NT/ Researchers optimize 3D printing of optically active nanostructures
Nanotechnology & nanomaterials biweekly vol.47, 8th January — 22nd January
TL;DR
- The shape, size and optical properties of 3-dimensional nanostructures can now be simulated in advance before they are produced directly with high precision on a wide variety of surfaces. Nanoprobes or optical tweezers with sizes in the nanometre range are now within reach.
- Researchers at Tohoku University have developed guidelines for a single-nanometer magnetic tunnel junction (MTJ), allowing for performance tailoring to meet the requirements of diverse applications, ranging from AI/IoT to automobiles and space technologies.
- A study published in Nature Nanotechnology presents an innovative graphene-based neurotechnology with the potential for a transformative impact in neuroscience and medical applications. This research, spearheaded by the Catalan Institute of Nanoscience and Nanotechnology (ICN2) together with the Universitat Autònoma de Barcelona (UAB) and other national and international partners, is currently being developed for therapeutic applications through the spin-off INBRAIN Neuroelectronics.
- Recent scientific advancements have opened new opportunities for the close observation of physical phenomena. Researchers at the University of Cambridge and the University of Newcastle recently introduced a new method to measure helium atom diffraction with microscopic spatial resolution.
- A KAIST research team has developed an anti-icing and de-icing film coating technology that can apply the photothermal effect of gold nanoparticles to industrial sites without the need for heating wires, periodic spray or oil coating of anti-freeze substances, and substrate design alterations.
- RNA is thought to have sparked the origin of life by self-copying. Researchers have now revealed the atomic structure of an ‘RNA copy machine’ through cryo-EM. This breakthrough sheds light on a primordial RNA world and fuels advancements in RNA nanotechnology and medicine.
- Scientists have developed a way to convert carbon dioxide (CO2), a potent greenhouse gas, into carbon nanofibers, materials with a wide range of unique properties and many potential long-term uses. Their strategy uses tandem electrochemical and thermochemical reactions run at relatively low temperatures and ambient pressure and could successfully lock carbon away to offset or even achieve negative carbon emissions.
- Researchers have developed a new theoretical model explaining one way to make black silicon. The new etching model precisely explains how fluorine gas breaks certain bonds in the silicon more often than others, depending on the orientation of the bond at the surface. Black silicon is an important material used in solar cells, light sensors, antibacterial surfaces and many other applications.
- Researchers at Columbia University have successfully synthesized the first 2D heavy fermion material. They introduce the new material, a layered intermetallic crystal composed of cerium, silicon, and iodine (CeSiI), in a research article published in Nature.
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
Spectral Tuning of Plasmonic Activity in 3D Nanostructures via High‐Precision Nano‐Printing
by Verena Reisecker, David Kuhness, Georg Haberfehlner, Michele Brugger‐Hatzl, Robert Winkler, Anna Weitzer, David Loibner, Martina Dienstleder, Gerald Kothleitner, Harald Plank in Advanced Functional Materials
The shape, size and optical properties of 3-dimensional nanostructures can now be simulated in advance before they are produced directly with high precision on a wide variety of surfaces. Nanoprobes or optical tweezers with sizes in the nanometre range are now within reach.
For around 20 years, it has been possible to modify surfaces via nanoparticles so that they concentrate or manipulate light in the desired way or trigger other reactions.
Such optically active nanostructures can be found in solar cells and biological or chemical sensors, for example.
In order to expand their range of applications, researchers at the Institute of Electron Microscopy and Nanoanalysis (Graz University of Technology) and the Graz Centre of Electron Microscopy (ZFE) have been working for more than one decade on manufacturing not only flat nanostructures, but in particular complex, free-standing 3D architectures.
The team led by Harald Plank, Verena Reisecker and David Kuhness has achieved two breakthroughs.
It is now possible to precisely simulate the required shapes and sizes of nanostructures in advance to achieve the desired optical properties, which can then be accurately produced.
They have also managed to completely remove chemical impurities, incorporated during initial production without negatively impacting the 3D nanoarchitectures.
