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Materials News

Current materials-related news gathered from around the Web that is frequently updated. Visit this page regularly to keep in touch with the latest in materials research. Please note that some external websites may require registration for access.

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• Fractal patterns may be key to semiconductor magnetism
  (Princeton Univ.)

  
  Credit: Roushan/Yazdani Research Group, Princeton University

  The viability of "spintronic" devices of the future requires precise control over semiconductor magnetism. This necessitates a detailed understanding of what happens at the exact transition point when a semiconductor changes from a metal to an insulator -- a phenomenon shrouded in mystery despite decades of examination. In a new study, researchers have observed electrons in a semiconductor, manganese-doped gallium arsenide, on the brink of the metal-insulator transition for the first time. Caught in the act, the electrons formed complex patterns resembling those seen in turbulent fluids, confirming some long-held predictions and providing new insights into how semiconductors can be turned into magnets.
  Reference
  Visualizing Critical Correlations Near the Metal-Insulator Transition in Ga_1-xMn_xAs
  Science 5 February 2010: Vol. 327. no. 5966, pp. 665 - 669 DOI: 10.1126/science.1183640
  (January 9, 2010)

   

• Switchable hardening of a ferromagnet at fixed temperature
  (Eurekalert/Univ. Chicago)

  
  Credit: University of Chicago

  Magnets that can readily switch their polarity are widely used in the computer industry for data storage, but they present an engineering challenge: A magnet's polarity must be easily switched when writing data to memory, but be difficult to switch when storing or reading it. These conflicting requirements are typically met by heating and softening the magnet for saving data, then cooling and hardening the magnet for storage and reading. But now researchers describe a method that avoids this complex heating operation.They can tune the softness of the magnet with the application of a small external magnetic field, which allows writing, storage and readout at a fixed temperature.
  Reference
  Switchable hardening of a ferromagnet at fixed temperature
  Proceedings of the National Academy of Sciences, Early Edition, Jan. 29, 2010. doi: 10.1073/pnas.0910575107
  (January 9, 2010)

   

• Nanoengineering graphene with oxygen
  (NanotechWeb)

  
  Credit: Nanotechnology

  Researchers have investigated graphene epoxide, theoretically using first-principles calculation, as an example of engineered graphene materials by functional groups. They investigated mechanical and electronic properties at various oxidation conditions. For regularly patterned epoxy structures, two phases are revealed to have considerable binding strength consistent with previous experimental observations: the clamped structure where the oxygen is adsorbed on the sp² bond and the unzipped structure where the epoxy binding breaks the sp² bond. For graphene functionalized by very high-density epoxy groups (the ratio between carbon and oxygen atoms is 4:1), a clamped phase is observed that is stabilized by an energy barrier of 0.58 eV. In less-dense graphene oxide, the unzipped phase becomes the only possibility where the sp² bond in the epoxy group is broken.
  Reference
  Engineering graphene by oxidation: a first-principles study
  Nanotechnology 21 (2010) 045704 doi: 10.1088/0957-4484/21/4/045704
  (February 9, 2010)

   

• TiO₂ nanotubes make good stents
  (NanotechWeb)

  Vascular implants can cause inflammatory reactions, such as restenosis and thrombosis, inside the body. The implants cause endothelial cells (which line the inside of blood vessels) to grow in number and the cells begin to "stick" to the surface of the devices. Restenosis happens when vascular smooth muscle cells (VSMCs), which surround the endothelial layer in cells, proliferate. Thrombosis is caused by proliferation of the endothelial cells themselves. One way to overcome these problems is to use drug-eluting stents that inhibit VSMC growth, but such devices can cause thrombosis later on. Ideally, a stent should not prevent endothelial cells from moving about, and at the same time stop the growth of VSMCs. A research team has now found that stents made from TiO₂ nanotubes might just be the ticket. They used a microarray analysis to compare how primary vascular cells grow on the flat nanotube surfaces. The results suggest that TiO₂ nanotubes encourage endothelial cells to travel while inhibiting VSMC growth. This is the optimal type of response needed from vascular cells in response to implants, like stents.
  Reference
  Whole Genome Expression Analysis Reveals Differential Effects of TiO2 Nanotubes on Vascular Cells
  Nano Lett., 2010, 10 (1), pp 143–148 DOI: 10.1021/nl903043z
  (February 8, 2010)

   

• Geometrical frustration in elemental boron
  (Physics Today)

  
  Credit: Phys. Rev. B

  The most stable form of boron at 0 K is unknown. The lowest-energy phase that experimenters have found, the β-rhombohedral phase, is stunningly complex and defect riddled: Each hexagonal unit cell has 423 atomic sites; on average only 320 of them are occupied. Researchers have now explained why the stable β-rhombohedral phase has so many empty sites. If boron were simple, the defects would disappear as boron attained its perfect crystalline structure. But according to calculations, the defects actually stabilize the β-rhombohedral phase. It turns out the defect sites in the crystal are arranged in a particular geometric configuration, a double-layer expanded kagome lattice. The researchers realized that the problem of how boron atoms fill empty sites is essentially the same as another problem: how antiferromagnetically coupled spins align themselves on an expanded kagome lattice, whose ground state is degenerate and disordered. Like spin ices, and ordinary water ice, boron's β-rhombohedral phase is geometrically frustrated. The hopping of defects between nearly degenerate configurations can also account for some of boron's peculiar and long-puzzling transport properties.
  Reference
  Geometrical frustration in an elemental solid: An Ising model to explain the defect structure of β-rhombohedral boron
  Phys. Rev. B 81, 020102(R) (2010) DOI: 10.1103/PhysRevB.81.020102
  (February 8, 2010)

   

• Different freezing behavior of water on positively and negatively charged surfaces
  (Chemistry World)

  
  Credit: Thinkstock Images

  For more than 150 years it has been known that electrical fields can affect the freezing point of supercooled water. However, it has been difficult to study the phenomenon in any detail because conducting surfaces promote nucleation of water in any event. Now, a team led by Igor Lubomirsky at the Weizmann Institute in Rehovot has devised an elegant experiment in which charge can be created on insulating surfaces to probe electrical effects on the freezing point of supercooled water. The researchers used the pyroelectric material lithium tantalate (LiTaO₃), which can develop a positive or negative electrical charge depending on temperature, as a surface upon which to study supercooled water droplets. They found that on a surface with no electric field, the droplets froze at around -12.5°C. On a positively charged surface, however, the freezing point was raised to -7°C, while if the surface was negatively charged the droplet did not freeze until the temperature reached -18°C. The exact mechanism remains a mystery.
  Reference
  Water Freezes Differently on Positively and Negatively Charged Surfaces of Pyroelectric Materials
  Science 5 February 2010: Vol. 327. no. 5966, pp. 672 - 675 DOI: 10.1126/science.1178085
  (February 8, 2010)

   

• Cancer cells destroyed by nanobubbles
  (Science Daily)

  
  Credit: Rice University

  Using lasers and nanoparticles, scientists have discovered a new technique for singling out individual diseased cells and destroying them with tiny explosions. The scientists used lasers to make "nanobubbles" by zapping gold nanoparticles inside cells. In tests on cancer cells, they found they could tune the lasers to create either small, bright bubbles that were visible but harmless or large bubbles that burst the cells. They tested the approach on leukemia cells and cells from head and neck cancers. They attached antibodies to the nanoparticles so they would target only the cancer cells, and they found the technique was effective at locating and killing the cancer cells. The nanobubble technology could be used for "theranostics," a single process that combines diagnosis and therapy.
  Reference
  Tunable plasmonic nanobubbles for cell theranostics
  Nanotechnology 21 085102 (2010)   doi: 10.1088/0957-4484/21/8/085102
  (February 5, 2010)

   

• Graphene transistor hits record 100 GHz
  (Physics World)

  
  Credit: Phaedon Avouris, IBM

  Researchers have made the fastest graphene transistor ever, with a cut-off frequency of 100 GHz. The device can be further miniaturized and optimized so that it could soon outperform conventional devices made from silicon, according to the authors. They began making their field-effect transistor (FET) by heating a wafer of silicon carbide (SiC) to create a surface layer of carbon atoms in the form of graphene. Parallel source and drain electrodes were then deposited on the graphene, leaving channels of exposed graphene between them. The next step is the trickiest – depositing a thin insulating layer onto the exposed graphene without adversely affecting its electronic properties. To do this, the team first laid down a 10 nm layer of poly-hydroxystrene – a polymer used in commercial semiconductor processing – to protect the graphene. Then a conventional oxide layer was deposited, followed by a metallic gate electrode. The gate length is relatively large at 240 nm, but it could be scaled down in the future.
  Reference
  100-GHz Transistors from Wafer-Scale Epitaxial Graphene
  Science 5 February 2010: Vol. 327. no. 5966, p. 662
  DOI: 10.1126/science.1184289
  (February 5, 2010)

   

• Room temperature germanium-on-silicon laser reported
  (Massachusetts Institute of Technology)

  
  Credit: MIT

  Researchers have demonstrated the first laser built from germanium that can produce wavelengths of light useful for optical communication. It’s also the first germanium laser to operate at room temperature. Unlike the materials typically used in lasers, germanium is easy to incorporate into existing processes for manufacturing silicon chips. So the result could prove an important step toward computers that move data — and maybe even perform calculations — using light instead of electricity. But more fundamentally, the researchers have shown that, contrary to prior belief, a class of materials called indirect-band-gap semiconductors can yield practical lasers. To achieve this, the group used two strategies. First, the group doped its germanium with phosphorous. Second, they “strained” the germanium by growing it directly on top of a layer of silicon.
  Reference
  A Ge-on-Si laser operating at room temperature
  Optics Letters To be published
  (February 4, 2010)

   

• Why spider webs glisten with dew
  (Nature)

  
  Credit: Nature

  Researchers have puzzled out how spider silk is able to catch the morning dew. A new study examines the silk of the hackled orbweaver spider Uloborus walckenaerius and why "Bright, pearl-like water drops hang on thin spider silk in the morning after fogging". Dry spider silk forms a necklace-like structure. Two main fibers support a series of separate rounded 'puffs', each made up of tiny, randomly intertwined nanofibrils. When water vapor condenses onto these puffs, they shrink into densely packed knots, shaped like spindles (or two cones with their bases stuck together). Thinner connecting stretches of nanofibrils, separating the knots, become more apparent; these areas are called 'joints'. The researchers studied the webs under both electron and light microscopes. They noticed that as water condenses on the web, droplets move towards the nearest spindle-knot, where they coalesce to form larger drops. Guided by their findings, the team also made their own artificial spider silk using nylon fibres dipped in a polymer solution that, when dried, formed spindle-knots similar to those in natural spider silk.
  Reference
  Directional water collection on wetted spider silk
  Nature 463, 640-643 (4 February 2010) | doi:10.1038/nature08729
  (February 3, 2010)

   

• 3-D scaffold provides clean, biodegradable structure for stem cell growth
  (University of Washington)

  
  Credit: University of Washington

  In 2005, medical researchers were shocked to discover that virtually all human embryonic stem cell lines were contaminated. Animal byproducts used to line Petri dishes had left traces on the human cells. If those cells had been implanted in a human body they likely would have been rejected by the patient's immune system. Even today, with new stem cell lines approved for use in medical research, there remains a risk that these cells will be contaminated in the same way. Most research labs still use animal-based "feeder layers" because it remains the cheapest and most reliable way to get stem cells to multiply. Scientists have now created an alternative. They have built a three-dimensional scaffold out of a natural material that mimics the binding sites for stem cells, allowing the cells to reproduce on a clean, biodegradable structure. Recent results show that human embryonic stem cells grow and multiply readily on the structure. The new cylindrical scaffold is made of chitosan, found in the shells of crustaceans, and alginate, a gelatinous substance found in algae. Chitosan and alginate have a structure similar to the matrix that surrounds cells in the body, to which cells can attach. Researchers first seeded the scaffold with 500,000 embryonic stem cells, and after 21 days the scaffold was completely saturated. Analysis of gene activity and testing in the lab and in mice showed that the new stem cells retained the same properties as their predecessors.
  Reference
  Feeder-free self-renewal of human embryonic stem cells in 3D porous natural polymer scaffolds
  Biomaterials Volume 31, Issue 3, January 2010, Pages 404-412, doi:10.1016/j.biomaterials.2009.09.070
  (February 3, 2010)

