Volume 10 Issue 11, November 2011

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.

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.

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.

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.

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.

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.

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.

The interaction between electron and nuclear spins in quantum dots is often seen as detrimental for the use of electron spin for quantum information processing. It is now shown, however, that such interaction can be used to coherently control the polarization of tens of thousands of nuclear spins, opening the way to experiments using nuclear rather than electron spin.

Josephson junctions have been intensely studied from a fundamental and technological point of view. It is now shown how by using ferromagnetic insulators for the barrier it is possible to strongly affect the superconducting current and in particular its magnetic and spin properties.

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.

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.

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.

Crystallization of a liquid usually starts at a solid surface — for instance, that of impurities or of a container's walls — and surface roughness is known to enhance crystal nucleation rates. It is now shown with polymer films patterned with spherical nanopores 15–120 nm in size that the shape of the pores can either enhance or hinder crystal nucleation.

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.

The fabrication of composite microfibres with tunable topography and chemical composition is now possible with a microfluidic method that mimics the fibre-spinning process of spiders. The method allows for the synthesis of a variety of structurally and spatially coded fibres for multiple applications, such as directional water harvesting and the co-culture of encapsulated cells.

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.

Biominerals exhibit properties, morphologies and hierarchical ordering that invariably surpass those of their synthetic counterparts. Artificial biominerals consisting of calcite crystals incorporating copolymer micelles have now been produced. The synthetic crystals show analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite.

The publication of Siméon Poisson's Traité de Mécanique in 1811 represented a milestone in our understanding of the properties of materials. Two hundred years on, concepts such as Poisson's ratio continue to provide a good metric for the development of enhanced structural materials. In this focus issue we take a look at some of the latest developments in the field.