I travelled to Fermilab and CERN to learn more about the changing geography of high-energy physics and how it affects individual researchers. In this behind-the-scenes podcast, you’ll hear senior scientists and early-career researchers talking candidly about their working lives, their reactions to the Tevatron’s shutdown and their plans for the future.
Artificial jellyfish engineered from rat heart cells
Scientists in the US have created an artificial jellyfish out of silicone and rat heart muscle cells. The creature, dubbed “Medusoid”, swims just like its living analogue by pumping water in and out of its dome-shaped body in rhythmic pulses. Ultimately, the researchers hope to apply the same reverse-bioengineering techniques to design better artificial hearts for medical implant.
The motivation behind this new work was borne out of team member Kevin Parker’s frustration with the state of the cardiac field. An applied physicist and bioengineer at Harvard University in the US, he worried that the drug-development pipeline for cardiac disease was “starting to look a little bit lean”.
“[Medicine is] kind of running out of ideas as to how to treat heart cellular problems,” he says, suggesting “We might just not understand the fundamental rules nature has for building a good muscular pump.”
On a trip to the aquarium, Parker was struck by the similarities between how jellyfish and the human heart pump fluid, and decided to try building a replica. It’s an unprecedented move, building an entire functioning organism, but Parker was adamant that he wanted to challenge the traditional view of synthetic biology that has thus far “focused on genetic manipulations of cells”.
Grow your own jellyfish
Jellyfish pump liquid to propel themselves through water by employing the same basic principles used by the human heart to pump blood around the body. Both use a smooth wave of muscular contractions to squeeze liquid quickly and forcefully from a cavity, which then refills slowly by elastic recoil. “In our engineered system, we needed to have these two components,” explains another team member John Dabiri, an expert in biological pulsing at the California Institute of Technology.
The team used rat cardiac cells, which were activated with a jolt of electricity, to provide the “power stroke”. These were arranged on a thin sheet of silicone polymer, which assumed the role of the jelly by slowly recovering the creature to its original shape ahead of the next stroke. Medusoid was built to resemble a juvenile moon jellyfish (Aurelia aurita). Less than a centimetre in diameter when flat, it possesses eight arm-like appendages that bend to give it a characteristic dome shape when it surges forward.
Morphologically and functionally, it’s a jellyfish; genetically it’s a rat Kevin Parker, Harvard University
In the quest to mimic the propulsion of real moon jellyfish, lead author of the paper on the new work published in Nature Biotechnology, Janna Nawroth, also at the California Institute of Technology, began by mapping the alignment of subcellular proteins in real specimens, using immunostaining – an antibody-based method used to detect a specific protein in a sample – techniques borrowed from forensic science. The blueprint she obtained was used to pattern the Medusoid’s silicone sheet with proteins and coax the rat cardiac cells into their desired arrangements upon it.
Looks like a jellyfish, swims like a jellyfish…
When the researchers put the Medusoid into salty water and applied an electric current, their creation proved to be as competent a swimmer as its real-life counterpart. Not only that – their detailed flow field measurements showed that the Medusoid had the mimicry down to such a fine art that it was even producing the same vortices that real jellyfish create at the end of each power stroke to sweep food up into their mouths. “We said – if we’re really good, we’ll be able to not just match the propulsion, we’ll be able to match the vortices of the feeding currents. And we were able to do that,” says Parker, adding “Morphologically and functionally, it’s a jellyfish; genetically it’s a rat.”
“I was surprised that with relatively few components – a silicone base and cells that we arranged – we were able to reproduce some pretty complex swimming and feeding behaviors that you see in biological jellyfish,” says Dabiri.
Landmark paper
Suwan Jayasinghe, a biophysicist from University College London who was not involved in the study, says the fact that the researchers managed to mimic the functionality and behaviour of the jellyfish in 3D is “unique” in a field where most people still focus on 2D systems. “There is no doubt that this is a landmark paper. The potential applications in humans are tremendous – it’s mind-blowing really.”
In the near future, the researchers hope that versions built with human heart cells could be used as an early screening device to study the effect of new heart drugs on pump function. In the longer term, they hope to build synthetic creatures with much more detailed musculature, and eventually to reverse-engineer a human heart. “This project is really just the beginning of what we see as a re-imagining of synthetic biology,” says Dabiri.
