Researchers at the Paul Scherrer Institute have managed to grow a material that is simultaneously ferromagnetic and antiferromagnetic. They grew layers of LuMnO3 on a crystal and found that close to the crystal the material exhibited ferromagnetism, but became antiferromagnetic farther away. The material's structure adapts itself to that of the underlying crystal, which creates this gradient. While varying ferromagnetism has previously been created by layering materials, this is the first time the feat was achieved in a single material. This has implications for the de-sign of compact digital storage media.
A South Korean city has begun testing an "electrified road" that allows electric public buses to recharge their batteries from buried cables as they travel. The Korea Advanced Institute of Science and Technology (KAIST), which developed the system, said it would be tested over the next four months on a 24-kilometre route in the southern city of Gumi.
Pick-up equipment underneath the bus, or Online Electric Vehicle (OLEV), sucks up power through non-contact magnetic charging from strips buried under the road surface. It then distributes the power either to drive the vehicle or for battery storage As a result it requires a battery only one-fifth the size of conventional electric vehicles. The system also eliminates the need for overhead wires used to power conventional trams or trolley buses. The technology does not come cheap, with each OLEV costing around $630,000.
"The technology is readily available but the question is how to bring down the cost," said Park Jong-Han, manager of the company that produced the OLEV prototypes. "Once the cost goes down, I believe more cities will be interested in commercialising the new transport network," Park told AFP. The system has already been partially trialled on a much smaller scale at an amusement park and on the KAIST campus.
Electrifying the road does not require major construction work, as the recharging stations only have to be buried along 10-15 per cent of the route at places such as bus stops.
Nanoscale thermometry has untold possible uses for biology, from basic research on how heat flows in living systems, hyperthermia research in magnetic treatments, to controlling gene expression with temperature. Researchers use a number of techniques for biological thermal sensing, including Raman spectroscopy and detection of fluorescing proteins. But all have problems, such as low sensitivity or the inability to make highly localized measurements. Now, a group led by physics professor Mikhail D. Lukin and chemistry professor Hongkun Park at Harvard University have harnessed a common defect in diamonds to develop an improved approach for nanometer-scale thermometry in biological systems ( Nature 2013, DOI: 10.1038/nature12373 ). In some diamonds, two adjacent carbons are replaced by a nitrogen and an empty spot called a nitrogen vacancy center. Minuscule temperature changes strain the lattice of such diamonds, which affects the quantum spin properties of the local defect and modifies its fluorescence properties. These changes can then be detected.
The group used microwave pulses to manipulate a diamond-lattice defect’s spin states,
and from resulting changes in fluorescence, researchers determined corresponding
temperature variations. The method, they found, is capable of detecting temperature
changes as small as 1.8 mK in areas as small as 200 nm across. The team then tested the thermometer in a living human cell, an embryonic fibroblast. They inserted nanodiamonds and gold nanoparticles into the cell. Laser light heated the gold nanoparticles, and the group monitored temperature gradients throughout the cell by observing changes in the nanodiamonds’ fluorescence. “I like this technique very much,” says Xinwei Wang , a mechanical engineering professor at Iowa State University, noting that in addition to being very sensitive, the technique’s spatial resolution is comparable or superior to that of widely used Raman techniques.
“This kind of sensitivity is extremely important when diagnosing thermal responses and studying chemical reactions in biosystems at the cellular level,” Wang says. Konstantin V. Sokolov, a physics professor at the University of Texas, Houston, calls the work “a precious solution” to the problem of measuring temperatures in biological systems on the nanometer scale. With improvement, the team says the technique may make it possible to observe real-time biological activity with subcell resolution.
This year's and now already 13th Ferrofluid Workshop in Benediktbeuern, Germany will take place from September 25-27, 2013.
Check out the details here:
A team led by Frank Caruso at the University of Melbourne has developed a simple one-pot recipe for a coating made of only Fe(III) and tannic acid, a polyphenol found in wood that is perhaps best known for improving the flavor of wood-casket-aged red wine. The coating is unusually versatile. It can cover all manner of nano- and microscopic objects, including
gold nanoparticles, calcium carbonate and silicon dioxide particles, and bacteria, regardless of whether the object to be coated is positively charged, negatively charged, or neutral ( Science 2013, DOI:10.1126/ science.1237265). The discovery is patentpending.
Since both Fe(III) and tannic acid are generally regarded as safe by regulators and are already used in food and biomedical applications, the coating could find uses right away in areas as diverse as drug delivery and corrosion protection, comments Christopher W.
Bielawski , a chemist at the University of Texas, Austin.
“This is going to make a big impact mainly because it is so simple,” he adds. “Many will wish that they had thought of it first.”
