computers.

“The bar magnets in computer memory are like shoelaces tied with a single knot; it takes almost no energy to undo them,” said Arthur McCray, a Northwestern University graduate student working in Argonne’s Materials Science Division (MSD). And any bar magnets malfunctioning due to some disruption will affect the others.

“By contrast, skyrmions are like shoelaces tied with a double knot. No matter how hard you pull on a strand, the shoelaces remain tied.”

The skyrmions are thus extremely stable to any disruption. Another important feature is that scientists can control their behavior by changing the temperature or applying an electric current.

Scientists have much to learn about skyrmion behavior under different conditions. To study them, the Argonne-led team developed an artificial intelligence (AI) program that works with a high-power electron microscope at the Center for Nanoscale Materials (CNM), a DOE Office of Science user facility at Argonne. The microscope can visualize skyrmions in samples at very low temperatures.

The team’s magnetic material is a mixture of iron, germanium and tellurium. In structure, this material is like a stack of paper with many sheets. A stack of such sheets contains many skyrmions, and a single sheet can be peeled from the top and analyzed at facilities like CNM.

“The CNM electron microscope coupled with a form of AI called machine learning enabled us to visualize skyrmion sheets and their behavior at different temperatures,” said Yue Li, a postdoctoral appointee in MSD.

“Our most intriguing finding was that the skyrmions are arranged in a highly ordered pattern at minus 60 degrees Fahrenheit and above,” said Charudatta Phatak, a materials scientist and group leader in MSD. ?”But as we cool the sample the skyrmion arrangement changes.” Like bubbles in beer foam, some skyrmions became larger, some smaller, some merge and some vanish.

At minus 270, the layer reached a state of nearly complete disorder, but order came back when the temperature returned to minus 60. This order-disorder transition with temperature change could be exploited in future microelectronics for memory storage.

“We estimate the skyrmion energy efficiency could be 100 to 1000 times better than current memory in the high performance computers used in research,” McCray said.

Energy efficiency is essential to the next generation of microelectronics. Today’s microelectronics already account for roughly 10% of the world’s electricity. And that number could double by 2030. More energy-efficient electronics must be found.

“We have a way to go before skyrmions find their way into any future computer memory with low power,” Phatak said. ?”Nonetheless, this kind of radical new way of thinking about microelectronics is key to next generation devices.”

Transient electron energy-loss spectroscopy of optically stimulated gold nanoparticles using picosecond pulsed electron beam

by Makoto Kuwahara, Lira Mizuno, Rina Yokoi, Hideo Morishita, Takafumi Ishida, Koh Saitoh, Nobuo Tanaka, Shota Kuwahara, Toshihide Agemura in Applied Physics Letters

Using a unique combination technology, a team of researchers from Nagoya University in Japan has analyzed the mechanisms of the light-matter interaction in nanomaterials at the smallest and fastest levels.

Nanomaterials, materials sized at the nanoscale between 1 and 100 nm, are increasingly important in both industry and everyday living. Their extraordinarily small size gives them unique properties not found in larger materials. These properties are also specific to the nature and environment of the material. To expand the library of nanomaterials that can be applied effectively, safely, and sustainably in products and manufacturing processes, we require a deeper understanding of even the smallest events occurring on and inside the nanoparticles.

To measure nanomaterials, scientists use a subfield of metrology known as nanometrology. Nanometrology measures length scales at the nanoscale. To give this some context, human hair is about 100,000 times wider. When particles are this small, scientists must also measure events that occur within mere fractions of a second. For example, a phenomenon called photoexcitation normally takes place in picoseconds, or one trillionth of a second. Specialized devices, therefore, are necessary to measure these almost instantaneous events.