Until now, three-dimensional nanostructures required a time consuming trial-and-error process until the product revealed the desired optical properties. This effort has finally been eliminated.
“The consistency between simulations and real plasmonic resonances of a wide range of nanoarchitectures is very high,” explains Harald Plank. “This is a huge step forward. The hard work of the last few years has finally paid off.”
The technology is currently the only one in the world that can be used to produce complex 3-dimensional structures with individual features smaller than 10 nanometres in a controlled, single step procedure on almost any surface.
For comparison, the smallest viruses are around 20 nanometres in size.
“The biggest challenge in recent years was to transfer the 3D architectures into high-purity materials without destroying the morphology,” explains Harald Plank. “This development leap enables new optical effects and application concepts thanks to the 3D aspect.” Nanoprobes or optical tweezers with sizes in the nanometre range are now within reach.
The researchers use focused electron beam induced deposition to produce the nanostructures. The relevant surface is exposed to special gases under vacuum conditions. A finely focused electron beam splits the gas molecules, whereupon parts of them change into a solid state and adhere to the desired location.
“By precisely controlling beam movements and exposure times, we are able to produce complex nanostructures with lattice- or sheet-like building blocks in a single step,” explains Harald Plank.
By stacking these nano-volumes on top of each other, three-dimensional structures can ultimately be constructed.
Single-nanometer CoFeB/MgO magnetic tunnel junctions with high-retention and high-speed capabilities
by Junta Igarashi et al. in npj Spintronics
Researchers at Tohoku University have developed guidelines for a single-nanometer magnetic tunnel junction (MTJ), allowing for performance tailoring to meet the requirements of diverse applications, ranging from AI/IoT to automobiles and space technologies.
The breakthrough will lead to high-performance spintronic non-volatile memory, compatible with state-of-the-art semiconductor technologies. The details were published in the journal npj Spintronics on January 4, 2024.
The key characteristic of non-volatile memory is its ability to retain data in the absence of an external power source. Consequently, extensive development efforts have been directed towards non-volatile memory because of its ability to reduce power consumption in semiconductor integrated circuits (ICs). Performance requirements for non-volatile memory vary according to specific applications. For instance, AI/IoT applications demand high-speed performance, while automotive and space technologies prioritize high retention capabilities.
Spin-transfer torque magnetoresistive random access memory (STT-MRAM), a type of non-volatile memory technology that stores data by utilizing the intrinsic angular momentum of electrons, known as spin, possesses the potential to address some of the limitations associated with existing memory technologies.
The basic building block of STT-MRAM is the magnetic tunnel junction (MTJ): two ferromagnetic layers separated by a thin insulating barrier. Scientists have long tried to meet the challenge of making MTJs smaller while meeting performance requirements, but many problems remain.
STT-MRAM, employing MTJs with dimensions in the range of several tens of nanometers, has been successfully developed for automotive semiconductors using 1X nm technology nodes. Looking ahead to future nodes, however, there is a need to scale down MTJs to single-digit nanometers, or X nm, while ensuring the capability to tailor performance according to specific applications.
To do this, the research group designed a means to engineer single-nanometer MTJs with a CoFeB/MgO stack structure, a de facto standard material system. Varying the individual CoFeB layer thickness and the number of [CoFeB/MgO] stacks allowed them to control the shape and interfacial anisotropies independently — something crucial for achieving high-retention and high-speed capabilities, respectively.
As a result, the MTJ performance can be tailored for applications ranging from retention-critical to speed-critical. At the size of single nanometers, shape-anisotropy enhanced MTJs demonstrated high retention (> 10 years) at 150°C, while interfacial-anisotropy enhanced MTJs achieved fast speed switching (10 ns or shorter) below 1 V.
“Since the proposed structure can be adapted to existing facilities in major semiconductor factories, we believe that our study provides a significant contribution to the future scaling of STT-MRAM,” said Junta Igarashi, one of the lead authors of the study.
Principal Investigator Shunsuke Fukami added that “Semiconductor industries generally tend to be conscious of long-lasting scaling. In that sense, I think this work should send a strong message to them that they can rely on the future of STT-MRAM to help usher in a low-carbon society.”
