Tag Archives: #materials

Why Deep Freezing Iron-based Materials Makes Them Both Magnetic & Superconducting (Physics)

Physicists at Bath have uncovered a new mechanism for enabling magnetism and superconductivity to co-exist in the same material.

Physicists at the University of Bath, in collaboration with researchers from the USA, have uncovered a new mechanism for enabling magnetism and superconductivity to co-exist in the same material. Until now, scientists could only guess how this unusual coexistence might be possible. The discovery could lead to applications in green energy technologies and in the development of superconducting devices, such as next-generation computer hardware.

As a rule, superconductivity (the ability of a material to pass an electrical current with perfect efficiency) and magnetism (seen at work in fridge magnets) make poor bedfellows because the alignment of the tiny electronic magnetic particles in ferromagnets generally leads to the destruction of the electron pairs responsible for superconductivity. Despite this, the Bath researchers have found that the iron-based superconductor RbEuFe4As4, which is superconducting below -236°C, exhibits both superconductivity and magnetism below -258°C.

Physics postgraduate research student David Collomb, who led the research, explained: “There’s a state in some materials where, if you get them really cold – significantly colder than the Antarctic – they become superconducting. But for this superconductivity to be taken to next-level applications, the material needs to show co-existence with magnetic properties. This would allow us to develop devices operating on a magnetic principle, such as magnetic memory and computation using magnetic materials, to also enjoy the benefits of superconductivity.

“The problem is that superconductivity is usually lost when magnetism is turned on. For many decades, scientists have tried to explore a host of materials that have both properties in a single material, and material scientists have recently had some success fabricating a handful of such materials. However, so long as we don’t understand why the coexistence is possible, the hunt for these materials can’t be done with as fine a comb.

“This new research gives us a material that has a wide temperature range where these phenomena co-exist, and this will allow us to study the interaction between magnetism and superconductivity more closely and in great detail. Hopefully, this will result in us being able to identify the mechanism through which this co-existence can occur.”

In a study published in Physical Review Letters, the team investigated the unusual behaviour of RbEuFe4As4 by creating magnetic field maps of a superconducting material as the temperature was dropped. To their surprise, they found the vortices (the points in the superconducting material where the magnetic field penetrates) showed a pronounced broadening near the temperature of -258°C, indicating a strong suppression of superconductivity as the magnetism turned on.

crystals coasted in gold
On the left: a crystal coated in gold – the gold coating allows the magnetic imaging tool to get within nanometers of the material’s surface. On the right: a magnetic picture of a segment of the crystal showing the vortices (dark holes) that were studied. © University of Bath

These observations agree with a theoretical model recently proposed by Dr Alexei Koshelev at Argonne National Laboratory in the USA. This theory describes the suppression of superconductivity by magnetic fluctuations due to the Europium (Eu) atoms in the crystals. Here, the magnetic direction of each Eu atom begins to fluctuate and align with the others, as the material drops below a certain temperature. This causes the material to become magnetic. The Bath researchers conclude that while superconductivity is considerably weakened by the magnetic effect, it is not fully destroyed.

“This suggests that in our material, the magnetism and superconductivity are held apart from each other in their own sub-lattices, which only minimally interact,” said Mr Collomb.

“This work significantly advances our understanding of these rare coexisting phenomena and could lead to possible applications in the superconducting devices of the future. It will spawn a deeper hunt into materials that display both superconductivity and magnetism. We hope it will also encourage researchers in more applied fields to take some of these materials and make the next-generation computing devices out of them.

“Hopefully, the scientific community will gradually enter an era where we move from blue-sky research to making devices from these materials. In a decade or so, we could be seeing prototype devices using this technology that do a real job.”

The American collaborators for this project were the Argonne National Laboratory, Hofstra University and Northwestern University.

Featured image: Magnetism can be generated simply by passing a current through a wire, but how it interacts with other physical phenomena (such as superconductivity) is shrouded in mystery. © University of Bath

Reference: D. Collomb, S. J. Bending, A. E. Koshelev, M. P. Smylie, L. Farrar, J.-K. Bao, D. Y. Chung, M. G. Kanatzidis, W.-K. Kwok, and U. Welp, “Observing the Suppression of Superconductivity in RbEuFe4As4 by Correlated Magnetic Fluctuations”, Phys. Rev. Lett. 126, 157001 – Published 14 April 2021. DOI: https://doi.org/10.1103/PhysRevLett.126.157001

Provided by University of Bath

Scientists Report New Wideband Two-Dimensional Nonlinear Optical Materials and Devices (Chemistry)

Recently, Chinese scientists reported a new class of two-dimensional (2D) third-order nonlinear optical (NLO) materials, called metallated graphynes. The new material, exhibits broadband (at both 532 and 1064 nm) saturable absorption NLO property and high laser damage threshold.

