MATERIALS ENGINEERING

When moisture condenses on a cool surface, droplets can form that are the right size to scatter light, fogging up glass. A new polymer coating draws droplets into nanopores and transforms them into a transparent sheet, improving vision.

BOSTON--If you're all fogged up, a new discovery may have you seeing more clearly. Fog is not just a weather nuisance for drivers; it can cause problems just about everywhere. Now, a new anti-fog glass coating is clearing the way for consumers.

Your bathroom mirror, eyeglasses, and your car windshield all fall victim to fog. It can happen anywhere moisture condenses on a cool surface.

Michael Rubner, a materials chemist and professor of Polymer Material Science at Massachusetts Institute of Technology in Boston, says, "When they condense they are just the right size to scatter light. If light gets scattered you can't see through those glasses anymore."

Michael created a polymer coating, made from different materials that transform the opaque droplets of water into a transparent sheet. "All of the process that we use to create these coatings is done with water," he says.

The process begins by dipping the glass into a solution of negatively charged tiny glass particle. After, it's dipped into another solution with positively charged polymers. Michael says: "We're forming what we call nanopores. The pores are so small that you can't see them with your eyes. They don't scatter light. But they're large enough so that when you put a drop of water onto the surface, it's drawn into those pores and spread across the surface instantaneously."

The effect allows you to continue seeing clearly through the piece of coated glass. This not only helps you at home, but even the military is looking for fog-free glass. Thomas Long, from Fosta-Tek Optics in Leominster, Mass., says, "The soldiers are faced with either having a foggy field of vision or taking those glasses off to improve their vision, but then being vulnerable to fragments of shrapnel ending their eyesight."

Michael says his coating promises to be long lasting for soldiers out in the field and to drivers just trying to see their way home. He's trying to find a cost-effective way to mass market the polymer coating and hopes it will be available in the next few years.

Courtesy: www.sciencedaily.com

New materials for car bodies may soon transform the auto industry. Auto engineers can mold these carbon-fiber-reinforced plastics into virtually any shape. The materials are both strong and light -- increasing fuel efficiency and safety at the same time.

TROY, Mich.-- Cars built entirely out of plastic could be the wave of the future, making metal a thing of the past when it comes to cars.

New, innovative cars made almost entirely of plastic are paving the way for what you may be driving in the future. Guan Chew, a mechanical engineer at Porsche Engineering Services in Troy, Mich., says, "With plastics you can design cars which are very bold, and that gives you an advantage to sell nicer cars."

Plastics have gained a lot of ground over traditional metals used in cars, making it possible to build almost an entire vehicle completely of non-metal material. Paul Ritchie, CEO and engineer at Porsche Engineering Services, says: "The Carrera GT is what we would refer to as a proving ground for one of our new materials. It's made essentially from reinforced plastic."

Mechanical engineers use a lightweight, high-strength aerospace material called carbon-fiber-reinforced plastic. It's used in the doors, hoods, fenders, chasis and also in support frames for the engine and transmission.

"You can mold the plastics into very complicated shapes that maybe you can't do in steel," Chew says. Looks aren't the only perks of plastic; plastics help cars lose weight to go farther on fuel.

New materials, like plastic, are usually tested on high-end vehicles first. Once the materials are proven to be more efficient and cost effective, they eventually filter down to affordable consumer vehicles.

Transporting energy without any loss, travelling in magnetically levitated trains, carrying out medical imaging (MRI) with small-scale equipment: all these things could come true if we had superconducting materials that worked at room temperature. Researchers at CNRS have now taken another step forward on the road leading to this ultimate goal. They have revealed the metallic nature of a class of so-called critical high-temperature superconducting materials.

This result, which was published in the 31 May 2007 issue of the journal Nature, has been eagerly awaited for 20 years. It paves the way to an understanding of this phenomenon and makes it possible to contemplate its complete theoretical description.

Superconductivity is a state of matter characterized by zero electrical resistance and impermeability to a magnetic field. For instance, it is already used in medical imaging (MRI devices), and could find spectacular applications in the transport and storage of electrical energy without loss, the development of transport systems based on magnetic levitation, wireless communication and even quantum computers.

However, for now, such applications are limited by the fact that superconductivity only occurs at very low temperatures. In fact, it was only once a way of liquefying helium had been developed, which requires a temperature of 4.2 kelvins (-269 °C), that superconductivity was discovered, in 1911 (a discovery for which the Nobel Prize was awarded two years later.)

Since the end of the 1980s (Nobel Prize in 1987), researchers have managed to obtain 'high temperature' superconducting materials: some of these compounds can be made superconducting simply by using liquid nitrogen (77 K, or -196 °C). The record critical temperature (the phase transition temperature below which superconductivity occurs) is today 138 K (-135 °C).