   

• Graphene FETs with large transport band gap at room temperature
  (NanotechWeb)

  
  Credit: P Avouris, IBM

  The fact that graphene lacks a bandgap limits its use in digital electronics based on current switching. Indeed, as a result, the on/off current switching ratio in graphene devices made so far is typically around 5, which is too low for practical applications. Scientists have now succeeded in opening up a large electrical bandgap in graphene at room temperature for the first time. Recently, researchers have also been studying bilayer graphene, which can develop a bandgap when a perpendicular electric field is applied. Until now, though, efforts to open up a large bandgap at room temperature have not been all that successful and higher on/off ratios were only possible at very low temperatures. In the new study, scientists demonstrated a bilayer field-effect transistor (FET) that has an electric-field induced bandgap of 120 meV and an off/ratio of as high as 100 at room temperature.
  Reference
  Graphene Field-Effect Transistors with High On/Off Current Ratio and Large Transport Band Gap at Room Temperature
  Nano Lett. Articles ASAP Publication Date (Web): January 21, 2010 (Letter) DOI: 10.1021/nl9039636
  (February 2, 2010)

   

• Carbon crystals in meteorite harder than diamond
  (Discovery News)

     
     Credit: iStockPhoto

  Researchers using a diamond paste to polish a slice of meteorite stumbled onto something remarkable: crystals in the rock that are harder than diamonds. A closer look with an array of instruments revealed two totally new kinds of naturally occurring carbon, which are harder than the diamonds formed inside the Earth. The researchers were polishing a slice of the carbon-rich Havero meteorite that fell to Earth in Finland in 1971. When they then studied the polished surface they discovered carbon-loaded spots that were raised well above the rest of the surface –- suggesting that these areas were harder than the diamonds used in the polishing paste. What apparently happened in the Havero meteorite is that graphite layers were shocked and heated enough to create bonds between the layers. They confirmed that they had, indeed, found a new "phase" or polymorph of crystalline carbon as well as a type of diamond that had been predicted to exist decades ago, but had never been found in nature until now.
  Reference
  Carbon polymorphism in shocked meteorites: Evidence for new natural ultrahard phases
  Earth and Planetary Science Letters Volume 290, Issues 1-2, 15 February 2010, Pages 150-154
  (February 2, 2010)

   

• Tungsten breaks tough aromatic carbon-carbon bond
  (Chemical & Engineering News)

     
     Credit: Nature

  A strong aromatic carbon-carbon bond can be cleaved with ease by a tungsten complex that inserts the metal between the two carbon atoms. The mechanism of this unusual bond breaking, which was observed in quinoxaline under mild conditions, could be extended to other systems, say the report’s authors, opening new avenues for functionalizing aromatic molecules. The scientsits discovered the tungsten complex’s bond-breaking ability while searching for a compound that would cleave C–N aromatic bonds. They had been working with molybdenum complexes but decided to switch to tungsten, which is a more aggressive metal. They were surprised to find that in the presence of the N-heterocyclic molecule quinoxaline, the tungsten complex breaks the aromatic C–C bond adjacent to the aromatic C–N bond, even though the C–N bond is typically more reactive.
  Reference
  Cleaving carbon–carbon bonds by inserting tungsten into unstrained aromatic rings
  Nature 463, 523-526 (28 January 2010) doi:10.1038/nature08730
  (February 1, 2010)

   

• Flexible sheets capture energy from movement
  (Technology Review)

  
  Credit: Frank Wojciechowski

  Researchers have created a flexible material that harvests record amounts of energy when stressed. The energy-harvesting rubber sandwiches ribbons of piezoelectric PZT between pieces of silicone. The rubber material can harness 80 percent of the energy applied when it is flexed--four times more than existing flexible piezoelectric materials. PZT is the most efficient piezoelectric material known, but its crystalline structure means that it must be grown at high temperatures, which normally melt a flexible substrate. The researchers got around this by making PZT at high temperatures and then transferring thin ribbons of the material onto silicone. Proof-of-concept tests show that the rubber-encased PZT ribbons maintain their high power-conversion efficiency.
  Reference
  Piezoelectric Ribbons Printed onto Rubber for Flexible Energy Conversion
  Nano Lett., Article ASAP DOI: 10.1021/nl903377u Publication Date (Web): January 26, 2010
  (February 1, 2010)

• Phase transitions of atoms on carbon nanotubes
  (Science)

  The nature of phase transitions changes with system dimensionality. Many aspects of two-dimensional systems have been explored by adsorbing rare gases on graphite surfaces. In a new study, scientists have reduced the dimensionality further by examining phase transitions of argon and krypton on single-walled carbon nanotubes, following the extent of surface coverage and mapping out phase transitions by using the nanotube as a resonator. Changing the conductance and thus the density of surface electrons also allowed exploration of the effect of adsorbate-surface interactions.
  Reference
  Phase Transitions of Adsorbed Atoms on the Surface of a Carbon Nanotube
  Science 29 January 2010: Vol. 327. no. 5965, pp. 552 - 555 DOI: 10.1126/science.1182507
  (January 29, 2010)

   

• Better Li-ion batteries with symbiotic coaxial nanocables
  (Chemistry World)

  
  Credit: Chemistry of Materials

  Nano-sized cables made with titanium dioxide (TiO₂)-coated carbon nanotubes could hold the key to developing new high-capacity lithium ion batteries. Graphite, used as the anode in current Li-ion batteries has a fairly low storage capacity and release rate. Now, researchers have developed an alternative by coating carbon nanotubes with a nanoporous layer of TiO₂. The result is a crystalline solid made up from 'coaxial cables' that are perfect for trapping lithium ions. The nanotubes form a highly conductive core and act as fast-track pathways for electron transfer in the structure, making the electrodes highly conductive. The two have interfacial contact, they form a symbiotic relationship that boosts their storage ability even further. The nanocables appeared reliable, showing almost no capacity loss after one hundred cycles.
  Reference
  Symbiotic Coaxial Nanocables: Facile Synthesis and an Efficient and Elegant Morphological Solution to the Lithium Storage Problem
  Chem. Mater., Article ASAP DOI: 10.1021/cm9036742 Publication Date (Web): January 22, 2010
  (January 29, 2010)

   

• Diamond becomes stronger under rapid compression
  (Lawrence Livermore National Laboratory)

  
  Credit: Eugene Kowaluk/LLE

  Diamond of course is one of the hardest solids on Earth. Surprisingly, very little is known about the strength of diamond at extreme conditions. But new research now shows that diamond becomes even stronger during rapid compression. Using high power lasers researchers have shown that when shock waves are applied to diamond, it can support almost a million times atmospheric pressure before being crushed. They measured the behavior of natural diamond crystals under shock-wave compression between 1 million and 10 million atmospheres of pressure, and the diamonds were crushed and melted in just a nanosecond. The diamonds exhibited considerable strength right up to the melting point.
  Reference
  Strength effects in diamond under shock compression from 0.1 to 1 TPa
  Phys. Rev. B 81, 014111 (2010)
  (January 28, 2010)

   

• Organic transistor mimics brain synapse
  (Physics World)

  
  Credit: Dominique Vuillaume

  Researchers claim to have made the first transistor that mimics connections in the human brain. The device, based on pentacene and gold nanoparticles, could lead to a new generation of neuro-inspired computers as well as help connect artificial structures to biological tissue. The scientists studied how electric charges flow through the device and discovered that they behave in the same way as chemical neurotransmitters moving through a synaptic connection in the brain. The team began by adding gold nanoparticles to the interface between an insulating layer (gate dielectric) and an organic transistor made of pentacene. They fixed the nanoparticles, which were 5, 10 and 20 nm in diameter, into the source-drain channel of the device using surface chemistry techniques and finished the structure by covering it with a 35 nm thick film of pentacene. The resulting device is called a nanoparticle organic memory field-effect transistor or "NOMFET".
  Reference
  An Organic Nanoparticle Transistor Behaving as a Biological Spiking Synapse
  Advanced Functional Materials Volume 20 Issue 2, Pages 330 - 337
  (January 28, 2010)

   

• Mismatched alloys are a good match for thermoelectrics
  (Science Daily)

  
  Credit: Junqiao Wu, Lawrence Berkeley National Lab.

  Employing some of the world's most powerful supercomputers, scientists have shown that mismatched alloys are a good match for the future development of high performance thermoelectric devices. Thermoelectrics hold enormous potential for green energy production because of their ability to convert heat into electricity. The computations showed that the introduction of oxygen impurities into a unique class of semiconductors known as highly mismatched alloys (HMAs) can substantially enhance the thermoelectric performance of these materials without the customary degradation in electric conductivity. Specifically, they showed that the hybridization of electronic wave functions of alloy constituents in HMAs makes it possible to enhance thermopower without much reduction of electric conductivity, which is not the case for conventional thermoelectric materials. The researchers predict a range of inexpensive, abundant, non-toxic materials in which the band structure can be widely tuned for maximal thermoelectric efficiency.
  Reference
  Enhancing the Thermoelectric Power Factor with Highly Mismatched Isoelectronic Doping
  Phys. Rev. Lett. 104, 016602 (2010)
  (January 28, 2010)

   

• Venus flytrap material captures radioactive waste
  (ScienceNOW)

  Of all the radioactive isotopes left over from nuclear weapons testing and nuclear power plants, cesium-137 is among the most dangerous. The soft, silvery-white metal has a half-life of 30 years, enters the body quickly, and can trigger cancer even decades after exposure. Removing cesium-137 from the environment has proven difficult, but researchers say they have a promising new way to clean it up: a flexible, porous solid that grabs cesium ions much like a Venus flytrap ensnares its prey. The new material is part of a class of materials made of spongelike frameworks of inorganic elements. The researchers made their framework from a mixture of gallium, tin, and sulfur, which formed sheets with holes. They also added dimethylammonium (DMA) ions. The sheets stacked atop one another with the holes running up and down through the material and with the DMA ions sitting in between the layers. When the cesium enters, it not only displaces DMA, it also binds to a sulfur atom in the lattice. This tugs on the framework and pulls the holes closed, thereby trapping the cesium inside, a bit like a molecular Venus flytrap. Further studies also showed that the material preferentially bound cesium ions even in the presence of chemically similar alkali metals.
  Reference
  Selective incarceration of caesium ions by Venus flytrap action of a flexible framework sulfide
  Nature Chemistry Published online: 24 January 2010 | doi:10.1038/nchem.519
  (January 27, 2010)

   

• Boron cluster forms unique ring system
  (Chemistry World)

  
  Credit: Nature Chemistry

  Scientists have discovered that the lowest energy form of B19^- boasts a pentagonal six-atom group sharing two pi-electrons, surrounded by thirteen boron atoms sharing ten electrons. Although concentric pi-systems have been seen in organic molecules, none have exactly this electronic configuration. This is the first time a concentric doubly pi-aromatic system is shown to exist in a non-carbon based structure. Replacing the central B6 unit with transition metals might produce boron-based nanosystems with tunable optical, electronic and magnetic properties, according to the authors.
  Reference
  A concentric planar doubly π-aromatic B19− cluster
  Nature Chemistry Published online: 24 January 2010 | doi:10.1038/nchem.534
  (January 26, 2010)

