Research articles

Photoconversion in organic photovoltaic cells, which relies on charge generation at donor/acceptor interfaces, is limited by short exciton-diffusion-lengths. Diluting an electron donor into a wide-energy-gap host material has now led to an ~50% increase in exciton diffusion length and enhanced power conversion efficiencies in planar heterojunction cells compared with optimized devices with an undiluted donor layer.

Supported metal nanoparticles play a pivotal role in areas such as nanoelectronics, energy storage and conversion, and catalysis, but their tendency to grow into larger crystallites is an issue for their stable performance. A strategy based on controlling not only size and composition but also the location of the metal nanoparticles, now reveals the impact of their three-dimensional nanospatial distribution on their catalytic stability.

Hydrogen embrittlement in metals has proved problematic for designing strong and reliable structural materials. Direct molecular dynamics simulations now reveal a ductile-to-brittle transition caused by the suppression of dislocation emission at the crack tip due to the aggregation of hydrogen.

Implantable neural microelectrodes are critical to neuroscience research and emerging clinical applications including brain-controlled prostheses. A composite electrode consisting of a carbon fibre core, an insulating polymer coating and a polythiophene-based recording pad has now been developed that shows reduced chronic reactive tissue response in rats compared with existing architectures, owing to its smaller size and improved mechanical compliance with brain tissue.

Layered oxides are important as electrode materials for batteries and because of the strong electronic correlations resulting from their unique structure. Electrochemical investigations of the layered P2-Na_xVO₂ system in sodium batteries together with in situ X-ray diffraction experiments now result in the elucidation of the room-temperature phase diagram of this system.

Some of the most challenging issues in energy conversion are the insufficient activity of the catalysts for the oxygen-reduction reaction, catalyst degradation and carbon-support corrosion. A class of mesostructured carbon-free metallic catalysts based on thin films and with tunable near-surface composition, morphology and structure that lead to an improved affinity for the electrochemical reduction of oxygen are now reported.

Semiconductor photoelectrodes for solar hydrogen production by water photoelectrolysis require stable and abundant visible-light absorbers such as iron oxide. Although this material suffers from poor transport properties for efficient charge-carrier generation and collection, these drawbacks can now be addressed by using resonant light trapping in ultrathin films designed as optical cavities.

Enhancing and optimizing the performance and durability of nanocatalysts for the oxygen reduction reaction is crucial for fuel-cell applications. A class of Pt–Co nanocatalysts consisting of ordered Pt₃Co intermetallic cores with a 2–3 atomic-layer-thick platinum shell now exhibit a large increase in mass activity and specific activity when compared with disordered alloy nanoparticles.

Altering the composition of the spacer layers present in iron-based superconductors is one strategy for increasing the temperature below which they superconduct. Now, intercalating FeSe with molecular spacer layers is also shown to enhance the superconducting transition temperature.

Various artificial cells that can store molecules in cages are designed to generate mechanical motion by dissipating energy through chemical reactions or through the reorganization of molecules. A hybrid biomimetic motor system consisting of a metal–organic framework and diphenylanaline peptides is now designed to release guest molecules in the isotropic direction via a bond-breaking framework.

The thermodynamic properties of magnetocaloric materials show significant promise for energy-efficient cooling applications. The demonstration that large and reversible magnetocaloric effects can be created by means of strain suggests a new approach for inducing them in other magnetic materials.

It is now shown that, unlike most semiconductors, plasmonic metal nanostructures constructively couple the energy of photons and thermal energy, with the reaction rate positively responding to both stimuli. These unique characteristics suggest that these photocatalysts could prove useful for heterogeneous catalytic processes that cannot be activated using conventional thermal processes on metals or photocatalytic processes on semiconductors.

The atomic structure of nanoparticles considerably influences their properties. A new methodology that is now able to measure the full three-dimensional atomic structure of free-standing nanoparticles will therefore provide a much better connection between their structure and properties.

Although the search for new zeolites has traditionally been based on trial-and-error approaches, more rational methods are now available. Using the principle of inverse sigma transformation, the reactivity of framework germanium atoms in strong mineral acid has now been exploited to selectively remove germanium from a germanosilicate zeolite.

Stacked lipid bilayers usually display smectic order. It is now found that multicomponent stacked bilayers can also exhibit columnar order, which arises from the coupling of interlayer smectic order and intralayer phase-separated domains, and propagates across hundreds of layers.

A major obstacle to fully understanding the catalytic mechanisms of oxygen reduction reactions and to designing more efficient catalysts is the lack of detailed information about the active site structure. Molecular local chemisorption sites and the long-range supramolecular arrangement of metallophthalocyanine molecules on a metal surface can now be controlled by the fine tuning of the overlayer coverage.

The effect of nanoscale surface roughness on heat transport across solid interfaces has remained contentious. Now, measurements of the pressure dependence of heat transport across polished nanoscale contacts formed between the tip of a scanning thermal microscope and a surface agree with a model that assumes quantum thermal transport across individual contact points.

Optical coatings usually consist of many multilayers of thin films to achieve the desired properties. A new approach using interference effects between an absorbing dielectric film and a metallic substrate now enables ultrathin optical coatings that could also find applications as thin solar cells or photodetectors.

The dynamical processes associated with the magnetization of a material can be drastically altered by the application of a spin current. This study now demonstrates the feasibility of selectively exciting coherent auto-oscillation modes in magnetic nanostructures.

The origin of the magnetism in manganese-doped gallium arsenide has been the subject of much debate. Now, hard X-ray angle-resolved photoemission has been used to probe the electronic structure of this material and clarify the mechanism through which the magnetism arises.