This new class of superconductors, which are easier and cheaper to use, has given fresh impetus to the race to find ever higher critical temperatures, with the ultimate goal of obtaining materials which are superconducting at room temperature. However, until now, researchers have been held back by some fundamental questions. What causes superconductivity at microscopic scales" How do electrons behave in such materials"

Researchers at the National Laboratory for Pulsed Magnetic Fields2, working together with researchers at Sherbrooke, have observed 'quantum oscillations', thanks to their experience in working with intense magnetic fields. They subjected their samples to a magnetic field of as much as 62 teslas (a million times stronger than the Earth's magnetic field), at very low temperatures (between 1.5 K and 4.2 K).

The magnetic field destroys the superconducting state, and the sample, now in a normal state, shows an oscillation of its electrical resistance as a function of the magnetic field. Such an oscillation is characteristic of metals: it means that, in the samples that were studied, the electrons behaved in the same way as in ordinary metals.

The researchers will be able to use this discovery, which has been eagerly awaited for 20 years, to improve their understanding of critical high-temperature superconductivity, which until now had resisted all attempts at modeling it. The discovery has been effective in sorting out the many theories which had emerged to explain the phenomenon, and provides a firm foundation on which to build a new theory. It will make it possible to design more efficient materials, with critical temperatures closer to room temperature.

Reference: Quantum oscillations and the Fermi surface in an underdoped high-Tc superconductor, Nicolas Doiron-Leyraud, Cyril Proust, David LeBoeuf, Julien Levallois, Jean-Baptiste Bonnemaison, Ruixing Liang, D. A. Bonn, W. N. Hardy, Louis Taillefer, Nature, 31 May 2007, Vol 447, pp 565-568.

A new paper published in the Journal of the American Chemical Society (JACS) by a team led by professor Francesc Illas of the UB’s Department of Physical Chemistry and director of the Laboratory of Computational Materials Science (CMSL) will help to broaden our understanding of the nature of superconducting materials and of the origin of the superconductivity phenomenon in high critical temperature materials.

Other participants in the study are Ibério de P. R. Moreira (UB) and Jacek C. Wojdel, currently at the ICMAB-CSIC. The study was carried out with the collaboration of the Barcelona Supercomputing Center (BSC) and the Catalonia Supercomputing Centre (CESCA).

Superconductors are materials that conduct electrical current with zero resistance at low temperatures. Superconductivity was discovered in 1911, and the researchers in this area of solid state physics have been regular recipients of the Nobel Physics Prize: H. K. Onnes (1913), who discovered this extraordinary phenomenon; J. Bardeen, L. Cooper and R. Schrieffer (1972), for the BCS Theory of Superconductivity, which explains how electron pairs are formed (Cooper pairs) and how they conduct electrical current with zero resistance; J.C. Bednorz and K.A. Müller (1987), for their work with ceramic superconducting materials (copper oxides or cuprates) at temperatures above 35 K (-238 ºC) and beyond the boiling point of liquid nitrogen (-196 ºC).

“No theory has been able to account properly for high temperature superconductivity, although it seems to bear a strong relationship with the magnetic properties of materials,” explains Francesc Illas, who is also director of the UB’s Institute of Theoretical and Computational Chemistry (IQTCUB).

In 2008, the discovery of a new family of high critical temperature iron and arsenic superconductors (AsFe) marked a second major revolution in the world of superconductivity. The new compounds, which do not contain copper (Cu) but which have oxygen (O), fluor (F) or arsenic (As) and iron (Fe), will help scientists to solve some of the mysteries in the area of solid state physics.

But are these two high temperature superconductor families really so different? For Francesc Illas, “the main purpose of our work is to stress that these new materials are not as different from cuprates as originally thought. This point is fundamental for defining a unified approach to the two families of superconducting materials.”

According to the new study, the two families of superconducting materials share a similar electronic structure: specifically, Fe and As compounds are antiferromagnetic and exhibit a strong spin frustration, that is, strong magnetic interactions that make the interpretation of experiments difficult.

Another innovation mentioned in the article is the use of sophisticated techniques such as hybrid functionals for the study of electronic structure. “In cuprates,” says Illas, “the most commonly used methodologies are standard LDA (Local Density Approximation) and GGA (Generalized Gradient Approximation), which predict these systems to have a strong metallic character. However, experimental studies on the undoped parent compounds – superconductivity only appears when doping these materials – have shown that cuprates have insulating properties and are antiferromagnetic, but not metallic”. Therefore, the study of these systems will require more elaborate methods than the standard LDA and GGA methods to obtain a satisfactory description of their electronic structure and properties.