   

• Random lasing in pi-conjugated polymer films
  (Eurekalert/Nature Physics)

  
  Credit: Randy Polson, University of Utah

  Scientists have previously discovered a new kind of laser generated by an electrically conducting polymer, but no one could explain how it worked. Now, a decade later, the researchers have found that these "random lasers" occur because of natural, mirror-like cavities in the polymer. To view the laser-generating cavities within the polymer, the scientists focused a green, conventional laser pulse on a thin film of the polymer, stimulating red random laser emission from the film. They revealed the mirror-like cavities by showing adjacent pixels with the same red light spectrum and the same above-average index of refraction. When they mapped areas of above-average refraction index within the polymer, those areas were connected to form loops, which act as mirror-like cavities to generate laser light. The cavities which are natural irregularities within the plastic thus act together like the mirrors in regular resonators that help amplify the light in a conventional laser.
  Reference
  Naturally occurring resonators in random lasing of -conjugated polymer films
  Nature Physics Published online: 24 January 2010 | doi:10.1038/nphys1509
  (January 26, 2010)

   

• X-rays drive formation of new crystals from peptide filaments
  (Science Daily)

  
  Credit: Yuri S. Velichko, Northwestern University

  A team of researchers has discovered that X-rays can trigger the formation of a new type of crystal: charged cylindrical filaments ordered like a bundle of pencils experiencing repulsive forces. Similar phenomena may occur naturally in biology, such as in the cytoskeleton filaments of cells, which control cell division and migration in cancer metastasis and many other processes. Crystal formation is usually based on attractive forces between atoms or molecules. The serendipitous discovery was made when the research team applied synchrotron X-ray radiation to a solution of peptide nanofibers they were studying. The researchers saw the solution go from clear to opaque. The X-rays increase the charge of the filaments, and thus a repulsive electrostatic force drives the crystallization -- a hexagonal stacking of filaments. Trapped in a three-dimensional network, the charged bundled filaments are unable to escape from each other. The crystals disappear when the X-rays are turned off, and the material is not significantly damaged by the radiation. As a result of repulsive forces, the filaments are positioned far apart from each other, with as much as 320 angstroms separating the filaments. This striking feature is not found in ordinary crystals where molecules are less than five angstroms apart.
  Reference
  Spontaneous- and X-rayTriggered Crystallization at Long Range in Self-Assembling Filament Networks
  Science DOI: 10.1126/science.1182340
  (January 26, 2010)

   

• Gd-Nanodiamond compound improves MRI contrast
  (Technology Review)

  
  Credit: American Chemical Society

  Magnetic resonance imaging (MRI) has become an indispensable medical diagnostic tool because of its ability to produce detailed, 3D pictures of tissue in the body. Radiologists often inject patients with contrast agents to make certain tissues, such as tumors, stand out more on the final image. Now, researchers have synthesized an MRI contrast agent that is 15 times more sensitive than the compounds currently used. This could allow less contrast agent to be used, thus reducing the potential for harmful side effects. The researchers created the new compound by chemically linking gadolinium ions to nanodiamond. Gadolinium, a rare-earth metal, is used in MRI contrast agents because of its strong paramagnetic properties. But alone, gadolinium is toxic, so it has to be bonded to other, biocompatible molecules to be used clinically.
  Reference
  Gd(III)-Nanodiamond Conjugates for MRI Contrast Enhancement
  Nano Lett., Articles ASAP (As Soon As Publishable) Publication Date (Web): December 28, 2009 (Letter) DOI: 10.1021/nl903264h
  (January 22, 2010)

   

• Colloids as models for epitaxial growth
  (Science)

  
  Credit: Ganapathy et al., Science

  Colloids are often used as analogs for atoms in order to study crystallization kinetics or glassy dynamics using particles that are much easier to observe and that move on much slower time scales. A new study considers whether the analogous behavior extends to the growth of epitaxial films, a technique that is used in manufacturing. Controlling the rate of addition of the colloidal particles allowed the mapping of diffusional pathways during film nucleation and growth on a patterned substrate. The same relationships used to describe atomistic growth could be applied to the colloidal systems, but certain growth barriers such as those found at step edges and corners were controlled by diffusion rather than energetics.
  Reference
  Direct Measurements of Island Growth and Step-Edge Barriers in Colloidal Epitaxy
  Science 22 January 2010: Vol. 327. no. 5964, pp. 445 - 448 DOI: 10.1126/science.1179947
  (January 22, 2010)

   

• Electromagnetic pulses punch holes through steel
  (The Economist)

  
  Credit: The Economist

  Electromagnetic pulses (EMPs) have been employed industrially to shape soft and light metals, such as aluminium and copper. Now a group of researchers has found a way to use an EMP device to shape and punch holes through industrys metallic heavyweightsteel. This could transform manufacturing by doing away with the need to use large, heavy presses to make goods ranging from cars to washing machines. They performed their trick by beefing up an existing electromagnetic-forming machine. Such machines use a bank of capacitors to discharge a current rapidly through a coil. The coil converts the current into a powerful magnetic field. When the component to be worked is placed next to such a machine, the coil induces in it a corresponding field. Like poles repel, and the repulsion between the two fields is strong enough to make the metal distort. The researchers boosted the power of their machine by strengthening its coil and speeding up the rate at which the capacitors dump their charge. The result is an extremely strong fieldone that delivers enough pressure when it hits the steel to punch out the material next to it, leaving a hole behind. The impact pressure on the steel is about 3,500 atmospheres. The machine is able to punch holes 30 mm in diameter through the type of sheet steel used to build car bodies, which is usually around 1 mm thick. The group have also used their machine to punch holes in hardened steel, including stainless steel. In addition, such a machine could also be used to form shapes out of the metal without the need to use a mould or a die.
  (January 21, 2010)

   

• Strong crystal size effect on deformation twinning
  (Nature)

  
  Credit: Nature

  Deformation twinning in crystals controls the mechanical behavior of many materials, however, its size-dependence has not been explored, and its origin and spatio-temporal features remain shrouded in mystery. In a new study, using micro-compression and in situ nano-compression experiments, the stress required for deformation twinning was found to increase drastically with decreasing sample size of a titanium alloy single crystal, until the sample size is reduced to one micrometer; below this point, deformation twinning is replaced by dislocation plasticity.
  Reference
  Strong crystal size effect on deformation twinning
  Nature 463, 335-338 (21 January 2010) | doi:10.1038/nature08692
  (January 21, 2010)

   

• Hydrogel self-heals in seconds
  (Chemistry World)

  
  Credit: Takuzo Aida

  Researchers have created a rapidly self-healing hydrogel material. The new material is remarkably tough compared to other hydrogels of the same kind - non-covalent hydrogels - which have until now been regarded as fairly weak. The researchers compare it to silicone rubber in terms of strength. If the gel is cut with a razor, it immediately sticks itself back together, healing in around three seconds. At 98 per cent water, the gel contains small amounts of just three other components: sodium polyacrylate, a branched molecule dubbed 'G3-binder', which is covered in guanidinium ions, and clay, in the shape of nanosheets. These are simply mixed together to make the gel, which forms in seconds. The binder molecules give the gel its self-healing properties by cross-linking the clay nanosheets. The positively charged guanidinium ions stick resolutely to negatively charged oxyanions on the surface of the clay. Cutting the gel rips these apart, but if the freshly cut surfaces are pushed against each other straight away, the reverse process occurs and the oppositely charged ions stick back together.
  Reference
  High-water-content mouldable hydrogels by mixing clay and a dendritic molecular binder
  Nature 463, 339-343 (21 January 2010) | doi:10.1038/nature08693
  (January 21, 2010)

   

• Never say never to a forbidden transition
  (Physics)

  
  Credit: J. Renger et al.
  Phys. Rev. Lett. (2009)

  Surface plasmon polaritons (SPPs) are electromagnetic waves that are coupled to charge density oscillations at a metal/dielectric interface, and result from light or free electrons hitting the metal surface. Up to now, the two standard ways of exciting an SPP on a metal with light have been to either use a nonpropagating, or “evanescent,” light wave, or to use a rough or artificially corrugated surface. A research team has now theoretically proposed and experimentally demonstrated a new route to SPP excitation from propagating light impinging directly on a flat surface of gold. Their method to produce this “free-space excitation” involves not one but three incident photons at a time, whose momenta add to give the right balance of in-plane momentum for SPP coupling. These SPPs were found to have well-defined energies, momenta, and directivity.
  Reference
  Free-Space Excitation of Propagating Surface Plasmon Polaritons by Nonlinear Four-Wave Mixing
  Phys. Rev. Lett. 103, 266802 (Published December 21, 2009)
  (January 20, 2010)

   

• Bubbles break spherical mold
  (Physical Review Focus)

  
  Credit: Phys. Rev. E, 81, 016308 (2010)

  Not all bubbles are round. In fact, a new laser-based technique has been developed to make square bubbles, donut bubbles, and V-shaped bubbles. The researchers who conducted the study claim that many other shapes can be made on-demand. These vapor bubbles and the liquid jets they create could have practical uses in moving and bending nanostructures, as well as for manipulating biological cells. For decades researchers have been controlling the onset of vapor bubbles by focusing lasers inside a liquid. The laser rapidly heats a small region of the liquid above the boiling point, so that a bubble literally explodes out of the liquid. As the bubble cools, the vapor recondenses and the bubble collapses on itself in less than a millisecond. The research team followed the path of earlier work going back to the 1970s, in which researchers placed a holographic plate in the beam line of a laser, to create multiple focal points. They used a newer device called a spatial light modulator, a two-dimensional reflective array that is essentially a computer-controlled holographic plate. Each pixel in the array separately controls the phase of the light ray bouncing off of it. When a lens concentrates all the rays, they interfere at the focal plane to create high intensity regions of any desired shape.
  Reference
  Nonspherical Laser-Induced Cavitation Bubbles
  Phys. Rev. E 81, 016308 (issue of January 2010)
  (January 20, 2010)

   

• Magnetic field assembles lithography mask
  (NanotechWeb)

  
  Credit: Chih-Hao Chang et al.

  A group of researchers has developed a tunable nanostructured lithography mask composed of self-assembled nanoparticles. The group was able to use magnetic fields to control the nanoparticle assembly, and therefore the shape of the "lithography mask," to pattern different geometries. In this new approach, called self-assembled ferrofluid lithography (SAFLi), the team used iron oxide nanoparticles (diameter ~10 nm) in a ferrofluid as a dynamic lithography mask. The particles, typically randomly dispersed in the solution, assemble to form ordered structures when external magnetic fields are applied. In the system proposed by the team, microfluidic channels confine the ferrofluid over photosensitive film, which is then exposed by ultraviolet light. The assembled nanoparticles have higher optical absorption than the liquid and function as a lithography mask by replicating the assembly pattern in the polymer film. The assembly pattern can be actively controlled by tuning the external field, which allows various geometries to be patterned.
  Reference
  Self-assembled ferrofluid lithography: patterning micro and nanostructures by controlling magnetic nanoparticles
  Nanotechnology 20 (2009) 495301, doi: 10.1088/0957-4484/20/49/495301
  (January 19, 2010)

   

• Nanoburrs target cardiovascular disease
  (Eurekalert)

  Researchers have built targeted nanoparticles that can cling to artery walls and slowly release medicine, an advance that potentially provides an alternative to drug-releasing stents in some patients with cardiovascular disease. The particles, dubbed "nanoburrs" because they are coated with tiny protein fragments that allow them to stick to target proteins, can be designed to release their drug payload over several days. They are one of the first such particles that can precisely home in on damaged vascular tissue. The particles, which are spheres 60 nanometers in diameter, consist of three layers: an inner core containing a complex of the drug and a polymer chain called PLA; a middle layer of soybean lecithin, a fatty material; and an outer coating of the polymer PEG, which protects the particle as it travels through the bloodstream. The drug can only be released when it detaches from the PLA polymer chain, which occurs gradually by a reaction called ester hydrolysis. The longer the polymer chain, the longer this process takes, so the researchers can control the timing of the drug's release by altering the chain length. So far, they have achieved drug release over 12 days, in tests in cultured cells.
  Reference
  Spatiotemporal controlled delivery of nanoparticles to injured vasculature
  Proceedings of the National Academy of Sciences, week of Jan. 18, 2010
  (January 19, 2010)

   

• Unusual case of symmetry-preserving isomerism
  (Highlights in Chemical Science)

  
  Credit: Chem. Commun.

