An Alternative to Kevlar – MIT and Caltech Create Nanotech Carbon Materials – Can withstand supersonic microparticle impacts
Engineers Develop a Simple Way to Desalinate Water Using Solar Energy – Reduced Costs + 4X Production Volume
An Alternative to Kevlar – MIT and Caltech Create Nanotech Carbon Materials – Can withstand supersonic microparticle impacts
Engineers Develop a Simple Way to Desalinate Water Using Solar Energy – Reduced Costs + 4X Production Volume
Superconductivity is a physical phenomenon where the electrical resistance of a material drops to zero under a certain critical temperature. Bardeen-Cooper-Schrieffer (BCS) theory is a well-established explanation that describes superconductivity in most materials. It states that Cooper pairs of electrons are formed in the lattice under sufficiently low temperature and that BCS superconductivity arises from their condensation.
While graphene itself is an excellent conductor of electricity, it does not exhibit BCS superconductivity due to the suppression of electron-phonon interactions. This is also the reason that most ‘good’ conductors such as gold and copper are ‘bad’ superconductors.
Researchers at the Center for Theoretical Physics of Complex Systems (PCS), within the Institute for Basic Science (IBS, South Korea) have reported on a novel alternative mechanism to achieve superconductivity in graphene. They achieved this feat by proposing a hybrid system consisting of graphene and 2D Bose-Einstein condensate (BEC).
Along with superconductivity, BEC is another phenomenon that arises at low temperatures. It is the fifth state of matter first predicted by Einstein in 1924. The formation of BEC occurs when low-energy atoms clump together and enter the same energy state, and it is an area that is widely studied in condensed matter physics.
A hybrid Bose-Fermi system essentially represents a layer of electrons interacting with a layer of bosons, such as indirect excitons, exciton-polaritons, etc. The interaction between Bose and Fermi particles leads to various novel fascinating phenomena, which piques interests from both the fundamental and application-oriented perspectives.
In this work, the researchers report a new mechanism of superconductivity in graphene, which arises due to interactions between electrons and “bogolons”, rather than phonons as in typical BCS systems. Bogolons, or Bogoliubov quasiparticles, are excitation within BEC which has some characteristics of a particle. In certain ranges of parameters, this mechanism permits the critical temperature for superconductivity up to 70 Kelvin within graphene.
The researchers also developed a new microscopic BCS theory which focuses specifically on the novel hybrid graphene-based system. Their proposed model also predicts that superconducting properties can be enhanced with temperature, resulting in the non-monotonous temperature dependence of the superconducting gap.
Furthermore, the research showed that the Dirac dispersion of graphene is preserved in this bogolon-mediated scheme. This indicates that this superconducting mechanism involves electrons with relativistic dispersion — a phenomenon that is not so well-explored in condensed matter physics.
“This work sheds light on an alternative way to achieve high-temperature superconductivity. Meanwhile, by controlling the properties of a condensate, we can tune the superconductivity of graphene. This suggests another channel to control the superconductor devices in the future.”, explains Ivan Savenko, the leader of the Light-Matter Interaction in Nanostructures (LUMIN) team at the PCS IBS.
Researchers unlocked the electronic properties of graphene by folding the material like origami paper.
Graphene strips folded in similar fashion to origami paper could be used to build microchips that are up to 100 times smaller than conventional chips, found physicists – and packing phones and laptops with those tiny chips could significantly boost the performance of our devices.
New research from the University of Sussex in the UK shows that changing the structure of nanomaterials like graphene can unlock electronic properties and effectively enable the material to act like a transistor.
The scientists deliberately created kinks in a layer of graphene and found that the material could, as a result, be made to behave like an electronic component. Graphene, and its nano-scale dimensions, could therefore be leveraged to design the smallest microchips yet, which will be useful to build faster phones and laptops.
Alan Dalton, professor at the school of mathematical and physics sciences at the University of Sussex, said: “We’re mechanically creating kinks in a layer of graphene. It’s a bit like nano-origami.”
“This kind of technology – ‘straintronics’ using nanomaterials as opposed to electronics – allows space for more chips inside any device. Everything we want to do with computers – to speed them up – can be done by crinkling graphene like this.”
