Superconductors conduct electricity with zero resistance below a critical temperature (Tc), leading to all manner of exciting applications. One of the dream scenarios is to discover a material that superconducts at room temperature. So-called “high-temperature superconductors” do exist but their transition point is still significantly below 0 °C. One of the factors hindering this research field is that we still have a very limited understanding of how high-temperature superconductors function.
In this video, Mark Dean of the Brookhaven National Laboratory (BNL) in New York explains how this endeavour can be aided by the bright X-rays produced at synchrotron facilities. Presenting from the beamline at the National Synchrotron Light Source II (NSLS-II), Dean introduces his own research on oxygen- and copper-based superconductors. He is investigating a mysterious weak ordering of electrons that occurs in these materials when they superconduct.
This video is part of our 100 Second Science series, in which researchers give concise presentations covering the spectrum of physics.
Bacteria that respond to magnetic fields and low oxygen levels may soon join the fight against cancer. Researchers in Canada have done experiments that show how magneto-aerotactic bacteria can be used to deliver drugs to hard-to-reach parts of tumours. With further development, the method could be used to treat a variety of solid tumours, which account for roughly 85% of all cancers.
Cancer cells in a growing tumour consume large amounts of oxygen and parts of the tumour will become starved of oxygen – or hypoxic. It is notoriously difficult to deliver tumour-destroying drugs to these hypoxic regions using conventional pharmaceutical nanocarriers, such as liposomes, micelles and polymeric nanoparticles.
Now, a team led by Sylvain Martel of the NanoRobotics Laboratory at the Polytechnique Montréal – including researchers at McGill University – has developed a method that exploits the magnetotactic bacteria Magnetoccus marinus (MC-1) to overcome this problem.
Tiny compass needles
A MC-1 bacterium has a chain of magnetic nanoparticles that acts like a microscopic magnetic compass needle. The bacteria live in saltwater estuaries in the northern hemisphere, where they use the Earths’s geomagnetic field to point them towards deeper water with low oxygen concentrations. The microbes do this because they thrive where oxygen concentrations are low. Indeed, the oxygen levels found in hypoxic regions of a tumour – about 0.5% – are perfect for MC-1.
The researchers created an artificial environment to allow these bacteria to migrate towards the hypoxic regions of tumours in live mice with colorectal cancers. “We first produce a weak magnetic field pointing towards the tumour to guide drug-loaded bacteria and make them swim towards the tumour (a process called magnetotaxis),” says Martel. “Once inside the tumour and sufficiently close to the hypoxic zones, we remove the magnetic field to allow the bacteria to use their internal oxygen sensors (aerotaxis) and follow the decreasing oxygen gradient in the tumour until they reach the 0.5% oxygen level.”
These bacteria can be used as general transport vehicles to carry a huge variety of therapeutic agents, such as various drug molecules, radiotherapeutic agents, stem cells and immunotherapeutics. “In the short term, we will be using our technique to study how it can enhance cancer treatment,” says Martel. “The possibilities are vast, since all therapeutic agents for treating solid tumours share a common problem – the effective delivery to the site of treatment.”
Therapeutic agents
Looking further into the future, the researchers say they would like to look into the efficacy of various therapeutic agents that are delivered using their new technique. They also hope to collaborate with other research groups around the world.
In the next few months the team will begin to develop medical protocols based on the technique. Also planned is the implementation of mathematical models to improve how magnetic fields are used to guide the bacteria. They will also continue doing studies of the safety of the technique, which Martel says “are encouraging so far”.
Robert Grosseteste was born sometime around the year 1170. By the time he died in 1253, he had gained a reputation as one of the leading scholars and philosophers of his age. However, some modern researchers have gone even further, calling him “the most brilliant scientist you’ve never heard of”.
“One idea he’s very famous for is a theory for the physical origin of the universe that, believe it or not, starts with a flash of light and expands out with a giant rapidly moving sphere – it’s a big bang theory of the universe,” says Tom McLeish, a physicist at Durham University.
McLeish is a member of the Ordered Universe Project, an interdisciplinary group of scientists and historians who are re-examining Grosseteste’s writings and, in many cases, “translating” his ideas into a modern mathematical form. This process has led the group in some unexpected and fruitful directions. For example, while the details of Grosseteste’s “big bang” are not compatible with modern theories – like other ancient and medieval scholars, he believed that the Earth was at the centre of the universe – McLeish notes that “physicists love playing with alternate realities and counterfactuals and toy models”. And as it turns out, analysing Grosseteste’s equations poses some interesting computational problems.