  Usually, two compounds with the same composition, atom-to-atom connectivity and symmetry would be expected to be chemically identical too. However, scientists investigating metal-organic frameworks have discovered a surprising exception to this rule by identifying two isomers with the same symmetry and bonding but different gas storage properties. A research team investigated a rod-like tetracarboxylate molecule which can bind to a metal atom from any one of four binding points, one at each corner of a rectangle. When it was heated with a copper salt at 75°C, a crystal phase formed (the alpha-phase) and at 65°C a phase with different properties (the beta-phase) formed. But when they carried out crystal analysis on these two compounds, they found that they had the same composition, the same atom-to-atom connectivity and the same symmetry. This type of symmetry-preserving isomerism has never been observed before in metal-organic frameworks, according to the authors.
  Reference
  An unusual case of symmetry-preserving isomerism
  Chem. Commun., 2010 DOI: 10.1039/b920995f
  (January 19, 2010)

   

• Methanol coupling catalyzed with gold
  (Science)

  
  Credit: Wittstock et al., Science

  Gold surfaces can be effective catalysts for partial oxidation reactions, in part because lower interaction strengths of molecules absorbed on gold allow products to desorb before further unwanted oxidations occur. One challenge in these reactions is the low rate of formation of reactive atomic surface oxygen. Researchers created high–surface area gold catalysts by leaching silver from gold-silver alloys. This material proved to be an effective catalyst for partial oxidative coupling of methanol, yielding methyl formate. Residual silver appears to play a key role in activating the dissociation of molecular oxygen.
  Reference
  Nanoporous Gold Catalysts for Selective Gas-Phase Oxidative Coupling of Methanol at Low Temperature
  Science 15 January 2010: Vol. 327. no. 5963, pp. 319 - 322 DOI: 10.1126/science.1183591
  (January 15, 2010)

   

• Copper complex converts CO₂ to oxalate
  (Science)

  
  Credit: Science

  Technology using chemicals that bind carbon dioxide already exists, but it's so expensive that using it on a large scale to suck CO₂ out of the air could increase energy demand—and the cost of energy—by at least one-third. A new study now reports a new copper-based catalyst that can capture CO₂, convert it to a different form, and then release it with a small fraction of the energy other techniques require. The new method targets the step that so far has proved to be the Achilles' heel of air capture: prying the trapped CO₂ loose so the capture compound can be used again. The complex binds carbon dioxide by stitching two CO2 molecules together into an oxalate. By adding a lithium salt to the solution, the lithium swipes the oxalate from the copper complex, creating lithium oxalate. Then applying a very small voltage of –0.03 volts to the copper complex restores it to its original form.
  Reference
  Electrocatalytic CO₂ Conversion to Oxalate by a Copper Complex
  Science 15 January 2010: Vol. 327. no. 5963, pp. 313 - 315 DOI: 10.1126/science.1177981
  (January 15, 2010)

   

• 3-D metamaterial nanolens for super-resolution imaging
  (Applied Physics Letters)

  
  Credit: Applied Physics Lett.

  Using metamaterials for super-resolution optical imaging beyond Abbe’s diffraction limit, wherein features of an object smaller than λ/2 wavelength cannot be imaged by conventional optics, has thus far been demonstrated only in the case of very thin metallic films or metal-dielectric multilayers. A new study now demonstrates super-resolution imaging by a low-loss three-dimensional metamaterial nanolens consisting of aligned gold nanowires embedded in a porous alumina matrix. This is the first direct experimental observation of a true bulk 3D superlens, i.e. a medium which coherently transports image information by propagating waves and evanescent waves over unprecedented 8x wavelength distances, according to the authors. All previous lenses have been of subwavelength thicknesses or 2-dimensional. The work opens up the real possibility of using metamaterials for actual applications, such as nanolithography and optoelectronics.
  Reference
  Super-resolution imaging using a three-dimensional metamaterials nanolens
  Appl. Phys. Lett. 96, 023114 (2010); doi:10.1063/1.3291677
  (January 15, 2010)

   

• Three-dimensional jamming and flows of soft glassy materials
  (Nature Materials)

  
  Credit: Nature Materials

  Jamming transitions of disordered dense systems such as foams, gels and colloidal suspensions, describe the change from a liquid to a solid state below the yield stress. The rheological behavior of such soft glassy materials is still not well understood. A new study now shows that a simple three-dimensional continuum description of the behavior of soft glassy materials can be built. First, when a flow is imposed in some direction there is no yield resistance to a secondary flow: these systems are always unjammed simultaneously in all directions of space. Also, these materials behave as simple liquids in the direction orthogonal to that of the main flow.
  Reference
  Three-dimensional jamming and flows of soft glassy materials
  Nature Materials, Published online: 10 January 2010 | doi:10.1038/nmat2615
  (January 14, 2010)

   

• Porous pseudocapacitor films of MoO₃
  (Nature Materials)

  
  Credit: Nature Materials

  Capacitive energy storage is technologically attractive because of its short charging times and its ability to deliver more power than batteries. The capacitive charge-storage properties of mesoporous films of MoO₃ with iso-oriented grains now lead to pseudocapacitive materials that offer increased energy density while still maintaining high power density. The authors show that the capacitive charge-storage properties of mesoporous films of iso-oriented -MoO₃ are superior to those of either mesoporous amorphous material or non-porous crystalline MoO₃.
  Reference
  Ordered mesoporous -MoO₃ with iso-oriented nanocrystalline walls for thin-film pseudocapacitors
  Nature Materials, Published online: 10 January 2010 | doi:10.1038/nmat2612
  (January 14, 2010)

   

• Sequencing DNA with graphene
  (Nature)

  
  Credit: ACS

  A device that could rapidly sequence a single strand of DNA passing through a gap in a piece of graphene has been proposed. The device would make use of graphene's conducting ability. The graphene would act as the electrodes to measure the conductance of DNA as it moved through the gap. Each of the four bases that make up DNA has a unique conductance, which would allow the DNA sequence to be read. Other nanopores have been devised for DNA sequencing, but graphene's innate conductance and sturdiness makes it more attractive.
  Reference
  Rapid Sequencing of Individual DNA Molecules in Graphene Nanogaps
  Nano Lett., Article ASAP DOI: 10.1021/nl9029237 Publication Date (Web): January 4, 2010
  (January 14, 2010)

   

• Silicon nanowires deliver biomolecules into living cells
  (Technology Review/Science)

  
  Credit: Hongkun Park, Harvard Univ.

  Many experiments in biology rely on manipulating cells: adding a gene, protein, or other molecule, for instance, to study its effects on the cell. But getting a molecule into a cell is much like breaking into a fortress; it often relies on biological tricks such as infecting a cell with a virus or attaching a protein to another one that will sneak it through the cell's membrane. Many of these methods are specific to certain types of cells and only work with specific molecules. A new report now offers a surprisingly simple and direct alternative: using nanowires as needles to poke molecules into cells. Researchers recently discovered that cells can be grown on beds of vertical silicon nanowires without apparent damage to the cells. The cells sink into the nanowires and within an hour are impaled by the tiny spikes. Even resting on this bed of needles, cells continue to grow and divide normally. This setup makes it possible to directly interface with the cell's interior through the nanowires.According to the authors, in theory, "one can put more or less any molecule in more or less any kind of cell."
  Reference
  Vertical silicon nanowires as a universal platform for delivering biomolecules into living cells
  PNAS, Published online before print January 11, 2010, doi: 10.1073/pnas.0909350107
  (January 13, 2010)

   

• Pressure-induced transformation of metal-organic framework structure
  (PhysOrg)

  
  Credit: ACS

  ZIF-8 is a commercially available metal-organic framework (MOF) with molecular-scale pores that can have valuable catalytic applications. Scientists have now discovered a new route to transform the structure of these porous materials at industrially-accessible high pressures. Normally, these materials spring back to their original structure after they have been compressed, almost like a spring, but above a certain pressure this material was seen to adopt a new structure. The researchers used highly-focused X-ray beams to observe the structure of the compound after it withstood varying degrees of pressure. The structural transition was found to occur at relatively modest pressures. Gas uptake measurements revealed that the materials porosity was modified for the new structure. This could be used to optimize its performance for specific applications in areas such as hydrogen storage for fuel cells. Thus, by exerting pressure on MOFs through the pelletization process, researchers can modify the compound's structure and storage properties.
  Reference
  Pressure-Induced Amorphization and Porosity Modification in a Metal−Organic Framework
  J. Am. Chem. Soc., 2009, 131 (48), pp 1754617547 DOI: 10.1021/ja908415z
  (January 13, 2010)

   

• Carbon nanotubes help electron pairs survive breakup
  (Physics)

  
  Credit: Herrmann et al.
  Phys. Rev. Lett. (2010)

  Can measurement of one quantum system instantaneously affect the measurement outcome of another, even if the systems are spatially separated? This question has never been clearly answered for solid-state materials. Now, a new experiment demonstrates that electrons entangled in a superconducting Cooper pair can be spatially separated into different arms of a carbon nanotube, a material thought favorable for the efficient injection and transport of split, entangled pairs. This work may help pave the way for tests of nonlocal effects in solid-state systems, as well as applications such as quantum teleportation and ultrasecure communication.
  Reference
  Carbon Nanotubes as Cooper-Pair Beam Splitters
  Phys. Rev. Lett. 104, 026801 (2010) Published January 11, 2010
  (January 12, 2010)

   

• Gold coat, microscopy methods for analyzing graphene
  (Chemical and Engineering News)

  
  Credit: Lianfeng Sun, NCNT, Beijing

  Advances in graphene have been hampered by the small number of microscopy and spectroscopy techniques capable of seeing graphene and distinguishing between samples of various thicknesses. According to a new study, graphene films between one and four atomic layers thick can be distinguished by coating them with a layer of gold. The gold layer adopts a unique appearance based on the number of graphene layers. Researchers used Raman microspectroscopy to benchmark the number of atomic layers in graphene samples and mapped out regions of differing thickness within a single sample. Then they evaporated gold onto the samples. They found that they could use scanning electron microscopy to recognize differences in the morphology, grain size, and general appearance of the gold films and that those differences depend directly on the number of underlying graphene layers. The SEM analysis can be done faster and with higher spatial resolution than the Raman analysis, they say.
  Reference
  Thickness-Dependent Morphologies of Gold on N-Layer Graphenes
  J. Am. Chem. Soc., Article ASAP DOI: 10.1021/ja909228n Publication Date (Web): December 23, 2009
  (January 12, 2010)

   

• Silicon microwires as photocathodes
  (Science)

