Research articles

Metal oxides can exchange charges with a wide variety of adsorbed organic molecules, which renders them useful in electronics and catalysis. A study on oxides with a range of electronic properties now shows that energy alignment at metal oxide/organic interfaces is universally governed by electron-chemical-potential equilibration.

Artificial materials that show negative refraction can be used for devices such as perfect lenses. The demonstration of negative refraction in nanostructured metal films, using a nonlinear optical effect—four-wave mixing—therefore opens new possibilities for optical devices.

It is shown that an elastic film on a viscoelastic substrate under biaxial compressive stress forms a hierarchical network of folds generated by repetitive wrinkle-to-fold transitions. The morphology of the hierarchical patterns can be controlled by modifying the geometry and boundary conditions of the membrane.

Oxide nanoprecipitates with typical sizes of smaller than five nanometres have been known to considerably enhance the mechanical properties of steel. An atomic-scale characterization is now able to directly verify the crystal structure of these stable oxide nanoclusters.

Different mechanistic processes explaining the catalytic activities of supported gold catalysts have been proposed. Au–Pd colloidal nanoclusters are now shown to exhibit high catalytic activity owing to an abundance of negatively charged Au atoms on the surface.

Semiconductor nanocrystals have for many years attracted attention for their optical properties and their potential use as superior fluorescence emitters. It is now shown that nanoplatelets can be controllably synthesized and have even more attractive properties.

Nonlinear optical upconversion processes in nanoparticles, which convert long-wavelength light into short-wavelength emission, are promising for applications such as biological imaging, optical data storage and others. The flexible tuning of upconversion properties in core–shell nanoparticles now offers unprecedented control over the nonlinear optical properties of the nanoparticles.

An electrochemical method that uses ion-selective membranes to electrically modulate ion concentrations in situ along a sciatic nerve in vitro allows for on-demand reversible inhibition of signal propagation as well as up to 40% reduction of the electrical threshold for stimulation. The method may be applicable in implantable neuroprosthetic devices.

Secondary batteries using organic electrode-active materials promise to surpass present lithium-ion batteries in terms of safety and price. Organic molecules with degenerate molecular orbitals as electrode-active materials are now used in high-capacity organic batteries exceeding 300 A h kg⁻¹.

The close relationship between crystal structure and electric polarization in ferroelectrics means that strain strongly influences their properties. The demonstration of how strain gradients leading to a higher-order effect, flexoelectricity, can be used to rotate electric polarization in thin films indicates new ways of controlling piezoelectricity by purely mechanical means.

Conjugated polymers are applied widely in organic optoelectronic devices. The performance of these devices depends critically on polymer morphology, which can be modified by solvent vapour annealing. This process has now been controlled on mesoscopic length scales, bridging the gap between single-molecule and bulk studies, and revealing long-range energy transport in ordered polymer aggregates.

Inorganic nanocrystals are attractive materials for solar-cell applications. However, their performance is often limited by an insufficient alignment of internal energy levels. A tuning of these energy levels has now been achieved by attaching two different molecules to a single nanocrystal, which significantly alters its electronic and optoelectronic properties.

It is easy to imagine that carbon nanotubes deform under strain, but the microscopic mechanism of deformation is difficult to relate to the large-scale one. Through aberration-corrected transmission microscopy the atomic displacement under bending is now mapped out, revealing unexpected details.

The electrical control of magnetic properties is a key requirement for the development of spintronic devices. The demonstration that the ferromagnetic phase transition in cobalt can be changed by applying an electric field at room temperature represents a significant step towards devices that can switch magnetism on and off electrically.

Monodisperse octapod-shaped inorganic nanocrystals suspended in suitable solvents are shown to self-assemble into chains of interlocked octapods, which in turn aggregate to form three-dimensional crystals. Such hierarchical self-assembly is supported by a simulation model of the octapods, which shows that the favourable interlocked configuration is encoded in the octapod’s shape.

Toothpaste, mayonnaise and other systems are soft particle glasses. In these, the soft particles are jammed so that the glasses behave like weak solids at rest but at sufficient stress flow like liquids. This has made their theoretical understanding difficult. A new micromechanical model is now able to predict the rheology of these soft particle glasses.

Activation of molecular hydrogen is an important step for many applications such as fuel cells and ammonia synthesis, but has so far required high temperatures and expensive noble-metal catalysts. Aluminium doped with small amounts of titanium is now shown to activate molecular hydrogen at temperatures as low as 90 K.

Self-assembled monolayers of thiols have applications ranging from surface coatings to nanomechanical sensors, where they transmit analyte-induced stress to a cantilever detector. For gold nanocrystals it is now shown that the adsorption of propanethiol alone can induce large chemical stress, with different directionality on curved and flat surfaces.

Iron-based superconductors all share the same building blocks. So why do local magnetic properties vary from one compound to another? A new theoretical model explains the variation in physical properties and links it to the structural differences, providing a description for a wide range of materials.

The use of flexible polymer substrates not only reduces weight and fabrication costs of solar cells, but their bendability also enables new applications. A careful design of Cu(In,Ga)Se₂ solar cells grown on polymer substrates now solves earlier fabrication issues, leading to conversion efficiencies matching those grown on rigid substrates.