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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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• Nanoplasmonic probing of catalysis
  (Science)

  
  Credit: Science

  An understanding of catalytic reactions on surfaces, such as those used in industrial processes, often requires some measure of reactant concentration on the surface. Often this is expressed as the surface coverage of metal particles that are dispersed on oxide supports. Although optical probes of surface coverage would be convenient, they usually lack sufficient sensitivity to detect the small number of molecules on the surface. A study now has used shifts in plasmon resonances to measure surface coverages. Researchers grew oxide coatings, decorated with metal catalyst particles, on a nanoscale gold disk, and found that these model catalysts are within the region of plasmon sensitivity. Reactions such as CO oxidation on platinum can be followed for different ratios of reactant gases with a sensitivity of 0.1 monolayer of surface coverage.
  Reference
  Nanoplasmonic Probes of Catalytic Reactions
  Science 20 November 2009, Vol. 326. no. 5956, pp. 1091 - 1094, DOI: 10.1126/science.1176593
  (November 20, 2009)

• Graphene-like honeycomb structured polymer synthesized
  (PhysOrg)

  
  Credit: RSC

  Researchers report the synthesis of a graphene-like porous polymer with atomic accuracy. Graphene of course consists of a two-dimensional carbon layer in which the carbon atoms are arranged on a hexagonal lattice, resembling a honeycomb. By inserting holes of a specific size and distribution into graphene sheets, it should be possible to impart the material particular electronic characteristics. For these reasons intensive research is being conducted worldwide into the synthesis and characterization of two-dimensional graphene-like polymers. Scientists have for the first time succeeded in synthesizing a graphene-like polymer with well defined pores. To achieve this feat the researchers allowed chemical building blocks of functionalized phenyl rings to “grow” spontaneously into a two-dimensional structure on a silver substrate. This created a porous form of graphene with pore diameters of a single atom and pore-to-pore spacings of less than a nanometer.
  Reference
  Porous graphenes: two-dimensional polymer synthesis with atomic precision
  Chem. Commun., 2009, 6919 - 6921, DOI: 10.1039/b915190g
  (November 20, 2009)

• Holes block light in very thin films
  (NanotechWeb)

  
  Credit:APS

  When an array of tiny holes is drilled into a metal foil and the light allowed through the holes is measured, it turns out – as physicists discovered back in 1998 – that much more is transmitted than if the light behaved like water passing though a screen. The light is absorbed by electrons on the surface of the metal, creating "surface plasmons" that travel via the holes to the dark side of the foil, where they re-emit the light. Now, researchers have discovered that this phenomenon, known as "extraordinary optical transmission", does not occur in foils that are thin enough to be semi-transparent to light. Instead, punching holes in such films leads to a significant reduction in the amount of light that gets through. The findings could be useful for creating new kinds of polarization filters and other components for photonic circuits.
  Reference
  How Holes Can Obscure the View: Suppressed Transmission through an Ultrathin Metal Film by a Subwavelength Hole Array, Phys. Rev. Lett. 103, 203901 (2009), DOI: 10.1103/PhysRevLett.103.203901
  (November 19, 2009)

• Ironing graphene sheets flat
  (Chemistry World)

  
  Credit: Nature

  Free-standing graphene in its equilibrium state spontaneously forms ripples, which can affect its properties. An important question to answer is whether this rippling occurs naturally, or was a result of being deposited on uneven surfaces. Researchers have found a way to iron out graphene by sticking them to flakes of mica. Rather than leaving 'ripples' characteristic of graphene sheets, the technique produces 'ultra flat' graphene. The chosen surface was a mica material, consisting of aluminosilicate layers linked by single layers of potassium ions. Sheet silicate materials are known for their ability to split perfectly down the potassium layer - leaving an atomically-smooth surface. The team looked at graphene sheets - freshly peeled from graphite onto the smooth mica surface - and found that the height variation across the graphene layer only changed by about one tenth of an ångström.
  Reference
  Ultraflat graphene, Nature 462, 339-341 (19 November 2009), doi:10.1038/nature08569
  (November 19, 2009)

• Small optical force can move nanoscale objects
  (Cornell University)

     
     Credit: Cornell Nanophotonics Group

  With a bit of leverage, researchers have used a very tiny beam of light with as little as 1 milliwatt of power to move a silicon structure up to 12 nanometers. That's sufficient to completely switch the optical properties of the structure from opaque to transparent. The technology could have applications in the design of micro-electromechanical systems (MEMS) -- nanoscale devices with moving parts -- and micro-optomechanical systems (MOMS). The researchers created a structure consisting of two thin, flat silicon nitride rings about 30 microns (millionths of a meter) in diameter mounted one above the other and connected to a pedestal by thin spokes. The ring waveguides are three microns wide and 190 nanometers thick, and the rings are spaced 1 micron apart. When light at a resonant frequency of the rings, in this case infrared light at 1533.5 nm, is fed into the rings, the force between the rings is enough to deform the rings by up to 12 nm, which the researchers showed was enough to change other resonances and switch other light beams traveling through the rings on and off.
  Reference
  Controlling photonic structures using optical forces, Nature advance online publication 15 November 2009, doi: 10.1038/nature08584
  (November 18, 2009)

• Quantum dots offer better way to harness waste heat
  (Eurekalert)

  More than half of the energy consumed worldwide is wasted, most of it in the form of excess heat. A new technology involving quantum dots would allow conversion of waste heat into electricity with an efficiency several times greater than existing devices. In experiments involving a different new technology, thermal diodes, researcheres demonstrated efficiency as high as 40 percent of the Carnot Limit. The calculations show that this new kind of system could ultimately reach as much as 90 percent of that ceiling. They carried out their analysis using a very simple system in which power was generated by a single quantum-dot device.
  Reference
  Quantum-coupled single-electron thermal to electric conversion scheme, Journal of Applied Physics, published online Nov. 13, 2009 http://link.aip.org/link/?JAPIAU/106/094315/1
  (November 18, 2009)

• Mn-based chromophore yields new blue pigment
  (Chemical and Engineering News)

     
     Credit: J. Am. Chem. Soc.

  By swapping a few indium atoms with manganese, chemists have created a new blue chromophore. The Mn-doped substance suggests a route to compounds that could replace existing blue pigments with ones that are cheaper, more stable, and environmentally benign. The researchers were doping YInO3 with Mn to make YIn1- xMnxO3. Although they expected to pull black or gray material from their furnace, they were surprised to see a bright blue powder instead. They determined that the color comes from the unusual trigonal bipyramidal coordination of Mn3+. This gives rise to energy levels in manganese’s d orbitals that result in an intense absorption in the red/green region of the visible spectrum. They were able to create other blue chromophores by doping Mn3+ into trigonal bipyramidal sites in other metal oxides, such as LuGaMgO4. They are using this strategy to design cost-effective blue pigments using cheaper materials.
  Reference
  Mn3+ in Trigonal Bipyramidal Coordination: A New Blue Chromophore, J. Am. Chem. Soc., DOI: 10.1021/ja9080666
  (November 17, 2009)

• Reliable way to grow graphene directly on silicon
  (Science Daily/Cornell University)

  
  Credit: Shivank Garg, Cornell

  Making graphene in large quantities is a challenge, and scientists have turned to methods as crude as using scotch tape to pull off a layer of graphene from graphite. Such methods would never survive manufacturing, especially since it would produce graphene with varying numbers of layers at random positions.A research team has now invented a simple way to make graphene electrical devices by growing the graphene directly onto a silicon wafer. Inspired by previous work in which scientists grew graphene on copper foil, the team grew the graphene directly onto silicon wafers coated with a special evaporated copper film. They then cut the graphene films into their desired shapes using such standard photolithography methods, and removed the underlying copper with a chemical solution. What was left was a graphene film that draped down over the silicon wafer with few defects.
  Reference
  Transfer-Free Batch Fabrication of Single Layer Graphene Transistors, Nano Lett., Article ASAP DOI: 10.1021/nl902790r
  (November 17, 2009)

• Graphene FETs get up to speed
  (NanotechWeb)

  
  Credit: Nano Letters

  Graphene could be ideal for making high-speed transistors, since electrons move through graphene at extremely high speeds thanks to the fact that they behave like relativistic particles with no rest mass. However, there is a serious problem holding back the technology. Interactions between graphene and the dielectric material used as the top gate causing scattering of charge carriers severely degrades the speed of the charge carriers (electrons and holes) in graphene, which ultimately limits device performance. In a new study, researchers have placed an organic polymer buffer layer between the graphene and conventional high-k dielectrics allowing carrier mobilities to remain high. The low-κ polymer buffer layer employed by the team suppresses interactions between the surface phonons of the high-κ material and graphene. Moreover, the amount of charged impurities associated with the polymer are expected to be lower, also resulting in less scattering.
  Reference
  Utilization of a Buffered Dielectric to Achieve High Field-Effect Carrier Mobility in Graphene Transistors, Nano Lett., Article ASAP DOI: 10.1021/nl902788u
  (November 16, 2009)

• Strain-induced piezoelectric effect in bismuth ferrite
  (Lawrence Berkeley National Lab)

  
  Credit: LBL

  The most widely used piezoelectric materials today are lead-based perovskite compounds, especially lead zirconate titanate (PZT). These perovskites display superior piezoelectric properties in areas where the phase of their crystal structure abruptly changes. Such areas, known as morphotropic phase boundaries, are produced via complex chemical alloying of a PZT-type perovskite’s metal and oxide constituents. While the technology is well established, lead is a potent neurotoxin that poses a serious threat to human health. A lead-free alternative to the current crop of piezoelectric materials has now been identified by researchers. They have been able to produce the piezoelectric effect by taking thin films of bismuth ferrite and applying a huge epitaxial strain. The bismuth ferrite wants to be in a rhombohedral phase but the epitaxial strain forces it into a tetragonal phase, creating a morphotropic phase boundary. When the strain was removed, the bismuth ferrite crystal structure reverted back to its original rhombohedral-like phase. By alternating between squeezing and relaxing, the researchers are able to shuttle the material back and forth between the two phases.
  Reference
  A Strain-Driven Morphotropic Phase Boundary in BiFeO₃, Science, 13 November 2009: Vol. 326. no. 5955, pp. 977 - 980 DOI: 10.1126/science.1177046
  (November 16, 2009)

• Spontaneous elimination of condensate droplets from superhydrophobic surfaces
  (Science)

  
  Credit: Boreyko and Chen

  When hot vapor comes in contact with a cold surface, such as a shower wall, liquid droplets are created that quickly coalesce and form a film. This condensation process is ubiquitous in natural as well as artificial environments. In industrial settings, preventing film formation is generally desirable because liquid films are poor heat conductors. However, it can be challenging to remove the droplets more quickly than they coalesce, particularly when nonvertical sample orientations preclude help from gravity. A research team has now demonstrated the spontaneous elimination of droplets from a horizontal surface. They prepared a superhydrophobic substrate consisting of carbon nanotubes deposited on silicon micropillars. Video imaging of the condensation of ambient moisture revealed that, after the droplets are formed, they initially coalesce without moving, then eventually reach a mobile phase where several droplets fuse and leave the surface of the sample in a dramatic out-of-plane jump. The energy for the jump is provided by the decrease in surface energy gained by coalescence; the average condensed droplet size is an order of magnitude smaller than that observed in gravitational removal.
  Reference
  Self-Propelled Dropwise Condensate on Superhydrophobic Surfaces, Phys. Rev. Lett. 103, 184501 (2009), DOI 10.1103/PhysRevLett.103.184501
  (November 13, 2009)

• Fluctuation electron microscopy images subcritical nuclei in a solid
  (Science)

  
  Credit: Science and Gordon Halloran
  www.icepaintingproject.com
  Photo: Allan Burns

  All materials search for the lowest accessible energy state. As temperature is increased in disordered materials, atoms diffuse and explore different chemical and structural configurations. Crystalline phases may be favored, but a very small crystal is unstable, so there is a "nucleation barrier" to overcome; only after reaching a critical size can the nucleus grow. Although we understand the thermodynamics of the nucleation process, observation of the actual atomic-scale complexity during nucleation has remained elusive, despite its importance to the properties of materials. Taking nucleation out of the "black box" is one of the grand challenges to "materials by design." A new study has demonstrated the use of fluctuation electron microscopy to image subcritical nuclei in a solid material, observing metastable structural states that facilitate later nucleation in amorphous films. The study was also applied to a technologically important case of "phase-change memory".
  Reference
  Observation of the Role of Subcritical Nuclei in Crystallization of a Glassy Solid, Science 326 (5955), 980 DOI: 10.1126/science.1177483
  (November 13, 2009)

• Fractional quantum Hall effect observed in graphene: Dirac electrons broken to pieces
  (Nature)

  
  Credit: Nature

  The fractional quantum Hall effect (FQHE) is a fascinating form of collective electronic behavior. It arises when electrons in a strong magnetic field applied at a right angle to the plane in which the electrons flow act together to behave like particles with a charge that is a fraction of an electron's charge. Its observation requires the use of two-dimensional systems virtually free of disorder. This is why, since its discovery by Daniel Tsui and Horst Strmer in 1982, the effect has been studied in ultrapure semiconductor heterostructures (devices that contain thin layers of one or more semiconductors) grown in an ultrahigh vacuum. Two new studies now show that the FQHE can also be observed in graphene.
  References
  News and Views: Dirac electrons broken to pieces, Nature 462, 170-171 (12 November 2009) | doi:10.1038/462170a
  Fractional quantum Hall effect and insulating phase of Dirac electrons in graphene, Nature 462, 192-195 (12 November 2009) | doi:10.1038/nature08522
  Observation of the fractional quantum Hall effect in graphene, Nature 462, 196-199 (12 November 2009) | doi:10.1038/nature08582
  (November 12, 2009)

