NT/ New method enables the synthesis of hundreds of new 2D materials
Nanotechnology & nanomaterials biweekly vol.51, 5th March — 18th March
TL;DR
- Materials that are incredibly thin, only a few atoms thick, exhibit unique properties that make them appealing for energy storage, catalysis, and water purification. Researchers at Linköping University, Sweden, have now developed a method that enables the synthesis of hundreds of new 2D materials. Their study has been published in the journal Science.
- A groundbreaking technology that enables the real-time display of colors and shapes through changes in nanostructures has been developed. This innovative technology, pioneered by the team in the School of Energy and Chemical Engineering at UNIST, has the potential to revolutionize various fields, such as smart polymer particles.
- A newly developed ‘GPS nanoparticle’ injected intravenously can home in on cancer cells to deliver a genetic punch to the protein implicated in tumor growth and spread, according to researchers. They tested their approach in human cell lines and in mice to effectively knock down a cancer-causing gene, reporting that the technique may potentially offer a more precise and effective treatment for notoriously hard-to-treat basal-like breast cancers.
- A nanotechnology pioneer has uncovered a transformative approach to harnessing the catalytic power of aluminum nanoparticles by annealing them in various gas atmospheres at high temperatures.
- In a new Nature Communications study, Columbia Engineering researchers report that they have built highly conductive, tunable single-molecule devices in which the molecule is attached to leads by using direct metal-metal contacts. Their novel approach uses light to control the electronic properties of the devices and opens the door to broader use of metal-metal contacts that could facilitate electron transport across the single-molecule device.
- Inspired by nature, nanotechnology researchers have identified ‘spontaneous curvature’ as the key factor determining how ultra-thin, artificial materials can transform into useful tubes, twists, and helices.
- It might look like a roll of chicken wire, but this tiny cylinder of carbon atoms — too small to see with the naked eye — could one day be used for making electronic devices ranging from night vision goggles and motion detectors to more efficient solar cells, thanks to techniques developed by researchers at Duke University.
- A NIMS research team has developed a technique that enables the nanoscale observation of heat propagation paths and behavior within material specimens. This was achieved using a scanning transmission electron microscope (STEM) capable of emitting a pulsed electron beam and a nanosized thermocouple — a high-precision temperature measurement device developed by NIMS. The research is published in Science Advances.
- A study, published in Nature Communications reported an enhancement in exciton mobility in a two-dimensional (2D) Ruddlesden-Popper perovskite (RPP).
- Materials scientists at Rice University are shedding light on the intricate growth processes of 2D crystals, paving the way for controlled synthesis of these materials with unprecedented precision.
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 an 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
Two-dimensional materials by large-scale computations and chemical exfoliation of layered solids
by Jonas Björk et al in Science
Materials that are incredibly thin, only a few atoms thick, exhibit unique properties that make them appealing for energy storage, catalysis and water purification. Researchers at Linköping University, Sweden, have now developed a method that enables the synthesis of hundreds of new 2D materials.
Since the discovery of graphene, the field of research in extremely thin materials, so-called 2D materials, has increased exponentially. The reason is that 2D materials have a large surface area in relation to their volume or weight. This gives rise to a range of physical phenomena and distinctive properties, such as good conductivity, high strength, or heat resistance, making 2D materials of interest both within fundamental research and applications.
“In a film that’s only a millimeter thin, there can be millions of layers of the material. Between the layers, there can be a lot of chemical reactions and thanks to this, 2D materials can be used for energy storage or for generating fuels, for example,” says Johanna Rosén, professor in Materials physics at Linköping University.
The largest family of 2D materials is called MXenes. MXenes are created from a three-dimensional parent material called a MAX phase. It consists of three different elements: M is a transition metal, A is an (A-group) element, and X is carbon or nitrogen. By removing the A element with acids (exfoliation), a two-dimensional material is created. Until now, MXenes has been the only material family created in this way.
The Linköping researchers have introduced a theoretical method for predicting other three-dimensional materials that may be suitable for conversion into 2D materials. They have also proved that the theoretical model is consistent with reality.