  
  Credit: Boettcher et al., Science

  Solar hydrogen generation will require the development of photocathodes with high surface area, durability, and efficiency. Silicon microwire arrays, which allow for greater light penetration, could achieve this goal if the carrier mobilities are sufficiently high so that surface reactions occur before charges recombine. A research team now report the electronic properties on positively doped silicon microwire arrays that were grown with copper catalysts and used in a methyl viologen redox system. Although equivalent efficiencies for normal solar fluxes were only 2 to 3%, the high internal efficiencies and low use of the available optical flux suggest that further improvements are possible.
  Reference
  Energy-Conversion Properties of Vapor-Liquid-SolidGrown Silicon Wire-Array Photocathodes
  Science 8 January 2010: Vol. 327. no. 5962, pp. 185 - 187 DOI: 10.1126/science.1180783
  (January 11, 2010)

   

• Nematic electronic order in iron superconductors
  (Science)

  
  Credit: Chuang et al., Science

  The properties of many high-temperature superconductors vary strongly as the composition of a doping element changes, and at sufficient under- or overdoping, other phases with different types of electronic ordering can form. In a new study, researchers have used scanning tunneling microscopy techniques to probe the electronic structure of an underdoped compound in the iron superconductor family, Ca(Fe1xCox)2As2. They observed periodic nanostructures oriented along FeFe bonds that exhibit an electronic ordering related to ordering seen in nematic liquid crystals. In particular, they present clear evidence of nanoscale electronic structures that run in one direction with a characteristic scale of 8a, where a is the spacing between Fe atoms. These structures apparently produce a dramatic anisotropy in the quasiparticle "dispersion" (i.e., the relation between the energy and the momentum).
  Reference
  Nematic Electronic Structure in the "Parent" State of the Iron-Based Superconductor Ca(Fe1xCox)2As2
  Science 8 January 2010: Vol. 327. no. 5962, pp. 181 - 184 DOI: 10.1126/science.1181083
  Perspectives: Electron Nematic Phases Proliferate
  Science 8 January 2010: Vol. 327. no. 5962, pp. 155 - 156 DOI: 10.1126/science.1183464
  (January 11, 2010)

   

• Giant nanowheel mystery solved
  (Chemistry World)

  
  Credit: Science

  Researchers have uncovered the mechanism behind how one of chemistry's most remarkable self-assembled structures, a giant molecular wheel made from molybdenum oxide, spontaneously manufactures itself. The finding is likely to have important implications for manipulating self-assembly reactions and devising new ways to create useful molecular architectures. Around 15 years ago, a team of scientists showed that a simple mixture of sodium molybdate, water and a reducing agent in low pH spontaneously forms giant donut-shaped molybdenum oxide molecular wheels. At nearly 4 nm across these were more than a magnitude larger than structures seen before, and represent a unique class of molecules. However, the mechanism of the self-assembly remained unknown. Now, another group has solved the mystery by carrying out the reaction in a flow chamber. Here the reactants are introduced into the chamber under constant flow. The consistent replenishment of the reactants at the point of entry sets up a steady state, enabling the early reaction products to accumulate close to the entry point. In this part of the chamber the researchers saw crystals precipitating from solution. X-ray crystallography showed that the crystals were flat discs consisting of 186 atoms of molybdenum, subsequently shown to consist of a 36-Mo central core contained within the 150-Mo hollow wheel. It seems that the 36-Mo clusters act as a template around which the molybdenums coalesce into a ring and the two anionic units are held together by sodium ions and hydrogen bonds. Under reducing conditions, the electrostatic repulsion eventually reaches the point at which the hub of the wheel is spat out: the smaller clusters act as temporary guest templates which form a host and then leave.
  Reference
  Unveiling the Transient Template in the Self-Assembly of a Molecular Oxide Nanowheel
  Science 1 January 2010, Vol. 327. no. 5961, pp. 72 - 74
  DOI: 10.1126/science.1181735
  (January 7, 2010)

   

• The minutiae of friction revealed
  (Nature)

  
  Credit: Nature

  The behaviour of systems as diverse as hard drives and earthquakes is influenced by frictional motion and its strength. What at first glance appears to be a continuous sliding process between touching surfaces is in fact a product of a series of 'slip' and 'stick' events on the microscopic scale. The mechanism of evolution of frictional strength at this level, though, is still unclear. A research team has now explored the evolution of the local contact area between two sliding bodies (PMMA plastic blocks) and the motion of their interface, and find that it involves four distinct phases. Within microseconds, all the contact area reduction has occurred. This is followed by a rapid slip phase, then a sharp transition to much slower slippage culminating in a 'stick' phase when motion is arrested. After several hundred microseconds the contact area begins to increase again. These results provide a basis for a better understanding of this kind of motion in many technologically important contexts.
  Reference
  Slip-stick and the evolution of frictional strength
  Nature 463, 76-79 (7 January 2010), doi:10.1038/nature08676
  (January 7, 2010)

   

• Nanodragster allows better control
  (Eurekalert/Rice Univ.)

  
  Credit: American Chemical Society

  Researchers are reporting the development of a "nanodragster" that may speed the course toward development of a new generation of molecular machines. The nanoscale "vehicle" outperforms previous nano-sized vehicles, according to the authors. The new vehicle addresses some of the problems associated with previously reported nano-cars. The front end has a smaller axle and wheels made of special materials that roll easier. The rear wheels sport a longer axle but are still made of buckyballs, which provide strong surface grip. These changes result in a "nanodragster" that can operate at lower temperatures than a regular nanocar and possibly has has better agility.
  Reference
  Molecular Machinery: Synthesis of a “Nanodragster”
  Org. Lett., 2009, 11 (24), pp 5602–5605 DOI: 10.1021/ol902312m
  (January 6, 2010)

   

• Ferropaper combines ordinary paper, ferrofluid
  (Purdue University)

  Researchers have created a magnetic "ferropaper" that might be used to make low-cost "micromotors" for surgical instruments, tiny tweezers to study cells and miniature speakers. The material is made by impregnating ordinary paper - even newsprint - with a ferrofluid, a mixture of mineral oil and "magnetic nanoparticles" of iron oxide. The nanoparticle-laden paper can then be moved using a magnetic field. Once saturated with this "ferrofluid" mixture, the paper is coated with a biocompatible plastic film, which makes it water resistant, prevents the fluid from evaporating and improves mechanical properties such as strength, stiffness and elasticity.
  (January 6, 2010)

   

• Opening the gate for molecular electronics
  (Chemistry World)

  
  Credit: Nature

  Researchers have shown that the current running through a transistor made of a single molecule can be regulated by tweaking its molecular orbital energies. This observation brings molecular electronics closer to behaving like conventional silicon-based devices. They used a battery of spectroscopic techniques to prove that their devices were true single molecule transistors. They also showed that an externally applied voltage was modulating the current by changing the molecular orbital energy levels of those molecules, and that different molecules behave differently depending on their orbital energy levels. To make the transistors, the team needed to trap their subject molecules in tiny gaps between the source and drain electrodes.They used electromigration, where large currents are passed through gold nanowires, making tiny breaks as gold atoms move around. If the nanowires are coated with the molecules they want to test, then sometimes as a gap forms molecules will get trapped between the two ends. The whole assembly sits on an oxidized aluminium base which acts as the gate electrode.
  Reference
  Observation of molecular orbital gating
  Nature 462, 1039-1043 (24 December 2009), doi:10.1038/nature08639
  (January 6, 2010)

   

• Molecular worm algorithm navigates inside chemical labyrinth
  (Lawrence Berkeley National Lab)

  
  Credit: Maciej Haranczyk

  With the passage of a molecule through the labyrinth of a chemical system being so critical to catalysis and other important chemical processes, computer simulations are frequently used to model potential molecule/labyrinth interactions. In the past, such simulations have been expensive and time-consuming to carry out, but now researchers have developed a new algorithm that should make future simulations easier and faster to compute, and yield much more accurate results. A key to the success of this new algorithm was its departure from the traditional treatment of molecules as hard spheres with fixed radii. Instead, the scientists constructed “molecular worms” from blocks connected by flexible links. These molecular worms provide a more realistic depiction of a molecule’s geometry, thereby providing a more accurate picture of how that molecule will navigate through a given chemical labyrinth. As a molecule navigates through a chemical system, its access to a particular site or place within that system determines the extent to which catalysis and other chemical reactions may occur. The scientists sucessfully tested the molecular worm algorithm on a typical alkane-cracking zeolite material.
  Reference
  Navigating molecular worms inside chemical labyrinths
  PNAS, December 22, 2009, vol. 106 no. 51, 21472-21477
  (January 5, 2010)

   

• Janus catalysts direct nanoparticle reactivity
  (Science)

  
  Credit: P. Huey, Science

  Soluble compounds that are used to speed up desired reactions—homogeneous catalysts—can end up in final products, where they pose a nightmare of a separation problem. Ideally, if these catalysts could be completely recovered, they could be recycled and kept out of the products, in which they could be toxic even at trace levels. One general approach to recovering such catalysts is "phase transfer," which takes advantage of the different solubility of compounds in water versus organic solvents. In a new study, researchers have converted solid nanoparticles that have solubility in both water and oils into catalysts that can operate in both phases. These catalysts can be recovered even from complex mixtures, such as those that result when biomass products are upgraded into fuels. They have developed nanoparticles that selectively locate at the interface between the aqueous and organic phases. They deposited carbon nanotubes on metal oxide nanoparticles, such as silicon oxide (silica) or magnesium oxide, with diameters of 50 nm or less. The oxides are hydrophilic and attracted to the water, while the carbon nanotubes are hydrophobic and prefer the organic layer. Like a large surfactant molecule, the nanoparticles compromise by sitting at the interface. Unlike surfactants, the nanoparticles are solids that can be separated with methods such as filtration.
  Reference
  Solid Nanoparticles that Catalyze Biofuel Upgrade Reactions at the Water/Oil Interface
  Science 1 January 2010: Vol. 327. no. 5961, pp. 68 - 72 DOI: 10.1126/science.1180769
  (January 5, 2010)

   

• Surprising reactivity of nano-gold may be partly due to oxide support
  (Chemical and Engineering News)

  
  Credit: Shao-Chun Li, Tulane Univ.

  Gold nanoparticles, a relatively new class of surprisingly active supported catalysts, may owe key aspects of their catalytic prowess to the titania (TiO2) support on which they are commonly dispersed, according to a new report. The unexpected discovery several years ago that goldan inert metalcan function as an active catalyst when prepared in nanoparticulate form touched off a wave of research into the precious metals catalytic capabilities. Researchers now report that titania alone facilitates the key steps in interconversion reactions between aniline and azobenzene and that the role of gold, at least in those reactions, may simply be to activate oxygen or hydrogen.
  Reference
  Reactivity of TiO2 Rutile and Anatase Surfaces toward Nitroaromatics
  J. Am. Chem. Soc., Article ASAP DOI: 10.1021/ja907865t Publication Date (Web): December 9, 2009
  (January 5, 2010)

• Polarization-induced hole doping in semiconductor heterostructures
  (Science)

  Many applications of semiconductor light-emitting diodes and lasers, such as reading optical disks, benefit from shorter wavelengths, but this requires materials with larger energy gaps between their valance and conduction bands. The electronic conductivity of these materials often has to be increased by doping with impurity atoms. However, in nitride materials, such as GaN and AlGaN, hole doping with acceptor atoms such as Mg is ineffective at room temperature. In a new study, researchers grew a gradient of AlGaN on the surface of GaN and found that the polarization of the layer could field-ionize the acceptor dopants efficiently at room temperature. The heterostructure was used successfully in a light-emitting diode that emits in the ultraviolet.
  Reference
  Polarization-Induced Hole Doping in Wide–Band-Gap Uniaxial Semiconductor Heterostructures
  Science 1 January 2010: Vol. 327. no. 5961, pp. 60 - 64 DOI: 10.1126/science.1183226
  (January 4, 2010)

   

• Superatoms mimic elements
  (Eurekalert/Penn State Univ.)