• New finFET promising for smaller transistors
  (Purdue University)

  
  Credit: Purdue University

  Researchers are developing and have demonstrated proof-of-concept for a new type of transistor, a finFET, that uses a finlike structure instead of the conventional flat design, possibly enabling faster and more compact circuits and computer chips. The fins in this case are made from indium-gallium-arsenide, and are formed using atomic layer deposition. In addition to making smaller transistors possible, finFETs also might conduct electrons at least five times faster than conventional silicon MOSFETs. The researchers have also been able to "grow" hafnium dioxide onto finFETs made of a III-V material using atomic layer deposition.
  (November 11, 2009)

• Electron beam device makes metal parts one layer at a time
  (Science Daily)

  
  Credit: NASA

  Layers mean everything to a new environmentally-friendly construction process called Electron Beam Freeform Fabrication, or EBF3. EBF3 works in a vacuum chamber, where an electron beam is focused on a constantly feeding source of metal, which is melted and then applied as called for by a drawing -- one layer at a time -- on top of a rotating surface until the part is complete. To make EBF3 work there are two key requirements: A detailed three-dimensional drawing of the object to be created must be available, and the material the object is to be made from must be compatible for use with an electron beam. The technique can handle two different sources of metal at the same time, either by mixing them together into a unique alloy or embedding one material inside another.
  (November 11, 2009)

• Photochromic contact lenses respond to UV light
  (Technology Review)

  
  Credit: Institute for Bioengineering
  and Nanotechnology, Singapore

  Transition lenses--which darken automatically in response to bright sunlight--have been available for eyeglasses for 40 years. But adapting this flexibility to contact lenses has proven challenging. Now researchers have developed UV-responsive, or photochromic, lenses that darken when exposed to ultraviolet light, protecting the eyes against the sun's damaging rays, and return to normal in the absence of UV. The key is a novel polymer laced with an intricate network of nano-sized tunnels that can be filled with dyes. The researchers created the spongy nanostructure material by mixing specific combinations of water, an oil solution with monomers commonly used in contact lenses, and a novel surfactant-- a compound that encourages mixing between water and oil solutions. The resulting material is studded with tiny pores and tunnels, which can be loaded with agents such as UV-sensitive dyes. The lens material's porous structure provides a flexible environment for dyes to transform from dark to light and back again
  (November 10, 2009)

• First direct imaging of catalytically active ZrWOx clusters
  (Eurekalert)

  Tungstated zirconia is a robust solid acid catalyst used for light alkane (C4C8) isomerization. Due to the absence of direct structural imaging information on the various supported WOx species, information on catalytically active sites has been limited. In a new study, researchers used high-angle annular dark-field (HAADF) imaging of WO₃/ZrO₂ catalysts in an aberration-corrected analytical electron microscope allows which for the first time achieved direct imaging of the various species present. Catalytic performance studies revealed that the most active catalytic species are tungsten oxide clusters that measure only 0.8 to 1 nm in diameter and are mixed with a few zirconium atoms emanating from the support. The team then deliberately deposited the catalytically active sub-nanometer mixed tungsten-zirconium oxide clusters onto a tungstated zirconia catalyst that previously had possessed low catalytic activity. The catalytic activity of the poor catalyst was found to have improved by two orders of magnitude, confirming the team's hypothesis about the identity and structure of the active species within the tungstated zirconia material.
  Reference
  Identification of active ZrWOx clusters on a ZrO2 support for solid acid catalysts, Nature Chemistry Published online: 8 November 2009, doi:10.1038/nchem.433
  (November 10, 2009)

• Solution-deposited sodium beta-alumina gate dielectrics
  (Johns Hopkins University)

  
  Credit: Nature Materials

  Sodium beta-alumina (SBA) is an interesting material with a very large ionic conductivity. A new study now shows that it is also an outstanding dielectric. The material is produced in a liquid state, which means it can easily be deposited onto a surface in a precise pattern for the formation of printed circuits. But when its heated, it forms a solid, thin transparent film. In addition, it allows for operation at low voltages, meaning it requires less power to induce useful current. The transparency and thinness of the material (the hardened film is only on the order of 100 atoms thick) for instance make it ideal for use in the increasingly popular e-book readers.
  Reference
  Solution-deposited sodium beta-alumina gate dielectrics for low-voltage and transparent field-effect transistors, Nature Materials 8, 898 - 903 (2009) Published online: 18 October 2009 | doi:10.1038/nmat2560
  (November 9, 2009)

• Microscopic springs made from nanotube composite
  (Chemistry World)

  
  Credit: Daniel Therriault, École Polytechnique de Montréal

  Researchers have developed a way to rapidly make tiny 3D objects out of a carbon nanotube-enriched polymer, using UV light to quickly set the structure in place. As a demonstration, the team made coiled springs half a millimetre in size. The micro-fabrication method uses 'direct-write assembly' in which a robot dispenses a liquid polymer that hardens as soon as it leaves the nozzle. Their material of choice is a polymer nanocomposite that is reinforced with carbon nanotubes. This makes the material strong enough to support its own weight and also makes it electrically conductive. The material is formed by dispersing nanotubes in a liquid thermosetting polymer; two UV lamps pointed at the nozzle cause it to solidify very rapidly as it is dispensed.
  Reference
  Ultraviolet-Assisted Direct-Write Fabrication of Carbon Nanotube/Polymer Nanocomposite Microcoils, Advanced Materials Early View, Published Online: 30 Oct 2009, DOI: 10.1002/adma.200902192
  (November 9, 2009)

• Better model for glass creation using a colloid
  (Harvard University)

  
  Credit: Harvard University

  Scientists have come up with what they believe is a new way to model the formation of glasses. They report a new wrinkle on an old model that seems to improve how well it mimics the behavior of glass. The model is a colloidial fluid, a liquid with tiny particles, or colloids, suspended evenly in it. Scientists model solidifying glasses using colloids by adding more particles to the fluid. This increases the particles concentration, making the fluid thicker, and making it flow more slowly. The advantage of this approach to studying glasses directly is size. The colloid particles are 1,000 times bigger than a molecule of a glass and can be observed with a microscope. The scientists created a colloid that behaves more like a glass in that way by using soft, compressible particles in the colloid instead of hard ones. This makes the particles squeeze together as more particles are added, making them flow more slowly, but delaying the point at which it solidifies, giving it a more glasslike behavior.
  Reference
  Soft colloids make strong glasses, Nature 462, 83-86 (5 November 2009) | doi:10.1038/nature08457
  (November 6, 2009)

• Universal equation describes how materials behave at the nanoscale
  (Physics World)

  
  Credit: Physics World and NASA

  Understanding how materials behave at the nanoscale is crucial for developing future nanotechnologies and continues to be a great challenge for both theoretical and experimental physicists alike. Now, a researcher has borrowed from 19th century physics to come up with a new "universal" equation that predicts how size affects the key physical properties of nanometer-sized structures, which behave very differently from their macroscopic counterparts. He developed his equation by analyzing and comparing how the size of nanoparticles affects the temperature at which they melt, become superconductors and become ferromagnetic (Curie temperature). He also considered the Debye temperature, which is related to how lattice vibrations conduct heat in a material. These four "characteristic" temperatures are key physical quantities for any material and all are inter-related. The equation is based on the diameter of the nanostructure, a parameter that is related to the surface-to-volume ratio, and the spin (S) of the particles involved in the considered material property. The equation has no adjustable parameters and works for all materials.
  Reference
  Universal size/shape-dependent law for characteristic temperatures, Physics Letters A, 2009, doi:10.1016/j.physleta.2009.10.054
  (November 6, 2009)

• Novel multi-axis force sensor balances sensitivity and bandwidth
  (Science)

  
  Credit: Smart Materials and Structures

  In a displacement force sensor, there is an inherent tradeoff between sensitivity (which requires large deflections to detect weak applied forces) and bandwidth (which requires small deflections to accommodate a wide range of applied forces). Similar tradeoffs apply to sensing in more than one direction while keeping the device compact. Researchers have now sought to optimize these tradeoffs in force sensor design. They fabricated a three-dimensional sensor by folding a laser-patterned Invar sheet, reinforcing it with glass-filled epoxy, and soldering the tabs together. Numerical analysis revealed almost no coupling between the deformation responses along the orthogonal axes. The device proved more sensitive than expected from the modeling studies, because of a lower than expected stiffness, and the bandwidth was also affected by the weight of the adhesive used. The authors demonstrated the sensor's capabilities by simultaneously measuring the lift and drag forces from the flapping wing of a fly-sized robotic insect.
  Reference
  A novel multi-axis force sensor for microrobotics applications, Smart Mater. Struct. 18 (2009) 125002
  (November 6, 2009)

• Moth eye inspires multifunctional anti-reflection surface
  (NanotechWeb)

  
  Credit: Nanotechnology

  The anti-reflection (AR) phenomenon has its origins in nature. For example, a sub-micron AR structure in the eyes of a night moth makes it easier for the insect to hide from predators. In nanotechnology, several dexterous and simple methods exist for producing AR surfaces and the most common way to suppress reflection is to apply thin films to a substrate. Alternative approaches include modifying the surface with a suitable pattern or introducing a porous material to the surface. In a new study, a research group modified the substrate surface to form a pyramid-shaped "moth eye"-structure. The multifunctional continuous-shaped nanoscale pattern offers a number of benefits – reflection reduction, wide-angle performance, controlled surface colour perception and hydrophobicity. To define the optimal shape of the pyramid structure, the researchers used numerical calculations based on rigorous diffraction theory.
  Reference
  A wide-angle antireflection surface for the visible spectrum, Nanotechnology 20 375301 doi: 10.1088/0957-4484/20/37/375301
  (November 5, 2009)

• Acidity regulation in microfluidic channels
  (Highlights in Chemical Technology)

  
    Credit: Veenhuis et al., Lab Chip

  Controlling pH in microfluidics could allow for new applications, such as for the activity of single enzymes to be measured. Current methods are slow or produce unwanted side-products. Researchers have now used an external electrode to adjust the number of positive ions in the solution. One plate is the conducting solution and the other is a metal plate and they are separated by a silicon nitride layer. Applying a negative voltage to the metal plate attracts positive ions to the nitride surface - removing them from the solution and making it more basic. Reversing the charge has the opposite effect - making a more acidic solution.
  Reference
  Field-effect based attomole titrations in nanoconfinement, Lab Chip, 2009 DOI: 10.1039/b913384d
  (November 4, 2009)

• Fullerene as replacement for noble metal catalysts for hydrogenation
  (Chemical and Engineering News)

  
  Credit: Chemical & Engineering News, ACS

  Transition-metal catalysts lie at the heart of global-scale hydrogenation processes, such as the ones used to refine crude oil and to synthesize the common fertilizer ammonia. Nonmetal hydrogenation catalysts could provide industry with substantial cost savings. But such catalysts typically require high temperatures and pressures or are ineffective at mediating hydrogenations with molecular hydrogen; they work instead with other hydrogen sources. Now, in a new paper, researchers report that nitroaromatic compounds are readily and selectively hydrogenated to aromatic amines by molecular hydrogen under mild conditions in the presence of a fullerene catalyst. Specifically, the team finds that bubbling hydrogen at atmospheric pressure through a room-temperature solution of nitrobenzene containing a small quantity of C60, while irradiating the reagents with ultraviolet light, yields aniline in nearly 100% yield. That level of catalytic performance is considered the hallmark of noble metals such as palladium and platinum.
  Reference
  A Nonmetal Catalyst for Molecular Hydrogen Activation with Comparable Catalytic Hydrogenation Capability to Noble Metal Catalyst, J. Am. Chem. Soc., Article ASAP DOI: 10.1021/ja9061097 Publication Date (Web): October 21, 2009
  (November 4, 2009)

• Wrapping solar cells around an optical fiber
  (Technology Review)

  
  Credit: Angewandte Chemie

  Dye-sensitized solar cells are flexible and inexpensive to make, but they tend to be inefficient at converting light into electricity. One way to boost the performance of any solar cell is to increase the surface area available to incoming light. So a group of researchers has made dye-sensitized solar cells with a much higher effective surface area by wrapping the cells around optical fibers. These fiber solar cells are six times more efficient than a zinc oxide solar cell with the same surface area, and if they can be built using cheap polymer fibers, they shouldn't be significantly more expensive to make. The advantage of a fiber-optic solar cell system over a planar one is that light bounces around inside an optical fiber as it travels along its length, providing more opportunities to interact with the solar cell on its inner surface and producing more current.
  Reference
  Optical Fiber/Nanowire Hybrid Structures for Efficient Three-Dimensional Dye-Sensitized Solar Cells, Angewandte Chemie International Edition Published Online: Oct 22 2009 11:26AM DOI: 10.1002/anie.200904492
  (November 3, 2009)

• Optomechanical crystal traps light and sound vibrations together
  (Caltech)