To succeed, the researchers used a three-step process. In the first step, they developed a theoretical model to predict which parent materials would be suitable. Using large-scale calculations at the National Supercomputer Center, the researchers were able to identify 119 promising 3D materials from a database and a selection consisting of 66,643 materials.
The next step was to try to create the material in the lab.
“Out of 119 possible materials, we studied which ones had the chemical stability required and which materials were the best candidates. First, we had to synthesize the 3D material, which was a challenge in itself. Finally, we had a high-quality sample where we could exfoliate and etch away a specific atom layers using hydrofluoric acid,” says Jie Zhou, assistant professor at the Department of Physics, Chemistry and Biology.
The researchers removed yttrium (Y) from the parent material YRu2Si2, which resulted in the formation of two-dimensional Ru2SixOy.
But to confirm success in the lab, verification is necessary — step three. The researchers used the scanning transmission electron microscope Arwen at Linköping University. It can examine materials and their structures down at the atomic level. In Arwen it is also possible to investigate which atoms a material is made up of using spectroscopy.
“We were able to confirm that our theoretical model worked well, and that the resulting material consisted of the correct atoms. After exfoliation, images of the material resembled the pages of a book. It’s amazing that the theory could be put into practice, thereby expanding the concept of chemical exfoliation to more materials families than MXenes,” says Jonas Björk, associate professor at the division of Materials design.
The researchers’ discovery means that many more 2D materials with unique properties are within reach. These, in turn, can lay the foundation for a plethora of technological applications. The next step for the researchers is to explore more potential precursor materials and scale up the experiments. Rosén believes that future applications are almost endless.
“In general, 2D materials have shown great potential for an enormous number of applications. You can imagine capturing carbon dioxide or purifying water, for example. Now it’s about scaling up the synthesis and doing it in a sustainable way,” says Rosén.
Dynamic Photonic Janus Colloids with Axially Stacked Structural Layers
by Juyoung Lee, Soohyun Ban, Kyuhyung Jo, Hyeong Seok Oh, Jinhyeok Cho, Kang Hee Ku in ACS Nano
A groundbreaking technology that enables the real-time display of colors and shapes through changes in nanostructures has been developed. This innovative technology, pioneered by Professor Kang Hee Ku and her team in the School of Energy and Chemical Engineering at UNIST, has the potential to revolutionize various fields, such as smart polymer particles.
Utilizing block copolymers, the research team has achieved the self-assembly of photonic crystal structures on a large scale, mimicking natural phenomena observed in butterfly wings and bird feathers.
By reflecting the shape and direction of nanostructures, this technology allows for the visualization of vibrant colors and intricate patterns in real time.
Block copolymers, composed of two or more different monomers covalently bonded in a block shape, were strategically employed to induce phase separation using a non-mixing liquid droplet.
Professor Ku emphasized the significance of this achievement, stating, “We have successfully generated hundreds of flawless photonic crystal structures through the autonomous organization of block copolymers, eliminating the need for external manipulation.”
Setting itself apart from conventional methods, this cutting-edge technology leverages internal nanostructures to create colors that are vivid, long-lasting, and sustainable.
Furthermore, its enhanced applicability in display technology is evident through its capability to pattern large areas efficiently.
The key innovation lies in the use of a polymer that can dynamically adjust the size of microstructures within particles in response to changes in the external environment.
By leveraging the unique properties of polystyrene-polyvinylpyridine (PS-b-P2VP) block copolymers, the structure, shape, and color of the particles can be tailored, reverting to their original state despite environmental variations.
Real-time monitoring of structural changes revealed that the size and color of micro-nanostructures adapt to fluctuations in alcohol concentration or pH value.
Notably, the particles produced through this technology exhibit an innovative ‘Ice Cream Cone’ shape structure, combining aspects of solids and liquids to visualize fluid vibrations and dynamically alter shape and color in response to external stimuli.
Professor Ku showed confidence about the potential applications of this research, stating, “This study opens doors to the creation of self-assembling optical particles, streamlining the complex process conditions typically associated with colloidal crystal structure and pattern formation.” She further noted, “The technology’s practical applications in smart paint and polymer particles across various industries are envisioned.”