In this podcast, you’ll hear from McLeish and other members of the Ordered Universe Project, including:
medieval historian Giles Gasper on who Grosseteste was and the difficulties of reading early copies of his works;
physicist Brian Tanner on putting Grosseteste’s ideas into modern mathematical form, and on the differences between observing natural phenomena and conducting experiments;
psychologist Hannah Smithson on Grosseteste’s ideas about colour and the rainbow, and what they tell us about how people perceive the world around them.
Tools are useful when they meet all the demands of a particular objective, and invaluable when they continue to meet requirements that are ever evolving over time. Atomic-layer deposition (ALD) was already a useful tool for thin films in the 1980s, although commercial applications were then limited to electroluminescent displays. By the 1990s, use of ALD was making inroads into the microelectronics industry, but it was not until the end of that decade that the great match between the fabrication requirements in nanotechnology and the precision and control the technique can achieve became apparent.
Interest in the technique was confirmed in the early 2000s, when the American Vacuum Society began an international conference series on ALD. Since then, more than 1200 research papers, 80 reviews and two books have been published on ALD in nanotechnology. Some of the latest research using this technique to make devices for energy and environmental applications have appeared in a recent focus collection of the journal Nanotechnology from IOP Publishing, which also publishes Physics World.
ALD is a variant of the widely used technique of chemical-vapour deposition (CVD), in which a thin film is grown on a substrate by exposing it to one or more volatile gases – known as precursors – that react or decompose on the substrate to produce a required structure. The big difference with ALD is that the precursors are never present at the same time. Instead, ALD involves exposing the surface of a material to atoms of the chemicals to be deposited in separate stages and then clearing the excess between each stage.
In each of these stages, the precursor molecules react with the surface in a self-limiting way, which means that the reaction stops when all of the reactive sites on the surface are consumed. As a result, the amount of material that can be deposited on the surface after a single exposure to all of the precursors (a so-called ALD cycle) is governed by the nature of the precursor–surface interaction. By varying the number of cycles, researchers can therefore grow materials uniformly and with high precision on arbitrarily complex and large substrates.
In a paper published in the late 1990s exploring how ALD might be useful in nanofabrication (Nanotechnology10 19), Mikko Ritala and Markku Leskelä of the University of Helsinki list the merits this tweak introduces. These include “accurate and simple film-thickness control, sharp interfaces, uniformity over large areas, excellent conformality, good reproducibility, multilayer processing capability and high film qualities at relatively low temperatures”. These attributes have proved particularly valuable for attempts to improve the efficiency and scalability of alternative-energy technologies.
Coating electrolytes on 3D structures
Many of the processes key to energy harvesting and storage devices are improved by the increased surface area that 3D structures bring. For lithium-ion batteries, a higher surface area means higher energy and power densities, as well as space to accommodate the addition and removal of lithium ions, which can introduce mechanical strain during use. Researchers studying lithium-ion batteries are therefore increasingly looking towards solid state as opposed to liquid electrolytes to avoid risks of leakage and corrosion, with sophisticated coating techniques to add electrolyte and counter-electrode layers to complex 3D nanostructures therefore being in high demand.
ALD not only provides pinhole-free coatings of solid-state electrolytes on 3D electrode structures, but it also lets researchers tailor the coating thickness, which can significantly improve performance. As Tsun-Kong Sham and Xueliang Sun and colleagues at the University of Western Ontario in Canada point out (Nanotechnology 25 504007), “It is expected that the lithium-phosphate thin films prepared by ALD can find potential applications as solid-state electrolytes for 3D all-solid-state micro lithium-ion batteries, which, as an emerging area, deserves more extensive investigation in the coming future.”
Supercapacitors are a particularly attractive energy resource in nanoelectronics, where space is at a premium. As with research on lithium-ion batteries, the advantages of 3D structures with solid-state electrolytes have been noted. Writing in the Nanotechnology focus collection (26 064002), Giuseppe Fiorentino, Frans Tichelaar and their colleagues at Delft University of Technology in the Netherlands report on supercapacitors made from carbon-nanotube bundles as high-aspect-ratio electrodes that can improve the capacitance by a factor of five. The electrode is coated with aluminium-oxide as the electrolyte, followed by titanium-nitride as the counter electrode. As Fiorentino’s team points out, the work is not only “the first known example of large-scale manufacturable nanostructured capacitors”, but also provides useful insights for coating such high-aspect-ratio nanostructures.