“Physicists really have a role to play here,” adds Parker. “Regenerative medicine is never going to be a possibility until we conquer the cell, and the cell is more of a physics problem than most people realize – it’s a microscale self-assembling self-fuelled system, and we need to understand the physics of the cell before we can use it as a building substrate.”
The work is published in Nature Biotechnology.
So you want to get published?
By Matin Durrani
For every researcher, getting published is the name of the game.
You might be a brilliant blogger, a terrific Tweeter or a frenetic Facebook fan, but having a scientific paper published in a professional scientific journal is still your best bet for getting your results recorded, archived, peer-reviewed and disseminated.
If you’re new to the publishing game, however, IOP Publishing, which publishes physicsworld.com, has brought out a handy little online introductory guide.
Aimed at early-career researchers, the guide is designed to provide an overview of academic publishing and advice on how to make the most of the process for sharing your research.
There are sections on choosing where to submit your paper, how to go about writing it, how the peer-review process operates, and what to do when you receive your referee’s report.
Check out the guide to getting published.
PS Talking of Facebook, we’ve started posting “images of the day” on our Facebook page. They seem to be quite popular, so let us know if you have any suggestions.
Farewell Sally Ride
Sally Ride talks to ground controllers during the six-day Challenger mission. (Courtesy: NASA)
By James Dacey
Sally Ride, the physicist and astronaut who became the first US woman in space, has sadly passed away aged 61. Ride made history as a crew member on the Challenger mission that blasted off from the Kennedy Space Center in Florida on 18 June 1983. Ride was also aboard the 13th shuttle flight, STS 41-G, which launched on 5 October 1984.
In 1989 Ride joined the University of California, San Diego as a professor of physics and director of the California Space Institute. In addition to holding this faculty position, Ride was also engaged in a number of other educational activities to encourage students to pursue careers in science and technology.
A statement released on her company’s website reads “Sally Ride died peacefully on 23 July 2012 after a courageous 17-month battle with pancreatic cancer.
“Sally lived her life to the fullest, with boundless energy, curiosity, intelligence, passion, joy and love. Her integrity was absolute; her spirit was immeasurable; her approach to life was fearless.”
X-rays probe the origins of hotspot volcanoes
Researchers in France have added a new twist to one of the most controversial debates in geophysics – how “hotspot” volcanoes such as the Hawaiian Islands are formed. By probing hot, pressurized rock samples with intense X-rays, they have shown that molten rock deep within the Earth’s mantle should be buoyant. This finding, the researchers say, supports the much-debated hypothesis that hotspot volcanoes are created by deep plumes of rock rising almost 3000 km to the Earth’s surface.
In geology, “hotspots” are regions of high volcanic activity that are not located at a tectonic plate boundary and are thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. Hot plumes originating from the boundary between the Earth’s outer core and lower mantle were first proposed in 1971 to explain volcanic regions that do not fit the theory of plate tectonics. The Hawaiian volcano chain, for instance, is located far from any plate boundaries, and so it has been suggested that it forms as the Pacific plate moves over a hotspot that is fed by a deep-seated mantle plume. Similar plumes have been proposed to explain volcanic activity in places as diverse as Iceland, Siberia and India’s Deccan Plateau.
Many predictions of the mantle-plume hypothesis, however, remain unconfirmed, prompting some geophysicists to develop an alternative model. The “plate hypothesis” involves much shallower processes such as internal deformations within tectonic plates that would allow magma to leak upwards from the upper mantle. Over the past decade, this model has attracted a dedicated army of supporters, creating a schism that today divides the geophysics community.
Hell on Earth
Now, a team of researchers led by Denis Andrault, a mineral physicist at Blaise Pascal University in Clermont-Ferrand, France, has tested one of the key requirements of the plume hypothesis: that molten rock at the core–mantle boundary should be buoyant enough to move upwards. To investigate this, the researchers set about recreating the hellish conditions found 2900 km below the Earth’s surface.
At the European Synchrotron Radiation Facility in Grenoble, tiny specks of rock nearly 10 times thinner than a human hair were compressed between the tips of two conical diamonds, subjecting the samples to immense pressures of up to 120 gigapascals. Then, infrared lasers heated the samples to temperatures as high as 4000 °C. “All of our observations show that the melting of the rocks follows the same laws of physics and chemistry as the melting of much larger samples,” says Andrault, “so the results can be confidently transferred from the micron scale up to the kilometre scale.”