Nanoporous graphene-based thin-film microelectrodes for in vivo high-resolution neural recording and stimulation
by Damià Viana, Steven T. Walston, Eduard Masvidal-Codina, Xavi Illa, Bruno Rodríguez-Meana, Jaume del Valle, Andrew Hayward, Abbie Dodd, Thomas Loret, Elisabet Prats-Alfonso, Natàlia de la Oliva, et al in Nature Nanotechnology
A study published in Nature Nanotechnology presents an innovative graphene-based neurotechnology with the potential for a transformative impact in neuroscience and medical applications. This research, spearheaded by the Catalan Institute of Nanoscience and Nanotechnology (ICN2) together with the Universitat Autònoma de Barcelona (UAB) and other national and international partners, is currently being developed for therapeutic applications through the spin-off INBRAIN Neuroelectronics.
Following years of research under the European Graphene Flagship project, ICN2 spearheaded in collaboration with the University of Manchester the development of EGNITE (Engineered Graphene for Neural Interfaces), a novel class of flexible, high-resolution, high-precision graphene-based implantable neurotechnology.
The results published in Nature Neurotechnology aim to contribute with innovative technologies to the blooming landscape of neuroelectronics and brain-computer interfaces.
EGNITE builds on the vast experience of its inventors in fabrication and medical translation of carbon nanomaterials.
This innovative technology based on nanoporous graphene integrates fabrication processes standard in the semiconductor industry to assemble graphene microelectrodes of a mere 25 µm in diameter.
The graphene microelectrodes exhibit low impedance and high charge injection, essential attributes for flexible and efficient neural interfaces.
Preclinical studies by various neuroscience and biomedical experts that partnered with ICN2, using different models for both the central and peripheral nervous system, demonstrated the capacity of EGNITE in recording high-fidelity neural signals with exceptional clarity and precision and, more importantly, afford highly targeted nerve modulation.
The unique combination of high-fidelity signal recording and precise nerve stimulation offered by EGNITE technology represents a potentially critical advancement in neuroelectronic therapeutics.
This innovative approach addresses a critical gap in neurotechnology, which has seen little advancement in materials over the last two decades. The development of EGNITE electrodes has the capacity to place graphene at the forefront of neurotechnological materials.
The technology presented today builds on the legacy of the Graphene Flagship, a European initiative that during the last decade strived to advance European strategic leadership in technologies that rely on graphene and other 2D materials.
2D Helium Atom Diffraction from a Microscopic Spot
by Nick A. von Jeinsen et al. Physical Review Letters
Recent scientific advancements have opened new opportunities for the close observation of physical phenomena. Researchers at University of Cambridge and University of Newcastle recently introduced a new method to measure helium atom diffraction with microscopic spatial resolution.
This method, outlined in a paper in Physical Review Letters, allows physicists to study electron-sensitive materials and better understand their morphology using helium microdiffraction.
“The scanning helium microscope has been developed across several research groups for over a decade with a focus on improving the resolution of the instrument and studying technological and biological samples,” Matthew Bergin, co-author of the paper, told Phys.org. “However, relatively little work had been done on using the matter wave aspect of the helium beam to study ordered surfaces with a scanning helium microscope.”
The recent study by Bergin and his colleagues builds on one of their previous papers published in Scientific Reports in 2020. In this previous work, the researchers observed the signature of diffraction from a microscopic spot on a sample, yet they could not directly measure its underlying diffraction pattern.
In their new paper, they set out to continue their work in this area. Their study’s underlying objective was to demonstrate that an atom-based matter wave could be used to form a diffraction pattern from spatially resolved regions of a surface.
“Due to the particle–wave duality of atoms, a helium beam directed at a lattice can behave like a wave and diffract from the periodic structure,” Bergin said. “Thermal energy helium atoms possess such a low energy (<100meV) that the obtained diffraction pattern is guaranteed to be uniquely sensitive to the surface structure.