Researchers prepared two free-standing mercurated graphyne nanosheets by applying an interface-assisted bottom-up method. The large-area nanosheets derived from the chemical growth have shown their layered molecular structural arrangement, controllable thickness and enhanced π-conjugation. The mercurated graphyne nanosheets are therefore having stable and outstanding broadband nonlinear saturable absorption properties.  

With the help of the absorption ability, the metallated graphynes are acting as saturable absorbers. And it has better pulse properties and Q-switched performances, especially comparing with traditional 2D materials (like graphene, black phosphorus).

The work reveals that the metallated graphyne materials can go beyond graphyne. The new material could not only be a new family of stable 2D carbon-rich materials under ambient conditions, but also possess unique properties and application prospects. It could be helpful in the future design of various structures for optoelectronic materials and devices.   

Besides, the nanosheets with controllable thickness and high transparency can be transferred on the optical glass and other substrates. It could be directly applied as free-standing films in optoelectronic devices.   

The new proposed nanosheet has advantages in optical property, mechanical processability and control of molecular dimensions. And this could be benefited the design of optoelectronic materials and fabrication of their devices in applications such as nonlinear optics, optical limiting, optical communications and so on. 

This work, published in Angewandte Chemie International Edition, was directed by the joint group of Prof. Wai-Yueng Wong from The Hong Kong Polytechnic University, Prof. XIE Zheng from the Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences, and Prof. WANG Zhengping from Shandong University. 

Featured image: Chemical Structures, Interface-assisted Preparation, and Nonlinear Optical Passively Q-switched Performances of Metallated Graphynes (Image by Wong et al.)

Reference: Dr. Linli Xu, Dr. Jibin Sun et al., “Metallated Graphynes as a New Class of Photofunctional 2D Organometallic Nanosheets”, Angewandte Chemie, Volume 133, Issue 20 p. 11427-11435. https://doi.org/10.1002/ange.202014835

Provided by Chinese Academy of Sciences

Research Team Develops New Class of Soft Materials (Material Science)

Innovation Opens New Possibilities for 3D-Printing Human Tissue

“I think you’re on mute.” This was the most-used phrase of 2020, according to Human Resources Online. Emblazoned on T-shirts and embossed on coffee-mugs, we used the meme to make fun of ourselves while learning video-conferencing tools like Zoom and Microsoft’s Teams.

But for the more than 7 million Americans who suffer from vocal disorders, not being heard is a serious matter. Many people who have normal speaking skills have great difficulty communicating when their voice box, the larynx, fails. This can occur if the vocal cords, the two bands of smooth muscle tissue in the larynx, suffer damage from an accident, surgical procedure, viral infection or cancer.

There is no replacement for the vocal cords when the damage is severe or permanent. Now, a team of materials scientists at the University of Virginia School of Engineering has developed a soft material with promise of new treatments in the future. Their novel soft material, called an elastomer, is very stretchable and 10,000 times softer than a conventional rubber, matching the mechanical properties of vocal cords. The elastomer can be 3D printed for use in health care.

LIHENG CAI, assistant professor of materials science and engineering and chemical engineering, oversees this research. Cai also holds a courtesy appointment in biomedical engineering and leads the SOFT BIOMATTER LAB at UVA. Cai’s lab works to understand and control the interactions between active soft materials, such as responsive polymers or biological gels, and living systems, such as bacteria or cells and tissues in the human body.

Cai’s post-doctoral researcher Shifeng Nian and Ph.D. student Jinchang Zhu co-first authored the team’s paper, “THREE-DIMENSIONAL PRINTABLE, EXTREMELY SOFT, STRETCHABLE, AND REVERSIBLE ELASTOMERS FROM MOLECULAR ARCHITECTURE-DIRECTED ASSEMBLY,” published and featured as a COVER ARTICLE in Chemistry of Materials. Collaborators include Baoxing Xu, associate professor of mechanical and aerospace engineering at UVA, who conducted simulations to understand the deformation of 3D-printed, extremely soft structures.

The team developed a novel strategy to make such 3D-printable soft elastomers. They used a new type of polymer with a special architecture reminiscent of the bottlebrush for cleaning small glassware, but on the molecular scale. The bottlebrush-like polymer, when linked to form a network, enables extremely soft materials mimicking biological tissues.

Cai began to prove the potential of bottlebrush polymers as a postdoctoral fellow at Harvard University’s John H. Paulson School of Engineering and Applied Sciences. Cai’s collaborative engineering of soft yet ‘dry’ rubber was published in ADVANCED MATERIALS.