  
  Credit: M. Eichenfield, et. al., Nature

  Researchers have created a nanoscale crystal device that, for the first time, allows scientists to confine both light and sound vibrations in the same nanoscale space simultaneously. The interactions between sound and light in this device—dubbed an optomechanical crystal—can result in mechanical vibrations with frequencies as high as tens of gigahertz, or 10 billion cycles per second. Being able to achieve such frequencies gives these devices the ability to send large amounts of information, and opens up a wide array of potential applications—everything from lightwave communication systems to biosensors capable of detecting (or weighing) a single macromolecule. It could also be used as a research tool by scientists studying nanomechanics. The researchers describe the design, fabrication and characterization of a planar, silicon-chip-based optomechanical crystal capable of co-localizing and strongly coupling 200-terahertz photons and 2-gigahertz phonons.
  [Optomechanical crystals, Nature advance online publication 18 October 2009 | doi:10.1038/nature08524]
  (November 3, 2009)

• Reversed Cherenkov radiation in left-handed metamaterial
  (Physics)

  
  Credit: Alan Stonebraker /APS

  When charged particles such as electrons travel through a dielectric medium with a speed greater than the phase velocity of the light in the medium, electromagnetic radiation is emitted that falls into a cone fanning out in the forward direction. This phenomenon is called Čerenkov radiation, familiar as the blue glow of an underwater nuclear reactor as it emits energetic charged particles. The angle of the Čerenkov emission cone is related in a simple way to the particle velocity. This unique feature enables a wide range of applications, from the measurement of fast particles in high-energy physics, the characterization of fission rate in nuclear reactors, to the detection of labeled biomolecules. Now, researchers have experimentally demonstrate that the direction of the cone of Čerenkov radiation can be reversed in an artificially engineered composite metamaterial.
  [Experimental Verification of Reversed Cherenkov Radiation in Left-Handed Metamaterial, Phys. Rev. Lett. 103, 194801 (2009) – Published November 2, 2009]
  (November 3, 2009)

• True solutions of single-walled carbon nanotubes
  (Chemistry World)

  
  Credit: Nature Nanotechnology

  Carbon nanotubes are particularly difficult to dissolve in solution because they tend to stick together in bundles. R esearchers have now used chlorosulfonic acid to dissolve single-walled carbon nanotubes (SWNTs). The tubes dissolve spontaneously, forming true solutions at low concentrations and liquid crystals at higher concentrations, but because the tubes are actually dissolved, they can be processed using standard techniques that are impossible with more usual suspensions of the tubes. According to the scientists, with chlorosulfonic acid, the dissolution is immediate and spontaneous, without the need to sonicate the mixture.
  [True solutions of single-walled carbon nanotubes for assembly into macroscopic materials, Nature Nanotechnology Published online: 1 November 2009 | doi:10.1038/nnano.2009.302]
  (November 2, 2009)

• Multiferroic behavior in metal-organic frameworks
  (Nature)

  A new paper describes a family of metal -organic frameworks (MOFs), porous crystalline materials, that are multiferroic, combining ferromagnetism with antiferroelectricity. Recent years have seen a considerable worldwide effort to discover broad classes of multiferroics, using a combination of materials chemistry, theoretical approaches and synthetic techniques. The new MOF compounds represent a completely new class of multiferroics — previously reported magnetoelectric perovskites were purely inorganic compounds, but MOFs are hybrid structures comprising metal ions in complex with organic molecules. The presence of organic molecules in the structures allows hydrogen bonds to form between the MOF's components. It is these bonds that are responsible for ordering the new MOFs in such a way as to engender multiferroic properties — a first in the field. The authors previously identified an antiferroelectric MOF structure that contained zinc ions (Zn2+). By replacing the zinc with magnetic transition-metal ions, such as iron(II) ions (Fe2+), they were able to make multiferroic materials.
  Reference
  Multiferroic behavior associated with an order-disorder hydrogen bonding transition in metal-organic frameworks (MOFs) with the perovskite ABX3 architecture, J Am Chem Soc. 2009 Sep 30;131(38):13625-7
  (November 2, 2009)

• Carbon nanotube arrays behave like conducting rubber
  (NanotechWeb)

  
  Credit: Nanotechnology

  Arrays of vertically aligned carbon nanotubes can be synthesized, but little is known about the mechanical properties of such arrays. An actuation study of vertically aligned carbon nanotube arrays by researchers reveals that the system moves as a solid cohesive unit. The team has obtained the effective Young's modulus for its design by comparing in situ experiments with electrostatic simulations. Although individual nanotubes have a tensile strength of tens to hundreds of GPa, thus stronger than steel, the arrays were found to have an effective Young's modulus of only ca 4 MPa, thus lower than rubber. This is believed to be due to nanotubes being able to slip and slide against each other in the low-density arrays. Taking the results a step further, the group has come up with a simple variable capacitor that exploits the reproducible movement of vertically aligned carbon nanotubes.
  [Determination of the effective Young's modulus of vertically aligned carbon nanotube arrays: a simple nanotube-based varactor, Nanotechnology, 20 (2009) 385710, doi: 10.1088/0957-4484/20/38/385710]
  (October 30, 2009)

• Nanoscale diffraction by convergent-beam ultrafast electron microscopy
  (Science)

  
  Credit: Science

  Electron diffraction is a versatile technique for discerning atomic-level structure of materials, but the data obtained are averaged over the micron–scale area sampled by the electrons, and therefore blur local distinctions in systems that are not strictly periodic. A recent approach to minimizing this problem has been to focus the electron beam impinging on the sample. Researchers have now applied convergent focusing to an ultrafast electron diffraction apparatus and were thus able to resolve picosecond structural dynamics in local regions tens of nanometers across. The technique was used to probe heterogeneous temperature changes in laser-heated silicon.
  Reference
  4D Nanoscale Diffraction Observed by Convergent-Beam Ultrafast Electron Microscopy, Science 30 October 2009:
  Vol. 326. no. 5953, pp. 708 - 712, DOI: 10.1126/science.1179314
  (October 30, 2009)

• Superconductivity sliced thin
  (Science)

  
  Credit: Robert J. Sundling and Science

  Since the initial characterization of high-temperature cuprate superconductors, an intriguing challenge has been determining the minimum number of copper oxide planes needed to support the superconducting state. The observation of superconductivity at interfaces of metallic oxides and insulators provides a route to addressing this question. A new report describes a method for layer-by-layer synthesis of alternating oxides of metal and insulators based on La and Cu. Layers three unit cells thick supported superconductivity with a transition temperature of 32 kelvin. When selected layers were then doped with Zn atoms to suppress superconductivity, the interface superconductivity was shown to arise from a single copper-oxide plane.
  References
  High-Temperature Superconductivity in a Single Copper-Oxygen Plane, Science 30 October 2009: Vol. 326. no. 5953, pp. 699 - 702 DOI: 10.1126/science.1178863
  (October 30, 2009)

• Plasmons shine a light on catalysis
  (Physics World)

  
  Credit: Science

  Researchers have devised a new way of monitoring catalytic processes in "real-life" situations. The technique uses collective electron oscillations called "surface plasmons" and is claimed to be better than current analytical methods, which often rely on ultrahigh vacuum (UHV) techniques and single-crystal samples. The new technique involves studying catalytic processes at realistic pressures and particle sizes. The team deposited about 30 nm of gold onto a glass slide, which was then dipped into a plastic colloid that was then dried to form a pattern of circles on the surface of the gold. Etching away the exposed gold left gold disks about 100 nm in diameter. The sample was then coated with a thin insulating film about 10 nm deep and then with nm-sized pieces of the catalyst platinum, covering 1020 % or less of the surface. When light from an ordinary lamp was shone through the slide, radiation at certain wavelengths was absorbed to create surface plasmons on the surfaces of the gold disks. The transmitted-light spectrum therefore has an absorption minimum at these wavelengths. The researchers discovered that the position of this minimum changed when certain molecules such as oxygen or carbon dioxide are adsorbed onto the surface of the platinum. The team used the technique to study several common catalytic reactions, including the oxidation of carbon monoxide to create carbon dioxide.
  [Nanoplasmonic Probes of Catalytic Reactions, Science, Published Online October 22, 2009 DOI: 10.1126/science.1176593]
  (October 29, 2009)

• Nonspecific cervical cancer cell detection using fluorescent silica beads
  (Materials Views)

  
  Credit: Igor Sokolov et al.

  Methods for detection of cancer cells are mostly based on traditional techniques used in biology, such as visual identification of malignant changes, cell-growth analysis or genetic tests. Despite being well developed, these methods are either insufficiently accurate or require a lengthy complicated analysis, which is impractical for clinical use. A recent study reported on observation of differences in surface physical properties of cancerous and normal human epithelial cervical cells. Specifically, they found a substantial difference in the brush layer on the cell surface. The used atomic force microscopy (AFM) to study adhesion of ultrabright fluorescent silica beaads to the cells. The silica beads were attached to the AFM cantilever, and consequently, touched the cell surfaces. The adhesion force needed to separate the bead from the cell was measured. The difference in adhesion, which has an essentially physical nature, was used to distinguish between cancerous and normal cells. High adhesion resulted in more particles adhering to cells. Utilizing fluorescent silica particle, one can easily measure the amount of fluorescent light coming from such cells. Using cells collected from cervical cancers of three cancer patients and cells extracted from tissue of healthy patients, the researchers found an unambiguous and clear difference.
  [Towards Nonspecific Detection of Malignant Cervical Cells with Fluorescent Silica Beads, Small 2009, 5, 2277 ; DOI: 10.1002/smll.200900434]
  (October 29, 2009)

• Metallic shape-memory foam shows giant response to magnetic fields
  (National Science Foundation)

  
  Credit: Markus Chmielus (Boise State University and Helmholtz Center Berlin), Xuexi Zhang (Northwestern University and Harbin Institute of Technology), Cassie Witherspoon (Boise State University), David C. Dunand (Northwestern University), Peter Müllner (Boise State University)

  Magnetic shape-memory alloys, or MSMAs, are solid crystals made up of a combination of materials that react to magnetic fields by either stretching out or contracting, not unlike a muscle. The amount of stretch or shrink exhibited by these alloys is called the magnetic field-induced strain (MFIS). A research group previously developed a metallic foam made from Ni-Mn-Ga that exhibited magnetic shape-memory properties without requiring it to be a single crystal. But the amount of strain that the foam exhibited was still relatively small. In the most recent work, they decided to make the foam with two different pore sizes, including some about the size of the crystallite grains, and some smaller than grain size. With the single-sized pores, they had achieved an MFIS of only 0.12 percent, equal to a rod one foot long stretching about one-hundredth of an inch. But with the two different pore sizes, the MFIS increased to anywhere from 2.0 to 8.7 percent. The present work on Ni–Mn–Ga foams with bimodal pore-size distribution is expected to create new avenues of research on other potential magnetic shape-memory alloy foams in general, yielding many fresh and interesting results.
  [Giant magnetic-field-induced strains in polycrystalline Ni–Mn–Ga foams, Nature Materials 8, 863 - 866 (2009) Published online: 13 September 2009 | doi:10.1038/nmat2527; News and Views: Magnetic shape memory: Magnetoelastic sponges, Nature Materials 8, 854 - 855 (2009) doi:10.1038/nmat2551]
  (October 29, 2009)

• Microcapsules deliver chemicals on demand
  (Eurekalert)

  
  Credit: The American Chemical Society

  Scientists are reporting development of new microcapsules that burst when exposed to light, releasing their contents in ways that could have wide-ranging commercial uses from home and personal care to medicine. The new microcapsules consist of nylon spheres about the size of a grain of sand. They enclose a liquid chemical sprinkled with carbon nanotubes. The nanotubes convert laser light to heat that bursts the nylon capsule, releasing the chemical. Using such a system, doctors, for example, might inject microcapsules containing anti-cancer drugs to specific cells and make the capsules burst upon exposure to laser light, delivering their contents precisely where and when they are needed in the body.
  [Chemicals On Demand with Phototriggerable Microcapsules, J. Am. Chem. Soc., 2009, 131 (38), pp 1358613587, DOI: 10.1021/ja905378v]
  (October 28, 2009)

• Unexpected behavior of beads in a box
  (Technology Review)

  
  Credit: Frank Rietz and Ralf Stannarius, University of Magdeburg

  In 1939, a Japanese researcher showed that a rotating drum half-filled with beads of different sizes causes the beads to demix forming into various patterns of segregation. This is a potentially interesting way to separate such mixtures. This and other work kickstarted an entirely new field focused on the strange behaviour of granular fluids. Now, researchers have found a curious corollary to this work. Instead of a rotating drum, they confine their mixture of small and large beads to a flat box which they then set rotating at slow speed so inertial effects are minimised. And instead of half filling the box, they almost totally fill it with beads. What actually happens is quite extraordinary. Above some filling threshold, the bead separation flow begins to show a rich pattern of convection. The scientists have been unable to explain these patterns using the known mechanisms of granular convection.
  [Convection rolls in a rotating box filled with beads, arXiv:0910.4897v1 [physics.flu-dyn]]
  (October 28, 2009)

• Why do red blood cells have asymmetric shapes even in a symmetric Flow?
  (Physics)

  
  Credit: Carin Cain and APS

  Coronary artery disease results from the formation of plaque in arteries, which blocks the transport of blood. The movement and deformation of red blood cells can also affect the flow of blood, and vice versa, but the mechanics of this relationship is still being explored. A research team, using simulations, has investigated how flow deforms red blood cells. Their numerical simulations show that an experimentally observed transition in the shape of red blood cells, from symmetric to asymmetric, occurs even when the cells (which the authors model as vesicles) move in a fluid with a symmetric flow velocity distribution. They suggest that this shape transition, which arises because the symmetric shape is unstable, may be able to influence the flow efficiency for red blood cells. As recent research links the chemical responses of red blood cells to their mechanics, such models of individual shape transitions of cells could offer further understanding of physiological flows.
  [Why Do Red Blood Cells Have Asymmetric Shapes Even in a Symmetric Flow? Phys. Rev. Lett. 103, 188101 (2009)]
  (October 27, 2009)