“Helium atom scattering is a well-established technique that uses the position and intensity of these diffraction peaks to study a sample surface, however till now these studies have been restricted to homogenous crystals that are at least several millimeters in size.”
In their experiments, Bergin and his colleagues used a scanning helium microscope that uses a pinhole to collimate a helium beam. With this microscope and a carefully designed strategy, they were able to collect diffraction patterns from a small region (~10um) of a sample, despite using a fixed detector.
“By carefully calibrating the instrument, we can move the sample positioning and rotation stages to vary the outgoing detection angle and sample azimuth while illuminating the same spot,” Bergin explained. “The result is that we can build an exclusively surface sensitive diffraction pattern from the small, illuminated area of the sample.”
The recent work by this research team demonstrates the feasibility of using atoms to collect a diffraction pattern from a microscopic region on a sample’s surface. Their proposed method could be used by other physicists to study diffraction patterns and gather new insight about materials that cannot be precisely examined using conventional atom scattering techniques.
“The spatially resolved capabilities of the instrument combined with the excellent surface sensitivity now allows us to use atom scattering to measure the material properties of small samples with interesting surface features, such as flakes of 2D materials,” Bergin added.
“At the University of Cambridge, work has already begun on applying the technique to measure diffraction from flakes of 2D materials. Meanwhile, colleagues at the University of Newcastle are developing a new measurement stage that can directly move the detector to collect diffraction patterns without any complex calibration or manipulation of the sample.”
Plasmonic metasurfaces of cellulose nanocrystal matrices with quadrants of aligned gold nanorods for photothermal anti-icing
by Jeongsu Pyeon et al in Nature Communications
A KAIST research team has developed an anti-icing and de-icing film coating technology that can apply the photothermal effect of gold nanoparticles to industrial sites without the need for heating wires, periodic spray or oil coating of anti-freeze substances, and substrate design alterations.
The group led by Professor Hyoungsoo Kim from the Department of Mechanical Engineering (Fluid & Interface Laboratory) and Professor Dong Ki Yoon from the Department of Chemistry (Soft Material Assembly Group) revealed that they have developed an original technique that can uniformly pattern gold nanorod (GNR) particles in quadrants through simple evaporation and have used this to develop an anti-icing and de-icing surface.
Many scientists in recent years have tried to control substrate surfaces through various coating techniques, and those involving the patterning of functional nanomaterials have gained special attention. In particular, GNR is considered a promising candidate nanomaterial for its biocompatibility, chemical stability, relatively simple synthesis, and its stable and unique property of surface plasmon resonance.
To maximize the performance of GNR, it is important to achieve a high uniformity during film deposition, and a high level of rod alignment. However, achieving both criteria has thus far been a difficult challenge.
Optical and thermal performance evaluation results of gold nanorod film and demonstration of plasmonic heater for anti-icing and de-icing. Credit: Nature Communications (2023). DOI: 10.1038/s41467–023–43511–9
To solve this, the joint research team utilized cellulose nanocrystal (CNC), a next-generation functional nanomaterial that can easily be extracted from nature. By co-assembling GNR on CNC quadrant templates, the team could uniformly dry the film and successfully obtain a GNR film with a uniform alignment in a ring-shape.
Compared to existing coffee-ring films, the highly uniform and aligned GNR film developed through this research showed enhanced plasmonic photothermal properties, and the team showed that it could carry out anti-icing and de-icing functions by simply irradiating light in the visible wavelength range.
Professor Kim said, “This technique can be applied to plastic, as well as flexible surfaces. By using it on exterior materials and films, it can generate its own heat energy, which would greatly save energy through voluntary thermal energy harvesting across various applications including cars, aircraft, and windows in residential or commercial spaces, where frosting becomes a serious issue in the winter.”
Professor Yoon added, “This research is significant in that we can now freely pattern the CNC-GNR composite, which was previously difficult to create into films, over a large area. We can utilize this as an anti-icing material, and if we were to take advantage of the plasmonic properties of gold, we can also use it like stained-glass to decorate glass surfaces.”