“The coating’s pH sensitivity is the really exciting aspect,” comments Phillip B. Messersmith , a biomedical engineer at Northwestern University. The coating forms above pH 6, but in more acidic environments it falls apart, revealing or releasing the contents of objects within it. One could envision using the coating as a way to deliver a drug to a cell’s acidic lysosome or endosome and then having the contents released in the organelle’s low-pH environment, he says. Researchers use “tannic acid” to describe a family of molecules that contain a central glucose with one to five polygalloyl groups of varying lengths that emanate from the sugar base. Every Fe(III) atom can coordinate three pairs of hydroxyl groups found on tannic acid and thus can complex up to three different tannic acid molecules. Meanwhile, the abundance of hydroxyl groups in tannic acid means that each tannic acid molecule can complex up to a dozen or so iron atoms. The result is a cross-linked coating that is about 10 nm thick, Caruso says.
The technique seems like it could be easily expanded, Bielawski says. “There are a lot of other polyphenols out there besides tannic acid, so there’s considerable potential for changing the surface chemistries of the coating and creating new applications.”
AN OBSTACLE to developing low-cost energy conversion devices is understanding why small differences in materials can strongly affect performance. Figuring out the relationship between the structure and function of an electrode material, for example, is especially challenging for nanoparticle aggregates.
Researchers have now developed an analytical procedure to scrutinize material structure and function with nanometer resolution across micrometer distances in such aggregates. The technique enables them to design a better electrode for solar energy conversion. The group used transmission electron microscopy (TEM) to image the spatial distribution and orientation of nanocrystals within aggregates.
Then, by using a conducting atomic force microscopy method, they correlated the TEM information with the pathways that electrons follow as they move through the material. They used the combo method to probe electron transport in various nanoparticle-based iron oxide electrodes. The electron-transport proficiency of this cheap material makes it useful for generating hydrogen via light-driven water splitting. Although the electrodes they studied were similar, some worked well, while others did not.
The key finding of the team, which includes Scott C. Warren of the University of North Carolina, Chapel Hill, is that the relative orientation of adjacent nanoparticles greatly affects charge transport. A small orientation mismatch is alright, but a large mismatch results in electrical barriers that block current flow between adjacent grains. The upshot is that by identifying “winning” crystal orientations and tailoring the preparation method to favor them throughout the electrode, the group made a device that achieves a record-setting photocurrent for this class of materials ( Nat. Mater. 2013, DOI: 10.1038/nmat3684).
“These results represent an important step forward in developing nanostructured materials for next-generation energy conversion devices,” says solar-fuel specialist Roel van de Krol of Technical University of Berlin. Boston College chemist Dunwei Wang adds that the study helps explain why some nanostructures function better than others. “This work will be of value to photoelectrochemistry studies in general,” he adds. — MITCH JACOBY, C&EN
CO2 gets a lot of attention - mostly negative - as a greenhouse gas. But if CO2 could be converted in a cost-effective manner to valuable products, the ubiquitous small molecule so often reviled for its role in climate change might start to lose its bad rap.
Working to make this happen is Siglinda Perathoner at the University of Messina in Italy. As a catalysis specialist, she and her co-workers have developed methods for preparing catalytic electrodes that consist of iron nanoparticles supported on carbon nanotubes (Fe/CNTs). The picture above shows the overall view, while the picture below zooms in (with HRTEM) onto the magnetic nanoparticles both inside and on the outside of the CNTs. In contrast to the liquid-phase reactions occurring in the electrocatalytic cells used by some researchers, their system converts CO2 in the gas phase. In this way, she sidesteps the need to separate products from a liquid mixture and avoids potential limitations in the amounts of the starting material that can be dissolved in aqueous solution.
Peratoner acknowledges that nanotubes decorated with Pt nanoparticles are more stable and in some cases more active catalysts than Fe/CNTs. Yet Fe/CNTs, especially ones doped with nitrogen, are highly active—for example, in producing isopropyl alcohol—and are especially attractive because of their low cost. For more information, check out her recent paper here.
Researchers who want to combine tiny volumes of liquid have few simple options when it comes to mixing for lab-on-a-chip applications or microliter bioassays. Passive diffusion is slow, and violent stirring can break droplets apart instead of mixing them together.Thanks to a team in Singapore, researchers can now reach for the world’s smallest magnetic stir bars. At just 17 μm long and 75 nm to 1.4 μm thick, these super small stir bars can mix as little as 4 pL of liquid (Angew. Chem. Int. Ed. 2013, DOI:10.1002/anie.201303249). A team at Nanyang Technological University led by Hongyu Chen created the stir bars from oleic acid-stabilized Fe3O4 nanoparticles that are 40 nm in diameter. They modified the nanoparticles with citric acid to render them water-soluble and dissolved them.
The team then used a magnet to align the nanoparticles and gave them a silica coating to ensure they stayed straight and rigid. They centrifuged the mixture to purify the stir bars, which they dispersed in solutions of various concentrations for stirring. While stirring, the nanosized stir bars remain suspended in solution indefinitely. And removing them is as simple as placing a stationary magnet beneath the droplet and letting the stir bars settle out of solution over the course of about five minutes.
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