Research articles

The formation of a NaTl lattice structure by DNA-mediated assembly of gold nanoparticles and virus-like protein nanoparticles is reported. The inorganic and organic components each form diamond-like frameworks that interpenetrate to give the NaTl lattice. These diamond-like structures are of interest for potential applications as photonic materials.

The fabrication of oxide thin-film heterostructures has improved considerably over the past few years. The first demonstration of the fractional quantum Hall effect in an oxide now attests to the potential of these compounds to rival conventional semiconductors.

The improvement of catalysts for the oxygen-reduction reaction is an important challenge for fuel cells and other electrochemical-energy technologies. A composite nanoporous Ni–Pt alloy with a tailored geometric architecture is now shown to exhibit high mass activity for oxygen reduction.

Flexible electronic devices that can be stretched without losing performance have seen increasing functionality. In particular, the demonstration of light-emitting diodes and photodetectors on flexible electronic substrates now opens the door to applications of flexible optoelectronic sheets in biomedicine and robotics.

Bilayer membranes encase several biological entities, for example cells and organelles. Their rupture under mechanical stress usually occurs by a pore-formation mechanism. Now, lipid-bilayer membranes spreading on a solid surface are shown to rupture in a series of rapid avalanches causing fractal membrane fragmentation.

Hydrophobic surfaces composed of an asymmetric array of polymer nanorods show unidirectional wetting behaviour relative to the orientation of the tilted nanorods. The surfaces, which are smooth on the microscale, can transport water droplets of microlitre capacity by a ratcheting mechanism resulting from the pillared substrate.

Excitons in polycrystalline films of organic semiconductors typically migrate distances of the order of tens of nanometres. Photoconductivity measurements in highly ordered rubrene now show that exciton diffusion can reach the micrometre range, opening a route to designing excitonic circuitry for applications in photocatalysis, photochemical sensing or photovoltaic energy conversion.

The oral delivery of small interfering RNA (siRNA) to diseased intestinal tissue is challenging because of the harsh environment created by gastrointestinal fluids and mucosa. Now, such delivery of siRNA to sites of intestinal inflammation is achieved using polythioketal nanoparticles and gene expression is successfully inhibited in the inflamed tissue.

DNA-functionalized, anisotropic nanostructures, such as triangular nanoprisms and nanorods, are shown to assemble by means of DNA hybridization into colloidal crystal structures. The crystallization parameters of these nanostructures, and hence the dimensionality and symmetry of the resultant superlattice, are strongly influenced by particle shape.

Domain walls in magnetic nanostructures could be used in information storage devices. The speed at which these domain walls can move when a magnetic field is applied has always been found to have a maximum. It is now shown that this can be increased by proper design of the magnetic structures, opening the way to faster and more reliable devices.

By using the spin Seebeck effect, the generation of an electric voltage from a heat gradient is demonstrated for the first time in an insulator. This finding extends the range of potential materials for thermoelectric applications, and provides a crucial piece of information for understanding the physics of the spin Seebeck effect.

The generation of an electric voltage from a heat gradient is demonstrated for the first time in the ferromagnetic semiconductor GaMnAs. This allows flexible design of the magnetization directions, a large spin polarization, and measurements across the magnetic phase transition. The effect is observed even in the absence of longitudinal charge transport.

In situ spectroscopic analysis of operating solid oxide electrochemical cells has proved to be difficult owing to high-vacuum requirements. Ambient-pressure X-ray photoelectron spectroscopy on single-chamber cells now suggests that surface reaction kinetics and electron transport on the electrodes are co-limiting processes.

The typical high-surface-area and voids of nanoscale cage structures make them attractive for catalysis, gas storage and drug delivery. Contrary to other metal–semiconductor particles, a ruthenium cage is now shown to grow selectively on the edges of a faceted copper sulphide nanocrystal.

Proton conductor oxides are promising materials for their use as electrolytes for reducing the operation temperature of solid-oxide fuel cells. Epitaxially oriented yttrium-doped barium zirconate films now show unprecedented proton conductivity in the 500–700 °C range.

Polymeric impurities in liquid crystals are known to perturb liquid-crystalline order. It is now shown that spatial gradients in the order, created by illuminating the materials with ultraviolet light, can be used to generate forces that allow the polymers to be concentrated or dispersed in the liquid crystal.

Actin filaments are a principal component of the cell cytoskeleton. Using micropatterning methods, physical influences on the growth of highly ordered actin structures are investigated. The spatial organization of actin nucleation sites is discovered to play an important role in establishing the architecture of actin networks.

Typically, electronic contributions have a very small effect on infrared absorption in solids. Now, however, a giant-infrared-absorption band of electronic origin has been observed in reduced graphene oxide. The band arises from the coupling of electronic states to the asymmetric stretch mode of a yet-unreported structure, consisting of oxygen atoms aggregated at edges of defects.

Flexible organic electronics could eventually be used to create electronic skin. Films of a pressure-sensitive microstructured elastomer are now used as the dielectric layer in organic field-effect transistors to create highly sensitive devices. The elastomer is also used in a matrix pressure sensor that can detect loads in numerous positions.

Flexible electronic devices should lead to new practical applications. Parallel arrays of inorganic nanowires have now been integrated into a flexible pressure-sensor array on a macroscopic scale. The sensor array operates at low voltage and acts as an artificial electronic skin, sensing pressure profiles with high spatial resolution.