Now, Cai and his team have developed a new way to use strong – yet reversible depending upon the temperature – associations to crosslink bottlebrush-like polymers to form a rubber. The idea is to use chemical synthesis to append one glassy polymer to each end of a bottlebrush-like polymer. Such glassy polymers spontaneously self-organize to form nanoscale spheres that are the same as that of plastic water bottles. They are rigid at room temperature but melt at high temperature; this can be exploited to 3D print soft structures. 

Their material’s elasticity can be fine-tuned from approximately 100 to 10,000 pascals on the scale of pressure the material can withstand. The lower limit, approximately 100 pascals, is a million times softer than plastics and 10,000 times softer than conventional 3D-printable elastomers. Moreover, they can be stretched up to 600%.

“Their extreme softness, stretchiness and thermostability bode well for future applications,” Cai said.

Cai credits Nian for developing the chemistry for synthesizing bottlebrush polymers with precisely controlled architecture to prescribe the softness and stretchability of elastomers. The elastomer can be used as an ink in a 3D printer to create a geometric shape with the qualities of rubber.

The 3D printer itself is about the size of a dorm room refrigerator. Zhu custom-designed the nozzle for the extruder system that shoots the materials in a prescribed amount in a 3D space, guided by a computer program specific to the object desired.

Nian earned his Ph.D. in chemistry from UVA in 2018, and joined Cai’s Soft Biomatter lab as a post-doc. “Dr. Cai’s group gives me an opportunity to expand my research from classical chemistry to materials development; we’re inventing a lot of cool materials with special mechanical, electrical and optical properties,” Nian said.

What’s cool about the team’s soft material is its ability to self-organize and assemble as each drop is deposited. When the silicone-based material is first loaded into the ink cartridge, it has the consistency of honey, half solid and half liquid. As printing progresses, the solvent binds the layers and then evaporates to seamlessly build the object. Moreover, you can re-do it if you make any mistakes, as the material is 100% reprocessable and recyclable.

“Conventional 3D-printable elastomers are intrinsically stiff; the process of printing often requires external mechanical support or post-treatment,” Cai said. “Here, we demonstrate our elastomer’s applicability as inks for direct-write printing 3D structures.”

Ph.D. student Jinchang Zhu calibrates the 3D printer.

To study the way the material’s molecules interconnect, Cai’s team collaborated with Guillaume Freychet and Mikhail Zhernenkov, beamline scientists at the U.S. Department of Energy’s Brookhaven National Laboratory. They conducted experiments using the NATIONAL SYNCHROTRON LIGHT SOURCE II’s  sophisticated X-ray tool, specifically the soft matter interfaces beamline, to reveal the inner makeup of the printed materials without damaging the samples.

“The SMI beamline is ideally suited for this type of research due to its high x-ray beam intensity, excellent energy and momentum transfer tunability, and very low background. Working with Cai’s team, we were able to see how the bottlebrush-like polymer assemble into a cross-linked network,” Zhernenkov said.

Cai estimates that the team is two or three years away from seeing their elastomers in practical use, an accelerated pace enabled by the team’s 3D-printing method. Sometimes called additive manufacturing, 3D printing is a research strength of UVA’s Department of Materials Science and Engineering; researchers in this arena seek to understand the physics underlying additive manufacturing processes as they create new material systems.

Improving health is just one motivator for their research.

“We believe our findings will stimulate the development of new soft materials as inks for 3D printing, which can be the basis for a broad range of adaptive devices and structures such as sensors, stretchable electronics and soft robotics,” Cai said.

A National Science Foundation CAREER award and ACS Petroleum Research Fund Doctoral New Investigator award support Cai’s research on the SUPER RUBBER he envisions for biomedical implants and tissue engineering, among other applications. His research team is continuing to work on printability to produce objects that are closer to their desired shape.

Featured image: Post-doctoral researcher Shifeng Nian seeks to understand and manipulate the properties of soft materials. © University of Virginia

Provided by University of Virginia

Materials Scientists Discover Faster, More Efficient Way to Manufacture Multifunctional Vascular Materials (Material Science)

Beckman researchers use frontal polymerization to manufacture environmentally-adaptive multifunctional materials in a matter of minutes instead of days.

Developing self-healing materials is nothing new for Nancy Sottos, Swanlund Endowed Chair, head of the Department of Materials Science and Engineering, and lead of the Autonomous Materials Systems Group.

Drawing inspiration from biological circulatory systems — such as blood vessels or the leaves on a tree — University of Illinois researchers have worked on developing vascularized structural composites for more than a decade, creating materials that are lightweight and able to self-heal and self-cool.

