Letters

Understanding how heat is transferred across interfaces is important for the efficiency of micro- and nanoscale electronic devices. Here, it is shown that there is a direct link between the bonding character of an interface and the thermal transport across it.

The substitution of oxygen by hydride anions in oxide materials to form oxyhydrides has been difficult to achieve because it requires highly reducing conditions without transferring an electron from the hydride. An oxyhydride of BaTiO₃ that is electronically conducting, stable in air and water at ambient conditions, and exchangeable with hydrogen gas at 400 °C, has now been prepared.

Ultrafast and intense optical pulses have been used to study spin-density-waves in pnictide compounds, which are known to exhibit unconventional superconductivity. The results show that the magnetic order follows lattice motion, which suggests that a spin–phonon coupling may play an important role in the formation of spin-density-waves and superconductivity.

Electromagnetic waves propagating on the surface of materials are used in a variety of applications such as on-chip photonics. The demonstration now of a nearly 100% efficient coupling of these surface waves to freely propagating waves promises to improve photonic applications such as surface–plasmon couplers, antireflection coatings and many more.

The maximum imaging resolution in classical optics is limited to approximately the wavelength of light used, and subwavelength resolution can only be achieved by advanced imaging schemes. The appeal of the super-oscillatory lens optical microscope described here is that it enables subwavelength imaging with, in principle, unlimited resolution using a modified conventional microscope.

Even though phase-change materials are used in optical as well as electronic information storage applications, some issues, such as their fast crystallization kinetics, remain poorly understood. The use of ultrafast differential scanning calorimetry now reveals that the fast kinetics is based on properties similar to those of fragile liquids.

A common route to obtain efficient thermoelectrics is to optimize the ratio between electrical and thermal conductivity. Typically, materials with a complex, glass-like phonon structure and therefore a very low thermal conductivity are studied. Now, a route showing that solid ions in a liquid-like state can have a low enough thermal conductivity to compete with the best existing thermoelectrics is proposed.

Although the superior electrochemical performance of supercapacitors capable of rapidly storing electrical energy is due to reversible ion adsorption in porous carbon electrodes, the molecular origin of this phenomenon is still poorly understood. A quantitative picture of the structure of an ionic liquid adsorbed inside realistically modelled microporous carbon electrodes is now proposed.

Magnetic tunnel junctions play an important role in controlling electron spin in spintronic devices. The reversible, remanent switching of electron-spin polarization in multiferroic tunnel junctions now enables significant technological possibilities for spin electronics.

The slow decay of photoconductivity in amorphous oxide semiconductors hampers their use in photosensor arrays with viable frame rates. A gated sensor architecture now provides direct control over the Fermi-level position in the semiconductor layer, and eliminates persistent photoconductivity by accelerating electron recombination with ionized oxygen vacancy sites.

Oxide materials show a versatile range of phenomena that in many cases can be controlled by growing thin films of oxides next to each other. The observation now that electrical conductance of domain walls in a ferroelectric can be tuned simply through the domain-wall orientation offers a flexible way of controlling functionality in complex oxides.

siRNA delivery has so far been hampered by carriers that inefficiently encapsulate RNA, and by its degradation prior to cellular uptake. Now, self-assembled crystalline microsponges consisting solely of cleavable RNA strands — which are converted to siRNA only after cellular uptake — achieve, with three orders of magnitude lower concentration, the same degree of gene silencing as conventional siRNA nanocarriers.

The observation of a superconductive current flowing through a topological insulator is considered the first step towards the observation of the elusive Majorana fermions. This is now achieved in a superconductor/topological insulator/superconductor junction in which direct evidence of Josephson supercurrents is reported.

The development of reliable diagnostic tools to investigate the performance of a battery in situ is required at present. Techniques based on magnetic resonance imaging are now shown to be able to non-invasively visualize and characterize the changes occurring in Li-ion battery electrodes and electrolyte.

Raman spectroscopy has already proved to be a powerful tool for studying the properties of single graphene layers. It is now shown that this technique can also provide information on the interaction between graphene sheets in multilayered graphene structures. In particular, a Raman peak corresponding to the interlayer shear mode, and probably linked to the interlayer coupling, is unveiled.

The large-scale synthesis of single-walled carbon nanotubes (SWCNTs) with controlled chirality—which could find applications in fields such as electronics—remains a great challenge. It is now shown that the growth rates of SWCNTs are directly proportional to their chiral angles, suggesting a route towards selective synthesis based on kinetic control.

Lumped elements such as resistors, capacitors and inductors play a crucial role in electronic circuits. Now, inspired by metamaterials technology, the experimental realization of lumped circuit elements for optical frequencies provides a standardized platform for applications such as mixing and multiplexing of optical signals.

Interfaces between insulating oxides have revealed exotic electronic and magnetic properties. It is now shown that a complex magnetic structure can emerge in an oxide superlattice, and that specific interfaces can unexpectedly exhibit exchange bias. The observations reveal the induction of antiferromagnetism in a material that is usually paramagnetic.

It is demonstrated that graphene coatings do not alter the wetting behaviour of copper, gold or silicon surfaces. Such wetting transparency—shown to occur only for surfaces where surface–water interactions are dominated by van der Waals forces—and graphene’s ability to suppress copper oxidation result in a 30–40% increase in condensation heat transfer on copper. The findings have implications for graphene-based coatings with independently tunable electronic and wetting properties.

Among other exotic properties graphene exhibits the highest thermal conductivity observed so far. This is true at least for graphene composed of only ¹²C atoms. However, it is now shown experimentally that regions of ¹³C atoms can substantially reduce the thermal conductivity. Aside from their fundamental importance, these results suggest that thermal conductivity can be tailored by varying the relative amounts of carbon isotopes used.