Cryo-EM structure and functional landscape of an RNA polymerase ribozyme
by Ewan K. S. McRae, Christopher J. K. Wan, Emil L. Kristoffersen, Kalinka Hansen, Edoardo Gianni, Isaac Gallego, Joseph F. Curran, James Attwater, Philipp Holliger, Ebbe S. Andersen in Proceedings of the National Academy of Sciences
RNA is thought to have sparked the origin of life by self-copying. Researchers from Aarhus University, Denmark, and MRC LMB Cambridge, England, have revealed the atomic structure of an “RNA copy machine” through cryo-EM. This breakthrough sheds light on a primordial RNA world and fuels advancements in RNA nanotechnology and medicine.
How the intricate molecular machinery of life arose from simple beginnings has been a long-standing question.
Several lines of evidence point towards a primordial”RNA world,” where an “RNA copy machine” (a so-called replicase) started making copies of itself and other RNA molecules to kick-start evolution and life itself.
However, the ancient replicase appears to have been lost in time and its role in modern biology has been taken over by more efficient protein machines. To support the RNA world hypothesis, researchers have been seeking to re-create an equivalent of the RNA replicase in the laboratory.
While such molecular “Doppelgangers” of the ancient replicas have been discovered, both their detailed molecular structure and mode of action has remained elusive due to the difficulty of determining the structure of dynamic RNA molecules.
In a research paper published in PNAS, a team of researchers now report the first atomic structure of an RNA replicase using cryogenic electron microscopy (cryo-EM). The RNA replicase being studied was developed by the Holliger lab (MRC LMB Cambridge, UK) to be efficient at copying long templates using nucleotide triplets in the eutectic ice phase (similar to slush-ice). Returning from postdoctoral studies in the Holliger lab, Emil L. Kristoffersen, currently assistant professor at Aarhus University, facilitated a collaboration with the Andersen lab (Aarhus University, Denmark) to determine the structure of the RNA replicase by cryo-EM. Interestingly, the structure shows striking similarities to protein-based polymerases with domains for template binding, polymerization, and substrate discrimination arranged in a molecular shape resembling an open hand.
“It was surprising to find that a ribozyme that we evolved artificially in the test tube would display features of naturally occurring protein polymerases. This indicates that evolution can discover convergent molecular solutions no matter if the material is RNA or protein,” explains Philipp Holliger, program leader at MRC LMB Cambridge, UK.
To better understand how the RNA replicase works, the researchers did a comprehensive mutational study to highlight the crucial elements of the RNA structure.
This analysis confirmed features of the catalytic site but also revealed the importance of two so-called kissing-loop interactions, which bind the scaffolding and the catalytic subunits together, as well as the importance of a specific RNA domain for fidelity, that is the accuracy with which the replicase copies RNA strands.
While the researchers could not determine the structure of the replicase “in-action” while actively copying RNA, it was possible to build a model for RNA-based RNA copying that is consistent with all experimental data.
“Cryo-EM is a powerful method for studying the structure and dynamical features of RNA molecules. By combing cryo-EM data with experiments, we were able to build a model of the inner workings of this complex RNA machine,” tells Ewan McRae, who did the cryo-EM work as a postdoc in the Andersen lab at Aarhus University but has now started his own research group at Houston Methodist Research Institute, Texas, USA.
The study provides an exciting first glimpse of an RNA replicase thought to reside at the very root of the tree of life.
The currently developed RNA-based replicases are however very inefficient (as compared to protein-based polymerases) and cannot yet sustain their own replication and evolution.
The structural insight provided by the reported study may help in designing more efficient replication mechanisms and thus get us closer to developing RNA world scenarios in the test tube.
“The properties of RNA replicases may be further improved by using chemical modifications that could exist in an RNA world. In addition, research into the origin of life leads to the discovery of several novel RNA building blocks that may be used in the emerging field of RNA nanotechnology and medicine,” explains Ebbe Sloth Andersen, associate professor at Aarhus University, Denmark.