According to the experts, studying the electronic structure of the new FeAs based compounds using LDA and GGA also gives erroneous results, as in the case of cuprates. “These techniques,” says Illas, “are unable to give an accurate description of strongly correlated systems (cuprates, new superconductor families, and so on); these limitations have been frequently described in the literature.” More sophisticated approaches are necessary to describe the electronic structure and properties of these magnetic materials.

The discovery of high critical temperature superconductivity is one of the most remarkable chapters in modern science. It is a major breakthrough in developing new technologies and compounds in solid state physics and materials science. Physics experts dream of establishing a satisfactory theoretical model of the electronic structure in order to understand the formation of the superconducting phase, and then to be able to synthesize superconductors at room temperature. This objective seems attainable but not in a near future. For the time being, the most realistic approach is to try to understand the properties of undoped superconducting parent compounds and to progressively understand the effect of doping in the electronic structure of these materials, an area of research in which Illas’s group is one of the leaders in Spain.

An international team including scientists from the London Centre for Nanotechnology (LCN) have just published findings in the journal 'Proceedings of the National Academy of Sciences' (PNAS) demonstrating the dramatic effects of quantum mechanics in a simple magnet.

The importance of the work lies in establishing how a conventional tool of material science -- neutron beams produced at particle accelerators and nuclear reactors -- can be used to produce images of the ghostly entangled states of the quantum world.

At the nano scale, magnetism arises from atoms behaving like little magnets called 'spins'. In ferromagnets -- the kind that stick to fridge doors -- all of these atomic magnets point in the same direction. In antiferromagnets, the spins were thought to spontaneously align themselves opposite to the adjacent spins, leaving the material magnetically neutral overall.

The new research shows that this picture is not correct because it ignores the uncertainties of quantum mechanics. In particular, at odds with everyday intuition, the quantum-mechanical physical laws which operate on the nano-scale allow a spin to simultaneously point both up and down. At the same time, two spins can be linked such that even though it is impossible to know the direction of either by itself, they will always point in opposite directions -- in which case they are 'entangled'.

With their discovery, the researchers demonstrate that neutrons can detect entanglement, the key resource for quantum computing.

One of the lead authors of the work, Professor Des McMorrow from the LCN, comments: "When we embarked on this work, I think it is fair to say that none of us were expecting to see such gigantic effects produced by quantum entanglement in the material we were studying. We were following a hunch that this material might yield something important and we had the good sense to pursue it."

The researchers' next steps will be to pursue the implications for high temperature superconductors, materials carrying electrical currents with no heating and which bear remarkable similarities to the insulating antiferromagnets they have studied, and the design of quantum computers.

Collaborative research between scientists in the UK and USA has led to a major breakthrough in the understanding of antiferromagnets, published in this week's Nature. Scientists at the London Centre for Nanotechnology, the University of Chicago and the Center for Nanoscale Materials at Argonne National Laboratory have used x-rays to see the internal workings of antiferromagnets for the very first time.

Unlike conventional magnets, antiferromagnets (such as the metal chromium) are materials which exhibit 'secret' magnetism, undetectable at a macroscopic level. Instead, their magnetism is confined to very small regions where atoms behave as tiny magnets. They spontaneously align themselves opposite to adjacent atoms, leaving the material magnetically neutral overall.

Professor Gabriel Aeppli, Director of the London Centre for Nanotechnology, said: "People have been familiar with ferromagnets for hundreds of years and they have countless everyday uses; everything from driving electrical motors to storing information on hard disk drives. We haven't been able to make the same strides with antiferromagnets because we weren't able to look inside them and see how they were ordered.

"This breakthrough takes our understanding of the internal dynamics of antiferromagnets to where we were ninety years ago with ferromagnets. Once you can see something, it makes it that much easier to start engineering it."

The magnetic characteristics of ferromagnets have been studied by scientists since Greek antiquity, enabling them to build up a detailed picture of the regions - or "magnetic domains" - into which they are divided. However, antiferromagnets remained a mystery because their internal structure was too fine to be measured.

The internal order of antiferromagnets is on the same scale as the wavelength of x-rays (below 10 nanometers). The latest research used x-ray photon correlation spectroscopy to produce 'speckle' patterns; holograms which provide a unique 'fingerprint' of a particular magnetic domain configuration.

Dr. Eric D. Isaacs, Director of the Center for Nanoscale Materials, said: "Since the discovery of x-rays over 100 years ago, it has been the dream of scientists and engineers to use them to make holographic images of moving objects, such as magnetic domains, at the nanoscale.

"This has only become possible in the last few years with the availability of sources of coherent x-rays, such as the Advanced Photon Source, and the future looks even brighter with the development of fully coherent x-ray sources called Free Electron Lasers over the next few years."