But now, a team of Beckman researchers led by Sottos and Mayank Garg, postdoctoral research associate and lead author of the newly published Nature Communications paper, “Rapid Synchronized Fabrication of Vascularized Thermosets and Composites,” have shortened a two-day manufacturing process to approximately two minutes by harnessing frontal polymerization of readily available resins.

“For the past several years we’ve been looking for ways to make vascular networks in high-performance materials,” Sottos said. “This is a real breakthrough for making vascular networks in structural materials in a way that saves a lot of time and saves a lot of energy.”

Synchronized manufacturing of a bioinspired structure with a hierarchical vascular network. © Beckman Institute

Garg said the simplest way to understand their work is to picture the composition of a leaf with its internal channels and structural networks. Now, imagine that the leaf is made from a tough structural material; inside, fluid flows through different spouts and channels of its interconnected vasculature. In the case of the researchers’ composites, the liquid is capable of a variety of functions, such as cooling or heating in response to extreme environments.

“We want to create these life-like structures, but we also want them to maintain their performance over substantially longer times compared to existing infrastructure by adopting an approach biology uses ubiquitously,” Garg said. “Trees have networks for transporting nutrients and water from the ground against gravity and transporting synthesized food from the leaf to the rest of the tree. The fluids flow in both directions to regulate temperature, grow new material, and repair existing material over the entire lifecycle of the tree. We try to replicate these dynamic functions in a non-biological system.”

However, creating these complex materials has historically been a long, daunting process for the Autonomous Materials Systems Group. In previous research on self-healing materials, researchers needed a hot oven, vacuum, and at least a day to create the composites. The lengthy manufacturing cycle involved curing the host material and subsequently burning or vaporizing a sacrificial template to leave behind hollow, vascular networks. Sottos said the latter process can take 24 hours. The more complicated the vascular network, the more difficult and time-consuming it is to remove.

To create the host materials, scientists opt for frontal polymerization, a reaction-thermal diffusion system that uses the generation and diffusion of heat to promote two different chemical reactions concurrently. The heat is created internally during solidification of the host and surplus heat deconstructs an embedded template in tandem to manufacture the vascular material. This means the researchers are able to shorten the process by combining two steps into one, creating the vascular networks as well as the polymerized host material without an oven. Additionally, the new process enables researchers to have more control in the creation of the networks, meaning the materials could have increased complexity and function in the future.

“With this research, we’ve figured out how to put in vascular networks by using frontal polymerization to drive the vascularization,” Sottos said. “It gets done in minutes now instead of days — and we don’t have to put it in an oven.”

Self-healing materials can be beneficial wherever strong materials are essential to maintain function under sustained damage — such as the construction of a skyscraper. But in the case of the researchers, the most likely applications are for planes, spaceships, and even the International Space Station. Sottos explained materials produced in this manner could be commercially manufactured in five to 10 years, though the researchers note that all required materials and processing equipment are currently commercially available.

Beckman Institute Director Jeff Moore, a Stanley O. Ikenberry Endowed Chair of chemistry, as well as Bliss Professor of aerospace engineering and Executive Associate Dean of The Grainger College of Engineering Philippe Geubelle were also involved in the project.

From a computational standpoint, Geubelle explained that he was able to capture the frontal polymerization and endothermic phase change taking place in the sacrificial templates.

“We performed adaptive, transient, nonlinear finite element analyses to study this competition and determine the conditions under which this simultaneous frontal polymerization and vascularization of the gel can be achieved,” he said. “This technology will lead to a more energy efficient and substantially faster way to create composites with complex microvascular networks.”

Mayank Garg © Beckman Institute

Thanks to the team’s interdisciplinary discovery, dynamic multifunctional materials are now easier to manufacture than ever before.

“This research is a combination of experimental work as well as computational work,” Garg said. “It requires synchronized communication among team members from various disciplines — chemistry, engineering, and materials science — to overhaul traditional non-sustainable manufacturing strategies.”

“There’s nothing better than to see ideas bubble up from students and postdocs in the AMS group resulting from interactions and joint group meetings,” Moore added. “The Moore Group has studied chain unzipping depolymerization reactions for years. I was delighted when I learned that the AMS team recognized how the thermal energy produced in a heat-evolving polymerization reaction could be synced to chain unzipping depolymerization in another material for the purpose of fabricating channels. The first time I saw Mayank’s results, I thought to myself, ‘I wish I’d have thought of that idea.’