Context-Responsive Nanoparticle Derived from Synthetic Zwitterionic Ionizable Phospholipids in Targeted CRISPR/Cas9 Therapy for Basal-like Breast Cancer
by Parikshit Moitra, David Skrodzki, Matthew Molinaro, Nivetha Gunaseelan, Dinabandhu Sar, Teresa Aditya, Dipendra Dahal, Priyanka Ray, Dipanjan Pan in ACS Nano
A newly developed “GPS nanoparticle” injected intravenously can home in on cancer cells to deliver a genetic punch to the protein implicated in tumor growth and spread, according to researchers from Penn State. They tested their approach in human cell lines and in mice to effectively knock down a cancer-causing gene, reporting that the technique may potentially offer a more precise and effective treatment for notoriously hard-to-treat basal-like breast cancers.
“We developed a GPS nanoparticle that can find the site where it is needed,” said corresponding author Dipanjan Pan, the Dorothy Foehr Huck & J. Lloyd Huck Chair Professor in Nanomedicine and professor of nuclear engineering and of materials science and engineering at Penn State. “Once there — and only there — it can deliver gene editing proteins to prevent the cancer cells from spreading. It was a difficult task, but we showed that the system works for basal-like breast cancers.”
Similar to triple-negative breast cancers, basal-like breast cancers may be less prevalent than other breast cancers, but they can be far more challenging to treat, largely because they lack the three therapeutic targets found in other breast cancers. They also tend to be aggressive, quickly growing tumors and shedding cells that spread elsewhere in the body. Those cells can seed additional tumors, a process called metastasis.
“Metastasis is a huge challenge, especially with cancers like triple-negative and basal-like breast cancers,” Pan said. “The cancer can be hard to detect and does not show up during a routine mammogram, and it primarily affects the younger or African American population who may not be receiving preventative care yet. The outcome can be very, very poor, so there’s a clear unmet clinical need for more effective treatments when the cancer isn’t caught early enough.”
The team fabricated a Trojan horse nanoparticle, disguising it with specially designed fatty molecules that look like naturally occurring lipids and packing it full of CRISPR-Cas9 molecules. These molecules can target the genetic material of a cell, identify a particular gene and knock it down, or render it ineffective. In this case, the system targeted human forkhead box c1 (FOXC1), which is involved in instigating metastasis.
Pan described the designer lipids as “zwitterionic,” meaning they have near neutral charge on the nanoparticle’s shell. This prevents the body’s immune system from attacking the nanoparticle — because it is disguised as a non-threatening, normal molecule — and can help release the payload, but only when the lipids recognize the low pH environment of the cancer cell. To ensure the lipids would only activate at that low pH, the researchers designed them to shift their charges to positive once they enter the more acidic tumor microenvironment, triggering the payload release.
But the body is a vast place, so how could the researchers ensure the CRISPR-Cas9 payload made it to the correct target? To ensure that the nanoparticle would bind to the right cells, they attached an epithelial cell adhesion molecule (EpCAM), which is known to attach to basal-like breast cancer cells.
“No one has ever attempted to target a basal-like breast like cancer cell with context-responsive delivery system that can genetically knockdown the gene of interest,” Pan said. “We’re the first to show that it can be done.”
Others have developed viral delivery systems, hijacking a virus particle to carry treatment to the cells, and non-viral delivery systems, using nanoparticles. The difference, Pan said, for his team’s approach is the surface lipid designed to respond only in the target environment, which reduces the potential for off-target delivery and harm to healthy cells. Also, he added, since the body doesn’t consider the lipids to be a threat, there’s less chance for an immune response, which they validated in their experiments.
The team first tested the approach in human triple-negative breast cancer cells, validating that the nanoparticle would deploy the CRISPR/Cas9 system in the correct environment. They confirmed that the nanoparticle could find its way to a tumor in a mouse model, deploy the system and successfully knock down FOXC1.
Next, Pan said, the researchers plan to continue testing the nanoparticle platform with the eventual goal of applying it clinically in humans.
“We are also exploring how else we might apply the platform technology,” Pan said. “We can customize the molecules on the surface, the payload it carries, and use it to encourage healing in other areas. There’s a lot of potential with this platform.”
