Research articles

A very large Rashba-type spin splitting, which is a consequence of spin–orbit interaction, has been observed in the heavy-element semiconductor BiTeI. The results show the possibility, in principle, of using the material in spintronics devices in which the electron spin is controlled by electric currents.

A two-component nanoparticle system that communicates and enhances in vivo drug delivery and diagnostics has been devised. The system comprises ‘signalling’ nanoparticles that target tumours and then broadcast the tumour’s location to ’receiving’ nanoparticles in circulation, which carry therapeutic or diagnostic cargos, hence amplifying tumour targeting.

Nanowires have many applications across a number of disciplines. So far, their length has been largely limited to mesoscale dimensions. Through the adaption of an iterative fibre-drawing process it is now possible to fabricate millions of ordered nanowires and nanotubes of almost infinite length.

Pure spin current—the flow of spin angular momentum involving no charge movement—could lead to highly efficient spintronic devices. It is now shown that through low-resistivity magnetic tunnelling junctions it is possible to induce spin accumulation in solid-state devices one hundred times higher than previously obtained. This is the main requirement for generation of large spin currents.

Neutron scattering and first-principles calculations show that the small thermal conductivity of PbTe is due to anharmonic coupling between the acoustic phonon modes and the optical ferroelectric ones. The results provide a microscopic picture of why many good thermoelectrics are found near a ferroelectric lattice instability.

Although X-ray tomography has proven to be an efficient tool for three-dimensional imaging, its application to light materials has not been too successful. A new X-ray spectroscopy tomography method has now been developed that allows the mapping of chemical bonding in various types of structures, as well as the imaging of soft materials in three dimensions.

Materials with zero refractive index show unusual waveguiding properties and, for example, can squeeze light through narrow passages. It is now suggested that such properties can also be realized in a non-metallic photonic crystal. Furthermore, such photonic crystals can also show a Dirac point in the band structure—offering further possibilities, such as guiding waves unperturbed around bends and obstacles.

Container walls are known to have a significant influence on the dynamics of glass formation. Computations now suggest that structural order is the origin of the slower dynamics of a glass-forming liquid near container walls.

The mechanical stresses within and between cells inside an advancing cellular monolayer are mapped experimentally. Cellular migration is found to be oriented in the direction of maximum principal stress indicating that cells collectively migrate to maintain minimal local intercellular shear stress.

In contrast to the long-range order of crystalline materials, non-crystalline compounds, such as metallic glasses, have a more inhomogeneous distribution of atoms on a local scale. Atomic force acoustic microscopy now demonstrates how these local variations translate into much stronger variations in local elastic properties of a metallic glass compared with its crystalline counterpart.

Plasmonic resonances are widely used for sensing applications. The plasmon resonance of a single nanoantenna structure is now used to detect changes in the dielectric properties of a nearby palladium nanoparticle exposed to hydrogen gas, enabling highly sensitive sensing in ultrasmall volumes. The approach can be easily extended to other sensing and catalysis schemes.

Although magnetic domain walls could one day be used for information storage, the current challenges to their use are the irreproducibility of their displacement and the limits to their maximum speed. It is now shown that the Rashba effect can be used to provide a solution to both these issues.

The energy-level alignment at the heterojunction critically influences the performance of organic photovoltaic devices. It is now shown that the surface dipole moments of individual organic semiconductor films can be tuned with surface-segregated monolayers before forming bilayer solar cells by a simple film-transfer method.

Production of chemical fuels by solar energy is an attractive and sustainable solution to our energy problems. A highly active photocathode, consisting of electrodeposited cuprous oxide with platinum nanoparticles is now activated for hydrogen evolution resulting from photelectrochemical water reduction.

Chemical vapour deposition is a promising route for large-scale graphene growth. It is now shown that—through the use of seeds—high-quality, large, single-crystal domains can be grown on a patterned arrangement, and can be used to carefully study the transport across grain boundaries.

The conversion of sunlight into electricity has been dominated by photovoltaic and solar thermal power generation. A highly efficient solar to electric energy conversion device based on nanostructured thermoelectric materials and high solar concentration is now demonstrated. The results show potential for cost effective solar thermoelectric generation.

Organic materials are rarely considered for thermoelectric applications, because their low electrical conductivity limits the thermoelectric figure of merit (ZT). It is now shown that by optimizing the oxidation level in a polymer, ZT can reach 0.25, which approaches the values desirable for devices.

The production of fuels from sunlight is crucial to the development of a sustainable energy system. Although noble metals are efficient catalysts for photoelectrochemical hydrogen evolution, earth-abundant alternatives are needed for large-scale use. Bioinspired molecular clusters based on molybdenum and sulphur are now shown to produce hydrogen at rates comparable to platinum.

Active gels—such as the cytoskeleton—are out-of-equilibrium networks that self-organize in complex, dynamic patterns. The mechanisms by which dynamic structures form are, however, poorly understood. Now, a generic mechanism of structure formation, analogous to nucleation and growth in passive systems, is found in a minimal active-gel consisting of actin filaments, molecular-motor filaments and crosslinkers.

Fourier-transform infrared (FTIR) spectroscopy is a widely used spectroscopic technique, particularly for infrared wavelengths. However, for imaging applications the spatial resolution of FTIR spectrometers is restricted by the diffraction limit. The use of an FTIR spectrometer to pick up the low signal from scanning near-field optical microscopy employing thermal radiation now enables infrared imaging with nanoscale resolution.