Featured image: Nancy Sottos © Beckman Institute

Editor’s note: The paper “Rapid Synchronized Fabrication of Vascularized Thermosets and Composites,” can be found at https://doi.org/10.1038/s41467-021-23054-7.

Provided by Beckman Institute

New Frontier For 3D Printing: Developed Soft Materials That Repair Themselves (Material Science)

The scientific community is concentrating many studies on the multiple applications of hydrogels , polymeric materials containing large quantities of water, potentially capable of reproducing the characteristics of biological tissues. This aspect is of particular importance in the field of regenerative medicine , which has long recognized and is using the potential of these materials. In order to be effectively used to replace organic tissues, hydrogels must meet two fundamental requirements: they must have a high geometric complexity and be able to self-repair themselves following damage, just like living tissues.

The development of these materials can now be easier and cheaper thanks to the use of 3D printing: the researchers of the MP4MNT (Materials and Processing for Micro and Nanotechnologies) team of the Department of Applied Science and Technology of the Politecnico , coordinated by Professor Fabrizio Pirri , have demonstrated for the first time the possibility of manufacturing hydrogels with complex architectures that can self-repair following a tear thanks to light-activated 3D printing . The research was published by the prestigious journal Nature Communication in an article entitled “3D-printed self-healing hydrogels via Digital Light Processing” ( DOI 10.1038 / s41467-021-22802-z)

Self-healing of complex geometries© Politecnico di Torino

In reality, hydrogels with self-healing or modelable properties in complex architectures through 3D printing had already been created in the laboratory, but in this case it is a solution that encompasses both characteristics, namely the complexity of the architecture and the ability to regenerate afterwards. of damage.

Furthermore, the hydrogel was made using materials available on the market, processed by a commercial printer , thus making the proposed approach extremely flexible and potentially applicable everywhere, with new development possibilities both in the biomedical field and in that of soft-robotics.

The research was developed as part of the HYDROPRINT3D doctoral project, funded by the Compagnia di San Paolo from the “Joint Projects with Top University” initiative and conducted by the doctoral student Matteo Caprioli , under the supervision of DISAT researcher Ignazio Roppolo , in collaboration with the research group of Professor Magdassi of the Hebrew University of Jerusalem (Israel).

“For several years – says Ignazio Roppolo – within the MP4MNT group a research unit has been created, coordinated by me and Dr. Annalisa Ch Japan, which is specifically concerned with developing new materials that can be processed through light-activated 3D printing. 3D printing is able to offer a synergistic effect between the design of the object and the intrinsic properties of the materials, allowing to obtain artifacts with unique characteristics. In our perspective, it is necessary to take advantage of this synergy to best develop the potential of 3D printing so that it can truly become an element present in our everyday life. And this study falls exactly in the wake of this philosophy ”.

This research represents a first step towards the development of highly complex devices that can exploit complex geometries and intrinsic self-repair properties in various fields. In particular, once the biocompatibility studies in progress at the Polytechnic Interdepartmental Polito BIO Med Lab have been refined , it will be possible to use these structures both for basic studies on cellular mechanisms and for applications in the field of regenerative medicine.

Reference: Caprioli, M., Roppolo, I., Chiappone, A. et al. 3D-printed self-healing hydrogels via Digital Light Processing. Nat Commun 12, 2462 (2021). https://doi.org/10.1038/s41467-021-22802-z

Provided by Politecnico Di Torino

Better Metric For Thermoelectric Materials Means Better Design Strategies (Material Science)

New quantity helps experimentally classify dimensionality of thermoelectric materials

Researchers from Tokyo Metropolitan University have shown that a quantity known as “thermoelectric conductivity” is an effective measure for the dimensionality of newly developed thermoelectric nanomaterials. Studying films of semiconducting single-walled carbon nanotubes and atomically thin sheets of molybdenum sulfide and graphene, they found clear distinctions in how this number varies with conductivity, in agreement with theoretical predictions in 1D and 2D materials. Such a metric promises better design strategies for thermoelectric materials.

Thermoelectric devices take differences in temperature between different materials and generate electrical energy. The simplest example is two strips of different metals welded together at both ends to form a loop; heating one of the junctions while keeping the other cool creates an electrical current. This is called the Seebeck effect. Its potential applications promise effective usage of the tremendous amount of power that is wasted as dissipated heat in everyday life, whether it be in power transmission, industrial exhaust, or even body heat. In 1993, it was theorized that atomically thin, one-dimensional materials would have the ideal mix of properties required to create efficient thermoelectric devices. The resulting search led to nanomaterials such as semiconducting single-walled carbon nanotubes (SWCNTs) being applied.