A research group led by Nagoya University faculty members, Associate Professor Makoto Kuwahara from the Institute of Materials and Systems for Sustainability (IMaSS) and Lira Mizuno, Rina Yokoi, and Hideo Morishita of the Graduate School of Engineering, investigated whether they could study such photoexcitation processes occurring on single nanoparticles. In collaboration with senior researchers at Hitachi Hightech Ltd., they developed an ultrafast electron microscope by combining a semiconductor photocathode with a ‘Negative Electron Affinity’ surface, pioneered by Nagoya University, with a general-purpose electron microscope. With the resulting microscope created by combining these technologies, we can observe events at the nanoscale. The researchers published their findings in Applied Physics Letters.

For the nanoparticles, the group used chemically synthesized gold nanotriangles. Gold is suitable for such experiments because it is a noble metal. This means it is stable under a range of conditions. Electrons in gold nanoparticles exhibit a phenomenon called ‘plasmon resonance’. When a gold nanoparticle undergoes photoexcitation with a specific wavelength of light, the electrons in the nanoparticle start moving, or oscillating. This intensifies the light, turning the gold nanoparticle into a bright antenna. For this reason, surface plasmons on gold are regularly used for sensing applications and are of great interest in energy conversion.

The plasmons in gold nanoparticles can be photoexcited using the ultrafast laser in the new custom-built ultrafast electron microscope while simultaneously allowing scientists to observe single gold nanoparticles. The researchers investigated two different plasmon phenomena by applying their new technique. They first observed the relaxation of the plasmons on the surface, which is a well-studied process. However, their new technique also allowed them to view the change in the plasmons inside the gold nanoparticles, even though the light only reached the surface of the nanoparticles. This is the first time a technique has revealed the relaxation process of these plasmons inside the gold nanoparticles, with important implications for the preparation of light-harvesting materials for energy conversion. The newly developed technique should help analyze potential materials by exposing ultrafast light-matter interactions.

“By understanding phenomena such as photoexcitation and relaxation processes and energy transport, we can improve photoresponsive properties and increase efficiency,” explains Kuwahara. “In particular, it can be a powerful tool to capture individual time changes in small structural materials with spatial resolution (such as those that exceed sub-micrometers). This has been difficult to achieve with conventional analytical methods using pulsed lasers as probes,” he continued. “We expect this achievement to enable the analysis of photoelectric and thermoelectric conversion materials and their applied devices that contribute to energy conservation. Our research should be useful for the development of light energy conversion, biosensors, and thermoelectric conversion devices.”

Experimental setup for transient EELS in the TR-TEM and the pump-probe system. The insets show enlarged schematic illustrations of the specimen position and a scanning transmission electron microscope (STEM) image in the TR-TEM.

An Advanced Thermal Decomposition Method to Produce Magnetic Nanoparticles with Ultrahigh Heating Efficiency for Systemic Magnetic Hyperthermia

by Ananiya A. Demessie, Youngrong Park, Prem Singh, Abraham S. Moses, Tetiana Korzun, Fahad Y. Sabei, Hassan A. Albarqi, Leonardo Campos, Cory R. Wyatt, Khashayar Farsad, Pallavi Dhagat, Conroy Sun, Olena R. Taratula, Oleh Taratula in Small Methods

Oregon State University scientists have invented a way to make magnetic nanoparticles that get hotter than any previous nanoparticle, improving their cancer fighting ability.

Faculty from the OSU College of Pharmacy spearheaded a collaboration that developed an advanced thermal decomposition method for producing nanoparticles able to reach temperatures in cancer lesions of up to 50 degrees Celsius, or 122 degrees Fahrenheit, when exposed to an alternating magnetic field.

Findings of the preclinical study led by Oleh Taratula and Olena Taratula were published today in the journal Small Methods.

Magnetic nanoparticles have shown anti-cancer potential for years, the scientists said. Once inside a tumor, the particles — tiny pieces of matter as small as one-billionth of a meter — are exposed to an alternating magnetic field. Exposure to the field, a non-invasive process, causes the nanoparticles to heat up, weakening or destroying the cancer cells.

“Magnetic hyperthermia shows great promise for the treatment of many types of cancer,” Olena Taratula said. “Many preclinical and clinical studies have demonstrated its potential to either kill cancer cells directly or enhance their susceptibility to radiation and chemotherapy.”

