Visit the Materials360® Plus and the Materials News pages on the MRS Website for continually updated research news and features Image in Focus Nano-Santa (One of three second place winners of the the Science as Art competition at the 2009 MRS Spring Meeting. Submitted by Adam Steele, Georgia Institute of Technology) [We invite you to submit your images for possible inclusion in this feature] Materials in Focus Not all iron superconductors are the same EELS finds atoms Single molecule switches light Half-metallicity in Fermi-level-tuned Heusler alloy for spintronics Non-destructive readout of ferroelectric states Nano Focus Self-erasing images use metastable nanoparticle inks Holey nanosheets for wastewater dye removal Bio Focus DNA sorts carbon nanotubes Upconverting luminescent nanomaterials used for bioimaging Energy Focus Reversible generation of aluminium hydride for hydrogen storage
Credit: Adam Steele, University of Illinois
Nano-Santa with his bag of nano-tubes. This was discovered on the surface of one of the authors' superhydrophobic nanocomposite coatings. It has been colored slightly using image processing for an artistic effect.
We are facing a new paradigm in superconductivity research with the discovery of superconductivity in iron pnictides and the iron chalcogenides. New results now lead, in concert with other recent experimental work, to a remarkable conclusion: iron chalcogenides, in seeming contrast to the iron pnictides, do not exhibit the characteristic Fermi-surface-induced magnetism, a spin-density-wave ordering, that the parent compounds of nearly all other iron-based superconductors share.
Researchers have pushed the sensitivity of electron energy loss spectroscopy (EELS) to the single-atom limit. This advance in EELS's analytical resolving power provides scientists the ability to pinpoint in solids the locations of lone atoms such as impurities and identify them chemically. The group probed carbon nanotubes loaded with a few fullerene cage molecules that had each been doped with one atom of a foreign element such as calcium or cerium. The method revealed the identity and positions of the individual foreign atoms within the nanotubes and differentiated between Ce3+ and Ce4+.
Researchers have made what they say is the world's smallest optical transistor ever — from a single dye molecule. The device, which works by weakening or amplifying a "source" laser beam depending on the power of a second "gating" beam, could bring all-optical circuits and optical computing a step closer. When the molecule is placed in an excited state by the gate beam, it can emit a photon, therefore amplifying the source beam. The key to making the new optical transistor is the tight focusing of light onto a single molecule at ultra-low temperatures. This focusing provides strong light-molecule coupling that allows the molecule to affect the laser light.
Heusler alloys are half-metals, in which the conduction band is split into two polarizations—one half occupied, the other empty—thus providing 100% spin polarized current transport. However, the materials studied so far have shown strongly temperature-dependent behavior due to the band structure, making them unsuitable for practical device applications. A new study now shows that Fermi-level tuning by the introduction of appropriate dopant atoms, a technique similar to electron or hole enrichment in semiconductors, can be applied to the Heusler alloy Co2FeAl0.5Si0.5.
A general problem in the electronics industry is that the insulating materials used in the continually shrinking capacitors and transistors start to leak charge when they become too thin. This leads to large power consumption and, in the case of memory, to difficulties in storing and retrieving information. In a new report, researchers show that this generally undesirable leakage current can in fact be very useful, allowing for direct reading of the polarization state through a simple measurement of the material's electrical resistance.
A technology that could make it possible to create documents that wipe themselves clean after they've been read, exploits the colour-changing ability of nanoparticles. A research team coated gold nanoparticles with a layer of hair-like molecules called 4-(11-mercaptoundecanoxy) azobenzene or MUA. When zapped with ultraviolet light, these filaments change their shape and charge distribution, causing the nanoparticles to congregate together and change color. The team dispersed the nanoparticles in a gel and sandwiched it between plastic sheets to produce a thin, red film. When they shone UV light at the film, they found they could print a range of images or write words onto the film in just a few seconds. The image's lifetime depends on the amount of MUA coated onto each nanoparticle. By varying this concentration, the chemists found they could control how long the images stayed visible, from hours to days.
Researchers have discovered that extremely thin sheets of nickel oxide with hexagonally shaped holes can absorb hazardous dyes from wastewater nearly as well as the best traditional methods. Metal oxides like NiO have the main advantage that the absorbed material can be burned off and the NiO can be reused. Additionally, the polar surface of the NiO nanosheets may provide some advantages in adsorbing certain substrates.
Carbon nanotubes are relatively easy to grow, but sorting them according to their electronic properties is time consuming and costly. Now, researchers have invented a way of isolating different types of nanotube by mixing them with DNA. The new technique involves mixing the SWNTs with a particular DNA sequence, which coats the surface of the nanotubes to form large, hybrid molecules. The researchers found that the chromatography system could be adjusted so that hybrids containing SWNTs of a specific chirality are first through the tube — and could therefore be isolated. The DNA is then removed from the SWNTs, leaving a relatively pure sample.
Researchers have developed an in vivo imaging method that offers a potentially safer and more stable alternative to current methods. They investigated the luminescent properties of yttrium-based nanomaterials and have used the materials to obtain images of blood vessels in mice. The method relies on a process called upconversion, in which particles absorb light of one wavelength and emit light of a shorter wavelength. This recent approach to imaging has many advantages over existing methods, such as the use of quantum dots.
Researchers have created a reversible route for generating aluminum hydride, a high capacity hydrogen storage material. They have developed a novel closed cycle for producing aluminum hydride (AlH3), also known as alane. Alane possesses the desired qualities as a hydrogen storage material, but had been considered impractical because of the high pressures required to combine hydrogen and aluminum to reform the hydride material. Alternate methods of production using chemical synthesis have typically produced stable metal chloride byproducts that make it practically impossible to regenerate the alane. The electrochemical cycle now demonstrated by the group for the production of alane avoids both of these issues.
Thursday, July 16, 2009
NEWS FROM THE WORLD OF MATERIALS
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