  
  Credit: Castleman et al., Penn State University

  Researchers have shown that certain combinations of elemental atoms have electronic signatures that mimic the electronic signatures of other elements. The researchers also showed that the atoms that have been identified so far in these mimicry events can be predicted simply by looking at the periodic table. They used photoelectron imaging spectroscopy to examine similarities between titanium monoxide and nickel, zirconium monoxide and palladium, and tungsten carbide and platinum. The amount of energy required to remove electrons from a titanium-monoxide molecule was found to be the same as the amount of energy required to remove electrons from a nickel atom. The same was true for the systems zirconium monoxide and palladium and tungsten carbide and platinum. The key is that all of the pairs are composed of isoelectronic species, which are atoms with the same electron configuration.
  Reference
  Superatom spectroscopy and the electronic state correlation between elements and isoelectronic molecular counterparts
  PNAS 10.1073/pnas.0911240107
  (January 4, 2010)

   

• Why nitrogen cannot dope ZnO p-type
  (Univ. California, Santa Barbara)

  
  Credit: Van de Walle et al., UCSB

  ZnO has been intensively pursued as an optoelectronic material, in hopes of developing it into a wide-band-gap light emitter that would compete with GaN-but with the advantage that large single-crystal substrates are commercially available. A large part of the effort has been directed at establishing p-type doping, which is very challenging in wide-band-gap oxides in general. Dozens of papers claiming observations of p-type conductivity have appeared in the scientific literature. A new computational study now suggests that nitrogen, which is widely believed to be a shallow acceptor in ZnO, is in fact a very deep acceptor and cannot lead to p-type conductivity.
  Reference
  Why nitrogen cannot lead to p-type conductivity in ZnO
  Appl. Phys. Lett. 95, 252105 (2009); doi:10.1063/1.3274043
  (January 4, 2010)

   

• Form-fitting photovoltaic artificial retina
  (IEEE Spectrum)

  
  Credit: iStockphoto, IEEE Spectrum

  Several teams of scientists and engineers have been trying for years to produce a practical retinal prosthesis for people afflicted by a progressive loss of photoreceptor cells. One problem all the researchers face is how to get power and data (the image) to a retinal chip that’s implanted at the back of a person’s eye. A research team has been working on what might seem like the obvious solution: using light entering the eye for both power and data. The new implant is designed as an array of miniature solar cells. The device—technically a subretinal implant, because it is placed behind the retina—is part of a system that includes a video camera that captures images, a pocket PC that processes the video feed, and a bright near-infrared LCD display built into video goggles. The pulsed 900-nanometer-wavelength image that shines into the eyes is enough to produce electricity in the chip. The researchers chose a near-infrared display because it is invisible.
  (December 23, 2009)

   

• New metamaterial lens has wide angle of view
  (Eurekalert/Duke Univ.)

  
  Credit: Duke Univ.

  Recognizing the limitations of traditional lenses, scientists have long been investigating other options, including those known as gradient index (GRIN) lenses. These are typically clear spheres, and while they have advantages over traditional lenses, they are difficult to fabricate and the focus point is spherical. Additionally, because most sensing systems are oriented in two dimensions, the spherical image doesn't always translate clearly on a flat surface. Researchers have now created a new lens made from a metamaterial that looks more like a miniature set of tan Venetian blinds. Yet its ability to focus the direction of electromagnetic rays passing through it dramatically surpasses that of a conventional lens. The prototype lens, which measures four inches by five inches and less than an inch high, is made up of more than 1,000 individual pieces of the same fiberglass material used in circuit boards and is etched with copper. The new lens has a wide angle of view, almost 180 degrees, and because its focal point is flat, it can be used with standard imaging technologies. The latest experiments were conducted with microwaves, and the researchers say it is theoretically possible to design lenses for wider frequencies.
  Reference
  Extreme-angle broadband metamaterial lens
  Nature Materials Published online: 20 December 2009, doi:10.1038/nmat2610
  (December 23, 2009)

   

• Ubiquity of chaotic magnetic-field lines
  (Physical Review Focus)

  
  Credit: Phys. Rev. E

  A magnetic field line can be thought of as the path taken by a hiker continuously walking where her compass needle points. Textbooks generally show magnetic field lines curling around current-carrying wires to form closed loops. However, in plasmas--where currents flow in complex arrangements--the magnetic field lines often don't close but instead wrap around themselves in three-dimensional space an infinite number of times. These chaotic magnetic fields have been studied for decades by those working on fusion reactors, as well as those trying to understand the atmosphere of the sun. The conventional wisdom has been that this chaos is confined to plasmas, but recent theoretical work has shown that chaotic magnetic fields also arise from the currents through special wire configurations, such as an undulating wire bent into a loop. Now, researchers have looked at even simpler wire arrangements, some of which are representative of the wiring inside ordinary electronic devices. They find that neat closed loops may be more the exception than the rule. Computer-based calculations show that magnetic field lines around simple wire configurations are tangled up like a ball of yarn. After accounting for the earth's magnetic field, the researchers conclude that these chaotic magnetic fields are ubiquitous in the circuits found in all modern electronic devices.
  Reference
  Ubiquity of Chaotic Magnetic-Field Lines Generated by Three-Dimensionally Crossed Wires in Modern Electric Circuits
  Phys. Rev. B 80, 235409 (2009) Phys. Rev. E 80, 067202 (issue of December 2009)
  (December 22, 2009)

   

• First graphene-based actuator demonstrated
  (NanotechWeb)

  
  Credit: Ruoff et al., Small

  Researchers have made the first actuator based on graphene. The "paper-like" device "curls" in response to external stimuli. The team found that bilayer paper-like materials based on carbon nanotubes and graphene-based platelets strongly deform in response to stimuli such as humidity or temperature. The researchers made their device from two neighboring layers composed of overlapping and stacked graphene oxide platelets (the first layer) and criss-crossed multiwalled carbon nanotubes (the second layer). Each layer is about 10 m thick and is formed by first filtering an aqueous suspension of MWCNTs and then filtering a similar solution of graphene oxide platelets. The finished device curls when humidity or temperature are increased and the amount of curling can be controlled by varying the thickness of the MWCNT layer.
  Reference
  Graphene-Based Actuators
  Small, Early View (Articles online in advance of print) Published Online: 18 Nov 2009
  (December 22, 2009)

   

• Nanoscale 3D imaging in a single shot
  (Chemistry World)

  
  Credit: Nature

  Typically, 3D images are constructed in two ways. One is by rotating a sample to take 2D pictures from many different angles - such as in x-ray crystallography - and the other is to take many planar slices and combine them together, such as in confocal microscopy. Researchers have come up with a new idea which is to collect data from a single beam using a curved surface allowing for reconstruction of an image in 3D. This process has been named 'ankylography', and is effectively a type of x-ray diffraction microscopy. First, a coherent beam of x-rays is fired at the target material and diffracted in all directions. A snapshot of this scattering pattern is then taken using a charge-coupled device (CCD) which measures the trajectory and intensity of the diffracted x-rays. They had to use a flat CCD, then mathematically calculate what the pattern on a spherical surface would be. The final step, once the diffraction pattern was collected, was to use computer algorithms developed by the team to reconstruct the image. So far, the team has resolved the 3D structure of a silicon surface to an accuracy of around 0.2 nm, and has been able to pick out surface features around 2nm in size on the surface of a poliovirus.
  Reference
  Three-dimensional structure determination from a single view
  Nature advance online publication 16 December 2009, doi:10.1038/nature08705
  (December 22, 2009)

   

• Twisting left and right gives logic another turn
  (Physics)

  
  Credit: Durgun et al.
  Phys. Rev. Lett. (2009)

  Germanium telluride can be thermally switched between a metastable crystalline phase and an amorphous state. In its crystalline form, it is a ferroelectric with spontaneous polarization. This structural transition would seem promising for data storage, through switching the crystalline (and hence ferroelectric) state on and off. However, applications involving germanium telluride have not been realized, primarily due to its high concentration of intrinsic vacancies. In addition to crystal structure, size also affects ferroelectric properties. In a new theoretical study, researchers have performed first-principle calculations on germanium telluride nanoplatelets. For platelets with a diameter larger than 2.7 nm, they predict the emergence of polarization vortices that should give rise to a ferrotoroidic ground state, with a spontaneous and reversible toroidal moment. The authors predict that the inhomogeneous strain would play a role in stabilizing the spiral. In addition to fundamental interest, this effect, together with the transition from crystalline to amorphous structure, can be used to record three spin states (right-hand spiral, left-hand spiral, and amorphous/off), which could be used for ternary logic.
  Reference
  Polarization Vortices in Germanium Telluride Nanoplatelets: A Theoretical Study
  Phys. Rev. Lett. 103, 247601 (Published December 7, 2009)
  (December 21, 2009)

• Stress-driven moving grain boundaries
  (Science)

  
  Credit: T. J. Rupert et al.., Science

  Classical models of fine-grained metals view grain boundaries as static objects, but this view has been challenged by recent experimental observations. Drawing on techniques used by the fracture mechanics community, a research team has now presented experiments on freestanding aluminum films that show specific geometries cause either stress or strain concentrations on deformation. Specimens fabricated with specially designed stress and strain concentrators were used. Confirming recent simulations, shear stresses were found to be a key driver of grain boundary motion.
  Reference
  Experimental Observations of Stress-Driven Grain Boundary Migration
  Science 18 December 2009: Vol. 326. no. 5960, pp. 1686 - 1690 DOI: 10.1126/science.1178226
  (December 21, 2009)

• Nano-pillars using electron beam lithography and electroplating
  (Science - Editor's Choice)

  
  Credit: Nano Lett., ACS

  Mechanical testing of submicrometer-sized metal pillars has shown significant strengthening on decreasing the pillar dimensions. Analysis of such experiments is complicated, however, because the traditional focused ion beam method for making the pillars causes damage through the implantation of Ga+ ions and leads to vertical tapering. Researchers have now turned to lithographic techniques, using an electron beam to pattern a poly(methylmethacrylate) (PMMA) film. The patterned film was in turn used to template pillar growth by deposition of gold or copper through electroplating. The plating conditions could be tuned to vary the microstructure of the pillars, which ranged from single crystals to twin domain and highly nanocrystalline structures. Pillars for compressive testing were fabricated by halting plating before reaching the top of the PMMA layer; for tensile testing, the pillars were overplated with a cap to facilitate gripping of the sample. The pillars showed little tapering and exhibited diameters as small as 25 nm, much smaller than the lower limit attainable by a focused ion beam.
  Reference
  Fabrication and Microstructure Control of Nanoscale Mechanical Testing Specimens via Electron Beam Lithography and Electroplating
  Nano Lett., Article ASAP DOI: 10.1021/nl902872w7
  (December 21, 2009)

• Photons filmed using electrons
  (e! Science News/CalTech)

  
  Credit: Ahmed Zewail, CalTech

  A technique, allowing for real-time, real-space visualization of fleeting changes in the structure of nanoscale matter, has now been used to image the evanescent electrical fields produced by the interaction of electrons and photons, and to track changes in atomic-scale structures. Photons generate an evanescent field in nanostructures, and electrons can gain energy from such fields, which makes them visible in a 4D microscope (which employs single electrons to introduce the dimension of time into traditional high-resolution electron microscopy). In what is being termed the photon-induced near-field electron microscopy (PINEM) effect, certain materials after being hit with laser pulses continue to "glow" for a short but measurable amount of time (on the order of tens to hundreds of femtoseconds). In their experiment, the researchers illuminated carbon nanotubes and silver nanowires with short pulses of laser light as electrons were being shot past. The evanescent field persisted for femtoseconds, and the electrons picked up energy during this time in discrete amounts (or quanta) corresponding to the wavelength of the laser light. This technique of visualization opens new vistas of imaging with the potential to impact fields such as plasmonics, photonics, and related disciplines. From a fundamental physics point of view, the scientists are able to image photons using electrons.
  Reference
  Photon-induced near-field electron microscopy
  Nature 462, 902-906 (17 December 2009), doi:10.1038/nature08662
  (December 17, 2009)

