Research articles

Organic ligands enhance the stability and the solution processability of semiconductor quantum dots, but they can impede charge transport in films of such nanoparticles. Passivation with atomic ligands now offers an alternative strategy that enables the fabrication of PbS colloidal-quantum-dot solar cells with power-conversion efficiencies of up to 6%.

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.

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.

Methodologies capable of directly visualizing and detecting gases are important for a wide variety of applications that involve instantaneous decision-making in complex environments and locations. A strategy for the capture and detection of gases by co-operative structural transformations of a flexible porous coordination polymer and fluorescent reporter molecules is now reported.

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.

First-principles calculations show that water molecules at the surface of crystalline ice have high variability in their binding energies. Such an amorphous character of a crystalline surface is unusual, and for ice it is a result of electrostatic frustration and the relaxation of geometric constraints. The findings have consequences for ice catalysis, surface pre-melting and growth.

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 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.

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.

In vitro experiments of a biomaterial's degradability rarely predict its in vivo behaviour. It is now shown that tracking the hydrolytic and enzymatic erosion of model materials by non-invasive fluorescence imaging allows the prediction of in vivo erosion from in vitro data. The approach should enable rapid screening of erodable biomaterials.

The coupling between electron spins and phonons could lead to a new typology of electronic devices. The effects of such coupling are now experimentally demonstrated by injecting sound waves into a magnetic strip. The results also help to explain the origin of the spin Seebeck effect, which has been controversial for a while.

The arrangement of defects in solid-state phases has an enormous influence on material properties. It is here shown that powerful X-rays can be used to change the properties of an oxide superconductor, thus effectively writing superconducting regions within an insulating matrix. The results open the way to the manipulation of superconductors and potentially other phases.

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.

A suspension of magnetic colloidal particles confined at a liquid–liquid interface and energized by an external periodic magnetic field self-assembles into star-shaped structures that can be magnetically manipulated to capture and transport smaller non-magnetic particles.

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.

Single-walled carbon nanotubes are shown to template the self-assembly of graphene nanoribbons inside the tubes on electron-beam irradiation of a random mixture of precursors containing C and S atoms. The nanoribbons, which adopt a helical shape, are stabilized by sulphur-terminated dangling bonds.

Superparamagnetic nanoparticles under an external magnetic field align in the field’s direction to minimize magnetic-dipole interactions. By modulating and fixing the alignment of magnetic nanoparticles in polymeric microcomponents through photopolymerization, magnetic nanocomposite microactuators were programmed to undergo complex motion, such as anisotropic bending and crawling.