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Insulator 4 Layers Heat Shield

Scientists manufacture 10 atoms thick heat shield to protect electronic devices

  • Stanford researchers demonstrated layers of materials having a thickness of just a few atoms stacked like paper sheets on top of the hot spots provide equivalent insulation to that of a 100 times thicker glass sheet.
  • Researchers used a graphene layer and three other materials having a thickness of three atoms for creating an insulator of four layers which has a thickness of 10 atoms.
  • The heat shield is very effective as on passing through each layer, atomic heat vibrations due to electrons-atom collisions are dampened, thereby losing energy.

These days smartphones, laptops come with a ton of features. Companies are making them more attractive with powerful enhancements both in design and technology. These come with a cost. In this case, devices get heated up quickly which if not controlled can lead to malfunctions and even explosion of devices.

To protect against these issues, scientists insert objects such as glass, plastic or even air layers for the purpose of insulation so that the components which generate heat such as microprocessors are prevented from damage and therefore make the use of the devices comfortable.

Researchers from the Stanford University have demonstrated that layers of materials having a thickness of just a few atoms which are stacked like paper sheets on top of the hot spots can provide equivalent insulation to that of a glass sheet that is 100 times thicker. In the near future, comparatively thinner heat shields will help in making electronic devices even more compact. The paper has been published in the journal Science Advances. Eric Pop, an electrical engineering professor said that now heat generated in electronic devices are being treated in a completely different fashion.

The heat generated from laptops or smartphones is in fact an inaudible form of sound having a high frequency. Electricity flows as the stream of electrons move through wires. In their motion, they collide with the atoms of the medium in which they are moving. With every collision, atoms of the medium vibrate and as the collisions increase the vibrations in the material generate energy which is felt as heat.

Viewing heat as a form of sound inspired scientists to draw upon principles of the physical world. Pop from his earlier stint as a radio DJ knew that recording studios are quiet due to the thick glass windows which block any external sound. This also applies to the present electronic devices. To make electronic devices thinner researchers borrowed the trick of homeowners who installed windows with air gaps between glass sheets with varying thickness to make homes quiet and warm. Sam Vaziri, lead author said that they similarly made an insulator which used several layers of material with a thickness of an atom instead of a thick glass sheet.

The atomically thin materials were only discovered 15 years ago. The first material was graphene comprising of one layer of carbon atoms. After that, researchers experimented with other materials that resembled a sheet. Researchers from Stanford used a graphene layer and three other materials having a thickness of three atoms for creating an insulator of four layers which has a thickness of 10 atoms. It is effective as on passing through each layer, atomic heat vibrations are weakened thereby losing energy.

For making these heat shields practical, scientists will have to find some technique by which they are easily produced. In the future, researchers wish to control vibrational energy inside materials similar to light and electricity. A new field of phononics is rising for understanding heat in solids as a type of sound.

Journal Ref: Ultrahigh thermal isolation across heterogeneously layered two-dimensional materials

Caltech researchers take a direct image of magic-angle twisted graphene sheets

Caltech researchers take a direct image of magic-angle twisted graphene sheets

Just over a year after researchers at MIT stunned the physics world with the discovery of the “magic angle” for stacked sheets of graphene, researchers at Caltech have directly observed and studied this material using a scanning tunnelling microscope that can image electronic properties at atomic-length scales.

Understanding the “magic angle”—a specific orientation between the stacked graphene that yields special electric properties—could pave the way to realizing the dream of room-temperature superconductors, which could transmit enormous electric currents while producing zero heat.

But first: what is the magic angle? Say you take two sheets of graphene—single-atom-thick lattices of carbon atoms—and lay one atop the other to create a bilayer material, then twist one of the sheets of graphene to shift their orientation to one another. As the orientation shifts, the electronic properties of the bilayer material will change with it. In early 2018, researchers at MIT discovered that, at a certain orientation (about 1.1 degrees of relative twist), the bilayer material, surprisingly, becomes superconducting and moreover, the superconducting properties can be controlled with the electric fields. Their discovery launched a new field of research into magic angle-oriented graphene, known as “twistronics.”

Engineers and physicists at Caltech have built upon that discovery by generating an image of the atomic structure and electronic properties of magic angle-twisted graphene, yielding new insight into the phenomenon by offering a more direct way of studying it. A paper on their work was published in the journal Nature Physics on August 5.

“This pulls back the shroud on twistronics,” says Caltech’s Stevan Nadj-Perge, corresponding author of the paper and assistant professor of applied physics and materials science in the Division of Engineering and Applied Science.