Tailoring the aluminum nanocrystal surface oxide for all-aluminum-based antenna-reactor plasmonic photocatalysts
by Aaron Bayles, Catherine J. Fabiano, Chuqiao Shi, Lin Yuan, Yigao Yuan, Nolan Craft, Christian R. Jacobson, Parmeet Dhindsa, Adebola Ogundare, Yelsin Mendez Camacho, Banghao Chen, Hossein Robatjazi, Yimo Han, Geoffrey F. Strouse, Peter Nordlander, Henry O. Everitt, Naomi J. Halas in Proceedings of the National Academy of Sciences
Catalysts unlock pathways for chemical reactions to unfold at faster and more efficient rates, and the development of new catalytic technologies is a critical part of the green energy transition.
The Rice University lab of nanotechnology pioneer Naomi Halas has uncovered a transformative approach to harnessing the catalytic power of aluminum nanoparticles by annealing them in various gas atmospheres at high temperatures.
According to a study published in the Proceedings of the National Academy of Sciences, Rice researchers and collaborators showed that changing the structure of the oxide layer that coats the particles modifies their catalytic properties, making them a versatile tool that can be tailored to suit the needs of different contexts of use from the production of sustainable fuels to water-based reactions.
“Aluminum is an earth-abundant metal used in many structural and technological applications,” said Aaron Bayles, a Rice doctoral alum who is a lead author on the paper. “All aluminum is coated with a surface oxide, and until now we did not know what the structure of this native oxide layer on the nanoparticles was. This has been a limiting factor preventing the widespread application of aluminum nanoparticles.”
Aluminum nanoparticles absorb and scatter light with remarkable efficiency due to surface plasmon resonance, a phenomenon that describes the collective oscillation of electrons on the metal surface in response to light of specific wavelengths. Like other plasmonic nanoparticles, the aluminum nanocrystal core can function as a nanoscale optical antenna, making it a promising catalyst for light-based reactions.
“Almost every chemical, every plastic that we use on a day-to-day basis, came from a catalytic process, and many of these catalytic processes rely on precious metals like platinum, rhodium, ruthenium and others,” Bayles said.
“Our ultimate goal is to revolutionize catalysis, making it more accessible, efficient and environmentally friendly,” said Halas, who is a University Professor, Rice’s highest academic rank. “By harnessing the potential of plasmonic photocatalysis, we’re paving the way for a brighter, more sustainable future.”
The Halas group has been developing aluminum nanoparticles for plasmonic photocatalysis reactions such as decomposition of dangerous chemical warfare agents and efficient production of commodity chemicals. The newly uncovered ability to modify the surface oxides on aluminum nanoparticles further increases their versatility for use as catalysts to efficiently convert light into chemical energy.
“If you’re doing a catalytic reaction, the molecules of the substance you’re looking to transform will interact with the aluminum oxide layer rather than with the aluminum metal core, but that metallic nanocrystal core is uniquely able to absorb light very efficiently and convert it into energy, while the oxide layer fulfills the role of a reactor, transferring that energy to reactant molecules,” Bayles said.
The properties of the nanoparticles’ oxide coating determine how they interact with other molecules or materials. The study elucidates the structure of this native oxide layer on aluminum nanoparticles and shows that simple thermal treatments — i.e. heating the particles to temperatures of up to 500 degrees Celsius (932 Fahrenheit) in different gasses — can change its structure.
“The crystalline phase, intraparticle strain and defect density can all be modified by this straightforward approach,” Bayles said. “Initially, I was convinced that the thermal treatments did nothing, but the results surprised me.”
One of the effects of the thermal treatments was to make the aluminum nanoparticles better at facilitating the conversion of carbon dioxide into carbon monoxide and water.
“Changing the alumina layer in this manner affects its catalytic properties, particularly for light-driven carbon dioxide reduction, which means the nanoparticles could be useful for producing sustainable fuels,” said Bayles, who is now a postdoctoral researcher at the National Renewable Energy Laboratory.
Bayles added that the ability “to use abundant aluminum in place of precious metals could be hugely impactful to combat climate change and opens the way for other materials to be similarly enhanced.”