However, there was an ongoing issue that prevented new designs and systems from being accurately characterized. The key properties of thermoelectric devices are thermal conductivity, electrical conductivity, and the Seebeck coefficient, a measure of how much voltage is created at the interface between different materials for a given temperature difference. As material science advanced into the age of nanotechnology, these numbers weren’t enough to express a key property of the new nanomaterials that were being created: the “dimensionality” of the material, or how 1D, 2D or 3D-like the material behaves. Without a reliable, unambiguous metric, it becomes difficult to discuss, let alone optimize new materials, particularly how the dimensionality of their structure leads to enhanced thermoelectric performance.

To tackle this dilemma, a team led by Professor Kazuhiro Yanagi of Tokyo Metropolitan University set out to explore a new parameter recently flagged by theoretical studies, the “thermoelectric conductivity.” Unlike the Seebeck coefficient, the team’s theoretical calculations confirmed that this value varied differently with increased conductivity for 1D, 2D and 3D systems. They also confirmed this experimentally, preparing thin films of single-walled carbon nanotubes as well as atomically thin sheets of molybdenum sulfide and graphene, archetypal materials in 1D and 2D respectively. Measurements conclusively showed that the thermoelectric conductivity of the 1D material decreased at higher values of conductivity, while the curve for 2D materials plateaued. They also note that this demonstrates how the dimensionality of the material is retained even when the material is prepared in macroscopic films, a great boost for efforts to leverage the specific dimensionality of certain structures to improve thermoelectric performance.

Combined with theoretical calculations, the team conclude that high thermoelectric conductivity, high conventional electrical conductivity, and low thermal conductivity are key goals for the engineering of new devices. They hope these measurable, tangible targets will bring much needed clarity and unity to the development of state-of-the-art thermoelectric devices.

This work was supported by JSPS KAKENHI Grants-in-Aid for Scientific Research (17H06124, 17H01069, 18H01816, 19J21142, 20H02573, 20K15117, 26102012, 25000003, 19K22127, 19K15383, 20H05189) and the JST CREST Program (MJCR17I5).

Featured image: Theoretical calculations of Seebeck coefficient and thermoelectric conductivity for 1D, 2D and 3D materials: (a)-(c) show how the Seebeck coefficient varies for 1D, 2D and 3D materials, while (d)-(f) show the thermoelectric conductivity for the same systems. No major changes in the shape of the curves are seen for (a)-(c); drastic changes are seen for (d)-(e) beyond a threshold range marked in yellow, making thermoelectric conductivity a much more sensitive, unambiguous measure for dimensionality. © Tokyo Metropolitan University

Reference: Yota Ichinose, Manaho Matsubara, Yohei Yomogida, Akari Yoshida, Kan Ueji, Kaito Kanahashi, Jiang Pu, Taishi Takenobu, Takahiro Yamamoto, and Kazuhiro Yanagi, “One-dimensionality of thermoelectric properties of semiconducting nanomaterials”, Phys. Rev. Materials 5, 025404 – Published 26 February 2021. https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.5.025404

Provided by Tokyo Metropolitan University

A Skoltech Method Helps Model the Behavior of 2D Materials Under Pressure (Material Science)

Scientists from the Skoltech Center for Energy Science and Technology (CEST) have developed a method for modelling the behavior of 2D materials under pressure. The research will help create pressure sensors based on silicene or other 2D materials. The paper was published in the ACS Nano journal.

Silicene, which is regarded as the silicon analogue of graphene, is a two-dimensional allotrope of silicon. In its normal state, a bulk silicon is a semiconductor with a diamond crystal type structure. As it thins down to one or several layers, its properties change dramatically. However, it has not yet been possible to study the change in the electronic properties of 2D materials at high pressure.

Scientists from Russia, Italy, the United States, and Belgium have developed a theoretical research method relying on quantum chemistry to study the electronic properties of 2D materials under pressure using silicene as an example. In contrast to carbon, which is stable in both 3D and 2D states, silicene is metastable and easy to interact with the environment.

“Silicon is a semiconductor in its bulk state and a metal in the 2D state. The properties of monolayer and multilayered silicene are extensively studied theoretically. Silicene is corrugated rather than flat due to the interactions between the neighboring silicon atoms. An increase in pressure should flatten silicene and change its properties, but this effect cannot yet been investigated experimentally,” explains Skoltech research scientist Christian Tantardini.

In most cases, experimental tools used to apply pressure to the material along the axis normal to its plane simultaneously produce compression in the in-plane directions of 2D material. Thus, the resulting measurements would hardly be accurate, so right now modelling appears to be the only plausible approach.