But at present, magnetic hypothermia can only be used for patients whose tumors are accessible by a hypodermic needle, Oleh Taratula said, and not for people with hard to reach malignancies such as metastatic ovarian cancer.

“With currently available magnetic nanoparticles, the required therapeutic temperatures — above 44 degrees Celsius — can only be achieved by direct injection into the tumor,” he said. “The nanoparticles have only moderate heating efficiency, which means you need a high concentration of them in the tumor to generate enough heat. And numerous studies have shown that only a small percentage of systemically injected nanoparticles accumulate in tumors, making it a challenge to get that high concentration.”

To tackle those problems, the scientists developed a new chemical manufacturing technique that resulted in magnetic nanoparticles with more heating efficiency. They demonstrated in a mouse model that the cobalt-doped nanoparticles will accumulate in metastatic ovarian cancer tumors following low-dose systemic administration, and that when exposed to an alternating magnetic field, the particles can rise in temperature to 50 degrees Celsius.

“To our knowledge, this is the first time it’s been shown that magnetic nanoparticles injected intravenously at a clinically recommended dose are capable of increasing the temperature of cancer tissue above 44 degrees Celsius,” Olena Taratula said. “And we also demonstrated that our novel method could be used for the synthesis of various core-shell nanoparticles. It could serve as a foundation for the development of novel nanoparticles with high heating performance, further advancing systemic magnetic hyperthermia for treating cancer.”

Core-shell nanoparticles have an inner core structure and an outer shell made from different components, she said. Researchers are especially interested in them because of the unique properties that can result from the combination of core and shell material, geometry and design.

Supercrystal engineering of atomically precise gold nanoparticles promoted by surface dynamics

by Qiaofeng Yao, Lingmei Liu, Sami Malola, Meng Ge, Hongyi Xu, Zhennan Wu, Tiankai Chen, Yitao Cao, María Francisca Matus, Antti Pihlajamäki, Yu Han, Hannu Häkkinen, Jianping Xie in Nature Chemistry

First insights into engineering crystal growth by atomically precise metal nanoclusters have been achieved in a study performed by researchers in Singapore, Saudi Arabia and Finland.

Ordinary solid matter consists of atoms organized in a crystal lattice. The chemical character of the atoms and lattice symmetry define the properties of the matter, for instance, whether it is a metal, a semiconductor or and electric insulator. The lattice symmetry may be changed by ambient conditions such as temperature or high pressure, which can induce structural transitions and transform even an electric insulator to an electric conductor, that is, a metal.

Larger identical entities such as nanoparticles or atomically precise metal nanoclusters can also organize into a crystal lattice, to form so called meta-materials. However, information on how to engineer the growth of such materials from their building blocks has been scarce since the crystal growth is a typical self-assembling process.

Now, first insights into engineering crystal growth by atomically precise metal nanoclusters have been achieved in a study performed by researchers in Singapore, Saudi Arabia and Finland. They synthesized metal clusters consisting of only 25 gold atoms, one nanometer in diameter. These clusters are soluble in water due to the ligand molecules that protect the gold. This cluster material is known to self-assemble into well-defined close packed single crystals when the water solvent is evaporated. However, the researcher found a novel concept to regulate the crystal growth by adding tetra-alkyl-ammonium molecular ions in the solvent. These ions affect the surface chemistry of the gold clusters, and their size and concentration were observed to have an impact on the size, shape, and morphology of the formed crystals. Remarkably, high-resolution electron microscopy images of some of the crystals revealed that they consist of polymeric chains of clusters with four-gold-atom interparticle links. The demonstrated surface chemistry opens now new ways to engineer metal cluster -based meta-materials for investigations of their electronic and optical properties.

The cluster materials were synthesized in the National University of Singapore, the electron microscopy imaging was done at the King Abdullah University of Science and Technology in Saud Arabia, and the theoretical modelling was done at the University of Jyvaskyla, Finland.

