Volume 13 Issue 1, January 2014

The energetic and kinetic behaviours of water-oxidation catalysts deposited on semiconductor electrodes are probed in situ, elucidating the junction formed between them, and transforming the design principles of the catalysts.

A study on carrier-collection efficiency in various organic photovoltaic systems now reveals that ultrafast relaxation of photoexcitations within the manifold of charge-transfer states does not impede mobile charge carrier generation.

Reversible strains up to 14% driven by changes in temperature or electric field have been realized in a thin film of bismuth ferrite oxide.

Planar patterns of colloidal microparticles have been manufactured with high yield over square centimetre areas by using magnetic-field microgradients in a paramagnetic fluid. This approach could evolve into technology capable of printing three-dimensional objects through programmable and reconfigurable 'magnetic pixels'.

Memory devices based on the spin-transfer-torque effect offer a range of attractive properties, such as speed of operation and low energy cost. This Progress Article outlines a strategy for assembling different nanodevices based on the spin-torque effect to achieve qualitatively different computing architectures.

The photoluminescent properties of electron spins at nitrogen–vacancy (NV) centres are promising for use in quantum information and magnetometry. It is now shown that the coherence times of NV centres in nanodiamonds can be engineered to be comparable to those of bulk diamond.

Size effects and geometry can significantly modify the properties of nanoparticles with direct impact on their biocompatibility and chemical reactivity. Using high-resolution electron microscopy it is now shown that strain gradients induced in the oxide shell of cuboid Fe nanoparticles can lead to oxide domain formation and shape evolution of the particles.

Oxide ion conductors are technologically relevant for applications in electrochemical devices such as sensors, separation membranes and fuel cells. Magnesium doping in Na_0.5Bi_0.5TiO₃—a piezoelectric material that suffers from high leakage conductivity—now results in a family of ionic conductors that could prove significant not only for dielectric-based applications but also for intermediate-temperature solid-oxide fuel cells.

A requirement for the reversible mechanical actuation of liquid-crystal elastomers is macroscale alignment. However, current processing techniques do not achieve reliable and robust alignment, which limits the practical use of these materials as actuators and artificial muscles. It is now shown that by introducing polymers with exchangeable covalent bonds, liquid-crystal elastomers can be easily processed and aligned, and subsequently remodelled.

Rare-earth hexagonal manganites are known for their multiferroic properties. Using parameters calculated from first principles, a theoretical description of the topological defects arising in these systems is now presented.

Spin-torque diodes enable the detection and rectification of radiofrequencies by means of spin-torque-induced ferromagnetic resonance between nanomagnets. Now, by using magnetic tunnel junctions with a MgO barrier and a FeB free-layer detection sensitivities in excess of those of semiconductor devices are demonstrated.

The propagation of light in photonic crystals with a honeycomb structure mirrors the behaviour of charges in graphene, therefore allowing for the investigation of electronic properties that cannot otherwise be accessed in graphene itself. This approach is now used to predict unexpected edge states that localize in the bearded edges of hexagonal lattices.

The efficiency of organic blends used for photovoltaic applications depends on their ability to convert photoexcited charges into free holes and electrons. It is now demonstrated that the lowermost energetic states formed at the donor/acceptor interface can reach conversion efficiencies close to 100%, and therefore do not behave as traps for charge carriers.

Failure caused by dendrite growth in rechargeable batteries with lithium metal anodes has prevented their widespread applicability. A microtomography study on lithium–polymer–lithium cells now reveals that at the early stage of dendrite formation dendritic structures lie within the electrode, underneath the polymer/electrode interface.

Layered oxides are promising for many applications ranging from energy conversion and storage to magnetic and electric devices. The oxygen storage ability of ferroelectric LuFe₂O_4+x is now demonstrated and the storage mechanism is believed to be governed by a complex oxygen intercalation/de-intercalation process with several intermediate metastable states.

Photoelectrochemical water-splitting devices require integrating electrocatalysts with light-absorbing semiconductors, but understanding charge-transfer processes at interfaces has proved difficult. Ion-permeable electrocatalysts deposited onto TiO₂ photoelectrodes now result in adaptive semiconductor/electrocatalyst junctions where both the effective interface barrier height and the photovoltage output change depending on the oxidation state of the electrocatalyst.

In wound healing, skin cells collectively migrate to maintain tissue cohesion despite the existence of inhomogeneities in the extracellular environment within the wound bed. Yet how the cell collective responds to heterogeneities in the extracellular matrix is not well understood. Now, it is shown that migrating human keratinocyte cell sheets form suspended multicellular bridges over non-adhesive regions on micropatterned substrates comprising alternating strips of fibronectin and non-adherent polymer.