“In our case, a new theoretical approach was the only solution. As pressure is applied only along one direction, we simulate the compression of our material and try to figure out what are the reason of the changes in the electronic structure, arrangement of silicon atoms and their hybridization under different pressures, and why the layers flatten,” Skoltech Senior Research Scientist Alexander Kvashnin comments.

Accurate prediction of the behavior of silicene or other 2D materials under pressure would make silicene a promising candidate for pressure sensors. When placed inside the sensor, silicene could help determine pressure based on the material’s response to compression. This kind of sensors could be used, for instance, in drilling rigs with a high requirement for pressure control to increase the drilling force without damaging the equipment.

“We used silicene in our modelling study to test the method which could also work for other 2D materials, including more stable ones that are already manufactured and used extensively, at zero pressure” says Xavier Gonze, a visiting professor at Skoltech and a professor at the Université catholique de Louvain (UCLouvain) in Belgium.

Featured image: Modeling the behavior of 2D materials under pressure © ACS Nano (2021). DOI: 10.1021/acsnano.0c10609

Christian Tantardini, Alexander G. Kvashnin, Carlo Gatti, Boris I. Yakobson, and Xavier Gonze, “Computational Modeling of 2D Materials under High Pressure and Their Chemical Bonding: Silicene as Possible Field-Effect Transistor”, ACS Nano 2021. https://pubs.acs.org/doi/10.1021/acsnano.0c10609

Provided by Skoltech

Moiré Effect: How to Twist Material Properties (Material Science)

2D materials have triggered a boom in materials research. Now it turns out that exciting effects occur when two such layered materials are stacked and slightly twisted.

The discovery of the material graphene, which consists of only one layer of carbon atoms, was the starting signal for a global race: Today, so-called “2D materials” are produced, made of different types of atoms. Atomically thin layers that often have very special material properties not found in conventional, thicker materials.

Now another chapter is being added to this field of research: If two such 2D layers are stacked at the right angle, even more new possibilities arise. The way in which the atoms of the two layers interact creates intricate geometric patterns, and these patterns have a decisive impact on the material properties, as a research team from TU Wien and the University of Texas (Austin) has now been able to show. Phonons – the lattice vibrations of the atoms – are significantly influenced by the angle at which the two material layers are placed on top of each other. Thus, with tiny rotations of such a layer, one can significantly change the material properties.

The Moiré Effect

The basic idea can be tried out at home with two fly screen sheets – or with any other regular meshes that can be placed on top of each other: If both grids are perfectly congruent on top of each other, you can hardly tell from above whether it is one or two grids. The regularity of the structure has not changed.

But if you now turn one of the grids by a small angle, there are places where the gridpoints of the meshes roughly match, and other places where they do not. This way, interesting patterns emerge – that is the well-known moiré effect.

The Moiré-effect: two grids are stacked and twisted. This leads to intricate patterns. © TU Wien

“You can do exactly the same thing with the atomic lattices of two material layers,” says Dr. Lukas Linhart from the Institute for Theoretical Physics at TU Wien. The remarkable thing is that this can dramatically change certain material properties – for example, graphene becomes a superconductor if two layers of this material are combined in the right way.

“We studied layers of molybdenum disulphide, which, along with graphene, is probably one of the most important 2D materials,” says Prof Florian Libisch, who led the project at TU Wien.  “If you put two layers of this material on top of each other, so-called Van der Waals forces occur between the atoms of these two layers. These are relatively weak forces, but they are strong enough to completely change the behaviour of the entire system.”

In elaborate computer simulations, the research team analysed the quantum mechanical state of the new bilayer structure caused by these weak additional forces, and how this affects the vibrations of the atoms in the two layers.

The angle of rotation matters

“If you twist the two layers a little bit against each other, the Van der Waals forces cause the atoms of both layers to change their positions a little bit,” says Dr Jiamin Quan, from UT Texas in Austin. He led the experiments in Texas, which confirmed the results of the calculations: The angle of rotation can be used to adjust which atomic vibrations are physically possible in the material.

“In terms of materials science, it is an important thing to have control over phonon vibrations in this way,” says Lukas Linhart “The fact that electronic properties of a 2D material can be changed by joining two layers together was already known before. But the fact that the mechanical oscillations in the material can also be controlled by this now opens up new possibilities for us. Phonons and electromagnetic properties are closely related. Via the vibrations in the material, one can therefore intervene in important many-body effects in a controlling way.” After this first description of the effect for phonons, the researchers are now trying to describe phonons and electrons combined, hoping to learn more about important phenomena like superconductivity.

The material-physical Moiré effect thus makes the already rich research field of 2D materials even richer – and increases the chances of continuing to find new layered materials with previously unattainable properties and enables the use of 2D materials as an experimental platform for quite fundamental properties of solids.