Next, the samples were mapped and probed using a high-pressure X-ray beam. By analysing the X-ray diffraction patterns and fluorescence spectra, the researchers determined the chemical compositions of the regions where the rock had melted or remained solid. This allowed them to calculate the distribution of iron between the solid and liquid phases – crucial for determining the buoyancy of the molten rock.
Sink or swim?
Andrault and colleagues discovered that the molten rock contained about twice as much iron as the solid rock. Combining this result with the liquid’s expected silica content, the researchers concluded that the melt would be buoyant.”“If there was a lot more iron in the liquid, as suggested in previous work, then the density of the molten rock would be significantly higher and the magma would sink towards the core–mantle boundary,” says Andrault. “This is not the case.”
Instead, Andrault proposes that the buoyant rock moves towards the Earth’s surface – an idea that tallies with the mantle-plume hypothesis. “The melt could penetrate through the mantle by at least two different mechanisms,” says Andrault. “One is related to the size of the liquid pond: if it is big enough, gravitational forces will finally succeed in moving the liquid upwards. Another mechanism involves the dissolution of mantle material at one end of the liquid drop and recrystallization at the other end, resulting in a progression of the liquid.”
Plumes versus plates
But not everyone is convinced. “The melt may be more buoyant than previously thought,” says Gillian Foulger of Durham University in the UK. “But melts don’t just zoom up like water in a plumbing pipe. They’re reabsorbed, they mix with other melts, they’re trapped, and they have to get through the transition zone.” Furthermore, she adds, the mantle-plume hypothesis involves solid materials, not liquids, convecting towards the surface.
Andrault admits that the fate of the liquid during its travel upwards is uncertain. “Still,” he says, “even if the liquid did crystallize, its composition and temperature would be very different from the mantle, and the material would likely be buoyant thanks to its relatively high silica content.”
So how might the “plumes versus plates” debate be resolved? Foulger believes that scientists need to test the predictions of the plume hypothesis at the Earth’s surface, looking for the geochemical signatures of lavas that have risen from the deep. Others believe that the answer lies in using large arrays of high-resolution, ocean-bottom seismometers to search for evidence of these ascending plumes. Either way, the debate is likely to rumble on for some time yet.
The research is described in Nature.
New chemical bonds possible in extreme magnetic fields
In the extreme magnetic fields of white dwarves and neutron stars, a third type of chemical bonding can occur. That is the finding of theoretical chemists in Norway, who have used computer simulations to show that as-yet-unseen molecules could form in magnetic fields much higher than those created here on Earth.
High-school chemistry students are taught that there are two types of chemical bond – ionic bonds, in which one atom donates an electron to another atom; and covalent bonds, in which the electrons are shared. In fact, real chemical bonds usually fall somewhere in between.
When two atoms come together, their atomic orbitals combine to form molecular orbitals. For each two atomic orbitals combined, two molecular orbitals are formed. One of these is lower in energy than either atomic orbital and is called the bonding orbital. The other “anti-bonding” orbital is higher in energy than either atomic orbital. Whether or not the atoms will actually bond is determined by whether the total energy of the electrons in the molecular orbitals is lower than the total energy of the electrons in the original atomic orbitals. If it is, bond formation will be energetically favoured and the bond will be formed.
Bonding and anti-bonding
The Pauli exclusion principle forbids a single orbital from holding more than two electrons (it can hold two if they have opposite spins). If the atomic orbital of each atom contained just one electron, both can go into the bonding orbital when the orbitals combine. Both electrons are therefore lowered in energy and the bond formation is energetically favoured. But if the atomic orbitals contained two electrons each, two of the four electrons would have to go into the anti-bonding molecular orbital. Overall, therefore, two electrons would have their energy lowered by bond formation, while two electrons would have their energy raised.
Under normal circumstances, the anti-bonding orbital is always raised in energy farther above the energy of the higher-energy atomic orbital than the bonding orbital is lowered below the energy of the lower-energy atomic orbital. This means that a chemical bond with both its bonding and its anti-bonding orbitals full would always have a higher energy than the atomic orbitals from which it would be formed. Such a bond would therefore not form. This is why noble-gas atoms, which have full outer atomic orbitals, almost never form molecules on Earth.
But now Kai Lange and colleagues at the University of Oslo have used a computer program developed by their group called LONDON to show this is not always true elsewhere. LONDON creates mathematical models of molecular orbitals under the influence of magnetic fields of about 105 T. This is much stronger than the 30–40 T fields that can be made in laboratories and that have little effect on chemical bonds.