“It was relatively easy to do these treatments and get big changes in catalytic behavior, which is surprising because aluminum oxide is famously not reactive — it is very stable,” Bayles said. “So for something that is a little bit more reactive — like titanium oxide or copper oxide — you might see even bigger effects.”
Photooxidation driven formation of Fe-Au linked ferrocene-based single-molecule junctions
by Woojung Lee, Liang Li, María Camarasa-Gómez, Daniel Hernangómez-Pérez, Xavier Roy, Ferdinand Evers, Michael S. Inkpen, Latha Venkataraman in Nature Communications
In a new Nature Communications study, Columbia Engineering researchers report that they have built highly conductive, tunable single-molecule devices in which the molecule is attached to leads by using direct metal-metal contacts. Their novel approach uses light to control the electronic properties of the devices and opens the door to broader use of metal-metal contacts that could facilitate electron transport across the single-molecule device.
As devices continue to shrink, their electronic components must also be miniaturized. Single-molecule devices, which use organic molecules as their conductive channels, have the potential to resolve the miniaturization and functionalization challenges faced by traditional semiconductors. Such devices offer the exciting possibility of being controlled externally by using light, but — until now — researchers have not been able to demonstrate this.
“With this work, we’ve unlocked a new dimension in molecular electronics, where light can be used to control how a molecule binds within the gap between two metal electrodes,” said Latha Venkataraman, a pioneer in molecular electronics and Lawrence Gussman Professor of Applied Physics and professor of chemistry at Columbia Engineering. “It’s like flipping a switch at the nanoscale, opening up all kinds of possibilities for designing smarter and more efficient electronic components.”
Venkataraman’s group has been studying the fundamental properties of single-molecule devices for almost two decades, exploring the interplay of physics, chemistry, and engineering at the nanometer scale. Her underlying focus is on building single-molecule circuits, a molecule attached to two electrodes, with varied functionality, where the circuit structure is defined with atomic precision.
Her group, as well as those creating functional devices with graphene, a carbon-based two-dimensional material, have known that making good electrical contacts between metal electrodes and carbon systems is a major challenge. One solution would be to use organo-metallic molecules and devise methods to interface electrical leads to the metal atoms within the molecule. Towards this goal, they decided to explore the use of organo-metallic iron-containing ferrocene molecules, which are also considered to be tiny building blocks in the world of nanotechnology. Just like LEGO pieces can be stacked together to create complex structures, ferrocene molecules can be used as building blocks to construct ultra-small electronic devices. The team used a molecule terminated by a ferrocene group comprising two carbon-based cyclopentadienyl rings that sandwich an iron atom. They then used light to leverage the electrochemical properties of the ferrocene-based molecules to form a direct bond between the ferrocene iron center and the gold (Au) electrode when the molecule was in an oxidized state (i.e. when the iron atom had lost one electron). In this state, they discovered that ferrocene could bind to the gold electrodes used to connect the molecule to the external circuitry. Technically, oxidizing the ferrocene enabled the binding of a Au0 to an Fe3+ center.
“By harnessing the light-induced oxidation, we found a way to manipulate these tiny building blocks at room temperature, opening doors to a future where light can be used to control the behavior of electronic devices at the molecular level,” said the study’s lead author Woojung Lee, who is a PhD student in Venkararaman’s lab.
Venkataraman’s new approach will enable her team to extend the types of molecular terminations (contact) chemistries they can use for creating single-molecule devices. This study also shows the ability to turn on and off this contact by using light to change the oxidation state of the ferrocene, demonstrating a light-switchable ferrocene-based single-molecule device. The light-controlled devices could pave the way for the development of sensors and switches that respond to specific light wavelengths, offering more versatile and efficient components for a wide range of technologies.
The researchers are now exploring the practical applications of light-controlled single-molecule devices. This could include optimizing device performance, studying their behavior under different environmental conditions, and refining additional functionalities enabled by the metal-metal interface.
