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assembled fullerenes initial nanoparticle growth and assembly objects. David Woolf, Marko Loncar and Angew. Chem. Int. Ed. through microdisks, a mechanism they liken Federico Capassso have now investigated doi:10.1002/anie.200904985 (2009) to biomineralization. the force originating from coupled SPPs between two metal plates. The force that tantalum to the rescue the researchers study is an analogue of Chem. Mater. doi:10.1021/cm9020782 (2009) the Casimir force between two uncharged metallic plates. In the case of SPPs, the One of the drawbacks of developing polymer precise forces between such structures

akeuchi electrolyte membrane fuel cells running on depend not only on the wavelength of light t small-organic-molecule fuels is the lack of used and its power, but also on the details of anode catalysts that effectively overcome the structure. Systems in which the plates are asayuki asayuki the kinetic barrier for complete oxidation of thin so that SPPs from all four faces interact m these complex molecules. Typical catalysts with each other allow the properties to be used, such as platinum, also suffer from better fine-tuned, so that, unlike in the case poisoning by carbon monoxide impurities of thick metal plates, not only attractive but associated with hydrogen production from also repulsive forces can be achieved. The Xuan Zhang / Xuan

© hydrocarbon reformation. Bruce van Dover strength of the force between the metal plates and colleagues now investigate the catalytic is slightly larger than the Casimir force, Assembling fullerenes into larger activity of platinum–tantalum systems by suggesting the use of these plasmonic effects superstructures is attractive as a route to means of extensive electrochemical and in controlling nanomechanical systems functional materials and as a potential structural characterization. A library of through light. approach for controlling their morphology thin-film systems containing Pt–Ta ordered when used in devices such as organic solar intermetallics were tested as methanol Covered in wrinkles cells. However, fullerenes usually need to be and formic acid oxidation catalysts with Nano Lett. doi: 10.1021/nl902729p (2009) functionalized with additional molecules a fluorescence-based parallel screening to be made to assemble into larger forms. method. The significant improvement in Now, Xuan Zhang and Masayuki Takeuchi catalytic activity was attributed to interactions make microspheres consisting of nanoplates between Ta suboxides and surface Pt. The of unfunctionalized fullerenes, using a most active catalyst surface was a Ta suboxide porphyrin polymer to control the assembly and Pt composite less than 1 nm in size, and through supramolecular interactions. The the interaction between these species led nay mutlu nay fullerene and porphyrin polymer are simply to less Pt carbon contamination during the Ü mixed in solutions of toluene, and the oxidation of methanol and formic acid. solvent is then allowed to evaporate. The size of the microspheres can be tuned by light forces changing the ratio of the two components, Opt. Expr. 17, 19996‑20011 (2009). istockphoto / g istockphoto

while changing the concentrations of the © two individual solutions before mixing As with any other particle, the produces different shapes such as rods. electromagnetic energy of photons can be Graphene has really come of age: it’s full The researchers also show that, no matter converted into other forms of energy or used of wrinkles — at least according to a study what the mixing ratio, very little of the to exert small amounts of radiation pressure by Ke Xu and colleagues at Caltech. Their porphyrin polymer is present in the final on surfaces. Similarly, surface plasmon scanning tunnelling microscopy images

spheres. They conclude that the polymer polaritons (SPPs) can also be used to generate of exfoliated graphene on SiO2 substrates directs the fullerenes to form the spheres by forces between closely separated metallic shows the ubiquitous presence of these corrugations, typically 3 nm high, 10 nm wide and up to 1 μm long. The atomic Holey nanowires J. Am. Chem. Soc. doi:10.1021/ja907043b (2009) resolution of the scanning tunnelling microscope showed that the typical Porous one‑dimensional nanostructures show promise for use in applications such hexagonal lattice of graphene transforms into as catalysis and bioengineering. Now, highly crystalline porous nanowires of layered‑ a triangular lattice on the wrinkles, which the hydroxide lanthanum acetate have been synthesized using a hydrothermal route. The researchers ascribe to a bending force that is previous syntheses of these types of material required high‑temperature post treatments strong enough to break the six-fold symmetry or a pre‑existing template. However, the hydrothermal route introduced by Xun Wang and of graphene. The electronic properties colleagues avoids this, and uses La(NO3)3·6H2O and a mixture of deionized water, ethanol, are also affected by the bending force, as oleylamine and acetic acid. They produce nanowires roughly 35 nm in diameter and up to a shown by measurements of the differential few micrometres in length, with a broad size distribution of pores and a positively charged conductance that reveal a finite density of surface. This, combined with the high crystallinity leads to high surface roughness such that states at the charge neutrality point — which a large area of each nanowire can interact with other species, improving their adsorption is instead zero in flat graphene. According to and catalysis properties. Importantly, the team demonstrate that the material can adsorb recent theoretical studies, this could indeed and release DNA fragments, and it can remove a common azo‑dye used in the textile be a consequence of large corrugations. If the industry from water. These results provide positive indications that the nanowires will find wrinkles are indeed ubiquitous, their details use in catalysis and environmental and bio‑related applications. are essential for understanding the electronic properties of graphene.

922 nature materials | VOL 8 | DECEMBER 2009 | www.nature.com/naturematerials

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