Changing the rules
Large fields could be relevant to those studying astronomical objects such as white dwarves – where magnetic fields can reach 105 T – and neutron stars, where fields could be as high as 1010 T. Under such conditions, the team has shown that the rules of bonding change. In particular, the anti-bonding orbital is lowered in energy when a diatomic molecule is subjected to a strong perpendicular magnetic field. Molecules with full bonding and anti-bonding orbitals, such as diatomic helium, can still be energetically favoured.
Team leader Trygve Helgaker explains the sophistication of LONDON enabled the group to perform calculations that others have found impossible. “We can do accurate calculations with all orientations of the molecule to the magnetic field,” he says. “People have done the same kinds of electronic-structure calculations before, but I believe their calculations were limited to the situation where the field is parallel to the molecular axis.”
The research is published in Science; in an accompanying commentary, Peter Schmelcher of the Institute for Laser Physics at the University of Hamburg, Germany, said “Atoms, molecules and condensed-matter systems exposed to strong magnetic fields represent a fascinating topic, and this work has added a key bonding mechanism.” Interestingly, while he accepts the fields present around a white dwarf will be unachievable in a laboratory in the foreseeable future, he sees an alternative way the group’s models might be tested experimentally. Rydberg atoms are highly excited atoms that can be the size of the dot of an “i”. Because the bond length between Rydberg atoms is so great, the Coulomb interaction is much smaller, and Schmelcher believes it might therefore be possible to use them to produce magnetic fields of comparable strength.
Which physics-based technology to emerge from the Second World War has had the most significant impact on society?
By James Dacey
There is a fascinating article in the current issue of the Bulletin of Atomic Scientists in which the historian Paul N Edwards tries to unravel the “entangled histories” of climate science and nuclear weapons. One of Edwards’ central arguments is that climate science is only in its relatively advanced current state because of the scientific work carried out in the field of nuclear-weapons research. He backs up this assertion by tracing the histories of the different aspects of climate science, from the atmospheric models that were initially developed to monitor nuclear fallout to the facilities that were founded for nuclear purposes but have since switched to climate interests as a result of shifts in political interests.
The article got me thinking about the huge role that politics plays in the development of new technologies, particularly when there is a focused political will, such as during times of war. This was clearly evident during the second half of the 20th century when societies across the developed world were dramatically transformed by technologies that had emerged from scientific and engineering advances of the Second World War. Work and leisure have been transformed by modern computing. The invention of the jet engine opened up the world to speedy travel. Von Braun’s rocket carved a path that led us to the Moon. Radar is used to scan the skies, tracking everything from planes to clouds. The harnessing of nuclear energy transformed power supplies, while the power wielded by nuclear weapons has been a dominant theme in global politics ever since the US developed The Bomb.
Clearly, all of these technologies have had vast impacts on the world. In this week’s Facebook poll we want you to answer the following question:
Which physics-based technology to emerge from the Second World War has had the most significant impact on society?
Nuclear power/weapons
Modern computing
The jet engine
Rocket systems
Radar and microwave technology
Have your say by visiting our Facebook page, and please feel free to explain your response – or suggest an alternative technology – by posting a comment below the poll.
In last week’s poll we asked you to exercise your brain in thinking about the role that physics can play in professional sport. We asked whether you think athletes could benefit from an understanding of the physics of their sports. The outcome was as conclusive as the outcome of a race involving the average university academic and the Jamaican sprinting phenomenon Usain Bolt. 93% of respondents had strong faith in the importance of physics as they selected the option “Yes, it could help them to perfect their techniques”, while the remaining 7% chose the option “No, any knowledge would be purely theoretical”.
We asked this question in connection with the July issue of Physics World, which looks at physics and sport, including features on the physical principles underpinning sport, and the roles technology plays in enabling and enhancing sporting performance. For a limited time this special issue is available as a free PDF download.
Thank you to everyone who took part and we look forward to hearing from you again in this week’s poll.
Do dolphins think nonlinearly?
Dolphins may rely on a nonlinear analysis method to “see” through clouds of bubbles that they create to trap fish, according to scientists at the University of Southampton in the UK. The researchers have devised a nonlinear sonar processing scheme that enables them to identify targets through clouds of bubbles, opening up the possibility that dolphins may employ similar tactics when they hunt by creating bubble nets that disorient their prey.