Ligand-induced incompatible curvatures control ultrathin nanoplatelet polymorphism and chirality
by Debora Monego, Sarit Dutta, Doron Grossman, Marion Krapez, Pierre Bauer, Austin Hubley, Jérémie Margueritat, Benoit Mahler, Asaph Widmer-Cooper, Benjamin Abécassis in Proceedings of the National Academy of Sciences
Inspired by nature, nanotechnology researchers have identified ‘spontaneous curvature’ as the key factor determining how ultra-thin, artificial materials can transform into useful tubes, twists and helices.
A greater understanding of this process — which mimics how some seed pods open in nature — could unlock an array of new chiral materials that are 1,000 times thinner than a human hair, with the potential to improve the design of optical, electronic, and mechanical devices.
Chiral shapes are structures that cannot be superimposed on their mirror image, much like how your left hand is a mirror image of your right hand but cannot fit perfectly on top of it.
Spontaneous curvature induced by tiny molecules can be used to change the shape of thin nanocrystals, influenced by the crystal width, thickness, and symmetry.
The research, published in the Proceedings of the National Academy of Sciences, was conducted by members of the National Centre for Scientific Research (CNRS) in France, together with their ARC Centre of Excellence in Exciton Science colleagues, based at the University of Sydney.
Imagine a piece of paper that, when dipped into a solution, twists or curls into a spiral without any external force. This is akin to what happens at the nanoscale with certain thin materials.
Researchers have discovered that when certain types of semiconducting nanoplatelets — extremely thin, flat crystals — are coated with a layer of organic molecules called ligands, they curl into complex shapes, including tubes, twists and helices. This transformation is driven by the different forces the ligands apply to the top and bottom surfaces of the nanoplatelets.
The significance of this finding lies in the ability to predict and control the shape of these nanoplatelets by understanding the interaction between the ligands and the nanoplatelet surface.
The inspiration for this research stems from observing natural phenomena where helical structures are prevalent, from the DNA in our cells to the spontaneous twisting of seed pods. These structures possess unique properties that are highly desirable in materials science for their potential applications in mechanics, electronics, and optics.
Nanoplatelets, with their ability to form helical structures, and exceptional optical properties due to quantum confinement, stand out as a prime candidate for creating new materials with specific characteristics. These could include materials that selectively reflect light, conduct electricity in novel ways, or have unique mechanical properties.
The implications of this research are considerable. By providing a framework to understand and control the shape of nanoplatelets, scientists have a new tool to design materials with precisely-tuned properties for use in technologies ranging from advanced electronics to responsive, smart materials.
For instance, nanoplatelets could be engineered to change shape in response to environmental conditions, such as temperature or light, paving the way for materials that adapt and respond to their surroundings. This could lead to breakthroughs in creating more efficient sensors.
Moreover, the study hints at the possibility of creating materials that can switch between different shapes with minimal energy input, a feature that could be exploited in developing new forms of actuators or switches at the nanoscale.
Band gap opening of metallic single-walled carbon nanotubes via noncovalent symmetry breaking
by Francesco Mastrocinque et al in Proceedings of the National Academy of Sciences
It might look like a roll of chicken wire, but this tiny cylinder of carbon atoms — too small to see with the naked eye — could one day be used for making electronic devices ranging from night vision goggles and motion detectors to more efficient solar cells, thanks to techniques developed by researchers at Duke University.
First discovered in the early 1990s, carbon nanotubes are made from single sheets of carbon atoms rolled up like a straw.
Carbon isn’t exactly a newfangled material. All life on Earth is based on carbon. It’s the same stuff found in diamonds, charcoal, and pencil lead. What makes carbon nanotubes special are their remarkable properties. These tiny cylinders are stronger than steel, and yet so thin that 50,000 of them would equal the thickness of a human hair.
They’re also amazingly good at conducting electricity and heat, which is why, in the push for faster, smaller, more efficient electronics, carbon nanotubes have long been touted as potential replacements for silicon.
However producing nanotubes with specific properties is a challenge.
Depending on how they’re rolled up, some nanotubes are considered metallic — meaning electrons can flow through them at any energy. The problem is they can’t be switched off. This limits their use in digital electronics, which use electrical signals that are either on or off to store binary states; just like silicon semiconductor transistors switch between 0 and 1 bits to carry out computations.
Duke chemistry professor Michael Therien and his team say they’ve found a way around this. The approach takes a metallic nanotube, which always lets current through, and transforms it into a semiconducting form that can be switched on and off.