Research on the magic angle requires an extreme level of precision to get the two sheets of graphene aligned at just the right angle. Old techniques for doing so necessitated embedding the graphene in an insulating material, which had the unfortunate side effect of preventing direct study of the sample. Instead, researchers had to use indirect methods of probing the graphene sample—for example, by taking measurements of how electrons flow through it. Nadj-Perge and his colleagues developed a new method of creating samples of magic angle-twisted graphene that can be used to align the two sheets of graphene very precisely while leaving it exposed for direct observation.

Using this technique, the researchers could learn more about the electronic properties of the material at the magic angle as well as study how these properties change as the twist angle moves away from the magic value. Their work provided several key insights that will guide future theoretical modeling and experiments, including the observation that the electronic correlation plays an important role near the charge-neutrality point—the angle at which the bilayer is electronically neutral.

“Previously, it was thought that correlation effects do not play a major role in charge neutrality,” Nadj-Perge says. “Closer, more detailed examination of samples like this could help us to explain why the exotic electronic effects near the magic angle exist. Once we know that, we could help pave the way for useful applications of it, perhaps even leading to room-temperature superconductivity one day.”

The paper is titled “Electronic correlations in twisted bilayer graphene near the magic angle.”Co-authors of the paper include Gil Refael, Taylor W. Lawrence Professor of Theoretical Physics; Jason Alicea, professor of theoretical physics; Caltech graduate students Youngjoon Choi, Harpreet Arora, Robert Polski, and Yiran Zhang; Caltech postdoctoral scholars Jeannette Kemmer, Yang Peng, Alex Thomson, Hechen Ren; as well as Felix von Oppen of Freie Universität Berlin in Germany; and Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Japan. This research was funded by the National Science Foundation, the Kavli Nanoscience Institute, the Institute for Quantum Information and Matter at Caltech, the Walter Burke Institute for Theoretical Physics at Caltech, the Deutsche Forschungsgemeinschaft, the Kwanjeong Educational Foundation, and the Transregional Collaborative Research Center 183.

single atomic layer graphite

Researchers discover quantum phenomenon to understand fundamental limits of graphene electronics

Scientists from the University of Manchester, Nottingham and Loughborough have discovered a quantum phenomenon for understanding the fundamental limits of graphene electronics. It describes the way electrons in one atomic-thin sheet of graphene scatter the vibrating carbon atoms that make the hexagonal crystal lattice. The study has been published in Nature Communications.

Applying magnetic field perpendicular to graphene plane, current-carrying electrons are forced to move in the “cyclotron orbits” which are closed and circular. In pure graphene, electrons escape from the orbit by bouncing off “phonon” while scattering. Phonons are particle-like bundles of momentum and energy and are “quanta” of sound waves that are associated with vibrating carbon atom. When graphene crystal is warmed from very low temperature, they are generated in large numbers.

The team passed a small electric current through graphene sheet for precisely measuring the amount of momentum and energy which is transferred between electron and phonon while scattering. It revealed that two kinds of phonons scatter electrons, transverse acoustic (TA) phonons where carbon atoms vibrate perpendicular to the direction in which phonon propagates and wave motion and longitudinal acoustic phonons (LA) where carbon atoms vibrate in the direction of phonon and wave motion. These accurately measure the speeds of two kinds of phonons which is difficult to make in a single atomic layer. It also shows that TA phonon scattering dominates LA phonon scattering.

This phenomenon is termed as magnetophonon oscillation and it was measured in many semiconductors several years before graphene was discovered. It has been known longer than the quantum Hall effect and is one of the oldest quantum transport phenomena.

Roshan Krishna Kumar and Laurence Eaves, co-authors in the work said that they were surprised to discover such magnetophonon oscillations in graphene and at the same time confused why it had not been discovered before in graphene. It had two key requirements. Scientists had to fabricate high-quality transistors of graphene having large areas at National Graphene Institute. It had not been discovered if the device dimensions were smaller than a few micrometers. 

Piranavan Kumaravadivel, University of Manchester and lead author of the paper said that macroscopic, millimeter-sized crystals were studied at the beginning of quantum transport experiments. The studied devices in most work on quantum transport on graphene are normally a few micrometers in size. Larger graphene devices are important for both applications and fundamental studies. 

The next ingredient is temperature. Graphene quantum transport experiments are carried out at ultra-cold temperatures for slowing the carbon atoms which are vibrating and “freeze-out” the phonons which break quantum coherence. So graphene is warmed so that phonons are active to cause the effect.

Mark Greenaway, Loughborough University who also worked on the quantum theory of this effect said that the result is quite exciting as it opens a new route for understanding the phonon properties in two-dimensional crystals and heterostructures. It will also help to understand electron-phonon interactions in promising materials which is vital for new devices and applications.

