NT/ New method to measure entropy production on the nanoscale
Nanotechnology & nanomaterials biweekly vol.52, 18th March — 2nd April
TL;DR
- Entropy, the amount of molecular disorder, is produced in several systems but cannot be measured directly. An equation developed by researchers at Chalmers University of Technology in Sweden, and Heinrich Heine University Düsseldorf, now sheds new light on how entropy is produced on a very short time scale in laser-excited materials.
- In the new paper, researchers describe how they nanoprinted tens of thousands of these challenging nanoparticles, stirred them into a solution, and then watched as they self-assembled into various promising crystal structures. More critically, these materials can shift between states in minutes simply by rearranging the particles into new geometric patterns.
- An international team of researchers from Queen Mary University of London, the University of Oxford, Lancaster University, and the University of Waterloo have developed a new single-molecule transistor that uses quantum interference to control the flow of electrons.
- High-power lasers are often used to modify polymer surfaces to make high-tech biomedical products, electronics and data storage components. Now Flinders University researchers have discovered a light-responsive, inexpensive sulfur-derived polymer receptive to low-power, visible light lasers — which promises a more affordable and safer production method in nanotech, chemical science and patterning surfaces in biological applications. Details of the novel system have just been published in Angewandte Chemie International Edition, featuring a laser-etched version of the famous “Mona Lisa” painting and micro-Braille printing even smaller than a pin head.
- A chemical reaction that plays a central role in ensuring the high capacity of Lithium–sulfur (Li–S) batteries is the so-called sulfur reduction reaction (SRR). This reaction has been widely studied, yet its kinetic tendencies at high current rates remain poorly understood. Researchers at the University of Adelaide, Tianjin University and Australian Synchrotron recently carried out a study aimed at delineating the kinetic trend of SRR, to inform the future development of high-power Li–S batteries. Their paper, published in Nature Nanotechnology, also introduces a nanocomposite carbon electrocatalyst that was found to boost the performance of Li–S batteries, attaining a discharge capacity retention of approximately 75%.
- A team led by Yuichiro Kato of the RIKEN Nanoscale Quantum Photonics Laboratory turned to another class of nanomaterials, known as 2D materials. These flat sheets are just a few atoms thick, but they can be much wider than a laser beam, and are far better at converting laser pulses into excitons.
- A 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.
- In a step toward nanofluidic-based neuromorphic — or brain-inspired — computing, engineers have succeeded in executing a logic operation by connecting two chips that use ions, rather than electrons, to process data.
- Water pollution from dyes used in textile, food, cosmetic and other manufacturing is a major ecological concern with industry and scientists seeking biocompatible and more sustainable alternatives to protect the environment. A new study has discovered a novel way to degrade and potentially remove toxic organic chemicals including azo dyes from wastewater, using a chemical photocatalysis process powered by ultraviolet light.
- During cell division, a ring forms around the cell equator, which contracts to divide the cell into two daughter cells. Together with researchers from Heidelberg, Dresden, Tübingen and Harvard, Professor Jan Kierfeld and Lukas Weise from the Department of Physics at TU Dortmund University have succeeded for the first time in synthesizing such a contractile ring with the help of DNA nanotechnology and uncovering its contraction mechanism. The results have been published in Nature Communications.
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
Ultrafast entropy production in pump-probe experiments
by Lorenzo Caprini et al in Nature Communications
Entropy, the amount of molecular disorder, is produced in several systems but cannot be measured directly. An equation developed by researchers at Chalmers University of Technology in Sweden, and Heinrich Heine University Düsseldorf, now sheds new light on how entropy is produced on a very short time scale in laser excited materials.
“New computational models give us new research opportunities. Extending thermodynamics for ultrashort excitations will provide novel insights into how materials function on the nanoscale,” says Matthias Geilhufe, Assistant Professor at the Department of Physics at Chalmers University of Technology.
Entropy is a measure of irreversibility and disorder and is central in thermodynamics. Two centuries ago, it was part of a conceptual breakthrough, building the theoretical framework for machines, fundamental for the industrial revolution. Today, we are seeing advances in new areas of nano and quantum devices, but still, entropy is a pivotal concept.
From a direct measure of the diffraction pattern, for instance, obtained from time-resolved X-ray scattering experiments, the ionic displacement can be deduced. Combining this measure with the shape of the THz laser pulse, they can calculate the ultrafast entropy production of the medium by applying our theoretical results.