The secret lies in special polymers — substances whose molecules are hooked together in long chains — that wind around the nanotube in an orderly spiral, “like wrapping a ribbon around a pencil,” said first author Francesco Mastrocinque, who earned his chemistry Ph.D. in Therien’s lab at Duke.
The effect is reversible, they found. Wrapping the nanotube in a polymer changes its electronic properties from a conductor to a semiconductor. But if the nanotube is unwrapped, it goes back to its original metallic state.
The researchers also showed that by changing the type of polymer that encircles a nanotube, they could engineer new types of semiconducting nanotubes. They can conduct electricity, but only when the right amount of external energy is applied.
“This method provides a subtle new tool,” Therien said. “It allows you to make a semiconductor by design.”
Practical applications of the method are likely far off. “We’re a long way from making devices,” Therien added.
Mastrocinque and his co-authors say the work is important because it’s a way to design semiconductors that can conduct electricity when struck by light of certain low-energy wavelengths that are common but invisible to human eyes.
In the future, for instance, the Duke team’s work might help others engineer nanotubes that detect heat released as infrared radiation, to reveal people or vehicles hidden in the shadows. When infrared light — such as that emitted by warm-blooded animals — strikes one of these nanotube-polymer hybrids, it would generate an electric signal.
Or take solar cells: This technique could be used to make nanotube semiconductors that convert a broader range of wavelengths into electricity, to harness more of the sun’s energy.
Because of the spiral wrapper on the nanotube surface, these structures could also be ideal materials for new forms of computing and data storage that use the spins of electrons, in addition to their charge, to process and carry information.
STEM in situ thermal wave observations for investigating thermal diffusivity in nanoscale materials and devices
by Hieu Duy Nguyen et al in Science Advances
A NIMS research team has developed a technique that enables the nanoscale observation of heat propagation paths and behavior within material specimens. This was achieved using a scanning transmission electron microscope (STEM) capable of emitting a pulsed electron beam and a nanosized thermocouple — a high-precision temperature measurement device developed by NIMS.
Public interest in energy conservation and recycling has grown considerably in recent years. This change has inspired scientists to develop next-generation materials/devices capable of controlling and utilizing heat with a high degree of precision, including thermoelectric devices able to convert waste heat into electricity and heat dissipation composites that can cool electronic components exposed to high temperatures.
It has been difficult to measure nanoscale heat propagation within materials because its characteristics (i.e., the amplitudes, velocities, paths and propagation mechanisms of traveling thermal waves) vary depending on the characteristics of a material (i.e., its composition and size and the types and abundance of defects within it) to which heat is applied. The development of new techniques enabling in-situ observation of how heat flows through the nanostructures of materials had therefore been anticipated.
This research team developed a nanoscale heat propagation observation technique using a STEM in which a pulsed nanosized electron beam is applied to a specific site of a material specimen, generating heat which is then measured in the form of changing temperatures using a nanosized thermocouple developed by NIMS.
Irradiating the specimen with a pulsed electron beam enables the periodic measurement of different thermal wave phases and the analysis of thermal wave velocities and amplitudes.
In addition, precise nanoscale repositioning of irradiation sites enables the imaging of temporal changes in thermal wave phases and amplitudes. These images can be used not only to perform nanoscale thermal conductivity measurements but also to create an animated video tracking heat propagation.
The complex relationships between the microstructures of materials and how heat flows through them may be elucidated by observing nanoscale heat propagation using the in-situ technique developed in this project.
The technique may allow the investigation of complex thermal conduction mechanisms within heat dissipation composites, evaluation of interfacial thermal conduction within micro welded joints and in-situ observation of thermal behavior within thermoelectric materials.
This may contribute to the development of high-performance, high-efficiency, next-generation thermal transport materials and thermoelectric materials/devices.
Boosting exciton mobility approaching Mott-Ioffe-Regel limit in Ruddlesden−Popper perovskites by anchoring the organic cation
by Yiyang Gong et al in Nature Communications
A study, published in Nature Communications and led by Prof. Liu Xinfeng from the National Center for Nanoscience and Technology (NCNST) of the Chinese Academy of Sciences (CAS), recently reported an enhancement in exciton mobility in a two-dimensional (2D) Ruddlesden-Popper perovskite (RPP).