Formation and impact of nanoscopic oriented phase domains in electrochemical crystalline electrodes

by Wenxiang Chen, Xun Zhan, Renliang Yuan, Saran Pidaparthy, Adrian Xiao Bin Yong, Hyosung An, Zhichu Tang, Kaijun Yin, Arghya Patra, Heonjae Jeong, Cheng Zhang, Kim Ta, Zachary W. Riedel, Ryan M. Stephens, Daniel P. Shoemaker, Hong Yang, Andrew A. Gewirth, Paul V. Braun, Elif Ertekin, Jian-Min Zuo, Qian Chen in Nature Materials

To design better rechargeable ion batteries, engineers and chemists from the University of Illinois Urbana-Champaign collaborated to combine a powerful new electron microscopy technique and data mining to visually pinpoint areas of chemical and physical alteration within ion batteries.

A study led by materials science and engineering professors Qian Chen and Jian-Min Zuo is the first to map out altered domains inside rechargeable ion batteries at the nanoscale — a 10-fold or more increase in resolution over current X-ray and optical methods.

The team said previous efforts to understand the working and failure mechanisms of battery materials have primarily focused on the chemical effect of recharging cycles, namely the changes in the chemical composition of the battery electrodes.

A new electron microscopy technique, called four-dimensional scanning transmission electron microscopy, allows the team to use a highly focused probe to collect images of the inner workings of batteries.

“During the operation of rechargeable ion batteries, ions diffuse in and out of the electrodes, causing mechanical strain and sometimes cracking failures,” said postdoctoral researcher and first author Wenxiang Chen. “Using the new electron microscopy method, we can capture the strain-caused nanoscale domains inside battery materials for the first time.”

Qian Chen said these types of microstructural heterogeneity transformations have been widely studied in ceramics and metallurgy but have not been used in energy storage materials until this study.

“The 4D-STEM method is critical to map otherwise inaccessible variations of crystallinity and domain orientations inside the materials,” Zuo said.

The team compared its 4D-STEM observations to computational modeling led by mechanical science and engineering professor Elif Ertekin to spot these variations.

“The combined data mining and 4D-STEM data show a pattern of nucleation, growth and coalescence process inside the batteries as the strained nanoscale domains develop,” Qian Chen said. “These patterns were further verified using X-ray diffraction data collected by materials science and engineering professor and study co-author Daniel Shoemaker.”

Qian Chen plans to further this research by creating movies of this process — something for which her lab is well known.

“The impact of this research can go beyond the multivalent ion battery system studied here,” said Paul Braun, a materials science and engineering professor, Materials Research Laboratory director and co-author of the study. “The concept, principles and the enabling characterization framework apply to electrodes in a variety of Li-ion and post-Li-ion batteries and other electrochemical systems including fuel cells, synaptic transistors and electrochromics.”

Nanostructure-induced L10-ordering of twinned single-crystals in CoPt ferromagnetic nanowires

by Ryo Toyama, Shiro Kawachi, Jun-ichi Yamaura, Takeshi Fujita, Youichi Murakami, Hideo Hosono, Yutaka Majima in Nanoscale Advances

The challenge of fabricating nanowires directly on silicon substrates for the creation of the next generation of electronics has finally been solved by researchers from Tokyo Tech. Next-generation spintronics will lead to better memory storage mechanisms in computers, making them faster and more efficient.

As our world modernizes faster than ever before, there is an ever-growing need for better and faster electronics and computers. Spintronics is a new system that uses the spin of an electron, in addition to the charge state, to encode data, making the entire system faster and more efficient. Ferromagnetic nanowires with high coercivity (resistance to changes in magnetization) are required to realize the potential of spintronics. Especially L10-ordered (a type of crystal structure) cobalt-platinum (CoPt) nanowires.

