Articles in 2011

An understanding of a material's microscopic architecture is important to improve its mechanical properties. Poisson's ratio, which celebrates its bicentenary this year, continues to provide a good metric for that.

The ability to control the nuclear spins in a semiconductor quantum dot is an important step towards a long-lived and controllable electron spin qubit.

Inclusion of organic molecules in inorganic crystals is thought to enhance their mechanical properties, yet obtaining high occlusion levels has been a challenge. It is now shown that synthetic calcite single crystals incorporating a significant amount of copolymer micelles have mechanical properties similar to biogenic calcite crystals.

Suspensions of octapod-shaped nanocrystals are seen to spontaneously interlock into chains, which in turn aggregate side-by-side to form three-dimensional crystals. The observed hierarchical self-assembly can be explained by the octapod's shape and the solvent-tunable van der Waals interactions.

Molecular ligands are widely used to functionalize gold nanoparticles, but their influence on the particle structure has been difficult to probe. Coherent X-ray diffraction has now reached sufficient sensitivity to resolve adsorption-induced near-surface stress in a single nanocrystal.

Surfaces are known to act as catalysts for the nucleation of crystals. Using polymer films patterned with nanopores, it is now shown that the shape of the pores can control the kinetics of surface-induced crystal nucleation.

It is often assumed that there is a conflict in structural materials between strength (resistance to non-recoverable deformation) and toughness (resistance to fracture), which cannot be optimized at the same time. In this review, new fundamental insight and lessons from nature demonstrate how this conflict can be resolved through a design on different length scales.

Poisson's ratio describes the resistance of a material to distort under mechanical load rather than to alter in volume. On the bicentenary of the publication of Poisson's Traité de Mécanique, the continuing relevance of Poisson's ratio in the understanding of modern materials is reviewed.

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.