Sunny side up ALD has been used to coat 3D structures in solar cells, reducing how far charge carriers must travel to reach electrodes. (Courtesy: iStockphoto/gyn9038)
Electrochemical cell structures can also take on elaborate hierarchical forms, as demonstrated by Xudong Wang and colleagues at the University of Wisconsin-Madison and the Forest Products Laboratory in the US. They have combined ALD and cellulose nanofibres to produce extensively branched structures for photo-electrochemical water splitting. Such a 3D titanium-dioxide fibre-nanorod heterostructure offers, they say, “a new route for a cellulose-based nanomanufacturing technique, which can be used for large-area, low-cost and green fabrication of nanomaterials as well as their utilizations for efficient solar-energy harvesting and conversion”.
As for solar-energy harvesting, ALD is already a well-entrenched technique in the field, and has been used to coat the inverse opals and other 3D structures often employed to reduce the distances that charge carriers must travel to reach electrodes. In the focus collection of Nanotechnology (26 064001), Alfred Iing Yoong Tok and colleagues at Nanyang Technological University in Singapore and the University of New South Wales in Australia review the application of ALD in solar-power technologies, focusing on its use for surface passivation, surface sensitization and band-structure engineering.
The potential for lateral confinement
As well as providing an excellent tool for coatings, ALD offers great potential for controlled lateral confinement. This aspect is the subject of detailed scrutiny in the catalysis work of Marcel Verheijen at Philips Innovation Services and Eindhoven University of Technology in the Netherlands. Coating thickness is still key for catalysis performance, as demonstrated by Ai-Dong Li and colleagues at Nanjing University in China. However, as the work by Verheijen and his colleagues in the group of Wilhelmus Kessels at the university identifies, ALD can also help with size matters. In a study of four ALD processes for the preparation of nanoparticle catalysts made from platinum and palladium, they identify the potential for size control, as well its dependence on process conditions (Nanotechnology 27 034001).
It is the ability to accommodate innovation that makes atomic-layer deposition so invaluable
It is perhaps the ability to accommodate innovation that makes ALD so invaluable. The use of plasmonic metamaterial absorbers has only really gained notice in the past few years, and ALD is already proving invaluable for work exploring the essential mechanisms in these systems, too. Xin Chen and colleagues at the Shanghai Institute for Technical Physics, for example, exploit ALD control over dielectric layers in order to distinguish between different plasmon modes. “We have demonstrated inversed plasmonic metamaterial absorber architectures with a tuneable ALD spacer layer, and thus identified the contributions of the gap plasmon and the interference-enhanced local surface plasmon resonance to the superior absorption in a step-by-step manner,” they say.
It is typical of science to break down problems into manageable pieces that can be tackled step by step. By breaking down deposition to an atomic level with step-by-step, self-limiting stages, ALD mirrors this approach and in so doing seems to provide a multipurpose tool for a diverse range of applications.
The Nanotechnology focus collection on energy and environmental applications of atomic-layer deposition is available at this link.
The time kept by atomic clocks in France and Germany has been compared for the first time using a new 1400 km optical-fibre link between labs in Paris and Braunschweig. Hailed as the first comparison of its kind made across an international border, the link has already shown that two of the most precise optical atomic clocks in Europe agree to within 5 × 10–17. The link is the first step towards a European network of optical clocks that will provide extremely stable and precise time signals for research in a number of scientific fields including fundamental physics, astrophysics and geosciences.
An optical atomic clock works by keeping a laser in resonance with an electronic transition between energy levels in an atom or ion – with the “ticks” of the clock being the frequency of the laser light. As with any clock, it is important to be able to compare the frequencies of two or more instruments to ensure that they are working as expected. Comparisons are also important for basic research, particularly for testing the fundamental physical laws and constants that are involved in the operation of atomic clocks.
Both of the clocks are based on the same optical transition in strontium atoms, which are held in optical lattices created by laser light. The clock at the LNE-SYRTE laboratory in Paris operates at an uncertainty of about 4.1 × 10–17 and the clock at the PTB Braunschweig laboratory at 1.8 × 10–17.
Gravitational shift
If they were side by side, the clocks would tick at exactly the same frequency. However, there is a 25 m difference in the elevation between the two locations, which means that the Earth’s gravitational field is not the same for both clocks – causing them to tick at slightly different frequencies. This gravitational redshift was confirmed by the link, which can detect differences in elevation as small as 5 m.
The link comprises two commercial-grade optical fibres that run between Paris and Braunschweig. The route is not the shortest distance between the two clocks, but rather takes a significant southward detour via Strasbourg on the French–German border. For every 1020 photons that begin the journey, only one would arrive at its destination. This 200 dB attenuation is compensated for by 10 or so special amplifiers along the route. The German portion of the link runs 710 km from Braunschweig to Strasbourg and is dedicated to connecting the clocks. The French portion, however, uses 705 km of an active telecommunications link that also carries Internet traffic. As a result, two different approaches were needed to amplify the clock signals on either side of the border.