Discovered in 2004, graphene is an atom-thick sheet of carbon atoms, which, due to its nano-sized width, is effectively a 2D material. Graphene is best known for its exceptional strength, but also for the material’s conductivity properties, which has already generated much interest in the electronics industry including from Samsung Electronics.
The field of straintronics has already shown that deforming the structure of 2D nanomaterials like graphene, but also molybdenum disulfide, can unlock key electronic properties, but the exact impact of different “folds” remains poorly understood, argued the researchers.
Yet the behavior of those materials offers huge potential for high-performance devices: for example, changing the structure of a strip of 2D material can change its doping properties, which correspond to electron density, and effectively convert the material into a superconductor.
The researchers carried an in-depth study of the impact of structural changes on properties such as doping in strips of graphene and of molybdenum disulfide. From kinks and wrinkles to pit-holes, they observed how the materials could be twisted and turned to eventually be used to design smaller electronic components.
Manoj Tripathi, research fellow in nano-structured materials at the University of Sussex, who led the research, said: “We’ve shown we can create structures from graphene and other 2D materials simply by adding deliberate kinks into the structure. By making this sort of corrugation we can create a smart electronic component, like a transistor, or a logic gate.”
The findings are likely to resonate in an industry pressed conform to Moore’s law, which holds that the number of transistors on a microchip doubles every two years, in response for growing demand for faster computing services.
The problem is, engineers are struggling to find ways to fit much more processing power into tiny chips, creating a big problem for the traditional semiconducting industry.
A tiny graphene-based transistor could significantly help overcome these hurdles. “Using these nanomaterials will make our computer chips smaller and faster. It is absolutely critical that this happens as computer manufacturers are now at the limit of what they can do with traditional semiconducting technology. Ultimately, this will make our computers and phones thousands of times faster in the future,” said Dalton.
Since it was discovered over 15 years ago, graphene has struggled to find as many applications as was initially hoped for, and the material has often been presented as a victim of its own hype. But then, it took over a century for the first silicon chip to be created after the material was discovered in 1824. Dalton and Tripathi’s research, in that light, seems to be another step towards finding a potentially game-changing use for graphene.
Graphene memristors open doors for biomimetic computing.
UNIVERSITY PARK, Pa. — As progress in traditional computing slows, new forms of computing are coming to the forefront. At Penn State, a team of engineers is attempting to pioneer a type of computing that mimics the efficiency of the brain’s neural networks while exploiting the brain’s analog nature.
Modern computing is digital, made up of two states, on-off or one and zero. An analog computer, like the brain, has many possible states. It is the difference between flipping a light switch on or off and turning a dimmer switch to varying amounts of lighting.
Neuromorphic or brain-inspired computing has been studied for more than 40 years, according to Saptarshi Das, the team leader and Penn State assistant professor of engineering science and mechanics.
What’s new is that as the limits of digital computing have been reached, the need for high-speed image processing, for instance for self-driving cars, has grown. The rise of big data, which requires types of pattern recognition for which the brain architecture is particularly well suited, is another driver in the pursuit of neuromorphic computing.
“We have powerful computers, no doubt about that, the problem is you have to store the memory in one place and do the computing somewhere else,” Das said.
The shuttling of this data from memory to logic and back again takes a lot of energy and slows the speed of computing. In addition, this computer architecture requires a lot of space. If the computation and memory storage could be located in the same space, this bottleneck could be eliminated.
“We are creating artificial neural networks, which seek to emulate the energy and area efficiencies of the brain,” explained Thomas Shranghamer, a doctoral student in the Das group and first author on a paper recently published in Nature Communications. “The brain is so compact it can fit on top of your shoulders, whereas a modern supercomputer takes up a space the size of two or three tennis courts.”
Like synapses connecting the neurons in the brain that can be reconfigured, the artificial neural networks the team is building can be reconfigured by applying a brief electric field to a sheet of graphene, the one-atomic-thick layer of carbon atoms. In this work they show at least 16 possible memory states, as opposed to the two in most oxide-based memristors, or memory resistors.
“What we have shown is that we can control a large number of memory states with precision using simple graphene field effect transistors,” Das said.
The team thinks that ramping up this technology to a commercial scale is feasible. With many of the largest semiconductor companies actively pursuing neuromorphic computing, Das believes they will find this work of interest.
In addition to Das and Shranghamer, the additional author on the paper, titled “Graphene Memristive Synapses for High Precision Neuromorphic Computing,” is Aaryan Oberoi, doctoral student in engineering science and mechanics.
