Research articles

Multiferroics show simultaneous electrical and magnetic order. The suggestion that ferroelectricity in an organic multiferroic is not driven by the usual atomic displacements but instead by ordering of electronic charges opens the possibility of a new group of multiferroic compounds.

The motion of dislocations under stress is a key process in crystal plasticity. The finding that at low temperatures differences between experiments and theoretical predictions of dislocation activation can be explained by quantum effects arising from crystal zero-point vibrations represents a significant advance in our understanding of plasticity.

Van der Waals interactions are critical to the understanding of functional metal/molecule interfaces in catalysis, molecular electronics and self-assembly. Such interactions have now been characterized at the single-molecule level through a combination of measurements of the stretching mechanics of molecular junctions and atomistic simulations.

Although nanoparticulate gold possesses remarkable catalytic activity towards oxidation reactions, catalytic activity usually cannot be observed in particles larger than 5 nm. Atomic insights into dealloyed nanoporous gold catalysts by transmission electron microscopy now demonstrate that surface defects are active sites for the catalytic oxidation of carbon monoxide and that residual silver stabilizes atomic steps.

Innovative solutions for the design of sustainable and efficient systems for the conversion and storage of renewable energy sources are needed, and one promising option is the production of hydrogen through water splitting. A nanoparticulate electrocatalytic material consisting of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer is now found to exhibit active hydrogen evolution, and can also be converted into a cobalt oxide film catalysing oxygen evolution.

Flexible strain-gauge sensors, which could eventually be used in electronic skin, generally require complex device architectures. A simple and highly sensitive resistive sensor for the detection of pressure, shear and torsion with discernible strain-gauge factors has now been fabricated using two interlocked arrays of platinum-coated polymer nanofibres.

Electron transport in semiconducting polymers is usually inferior to hole transport, which is ascribed to charge trapping on defect sites. The observation of an identical electron-trap distribution in a range of materials now points to a common origin of these states that, as calculations suggest, may be related to hydrated oxygen complexes.

Heterostructures of very thin films have been used for decades in research and industry. Now a transmission electron microscopy study demonstrates the possibility of realizing perfect structures built by piling up one-atom-thick layers of graphene and boron nitride.

Heterointerfaces of organic semiconductors can show high electrical conductivity, but the details of their electronic structure remain largely unexplored. Schottky-gated heterostructures have now been used to probe the interface between single crystals of rubrene and PDIF-CN₂, showing that charge transport is due to electrons whose mobility exhibits band-like behaviour down to ~150 K.

The interaction between electrons and phonons is important for many materials properties. The finding that phonon modes of a superconducting thin film can influence the properties of an adjacent normal conductor, even over comparatively long distances, suggests new ways of controlling electron–phonon interactions.

The sustained release of both hydrophilic and hydrophobic immunomodulators for metastatic melanoma by nanoscale liposomal polymeric gels administered intratumorally or systemically is demonstrated. It is also shown that such a co-delivery approach delays tumour growth and increases the survival of tumour-bearing mice, and that its efficacy results from the activation of both innate and adaptative immune responses.

Many nanomaterials can induce cell autophagy, which can be either a concern in most in vivo situations or a benefit when exploited in cancer therapeutics. A family of short synthetic peptides that have a varied affinity to lanthanide oxide and lanthanide-based upconversion nanocrystals are now used to tune the degree of interaction between cells and nanocrystals, and thus the nanocrystals’ autophagy-inducing activity.

The length scale at which phenomena such as ferroelectricity is still present is of fundamental relevance for nanoscale applications. A high-resolution transmission electron microscopy study now shows how ferroelectricity can persist in nanoparticles down to about 5 nm in diameter, pointing the way towards the ultimate size limit for ferroelectric applications.

Electrostatic force microscopy with sub-piconewton resolution can now be used for the label-free identification of single dielectric nanoparticles of similar morphology but distinct low-polarizable materials. The technique can also distinguish between empty and DNA-containing virus capsids, and should be extensible to the characterization of surface and subsurface dielectric properties of nanoscale dielectrics and biological macromolecules in general.

Graphene is often referred to as the strongest material in existence. That may be so for a perfect crystal, but most graphene sheets are polycrystalline, and the grain boundaries affect their mechanical properties. A new study reveals that both the density and detailed arrangement of the defects that form the grain boundaries play a significant part in determining the strength of a polycrystalline graphene sheet.

Calcium-rich non-collagenous proteins in the extracellular matrix of bone are believed to be involved in the different steps of bone mineralization. It is now shown that in the absence of these proteins collagen can initiate and orient growing apatite crystals in vitro, and influence both their structural characteristics on the atomic scale and their larger-scale three-dimensional distribution in bone.

Tissues with perfusable vascular networks can be fabricated through layer-by-layer assembly, bioprinting or sacrificial moulding, but current approaches are slow, have limited resolution, or place significant constraints on the materials or the processing conditions. A rapid and general vascular casting approach using carbohydrate glass as a sacrificial template to generate tissues containing cylindrical networks that can be lined with endothelial cells and perfused with blood under high-pressure pulsatile flow is now reported.

Conventional methods for the selection of tumorigenic cells from cancer cell lines rely on stem-cell markers. It is now shown that soft fibrin gels promote the growth of colonies of tumorigenic cells from single cancer cells from mouse or human cancer cell lines, and that as few as ten fibrin-cultured cells can lead to the formation of tumours in mice more efficiently than marker-selected cells.

The interaction between spins in magnetic materials gives rise to a number of interesting effects. An example is the discovery of an unusual magnetic state based on a long-range ordering force between magnetic domain walls that is analogous to the interaction between protons and neutrons in atomic nuclei.

The spatial organization of porous coordination-polymer crystals into higher-order structures is critical for their integration in heterogeneous catalysts, separation systems and electrochemical devices. A method for spatially controlling the nucleation site leading to the formation of mesoscopic architecture in porous coordination polymers, in both two and three dimensions, is now demonstrated.