CO2 fixation into carbon nanofibres using electrochemical–thermochemical tandem catalysis
by Zhenhua Xie, Erwei Huang, Samay Garg, Sooyeon Hwang, Ping Liu, Jingguang G. Chen in Nature Catalysis
Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and Columbia University have developed a way to convert carbon dioxide (CO2), a potent greenhouse gas, into carbon nanofibers, materials with a wide range of unique properties and many potential long-term uses. Their strategy uses tandem electrochemical and thermochemical reactions run at relatively low temperatures and ambient pressure. As the scientists describe in the journal Nature Catalysis, this approach could successfully lock carbon away in a useful solid form to offset or even achieve negative carbon emissions.
“You can put the carbon nanofibers into cement to strengthen the cement,” said Jingguang Chen, a professor of chemical engineering at Columbia with a joint appointment at Brookhaven Lab who led the research. “That would lock the carbon away in concrete for at least 50 years, potentially longer. By then, the world should be shifted to primarily renewable energy sources that don’t emit carbon.”
As a bonus, the process also produces hydrogen gas (H2), a promising alternative fuel that, when used, creates zero emissions.
The idea of capturing CO2 or converting it to other materials to combat climate change is not new. But simply storing CO2 gas can lead to leaks. And many CO2 conversions produce carbon-based chemicals or fuels that are used right away, which releases CO2 right back into the atmosphere.
“The novelty of this work is that we are trying to convert CO2 into something that is value-added but in a solid, useful form,” Chen said.
Such solid carbon materials — including carbon nanotubes and nanofibers with dimensions measuring billionths of a meter — have many appealing properties, including strength and thermal and electrical conductivity. But it’s no simple matter to extract carbon from carbon dioxide and get it to assemble into these fine-scale structures. One direct, heat-driven process requires temperatures in excess of 1,000 degrees Celsius.
“It’s very unrealistic for large-scale CO2 mitigation,” Chen said. “In contrast, we found a process that can occur at about 400 degrees Celsius, which is a much more practical, industrially achievable temperature.”
The trick was to break the reaction into stages and to use two different types of catalysts — materials that make it easier for molecules to come together and react.
“If you decouple the reaction into several sub-reaction steps you can consider using different kinds of energy input and catalysts to make each part of the reaction work,” said Brookhaven Lab and Columbia research scientist Zhenhua Xie, lead author on the paper.
The scientists started by realizing that carbon monoxide (CO) is a much better-starting material than CO2 for making carbon nanofibers (CNF). Then they backtracked to find the most efficient way to generate CO from CO2.
Earlier work from their group steered them to use a commercially available electrocatalyst made of palladium supported on carbon. Electrocatalysts drive chemical reactions using an electric current. In the presence of flowing electrons and protons, the catalyst splits both CO2 and water (H2O) into CO and H2.
For the second step, the scientists turned to a heat-activated thermocatalyst made of an iron-cobalt alloy. It operates at temperatures around 400 degrees Celsius, significantly milder than a direct CO2-to-CNF conversion would require. They also discovered that adding a bit of extra metallic cobalt greatly enhances the formation of the carbon nanofibers.
“By coupling electrocatalysis and thermocatalysis, we are using this tandem process to achieve things that cannot be achieved by either process alone,” Chen said.
To discover the details of how these catalysts operate, the scientists conducted a wide range of experiments. These included computational modeling studies, physical and chemical characterization studies at Brookhaven Lab’s National Synchrotron Light Source II (NSLS-II) — using the Quick X-ray Absorption and Scattering (QAS) and Inner-Shell Spectroscopy (ISS) beamlines — and microscopic imaging at the Electron Microscopy facility at the Lab’s Center for Functional Nanomaterials (CFN).
On the modeling front, the scientists used “density functional theory” (DFT) calculations to analyze the atomic arrangements and other characteristics of the catalysts when interacting with the active chemical environment.
“We are looking at the structures to determine what are the stable phases of the catalyst under reaction conditions,” explained study co-author Ping Liu of Brookhaven’s Chemistry Division who led these calculations. “We are looking at active sites and how these sites are bonding with the reaction intermediates. By determining the barriers, or transition states, from one step to another, we learn exactly how the catalyst is functioning during the reaction.”