In addition to producing the first antiferromagnet holograms, the research also showed that their magnetic domains shift over time, even at the lowest of temperatures. The most likely explanation for this can be found in quantum mechanics and the experiments open the door to the future exploitation of antiferromagnets in emerging technologies such as quantum computing.

"The key finding of our research provides information on the stability of domain walls in antiferromagnets," said Oleg Shpyrko, lead author on the publication and researcher at the Center for Nanoscale Materials. "Understanding this is the first step towards engineering antiferromagnets into useful nanoscale devices that exploit it."

Work at the London Centre for Nanotechnology was funded by a Royal Society Wolfson Research Merit Award and the Basic Technologies program of Research Councils UK. Work at the Center for Nanoscale Materials and the Advanced Photon Source was supported by the DOE Office of Science, Office of Basic Energy Sciences. The work at the University of Chicago was supported by the National Science Foundation.

Imagine unloading a pile of bricks onto the ground and watching the bricks assemble themselves into a level, straight wall in only a few minutes. While merely a fantasy for builders in the everyday world, these types of self-assembled structures are a reality for those who build materials in the nanoworld.

Michael C. Tringides, a senior physicist at the U.S. Department of Energy's Ames Laboratory, has shown that nanoscale "straight wall" lead islands on silicon are spontaneously and quickly created by unusually mobile atoms.

Several years ago, Tringides' research group was the first to observe that lead atoms deposited on a silicon surface at low temperatures self-organize into uniform-height island nanostructures. The laws of quantum mechanics – specifically, Quantum Size Effects – determine why lead atoms stack up to create uniform islands while other nanostructure systems organize into islands that vary in height.

How the lead-on-silicon islands organized into uniform-height islands remained a mystery until Tringides' team made the surprising discovery that when lead atoms move along the surface of a silicon substrate, the lead atoms exhibit a liquid-like motion instead of the typical random-type diffusion observed in other systems. The liquid-like motion of atoms was observed using scanning tunneling microscopy at Ames Lab and low energy electron microscopy performed by collaborators in Hong Kong.

"One big surprise was that the atoms were moving a lot at such a low temperature: 150 degrees Kelvin or minus 123 degrees Celsius," said Tringides. "The other surprise was that the atoms weren't moving randomly like individual atoms as we would expect. In this particular case, it seemed like the whole layer of lead atoms was moving like a liquid.

Fluid-like motion of the lead atoms explains why the layer moves so easily and forms uniform islands so quickly.

"When applying nanotechnology, it's very important to be able to make nanostructures of the same dimension using a method that others can easily replicate," said Tringides. "And, it's important that the growth process is fast."

Tringides' work succeeds in terms of uniformity and speed. The lead islands self-organize on silicon in only two to three minutes. Also, better understanding of how the lead islands grow will help researchers see if other systems show the same liquid-like behavior at low temperatures.

With such promising findings in hand, Tringides' team, which includes associate scientist Myron Hupalo and graduate students Steven Binz and Jizhou Chen, further investigated the possible use of these unusual lead islands on silicon as templates to study typical atomic processes, such as adsorption, nucleation and atom bonding. These processes are important in the study of reactivity and catalysis.

During those experiments, Tringides' group made another unexpected discovery. Normally atomic processes depend on an element's chemical nature, but the group found that when it came to lead islands, quantum mechanics had another surprise in store: The atomic processes depend dramatically on whether the island height is odd or even rather than its chemical nature. Tringides' group made this intriguing observation in a large lead island that had formed over a step on the original silicon surface. The top of the large island was flat as expected.

"But, the part of the island sitting on the higher terrace of silicon was four layers high, and the other part of the island sitting on the lower terrace was five layers," said Tringides.

The group studied nucleation on this unusual island by adding a very small amount of lead to its surface, creating many new small islands on top of the large island. Examination revealed that the density of the new islands was 60 times higher on the four-layer part of the island than on the five-layer part even though the two parts of the island were connected, suggesting that atom bonding is easier on the four-layer islands.

"The island was made up of the same element, lead, throughout," said Tringides. "So, we would expect the two parts of the island to communicate with each other, and atoms should be able to easily move from left to right and right to left among both halves of the island, so the density of the new small islands should have been the same in both parts."

Instead, the two halves of the island behaved like two separate islands. The four-layer section of the island has similar characteristics to independent four-layer islands, and the five-layer section behaved like other five-layer islands.

"For the purpose of growing materials, the two-part island indicates that we may not have to change the element to create variation in material properties," said Tringides. "Instead, we may be able to just change the height of the island."

"This is promising because it's easier to change the geometry of an island than to go out and find a new, exotic material," he added.

Tringides plans further experiments using gas adsorption to test the relationship between material reactivity and island height.

The Department of Energy's Office of Science, Basic Energy Sciences Office funded the work.