Conventional fabrication processes for L10-ordered nanowires involve heat treatment to improve the physical and chemical properties of the material, a process called annealing on the crystal substrate; the transfer of a pattern onto the substrate through lithography; and finally the chemical removal of layers through a process called etching. Eliminating the etching process by directly fabricating nanowires onto the silicon substrate would lead to a marked improvement in the fabrication of spintronic devices. However, when directly fabricated nanowires are subjected to annealing, they tend to transform into droplets as a result of the internal stresses in the wire.

Recently, a team of researchers led by Professor Yutaka Majima from the Tokyo Institute of Technology has found a solution to the problem. The team reported a new fabrication process to make L10-ordered CoPt nanowires on silicon/silicon dioxide (Si/SiO2) substrates.

Talking about their research, published in Nanoscale Advances, Prof. Majima says, “Our nanostructure-induced ordering method allows the direct fabrication of ultrafine L10-ordered CoPt nanowires with the narrow widths of 30nm scale required for spintronics. This fabrication method could further be applied to other L10-ordered ferromagnetic materials such as iron-platinum and iron-palladium compounds.”

In this study, the researchers first coated a Si/SiO2 substrate with a material called a ‘resist’ and subjected it to electron beam lithography and evaporation to create a stencil for the nanowires. Then then deposited a multilayer of CoPt on the substrate. The deposited sampled were then ‘lifted-off’, leaving behind CoPt nanowires. These nanowires were then subjected to high temperature annealing. The researchers also examined the fabricated nanowires using several characterization techniques.

They found that the nanowires took on L10-ordering during the annealing process. This transformation was induced by atomic interdiffusion, surface diffusion, and extremely large internal stress at the ultrasmall 10 nm scale curvature radii of the nanowires. They also found that the nanowires exhibited a large coercivity of 10 kiloOersteds (kOe).

Typical top-view scanning electron microscope (SEM) images of [Co (3.6 nm)/Pt (4.8 nm)]6 multilayer nanowires on Si/SiO2 substrates (a) before and (b) after annealing at 650 °C for 90 min.

According to Prof. Majima, “The internal stresses on the nanostructure here induce the L10-ordering. This is a different mechanism than in previous studies. We are hopeful that this discovery will open up a new field of research called ‘nanostructure-induced materials science and engineering.’”

The wide applicability and convenience of the novel fabrication technique are sure to make a significant contribution to the field of spintronics research.

Single-chirality nanotube synthesis by guided evolutionary selection

by Boris I. Yakobson, Ksenia V. Bets in Science Advances

Like a giraffe stretching for leaves on a tall tree, making carbon nanotubes reach for food as they grow may lead to a long-sought breakthrough.

Materials theorists Boris Yakobson and Ksenia Bets at Rice University’s George R. Brown School of Engineering shows how putting constraints on growing nanotubes could facilitate a “holy grail” of growing batches with a single desired chirality.

Their paper in Science Advances describes a strategy by which constraining the carbon feedstock in a furnace would help control the “kite” growth of nanotubes. In this method, the nanotube begins to form at the metal catalyst on a substrate, but lifts the catalyst as it grows, resembling a kite on a string.

Carbon nanotube walls are basically graphene, its hexagonal lattice of atoms rolled into a tube. Chirality refers to how the hexagons are angled within the lattice, between 0 and 30 degrees. That determines whether the nanotubes are metallic or semiconductors. The ability to grow long nanotubes in a single chirality could, for instance, enable the manufacture of highly conductive nanotube fibers or semiconductor channels of transistors.

Normally, nanotubes grow in random fashion with single and multiple walls and various chiralities. That’s fine for some applications, but many need “purified” batches that require centrifugation or other costly strategies to separate the nanotubes.

The researchers suggested hot carbon feedstock gas fed through moving nozzles could effectively lead nanotubes to grow for as long as the catalyst remains active. Because tubes with different chiralities grow at different speeds, they could then be separated by length, and slower-growing types could be completely eliminated.

One additional step that involves etching away some of the nanotubes could then allow specific chiralities to be harvested, they determined.