“A system usually wants to evolve to a state with large disorder, i.e. maximum entropy. It can be compared to a sugar cube dissolving in a glass. While the sugar dissolves, the system composed of water and sugar slowly increases its entropy. The reverse process — a spontaneous formation of a sugar cube — is never observed,” says Matthias Geilhufe.
“If we turn to how entropy is formed in devices, they all need to be turned on and off, or need to move something from A to B. As a consequence, entropy is produced. In some cases, we would like to minimize the entropy production, for example to avoid information loss,” says Matthias Geilhufe.
While entropy has become a well-established concept, it cannot be measured directly. However, Matthias Geilhufe together with researchers Lorenzo Caprini and Hartmut Löwen at Heinrich Heine University Düsseldorf, have developed a computational model to measure entropy production on a very short time scale in laser excited crystalline materials.
Crystalline materials are essential for various technologies that transfer and store information over short periods, such as semiconductors in computers or magnetic storage spaces. These materials are made up of a regular crystalline lattice, whereby atoms are arranged in repeating patterns.
Laser light can shake the atoms into a collective motion which physicists call phonons. Astonishingly, phonons often behave as if they were particles. They are called quasiparticles, to distinguish them from actual particles like electrons or ions.
What the researchers have now discovered, is that the phonons — the lattice vibrations in the crystalline materials — can produce entropy in the same way as bacteria in water as shown by previous research in biological physics by Caprini and Löwen.
By the very nature of the phonon being a quasiparticle in a crystal, it can be shown that the same mathematical pattern holds as for their biological counterparts in water. This insight precisely determines the entropy and heat production in laser-excited materials and allows us to understand or even change their properties on demand.
The researchers’ computational model can also be applied to other types of material excitations and thus opens a new perspective in the field of research on ultrafast materials.
“In the long run, this knowledge can be useful for tailoring future technologies, or lead to new scientific findings,” says Matthias Geilhufe.
Direct observation of phase transitions in truncated tetrahedral microparticles under quasi-2D confinement
by David Doan et al. in Nature Communications
In nanomaterials, shape is destiny. That is, the geometry of the particle in the material defines the physical characteristics of the resulting material. “A crystal made of nano-ball bearings will arrange themselves differently than a crystal made of nano-dice and these arrangements will produce very different physical properties,” said Wendy Gu, an assistant professor of mechanical engineering at Stanford University, introducing her latest paper which appears in the journal Nature Communications.
“We’ve used a 3D nanoprinting technique to produce one of the most promising shapes known — Archimedean truncated tetrahedrons. They are micron-scale tetrahedrons with the tips lopped off.”
In the paper, Gu and her co-authors describe how they nanoprinted tens of thousands of these challenging nanoparticles, stirred them into a solution, and then watched as they self-assembled into various promising crystal structures. More critically, these materials can shift between states in minutes simply by rearranging the particles into new geometric patterns.
This ability to change “phases,” as materials engineers refer to the shapeshifting quality, is similar to the atomic rearrangement that turns iron into tempered steel, or in materials that allow computers to store terabytes of valuable data in digital form.
“If we can learn to control these phase shifts in materials made of these Archimedean truncated tetrahedrons it could lead in many promising engineering directions,” she said.
Archimedean truncated tetrahedrons (ATTs) have long been theorized to be among the most desirable of geometries for producing materials that can easily change phase, but until recently were challenging to fabricate — predicted in computer simulations yet difficult to reproduce in the real world.
Gu is quick to point out that her team is not the first to produce nanoscale Archimedean truncated tetrahedrons in quantity, but they are among the first, if not the first, to use 3D nanoprinting to do it.
“With 3D nanoprinting, we can make almost any shape we want. We can control the particle shape very carefully,” Gu explained. “This particular shape has been predicted by simulations to form very interesting structures. When you can pack them together in various ways they produce valuable physical properties.”
ATTs form at least two highly desirable geometric structures. The first is a hexagonal pattern in which the tetrahedrons rest flat on the substrate with their truncated tips pointing upward like a nanoscale mountain range. The second is perhaps even more promising, Gu said.
It is a crystalline quasi-diamond structure in which the tetrahedrons alternate in upward- and downward-facing orientations, like eggs resting in an egg carton. The diamond arrangement is considered a “Holy Grail” in the photonics community and could lead in many new and interesting scientific directions.
