Research articles

Solid electrolytes can improve the safety of the next generation of high-energy batteries, but they still suffer from low ionic conductivities and stability. Li₁₀GeP₂S₁₂ exhibits high lithium ionic conductivity at room temperature and should be practically advantageous with regard to device fabrication, stability and safety.

Three-dimensional photonic devices are of interest as light emitters, detectors or waveguides. However, so far their fabrication has remained a challenge. The template-directed epitaxy of three-dimensional semiconductor structures now offers a new strategy for the realization of photonic devices, demonstrated by the realization of a three-dimensional photonic crystal light-emitting diode.

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.

Acoustic rectifiers are of relevance for applications such as biomedical ultrasound imaging. In these systems, amplification increases gradually with signal amplitude. A new approach based on bifurcation in chaotic systems now enables a sharp switching between rectification states that could be used in nonlinear acoustic devices.

The combined magnetic and thermoelectric properties of nanostructures have recently attracted considerable attention. It is now demonstrated that the Seebeck coefficient in a magnetic tunnelling junction is strongly dependent on the magnetic configuration.

Graphite remains stable at pressures higher than those of its equilibrium coexistence with diamond. This has proved hard to explain, owing to the difficulty in simulating the transition with accuracy. Ab initio calculations using a trained neural-network potential now show that the stability of graphite and the direct transformation of graphite to diamond can be accounted for by a nucleation mechanism.

The energy and power density of lithium-ion batteries depends to a large extent on storing lithium by incorporation in the crystal structure of the cathode. The reason that LiFePo₄ functions as a cathode at a reasonable rate is now explained theoretically by the availability of a single phase-transformation path at low overpotential.

Typically, the light-emission of semiconductors always occurs from thermalized electrons, as electrons excited above the bandgap energy relax quickly. In contrast, non-thermalized excitonic light emission has now been observed in nanowires using resonant plasmonic nanocavities. The much higher radiative light-emission rates of the hot excitons suggest their use for ultrafast nanophotonic devices.

The in vivo optical detection of bacterial infections requires highly specific imaging probes with small affinity to mammalian tissue. It is now shown that fluorescent dyes that are conjugated to maltohexaose can be internalized rapidly via the bacteria-specific maltodextrin transport pathway, enabling the in vivo imaging of Escherichia coli down to 10⁵ colony-forming units.

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

The low-temperature solution growth of ZnO nanostructures could enable the bottom-up fabrication of integrated electronic devices, but controlling their morphology has been challenging. It is now shown that the geometry of hydrothermally synthesised ZnO nanowires can be tuned precisely if the growth of selected crystal faces is inhibited by the competitive adsorption of non-zinc ions.

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.

Spin current, that is, the flow of angular momentum without charge transfer, may be used in efficient spintronics devices. One problem is that spin current tends to decrease, owing to spin–orbit interaction. It is now shown that through interaction with spin waves it is possible to reverse this effect and enhance the spin current back.

Spin injection from a magnetic electrode into the non-magnetic active element of a spintronics device is seriously hampered by the impedance mismatch between the two materials. One common solution is to use high-quality tunnel barriers. An alternative strategy is now demonstrated through spin pumping based on dynamical spin exchange.

The electronic properties of inorganic devices such as memristors can be used to simulate neurological behaviour. In particular, ionic and electronic effects in a silver sulphide device are now shown to mimic short- and long-term synaptic functions.

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.

In macroscopic spin valves, the current between two magnetic electrodes can be tuned by external magnetic fields. Here, a molecular-scale spin valve is demonstrated in which a single-molecule magnet, through its localized magnetic moment, modulates the conductance of a single-walled carbon nanotube quantum dot with magnetoresistance ratios reaching 300%.

Polymer electrolyte membranes selectively transport ions and polar molecules, and are of interest for applications such as polymeric batteries, fuel cells, mechanical actuators and water purification. Transport anisotropy is now shown to linearly depend on the degree of alignment, indicating that membrane stretching only causes domain reorientation without affecting channel dimensions or defect structure.

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.