The lab’s work to define the mechanisms of nanotube growth led them to think about whether the speed of growth as a function of individual tubes’ chirality could be useful. The angle of “kinks” in the growing nanotubes’ edges determines how energetically amenable they are to adding new carbon atoms.

“The catalyst particles are moving as the nanotubes grow, and that’s principally important,” said lead author Bets, a researcher in Yakobson’s group. “If your feedstock keeps moving away, you get a moving window where you’re feeding some tubes and not the others.”

The paper’s reference to Lamarck giraffes — a 19th-century theory of how they evolved such long necks — isn’t entirely out of left field, Bets said.

“It works as a metaphor because you move your ‘leaves’ away and the tubes that can reach it continue growing fast, and those that cannot just die out,” she said. “Eventually, all the nanotubes that are just a tiny bit slow will ‘die.’”

Speed is only part of the strategy. In fact, they suggest nanotubes that are a little slower should be the target to assure a harvest of single chiralities.

Uniform versus localized feedstock gas distribution. (A) Nanotubes of helicities χ = 1, 2,…, Χ, shown ordered by growth constants kχ in uniform atmosphere attain the lengths in proportion to kχ, as shown; top inset illustrates the kite growth (2128) with the tube tip–catalyst moving freely as it grows. (B) Localized feedstock concentration c(x), shaded blue, moves at speed V, while different CNTs achieve steady-state positions according to the kχ values; the selected one is marked s.

Because nanotubes of different chiralities grow at their own rates, a batch would likely exhibit tiers. Chemically etching the longest nanotubes would degrade them, preserving the next level of tubes. Restoring the feedstock could then allow the second-tier nanotubes to continue growing until they are ready to be culled, Bets said.

“There are three or four laboratory studies that show nanotube growth can be reversed, and we also know it can be restarted after etching,” she said. “So all the parts of our idea already exist, even if some of them are tricky. Close to equilibrium, you will have the same proportionality between growth and etching speeds for the same tubes. If it’s all nice and clean, then you can absolutely, precisely pick the tubes you target.”

The Yakobson lab won’t make them, as it focuses on theory, not experimentation. But other labs have turned past Rice theories into products like boron buckyballs.

“I’m pretty sure every single one of our reviewers were experimentalists, and they didn’t see any contradictions to it working,” Bets said. “Their only complaint, of course, was that they would like experimental results right now, but that’s not what we do.”

She hopes more than a few labs will pick up the challenge.

“In terms of science, it’s usually more beneficial to give ideas to the crowd,” Bets said. “That way, those who have interest can do it in 100 different variations and see which one works. One guy trying it might take 100 years.”

Yakobson added, “We don’t want to be that ‘guy.’ We don’t have that much time.”

Electrostatic discharge prevention system via body potential control based on a triboelectric nanogenerator

by Cheoljae Lee, Minsu Heo, Hyosik Park, Hyeonseo Joo, Wanchul Seung, Ju-Hyuck Lee in Nano Energy

The research team led by Professor Ju-Hyuck Lee of the Department of Energy Science and Engineering at DGIST (President Yang Kuk) developed a static prevention technology using a triboelectric nanogenerator through collaborative research with Dr. Wanchul Seung of Global Technology Research at Samsung Electronics. The findings of this study facilitate improved and more efficient static prevention with commercialization potential by expanding the application range of triboelectric nanogenerators.

Recent developments in semiconductors and small electronic components have increased the interest in static prevention, as static damage to small components leads to an increased defect rate. Currently, companies use a combination of various anti-static products such as wired grounding wristbands, antistatic mats, shoes, and ionizers. However, these methods result in increased equipment costs and operational inconveniences. Therefore, an efficient and simple static-prevention method is required.

The research team focused on the cause of static conditions. The human body is generally static owing to the electric potential difference between the body and an object when both come in contact. The cause of this electric potential difference has been found in recent studies on triboelectric series between materials. Because the human skin is on the positive (+) side of the triboelectric series, it becomes positively charged (anode) when it contacts typically used objects such as shoes and clothes, sharply increasing the body electric potential to positive (+), causing static. The measurement results of the research team showed that the electric potential of the body increased by more than 100 V after walking for approximately 10 s.