Research Paper: https://www.nature.com/articles/s41467-019-11379-3

graphene structure

Researchers demonstrate production of graphene using bacteria

Researchers have figured out a novel method to produce graphene, an amazing substance in a cheaper way with the help of bacteria. Graphene is a very useful material in filtering water, dyeing hair and great strengthening of substances. The study has been published in ChemistryOpen.

When the bacterium Shewanella oneidensis is mixed with oxidized graphite or graphene oxide (which is comparatively easy to produce but not conductive due to oxygen groups), the oxygen groups are withdrawn and conductive graphene is obtained as the product. It is inexpensive, quicker and more eco-friendly than the existing methods to produce the substance. It can also be stored for a long period of time making it appropriate for various applications. Using this method, we can produce graphene at a scale required for computing and medical devices of the next generation.

“For real applications, you need large amounts,” says biologist Anne Meyer from the University of Rochester in New York.

Using the new method, Meyer and her colleagues were able to make graphene that’s thinner, more stable, and longer-lasting than graphene that’s produced by chemical manufacturing. This will unlock all sort of opportunities for less costly bacteria-produced graphene and can be used in field-effect transistor (FET) biosensors.  It is a tool that identifies specific biological molecule such as glucose tracking for diabetics.

Bacteria production method leaves back specific oxygen group. It makes resulting graphene compatible to link with specific molecules. Graphene material obtained from this method can be used as conductive ink in circuit boards, computer keyboards or in small wires to unfreeze car windscreen or to produce one-sided conductive graphene by twisting the bacteria process. It can also lead to the creation of innovative computer technologies and medical equipment.

At present, graphene is produced by different chemical methods using graphite or graphene oxide compared to the past method where graphite was extracted by graphite blocks using sticky tape. The new method of production is the most favorable one to date without the use of unpleasant chemicals. Prior to scaling up and using it to develop next-generation devices, lots of research needs to be done to study the bacteria process. However, the future of this extraordinary material continues to look bright. Meyer said that bacterially produced graphene material will guide to much better applicability for product development and development of nanocomposite materials.

Journal: https://onlinelibrary.wiley.com/doi/full/10.1002/open.201900186

Graphene goes to space

Graphene goes to space

The Materials Science Experiment Rocket (MASER) 14 was launched from the European Space Centre in Esrange, Sweden, in collaboration with the European Space Agency (ESA) and the Swedish Space Corporation (SSC).

This rocket launch is the next step towards our major milestone: bringing graphene to the International Space Station

–Andrea Ferrari

The experiment aims to test the possibilities of printing graphene inks in space. Graphene inks can be used in the production of batteries, supercapacitors, printed electronics, and more. If researchers are able to demonstrate how these inks work in space, astronauts could potentially print their own devices on the go, or they can repair electronics with graphene ink printers.

The experiments conducted this week were a collaboration led by the University of Brussels, with Cambridge, Pisa, and ESA. The inks that were tested in the experiments were produced by the research group of Professor Andrea Ferrari, Director of the Cambridge Graphene Centre.

Studying the different self-assembly modes of graphene into functional patterns in zero gravity will enable the fabrication of graphene electronic devices during long-term space missions, as well as help understand fundamental properties of graphene printing on Earth.

Cambridge researchers pioneered the use of liquid phase exfoliation, one of the most common means of producing graphene, to prepare inks from graphene and related materials. Such inks are now used to print devices ranging from flexible electronic sensors and gauges to batteries and supercapacitors.

The experiments will allow researchers to better understand the fundamentals of the printing process on Earth, by removing the presence of gravity and studying how graphene flakes self-assemble.

These experiments are a first step towards making graphene printing available for long term space exploration, since astronauts may need to print electronic devices on demand during long-term missions. Graphene-based composites may also be used to offer radiation protection, a compulsory requirement for human spaceflight, for example during Mars-bound missions.

During its short flight, the MASER rocket experiences microgravity for six minutes, during which time the researchers carry out the tests of graphene’s properties. When the rocket returns to Earth, the samples are retrieved and analyses are carried out. The rocket tests are an extension of a zero-gravity parabolic flight in May 2018, where experiments were conducted during just 24 seconds of microgravity.

“There is no better way to validate graphene’s potential than to send it to the environment it will be used in,” said Carlo lorio, leader of the space activities carried out by the Graphene Flagship, and a researcher at Graphene Flagship partner Université Libre de Bruxelles. “Graphene has unique conductivity properties that scientists are continuing to take advantage of in new processes, devices and in this case, coatings. Experiments like these are fundamental to graphene’s success and integral for building the material’s reputation as the leading material for space applications.”