Second connection
The optical clock at PTB Braunschweig is already linked to the Max Planck Institute for Quantum Optics (MPQ) in Garching near Munich. This is done via a 920 km pair of optical fibres, and researchers at the MPQ plan to use the clock signal to make extremely precise spectroscopy measurements. A further expansion of this network would provide researchers in other labs in Europe with access to high-precision clock signals.
Applications could include measuring a fundamental physics constant in several different locations – to confirm that the value of the constant is indeed constant. Other possible uses include precision measurements in spectroscopy that look for evidence of physics beyond the Standard Model and making very precise measurements of the shape and density of the Earth.
Surf’s up: Garrett Lisi when he is not winning bets with Nobel laureates. (CC BY-SA 3.0/Cjean42)
By Hamish Johnston
The “nightmare scenario” of particle physics has a new meaning thanks to a bizarre video that appears to have been made by some scientists at CERN. The video seems to have been filmed at night at CERN’s main campus in Geneva and depicts an occult ceremony in which a woman is stabbed. While the video appears to be a spoof and there is no indication that anyone was actually harmed in its making, CERN officials are rightly concerned that such violent scenes were filmed on their premises. “CERN does not condone this type of spoof, which can give rise to misunderstandings about the scientific nature of our work,” a spokesperson told Agence France-Presse.
The UK fusion scientist Ian Chapman has been named as the next chief executive of the UK Atomic Energy Authority (UKAEA). On 1 October Chapman will succeed Steve Cowley, who has been head of the authority since 2009 and will become president of Corpus Christi College at the University of Oxford.
As head of the UKAEA, Chapman will lead the UK’s magnetic confinement fusion research programme at the Culham Science Centre in Oxfordshire. He will oversee the upgrade of the Mega Amp Spherical Tokamak, which is set to be ready in 2017, as well as the operation of the Joint European Torus (JET) – one of the world’s largest nuclear fusion devices. He will also lead the UKAEA’s other activities at Culham, including the recently opened Materials Research Facility, the RACE robotics centre and the Oxford Advanced Skills apprentice training facility.
With an MSc in mathematics and physics from Durham University, Chapman began working at Culham in 2004 while completing a PhD with Imperial College London. In 2014 he was named head of tokamak science at Culham and then became fusion programme manager a year later. Aged just 34, Chapman will be one of the youngest chief executives of a major research facility. “While I am young, I am also experienced,” he says. “I hope my profile means that fusion, and its huge potential to give the world cleaner energy, will get noticed.”
Broad portfolio
Chapman comes into the job at a crucial time for UK research following the country’s vote to leave the EU, which will be tricky to manage for Culham. The European Consortium for the Development of Fusion Energy – jointly run by 26 European member states and Switzerland – funds JET’s experiments. Cash for this is secure until 2018, but what happens after then is unknown. But Chapman told Physics World that he is confident about Culham’s future. “Science is an international endeavour,” he says. “I am positive for the future as we have a broad portfolio of activities.”
Indeed, the experiments carried out at JET will be crucial to the success of the ITER fusion experiment currently being built in Cadarache, France, when it turns on in the coming decade. While Chapman calls ITER “the most important experiment mankind has ever done”, he admits it is a “big challenge, with a lot of difficulties”. Yet he hopes that his appointment will inspire the next generation of scientist and engineers to make a success of the device. “It is my personal ambition to deliver fusion,” he adds.
Chapman’s appointment is backed by Culham’s outgoing boss. “Ian has risen quickly for good reason: he is a world-class scientist, a thoughtful manager, and a strategic thinker of the first order – astonishing in one so young,” says Cowley. “Culham is a precious UK asset and I am pleased that it will be in such good hands.”
Vast conspiracy: contrails over Horfield Common in Bristol.
By Hamish Johnston
Is there a government-led conspiracy that uses aeroplanes to lace the atmosphere with chemicals? Of course there isn’t, and now there is a peer-reviewed study that says so.
Dubbed the “secret large-scale atmospheric programme” (SLAP), the conspiracy concerns condensation trails (contrails) that can often be seen high up in the sky. These are the lines of cloud that are formed when water condensates around particulate matter in the exhaust from jet engines. But are those contrails actually “chemtrails” that are spreading noxious substances far and wide?
Quantum mechanics wreaks even more havoc with conventional ideas of causality than some have suspected – according to a team of researchers based in Australia, with collaborators in Scotland and Germany. They have shown that even allowing causality to be nonlocal – so that an event in one place can have an influence on another, distant place – is not enough to explain how quantum objects behave.