• Bacteria power micro-ratchet
  (Physics World)

  
  Credit: Roberto Di Leonardo, Univ. Rome

  In contrast to the random motion of tiny objects placed in a bath of molecules at thermal equilibrium, miniature asymmetrically shaped cog wheels rotate continuously in one direction when exposed to swimming bacteria, according to the finding of a group of scientists who built ratchets just a few hundredths of a millimeter across and filmed their motion when immersed in solutions containing E. coli. They exploit the fact that a collection of bacteria immersed in a liquid represents a non-equilibrium thermodynamic system by virtue of the self-propulsion of the bacteria. This non-equilibrium system, they say, should confer ordered motion on an asymmetrically shaped object. Using electron-beam lithography they etched out 10,000 saw-tooth gear wheels from the polymer SU8, each just 48 m across and 10 m thick (a volume equivalent to that of about 20,000 bacteria). They then dispersed the gear wheels in a suspension of E. coli, and hung a droplet of this liquid from the underside of a glass slide. This allowed the gear wheels to accumulate on the liquid-air interface, where they were held by capillary forces and free from the strong adhesion they would experience next to a solid surface. The researchers observed that bacteria would strike the long-edge of each tooth and either bounce off or have their movement blocked by the next short-edge. Given that bacteria do not stop swimming when they meet an obstacle or blockage, this caused them to push continuously against the short edge, with the combined motion of many such bacteria causing the gear wheel to rotate in one specific direction.
  [A bacterial ratchet motor, arXiv:0910.2899v1 [cond-mat.stat-mech] (2009)]
  (October 26, 2009)

• Acoustic magnifying hyperlens demonstrated
  (Science Daily)

  
  Credit: Xiang Zhang research group
  University of California, Berkeley

  The first acoustic hyperlens, that provides an eightfold boost in the magnification power of sound-based imaging technologies, has been demonstrated. Clever physical manipulation of the imaging sound waves enables the hyperlens to resolve details smaller than one sixth the length of the waves themselves. The key to this success is the capturing of information contained in evanescent waves. The researchers fashioned their acoustic hyperlens from 36 brass fins arranged in the shape of a hand-held fan. Each fin is approximately 20 centimeters long and three millimeters thick. The fins, embedded in the brass plate from which they were milled, extend out from an inner radius of 2.7 centimeters to an outer radius of 21.8 centimeters, and span 180 degrees in the angular direction.
  [Experimental demonstration of an acoustic magnifying hyperlens, Nature Materials Published online: 25 October 2009, doi:10.1038/nmat2561]
  (October 26, 2009)

• Metamaterial used to glimpse weak magnetic field of light
  (Science)

  
  Credit: Science

  It is of course well-known that light is an electromagnetic wave. An intricate mechanism generates magnetic fields around the electric fields, and vice versa. In the optical-wavelength range, experimental studies have been limited to probing only the electric-field components. A new paper now reports direct measurements of the magnetic-field components of light obtained with a nanostructured metallic probe at the tip of a sharp glass fiber. Using concepts from the field of metamaterials, the researchers fabricated a metallic split-ring resonator at the tip of a glass fiber, which serves as a near-field optical probe. The asymmetry created by the gap in the split ring causes the magnetic field to interact strongly with the nanostructure. This interaction couples the light into the structure and creates a measurable light signal at the other end of the fiber. They subsequently mixed this signal with reference light from the laser and extracted the amplitude and phase of the measured magnetic-field component at the fiber tip. As an initial demonstration, the researchers analyzed the magnetic field above an optical waveguide made from silicon nitride and showed convincingly that the detected magnetic-field signal is exactly 90 out of phase with the electric-field signal. When they replaced the split ring with a continuous ring, the signal vanished completely.
  References:
  Probing the Magnetic Field of Light at Optical Frequencies, Science 23 October 2009: Vol. 326. no. 5952, pp. 550 - 553 DOI: 10.1126/science.1177096
  Glimpsing the Weak Magnetic Field of Light, Science 23 October 2009: Vol. 326. no. 5952, pp. 529 - 530 DOI: 10.1126/science.1181552
  (October 23, 2009)

• Self-assembled arrays of peptide nanotubes
  (Nature Nanotechnology)

  
  
  Credit: Nature Nanotechnology
  

  Peptide building blocks provide biocompatibility, chemical versatility, biological recognition abilities and facile synthesis, making them attractive organic building blocks for bionanotechnology applications. Recently, aromatic dipeptide nanotubes (ADNTs) that are a family of well-ordered nanostructures have been identified. These can be self-assembled from simple building blocks. A new study now demonstrates the formation of self-assembled arrays of ADNT biomolecular structures using vapor deposition. The vapor deposition enables the fabrication of ADNT-based devices and surfaces with the potential for scaling up. The study also identified potential applications for this material including energy storage, smart windows and microfluidic devices.
  [Self-assembled arrays of peptide nanotubes by vapour deposition, Nature Nanotechnology Published online: 18 October 2009, doi:10.1038/nnano.2009.298]
  (October 22, 2009)

• Nano-agriculture: Carbon nanotubes affect seed germination
  (Science Daily)

  
  Credit: ACS Nano

  A new study suggests that carbon nanotubes (CNTs) could have beneficial effects in agriculture. Tomato seeds exposed to CNTs germinated faster and grew into larger, heavier seedlings than other seeds. The scientists in the study have reported the first evidence that CNTs penetrate the hard outer coating of seeds, and have beneficial effects. Nanotube-exposed seeds sprouted up to two times faster than control seeds and the seedlings weighed more than twice as much as the untreated plants. Those effects may occur because nanotubes penetrate the seed coat and likely boost water uptake.
  [Carbon Nanotubes Are Able To Penetrate Plant Seed Coat and Dramatically Affect Seed Germination and Plant Growth, ACS Nano, Article ASAP DOI: 10.1021/nn900887m]
  (October 22, 2009)

• Unraveling the structure of DNA during overstretching
  (Chemistry World)

  
  Credit: PNAS

  It was shown two decades ago that when a molecule of double-stranded DNA is pulled from either end, it undergoes a peculiar transition. Initially the molecule resists stretching. Then, at a force of 65 piconewtons, the polymer suddenly surrenders and stretches to 1.7 times its original length with little additional force. It then becomes resistant to stretching once more. Two competing ideas arose to explain this behavior. The first suggested that the DNA remains intact, but that at 65 pN the helix unwinds to form a straight ladder and that the base pairs - the 'rungs' of the ladder - tilt. The second idea was that the strands of DNA come apart - that the rungs of the ladder break, forming lengths of single-stranded DNA. Researchers have now carried out a well-established DNA-stretching experiment using optical tweezers and two different fluorescent tags. It was found that at the transition force, the zipper starts to come apart at either end, but remains zipped in the middle. In other words, the DNA comes apart at either end, and under tension this single-stranded DNA is 70 per cent longer than double-stranded DNA.
  [Unraveling the structure of DNA during overstretching by using multicolor, single-molecule fluorescence imaging, PNAS, DOI: 10.1073/pnas.0904322106]
  (October 22, 2009)

• Kinks in nanowires yield 2-D, 3-D superstructures
  (Eurekalert/Harvard University)

  
  Credit: Bozhi Tian, Lieber Group, Harvard University

  Researchers have introduced kinks into straight semiconductor nanowires, transforming them into zigzagging two- and three-dimensional structures with correspondingly advanced functions. The approach involves the controlled introduction of triangular "stereocenters" -- essentially, fixed 120º joints -- into nanowires, structures that have previously been rigidly linear. These stereocenters, analogous to the chemical hubs found in many complex organic molecules, introduce kinks into 1-D nanostructures, transforming them into more complex forms. The researchers were able to introduce stereocenters as nanowires self-assembled. They halted growth of the 1-D nanostructures for 15 seconds by removing key gaseous reactants from the chemical brew in which the process was taking place, replacing these reactants after joints had been introduced into the nanostructures. This approach resulted in a 40 percent yield of bent nanowires, which could then be purified to achieve higher yields.
  [Single-crystalline kinked semiconductor nanowire superstructures, Nature Nanotechnology Published online: 18 October 2009 | doi:10.1038/nnano.2009.304]
  (October 21, 2009)

• Metamaterials used to create portable black hole
  (Nature)

  
  Credit: Q. Cheng and T. J. Cui,
  Southeast University, Nanjing, China

  Physicists have created a portable black hole for microwave radiation using metamaterials. The device, which measures just 22 centimetres across, can suck up microwave light and convert it into heat. The new meta-black hole also bends light, but in a very different way. Rather than relying on gravity, the black hole uses a series of metallic 'resonators' arranged in 60 concentric circles. The resonators affect the electric and magnetic fields of a passing light wave, causing it to bend towards the centre of the hole. It spirals closer and closer to the black hole's 'core' until it reaches the 20 innermost layers. Those layers are made of another set of resonators that convert light into heat. The result: what goes in cannot come out.
  [An electromagnetic black hole made of metamaterials, arXiv:0910.2159v1 [physics.optics]]
  (October 21, 2009)

• Reaching a new TEM resolution standard
  (Physics)

  
  Credit: Alan Stonebraker/APS

  A research group has demonstrated that their unique setup of using aberration-corrected and monochromated transmission electron microscopy at 80 kV can image the hexagonal lattice structure of boron nitride, and identify the atomic positions of both boron and nitrogen atoms in single-layer boron nitride. Beyond this milepost in imaging resolution, the group shows they can synthesize TEM samples of hexagonal boron nitride with conventional ex situ preparation techniques, like exfoliation and plasma etching. In agreement with previous studies, they have shown that vacancies in boron nitride are predominately associated with missing boron atoms in single-layer boron nitride, as well as at the edges of boron nitride sheets. Yet this work goes further than any of the previous studies by showing that the combination of aberration-corrected TEM at 80 kV with a monochromated electron source can achieve ultrahigh resolution imaging down to single atoms. The findings also provide a roadmap to identifying the chemical sensitivity of high-resolution images as a function of sample thickness.This opens a new path to quantifying the image resolution and chemical sensitivity in next generation transmission electron microscopy instrumentation.
  [Atomically thin hexagonal boron nitride probed by ultrahigh-resolution transmission electron microscopy, Phys. Rev. B 80, 155425 (2009)]
  (October 21, 2009)

• Electrons reveal DNA without destroying it
  (Physics World)

  
  Credit: EU NEST Programme - Structural Information of
  Biological Molecules at Atomic Resolution

  The ultimate limitation of using X-ray crystallography for biological samples is that it works by averaging over millions of molecules in a crystal. This inevitably means that some of the finer details of the molecular world could remain undiscovered. Moreover, there are many protein molecules that are very difficult or impossible to crystallize. The obvious technological solution for researchers is to replace X-ray crystallography with high-energy electron microscopes. The trouble is that biological matter can be very delicate and so the radiation used in these techniques can damage or destroy the biomolecules under observation. Researchers have now suggested a way around this problem by creating a form of microscopy that utilizes lower-energy electrons. To demonstrate their new technique, the researchers isolated a strand of DNA and exposed it to a beam of low-energy electrons over the course of 70 min. By tracking the electrons that are scattered elastically, they were able to build up holographic images of the DNA. Underlying the new technique is the fact that, at certain energies, the electron radiation causes no damage to the DNA. The scientists report successful imaging at a number of discrete energy points up to 230 eV. They admit that they do not fully understand why these "energy windows" exist but they conclude that elastic scattering must dominate at these frequencies.
  [Non-destructive Imaging of Individual Bio-Molecules, arXiv:0910.1499v1 [physics.bio-ph]]
  (October 20, 2009)

• Microwave-assisted preparation of narrow-bandgap conjugated polymers for solar cells
  (Eurekalert/Nature Chemistry)

  In a new paper, a research group has announced an advance in the synthesis of organic polymers for plastic solar cells. They used microwave heating in combination with the screening of comonomer reactant ratios to obtain donoracceptor copolymers with high average molecular weights and properties that make them suitable for solar cell incorporation. They were able to reduce reaction time by 99%, from 48 hours to 30 minutes, and increase the average molecular weight of the polymers by a factor of more than 3. The reduced reaction time effectively cuts production time for the organic polymers by nearly 50%, since reaction time and purification time are approximately equal in the production process, in both laboratory and commercial environments. The higher molecular weight of the polymers, reflecting the creation of longer chains of the polymers, has a major benefit in increasing current density in plastic solar cells by as much as a factor of more than four.
  [Streamlined microwave-assisted preparation of narrow-bandgap conjugated polymers for high-performance bulk heterojunction solar cells, Nature Chemistry Published online: 18 October 2009 | doi:10.1038/nchem.403]
  (October 20, 2009)

• Paper stacks provide realistic medium for growing cells
  (Eurekalert)