X-ray diffraction and x-ray absorption experiments at NSLS-II tracked how the catalysts change physically and chemically during the reactions. For example, synchrotron x-rays revealed how the presence of electric current transforms metallic palladium in the catalyst into palladium hydride, a metal that is key to producing both H2 and CO in the first reaction stage.
For the second stage, “We wanted to know what’s the structure of the iron-cobalt system under reaction conditions and how to optimize the iron-cobalt catalyst,” Xie said. The x-ray experiments confirmed that both an alloy of iron and cobalt plus some extra metallic cobalt are present and needed to convert CO to carbon nanofibers.
“The two work together sequentially,” said Liu, whose DFT calculations helped explain the process. According to our study, the cobalt-iron sites in the alloy help to break the C-O bonds of carbon monoxide. That makes atomic carbon available to serve as the source for building carbon nanofibers. Then the extra cobalt is there to facilitate the formation of the C-C bonds that link up the carbon atoms,” she explained.
“Transmission electron microscopy (TEM) analysis conducted at CFN revealed the morphologies, crystal structures, and elemental distributions within the carbon nanofibers both with and without catalysts,” said CFN scientist and study co-author Sooyeon Hwang.
The images show that, as the carbon nanofibers grow, the catalyst gets pushed up and away from the surface. That makes it easy to recycle the catalytic metal, Chen said.
“We use acid to leach the metal out without destroying the carbon nanofiber so we can concentrate the metals and recycle them to be used as a catalyst again,” he said.
This ease of catalyst recycling, commercial availability of the catalysts, and relatively mild reaction conditions for the second reaction all contribute to a favorable assessment of the energy and other costs associated with the process, the researchers said.
“For practical applications, both are really important — the CO2 footprint analysis and the recyclability of the catalyst,” said Chen. “Our technical results and these other analyses show that this tandem strategy opens a door for decarbonizing CO2 into valuable solid carbon products while producing renewable H2.”
If these processes are driven by renewable energy, the results would be truly carbon-negative, opening new opportunities for CO2 mitigation.
Orientation-dependent etching of silicon by fluorine molecules: A quantum chemistry computational study
by Omesh Dhar Dwivedi, Yuri Barsukov, Sierra Jubin, Joseph R. Vella, Igor Kaganovich in Journal of Vacuum Science & Technology A
Researchers at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have developed a new theoretical model explaining one way to make black silicon. The new etching model precisely explains how fluorine gas breaks certain bonds in the silicon more often than others, depending on the orientation of the bond at the surface. Black silicon is an important material used in solar cells, light sensors, antibacterial surfaces and many other applications.
Black silicon is made when the surface of regular silicon is etched to produce tiny nanoscale pits on the surface. These pits change the color of the silicon from gray to black and, critically, trap more light, an essential feature of efficient solar cells.
While there are many ways to make black silicon, including some that use the charged, fourth state of matter known as plasma, the new model focuses on a process that uses only fluorine gas.
PPPL Postdoctoral Research Associate Yuri Barsukov said the choice to focus on fluorine was intentional: the team at PPPL wanted to fill a gap in publicly available research.
While some papers have been published about the role of charged particles called ions in the production of black silicon, not much has been published about the role of neutral substances, such as fluorine gas.
“We now know — with great specificity — the mechanisms that cause these pits to form when fluorine gas is used,” said Barsukov, one of the authors of a new paper about the work.
“This kind of information, published publicly and openly available, benefits us all, whether we pursue further knowledge into the basic knowledge that underlines such processes or we seek to improve manufacturing processes.”
The new etching model precisely explains how fluorine gas breaks certain bonds in the silicon more often than others, depending on the orientation of the bond at the surface.
As silicon is a crystalline material, atoms bond in a rigid pattern.
These bonds can be characterized based on the way they are oriented in the pattern, with each type of orientation, or plane, identified by a bracketed number, such as (100), (110) or (111).
“If you etch silicon using fluorine gas, the etching proceeds along (100) and (110) crystal planes but does not etch (111), resulting in a rough surface after the etching,” explained Barsukov.