The Army Research Office supported this work. The team has filed for a patent on this invention.
Tiny bubbles can solve large problems. Microbubbles—around 1-50 micrometers in diameter—have widespread applications. They’re used for drug delivery, membrane cleaning, biofilm control, and water treatment. They’ve been applied as actuators in lab-on-a-chip devices for microfluidic mixing, ink-jet printing, and logic circuitry, and in photonics lithography and optical resonators. And they’ve contributed remarkably to biomedical imaging and applications like DNA trapping and manipulation.
Given the broad range of applications for microbubbles, many methods for generating them have been developed, including air stream compression to dissolve air into liquid, ultrasound to induce bubbles in water, and laser pulses to expose substrates immersed in liquids. However, these bubbles tend to be randomly dispersed in liquid and rather unstable.
According to Baohua Jia, professor and founding director of the Centre for Translational Atomaterials at Swinburne University of Technology, “For applications requiring precise bubble position and size, as well as high stability—for example, in photonic applications like imaging and trapping—creation of bubbles at accurate positions with controllable volume, curvature, and stability is essential.” Jia explains that, for integration into biological or photonic platforms, it is highly desirable to have well controlled and stable microbubbles fabricated using a technique compatible with current processing technologies.
Balloons in graphene
Jia and fellow researchers from Swinburne University of Technology recently teamed up with researchers from National University of Singapore, Rutgers University, University of Melbourne, and Monash University, to develop a method to generate precisely controlled graphene microbubbles on a glass surface using laser pulses. Their report is published in the peer-reviewed, open-access journal, Advanced Photonics.
The group used graphene oxide materials, which consist of graphene film decorated with oxygen functional groups. Gases cannot penetrate through graphene oxide materials, so the researchers used laser to locally irradiate the graphene oxide film to generate gases to be encapsulated inside the film to form microbubbles—like balloons. Han Lin, Senior Research Fellow at Swinburne University and first author on the paper, explains, “In this way, the positions of the microbubbles can be well controlled by the laser, and the microbubbles can be created and eliminated at will. In the meantime, the amount of gases can be controlled by the irradiating area and irradiating power. Therefore, high precision can be achieved.”
Such a high-quality bubble can be used for advanced optoelectronic and micromechanical devices with high precision requirements.
The researchers found that the high uniformity of the graphene oxide films creates microbubbles with a perfect spherical curvature that can be used as concave reflective lenses. As a showcase, they used the concave reflective lenses to focus light. The team reports that the lens presents a high-quality focal spot in a very good shape and can be used as light source for microscopic imaging.
Lin explains that the reflective lenses are also able to focus light at different wavelengths at the same focal point without chromatic aberration. The team demonstrates the focusing of a ultrabroadband white light, covering visible to near-infrared range, with the same high performance, which is particularly useful in compact microscopy and spectroscopy.
Jia remarks that the research provides “a pathway for generating highly controlled microbubbles at will and integration of graphene microbubbles as dynamic and high precision nanophotonic components for miniaturized lab-on-a-chip devices, along with broad potential applications in high resolution spectroscopy and medical imaging.”
Posted By Graphene Council, Friday, June 26, 2020
Overwhelming European demand sees Australia’s battery anode company Talga Resources plan for expanded output at its new Swedish battery anode factory.
Expressions of interest received for Talga’s lithium-ion battery anode products exceed 300% of planned annual capacity of the Vittangi Anode Project, the company says.
Talnode products are now in 36 active commercial engagements covering the majority of planned European li-ion battery manufacturers and six major global automotive OEMs.
Talga says it’s expanding the scale of the Niska scoping study for the Vittangi Project to review larger anode production options as a result of this significant interest.
Li-ion battery megafactories are set to require more than 2.5 million tonnes per annum (tpa) active anode material by 2029, up from about 450,000 tpa anode production today, with Europe the fastest growing market.
That’s because worldwide li-ion battery demand continues to rapidly increase, with global battery manufacturing capacity set to exceed 2.5 tera-Watt hours (TWh) per annum by 2029 across 142 battery plants.
“Our engagement with European battery companies and automotive OEMs has grown rapidly, with customers attracted by the potential of locally produced anode at competitive costs and with world-leading sustainability,” Talga managing director Mark Thompson says.