  
  Credit: Ratmir Derda, Harvard University

  Researchers have realized that by growing cells on several sheets of uncoated paper, they can solve a problem that has bedeviled biologists for years: how to easily grow and study cells that mimic the three-dimensionality of real tissue. This work will simplify creation of realistic, three-dimensional models of normal or cancerous tissue -- potentially making it faster and easier to find drugs that fight cancer and other diseases. Currently, researchers grow cells in a Petri dish, creating a thin, two-dimensional layer of cells. If they want to do a better job of mimicking real tissue, they culture the cells in a gel. But because cells in different locations get vastly different amounts of oxygen and food, these cultures fail to mimic real tissues. And studying the cells from different parts of these gels without destroying the 3D culture is tricky. By growing the cells in a thin layer of gel supported by paper, and then stacking those pieces of paper, the scientists showed they could recreate the benefits of two-dimensional research – where cells receive a uniform amount of oxygen and food -- while also closely mimicking real tissue. In this case, they engineered a 3D tumor on paper that exhibited behaviors similar to a cancer in the body.
  [Paper-Supported Three-Dimensional Cell Culture for Tissue-Based Bioassays, Proceedings of the National Academy of Sciences, to be published]
  (October 20, 2009)

• Nanoscale test tube used to study Ge thermodynamics
  (Science)

  
  Credit: Science

  When a material is confined to nanoscale volumes, the very high proportion of surface to bulk can alter its thermodynamic properties. This has been studied in the past using in situ electron microscopy, but in most cases the volume of the material is not constrained. In a new study, researchers have examined the thermodynamics of a germanium nanowire attached to a gold seed and coated with a carbon shell to restrict its volume, measuring the reaction temperature, as well as the liquid composition without changes in volume throughout the heating cycle. This enabled monitoring of phase behavior while the germanium was being heated, and tracking solid-state diffusion across the confined interface.
  [Phase Transitions, Melting Dynamics, and Solid-State Diffusion in a Nano Test Tube, Science 16 October 2009: Vol. 326. no. 5951, pp. 405 - 407 DOI: 10.1126/science.1178179]
  (October 16, 2009)

• Packing of granular polymer chains
  (Science)

  
  Credit: Science

  The optimal packing of spheres, and the somewhat lower densities obtained in the compaction of granular materials are well studied problems. What is less clear is what happens when the spheres are connected, as in the case of polymeric materials—often represented by connected sphere models. A new study has examined the packing of chains of metal beads commonly used for securing bathroom drain plugs or for raising or lowering window blinds. Both the length of the chains, and whether they were linear or looped, influenced the overall packing density. Jamming the chains together captured the key physics of the glass transition of polymeric materials. X-ray tomography indicated that long chains pack into a low-density structure whose mechanical rigidity is mainly provided by the backbone. On compaction, randomly oriented, semi-rigid loops formed along the chain, and the packing of chains can then be understood as the jamming of these elements. Close similarities between the packing of chains and the glass transition in polymers was found.
  [The Packing of Granular Polymer Chains, Science 16 October 2009: Vol. 326. no. 5951, pp. 408 - 410 DOI: 10.1126/science.1177114]
  (October 16, 2009)

• Deterministic control of ferroelastic switching in multiferroics
  (Nature Nanotechnology)

  Multiferroic materials show coupled ferroelectric, ferromagnetic and ferroelastic orderings. However, thus far, deterministic control of non-ferroelectric order in these materials, such as ferroelasticity, has not been demonstrated. Now, in a new study, researchers have used a scanning probe microscope (SPM) tip to deterministically control ferroelastic domain patterns in rhombohedral multiferroic BiFeO₃. By applying a voltage to the SPM tip while it is in motion, it is possible to manipulate the strain and magnetic order parameters by electric field manipulation. This makes it possible to engineer predefined ferroelectric domain patterns, including long sought closure domains, as a basis for the creation of toroidal vortex states and other exotic topological defect states. The deterministic control of ferroelastic domain patterns can be extended to other low symmetry systems, enabling magnetoelectric, strain coupled and related devices.
  [Deterministic control of ferroelastic switching in multiferroic materials, Nature Nanotechnology Published online: 11 October 2009 | doi:10.1038/nnano.2009.293]
  (October 16, 2009)

• Quasicrystal structures may be more normal than assumed
  (Nature/Scientific American)

  
  Credit: Talapin et al, Nature 2009

  Since their discovery in 1984, quasicrystals have been found in many highly synthesized materials and in one mineral of apparently natural origin—an alloy of aluminum, copper and iron found in Russia. But a new study shows that quasicrystals may be a fairly natural way for objects to pack themselves together and may not require much manipulation to take shape. The researchers involved report that various pairings of nanoparticles, when mixed in solution and left to evaporate, coalesce into quasicrystal structures. That a variety of particle pairs—two different iron oxides mixed with gold as well as lead sulfide paired with palladium—can successfully self-assemble into quasicrystals suggests that it may be a more common arrangement than had been thought. The only real common ground in the pairings seemed to be a relatively consistent ratios among the sizes of the different nanoparticles.
  [Quasicrystalline order in self-assembled binary nanoparticle superlattices, Nature 461, 964-967 (15 October 2009), doi:10.1038/nature08439; News & Views: Quasicrystals from nanocrystals, Nature 461, 892-893 (15 October 2009), doi:10.1038/461892a]
  (October 15, 2009)

• Magnetricity: Magnetic electricity reported in spin ices
  (BBC News/Nature)

  
  Credit: S. Bramwell

  Researchers have discovered a magnetic equivalent to electricity: single magnetic charges that can behave and interact like electrical ones. The work is the first to make use of the magnetic monopoles that exist in special crystals known as spin ices. The team showed that monopoles gather to form a "magnetic current" like electricity. Recently, two research groups independently reported the existence of monopoles - "particles" which carry an overall magnetic charge. But they exist only in the spin ice crystals. These crystals are made up of pyramids of charged atoms, or ions, arranged in such a way that when cooled to exceptionally low temperatures, the materials show tiny, discrete packets of magnetic charge. Now one of those teams has gone on to show that these "quasi-particles" of magnetic charge can move together, forming a magnetic current just like the electric current formed by moving electrons.
  [Measurement of the charge and current of magnetic monopoles in spin ice, Nature 461, 956-959 (15 October 2009) | doi:10.1038/nature08500; News & Views: Wien route to monopoles, Nature 461, 888-889 (15 October 2009)]
  (October 15, 2009)

• Elusive Persistent Current in metal rings measured
  (ECNMag.com)

  
  Credit: Harris et al., Yale Univ.

  Scientists have made the first definitive measurements of persistent current, a small but perpetual electric current that flows naturally through tiny rings of metal wire even without an external power source. The team used nanoscale cantilevers, an entirely novel approach, to indirectly measure the current through changes in the magnetic force it produces as it flows through the ring. The counterintuitive current is the result of a quantum mechanical effect that influences how electrons travel through metals, and arises from the same kind of motion that allows the electrons inside an atom to orbit the nucleus forever.
  [Persistent Currents in Normal Metal Rings, Science 9 October 2009: Vol. 326. no. 5950, pp. 272 - 275 DOI: 10.1126/science.1178139]
  (October 14, 2009)

• Single molecule diode with controlled orientation
  (Chemistry World)

  
  Credit: Nature Chemistry

  A new study shows how it is possible to measure the diode properties of a single molecule and how the orientation of the molecule between two electrodes can be controlled. The findings are a significant advance in the expanding field of molecular electronics. The researchers selected as a candidate molecular diode an asymmetric linear molecule consisting of a pair of pyrimidinyl rings covalently linked to a pair of phenyl rings. The bipyrimidinyl moiety is electron-deficient, while the biphenyl block is electron rich. To measure the diode properties of the molecule the researchers attached either end to a gold electrode. One electrode consists of a flat gold substrate while the other is the gold-coated tip of a scanning tunnelling microscope (STM). The link between the molecule and the gold is made through a thiol group.
  [Rectification and stability of a single molecular diode with controlled orientation, Nature Chemistry Published online: 11 October 2009, doi:10.1038/nchem.392]
  (October 14, 2009)

• How perfect can graphene be?
  (PhysOrg)

  

  Researchers have investigated the purest graphene to date, and have found that the material possesses unprecedented high electronic quality. The discovery has raised the bar for this relatively new material, and challenges scientists to find just how perfect graphene can be. In a study published earlier this year, another team of scientists discovered a form of graphene composed of well-defined graphene flakes in the form of sheets located on - yet decoupled from - the surface of bulk graphite. Not only is this graphene well-structured, but the underlying graphite also serves as a well-matched substrate for investigating the graphene layer, which is what the scientists did in the current study. They found that their naturally occurring graphene sample possessed a carrier mobility almost two orders of magnitude higher than other types of graphene, and a scattering time that significantly exceeds those reported in any man-made graphene samples. Both properties could open the doors for future developments in graphene technologies.
  [How Perfect Can Graphene Be? Phys. Rev. Lett. 103, 136403 (2009)]
  (October 14, 2009)

• Tuning NiFe nanocatalyst composition to control chirality of carbon nanotubes
  (Science Daily)

  A study shows that the composition of a catalyst of mixed metals commonly used to grow nanotubes can control the chirality of the nanotubes. They found that a mixed iron and nickel catalyst was effective. When using a nickel catalyst, typically one]third of nanotubes grown are metallic while about two]thirds are semiconducting. The researchers explored the chiralities of nanotubes formed by varying the composition of NixFe1-x nanocatalysts. Of the compositions tested, a catalyst of 27 percent nickel and 73 percent iron produced the most dramatic result, wherein the vast majority of the nanotubes were semiconducting.
  [Linking catalyst composition to chirality distributions of as-grown single-walled carbon nanotubes by tuning NixFe1-x nanoparticles, Nature Materials Published online: 20 September 2009, doi:10.1038/nmat2531]
  (October 13, 2009)

• Growing geodesic carbon nanodomes en route to graphene
  (Physics)

  
  Credit: Alan Stonebraker/APS

  Researchers report photoelectron spectroscopy data that suggests that en route to forming continuous sheets, graphene islands grow on an iridium surface in the form of microscopic domes. According to their model, the domes consist of circular islands of graphene that are attached via strong chemical bonds to the close-packed iridium surface at the islands perimeter, but are not chemically attached in the center. The islands grow by attaching atoms and smaller islands to their edges. To characterize these islands, the authors used high-resolution photoelectron spectroscopy, which produces a spectrum of the core electronic energy levels present in the atoms at the surface. These energy levels are sensitive to the chemical environment of the atom, and, for instance, are different for iridium atoms deep in the bulk compared to iridium atoms at the surface. Likewise, carbon atoms in different bonding configurations at the surface will have different electronic energy levels
  [Growth of Dome-Shaped Carbon Nanoislands on Ir(111): The Intermediate between Carbidic Clusters and Quasi-Free-Standing Graphene, Phys. Rev. Lett. 103, 166101 (2009) Published October 12, 2009]
  (October 13, 2009)

• Photonic crystal blocks heat more effectively than vacuum
  (Physical Review Focus)

  Hot soup in a thermos is surrounded by a vacuum between the inner and outer walls, which prevents heat from conducting directly through the sides, as it would if the walls were a one-piece solid. But the soup still loses heat by "glowing" in infrared light because the light radiated through the walls takes energy away with it. Last year, researchers studied a photonic crystal - a stack of alternating silicon and vacuum layers - theoretically, calculating the thermal conductance--the ease with which infrared photons could pass through. The team evaluated different layer-thicknesses, numbers of layers, and temperatures and showed that for a 100-micron-thick stack containing 10 one-micron-thick silicon layers, at room temperature and above, the thermal conductance plunged to about half that of a vacuum. In a new paper, they have undertaken a complete theoretical analysis of the problem. They calculated the fraction of all frequencies that the photonic crystal allows through. They found that this fraction, and therefore the thermal conductance, does not depend on the thickness of the individual layers but only on how fast light travels in the solid layers--the solid's index of refraction.
  [Universal Features of Coherent Photonic Thermal Conductance in Multilayer Photonic Band Gap Structures, Phys. Rev. B (to be published) ]
  (October 13, 2009)

• Heat diode paves the way for thermal computing
  (Technology Review)

     
     Credit: Kobayashi et al.