Most importantly, however, when properly engineered, future materials made of 3D printed particles can be rearranged rapidly, switching easily back and forth between phases with the application of a magnetic field, electric current, heat, or other engineering method.
Gu said she can imagine coatings for solar panels that change throughout the day to maximize energy efficiency, new-age hydrophobic films for airplane wings and windows that mean they never fog or ice up, or new types of computer memory. The list goes on and on.
“Right now, we’re working on making these particles magnetic to control how they behave,” Gu said of her latest research already underway using Archimedean truncated tetrahedron nanoparticles in new ways. “The possibilities are only beginning to be explored.”
Quantum interference enhances the performance of single-molecule transistors
by Zhixin Chen et al in Nature Nanotechnology
An international team of researchers from Queen Mary University of London, the University of Oxford, Lancaster University, and the University of Waterloo have developed a new single-molecule transistor that uses quantum interference to control the flow of electrons.
Transistors are the basic building blocks of modern electronics. They are used to amplify and switch electrical signals, and they are essential for everything from smartphones to spaceships. However, the traditional method of making transistors, which involves etching silicon into tiny channels, is reaching its limits.
As transistors get smaller, they become increasingly inefficient and susceptible to errors, as electrons can leak through the device even when it is supposed to be switched off, by a process known as quantum tunneling. Researchers are exploring new types of switching mechanisms that can be used with different materials to remove this effect.
In the nanoscale structures that Professor Jan Mol, Dr. James Thomas, and their group study at Queen Mary’s School of Physical and Chemical Sciences, quantum mechanical effects dominate, and electrons behave as waves rather than particles. Taking advantage of these quantum effects, the researchers built a new transistor.
The transistor’s conductive channel is a single zinc porphyrin, a molecule that can conduct electricity. The porphyrin is sandwiched between two graphene electrodes, and when a voltage is applied to the electrodes, electron flow through the molecule can be controlled using quantum interference.
Interference is a phenomenon that occurs when two waves interact with each other and either cancel each other out (destructive interference) or reinforce each other (constructive interference). In the new transistor’s case, researchers switched the transistor on and off by controlling whether the electrons interfere constructively (on) or destructively (off) as they flow through the zinc porphyrin molecule.
The researchers found that the new transistor has a very high on/off ratio, meaning that it can be turned on and off very precisely. Destructive quantum interference plays a crucial role in this by eliminating the leaky electron flow from quantum tunneling through the transistor when it is supposed to be switched off.
They also found that the transistor is very stable. Previous transistors made from a single molecule have only been able to demonstrate a handful of switching cycles. However, this device can be operated for hundreds of thousands of cycles without breaking down.
“Quantum interference is a powerful phenomenon that has the potential to be used in a wide variety of electronics applications,” said lead author Dr. James Thomas, Lecturer in Quantum Technologies at Queen Mary. “We believe that our work is a significant step towards realizing this potential.”
“Our results show that quantum interference can be used to control the flow of electrons in transistors and that this can be done in a way that is both efficient and reliable,” said co-author Professor Jan Mol. “This could lead to the development of new types of transistors that are smaller, faster, and more energy-efficient than current devices.”
The researchers also found that the quantum interference effects could be used to improve the transistor’s subthreshold swing, which is a measure of how sensitive the transistor is to changes in the gate voltage. The lower the subthreshold swing, the more efficient the transistor is.
The researchers’ transistors had a subthreshold swing of 140 mV/dec, which is better than subthreshold swings reported for other single-molecule transistors and comparable to larger devices made from materials such as carbon nanotubes.
The research is still in its initial stages, but the researchers are optimistic that the new transistor could be used to create a new generation of electronic devices. These devices could be used in a variety of applications, starting from computers and smartphones and ending with medical devices.
Modification of Polysulfide Surfaces with Low‐Power Lasers
by Abigail Mann et a in Angewandte Chemie International Edition
High-power lasers are often used to modify polymer surfaces to make high-tech biomedical products, electronics and data storage components. Now Flinders University researchers have discovered a light-responsive, inexpensive sulfur-derived polymer receptive to low-power, visible light lasers — which promises a more affordable and safer production method in nanotech, chemical science and patterning surfaces in biological applications. Details of the novel system have just been published in Angewandte Chemie International Edition, featuring a laser-etched version of the famous “Mona Lisa” painting and micro-Braille printing even smaller than a pin head.
