Research articles

The frictional properties of a two-dimensional colloidal crystal reveal that excitations known as kinks and antikinks form when the crystal is dragged along a solid surface. This phenomenon, which was predicted previously but never observed, demonstrates the potential of using colloidal crystals to study frictional properties that are otherwise difficult to characterize.

Magnons are quanta of spin-wave excitations and are likely to play a major role in the physical mechanisms of combining spin and heat transport. Now, a new device that enables the properties of magnons to be measured independently of the thermoelectric contribution of electrons and phonons is shown, providing crucial information for understanding the physics of electron–magnon interactions, magnon dynamics and thermal spin transport.

Electrochemical oxidation of metals produces anodic oxides with highly regular arrangements of pores; however, the mechanisms of pore initiation and self-ordering are not well understood. Now, a quantitative analysis method is proposed that examines the roles of oxide dissolution and ionic conduction in the morphological stability of anodic oxide films.

The coherence lifetime of a material system to be used in quantum information protocols has to be long enough for several quantum operations to occur before the system loses its quantum coherence. The spins of impurities in silicon have been shown to have coherence lifetimes up to tens of milliseconds, but now all records are beaten with those in high-purity silicon reaching a few seconds.

Colloidal particles adsorbed at liquid interfaces are commonly assumed to be at equilibrium, but holographic microscopy experiments now reveal that microspheres bound to a water/oil interface may take months to equilibrate. The observed ageing dynamics agree with a model of thermally activated hopping of the particle/interface contact line over nanoscale surface defects, and have implications for understanding the interactions between adsorbed colloidal particles.

Many synthetic polymer nanoparticles used for non-viral gene delivery contain excess cations on their surface, which makes the particles cytotoxic and the delivery of genes inefficient. Terpolymers with a low charge density, high molecular weight and increased hydrophobicity are now shown to have minimal toxicity, and to efficiently deliver the apoptosis-inducing TRAIL gene to transplanted tumours in mice.

Photonic devices on silicon offer the benefit of combining advanced electronic functionality with the high bandwidth of silicon photonics. Now, efficient second-order nonlinear activity in silicon waveguides strained by a silicon nitride top layer considerably advances the potential of all-optical data management on a silicon platform.

A key step in fuel-cell energy-conversion processes is electro-oxidation of the fuel at the anode, but ways to improve electrocatalytic activity remain unclear. Using ceria–metal structures, H₂-oxidation reactions are shown to be dominated by electrocatalysis at the oxide/gas interface with minimal contributions from the oxide/metal/gas triple-phase boundaries.

Vesicles can rupture as a result of an imbalance in osmotic pressure between their inside and the exterior. Such an ‘osmotic shock’ has now been multiplexed in a coordinated fashion within an ordered material in which a minor component swells and ruptures, thus leading to a porous bicontinuous structure. Such perforated ordered materials may find applications in photonics, optoelectronics and nanofiltration.

The relay mechanism in which hydrogen atom transfer occurs along hydrogen bonds plays a crucial role in many functional compounds. Using a scanning tunnelling microscope, the transfer of hydrogen atoms along hydrogen-bonded chains assembled on a Cu(110) surface is shown to be controllable and reversible.

A local atom probe has been used to study the transport properties of graphene, revealing the different effects of surface steps and changes in layer thickness on substrates. Understanding the details of the defect-induced degradation of transport properties is essential for improving the efficiency of devices.

Highly monodisperse silver polyhedral nanocrystals passivated with polymers are shown to behave as quasi-hard particles that self-assemble by sedimentation into millimetre-sized supercrystals, which correspond to the particles' three-dimensional densest packings. Monte Carlo simulations confirm the observed self-assembled structures, including an exotic structure for octahedra that is stabilized by depletion forces induced by an excess of polymer in solution.

One of the interesting features of graphene is that its properties change with the number of layers. A procedure to create monolithic devices with elements made out of different numbers of graphene layers is now shown, and a practical demonstration of this method is given by realizing transistor arrays with chemical-sensing functionalities.

Persistent phosphors are known from applications such as night-vision goggles where they produce a characteristic green afterglow. The discovery of persistent phosphors that instead operate at near-infrared wavelengths with much longer afterglows may now enable new applications in night-vision surveillance and in bio-imaging.

Molecular hydrogen is expected to display metallic properties under high pressures, but so far experiments performed at low temperatures ( 100 K) have showed that hydrogen remains insulating up to 300 GPa. A transformation of normal molecular hydrogen to a conductive and metallic state at room temperature is now observed above 220 GPa.

Metamaterials are widely studied for their optical properties offering applications such as perfect lenses or cloaking. As is now shown, the interaction between the individual elements of metamaterials can also be used to design magnetoelastic metamaterials, which are able to change their structure in response to light.

The possibility of controlling magnetization by spin-polarized current could lead to devices more energy-efficient than traditional ones using external magnetic fields. Now, an even more efficient method has been demonstrated by using electric-field pulses to switch the magnetization in FeCo magnetic cells.

The possibility of controlling magnetization by spin-polarized current could lead to devices more energy-efficient than traditional ones using external magnetic fields. Now, an even more efficient method has been demonstrated by using electric-field pulses to switch the magnetization in a CoFeB/MgO/CoFeB magnetic tunnelling junction.

Plasmonic nanostructures are known to be an attractive platform for highly sensitive molecular sensors, although they often lack specificity. A plasmonic device with a sharp optical resonance tuned to biomolecules selectively captured on the surface of the device now offers a versatile yet highly specific platform for molecular sensing.

Polymer-based bulk-heterojunction solar cells have shown some of the highest photoconversion efficiencies in organic photovoltaics, but polymer polydispersity impacts their performance. A small-molecule donor is now reported that enables the fabrication of bulk-heterojunction devices with low acceptor content and photoconversion efficiencies of up to 6.7%.