Research articles

Coherent X-ray diffraction spectroscopy has recently emerged as a powerful tool for imaging strain at the nanoscale. Developments in both fabrication and experimental techniques have now enabled all nine components of the strain tensor in a nanorod to be determined, demonstrating the ability of coherent X-ray diffraction spectroscopy to yield measurements of strain in three dimensions with a resolution of a few tens of nanometres.

One of the more promising uses of metamaterials is in imaging, where the capability to control the propagation of light could lead to new applications. In particular, the realization of a broadband metamaterial lens that has an almost complete hemispherical field of view that is focused on a flat plane represents a significant step towards such new uses.

Surfaces with physicochemical properties that can be modulated using external stimuli offer great promise for designing responsive or adaptive materials. Now, biocompatible dynamic scaffolds based on thin hydrogel coatings that reversibly hide and display surface chemical patterns in response to temperature changes have been fabricated.

Electrostatic control of spin polarization is a promising route for developing efficient spintronic devices, but is challenging for materials with a small spin–orbit interaction. It is now shown that an electric field can be used to vary the spin polarization in a silicon quantum well by exploiting the discrete nature of the energy levels. This route may work for other inorganic and organic materials.

The existence of topological conducting surfaces on insulators has been demonstrated by angular photoemission spectroscopy, but the number of transport experiments on these systems have so far been scarce. Transport evidence of topological surface states is now shown in Bi₂Se₃ nanoribbons through the observation of Aharonov–Bohm oscillations.

Surface-enhanced Raman scattering has been widely used for chemical sensing, even though the large nonlinearity of the effect makes reproducible sensing difficult. A DNA-based assembly technique now offers a means of precise engineering of gap distances in nanoparticle dumbbells for a robust surface-enhanced Raman sensing of DNA and RNA molecules.

Demagnetization in metals occurs on very different timescales depending on the material. It is now shown that electron–phonon-mediated spin scattering describes the process of demagnetization well in every case, and the differences in timescale are mainly determined by the ratio between Curie temperature and the atomic magnetic moment.

An important challenge in medicine is the efficient delivery of drugs in the body using non-toxic nanocarriers. Porous metal–organic frameworks with imaging properties are now used as nanoscale carriers for the controlled delivery of antitumour and retroviral drugs against cancer and AIDS.

Surface plasmon polaritons allow the control of light on a scale much smaller than its wavelength, and thus are important for nanophotonic applications. The demonstration of an electrical source of surface plasmon polaritons compatible with silicon electronics takes a step towards such integrated plasmonic circuits.

Chiral nematic liquid-crystal phases consist of rod-shaped molecules that have a preference to twist. However, applied fields force them to exist without the twist. Introducing particle-like twists, so called torons, using laser light relieves this frustration by facilitating the reappearance of the twist. The presence of torons could extend the use of liquid crystals in electro-optic and photonic devices.

The morphology and structure of polymer blends is central to charge-carrier, exciton and photon management in organic light-emitting diodes, transistors and solar cells. A broadly applicable approach, based on mixing a photocrosslinkable moiety into semiconducting polymers, enables the simple formation of heterostructured blends with control of morphology and structure for use in all types of device.

Metal nanoparticles with controlled composition and size are attractive candidates for heterogeneous catalysis. Now, a distillation-like process is shown to result in the synthesis of bimetallic PtRh nanoparticles with precise compositional control and high temperature stability.

Dye-sensitized solar cells are a promising technology for sustainable energy generation. Most dyes in these types of solar cell act as sensitizers for injecting electrons into n-type semiconductors. But the development of a sensitizer that can efficiently inject holes into p-type semiconductors makes possible the realization of tandem cells that could exploit the two approaches together.

Lithium-ion batteries have contributed to the commercial success of portable electronics, and should affect higher-volume applications such as plug-in hybrid electric vehicles. A fluorosulphate insertion positive electrode showing promising electrochemical performance is now reported.

Biocompatible, lithographically defined, ferromagnetic microdiscs that have a spin-vortex ground state oscillate when activated by an alternating magnetic field. This oscillation compromises the integrity of the cell membrane and initiates programmed cell death in ∼90% of cancer cells in vitro, even with a low-frequency field applied for only ten minutes.

Occasionally, organic crystalline materials contract when heated (negative thermal expansion), and the mechanisms responsible for this phenomenon are poorly understood. The arrangement of dumbbell-shaped molecules in an organic material is shown to give rise to its negative thermal expansion. The packing and intermolecular interactions facilitate a cooperative mechanical response to temperature causing a decrease in lattice dimensions.

Using a liquid gate has allowed electrically induced superconductivity in a solid specimen by means of carrier accumulation on the surface. But this phenomenon was limited to materials that became superconductors at low carrier density. It is now shown that superconductivity can be induced in a much wider range of materials by using an ionic liquid.

Liquid-crystal gel networks of neurofilament assemblies play a key part in the mechanical stability of neuronal processes, and disruptions in the networks are a hallmark of motor-neuron diseases. Under pressure, these networks are shown to undergo an abrupt transition from expanded to condensed states, with distinct mechanical properties, helping to explain possible disruption mechanisms.

The structure of magnetic nanoparticles has a strong influence on the properties of these materials at present being considered for magnetic-storage applications. It is now shown that size and shape of magnetic nanoparticles such as CoPt affect the transition from an ordered to a disordered phase, highlighting the need to take morphology into account to understand the structural properties.

Synthesizing magnetic nanostructures, which could potentially be used in spintronic applications, is quite challenging owing to the difficulty in incorporating magnetic impurities in a non-magnetic matrix. It is now shown that up to 10% Mn can be incorporated in CdSe nanoribbons by nucleation-controlled doping, giving rise to very strong magnetic effects.