“This could be a way to reduce the need for expensive, specialized equipment, including high-power lasers with hazardous radiation risk, while also using more sustainable materials. For instance, the key polymer is made from low-cost elemental sulfur, an industrial byproduct, and either cyclopentadiene or dicyclopentadiene,” says Matthew Flinders Professor of Chemistry Justin Chalker, from the Flinders University.
“Our study used a suite of lasers with discreet wavelengths (532, 638 and 786 nm) and powers to demonstrate a variety of surface modifications on the special polymers, including controlled swelling or etching via ablation. The facile synthesis and laser modification of these photo-sensitive polymer systems were exploited in applications such as direct-write laser lithography and erasable information storage,” says Dr. Chalker, from the Flinders University Institute for NanoScale Science and Engineering.
As soon as the laser light touches the surface, the polymer will swell or etch a pit to fashion lines, holes, spikes and channels instantly.
The discovery was made by Flinders University researcher and co-author Dr. Christopher Gibson during what was thought to be a routine analysis of a polymer first invented in the Chalker Lab in 2022 by Ph.D. candidate Samuel Tonkin and Professor Chalker.
Dr. Gibson says, “The novel polymer was immediately modified by a low-power lasers — an unusual response I had never observed before on any other common polymers. We immediately released that this phenomenon might be useful in a number of applications, so we [built] a research project around the discovery.”
“The outcome of these efforts is a new technology for generating precise patterns on the polymer surface,” she says. “It is exciting to develop and bring new microfabrication techniques to sulfur-based materials. We hope to inspire a broad range of real-world applications in our lab and beyond.”
Potential applications include new approaches to storing data on polymers, new patterned surfaces for biomedical applications, and new ways to make micro- and nanoscale devices for electronics, sensors and microfluidics.
With support from research associate Dr. Lynn Lisboa and Samuel Tonkin, the Flinders team conducted detailed analysis of how the laser modifies the polymer and how to control the type and size of modification.
Dr. Lisboa adds, “The impact of this discovery extends far beyond the laboratory, with potential use in biomedical devices, electronics, information storage, microfluidics, and many other functional material applications.
Developing high-power Li||S batteries via transition metal/carbon nanocomposite electrocatalyst engineering
by Huan Li et al in Nature Nanotechnology
Researchers at the University of Adelaide, Tianjin University and Australian Synchrotron recently carried out a study aimed at delineating the kinetic trend of SRR, to inform the future development of high-power Li–S batteries. Their paper, published in Nature Nanotechnology, also introduces a nanocomposite carbon electrocatalyst that was found to boost the performance of Li–S batteries, attaining a discharge capacity retention of approximately 75%.
Despite these advantages, the deployment of Li–S batteries has so far been limited, as many of these batteries also have a low cycle life and a high self-discharge rate. In addition, the predicted high energy density of Li–S batteries often becomes far lower when in real applications, due to the high rates at which they charge and discharge.
A chemical reaction that plays a central role in ensuring the high capacity of Li–S batteries is the so-called sulfur reduction reaction (SRR). This reaction has been widely studied, yet its kinetic tendencies at high current rates remain poorly understood.
“The activity of electrocatalysts for the sulfur reduction reaction (SRR) can be represented using volcano plots, which describe specific thermodynamic trends,” Huan Li, Rongwei Meng and their colleagues wrote in their paper. “However, a kinetic trend that describes the SRR at high current rates is not yet available, limiting our understanding of kinetics variations and hindering the development of high-power Li||S batteries. Using Le Chatelier’s principle as a guideline, we establish an SRR kinetic trend that correlates polysulfide concentrations with kinetic currents.”
To further examine the kinetic trend of the SRR at high currents, the researchers also collected synchrotron X-ray adsorption spectroscopy measurements and ran various molecular orbital computations. Overall, their results suggest that orbital occupancy in catalysts based on transition metals is linked to the concentration of polysulfide in batteries, and consequently also SRR kinetic predictions.
Based on the kinetic trend they delineated, Li, Meng and their collaborators designed a new nanocomposite electrocatalyst comprised of a carbon-based material and CoZn clusters. They then integrated this catalyst in a Li–S battery cell and tested its performance, focusing on its charge-discharge rates.