• Thermochemical nanolithography patterns multiple chemicals on a chip
  (Eurekalert/Georgia Tech)

  
  Credit: Eric Huffman, Georgia Tech

  Scientists have developed a thermochemical nanolithographic technique that can produce high-resolution patterns of at least three different chemicals on a single chip at writing speeds of up to one millimeter per second. The chemical nanopatterns can be tailor-designed with any desired shape and have been shown to be sufficiently stable so that they can be stored for weeks and then used elsewhere. Using an atomic force microscope (AFM), the researchers heat a silicon tip and run it over a thin polymer film. The heat from the tip induces a local chemical reaction at the surface of the film. This reaction changes the film's chemical reactivity and transforms it from an inert surface to a reactive one that can selectively attach other molecules. The technique produces multiple chemical patterns on the same chip by using the AFM to heat a polymer film and change its reactivity. The chip is then dipped into a solution, which allows chemicals (for example, proteins or other chemical linkers) in the solution to bind to the chip on the parts where it has been heated. The AFM then heats the film in another spot. The chip is dipped into another solution and again another chemical can bind to the chip. The scientists show they can pattern amine, thiol, aldehyde and biotin using this technique. But in principle it could be used for almost any chemical. The work also shows that the chemical patterns can be used to organize functional materials at the surface, such as proteins and DNA.
  Reference
  Thermochemical Nanolithography of Multifunctional Nanotemplates for Assembling Nano-Objects
  Advanced Functional Materials Volume 19 Issue 23, 2009, Pages 3696 - 3702
  (December 17, 2009)

• Bacteria power simple machines
  (Eurekalert/Argonne National Lab)

  Researchers have discovered that common bacteria can turn microgears when suspended in a solution, providing insights for the design of bio-inspired dynamically adaptive materials for energy. Microgears with slanted spokes were placed in the solution along with common aerobic bacteria, Bacillus subtilis. The bacteria appeared to swim around the solution randomly, but occasionally the organisms collided with the spokes of the gear and began turning it in a definite direction. A few hundred bacteria work together to turn the gear. When multiple gears were placed in the solution with the spokes connected like in a clock, the bacteria began turning both gears in opposite directions causing the gears to rotate in synchrony for a long time.
  Reference
  To be published in the Proceedings of the National Academy of Sciences
  (December 17, 2009)

• Functionalized silicon micro-rings streamline detection of disease indicators
  (Chemical and Engineering News)

      
     Credit: Ji-Yeon Byeon

  Label-free biosensing technologies such as surface plasmon resonance spectroscopy appeal to researchers because they avoid interference from fluorescent or other tags. But these platforms can sometimes lose sensitivity when measuring multiple analytes simultaneously. Now, researchers have developed a system that has no such sensitivity trade-off. The technology relies on an established type of silicon microstructure functionalized with antibodies. The structures, called silicon photonic micro-ring resonators, are highly sensitive to changes in refractive index that occur when a biomarker binds its corresponding antibody. The team used an array of resonators to quantify five disease biomarkers in a buffered sample at the same time.
  Reference
  Quantitative, Label-Free Detection of Five Protein Biomarkers Using Multiplexed Arrays of Silicon Photonic Microring Resonators
  Anal. Chem., Article ASAP DOI: 10.1021/ac902451b Publication Date (Web): December 9, 2009
  (December 16, 2009)

   

• Where the rubber meets the road
  (Physical Review Focus)

  
  Credit: O. Wright, Hokkaido Univ.

  The interface between two seemingly smooth surfaces, is actually a world of caverns and columns, stalactites and stalagmites, at the nanoscale. Researchers studying how a tire grips the road or how a cell hangs onto a surface want to explore this complex landscape in detail. But there is currently no way to do so while the two objects are in contact. Instead, researchers usually press one object into the other, remove it, and then image the indentation it leaves using an atomic force microscope. Now a team has seen the details of a live contact. In their setup, a mechanical arm presses a ceramic ball, a few millimeters in diameter, down onto a 110-nanometer-thick film of chromium coating a sapphire surface. From below, a laser fires a 200-femtosecond pulse up into the sapphire, focused on a 2-micron-wide spot at the boundary of the sapphire and chromium. This "pump" pulse heats the material, which makes it expand suddenly and send a short ripple of high-frequency sound (up to 100 GHz) upward, toward the sphere. The sound bounces off the chromium-sphere interface, returns to the sapphire-chromium interface, and is then probed by a second laser pulse. This "probe" pulse reflects back to a detector, and the intensity of this reflection is a measure of the strength of the acoustic echo, thanks to a phenomenon called the photoelastic effect.
  Reference
  Nanoscale mechanical contacts probed with ultrashort acoustic and thermal waves
  Phys. Rev. B 80, 235409 (2009)
  (December 16, 2009)

• Cerium in phosphate glasses yields better UV, radiation blocking
  (Science Daily/Penn State University)

  Cerium exists in two states in glasses, cerium (III) and cerium (IV), both of which strongly absorb ultraviolet light. For years, cerium has been added to silicate glass to enhance its ultraviolet absorbing capacity. The problem has always been that silicate glass can only dissolve so much cerium before it becomes saturated. Also, with high concentrations of cerium, silicate glass begins to turn yellow -- an undesirable characteristic for such things as windows or sunglasses. Phosphate glasses have a more flexible structure then silicate glasses, which allow higher percentages of cerium to be incorporated before it begins to color. Researchers have now synthesized and compared 11 glasses with varying concentrations of cerium, aluminum, phosphorus and silica. They found that they could make phosphate glasses with 16 times more cerium oxide than silicate glasses while maintaining the same coloration and ability to absorb ultraviolet light.
  Reference
  Synthesis and properties of cerium aluminosilicophosphate glasses
  Journal of Non-Crystalline Solids, Volume 355, Issues 52-54, 15 December 2009, Pages 2622-2629 doi:10.1016/j.jnoncrysol.2009.09.004
  (December 16, 2009)

• Breaking some of the strongest chemical bonds
  (Chemistry World)

  
  Credit: Nature Chemistry

  Although nitrogen makes up 78 per cent of the atmosphere, it is not used in many industrial processes as the triple bond is difficult to break. The exception is the Haber process to make ammonia - but this requires high pressures and temperatures, as well as hydrogen gas that usually comes from fossil fuel sources. Alternative chemistry to break the N₂ triple bond is highly sought after and could be in great demand in the future. Now, researchers have found a new way to do this - and surprisingly, it works at room temperature. Key to the process is a compound called hafnocene, which is a complex of hafnium metal ions with cyclopentadiene and chlorine ligands. The complex can be activated to react with N₂ by switching the chlorine for iodine - causing each N₂ molecule to be complexed between two hafnocenes. This bonding effectively reduces the triple bond to a single N-N bond. At this stage, carbon monoxide is added, which breaks the final N-N bond and forms new C-N bonds. By varying the amount of CO added, different organic compounds can be made. The downside is that the process is stoichiometric, rather than catalytic - meaning that one hafnium compound is required for every N₂ molecule that is cleaved.
  Reference
  Dinitrogen cleavage and functionalization by carbon monoxide promoted by a hafnium complex
  Nature Chemistry Published online: 13 December 2009 | doi:10.1038/nchem.477
  (December 15, 2009)

• Van Hove singularities observed in graphene
  (NanotechWeb)

  
  Credit: E Andrei

  When two pieces of fine mesh are placed one on top of the other and then rotated, new, more complicated patterns appear. As you keep on twisting, the patterns change like in a kaleidoscope. These so-called Moiré patterns have been known for a long time and were recently observed in scanning tunnelling microscope (STM) images of stacked layers of graphene. Besides forming pretty patterns, such twists also cause dramatic changes in graphene's electronic properties. Now, a research team has shown that the twists induce sharp peaks in the electronic density of states (or Van Hove singularities) that can be seen as peaks in the tunnelling spectra. Remarkably, the energy of these peaks varies continuously with the twist angle so that their position can be tuned at will. This opens up the prospect of 'twist-engineering' the electronic properties of graphene.
  Reference
  Observation of Van Hove singularities in twisted graphene layers
  Nature Physics Published online: 29 November 2009, doi:10.1038/nphys1463
  (December 15, 2009)

   

• Universality of the glass transition
  (Physics)

  
  Credit: Kawasaki et al.
  Phys. Rev. Lett. 99, 215701 (2007)

  A molecular liquid cooled to below its freezing point (i.e., supercooled) can become a glass. A colloidal fluid, a collection of suspended particles undergoing Brownian motion, can form a colloidal glass under increasing pressure. Though both scenarios are examples of the so-called glass transition, researchers have disagreed on whether the two phenomena are related, that is, on whether temperature or pressure plays a more important role in the formation of a glass. In a recent paper, researchers show that there is a limit in which the relaxation behavior near the glass transition can be understood without separately invoking temperature T and pressure p; the data collapses on a curve determined by their ratio T/p. This equivalence indicates that there is indeed a hitherto overlooked universal aspect to glass transition.
  Reference
  Equivalence of Glass Transition and Colloidal Glass Transition in the Hard-Sphere Limit
  Phys. Rev. Lett. 103, 245701 (Published December 10, 2009)
  (December 15, 2009)

   

• New method yields very long boron nitride nanotubes
  (ScienceNOW)

  
  Credit: Michael Smith

  Researchers have long been able to make nanotubes out of carbon, but they have struggled to craft them from boron nitride. The two have about the same strength, but boron nitride nanotubes (BNNTs) can survive temperatures that are twice as high as those carbon nanotubes can survive--800C and higher. Scientists have only been able to create high-quality tubes a micron long; larger versions have been riddled with defects in the crystalline structure. Now, a team of materials scientists describe the first creation of high-quality, uniformly crystalline BNNTs in large quantities. Each piece of fiber is long enough that it can be spun into user-friendly yarn. To do this, the researchers aimed a laser at a cake of boron inside a chamber filled with nitrogen. This forms a plume of boron gas that shoots upward. A cooled metal wire is then inserted into the gas, causing the gas to cool and form liquid droplets. The droplets combine with the nitrogen to self-assemble into BNNTs. That explosive reaction quickly produces masses of high-quality BNNTs that look like mounds of cotton candy--more high-quality BNNTs than anyone has ever been able to make at once. The fibers show all of the important properties--strength, piezoelectric activity, conductivity, and stability at high temperatures--that have made BNNTs so sought after. And all with a method that can be done with commercially available materials and tools.
  Reference
  Very long single- and few-walled boron nitride nanotubes via the pressurized vapor/condenser method
  Nanotechnology 20 505604 (2009), doi: 10.1088/0957-4484/20/50/505604
  (December 14, 2009)

• Nanosensors measure cancer biomarkers in whole blood
  (Eurekalert/Yale University)

  
  Credit: Mark Reed/Yale University

  A research team has used nanosensors to measure cancer biomarkers in whole blood for the first time. Their findings could simplify the way physicians test for biomarkers of cancer and other diseases. They used nanowire sensors to detect and measure concentrations of two specific biomarkers: one for prostate cancer and the other for breast cancer. Whole blood is a complicated solution containing proteins and ions and other things that affect detection. To overcome the challenge of whole blood detection, the researchers developed a novel device that acts as a filter, catching the biomarkersin this case, antigens specific to prostate and breast canceron a chip while washing away the rest of the blood. Creating a buildup of the antigens on the chip allows for detection down to extremely small concentrations, on the order of picograms per milliliter, with 10 percent accuracy.
  Reference
  Label-free biomarker detection from whole blood
  Nature Nanotechnology, Published online: 13 December 2009, doi:10.1038/nnano.2009.353
  (December 14, 2009)