”As we progress Talnode-C through commercial qualification stages with customers it is pleasing to note that interest now greatly exceeds our original planned production, and that the need to review expansion options has arisen this early.”
The increased interest means the company is targeting completion of the Niska scoping study in Q3 2020.
While COVID-19 has severely impacted EV sales in the short term, Bloomberg New Energy Finance data shows EV sales hold up better than internal combustion engine (ICE) vehicles due to new (lower cost) models and supportive government policies.
In the quarters prior to the COVID-19 outbreak, EV sales as a percentage of total passenger vehicles rose rapidly in the EU, with Germany and France recording increases of 100% during the period.
Numerous countries across Europe have implemented some form of financial incentives towards customer uptake of EVs, and post COVID-19 these have increased markedly in some countries.
Talga is entering the European market at a time when 100% of anode supply is still sourced from Asia. The company’s marketing team reports that, post COVID-19, localisation is becoming an increasingly significant factor influencing customer’s purchasing decisions.
Researchers at Swinburne University of Technology’s Centre for Translational Atomaterials have developed a highly efficient solar absorbing film that absorbs sunlight with minimal heat loss and rapidly heats up to 83°C in an open environment.
The graphene metamaterial film has great potential for use in solar thermal energy harvesting and conversion, thermophotovoltaics (directly converting heat to electricity), solar seawater desalination, wastewater treatment, light emitters and photodetectors.
The researchers have developed a prototype to demonstrate the photo-thermal performance and thermal stability of the film. They have also proposed a scalable and low-cost manufacturing strategy to produce this graphene metamaterial film for practical applications.
“In our previous work, we demonstrated a 90 nm graphene metamaterial heat-absorbing film,” says Professor Baohua Jia, founding Director of the Centre for Translational Atomaterials.
“In this new work, we reduced the film thickness to 30 nm and improved the performance by minimising heat loss. This work forms an exciting pillar in our atomaterial research.”
Lead author Dr. Keng-Te Lin says: “Our cost-effective and scalable structured graphene metamaterial selective absorber is promising for energy harvesting and conversion applications. Using our film an impressive solar to vapour efficiency of 96.2 percent can be achieved, which is very competitive for clean water generation using renewable energy source.”
Co-author Dr. Han Lin adds: “In addition to the long lifetime of the proposed graphene metamaterial, the solar-thermal performance is very stable under working conditions, making it attractive for industrial use. The 30 nm thickness significantly reduced the amount of the graphene materials, thus saving the costs, making it accessible for real-life applications.”
Electrons can behave like a viscous liquid as they travel through a conducting material, producing a spatial pattern that resembles water flowing through a pipe. So say researchers in Israel and the UK who have succeeded in imaging this hydrodynamic flow pattern for the first time using a novel scanning probe technique. The result will aid developers of future electronic devices, especially those based on 2D materials like graphene in which electron hydrodynamics is important.
We are all familiar with the distinctive patterns formed by water flowing in a river or stream. When the water encounters an obstacle – such as the river bank or a boat – the patterns change. The same should hold true for electron flow in a solid if the interactions between electrons are strong. This rarely occurs under normal conditions, however, since electrons tend to collide with defects and impurities in the material they travel through, rather than with each other.
Conversely, if a material is made very clean and cooled to low temperatures, it follows that electrons should travel across it unperturbed until they collide with its edges and walls. The resulting ballistic transport allows electrons to flow with a uniform current distribution because they move at the same rate near the walls as at the centre of the material.
If the temperature of this material is then increased, the electrons can begin to interact. In principle, they will then scatter off each other more frequently than they collide with the walls. In this highly interacting, hydrodynamic regime, the electrons should flow faster near the centre of a channel and slower near its walls – the same way that water behaves when it flows through a pipe.
In recent years, researchers have created extremely clean samples from 2D materials such as graphene to act as testbeds for studying electron hydrodynamics. The vast majority of this work, however, involved measuring electron transport, which only probes the physics of electrons at fixed positions along the perimeter of the device.
“Hydrodynamics, on the other hand, brings to mind dynamic images of electrons swirling around with interesting spatial patterns,” says Joseph Sulpizio, who is one of the lead authors of this new study. “Such patterns have been predicted in theory but never imaged spatially.”