Exciton mobility is a critical factor influencing the optoelectronic properties of 2D RPP. However, the mobility of 2D RPP is observed to be one order of magnitude lower than that of the corresponding 3D perovskite. Various factors such as exciton-exciton annihilation, interlayer coupling, and defects can impact the exciton transport behavior in 2D RPP.
Despite substantial progress, the precise correlation between exciton transport and lattice properties, especially concerning exciton-lattice interactions, remains elusive. Furthermore, there is an urgent need to adjust exciton-phonon interactions to tailor exciton transport characteristics for applications in 2D perovskite-based optoelectronics.
Prof. Liu’s group at NCNST, and the collaborators from South China Normal University and Peking University, achieved a boosted exciton mobility approaching the Mott-Ioffe-Regel Limit (MIR) in 2D RPP by anchoring the soft butyl ammonium cation with a polymethyl methacrylate (PMMA) network at the surface.
The researchers directly monitored ultrafast exciton propagation process in (BA)2(MA)n-1PbnI3n+1 R-P perovskites by time-resolved photoluminescence microscopy. They revealed that the free exciton mobilities in exfoliated thin flakes can be improved from around 8 cm2V-1s-1 to 280 cm2V-1s-1. The mobility of the latter is close to the theoretical limit of Mott-Ioffe-Regel criterion.
Combining optical measurements and theoretical studies, the researchers revealed that the enhanced exciton mobility is attributed to the anchoring of surface BA molecules by the PMMA network, which significantly improves the lattice rigidity and reduces the disorder.
As a result, the deformation potential scattering rate reduces by eight times at room temperature, leading to the transition of exciton propagation from the hopping regime to the band-like transport regime.
These findings offer valuable insights into the mechanisms of exciton transport in 2D perovskites with a soft lattice and shed light on how to tune exciton transport properties through lattice engineering.
Toward Controlled Synthesis of 2D Crystals by CVD: Learning from the Real-Time Crystal Morphology Evolutions
by Jing Zhang et al in Nano Letters
Materials scientists at Rice University are shedding light on the intricate growth processes of 2D crystals, paving the way for controlled synthesis of these materials with unprecedented precision.
Two-dimensional materials such as graphene and molybdenum disulfide (MoS2) exhibit unique properties that hold immense promise for applications in electronics, sensors, energy storage, biomedicine and more. However, their complex growth mechanisms — inconsistent correlations exist between how the conditions for growth affect the shapes of crystals — have posed a significant challenge for researchers.
A research team at Rice’s George R. Brown School of Engineering tackled this challenge by developing a custom-built miniaturized chemical vapor deposition (CVD) system capable of observing and recording the growth of 2D MoS2 crystals in real time. The work is published online in the journal Nano Letters.
Through the use of advanced image processing and machine learning algorithms, the researchers were able to extract valuable insights from the real-time footage, including the ability to predict the conditions needed to grow very large, single-layer MoS2 crystals.
Study co-author Jun Lou, professor and associate chair of the Department of Materials Science and Nanoengineering at Rice, said this interdisciplinary approach represents a significant step forward in the field of scalable synthesis of 2D materials.
“By combining real-time experimental observations with cutting-edge machine learning techniques, we have demonstrated the potential to predict and control the growth of 2D crystals with excellent accuracy,” Lou said.
The research team’s findings have far-reaching implications for the future of 2D materials. Driven by their success with MoS2, the researchers believe that their approach can be extended to other 2D materials and heterostructures, offering a powerful platform for designing and engineering next-generation 2D materials with tailored properties.
“For example, in electronics, being able to robustly synthesize 2D crystals like MoS2 at scale could lead to faster and more efficient devices,” Lou said. “In sensors, it could lead to more sensitive and selective devices.”
“This research is an important step toward realizing the full potential of 2D materials and paves the way for the development of innovative technologies that could revolutionize a wide range of industries,” said Ming Tang, associate professor of materials science and nanoengineering and study co-author.
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