• Transient life of a protein between active states
  (Scientific Computing)

  
  Credit: Cell

  Understanding the speedy atomic mechanisms at work when a protein transitions from one shape to another has been an elusive scientific goal for years, but an essential one for elucidating the full panoply of protein function. How do proteins transition, or interconvert, between distinct shapes without unfolding in the process? Until now, this question has been a hypothetical one, approached by computation only, rather than experimentation. Researchers have revealed for the first time computationally and experimentally the molecular pathway that a protein takes to cross the energy barrier, the "climb over the mountain." The study reports how folded proteins can efficiently change shape while avoiding unfolding, a critical requirement for any protein in the cell. Using computation and nuclear magnetic resonance (NMR) spectroscopy, the researchers were able to experimentally measure how fast the signaling nitrogen regulatory protein jumps from one shape to another, and to shed light into the atomistic pathway.
  Reference
  Transient Non-native Hydrogen Bonds Promote Activation of a Signaling Protein
  Cell, Volume 139, Issue 6, 1109-1118, 11 December 2009 doi:10.1016/j.cell.2009.11.022
  (December 14, 2009)

• Inexpensive plastic flash memory for flexible devices
  (Technology Review/Science)

  
  Credit: Science

  Researchers have created a new kind of plastic low-cost flash memory that could find its way into novel flexible electronics. Conventional flash memory stores data electrically, in specially designed silicon transistors. The new prototype plastic flash memory cannot match silicon's storage density, long-term stability, or number of rewrite cycles. But its low cost could make it possible to integrate flash memory into more unconventional electronics. The key to making the plastic memory device work is a hybrid insulating layer made of a polymer and a metal oxide. This layer electrically isolates the metal gate in which charges are stored. An applied voltage causes the metal gates to accumulate charge--charged and uncharged gates represents binary 1s and 0s, as in silicon flash. The better the insulator works, the longer the data can be stored before the electrons leak away and the data degrades. The researchers start by placing metal transistor gates on top of a plastic substrate. Then a thin layer of aluminum oxide is deposited on top and the plastic film is submerged in a solution containing an insulating polymer. The polymer finally self-assembles on the surface of the aluminum oxide.
  Reference
  Organic Nonvolatile Memory Transistors for Flexible Sensor Arrays
  Science 11 December 2009: Vol. 326. no. 5959, pp. 1516 - 1519 DOI: 10.1126/science.1179963
  (December 11, 2009)

• Battery made of paper charges up
  (Proc. National Acad. Sciences/Stanford University)

  
  Credit: Stanford Univ.

  Batteries made from plain copier paper could make for future energy storage that is truly paper thin. The approach relies on the use of carbon nanotubes - tiny cylinders of carbon - to collect electric charge. Because of its structure of millions of tiny, interconnected fibers, paper is a good candidate to hold on to carbon nanotubes, providing a scaffold on which to build devices. However, paper is also mechanically tough, and can be bent, curled or folded. The researchers started with off-the-shelf copier paper, painting it with an "ink" made of carbon nanotubes. The coated paper is then dipped in lithium-containing solutions and an electrolyte to provide the chemical reaction that generates a battery's electric current. The paper acts to collect the electric charge from the reaction. Using paper in this way could reduce the weight of batteries, typically made with metal current collectors, by 20%. The team's batteries are also capable of releasing their stored energy quickly. daptations to the technique in the future could allow for simply painting the nanotube ink and active materials onto surfaces such as walls.
  Reference
  Highly conductive paper for energy-storage devices
  Proc. National Acad. Sciences, Published online before print December 7, 2009, doi: 10.1073/pnas.0908858106
  (December 11, 2009)

• Entropy alone creates quasicrystals from tetrahedra
  (Eurekalert/University of Michigan)

  
  Credit: Nature

  In a study that elevates the role of entropy in creating order, researchers show that tetrahedra can spontaneously organize into complex quasicrystals. Entropy is a measure of the number of ways the components of a system can be arranged. While often linked to disorder, entropy can also cause objects to order. The scientists used computer simulation to find the arrangement of tetrahedrons that would yield the densest packing---that would fit the most tetrahedrons in a box. The tetrahedron was for decades conjectured to be the only solid that packs less densely than spheres, until just last year when a mathematician found an arrangement that proved that speculation wrong. This latest study bests that organization and discovered what is believed to be the densest achievable packing of tetrahedrons. The more significant finding is that the tetrahedrons can unexpectedly organize into intricate quasicrystals at a point in the computer simulation when they take up roughly half the space in the theoretical box. This is the first result showing such a complicated self-arrangement of hard particles without help from attractive interactions such as chemical bonds, according to the authors.
  Reference
  Disordered, quasicrystalline and crystalline phases of densely packed tetrahedra
  Nature 462, 773-777 (10 December 2009), doi:10.1038/nature08641
  (December 11, 2009)

• Giant magnetoresistance goes electric
  (Physics)

  
  Credit: A. Aziz et al., Phys. Rev. Lett.

  Giant magnetoresistance (GMR) has led to promising devices that may one day be used for spin-dependent electronic applications (spintronics). An example is a magnetic heterostructure, called a spin valve, consisting of alternating ferromagnetic and nonmagnetic layers, whose resistance can be controlled by magnetism. When a current is passed through these structures, the electrons scatter differently depending on the electron spin, so the resistance of the structure depends on the relative magnetic orientation of the ferromagnetic layers. This resistance is linear and current independent. In a recent work, researchers have studied the transport properties of a dual spin valve structure of Co90Fe10/Cu/permalloy (Ni80Fe20)/Cu/Co90Fe10. The dual spin valve is in an unconventional configuration in which the outer ferromagnetic layers are antiparallel, canceling the linear magnetoresistance. However, when the spin populations are far from equilibrium, the researchers observe a nonlinear, current-dependent magnetoresistance. While the exact physical mechanism of this nonlinear effect has not been established, the authors attribute the effect to current-dependent interfacial and bulk scattering asymmetries in the permalloy layer.
  Reference
  Nonlinear Giant Magnetoresistance in Dual Spin Valves
  Phys. Rev. Lett. 103, 237203 (Published December 4, 2009)
  (December 9, 2009)

• Caught on film: Metal atoms in carbon nanotubes
  (Chemistry World)

  
  Credit: Angew. Chem. Int. Ed.

  An international team of researchers has been able to film individual metal atoms as they move around and react within the confines of a carbon nanotube. As well as demonstrating the power of the imaging technique, the work has shown that the interior of carbon nanotubes may not be as inert as previously assumed. The researchers trapped single atoms of the heavy metal dysprosium within hollow fullerene spheres made up of 82 carbon atoms, and enclosed a series of these dysprosium-seeded cages within single-walled carbon nanotubes, with the fullerenes stringing themselves along the nanotube like peas in a pod. Using an aberration-corrected TEM (transmission electron microscope), the team was able directly to observe the dysprosium atoms interacting with the carbon atoms of the fullerene and nanotube. The researchers watched as the dysprosium atoms began to chew away at the wall of the fullerene cage, eventually escaping. Neighbouring ruptured cages then fused together to create small nanotubes. Meanwhile, the liberated dysprosium atoms gradually clustered together and then attacked the wall of the main nanotube, causing the wall to break open and then form a new cap at that point.
  Reference
  Observations of Chemical Reactions at the Atomic Scale: Dynamics of Metal-Mediated Fullerene Coalescence and Nanotube Rupture
  Angewandte Chemie International Edition, Early View (Articles online in advance of print), Published Online: 26 Nov 2009, DOI: 10.1002/anie.200902243
  (December 9, 2009)

• Attacking cancer tumors with tiny discs
  (Physics World)

  
  Credit: Physics World and H. P. Jarvie et al.

  The idea that magnetic particles could be used to target cancer tumors has been in the research community for several decades. The general principle is that drugs intended to destroy targeted cells could be attached to magnetic particles and guided to the appropriate places in the human body using external magnetic fields. Given the precision promised by this approach, it could offer obvious advantages over the crude targeting of chemotherapy, which can leave patients feeling extremely unwell. Despite their early promise, however, these therapies have yet to yield much success in the field of oncology, mainly due to a number of technical issues. Now, researchers have designed a technique in which the particles themselves attack the cancerous cells by exerting a mechanical force. Using a gold-shelled iron-based alloy that they developed, the researchers have created tiny circular discs that are just 60 nm thick with diameters of approximately 1 µm. In this geometry, the magnetic moments are following the disc circumference and form a vortex-like structure with almost perfect closure of the magnetic flux within the disc itself. Instead of been guided by a magnetic field, the tiny discs are coated in antibodies that are able to hone in on the affected cells. Once a disc is alongside a cancerous cell, an alternating magnetic field can be applied, which causes the vortex structure in the disc plane to shift and the magnetic disk to oscillate. Therefore the disks exert a lateral force towards the targeted cancer cell. This very small force, in the order of a few tens of pN, is strong enough to trigger the redistribution of calcium inside the cancer cell that can result in cell death known as apoptosis.
  Reference
  Biofunctionalized magnetic-vortex microdiscs for targeted cancer-cell destruction
  Nature Materials Published online: 29 November 2009 | doi:10.1038/nmat2591
  (December 8, 2009)

   

• Nailing down nickel for electrocatalysis
  (Science)

  
  Credit: Science

  Electrocatalysis is central to the further development of proton-exchange membrane (PEM) electrolyzers and fuel cells, which can operate as compact units for powering homes or vehicles. A single device could both store energy by generating hydrogen during times of electrical surplus and release energy by oxidizing the hydrogen fuel at times of excess demand. Today, this goal is best achieved with expensive, noble metal catalysts. However, reversible catalysts based on abundant materials are essential for such devices to have a substantial impact on sustainable energy systems. The authors of a new study report a hydrogen electrode based on nickel, an abundant element, in which the catalyst is immobilized on a carbon nanotube support. This catalyst effects the reversible interconversion between hydrogen ions (H⁺) and hydrogen (H₂) under aqueous conditions, and provides an important initial step toward a practical, non-noble metal hydrogen electrode.
  Reference
  From Hydrogenases to Noble MetalFree Catalytic Nanomaterials for H2 Production and Uptake
  Science 4 December 2009: Vol. 326. no. 5958, pp. 1384 - 1387 DOI: 10.1126/science.1179773
  (December 8, 2009)

• Evaporative lithography used to pattern colloidal films
  (Science - Editor's Choice)

  
  Credit: Phil. Trans. R. Soc. A

  There are many approaches available for patterning soft materials such as colloidal films, but they often require multiple processing steps and allow for deposition of only a few particle layers. A new method called evaporative lithography overcomes these limitations. Researchers show that the method also allows for the creation of patterns from binary mixtures of particles. Evaporative lithography exploits the fact that when aqueous and organic droplets dry, particles within the droplets are deposited in different patterns. Aqueous droplet evaporation leads to the familiar coffee-ring effect, whereas when nonaqueous droplets evaporate, most particles are deposited at the center. Use of a mask modulates the evaporative landscape of a drying droplet or film, resulting in pattern formation. The authors demonstrate generation of diverse patterns by tuning the mask design, mixture composition, and particle size ratio for an aqueous mixture of silica microspheres and sulphonated polystyrene nanoparticles.
  Reference
  Evaporative lithographic patterning of binary colloidal films
  Phil. Trans. R. Soc. A 28 December 2009 vol. 367 no. 1909 5157-5165 doi: 10.1098/rsta.2009.0157
  (December 8, 2009)