Archive for the ‘Materials Science’ Category

Is this the most boring experiment ever?

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Scientists watch drops of pitch form – and there have been eight in 75 years

  • Experiment began in 1927 to prove pitch is a liquid
  • In 75 years, just EIGHT drops have fallen
  • The rate is slowing, and last drop fell 12 years ago
  • Current custodian has watched since 60s – but has missed all five drops that have fallen
  • Drop ‘could’ fall this year, but 2013 ‘is a better bet’

A lump of the black substance, which can be broken with a hammer, was put into a glass funnel – and the waiting began.The experiment has been running now for 85 years and it is estimated that it will last for another century

It’s the world’s longest-running experiment – and the very, very patient scientists in charge are waiting for a single drop of pitch to fall, 12 YEARS after the last one fell.
The ‘pitch drop’ experiment began in 1927 and was designed to show that solid-looking pitch was, in fact, a liquid.
The experiment has been running now for 85 years and it is estimated that it will last for another century…..

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Written by physicsgg

May 14, 2012 at 7:27 am

Move over graphene, silicene is the new star material

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New kid on the block (Image: Ayandatta)

AFTER only a few years basking in the limelight, wonder material graphene has a competitor in the shape of silicene. For the first time, silicon has been turned into a sheet just one atom thick. Silicene is thought to have similar electronic properties to graphene but ought to be more compatible with silicon-based electronic devices.

Patrick Vogt of Berlin’s Technical University in Germany, and colleagues at Aix-Marseille University in France created silicene by condensing silicon vapour onto a silver plate to form a single layer of atoms. They then measured the optical, chemical and electronic properties of the layer, showing it closely matched those predicted by theory (Physical Review Letters, DOI: 10.1103/PhysRevLett.108.155501).

Silicene may turn out to be a better bet than graphene for smaller and cheaper electronic devices because it can be integrated more easily into silicon chip production lines.

In 2010, another Aix-Marseille group led by Bernard Aufray attempted create silicene using a similar approach but failed to present convincing evidence that it was present. Michel Houssa of the Catholic University of Leuven (KUL) in Belgium, who was not involved in the new work, says: “In my opinion, this is the first compelling evidence that silicene can be grown on silver.”

He says an important challenge now will be to grow silicene on insulating substrates to learn more about its electrical properties and understand how they can be exploited to build future electronic devices.
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Written by physicsgg

April 30, 2012 at 1:14 pm

Posted in Materials Science, TECHNOLOGY

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‘Magnetic Josephson effect’ seen for the first time

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Micrographs showing a loop of superconducting material used to demonstrate coherent quantum phase slip. The image on the left shows the loop of superconductor and the image on the right is a magnified section showing how the superconductor narrows to a nanowire. The magnetic field is applied perpendicular to the loop. (Courtesy: RIKEN)

A fundamental prediction of superconductivity theory has been demonstrated in the lab for the first time. An international team of physicists has observed coherent quantum phase slip, a phenomenon similar to the well-known Josephson effect in which magnetic flux takes the place of electric charge. Its discovery has fundamental implications for our understanding of macroscopic quantum systems and could also lead to intriguing applications, including a possible way to produce a qubit in a quantum computer.
In 1962 the British physicist Brian Josephson developed a theory of how superconducting electrons tunnel across a thin insulating layer between two superconductors – a structure now called a Josephson junction. This was quickly verified in the lab and Josephson was awarded the 1973 Nobel Prize for Physics. The Josephson junction has become an important technology in its own right. For example, superconducting quantum interference devices (SQUIDs) that, depending on their design, use either one or two Josephson junctions are among the most sensitive magnetometers to have been invented. The devices have also shown promise as possible quantum bits (qubits) in quantum computers….
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Written by physicsgg

April 21, 2012 at 6:40 pm

Orbiton: a new quasiparticle

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Spin–orbital separation in the quasi-one-dimensional Mott insulator Sr2CuO3
J. Schlappa et al
When viewed as an elementary particle, the electron has spin and charge. When binding to the atomic nucleus, it also acquires an angular momentum quantum number corresponding to the quantized atomic orbital it occupies. Even if electrons in solids form bands and delocalize from the nuclei, in Mott insulators they retain their three fundamental quantum numbers: spin, charge and orbital. The hallmark of one-dimensional physics is a breaking up of the elementary electron into its separate degrees of freedom. The separation of the electron into independent quasi-particles that carry either spin (spinons) or charge (holons) was first observed fifteen years ago. Here we report observation of the separation of the orbital degree of freedom (orbiton) using resonant inelastic X-ray scattering on the one-dimensional Mott insulator Sr2CuO3. We resolve an orbiton separating itself from spinons and propagating through the lattice as a distinct quasi-particle with a substantial dispersion in energy over momentum, of about 0.2 electronvolts, over nearly one Brillouin zone…
Read more: Nature (2012) doi:10.1038

Read also:
1. Electron ‘split-personality’ seen in new quasi-particle

2. Introducing the ‘orbiton’

Written by physicsgg

April 19, 2012 at 8:46 am

Posted in Materials Science, QUANTUM PHYSICS

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Red Wine, Tartaric Acid And The Secret Of Superconductivity

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Last year, physicists discovered that red wine can turn certain materials into superconductors. Now they’ve found that Beaujolais works best and think they know why

Last year, a group of Japanese physicists grabbed headlines around the world by announcing that they could induce superconductivity in a sample of iron telluride by soaking it in red wine. They found that other alcoholic drinks also worked–white wine, beer, sake and so on–but red wine was by far the best.