  There's no escaping the insidious effects of heat in microchips. But there may now be a way of controlling it. Researchers have built a rectifier that allows a heat current to travel in one direction but not the other. For some time, researchers have predicted that thermal rectifiers would be possible with materials which have thermal conductivities that change with temperature. The trick is to find a material with a high thermal conductivity at low temperatures and a low thermal conductivity at high temperatures, and then to marry it with a material with exactly the opposite characteristic. The researchers found just such a match in two types of perovskite cobalt oxides (LaCoO3 and La0.7Sr0.3CoO3). Glued together, they form a diode-like device that allows a heat current to pass in one direction but not the other. That's impressive because it's the first time anybody has demonstrated heat rectification in a bulk solid (it's been done with individual electrons in superconductors and in single nanotubes). One obvious application is in heat sinks for microchips but some significant improvements will be needed to carry the kind of heat currents involved.
  [An oxide thermal rectifier, arXiv:0910.1153v1 [cond-mat.mtrl-sci]]
  (October 9, 2009)

• A road of no return for microwaves
  (Eurekalert)

  Light readily bounces off obstacles in its path. Some of these reflections are captured by our eyes, thus participating in the visual perception of the objects around us. In contrast to this usual behavior of light, researchers have implemented for the first time a one-way structure in which microwave light flows losslessly around obstacles or defects. This concept, when used in lightwave circuits, might one day reduce their internal connections to simple one-way conduits with much improved capacity and efficiency. If a light beam is observed propagating in a particular direction, one can also shine a light beam to propagate in the opposite (backward) direction. In a dramatic departure from this common phenomenon, the researchers implemented and experimentally tested so-called topological photonic crystals that completely prohibit the existence of any lightwave back-reflections. The results show the first experimental observation of the fascinating new phenomena and capabilities associated with microwave light propagating in this uniquely designed waveguide.
  [Observation of unidirectional backscattering-immune topological electromagnetic states, Nature 461, 772-775 (8 October 2009) | doi:10.1038/nature08293]
  (October 9, 2009)

• Obtaining dielectric constants at the nanoscale
  (NanotechWeb)

  
  Credit: Nanotechnology

  A convenient way to measure the dielectric constant of thin films at the nanoscale has been developed by researchers. The method, which is based on electrostatic force microscopy, can be applied using any commercial atomic force microscope (AFM) and requires no additional, sophisticated electronics. The simple method of measuring the static dielectric constant is applicable to a wide range of thin film structures from solid state materials to biomembranes. Using an accurate analytical model, the researchers can extract the dielectric constant from DC electrostatic force measurements made with a commercial AFM. The method has been validated on thin silicon dioxide films and purple membrane monolayers, providing results that are in agreement with those recently obtained by nanoscale capacitance microscopy using a current-sensing approach.
  [Quantitative dielectric constant measurement of thin films by DC electrostatic force microscopy, Nanotechnology 20 395702 (2009 ) doi: 10.1088/0957-4484/20/39/395702]
  (October 9, 2009)

• Fixing bones with dissolvable metallic glass
  (Physics World)

  
  Credit: Jrg Lffler et al., ETH Zurich

  Doctoring broken bones in the future could be easier and simpler thanks to a metallic glass material that can be used to make dissolvable screws, pins or plates. Bone fractures or breaks are now routinely fixed in place with metal implants to encourage healing. These are usually made from corrosion-resistant steel or titanium, but have to be removed in a second operation once the bones have mended. In an effort to make this extra surgery a thing of the past, materials scientists have designed a metallic glass that dissolves harmlessly in the body. The idea is to make small supporting objects from this material, such as pins or nails, which would disappear over time. The team adjusted the components of the alloy to 60% magnesium, 35% zinc and 5% calcium, moulded in the form of metallic glass.
  [MgZnCa glasses without clinically observable hydrogen evolution for biodegradable implants, Nature Materials, Published online: 27 September 2009 | doi:10.1038/nmat2542]
  (October 6, 2009)

• Graphite mimics magnetism of iron
  (Eurekalert)

  
  Credit: Kees Flipse, Eindhoven University of Technology

  Researchers have shown for the first time why ordinary graphite is a permanent magnet at room temperature. Graphite is a layered compound with a weak interlayer interaction between the individual carbon (graphene) sheets. Hence, this makes graphite a good lubricant. It is unexpected that graphite is ferromagnetic. The researchers demonstrated direct evidence for ferromagnetic order and explained the underlying mechanism. In graphite, well-ordered areas of carbon atoms are separated by 2 nanometer wide boundaries of defects. The electrons in the defect regions behave differently compared to the ordered areas, showing similarities with the electron behaviour of ferromagnetic materials like iron and cobalt. The researchers found that the grain boundary regions in the individual carbon sheets are magnetically coupled, forming 2-dimensional networks. This interlayer coupling was found to explain the permanent magnetic behavior of graphite. The researchers also show experimental evidence for excluding magnetic impurities to be the origin of ferromagnetism.
  [Room-temperature ferromagnetism in graphite driven by two-dimensional networks of point defects, Nature Physics Published online: 4 October 2009 | doi:10.1038/nphys1399]
  (October 6, 2009)

• Material to chill dirty fuel cells
  (Technology Review)

     
     Credit: Meilin Liu, Georgia Tech

  Solid-oxide cells can run on almost any fuel. But running them efficiently requires high temperatures, which raises prices. Now researchers at Georgia Tech have developed an anode material that resists the buildup of sulfur and carbon that can occur at lower temperatures. With further development, the material might be incorporated into cheaper solid-oxide fuel cells that run efficiently at lower temperatures. The new anode material resists sulfur poisoning and carbon coking, even when running at low temperatures, and without compromising performance. The new anode material is a composite of nickel and a ceramic that contains small amounts of two rare-earth metals.material, and has so far been tested over a period of 1,000 hours at temperatures ranging from 500 °C to 700 °C.
  [Enhanced Sulfur and Coking Tolerance of a Mixed Ion Conductor for SOFCs: BaZr0.1Ce0.7Y0.2–xYbxO3–], Science 2 October 2009: Vol. 326. no. 5949, pp. 126 - 129 DOI: 10.1126/science.1174811]
  (October 5, 2009)

• Forming nano-diamond from carbon nanotubes
  (Physical Review Focus)

  
  Credit: A. R. Muniz, et al., Phys. Rev. B

  In order to make nanoscale diamond crystals, researchers have used various tricks, including recipes involving carbon nanotubes. Now a research team explains at the atomic level how nanotubes can convert to diamonds. Their computational studies show that it is possible for carbon atoms from adjacent walls of multi-walled nanotubes to bond to each other to form both the cubic and hexagonal structures of diamond. Their strength and hardness may make them useful components of nanoscale machines.
  [Analysis of Diamond Nanocrystal Formation from Multiwalled Carbon Nanotubes, Phys. Rev. B (to be published) ]
  (October 5, 2009)

• Bioinspired solution to scaling up graphene nanoribbons
  (NanotechWeb)

  
  Credit: Nanotechnology

  Graphene nanoribbons present intriguing electronic properties due to their characteristic size and edge shape, and have been suggested for a wide range of uses from electronics to electromechanical systems. However, there are hurdles to achieving larger-scale applications of graphene nano-ribbons. Specifically, the need for nanoscale precision, the material’s structural instability at elevated temperature, and its chemical activity along open edges. In a new study, researchers are proposing the use of hierarchical assemblies of graphene nanoribbons connected through hydrogen bonds, inspired by biological structures found in nature such as proteins and DNA macromolecules. The selective and directional binding of the hydrogen bond enables the design and synthesis of scalable graphene nanoribbon materials linking nano to macro. The team used a bottom-up atomistic simulation approach based on first principles calculations.
  [Hierarchical graphene nanoribbon assemblies feature unique electronic and mechanical properties, Nanotechnology 20 375704 (2009) doi: 10.1088/0957-4484/20/37/375704]
  (October 5, 2009)

• Atomtronics: Electronics without solids
  (Physics)

  
  Credit: R. Pepino et al., Phys. Rev. Lett.

  In the emerging field of atomtronics, theorists imagine analogs of standard electronic circuit elements made from ultracold atoms moving in an optical latticean array of potential energy wells created by lasers. The idea is to someday use such a circuit to study basic many-body physics in a completely controlled and adjustable system, without the messiness of crystal defects or impurities found in real semiconductors. There have been several proposals for atomtronics components. Now, in a new paper, researchers propose complete atomtronic circuits, including new concepts for a diode, transistor, and battery.
  [Atomtronic Circuits of Diodes and Transistors, Phys. Rev. Lett. 103, 140405 (Published September 28, 2009)]
  (October 1, 2009)

• Nanosensing transistors controlled by stress
  (Technology Review)

  
  Credit: ACS/Nano Letters

  Nanoscale sensors have many potential applications, bu they typically have to be integrated with bulky power sources and integrated circuits. Now researchers have demonstrated a nanoscale sensor that does not need these other parts. The new sensors consist of freestanding nanowires made of zinc oxide. When placed under stress, the nanowires generate an electrical potential, functioning as transistors. The researchers are taking advantage of the semiconducting properties of zinc oxide nanowires--the electrical potential generated when the new nanowires are bent, allowing them to act as transistors. They used a vertical zinc oxide wire 25 nanometers in diameter to make a field-effect transistor. The nanowire is partially embedded in a substrate and connected at the root to gold electrodes that act as the source and the drain. When the wire is bent, the mechanical stress concentrates at the root, and charges build up. This creates an electrical potential that acts as a gate voltage, allowing electrical current to flow from source to drain, turning the device on. The group has tested various triggers, including using a nanoscale probe to nudge the wire, and blowing gas over it.
  [Piezoelectric Potential Gated Field-Effect Transistor Based on a Free-Standing ZnO Wire, Nano Lett., Article ASAP DOI: 10.1021/nl901606b]
  (October 1, 2009)

• First atomic-scale map of quantum dots created
  (Science Daily/University of Michigan)

  
  Credit: University of Michigan

  Researchers have created the first atomic-scale maps of quantum dots, a major step toward the goal of producing "designer dots" that can be tailored for specific applications. Engineers are gaining the ability to manipulate the atoms in quantum dots to control their properties and behavior through directed assembly. But progress has been slowed, until now, by the lack of atomic-scale information about the structure and chemical makeup of quantum dots. The new atomic-scale maps will help fill that knowledge gap, clearing the path to more rapid progress in the field of quantum-dot directed assembly. To create the maps, the team illuminated the dots with a brilliant X-ray photon beam at the Advanced Photon Source.
  [Atomic-scale mapping of quantum dots formed by droplet epitaxy, Nature Nanotechnology Published online: 27 September 2009 | doi:10.1038/nnano.2009.271]
  (October 1, 2009)

• Scientists shrink X-ray source
  (Nature)

  
  Credit: Nature / Tom Tracy Photography / Alamy

  Scientists currently use synchrotrons to generate high-quality X-rays. Synchrotrons are large, costly and usually in high-demand by scientists. Researchers have now developed another way to generate electrons to create X-rays. Rather than using conventional magnets to guide and accelerate electrons, the team used a powerful laser beam and a small cell of hydrogen gas. They shot a brief, 37-femtosecond (10-15 seconds) pulse into the cell to blow the electrons off the hydrogen atom's nuclei. But electrical attraction causes the electrons to snap back towards the positive ions, so for a brief period after the pulse the electrons vibrate back and forth around the hydrogen atom's positive core, producing a wave. As they do so, a few electrons break loose and ride the crest of the electron wave. The electrons then sail through a series of magnetic lenses, which feed them into a second series of magnets that cause them to wiggle back and forth releasing low-energy 18-nanometer wavelength X-rays as they go.
  [Laser-driven soft-X-ray undulator source, Nature Physics Published online: 27 September 2009 | doi:10.1038/nphys1404]
  (September 30, 2009)

• Super-thin nanowires made inside nanotubes
  (Chemistry World)

  
  Credit: Wiley-VCH

  Atom-thin metal wires show many novel electronic properties - but the wires are so fragile and prone to oxidation that they have been difficult to study. Researchers have solved this problem by growing the wires encased within protective nanotubes. This means that their properties can be measured and mapped. Carbon nanotubes and metal powder (usually of a metal that sublimes at a relatively low heat) were placed in a glass tube and heated to around 500-600C'. The vaporised metal atoms fill up the hollow centers of the nanotubes and solidify into wires. By varying the width of the nanotube, the team was able to control the thickness of the wires - varying them from a few atoms in diameter down to a chain of single atoms.
  [High-Yield Synthesis of Ultrathin Metal Nanowires in Carbon Nanotubes, Angew. Chem. Int. Ed., 2009, DOI: 10.1002/anie.200902615]
  (September 30, 2009)

• Light-induced conversion of metallic to semiconductor carbon nanotubes
  (Chemistry World)

  
  Credit: ACS, Nano Letters

  A simple and scalable way to purify mixtures of carbon nanotubes has been developed. The process uses ultraviolet light and air to produce purified semiconducting nanotubes. Nanotubes can be either highly conductive (metallic) or semiconducting, depending on how their component carbon atoms are aligned. Up to a third of the nanotubes in a freshly synthesised sample can be the metallic form, and this blend is troublesome when trying to use nanotubes in electronic devices such as transistors that rely on semiconductance. The electrical current will just travel down the metallic tubes, as they are the path of least resistance. Previous attempts to overcome this problem have relied on trying to selectively separate out the metallic tubes. Now, a research team has found a much easier way to homogenize the tubes: using ultraviolet light to oxidise them, a process which forms defects in the carbon structure of the metallic tubes, turning them semiconducting.
  [Scalable Light-Induced Metal to Semiconductor Conversion of Carbon Nanotubes, Nano Lett., Article ASAP DOI: 10.1021/nl901802m, Publication Date (Web): September 15, 2009]
  (September 29, 2009)

• Glow of bead creates recoil
  (Physical Review Focus)

  
  Credit: D. Petrov/ICFO/ICREA

  A pair of recent studies suggests that a common laser-and-microscope technique is sensitive enough to measure the recoil felt by a micron-sized silica bead emitting light from its surface. Researchers used lasers to trap a bead and measure the forces acting on it, while simultaneously recording the light generated by molecules coating the bead's surface. They report that the forces acting on the bead were correlated with the intensity of emitted light, as would be expected if emitted photons were nudging a bead back and forth like the exhaust from tiny thrusters. The experiments used a type of photonic force microscopy (PFM), which is used to measure forces acting on microscopic beads suspended in liquid. PFM specialists first isolate a bead in the focus of a laser beam, creating an optical trap. The bead then acts like a tethered buoy. Liquid molecules randomly nudge it, but the trapping laser exerts a spring-like force that draws the bead back to its starting point. By tracking the position of the bead using a separate laser, researchers can measure the size of the beads jostling motions in the trap, which tells them the strength of the fluctuating forces acting on it.
  [Measurement of Mechanical Forces Acting on Optically Trapped Dielectric Spheres Induced by Surface Enhanced Raman Scattering, Phys. Rev. Lett. 102, 87401 (issue of 26 February 2009); Experimental Analysis of Recoil Effects Induced by Fluorescence Photons, Phys. Rev. E (to be published)]
  (September 29, 2009)

• Perfect imaging without negative refraction
  (Eurekalert)