“The Graphene Flagship has pioneered the exploration of graphene for space applications since 2017,” said Ferrari, who is also Science and Technology Officer of the Graphene Flagship and Chair of its Management Panel. “With three microgravity campaigns in parabolic flights already concluded and a fourth one on the way, this rocket launch is the next step towards our major milestone: bringing graphene to the International Space Station. Space is the limit for graphene. Or, is it?”

Materials provided by the University of Cambridge

The Bukobot Reprap 3D Printer

Graphene based ink that could be used for printing energy storage devices

Scientists have developed an ink based on graphene nanosheets and also demonstrated that this ink can be used for printing 3D structures. This ink based on graphene can be produced on a large scale at very low costs in an eco-friendly manner. This can result in the wide-scale development of a large variety of printable energy storage equipment.

The group of researchers led by Jingyu Sun and Zhongfan Liu from Soochow University and  Beijing Graphene Institute respectively have published a study on their work in ACS Nano journal.

Sun said that their work makes use of the green synthesis of graphene nanosheets that are nitrogen-doped on a salt template with the help of chemical vapour deposition. This gives the room for exploring derived inks in the field of printable energy storage in a greater way.

A major goal in the research of graphene is to make the production of graphene possible at a wide scale assuring both high quality and affordable costs. The production methods used so far resulted in a low quality of graphene with a high number of structural defects and chemical based impurities. Thus it has not been possible to prepare good quality graphene inks.

In this new technique, researchers have used NaCl crystals for growing nitrogen-doped graphene nanosheets with the help of chemical vapour deposition technique as a result of which nitrogen and carbon molecules diffuse on the surface of NaCl crystals. NaCl was chosen due to its wide availability, low cost and high water solubility. For removing sodium chloride, the coated crystals are dipped in water as a result of which NaCl dissolves leaving behind the very pure nitrogen-doped graphene cages. The last step involves giving treatment to the cages with ultrasound as a result of which they transform to two-dimensional nanosheets that are nearly 5-7 layers of graphite in thickness.

These nanosheets have very fewer defects and they are of the perfect size for printing as they are of 5 micrometres in length, whereas the bigger flakes block the nozzle. For putting to test, the actual effectiveness of the ink, a large number of 3D structures were built using the inks. Scientists used the ink as a conductive additive for electrode and then used the composite ink for printing flexible electrodes to be used in supercapacitors with a large power density.

Additionally, scientists also used the ink for printing interlayers for the Li-S batteries. These batteries showed better-enhanced performance with increased conductivity.

Graphene

Researchers demonstrate working of quantum computers with help of graphene

A new material consisting of only one sheet of carbon atoms can give rise to new and unique designs of optical quantum computing devices. Researchers from the University of Vienna and Institute of Photonic Sciences, Barcelona have proved that tailored structures of graphene lead to the interaction of singular photons. The study has been published in the npj Quantum Information.

Photons interact with the environment to a very less degree, which makes it quite suitable for the storage and transmission of quantum information. However this same property makes it very difficult to interpret the information which has been stored in them.

For building a quantum photonic computer, it is essential for a photon to alter the state of second. This is called a quantum logic gate and a quantum computer requires millions of these. This can be achieved with the help of a ‘non-linear material’, in which there is interaction of two photons. But the standard non-linear materials are not efficient to construct a quantum logic gate.

However it has been recently understood that the nonlinear interactions can be highly improved with the help of plasmons. Plasmons make the light bind to the electrons which are located at the surface. Then these electrons facilitate a very strong interaction between the photons. In presence of these positives, a drawback is that the plasmons decay in the standard materials before the actual quantum effects can occur.

Philip Walther, from University of Vienna who led the team of researchers made a proposal to manufacture plasmons in the graphene material. Graphene has been only discovered in 2004 by Andre Geim and Konstantin Novoselov at University of Manchester. Though it was observed way back in 1962, it had not been independently isolated and studied then. For their work, the duo was awarded the Nobel Prize in Physics in 2010.

The unique arrangement of electrons in graphene leads to strong nonlinear interactions, which allows the plasmons to remain for a long duration. In the graphene quantum logic gate, scientists have demonstrated that if singular plasmons in nanoribbon are made from graphene, then it allows for the interaction of electrical fields of two plasmons in different nanoribbons. This makes way for quantum computation if each of the plasmons remain in their ribbons, since many gates can be applied to them.

Irati Alonso Calafell, who is the first author on this paper remarked that strong non linear interaction in graphene does not allow two plasmons to be in the same ribbon.