Articles in 2014

A porous organic-cage molecule is shown to exhibit unprecedented performance for the separation of rare gases, with selectivity arising from a precise size match between the rare gas and the organic-cage cavity.

Many catalytic reactions exhibit oscillatory behaviour but these oscillations are not well understood for catalysts consisting of supported nanoparticles. The study of oscillatory CO oxidation catalysed by Pt nanoparticles now reveals that periodic changes in the CO oxidation are synchronous with a periodic refacetting of the Pt nanoparticles.

The performance of solar cells based on organic–inorganic perovskites strongly depends on the device architecture and processing conditions. It is now shown that solvent engineering enables the deposition of very dense perovskite layers on mesoporous titania, leading to photovoltaic devices with a high light-conversion efficiency and no hysteresis.

For high-power white-light-emitting diodes (LEDs) to become a technological reality there is a need to find more efficient red-emitting phosphor materials. Eu²⁺-doped Sr[LiAl₃N₄], a member of the nitridoaluminates compound class, is now proved to be a high-performance narrow-band red-emitting phosphor material that can be easily coupled with existing GaN-based blue-LED technology for use in white LEDs.

Peptide-based nanofibres with bioactive proteins attached can now be made such that the protein ligands are introduced in a controlled manner. This tailoring of the nanofibre’s composition enables the ratio of multiple different proteins to be highly tuned within the assemblies. By changing the protein content of the nanofibres, it is possible to adjust the antibody responses in mice to the different nanofibres.

Malignant phenotypes in the mammary epithelium have been correlated to increases in extracellular matrix stiffness. It is now shown that the effect of matrix stiffness in normal mammary epithelial cells can be offset by an increase in basement-membrane ligands and that both the stiffness and composition of the matrix are sensed by the β4 integrin. The results suggest that the relationship between matrix stiffness and composition is a more relevant predictor of breast-cancer progression.

The fracture behaviour of micro- and macroscale bone is shown to be different. In situ micropillar compression experiments on ovine bone demonstrate that microscale lamellar bone is strong and ductile, and shows no damage, whereas on the macroscale, bone shows little ductility and fails in a quasi-brittle manner.

Although several techniques have been reported to obtain electron-rich colloidal quantum dots, these materials usually suffer from poor stability under air exposure. It is now shown that the use of strongly bound ligands and a careful ligands-exchange strategy lead to air-stable n-type quantum dots that can be used in solar cells and chemical sensors.

Nanoparticle-based fluorescence imaging does not usually allow cell membrane-bound particles and intracellular particles to be distinguished from each other. Now, using functionalized silver nanoparticles as plasmonic probes, this distinction can be made following a rapid, non-toxic etching process that selectively removes the extracellular nanoparticles but leaves the intracellular nanoparticles unharmed.

Acoustic impedance-matched surfaces do not reflect incident waves. Traditional means of acoustic absorption have so far resulted in imperfect impedance matching and bulky structures, or require costly and sophisticated electrical design. Inspired by electromagnetic metamaterials, a subwavelength acoustically reflecting surface with hybrid resonances and impedance-matched to airborne sound at tunable frequencies is now demonstrated.

Perovskite oxides have attracted significant attention as energy conversion materials owing to their unique physical and electronic properties. Anion-based intercalation pseudocapacitance as well as oxygen intercalation in a nanostructured lanthanum-based perovskite (LaMnO₃) have now been exploited for fast energy storage.

Disordered photonic materials have the ability to control the flow of light through random multiple scattering. This has the drawback of randomizing both the direction and phase of the propagating light. Now, confined and interacting light modes are demonstrated for a two-dimensional disordered photonic structure.

At sufficiently low temperature, liquid water crystallizes into ices with cubic or hexagonal symmetry. A simulation study now shows that the nucleation of water into atomic stackings of cubic and hexagonal ices occurs through a metastable precursor phase with tetragonal symmetry, and that this scenario provides an explanation for the unusual pressure dependence of water’s homogeneous crystal-nucleation temperature.

Mode-selective vibrational excitations can be used to transiently induce a range of phenomena in strongly correlated states of matter. It is now shown that by exciting apical oxygen distortions in the cuprate system YBa₂Cu₃O_6.5, an unusual photoconductive effect is induced both at low and at high temperatures.

Molecular switches regulate many fundamental processes in natural and artificial systems. An electrochemical platform in which a proton carrier switches the activity of a catalyst is now presented. A hybrid bilayer membrane allows the regulation of proton transport to a Cu-based molecular oxygen reduction reaction catalyst.

Enzymes involved in copper metabolism and residing within bacterial outer layers are used to polymerize monomers bound to the bacterial cell surface. The composition of the polymers is affected by templating processes and hence the polymers are specific binding agents for the bacteria on which they are grown.

The energy interaction between different exciton species is affected by the optical environment in which they are embedded. It is now shown that mixed exciton–polariton states in strongly coupled microcavities can facilitate energy transfer between organic dyes at length scales greater than the Förster transfer radius.

Cell behaviour is in part regulated by the rigidity of their environment, yet the underlying mechanisms have remained unclear. It is now shown for breast myoepithelial cells expressing two types of integrin that rigidity sensing and adaptation can be explained by a clutch-bond model that considers the different rates of binding and unbinding between the integrins and the extracellular matrix.

Heterostructures consisting of ferromagnets and heavy metals have become a focus of interest because their strong spin–orbit coupling allows for efficient current-induced magnetization switching phenomena. Now, a magnetically doped topological insulator bilayer is shown to display a range of appealing characteristics for current-induced magnetization switching, including a significantly enhanced efficiency.

Methods to achieve large-scale production of defect-free graphene are needed to enable the commercial development of graphene-based devices. It is now shown that high-shear mixing is an effective way to exfoliate graphene and other two-dimensional materials in liquid volumes up to hundreds of litres.