“When the electrocatalyst is used in a sulfur-based positive electrode (5 mg cm−2 of S loading), the corresponding Li||S coin cell (with an electrolyte:S mass ratio of 4.8) can be cycled for 1,000 cycles at 8°C (that is, 13.4 A gS−1, based on the mass of sulfur) and 25°C,” the researchers wrote.
“This cell demonstrates a discharge capacity retention of about 75% (final discharge capacity of 500 mAh gS−1) corresponding to an initial specific power of 26,120 W kgS−1 and specific energy of 1,306 Wh kgS−1.”
Overall, the recent study by Li, Meng and their colleagues shows that increased polysulfide concentrations promote faster SRR kinetics; thus, catalysts that boost polysulfide concentration could speed up this reaction. This result was validated both via theoretical computations and experimental measurements.
Building on their observations, the researchers already introduced one electrocatalyst that was found to enhance the capacity retention and cyclic stability of an Li–S battery. In the future, their work could inspire the design of other promising catalysts, potentially contributing to the development of new high-power Li–S battery technologies.
Resonant exciton transfer in mixed-dimensional heterostructures for overcoming dimensional restrictions in optical processes
by N. Fang et al in Nature Communications
A flat sheet of atoms can act as a kind of antenna that absorbs light and funnels its energy into carbon nanotubes, making them glow brightly. This advance could aid the development of tiny future light-emitting devices that will exploit quantum effects.
Carbon nanotubes resemble very thin, hollow wires with a diameter of just a nanometer or so. They can generate light in various ways. For example, a laser pulse can excite negatively charged electrons within the material, leaving positively charged “holes.” These opposite charges can pair up to form an energetic state known as an exciton, which may travel relatively far along a nanotube before releasing its energy as light.
In principle, this phenomenon could be exploited to make highly efficient nanoscale light-emitting devices.
Unfortunately, there are three obstacles to using a laser to generate excitons within carbon nanotubes. First, a laser beam is typically 1,000 times wider than a nanotube, so very little of its energy is actually absorbed by the material. Second, the light waves must align perfectly with the nanotube to deliver their energy effectively. Finally, the electrons in a carbon nanotube can only absorb very specific wavelengths of light.
To overcome these limitations, a team led by Yuichiro Kato of the RIKEN Nanoscale Quantum Photonics Laboratory turned to another class of nanomaterials, known as 2D materials. These flat sheets are just a few atoms thick, but they can be much wider than a laser beam, and are far better at converting laser pulses into excitons.
The researchers grew carbon nanotubes over a trench carved from an insulating material. They then placed an atomically thin flake of tungsten diselenide on top of the nanotubes. When laser pulses hit this flake, they generated excitons that moved into the nanotube and along its length, before releasing light of a longer wavelength than the laser. It took just one trillionth of a second for each exciton to pass from the 2D material into the nanotube.
By testing nanotubes with a range of different structures that affect crucial energy levels within the material, the researchers identified ideal nanotube forms that facilitate the transfer of excitons from the 2D material.
Based on this result, they intend to use band engineering — a useful concept in semiconducting engineering to realize devices with superior properties — at the atomically thin scale.
“When band engineering is applied to low-dimensional semiconductors, new physical properties and innovative functionalities are expected to emerge,” says Kato.
“We hope to utilize this concept to develop photonic and optoelectronic devices that are just a few atomic layers thick,” adds Kato. “If we can shrink them to the atomically thin limit, we expect novel quantum effects to emerge, which may become useful for future quantum technologies.”
STEM in situ thermal wave observations for investigating thermal diffusivity in nanoscale materials and devices
by Hieu Duy Nguyen, Isamu Yamada, Toshiyuki Nishimura, Hong Pang, Hyunyong Cho, Dai-Ming Tang, Jun Kikkawa, Masanori Mitome, Dmitri Golberg, Koji Kimoto, Takao Mori, Naoyuki Kawamoto 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.
Nanofluidic logic with mechano–ionic memristive switches
by Theo Emmerich, Yunfei Teng, Nathan Ronceray, Edoardo Lopriore, Riccardo Chiesa, Andrey Chernev, Vasily Artemov, Massimiliano Di Ventra, Andras Kis, Aleksandra Radenovic in Nature Electronics
Memory, or the ability to store information in a readily accessible way, is an essential operation in computers and human brains. A key difference is that while brain information processing involves performing computations directly on stored data, computers shuttle data back and forth between a memory unit and a central processing unit (CPU). This inefficient separation (the von Neumann bottleneck) contributes to the rising energy cost of computers.
