Articles in 2011

Bioactive proteins within hydrogel scaffolds used to culture cells can guide cellular activities, but the control of the location of the proteins has proved difficult. Using the multiphoton laser of a confocal microscope, simultaneous patterning of two growth factors, which remain bioactive after immobilization, is now shown in three-dimensional hydrogels. The technique should be applicable to the patterning of a variety of proteins.

Increasing the energy density of lithium-ion batteries is crucial for consumer electronics and electric-vehicle applications. A polyanionic material that crystallizes in the triplite structure by substituting 5at.% of Mn for Fe in a fluorosulphate material now exhibits an enhanced potential of 3.90 V for the Fe²⁺/Fe³⁺ redox couple.

With only a few known useful room-temperature multiferroics, other ways of achieving materials showing magnetism as well as electrical polarization are sought. The discovery that the ferroelectric BaTiO₃ also shows magnetism at room temperature at the interface with iron or cobalt marks a new approach to achieving multiferroic properties.

Angle-resolved photoemission spectroscopy is possibly the most widely used technique to probe the electronic structure of crystals. Unfortunately the technique is usually too sensitive to surface properties. It is now demonstrated that by using hard X-rays as the incident radiation it is possible to probe the electronic structure in the bulk.

A crucial aspect for many applications of nanoparticles is the ability to control their size and, in particular, the size homogeneity within a nanoparticle ensemble. An approach to form highly monodisperse particles through simple solid-state reactions is now demonstrated. The results could lead to efficient ways to control size distributions through simple thermal treatments.

Developing oxygen-electrode catalysts with high activity at low cost for renewable energy applications such as water splitting and fuel cells is challenging. A hybrid material of Co₃O₄ nanocrystals grown on reduced graphene oxide exhibits enhanced catalytic performance for the oxygen reduction and oxygen evolution reactions.

Colloidal suspensions often contain mixtures of particles that must be sorted by size or density, but the sediment structure resulting from polydisperse particles settling rapidly remains unclear. Bidisperse colloids with soft-sphere interactions are now shown to spontaneously arrange into two macroscopic layers after sedimentation.

On standard tissue culture platforms, mesenchymal stem cells tend to spontaneously differentiate with the loss of multi-lineage potential. Now, a robust and reproducible nanotopographical platform has been shown to maintain stem cell phenotype and promote stem cell growth over several months whilst implicating mechanisms for the observed stem cell behaviour

Resistive switching is a promising technology to replace current non-volatile memory technologies such as flash. The demonstration of a fast, stable and highly scalable resistive-switching memory device represents a significant advance towards the practical implementation of this technology.

The ability to withstand shear is one of the properties that distinguishes a solid from a liquid. The proposal of an elastic metamaterial that in one direction only supports compressional waves, and therefore is fluid-like, and in the other supports compressional as well as shear waves represents a hybrid between fluids and solids that may lead to new applications.

The advance of nuclear technologies is strongly linked to the development of enhanced radiation-tolerant materials. Indentation measurements of irradiated copper nanopillars now demonstrate that in situ testing can offer a convenient method to determine bulk-like yield strengths and simultaneously identify deformation mechanisms.

Electrochemical energy can be produced by using solar energy to oxidize water, providing an abundant source of electrons, which are needed in fuel synthesis. The operation of an efficient and stable semiconductor nanocomposite anode, made of a protective TiO₂ layer that protects a silicon substrate during photoelectrochemical water oxidation in both dark and light conditions, is now reported.

A very large Rashba-type spin splitting, which is a consequence of spin–orbit interaction, has been observed in the heavy-element semiconductor BiTeI. The results show the possibility, in principle, of using the material in spintronics devices in which the electron spin is controlled by electric currents.

A two-component nanoparticle system that communicates and enhances in vivo drug delivery and diagnostics has been devised. The system comprises ‘signalling’ nanoparticles that target tumours and then broadcast the tumour’s location to ’receiving’ nanoparticles in circulation, which carry therapeutic or diagnostic cargos, hence amplifying tumour targeting.

Pure spin current—the flow of spin angular momentum involving no charge movement—could lead to highly efficient spintronic devices. It is now shown that through low-resistivity magnetic tunnelling junctions it is possible to induce spin accumulation in solid-state devices one hundred times higher than previously obtained. This is the main requirement for generation of large spin currents.

Neutron scattering and first-principles calculations show that the small thermal conductivity of PbTe is due to anharmonic coupling between the acoustic phonon modes and the optical ferroelectric ones. The results provide a microscopic picture of why many good thermoelectrics are found near a ferroelectric lattice instability.

Container walls are known to have a significant influence on the dynamics of glass formation. Computations now suggest that structural order is the origin of the slower dynamics of a glass-forming liquid near container walls.

The mechanical stresses within and between cells inside an advancing cellular monolayer are mapped experimentally. Cellular migration is found to be oriented in the direction of maximum principal stress indicating that cells collectively migrate to maintain minimal local intercellular shear stress.

In contrast to the long-range order of crystalline materials, non-crystalline compounds, such as metallic glasses, have a more inhomogeneous distribution of atoms on a local scale. Atomic force acoustic microscopy now demonstrates how these local variations translate into much stronger variations in local elastic properties of a metallic glass compared with its crystalline counterpart.

Plasmonic resonances are widely used for sensing applications. The plasmon resonance of a single nanoantenna structure is now used to detect changes in the dielectric properties of a nearby palladium nanoparticle exposed to hydrogen gas, enabling highly sensitive sensing in ultrasmall volumes. The approach can be easily extended to other sensing and catalysis schemes.