Unlike solid objects such as the sea floor or fish – which reflect acoustic signals linearly, as straight-forward echoes – bubbles reflect nonlinearly. This means that acoustic echoes from bubbles contain harmonic frequencies in addition to the fundamental frequencies of the outgoing signal – producing a “clutter” that is incredibly confusing to sonar. And to make matters worse, bubbles are extremely efficient at reflecting sound.
“Bubbles are the most powerful naturally occurring acoustic objects in water,” explains team member Timothy Leighton. “When you send sound at them, they’ll emit sound rather like any instrument would – if you shout at a guitar, the strings will rattle back at you.”
Blinded by bubbles
Given this, Leighton was taken aback when he saw a wildlife documentary showing dolphins purposely blowing nets of bubbles to catch fish. “There should be no way the dolphins’ sonar can get through these bubbles – it’s like they’re making fog while hunting and blinding their own sonar,” he says. “Unless there’s something spectacularly good about their sonar that we haven’t discovered yet.”
Considered alongside manmade sonar devices, a dolphin’s sonar equipment appears fairly mediocre in terms of the frequencies it can cover and the power it can generate. Dolphins’ agility and speed in the water lends them the advantage of being able to send sonar from a number of different directions and thereby see in 3D, but, even so, the bubble problem remains.
“They’ve got these huge brains though, and they’ve been living in the oceans for 10 million years where there’s always bubble clutter. Why shouldn’t they have developed a way of navigating it?” asks Leighton.
Mathematical minds
Inspired by dolphins, Leighton has spent the last decade attempting to design a sonar scheme that can penetrate bubble clouds. His most recent proposal focuses on the variation in amplitude between the successive clicking sounds that dolphins are known to make as they use echolocation.
If a dolphin sends out two successive clicks, with the second being 1/3 the amplitude of the first, a fish will return faithful echoes of these sounds while a bubble will mainly return sounds in the second harmonic at a specific amplitude. For example, if the original clicks are sent with amplitudes of 1 and 1/3, respectively, then a fish will return sounds with amplitudes of 1 and 1/3, while a bubble will return sounds with amplitudes 1 and 1/9.
In Leighton’s scheme, the sonar processor (or dolphin) multiplies the second returned click by 3 and then chooses to add or subtract this from the amplitude of the first returned click. In the sum, the linear echo from the fish is accentuated; in the subtraction, the nonlinear echo is suppressed a little, but the linear echo from the fish disappears altogether. Comparing these two pictures allows the receiver to distinguish between fish and bubbles.
When Leighton and colleagues tested this theory out in a 200-tonne tank of water with a sonar source that produced dolphin-like click trains, they found that, indeed, they were able to “see” a target within a cloud of bubbles. Although this proves nothing about the tactics dolphins employ, it shows that it is possible for dolphin pulses to see through bubble clouds, given the right processing.
Behaviour bypass
But is it plausible that dolphins’ brains recognize that bubbles and fish scatter sound differently, and that they then subconsciously add and subtract echoes to distinguish targets from bubbles? Simon Ingram, a dolphin biologist at the University of Plymouth’s Marine Institute in the UK wonders if the underwater acousticians might have missed the biological point slightly.
“We need to zoom out and think about the biology behind this particular foraging method. Dolphins cast a bubble net around a concentrated ball of fish that they’ve already worked cooperatively to aggregate together,” he says. “Why do they even need to be able to see the individual fish inside that bubble curtain?”
Once the net is created, he suggests, the dolphins could pierce it at speed and snatch their prey using echolocation once they are within it.
Field observations needed
Sonar expert Hugh Griffiths of University College London says he has “huge admiration” for the work, which he labels “very novel”.
“I think you would need to do quite a bit more work before you could say for certain that dolphins are using this, but it’s certainly plausible,” he says. Along with Ingram and the Southampton team, he agrees that field observations are the next step in either adding weight to or ruling out the theory.
If wild dolphins can be recorded dropping the frequency of their sounds while employing the bubble-net hunting strategy – specifically to at least half that of their upper hearing limit – it would be a strong indication that they could be using nonlinear processing. But even then, says Leighton, a conclusive answer might prove elusive.
“It’s an extremely difficult thing to do, to work out what mental signal processing a creature such as a dolphin does. Controlling an activity where you’ve got 200 dolphins blowing nets, snapping away with their teeth in the wild and not interfering in that process while you make a measurement – you can see it’s almost impossible to do.”
The work is published in the Proceedings of the Royal Society A.