Since the 1970s, researchers have been working on the concept of a memristor (memory resistor); an electronic component that can, like a synapse, both compute and store data. But Aleksandra Radenovic in the Laboratory of Nanoscale Biology (LBEN) in EPFL’s School of Engineering set her sight on something even more ambitious: a functional nanofluidic memristive device that relies on ions, rather than electrons and their oppositely charged counterparts (holes). Such an approach would more closely mimic the brain’s own — much more energy-efficient — way of processing information.
“Memristors have already been used to build electronic neural networks, but our goal is to build a nanofluidic neural network that takes advantage of changes in ion concentrations, similar to living organisms,” Radenovic says.
“We have fabricated a new nanofluidic device for memory applications that is significantly more scalable and much more performant than previous attempts,” says LBEN postdoctoral researcher Théo Emmerich. “This has enabled us, for the very first time, to connect two such ‘artificial synapses’, paving the way for the design of brain-inspired liquid hardware.”
Memristors can switch between two conductance states — on and off — through manipulation of an applied voltage. While electronic memristors rely on electrons and holes to process digital information, LBEN’s memristor can take advantage of a range of different ions. For their study, the researchers immersed their device in an electrolyte water solution containing potassium ions, but others could be used, including sodium and calcium.
“We can tune the memory of our device by changing the ions we use, which affects how it switches from on to off, or how much memory it stores,” Emmerich explains.
The device was fabricated on a chip at EPFL’s Center of MicroNanoTechnology by creating a nanopore at the center of a silicon nitride membrane. The researchers added palladium and graphite layers to create nano-channels for ions. As a current flows through the chip, the ions percolate through the channels and converge at the pore, where their pressure creates a blister between the chip surface and the graphite. As the graphite layer is forced up by the blister, the device becomes more conductive, switching its memory state to ‘on’. Since the graphite layer stays lifted, even without a current, the device ‘remembers’ its previous state. A negative voltage puts the layers back into contact, resetting the memory to the ‘off’ state.
“Ion channels in the brain undergo structural changes inside a synapse, so this also mimics biology,” says LBEN PhD student Yunfei Teng, who worked on fabricating the devices — dubbed highly asymmetric channels (HACs) in reference to the shape of the ion flow toward the central pores.
LBEN PhD student Nathan Ronceray adds that the team’s observation of the HAC’s memory action in real time is also a novel achievement in the field.
“Because we were dealing with a completely new memory phenomenon, we built a microscope to watch it in action.”
Enhanced Photocatalytic Degradation of Methyl Orange Using Nitrogen‐Functionalized MesoporousTiO2 Decorated with Au9 Nanoclusters
by Anahita Motamedisade, Amir Heydari, Yanting Yin, Abdulrahman S. Alotabi, Gunther G. Andersson in Solar RRL
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Au9 clusters deposited as co-catalysts on S-modified mesoporous TiO2 for photocatalytic degradation of methyl orange
by Anahita Motamedisade, Amir Heydari, D.J. Osborn, Abdulrahman S. Alotabi, Gunther G. Andersson in Applied Surface Science
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Au9 nanocluster adsorption and agglomeration control through sulfur modification of mesoporous TiO2
by Anahita Motamedisade, Martin R. Johnston, Amjad E.H. Alotaibi, Gunther A. Andersson in Physical Chemistry Chemical Physics
Water pollution from dyes used in textile, food, cosmetic and other manufacturing is a major ecological concern with industry and scientists seeking biocompatible and more sustainable alternatives to protect the environment.
A new study led by Flinders University has discovered a novel way to degrade and potentially remove toxic organic chemicals including azo dyes from wastewater, using a chemical photocatalysis process powered by ultraviolet light.
Professor Gunther Andersson, from the Flinders Institute for NanoScale Science and Technology, says the process involves creating metallic ‘clusters’ of just nine gold (Au) atoms chemically ‘anchored’ to titanium dioxide which in turn drives the reaction by converting the energy of absorbed UV light.
The gold nanocluster cocatalysts enhance the photocatalytic work of the titanium dioxide and reduce the time required to complete the reaction by a factor of six, according to a new journal article in Solar RRR.