  A report shows that there is a way to create a perfect image without using a metamaterial. Inspired by James Clerk Maxwell's findings, first expounded in the 1850s, the report is reintroducing the idea of a 'fish-eye' lens; a lens that can work in any direction but had not, until now, been modeled to fully account for the wave-like properties of light. While the work is only theoretical at present, it will be exciting news to silicon chip manufacturers as the resolution limit of lenses limits the microchip technology needed for making ever faster computers. While this development will not overcome the problems posed by the physical limits of smaller and smaller chip circuitry, it will give chipmakers freedom to photograph ever smaller, and more compact, structures of billions of tiny transistors on silicon chips to meet the insatiable appetite for faster and smaller computers.
  [Perfect imaging without negative refraction, New J. Phys. 11 093040 (2009) doi: 10.1088/1367-2630/11/9/093040]
  (September 29, 2009)

• Nanoscale organic single-crystal cross-wire circuits
  (Science Daily)

  
  Credit: Asmus Dohn

  New data shows that organic nanoscale wires could be an alternative to silicon in computer chips. Researchers have developed nanoscale electric contacts out of organic and inorganic nanowires. In the contact they crossed the wires like "Mikado sticks" and coupled several contacts together in an electric circuit. They used organic nanowires combined with tin oxide nanowires in a so-called hybrid circuit. The nanowires cross in a device consisting of 4-6 active transistor moieties. The devices have low operational current, high mobility and good stability, essential for the material to be able to compete with silicon.
  [Assembly of Nanoscale Organic Single-Crystal Cross-Wire Circuits, Advanced Materials Early View (Articles online in advance of print) Published Online: 12 Aug 2009]
  (September 17, 2009)

• Nanodiamonds deliver genes
  (NanotechWeb)

  
  Credit: Nanotechnology

  Nanodiamonds could be used as efficient gene delivery vehicles, according to new work. The nanomaterials are less toxic to cells compared to other carbon-based materials like carbon nanotubes and are inherently biocompatible. They showed that modifying nanodiamond surfaces with polyethyleneimine 800 (PEI800) a commercially available polymer commonly used in gene delivery enhances gene delivery into cells by 70 times compared to using PEI800 alone. The scientists used a green fluorescent protein-coding DNA sequence to demonstrate how genes could successfully be delivered into the cells. When introduced in particle form, the nanodiamond-PEI800-DNA complexes produce genetic changes that make the cells fluoresce. This indicates that gene delivery has taken place.
  [Polymer-Functionalized Nanodiamond Platforms as Vehicles for Gene Delivery, ACS Nano, August 31, 2009, Article ASAP DOI: 10.1021/nn900865g]
  (September 17, 2009)

• Super-thin batteries made from paper and algae
  (Royal Society of Chemistry)

  
  Credit: Nano Letters

  Algae, paper and salt-water are the key components of new thin and flexible batteries. Cellulose obtained from the bright green Cladophora algae proved to be key to the project, as it boasts a unique nanostructure with a high surface area. Although the batteries have lower voltage and power density than conventional batteries, their low cost and flexibility hold great promise for applications where metal-based batteries are impractical. To make the batteries, the team separated two cellulose electrodes with filter paper soaked in salt water. One of the electrodes is coated with a very thin layer of oxidised polypyrrole (PPy) while the other is coated with reduced polypyrrole. The potential difference between the two layers provides the voltage of the battery, as during charging and discharging, chloride ions move from one electrode to the other, similar to the way lithium ions cycle in lithium batteries. A major advantage of the research is the simple and environmentally-friendly production method.
  [Ultrafast All-Polymer Paper-Based Batteries, Nano Lett., Article ASAP, September 9, 2009, DOI: 10.1021/nl901852h]
  (September 16, 2009)

• On-off membrane for drug delivery
  (Royal Society of Chemistry)

  
  Credit: Nano Letters

  A new type of membrane that can be made reversibly porous at the flick of a switch has been developed. A drug contained within a membrane-based implant could be released 'on demand', making it a potentially useful and novel way for the controlled delivery of drugs such as anaesthetics. Once the dose has been delivered, the membrane can be re-sealed until the next dose is required. A research team harnessed the thermosensitive properties of poly(N-isopropylacrylamide) (PNIPAM) to form the basis of the new system. This material can form a hydrogel which is swollen in its native state but which collapses upon heating. The researchers embedded nanoscale particles of PNIPAM-based gels in an ethyl cellulose membrane so that clumps of the particles spanned the width of the membrane. They also entrapped magnetite nanoparticles within the membrane matrix. When the membrane is exposed to an oscillating magnetic field, the magnetite nanoparticles heat up, in turn warming the PNIPAM by a few degrees - sufficient to cause the particles to collapse but not so high as to affect surrounding tissue. This leaves voids in the membrane, opening up channels from one side to the other.
  [A Magnetically Triggered Composite Membrane for On-Demand Drug Delivery, Nano Lett., Article ASAP (2009) DOI: 10.1021/nl9018935]
  (September 16, 2009)

• Friction force differences for sorting nanotubes
  (e! Science News/Georgia Tech)

  
  Credit: Christian Klinke
  University of Hamburg

  Researchers have reported measuring different friction forces when a carbon nanotube slides along its axis compared to when it slides perpendicular to its axis. This friction difference has its origins in soft lateral distortion of the tubes when they slide in the transverse direction. The findings not only could provide a better understanding of fundamental friction issues, but from a more practical standpoint, offer a new tool for assembling nanotubes into devices and clarify the forces acting on them. Asymmetries in the friction could potentially also be used in sorting nanotubes according to their chirality, a property that is now difficult to measure with other means.
  [Hindered rolling and friction anisotropy in supported carbon nanotubes, Nature Materials Published online: 13 September 2009, doi:10.1038/nmat2529]
  (September 16, 2009)

• Understanding magnetization reversal of nanoscale islands
  (Physics)

  
  Credit: Alan Stonebraker

  Magnetic nanoparticles form the basis of today’s magnetic recording technology, and are also of more fundamental interest because of their rich magnetic behavior, which strongly depends on their size and drastically differs from that of bulk magnets. A key factor for successful application is the stability of a magnetic bit against thermal fluctuations, i.e., the probability that a cluster spontaneously reverses its net spin by switching between two energetically equivalent but opposite orientations. A widely accepted view is that, for nanoscale particles, all atoms flip their spins in unison. The probability then depends just on the number of spins and on a parameter—the magnetic anisotropy—describing the preference for spins to orient themselves along certain crystallographic directions. In a current paper, the authors question this simple picture. They unveil the existence of a more complex relaxation mechanism, highly sensitive to the morphology of the cluster, which controls the magnetic switching of islands consisting of barely 30 iron atoms.
  [Magnetization Reversal of Nanoscale Islands: How Size and Shape Affect the Arrhenius Prefactor, Phys. Rev. Lett. 103, 127202 (2009) – Published September 14, 2009]
  (September 15, 2009)

• Self-repairing polymer system heals on heating
  (Royal Society of Chemistry)

  
  Credit: Royal Society of Chemistry

  A polymer system based on weak, reversible bonds that can heal itself when heated has been created. A research team designed a polymeric structure which holds together using aromatic electronic interactions and can easily repair damage to itself when heated to a modest temperature. Previous self-healing polymers have relied on stronger interactions and often require additives to facilitate the healing process. The system uses two polymers, one larger than the other. The larger polymer naturally folds itself up to maximise attractive interactions, leaving tweezer-shaped electron-deficient receptor units. A smaller, linear polymer with an aromatic end group inserts into the folds of the larger polymer, forming Pi - Pi stacking interactions. At room temperature, the polymer mix forms a flexible, self-supporting material. When the temperature is raised, the interactions holding the structure together are weakened, which allows the polymers to flow into the damaged area.
  [A self-repairing, supramolecular polymer system: healability as a consequence of donoracceptor pi-pistacking interactions, Chem. Commun., 2009, DOI: 10.1039/b910648k]
  (September 14, 2009)

• Opto-electronic nose sniffs out toxic gases
  (Eurekalert/Univ. Illinois)

  
  Credit: Kenneth Suslick, University of Illinois

  A research team has developed an artificial nose for the general detection of toxic industrial chemicals (TICs) that is simple, fast and inexpensive and works by visualizing odors. This sensor array could be useful in detecting high exposures to chemicals that pose serious health risks in the workplace or through accidental exposure. The device is in essence a digital multidimensional extension of litmus paper. There is a six by six array of different nanoporous pigments whose colors change depending on their chemical environment. The pattern of the color change is a unique molecular fingerprint for any toxic gas and also indicates its concentration. By comparing that pattern to a library of color fingerprints, the researchers can identify and quantify the TICs in a matter of seconds.
  [An optoelectronic nose for the detection of toxic gases, Nature Chemistry, Published online: 13 September 2009 | doi:10.1038/nchem.360]
  (September 14, 2009)

• Ultrathin zeolite nanosheet catalysts on demand
  (Royal Society of Chemistry)

  
  Credit: Nature

  A research team has taken acidic zeolite catalysts to the limit in terms of thickness - creating ultrathin nano-sheets that are efficient and long-lived catalysts for hydrocarbon cracking and other petrochemical applications. Zeolites are already used in the petrochemicals industry, but making the catalysts very thin means that reactant molecules can easily diffuse into the zeolite structure and product molecules can get out quickly. This improves the efficiency of the catalyst and reduces unwanted side reactions that can produce polymeric hydrocarbon 'coke' that clogs the zeolite pores and eventually kills the catalytic activity. To make the thin sheets, the team used a surfactant as a template to direct the growth of the MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite structure. The surfactant molecule has a polar 'head' group - with two quaternary ammonium groups around which the aluminosilicate zeolite crystal grows - and a long hydrocarbon 'tail', which prevents the sheets from aggregating together into larger, three dimensional crystals. When the surfactant is removed, these flakes pile up randomly with gaps in between which further aids diffusion to the catalyst sites.
  [Stable single-unit-cell nanosheets of zeolite MFI as active and long-lived catalysts, Nature 461, 246-249 (10 September 2009) | doi:10.1038/nature08288]
  (September 14, 2009)

• Carbon nanotubes form very efficient photodiodes
  (Cornell University)

  
  Credit: Nathan Gabor, Cornell

  Researchers have fabricated, tested and measured a simple photodiode, formed from an individual carbon nanotube, and found it to be extremely efficient. The nanotube was wired between two electrical contacts and close to two electrical gates, one negatively and one positively charged. Shining lasers of different colors onto different areas of the nanotube, they found that higher levels of photon energy had a multiplying effect on how much electrical current was produced, and they observed highly efficient generation of electron-hole pairs due to impact excitation.
  [Extremely Efficient Multiple Electron-Hole Pair Generation in Carbon Nanotube Photodiodes, Science 11 September 2009: Vol. 325. no. 5946, pp. 1367 - 1371 DOI: 10.1126/science.1176112]
  (September 11, 2009)

• Non-tapered InN nanowires exhibit record narrow linewidths
  (NanotechWeb)

  
  Credit: Nanotechnology

  Researchers have come up with a way of making non-tapered, nearly homogeneous, and electronically pure InN nanowires on Si using molecular beam epitaxy. While conventional InN nanowires have been grown by introducing indium and nitrogen species to the substrate surface simultaneously, this latest approach involves the deposition of a thin indium layer prior to growth initiation, which can act as a seed to promote the nucleation and formation of InN nanowires. The presence of well-defined nucleation centres, in conjunction with optimized growth parameters, enables the formation of non-tapered InN nanowires directly on Si substrates. The resulting InN nanowires exhibit excellent optical properties. Their photoluminescence linewidths are nearly a factor of 510 times smaller than those of conventionally grown InN nanowires.
  [Molecular beam epitaxial growth and characterization of non-tapered InN nanowires on Si(111), Nanotechnology 20 (2009) 345203 (6pp) doi: 10.1088/0957-4484/20/34/345203]
  (September 11, 2009)

• Liquid crystals bend over backwards for electricity
  (Highlights in Chemical Technology)

  
  Credit: Antal Jkli et al., Kent State University

  In a new study, scientists have made use of a property called flexoelectricity, where materials, such as LCs, convert mechanical energy into electrical energy when they are flexed. Bent-core nematics (BCNs) - LCs made from banana-shaped molecules - are particularly flexoelectric but because of their fluidity, they are not robust or flexible enough to use in energy conversion devices. To get around this problem, the team used the rubbery properties of a LC elastomer (LCE) to provide a flexible support for the BCN. By swelling the LCE with a BCN, they obtained lightweight films that preserve the pure BCN's strong flexoelectricity but in a more robust and flexible form. The new BCN-LCE material can be used over a wider temperature range than the pure BCN, increasing its viability for device application.
  [Flexoelectricity of a calamitic liquid crystal elastomer swollen with a bent-core liquid crystal, J. Mater. Chem., 2009, DOI: 10.1039/b911652d]
  (September 10, 2009)

• Lithographically deposited graphite as data storage medium
  (Science Daily/Rice University)

  
  Credit: Rice University

  Researchers in a new study show how they've used industry-standard lithographic techniques to deposit 10-nanometer stripes of amorphous graphite onto silicon. This facilitates the creation of potentially very dense, very stable nonvolatile memory for all kinds of digital devices. Graphite makes a good, reliable memory "bit" for reasons that aren't yet fully understood. The lab found that running a current through a 10-atom-thick layer of graphite creates a complete break in the circuit -- literally, a gap in the strip a couple of nanometers wide. Another jolt repairs the break. The process appears to be indefinitely repeatable, which provides addressable ones and zeroes, just like today's flash memory devices but at a much denser scale.
  [Lithographic Graphitic Memories, ACS Nano, Article ASAP DOI: 10.1021/nn9006225]
  (September 10, 2009)