The question, of course, is why. What is it about red wine that does the trick?

Today, these guys provide an answer, at least in part. Keita Deguchi at the National Institute for Materials Science in Tsukuba, Japan, and a few buddies, say the mystery ingredient is tartaric acid and have the experimental data to show that it plays an important role in the process.

First, some background. Iron-based superconductors were discovered in 2008 and have since become the focus of intense interest. Deguchi and co study iron telluride which does not superconduct unless some of the telluride atoms are replaced with sulphur, forming FeTeS.

But even then, FeTeS doesn’t superconduct unless it goes through a final processing stage; heating it in water, for example.

Nobody knows what this process does or how it can convert an ordinary material into a superconductor. But some liquids are better than others, as determined by the fraction of the sample they convert into a superconductor.

This is the stage Deguchi and co have been puzzling over. Their approach is to make a sample of FeTeS, cut it up into slices and then heat each slice in a different liquid.

Water works quite well but whiskey, shochu and beer are all better. And of course, red wine is the best of all.

Now Deguchi and co have repeated the experiment with different types of red wine to see which works best. They’ve used wines made with a single grape variety including gamay, pinot noir, merlot, carbernet sauvignon and sangiovese.

It turns out that the best performer is a wine made from the gamay grape–for the connoisseurs, that’s a 2009 Beajoulais from the Paul Beaudet winery in central France.

They then analysed the wines to see which ingredient correlated best with superconducting performance and settled on tartaric acid as the likely culprit. The Beaujolais has the highest tartaric acid concentration.

Finally, they repeated the experiment using a mixture of water and tartaric acid to find out how well it performed.

Interestingly, they found that the solution performed better than water alone but not as well as the Beaujolais.

So while tartaric acid is clearly part of the answer, there must be another component of red wine that somehow encourages the transition to a superconducting state.

That’s a useful step forward for a team clearly dedicated to unravelling the mysterious powers of alcohol. On that basis alone, the work must be applauded.

However, there are still plenty of unanswered questions here, not least of which is how the superconducting transition process occurs at all in the presence of these liquids.

Corkscrews on standby.

Ref: Tartaric Acid In Red Wine As One Of The Key Factors To Induce Superconductivity In FeTe0.8S0.2
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Written by physicsgg

March 22, 2012 at 4:33 pm

Actuation at a distance

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…of microelectromechanical systems using photoelectrowetting: proof-of-concept

Principle of photoelectrowetting-on-semiconductors

Microelectromechanical devices could soon be remotely controlled using light thanks to a proof-of-concept experiment demonstrating ‘photoelectrowetting’

Moving water is fairly straightforward on the human scale: a pump or a bucket will usually do the trick. But in the last couple of decades, various teams have begun to study ways of moving liquids around on the much smaller scale of micrometres.

Their goal is to create devices, such as a lab-on-a-chip, that can carry out self-contained chemical and biological tests on tiny samples. To that end, researchers have developed various new ways to move liquid around using exotic pumps relying on things like electric fields. So-called microfluidic devices are having a big impact in areas from pathogen identification to environmental monitoring

Last year, Steve Arscott at the The University of Lille in France added another tool to this armoury. He showed that light could modify the wetting angle of a conducting droplet sitting on an insulated conductor.

This system is essentially a capacitor: one conductor separated from another by an insulating layer. Physicists have known for some time that changing the voltage in such a capacitor sets up a force that alters the wetting angle of the droplet. This effect, known as electrowetting, is the basis for various kinds of electric pumps.

Photoelectrowetting works in a similar way, says Arscott. With a voltage across the capacitor, the incident light generates charge pairs within the droplet that influence the electric field in the capacitor and this changes the wetting angle.

That was an interesting advance because it raised the prospect of pumping small volumes of water using light and very little power (since there is almost no flow of current).

Today, he and his pal Matthieu Gaude put the photoelectrowetting effect into action. These guys have made a cantilever sitting above an insulated conductor and placed a droplet of water between them so that it fills the gap by capillary action (see above).

Zapping this system with light changes the wetting angle the droplet makes with the cantilever and the electrode below. This makes the droplet thinner, pulling the cantilever down.

The ability to actuate at a distance using light alone could have many applications because it eliminates the need for the complex circuitry and pumps now used to transport droplets. It could also allow optical addressing of autonomous, wireless sensors.

