Volume 10 Issue 9, September 2011

Versatile room-temperature control of spin currents without a net charge flow paves the way for new methods to transfer and process information.

The solvent-based electrolytes used at present in lithium-ion batteries can be unsafe for large-scale applications. A crystalline electrolyte with high ionic conductivity could soon enable all-solid energy storage systems.

Single-walled carbon nanotubes have been used as test tubes for chemical reactions in an electron microscope. It is now shown that they can also act as reactors for the synthesis of narrow, helically twisted graphene nanoribbons through electron irradiation of functionalized fullerenes.

The coarsening mechanism, by which larger droplets in a solid-state matrix consume smaller ones, can effectively be reversed in the case of core–shell precipitates, leading to a nearly monodisperse droplet size distribution.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.