Featured image: Two layers of a 2D-material are stacked, which influences the properties of the material. © Erik Zumalt, Lukas Linhart

Original publication

J. Quan et al., Phonon renormalization in reconstructed MoS2 moiré superlattices, Nature Materials, 2021.

Provided by Tu Wein

Study Could Help Develop Biosensors For Non-invasive Diagnosis of Diseases (Material Science)

Brazilian researchers tested the capacity of different materials to produce sensors for the detection of PCA3, a gene that is overexpressed in prostate cancer. The technique can also be used to diagnose infectious diseases, including COVID-19.

The efficacy of biosensors used in clinical tests depends critically on the surface of the device on which the biorecognition molecules are immobilized. This surface can be adjusted and sometimes controlled using self-assembled molecular monolayers as matrices. The monolayers are films made up of organic molecules that under the right conditions assemble spontaneously on metal surfaces via chemical bonds between the sulfur atoms and the metal. 

A study conducted at the University of São Paulo’s São Carlos Physics Institute (IFSC-USP) in Brazil compared the performances of two types of self-assembled monolayers, one consisting of mercaptoacetic acid (MAA) in water and ethanol, and another of 11-mercaptoundecanoic acid (11-MUA) in ethanol. The respective films were evaluated in terms of their capacity to produce sensors for detection of the gene PCA3, which is specific to prostate cancer cells.

“We showed that efficient immobilization of a simple DNA strip to detect the gene PCA3 can be achieved even in less organized monolayers, provided the terminal groups are ionized,” Paulo Augusto Raymundo Pereira, lead author of the study, told Agência FAPESP.

An article reporting the findings is published in The Journal of Physical Chemistry C.

The study was supported by FAPESP via a postdoctoral fellowship awarded to Raymundo-Pereira, and a scholarship and a Regular Research Grant awarded to other participants. Another source of funding was the Thematic Project Toward a convergence of technologies: from sensing and biosensing to information visualization and machine learning for data analysis in clinical diagnosis, led by Osvaldo Novais de Oliveira Junior, Raymundo-Pereira’s research advisor.

“The study showed that the differences in performance between biosensors made with MAA film and 11-MUA film are not due solely to monolayer organization. Carboxylate group ionization is important. For this reason, it’s necessary to know the right conditions for formation of the film with these characteristics,” Raymundo-Pereira said.

Because MAA has proved promising for biosensor matrices, the comparison of the different preparation conditions investigated in the study can contribute to the production of high-quality films. “This knowledge can help construct other types of matrix prepared with monolayers,” Raymundo-Pereira said. “It’s now available to any researcher. As a side-effect, our own group has created another biosensor to detect the novel coronavirus.”

He stressed the importance of constructing non-invasive biosensors, especially in light of the growing use of telemedicine during the pandemic because of social distancing. “In the diagnosis and monitoring of prostate cancer, which was our proof of concept, the standard procedure is to quantify the level of prostate-specific antigen or PSA,” he said. “This entails taking a blood sample from the patient, which is an invasive procedure. Moreover, the result isn’t always conclusive as a large proportion of false-positives result from high levels of PSA associated with inflammation of the prostate, for example. In this case, the medical recommendation is biopsy, which is even more invasive. The antigen expressed by the gene PCA3 can be detected in urine by users of a biosensor that could be sold by drugstores.”

“Both contributions of the study relate to more accurate diagnosis of prostate cancer and the possibility of replacing such detection methods as PCR (polymerase chain reaction), which is essential to diagnose not just cancer but also other diseases, including COVID-19,” Oliveira Junior said.

Besides the IFSC-USP group, the study involved researchers at the Brazilian National Nanotechnology Laboratory (LNNano), run by the Brazilian Center for Research in Energy and Materials (CNPEM) in Campinas, in the state of São Paulo; Hospital de Amor in Barretos, also in São Paulo; and Instituto de Pesquisa Pelé Pequeno Príncipe in Curitiba, Paraná state.

The article “Influence of the molecular orientation and ionization of self-assembled monolayers in biosensors: application to genosensors of prostate cancer antigen 3” is at: pubs.acs.org/doi/10.1021/acs.jpcc.0c09055.

Featured image: Brazilian researchers tested the capacity of different materials to produce sensors for the detection of PCA3, a gene that is overexpressed in prostate cancer. The technique can also be used to diagnose infectious diseases, including COVID-19 (prototype of the biosensor produced at the University of São Paulo: the device can be used to detect biomarkers non-invasively / Paulo A. Raymundo-Pereira, IFSC-USP)

Provided by FAPESP