Check out some physics and sport
By Matin Durrani
Ernest Rutherford used to enjoy “noisy and appalling” golf at Cambridge with his Trinity College colleagues. Niels Bohr was a keen footballer who played in goal for the top Danish side Akademisk Boldklub in the early 1900s. Arthur Eddington was a passionate cyclist who coined the “Eddington number”, E, which is the number of days on which you have cycled at least E miles. (He reached an incredible 84.) And, of course, CERN physicists are handily placed for a spot of Alpine hiking, climbing and skiing.
But for some physicists, sport is more than just something they take part in – it is what they study too. This month’s issue of Physics World looks at some of the challenges in the “physics of sport”, including:
• the effects of technology and rule change on sporting performance;
• the physics of the prosthetic devices that are leading disabled athletes like Oscar Pistorius to success;
• and how gymnasts, divers and long-jumpers are all unconscious masters of manipulating the law of conservation of angular momentum.
Members of the Institute of Physics (IOP) can enjoy the entire new issue online through the digital version of the magazine by following this link or by downloading the Physics World app onto your iPhone or iPad or Android device, available from the App Store and Google Play, respectively.
But for those of you who are not yet members of the IOP, to show you what you’re missing out on, we’re offering for a limited period only the opportunity to download a free PDF of the July issue via this link. The PDF version doesn’t contain all the features of the digital issue, which include reading articles in plain-text or page-view formats, the ability to share articles and have them read out loud, as well in-built multimedia content.
Remember that if you’re not yet a member, you can join the IOP as an imember for just £15, €20 or $25 a year via this link. Being an imember gives you a full year’s access to Physics World both online and through the apps.
Click here to download a free PDF of the July issue of Physics World.
Graphene defects tracked as they creep and climb
Researchers in the UK and Japan have succeeded in tracking dislocations with unprecedented resolution as the defects move through graphene – a sheet of carbon just one atom thick. The work may help scientists better understand plasticity in 2D structures and how dislocation motion affects the mechanical properties of graphene and other technologically important materials.
The strength of a material and how it deforms under a load are often related to how dislocations – lattice defects such as an extra half plane of atoms – move through a material. Although dislocations in 3D samples have been studied using high-resolution transmission electron microscopy (TEM), it is much more challenging to examine 2D materials such as graphene. This is because the high-energy electrons normally used for imaging in TEM will quickly destroy carbon-based nanomaterials like graphene.
In order to study graphene, the accelerating voltage of the electrons in TEM needs to be reduced to relatively low values of about 80 kV to limit damage. The problem, however, is that doing TEM with such low-energy electrons results in an increase in spherical and chromatic aberrations that blur the images and reduce their spatial resolution. Although newer electron microscopes contain in-built hardware that can correct for spherical aberrations, this resolution is still not high enough to allow scientists to locate the exact positions of individual atoms in graphene.
Reducing energy spread
Now, Jamie Warner and colleagues at the University of Oxford have teamed up with a researcher at the Japan Electron Optics Laboratory in Tokyo to reduce chromatic aberration effects by passing the electrons through a monochromator and so improve spatial resolution. The technique reduces the energy spread of the electrons before they actually hit the sample.
“Our approach allows for sub-angstrom resolution at 80 kV and the ability to pinpoint the exact position of single carbon atoms within the graphene lattice,” explains Warner. “We used this enhanced resolution to study edge dislocations (a unique form of defect that distorts the lattice structure) in graphene for the first time with true atomic resolution.”
The researchers were also able to measure carbon–carbon bond elongation and compression within a dislocation too, and map the strain caused by the dislocations using an image-processing technique known as geometrical phase analysis (GPA). “We found that we could not only map the full strain tensor from the dislocations, but also study how the strain fields moved as dislocations shift positions, or ‘creep and climb’, within the lattice,” says Warner. Comparing these experimental strain maps with those predicted by theory shows a good match with the so-called Foreman dislocation model, he adds.
Impurities are next
The researchers say that the results provide a detailed map of how the atoms in dislocations are configured in graphene, and will help them better understand how plasticity emerges in the material. They are now studying single substitutional impurity atoms in graphene and how these induce strain within the lattice. “We have already discovered that only some defect structures are stable,” says Warner. “We can readily create highly disordered regions within graphene, but in many cases these can ‘unwind’ and revert back to a pristine lattice.”
The team is also busy compiling a catalogue of defect and impurity families in the carbon material.
The results are published in Science.
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