Incidentally. that’s not unlike the light actuation of metamaterials we looked at yesterday. Perhaps there’s a new era of light actuation ahead.

Written by physicsgg

January 18, 2012 at 2:32 pm

Flies walk on air in levitation experiment

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Scientists have used magnetic fields to ‘levitate’ flies in the first weightless tests conducted outside space
The technique, known as ”diamagnetic levitation”, allows water and organic based materials to become weightless.
Floating freely inside a plastic tube, the flies were observed closely to spot any changes in their behaviour.
The scientists confirmed effects previously seen in similar experiments in Earth orbit. The flies walked more quickly and more frequently while floating in zero gravity than they did on the ground.
Previously it was not clear whether the changing G-forces associated with space flight may have affected the flies.
The research is published today in the Journal of the Royal Society Interface.
Author Dr Richard Hill, from the University of Nottingham, and colleagues wrote: ”This study shows that the walking speed of fruit flies and their ‘activity’ is altered significantly by counteracting gravitational force.
”Diamagnetic levitation enabled us to maintain tight control over the experimental conditions of all the experimental subjects. This allowed us to identify, unambiguously, the alteration of effective gravity as the cause of the anomalous behaviour.
”Four billion years of evolution have equipped life on Earth to withstand the stresses generated by the ever-present pull of gravity. Here, we have shown that diamagnetic levitation can be used to investigate directly the influence of changing gravity on the locomotion of a complex multi-cellular organism, and that close comparison can be made with experiments performed in space.”
Magnetic fields have been used in previous studies to levitate organic materials, as well as small living organisms and even a live frog.
”Diamagnetic material is weakly repelled from magnetic fields, compared with the more commonly known ‘magnetic’…materials such as iron, which are strongly attracted to a magnetic field,” the scientists wrote. ”The diamagnetic force, balancing the weight of the levitating object, acts at the molecular level throughout the body of the object, just as the centrifugal force balances the gravitational force on an object in Earth orbit.”

Read also: Levitating fruit flies help scientists understand how astronauts are affected by zero gravity

Written by physicsgg

January 4, 2012 at 4:39 pm

How Superconductors Can Detect Gravitational Waves

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Superconducting metal bars could revolutionise the detection of gravitational waves, says physicists

Gravitational waves are vibrations in the fabric of spacetime. They are among the most exciting phenomena in the universe because they are generated by exotic processes such as collisions between black holes and even in the moment of creation itself, the Big Bang.

So finding a way to study them is a big deal for astronomers.

But there’s a problem. Gravitational waves squeeze and stretch space as they travel but their effects are tiny. Physicists calculate that the waves passing through Earth are changing the distance between London and New York by about the width of a uranium nucleus.

That makes them tough to spot, although he current generation of gravitational detectors ought to be able to detect this level of change (unless somebody’s got their numbers badly wrong).

Nevertheless, nobody has spotted a gravitational wave directly.

So a new way to find these beasts will surely be of interest. Today Armen Gulian at Chapman University in Maryland and a few pals outline a new type of detector that has the potential to be much smaller than today’s behemoths.

Conventional detectors are giant L-shaped interferometers with each arm being many hundreds of metres long. At the end of each arm is a mirror so a laser beam can bounce back and forth along the arms and then be made to interfere with itself.

Any change in the length of the arms ought to show up in any changes in the resultant interference pattern.

Gulian and co have a different idea. They imagine a bar of superconducting metal being hit by a gravitational wave. The waves act on all masses within the bar but the resulting movement of the metallic lattice, which is bound in place, will be very different from the movement of superconducting electrons, which are entirely unbound and free to move.

“Thus, the wave will tend to accelerate the electrons back and forth, towards and away from the ends of the bar,” they say.

Next, they place another superconducting bar at the end of the first but at right angles to it. While the first bar is squeezed by a gravitational wave, the second will be stretched. So the electrons in this bar will oscillate too, albeit shifted by half a period relative to the first.

Finally, if these bars are connected by a superconducting wire, an oscillating current should flow through it.

There are a few other subtleties to the design, largely to cope with the nature of superconductors, but this is essentially the principle they outline.

They go on to sketch the way a small such detector might work, made of bars just a few tens of centimetres long. A gravitational wave ought to generate a current of a few femtoamperes, a level that could be detectable with off-the shelf equipment.

Noise might be a problem, however. But Gulian and co say that if the frequency of the oscillations are known in advance much of the noise can be filtered out. In addition, the detector could be placed inside a magnetic bottle to screen out magnetic noise.

That’s an interesting idea which looks as if it could be considerably cheaper and simpler than the next generation of laser-based gear now being designed for future space missions such as LISA, (the laser interferometer space antenna). Worth looking at in more detail.

Ref: : Superconducting Antenna Concept for Gravitational Wave Radiation

Written by physicsgg

November 15, 2011 at 2:37 pm