As a solution, a method for transmitting negative charges to the body was developed. Using a triboelectric nanogenerator, the physical energy generated through body movements, such as walking, can be converted into electrical energy. A rectifier provides a negative charge to the body. The team observed that the electric potential of the body decreased to a negative value. The team also confirmed that the rate of decrease in the body electric potential varies based on the output (voltage, current, and charge) of the triboelectric nanogenerator, and the type and surface area of the discharger. A static prevention system with an appropriate triboelectric nanogenerator was applied to the sole of the shoe using the aforementioned variables. Consequently, an increase in the electric potential of the body was prevented. This is significantly more efficient than existing wireless antistatic wristbands in the market.

Professor Ju-Hyuck Lee of the Department of Energy Science and Engineering at DGIST stated, “This study provides a highly cost-efficient method with high-commercialization potential and is expected to effectively prevent static without causing inconvenience to work compared to the existing static prevention equipment.”

Picophotonics: Anomalous Atomistic Waves in Silicon

by Sathwik Bharadwaj, Todd Van Mechelen, Zubin Jacob in Physical Review Applied

Researchers at Purdue University have discovered new waves with picometer-scale spatial variations of electromagnetic fields which can propagate in semiconductors like silicon. The research team, led by Dr. Zubin Jacob, Elmore Associate Professor of Electrical and Computer Engineering and Department of Physics and Astronomy (courtesy), published their findings in APS Physics Review Applied in a paper titled, “Picophotonics: Anomalous Atomistic Waves in Silicon.”

“The word microscopic has its origins in the length scale of a micron which is a million times smaller than a meter. Our work is for light matter interaction within the picoscopic regime which is far smaller, where the discrete arrangement of atomic lattices changes light’s properties in surprising ways,” says Jacob.

These intriguing findings demonstrate that natural media host a variety of rich light-matter interaction phenomena at the atomistic level. The use of picophotonic waves in semiconducting materials may lead researchers to design new, functional optical devices, allowing for applications in quantum technologies.

Light-matter interaction in materials is central to several photonic devices from lasers to detectors. Over the past decade, nanophotonics, the study of how light flows on the nanometer scale in engineered structures such as photonic crystals and metamaterials have led to important advances. This existing research can be captured within the realm of classical theory of atomic matter. The current finding leading to picophotonics was made possible by a major leap forward using a quantum theory of atomistic response in matter. The team consists of Jacob as well as Dr. Sathwik Bharadwaj, research scientist at Purdue University, and Dr. Todd Van Mechelen, former post-doc at Purdue University.

The long-standing puzzle in the field was the missing link between atomic lattices, their symmetries and the role it plays on deeply picoscopic light fields. To answer this puzzle, the theory team developed a Maxwell Hamiltonian framework of matter combined with a quantum theory of light induced response in materials.

“This is a pivotal shift from the classical treatment of light flow applied in nanophotonics,” says Jacob. “The quantum nature of light’s behavior in materials is the key for the emergence of picophotonics phenomena.”

Bharadwaj and colleagues showed that hidden amidst traditional well-known electromagnetic waves, new anomalous waves emerge in the atomic lattice. These light waves are highly oscillatory even within one fundamental building block of the silicon crystal (sub-nanometer length scale).

“Natural materials itself have rich intrinsic crystal lattice symmetries and light is strongly influenced by these symmetries,” says Bharadwaj. “The immediate next goal is to apply our theory to the plethora of quantum and topological materials and also verify the existence of these new waves experimentally.”

“Our group has been leading the frontier of research on pico-scale electrodynamic fields inside matter at the atomistic level,” says Jacob. “We recently initiated the picoelectrodynamics theory network where we are bringing together diverse researchers to explore macroscopic phenomena stemming from microscopic pico-electrodynamic fields inside matter.”

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