As the gas etches away at the silicon unevenly, pits are created on the surface of the silicon. The rougher the surface, the more light it can absorb, making rough black silicon ideal for solar cells. Smooth silicon, in contrast, is an ideal surface for creating the atomic-scale patterns necessary for computer chips.
“If you want to etch silicon while leaving a smooth surface, you should use another reactant than fluorine. It should be a reactant that etches uniformly all crystalline planes,” Barsukov said.
Two-dimensional heavy fermions in the van der Waals metal CeSiI
by Xavier Roy in Nature
Researchers at Columbia University have successfully synthesized the first 2D heavy fermion material. They introduce the new material, a layered intermetallic crystal composed of cerium, silicon, and iodine (CeSiI), in a research article published in Nature.
Heavy fermion compounds are a class of materials with electrons that are up to 1,000 times heavier than usual. In these materials, electrons get tangled up with magnetic spins that slow them down and increase their effective mass. Such interactions are thought to play important roles in a number of enigmatic quantum phenomena, including superconductivity, the movement of electrical current with zero resistance.
Researchers have been exploring heavy fermions for decades, but in the form of bulky, 3D crystals. The new material synthesized by Ph.D. student Victoria Posey in the lab of Columbia chemist Xavier Roy will allow researchers to drop a dimension.
“We’ve laid a new foundation to explore fundamental physics and to probe unique quantum phases,” said Posey.
One of the latest materials to come out of the Roy lab, CeSiI is a van der Waals crystal that can be peeled into layers that are just a few atoms thick. That makes it easier to manipulate and combine with other materials than a bulk crystal, in addition to possessing potential quantum properties that occur in 2D.
“It’s amazing that Posey and the Roy lab could make a heavy fermion so small and thin,” said senior author Abhay Pasupathy, a physicist at Columbia and Brookhaven National Laboratory. “Just like we saw with the recent Nobel Prize to quantum dots, you can do many interesting things when you shrink dimensions.”
With its middle sheet of silicon sandwiched between magnetic cerium atoms, Posey and her colleagues suspected that CeSiI, first described in a paper in 1998, might have some interesting electronic properties. Its first stop (after Posey figured out how to prepare the extremely air-sensitive crystal for transport) was a Scanning Tunneling Microscope (STM) in Abhay Pasupathy’s physics lab at Columbia.
With the STM, they observed a particular spectrum shape characteristic of heavy fermions. Posey then synthesized a non-magnetic equivalent to CeSiI and weighed the electrons of both materials via their heat capacities. CeSiI’s were heavier.
“By comparing the two — one with magnetic spins and one without — we can confirm we’ve created a heavy fermion,” said Posey.
Samples then made their way across campus and the country for additional analyses, including to Pasupathy’s lab at Brookhaven National Laboratory for photoemission spectroscopy; to Philip Kim’s lab at Harvard for electron transport measurements; and to the National High Magnetic Field Laboratory in Florida to study its magnetic properties. Along the way, theorists Andrew Millis at Columbia and Angel Rubio at Max Planck helped explain the teams’ observations.
From here, Columbia’s researchers will do what they do best with 2D materials: stack, strain, poke, and prod them to see what unique quantum behaviors can be coaxed out of them. Pasupathy plans to add CeSiI to his arsenal of materials in the search for quantum criticality, the point where a material shifts from one unique phase to another. At the crossover, interesting phenomena like superconductivity may await.
“Manipulating CeSiI at the 2D limit will let us explore new pathways to achieve quantum criticality,” said Michael Ziebel, a postdoc in the Roy group and co-corresponding author, “and this can guide us in the design of new materials.”
Back in the chemistry department, Posey, who has perfected the air-free synthesis techniques needed, is systematically replacing the atoms in the crystal — for example, swapping silicon for other metals, like aluminum or gallium — to create related heavy fermions with their own unique properties to study.
“We initially thought CeSiI was a one-off,” said Roy. “But this project has blossomed into a new kind of chemistry in my group.”
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