Sulpizio and the other researchers, led Shahal Ilani at Israel’s Weizmann Institute for Science in collaboration with Andre Geim’s group at Manchester University, have now imaged the most fundamental spatial pattern of hydrodynamic electron flow for the first time. They obtained this parabolic or Poiseuille current profile by studying electrons travelling through a conducting graphene channel sandwiched between two hexagonal boron nitride layers equipped with electrical contacts.
Under an applied electric field, the electrons produce a voltage gradient along the current flow direction. Unfortunately, this local voltage gradient is the same for both hydrodynamic and ballistic electron flow and so cannot be used to distinguish between the two regimes. Ilani and colleagues overcame this problem by applying a weak magnetic field to the sample, which produces another voltage – the Hall voltage – perpendicular to the direction of the current. The gradient of this voltage is very different for hydrodynamic and ballistic flow.
The researchers imaged the Hall voltage profile for both flow regimes using a scanning probe recently developed in their laboratory. This ultraclean carbon nanotube single-electron-transistor-based device is held at cryogenic temperatures and is extremely sensitive to local electrostatic fields. The current flowing through it is thus indicative of the local potential of the sample and voltage gradients associated with the Hall voltage.
By measuring this current, the team was also able to observe the transition between the regime in which electron-electron scattering dominates and that in which the electrons flow ballistically. “As expected, we observed a flat Hall field profile across the graphene channels at low temperatures,” Sulpizio tells Physics World. “Upon heating, however, the profile becomes strongly parabolic, revealing less current flow near the walls and more near the centre, which indicates the transition to hydrodynamic/Poiseuille flow.”
Magic-angle graphene reveals a host of new states
The implications of the work, which has been published in Nature, are many, he says. Electron hydrodynamics only emerges at elevated temperatures (in contrast to many other kinds of electronic phenomena that exist only at very low temperatures) and this will be relevant for technological devices like computer chips that operate at room temperature. It will also be relevant in 2D van der Waals heterostructures like those made from graphene, and especially when they are super-clean. This behaviour is likely to play an important role in new generations of devices made from these materials.
“Looking further ahead, it might even be possible one day to engineer fundamentally new kinds of electronic devices that directly exploit electron hydrodynamics,” Sulpizio says. “When electrons interact hydrodynamically, their viscosity results in highly non-local spatial flow patterns that might be technologically advantageous.”
A toothpaste-like composite with hexagonal boron nitride developed by researchers at Rice University is an effective electrolyte and separator in lithium-ion batteries intended for high-temperature applications in a number of industries, including aerospace and oil and gas. (Source: Jeff Fitlow/Rice University)
One major and dangerous problem with lithium-ion batteries is that they can catch fire when heated to high temperatures, an issue that has caused damage and even death when devices ignited without warning.
Now researchers at Rice University have come up with a solution to this very serious safety problem in the form of a combined electrolyte and separator for rechargeable lithium-ion batteries that supplies energy at usable voltages and in high temperatures. The material is a toothpaste-like composite that is capable of performing well at and withstanding high temperatures without combusting.
The problem with most current lithium-battery chemistries is that they present safety concerns when heated beyond 50C (122F) due to the electrolyte/separator combination used in them, explained Marco-Tulio Rodrigues, a Rice graduate student and one of the authors of a paper on the research published in Advanced Materials Science.
The work of the Rice team addresses both the issue of developing a separator that will not cause a short circuit and an electrolyte that doesn’t have the tendency to catch fire, he said.
The batteries made with the components they developed functioned as intended in temperatures of 50C (122F) for more than a month without losing efficiency, according to researchers. Moreover, test batteries consistently operated from room temperature to 150C (302F), setting one of the widest temperature ranges ever reported for such devices, they said.
To solve the electrolyte problem, researchers used solutions based on ionic liquids in the electrolytes, which have largely been proposed as substitutes for organic solvents in the electrolyte of lithium-ion batteries because they present a much higher thermal stability, Rodrigues explained.
“These chemicals are basically special salts with a very low melting point, in such a way that they are liquid at room temperatures,” he said. “They are completely nonflammable and they do not evaporate at all until they decompose, which occurs beyond 350C (662F).”
With the electrolyte situation solved, researchers turned their attention to finding a new separator, which they addressed with a material called hexagonal boron nitride, also known as white graphene.