“These types of heterogeneous semiconductor-mediated photocatalysis systems provide a significant advantage over other advanced chemical processes,” says Professor Andersson, from the College of Science and Engineering. “It can facilitate the mineralisation of a large range of organic pollutants, like azo dyes, into water and carbon dioxide molecules with a high degradation efficiency. A variety of physical, chemical and biological processes are currently used to remove carcinogenic and recalcitrant organic compounds from water.”
A wide range of chemical industries, including dye manufacture, textile and cosmetics production, release toxic and non-biodegradable dyes into the environment. Nearly half of the dyes used in the textile and dye industry are azo dyes. Methyl orange is widely used as a water-soluble azo dye.
With this in mind, the Flinders University nanotech researchers have also demonstrated the usefulness of this gold cluster cocatalyst and modified semiconductors for synthesis of the novel photocatalysis systems for degradation of methyl orange.
This study, just published in Applied Surface Science, tested the photocatalysis in a vortex fluidic device developed at Flinders University in Professor Colin Raston’s nanotechnology laboratory.
Co-author Flinders PhD Dr Anahita Motamedisade says traditional wastewater treatment methods often do not effectively remove dangerous contaminants from wastewater.
“The reason for this is that some chemicals, especially those with aromatic rings, are resistant to chemical, photochemical and biological degradation, says Dr Motamedisade, who is now a research fellow at the Centre for Catalysis and Clean Energy at Grifffith University. “In addition, they generate dangerous by-products by oxidizing, hydrolysing, or undergoing other chemical reactions of synthetic dyes containing wastewater, which are detectable wherever they are disposed of. We hope to build onto these more sustainable and thorough photocatalytic degradation processes to help completely remove the toxins and tackle this global problem.”
Triggered contraction of self-assembled micron-scale DNA nanotube rings
by Maja Illig et al in Nature Communications
During cell division, a ring forms around the cell equator, which contracts to divide the cell into two daughter cells. Together with researchers from Heidelberg, Dresden, Tübingen and Harvard, Professor Jan Kierfeld and Lukas Weise from the Department of Physics at TU Dortmund University have succeeded for the first time in synthesizing such a contractile ring with the help of DNA nanotechnology and uncovering its contraction mechanism. The results have been published in Nature Communications.
In synthetic biology, researchers try to recreate crucial mechanisms of life in vitro, such as cell division. The aim is to be able to synthesize minimal cells. The research team led by Professor Kerstin Göpfrich from Heidelberg University has now synthetically reproduced contractile rings for cell division using polymer rings composed of DNA nanotubes.
The formation of a ring that constricts and separates dividing cells is an important step in natural cell division. In nature, this is achieved by machinery of proteins: motor proteins powered by chemical energy from ATP hydrolysis pull together a ring of filaments of the protein actin. Adenosine triphosphate, or ATP, is a molecule that occurs in all living cells and supplies the energy for numerous cellular processes.
The contraction mechanism of the DNA rings developed by the researchers no longer relies on motor proteins powered by ATP hydrolysis. Instead, a molecular attraction between ring segments can trigger the contraction of the polymer rings.
This molecular attraction can be induced in two ways: either by crosslinking molecules with two “sticky” ends that can connect two polymer segments, or by means of the depletion interaction, where the polymers are surrounded by “crowder” molecules that press the segments together. This mechanism consumes no chemical energy, meaning that no energy source needs to be incorporated in the synthetic cell for the mechanism to function.
Professor Jan Kierfeld, Professor of Theoretical Physics, and doctoral researcher Lukas Weise are working in the field of biological physics. As part of their research work, they have developed a theoretical description and a molecular dynamics simulation of the contraction mechanism, which match the experimental results of their research partners.
To this end, they devised special methods for simulating the DNA rings on a realistic scale. Theory and the simulation make it possible to explain quantitatively how the polymer rings form and contract.
“This means we are able not only to predict that an increased concentration of ‘crowder’ molecules will make the ring smaller but also by how much smaller,” says Professor Kierfeld. In this way, it is possible to determine how the diameter of the DNA ring can be precisely controlled, which is highly significant for future applications of contractile rings in synthetic biology.
Mechanisms for cell division are an important step towards an artificial cell, the construction of which facilitates a better understanding of the functional mechanisms of natural cells and, thus, of the foundations of life.
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