• Basic molecular structure of cement decoded
  (Massachusetts Institute of Technology)

  The three-dimensional crystalline structure of cement hydrate - the paste that forms and quickly hardens when cement powder is mixed with water - has eluded scientific attempts at decoding, despite the fact that concrete is the most prevalent man-made material on earth and the focus of a multibillion-dollar industry that is under pressure to clean up its act. The manufacture of cement is responsible for about 5 percent of all carbon dioxide emissions worldwide. A new report now announces the decoding of the three-dimensional structure of the basic unit of cement hydrate by a group of researchers. Scientists have long believed that at the atomic level, cement hydrate (or calcium-silica-hydrate) closely resembles the rare mineral tobermorite, which has an ordered geometry consisting of layers of infinitely long chains of three-armed silica molecules (called silica tetrahedra) interspersed with neat layers of calcium oxide. But the team found that the calcium-silica-hydrate in cement isn't really a crystal. It's a hybrid that shares some characteristics with crystalline structures and some with the amorphous structure of frozen liquids, such as glass or ice.
  [A realistic molecular model of cement hydrates, PNAS, Published online before print September 8, 2009, doi: 10.1073/pnas.0902180106 ]
  (September 9, 2009)

• Anisotropy of hardness of ReB₂ and OsB₂
  (Physical Review Focus)

  
  Credit: Phys. Rev. B

  Over the past few years, researchers have been developing layered "transition-metal diborides," such as OsB2, materials whose hardness rivals that of diamond but that don't require high temperatures and pressures to produce. One striking property of these materials is their extremely direction-dependent hardness, and there is no theory to explain it. A theory that captures this behavior should also be more reliable for predicting hardness in other materials. Now, by extending his previous work on more conventional materials, a researcher is attempting to fill this gap. He previously developed a formula that combined the contributions of the various types of bonds in a crystal to calculate its hardness, but included bonds in all directions in the crystal with equal weight. He adapted his earlier model by mathematically weighting the contributions of each bond to the total hardness based on its direction, with bonds perpendicular to the applied force being given the most weight. In the transition-metal diborides, his model explains the greater hardness in the direction perpendicular to the layers that contain strong boron-boron bonds. As for other materials, this "extremely simple" calculation is useful for guessing the properties of new materials that haven't been made yet.
  [Anisotropy of Hardness from First Principles: The Cases of ReB2 and OsB2 Phys. Rev. B 80, (2009) 060103]
  (September 9, 2009)

• Magnetic monopole analogs observed in spin ices
  (Science)

  
  Credit: L. D. C. Jaubert and P. C. W. Holdsworth,
  Nature Physics

  For decades, scientists have searched for magnetic monopoles--particles that, unlike traditional magnets, have just a north or south pole. Now, two teams of researchers independently report observations of the next best thing: tiny ripples in solid materials that act like the elusive particles. They have spotted analogs of monopoles in crystals called "spin ices," in which magnetic ions arrange themselves like the hydrogen ions in ice. The magnetic ions sit at the tips of four-sided pyramids or tetrahedra connected corner to corner. At temperatures near absolute zero, they should organize themselves by a simple rule: In each tetrahedron, two ions point their north poles inward toward the center and two point outward. Flaws in this pattern are the monopoles. If one ion flips--perhaps because it gets energized by the thermal energy in the crystal--it leaves one tetrahedron with three ions pointing inward and the neighboring tetrahedron with only one ion pointing inward. The two imbalanced tetrahedra act like north and south magnetic poles, respectively. If nearby spins also flip, the imbalances can shift independently from one tetrahedron to the next, so that the north and south poles end up connected only by a string of ions that point from one to the other. Thus the imbalanced tetrahedra become magnetic monopoles. One group shined polarized neutrons on their sample of the spin ice holmium titanate and measured the scattering at various angles to reveal the underlying pattern of two ions facing in and two facing out. They then showed that, as the sample warmed, the scattering changed just as computer models predicted it would if monopoles were emerging. The other group applied a magnetic field to stretch out the strings connecting the imbalanced tetrahedra in the spin ice dysprosium titanate; it then used neutron scattering to reveal the presence of the strings and, hence, the monopoles at their ends.
  [Magnetic Coulomb Phase in the Spin Ice Ho2Ti2O7, Science Published Online September 3, 2009 DOI: 10.1126/science.1177582; Dirac Strings and Magnetic Monopoles in Spin Ice Dy2Ti2O7, Science, Published Online September 3, 2009 DOI: 10.1126/science.1178868]
  (September 8, 2009)

• Acoustic tweezers pattern living cells, microparticles
  (Physics World)

  
  Credit: Tony Jun Huang, Jinjie Shi, Penn State Univ.

  Researchers have unveiled a new chip-based device capable of manoeuvring tiny objects using sound. These "acoustic tweezers" could provide a simpler and more energy-efficient alternative to the more established technology of optical tweezers, say the researchers. In addition, the small size and delicate functioning of the device could eventually lead to new "lab-on-a-chip" applications in medicine and industry. The acoustic tweezers exploit a phenomenon known as surface acoustic waves (SAW) sound waves that penetrate just one wavelength into a material when propagating along its surface. The researchers combined two SAWs in their device to generate a standing wave across a chip. When a microscopic object is placed in the standing wave, it moves along a pressure gradient until it reaches a node that is, a point where the two waves cancel each other out and the object comes to a complete standstill. The device is fabricated on a piezoelectric chip. To demonstrate the acoustic tweezers, the researchers arranged a series of fluorescent polystyrene beads about 1.9 m in diameter into a grid pattern. They then carried out the same demonstration using the red blood cells of a cow and the bacteria E.Coli.
  [Acoustic tweezers: patterning cells and microparticles using standing surface acoustic waves (SSAW), Lab Chip, 2009, DOI: 10.1039/b910595f]
  (September 8, 2009)

• Nanosieve completes efforts of Knudsen
  (NanotechWeb)

  
  Credit: Nanotechnology

  In the early 1900s, Knudsen proposed that the transition gas flow through capillaries could be approximated as the superimposition of viscous and molecular fluxes. However, he had to include correction terms to account for wall interaction effects. The intermolecular collisions will limit the molecular transport drastically when the length of the capillary is well above the mean-free-path of the gas. In a new study, researchers have used laser-assisted nano-fabrication techniques to realize an ultra-thin inorganic membrane with precisely defined perforations for the study of gas-flow behaviour at the nanoscale. The nanosieve has been observed to exhibit transition gas-flow behaviour around atmospheric pressure and ambient temperature. The fine lip thickness (45 nm) of the nanopores with respect to their diameter (120 nm) minimizes the interactions between molecules and the inner pore wall and simplifies the analysis of transition flow. Due to the absence of these collisions, the transition flux can be quantified by the superimposition of viscous and molecular fluxes without the need for higher order slip correction.
  [Transition flow through an ultra-thin nanosieve, Nanotechnology 20 (2009) 305304, doi: 10.1088/0957-4484/20/30/305304]
  (September 4, 2009)

• Microcapsules with carbon nanotubes suspensions used to repair circuits
  (Royal Society of Chemistry)

  
  Credit: Jeffrey Moore, Univ. Illinois at Urbana-Champaign

  Scientists have developed a first aid kit for electrical systems that could stop circuits failing and lead to safer, longer lasting batteries. They made microcapsules with robust walls using an in situ emulsification polymerization of urea-formaldehyde and filled them with carbon nanotubes (CNTs). They then ruptured the microcapsules using vigorous stirring and measured the contents' ability to conduct electricity between two electric probes separated by around 100 micrometres. As the applied voltage was swept from minus to plus 50 volts, the CNTs migrated towards the probe tips. They aligned with the electric field and completed the circuit, enabling the current to flow. The best capsules were between 280 and 350 micrometres - smaller ones were too difficult to break and larger ones broke too easily.
  [Microcapsules containing suspensions of carbon nanotubes, J. Mater. Chem., 2009, 19, 6093 DOI: 10.1039/b910673a]
  (September 3, 2009)

• Designing 3D DNA crystals
  (Royal Society of Chemistry)

  
  Credit: Nature

  DNA triangles can be designed to self-assemble into three dimensional, macro-sized crystals have been developed. These crystals could prove useful in helping determine the structure of other biomolecules, as well as in drug design and molecular electronics. The crystals are made up of sub-units called DNA tensegrity triangles - these consist of three helices of DNA constructed into a triangle with three-fold rotational symmetry, where the direction of the helix axes are each on different planes. Each of the ends of the helices have two unpaired nucleotides, called 'sticky ends'. It is these that stick to complementary pairs of bases on other triangles during the self-assembly process, creating well-ordered three dimensional crystals approximately 0.25 mm in size. The helically repeating nature of DNA facilitates the construction of a periodic array. The rationally designed crystals have different numbers of nucleotide pairs in the DNA helices, ranging from 21 to 42, and therefore have different sized lattice holes.
  [From molecular to macroscopic via the rational design of a self-assembled 3D DNA crystal, Nature 461, 74-77 (3 September 2009), doi:10.1038/nature08274]
  (September 3, 2009)

• Graphene-based nanomaterial with magnetic properties
  (Virginia Commonwealth University)

  
  Credit: Puru Jena, VCU

  A team of researchers has designed a new graphene-based, magnetic nanomaterial that acts as a semiconductor. They used computer modeling to design the new material they called graphone. Although graphene’s properties can be significantly modified by introducing defects and by saturating with hydrogen, it has been very difficult for scientists to manipulate the structure to make it magnetic. The new material predicted – graphone – makes graphene magnetic simply by controlling the amount of hydrogen coverage – basically, how much hydrogen is put on graphene. It avoids previous difficulties associated with the synthesis of magnetic graphene. Thus the semi-hydrogenation provides a very unique way to tailor magnetism.
  [Ferromagnetism in Semihydrogenated Graphene Sheet, Nano Lett., Article ASAP (August 31, 2009) DOI: 10.1021/nl9020733]
  (September 3, 2009)

• Metallofullerenes as data storage units
  (PhysOrg.com)

  
  Credit: Empa, Swiss Federal Laboratories for
  Materials Testing and Research

  Interest is growing in the use of metallofullerenes - carbon “cages” with embedded metallic compounds - as materials for miniature data storage devices. Researchers have discovered that metallofullerenes are capable of forming ordered supramolecular structures with different orientations. By specifically manipulating these orientations it might be possible to store and subsequently read out information. The researchers have been studying metallofullerenes and have been able to show that, when deposited on a surface, these form ordered islands with domains of identically orientated molecules. Different orientations have, however, been found for the endohedral metallic compounds. Provided an external stimulus could be found which would be able to bring about a change between different orientations - like a switch - the basic mechanism for data storage would have been achieved.
  [Looking inside an endohedral fullerene: Inter- and intramolecular ordering of Dy3N@C80 (Ih) on Cu(111), Phys. Rev. B 80, 081403 (Published August 11, 2009)]
  (September 2, 2009)

• Nano printing goes large
  (Technology Review)

     
     Credit: ACS Nano

  Nanoimprint lithography uses mechanical force to press out a nanoscale pattern and can make much smaller features than optical lithography, which is reaching its physical limits. The technique was developed as a tool for miniaturizing integrated circuits. So far, however, it's been difficult to scale up nanoimprint lithography reliably. Researchers have now developed a stamp that can be used for roll-to-roll nanoimprinting over large areas. The setup uses a polymer mold wrapped around a rolling cylinder to press a pattern into a resist that sits on top of either a rigid glass backing or a polymer one. To make the finished component, the pattern is then fixed by a flash of ultraviolet light. The process can be done continuously at a rate of a meter per minute, and features as small as 50 nanometers over an area six inches wide have been printed. That resolution isn't good enough to make integrated circuits, but it is adequate for printing optical devices such as light concentrators and gratings.
  [Large-Area Roll-to-Roll and Roll-to-Plate Nanoimprint Lithography: A Step toward High-Throughput Application of Continuous Nanoimprinting, ACS Nano, 2009, 3 (8), pp 2304–2310 DOI: 10.1021/nn9003633]
  (September 2, 2009)

• Plasmonic laser puts the squeeze on light
  (Physics World)

  
  Credit: Xiang Zhang, UC Berkeley

  In a new report, researchers claim to have created the smallest semiconductor laser ever. The new nanoscale device can generate light in a space just 5 nm in size, which is 100 times smaller than the spot produced by conventional lasers. Normally, light cannot be focused to a spot smaller than half its wavelength – something known as the diffraction limit. However, in recent years, scientists have succeeded in compressing light down to the nanoscale by coupling it to the electrons that oscillate collectively at the surface of metals – called surface plasmons. The resulting excitations of light and electrons are known as "surface plasmon polaritons" or SPPs. The researchers constructed a hybrid device consisting of a cadmium sulphide semiconductor nanowire separated by a 5 nm thick insulating layer from a metallic silver surface. This structure – dubbed a "hybrid plasmonic waveguide" by the researchers – can concentrate light into an area as much as 100 times smaller than a diffraction-limited spot. And, because it is non-metallic, it poses little resistance so that SPPs can survive for longer. They can then amplify the SPPs present by shining light onto the structure.
  [Plasmon lasers at deep subwavelength scale, Nature advance online publication 30 August 2009 | doi:10.1038/nature08364]
  (September 1, 2009)