Without cause and effect, science would be impossible. You could never use an observation to deduce anything about the underlying mechanism that caused it. But quantum mechanics challenges our commonsense picture of causality – for example by implying that some things happen at random, with no apparent cause, or that an action in one place can seem to have an effect elsewhere, even if the two locations cannot interact.
This kind of nonlocality has become widely accepted in quantum theory, thanks to experiments on so-called entangled states. Here two or more quantum entities, such as photons of light, acquire interdependent properties, revealed by correlations in the measured values of their properties. For example, pairs of polarized photons can be entangled so that, if one has horizontal polarization, the other has vertical polarization.
Action at a distance?
Because quantum properties have inherent randomness, these correlations are typically revealed in averages of many measurements. The twist is that quantum mechanics seems to insist that these properties are not fixed until they are measured. This seems to imply that a measurement on one entangled photon affects the other instantaneously across space.
Perhaps quantum mechanics is incomplete, though, and the properties were actually fixed within the particles all along. This “local realist” picture, in which quantum particles have intrinsic, localized properties even if we can’t see them directly, was assumed by Albert Einstein and colleagues in 1935 when they argued that such instant action at a distance creates a paradox for quantum mechanics.
But after Northern Irish physicist John Bell showed in 1964 how to distinguish between the predictions of local realism and those of quantum mechanics, numerous experiments have shown that the quantum picture seems to be correct. There’s no real instantaneous action at a distance, because we can’t think of the measurement on one particle as “causing” some “effect” on the other.
Painting a realist picture
It’s still possible, however, to explain Bell-type tests of quantum correlations in a “realist” picture (where quantum objects possess fixed properties before measurement) if other of his assumptions are rejected. If, say, causation itself were nonlocal, so that an intervention in one place is felt elsewhere, then a measurement on one photon might directly influence that on the other, creating the correlation between them.
The new experiments, says Martin Ringbauer of the University of Queensland, who led the Australian group, “consider this class of realist models, where Bell’s central assumption of local causality is relaxed.”
To test whether a realist but nonlocally causal model is able to explain quantum phenomena, the team devised Bell-type experiments where such a model makes different predictions from quantum mechanics. First they performed a modified version of one of the earliest such experiments on entangled photons in the 1970s, called a Clauser-Horne-Shimony-Holt (CHSH) test.
Causality, not correlation
To test for causal effects and not just correlation in this test, they did not simply make passive measurements of photon polarization but actively intervened to change the outcome. “Imagine you are watching someone flick a light switch and observe that the light goes on and off in perfect correlation”, says Ringbauer. “You can’t tell whether the switch causes the light to go on, or the light going on causes the person to flick the switch, or there is some hidden common cause that is responsible for both the light going on and the person flicking the switch.”
However, if you’re in control of the switch yourself, you can tell the difference. In their experiment, Ringbauer and colleagues fixed the outcome of measurement on one photon by inserting optical devices that affected its polarization before the measurement was made. They then looked for a concurrent change in the statistics of the other. Because they saw none, they concluded that there could be no nonlocal causality at play in which measurement outcomes on one photon could cause changes in those on the other.
The team then did a more complicated experiment involving three possible measurement settings as opposed to just two for the CHSH experiment. This allowed them to verify that their conclusions are independent of the specific apparatus used to do the tests. In other words, the results do not depend on any particular type of intervention.
Radical revisions
The only way now that one might rescue some kind of classical (realist) causal interpretation of quantum correlations involves more radical revisions of Bell’s assumptions, says Ringbauer – for example, backwards-in-time causation or a “many-worlds” interpretation of quantum mechanics with multiple parallel universes.
Caslav Brukner, a quantum theorist at the University of Vienna, told physicsworld.com: “I like the work since it excludes a large class on nonlocal causal theories.” Previous tests looked only at a very specific version of such theories, he adds.
The experiment “is not only important from the perspective of quantum foundations, but might also have implications in quantum cryptography,” says Ognyan Oreshkov of the Free University of Brussels in Belgium – for example in cases where one can’t guarantee that the measurements made by the sender and receiver are kept secret.
I’m pleased to say that the latest focus issue of Physics World, which explores the many fascinating applications of vacuum science and technology, is now out.
Plasma processing is a strong theme this year, as we discover why tools and techniques developed as part of the boom in semiconductor fabrication are now benefiting biomaterials. Elsewhere, we reflect on the strengths of the vacuum community with outgoing IUVSTA president Mariano Anderle.
And, as always, this vacuum focus issue provides a great chance to catch up with major industry players, including Pfeiffer Vacuum, Agilent, Honeywell and Edwards, to examine the latest instrument upgrades and trends across the sector.
By Matin Durrani