Research articles

Using optical antennas in optoelectronic devices could lead to improved device performance. Photoemission from the inner core of core–shell single-walled nanotube structures where the optical bandgap of the core is smaller than that of the outer shells demonstrates that these structures channel excitons thereby acting as optical concentrators.

The selective reaction of one part of a bifunctional molecule is a fundamental challenge in heterogeneous catalysis. Modifying a supported palladium catalyst with alkanethiol self-assembled monolayers is now shown to increase selectivity for the hydrogenation of 1-epoxy-3-butane to 1-epoxybutane.

Biochemical assays that use magnetic beads are at present in frequent use. Colour-barcoded magnetic microparticles have now been created without using multiple pigmentations. The coding capacity far exceeds that of alternative spectral encoding systems and is demonstrated in a practical bioassay for DNA detection and identification.

Measuring charge transport on the surface of an organic semiconductor crystal in field-effect transistors is difficult. Now solution-processed thin films have been used in a field-effect transistor allowing spectroscopic characterization of the carrier over a large temperature range. The measurements provide information on the nonlinear transport properties observed at low temperatures.

Graphene films are usually made from domains with different orientations. How does this affect transport? A theory of charge transmission through graphene grain boundaries now predicts two distinct transport behaviours depending on the grain-boundary structure. The results could provide important information for the design of efficient graphene-based electronic devices.

Structure–property relationships between material properties and stem cell behaviour are investigated using high-throughput methods. The data identify the optimal substrates within a range of different polymeric surfaces to support the growth and self-renewal of human embryonic stem cells from fully dissociated single cells.

Single phosphorus dopants in silicon are one of the physical systems that could be used for quantum information technology. It is now shown that bismuth dopants have similar properties to their phosphorus counterparts, and could offer even more possibilities for quantum information applications.

Terahertz emitters, such as quantum cascade lasers (QCLs), are of interest for applications in imaging and sensing. Nevertheless, performance problems such as power out-coupling efficiency have limited their technological potential. However, a study now shows that subwavelength surface patterning of terahertz QCLs leads to significantly enhanced beam collimation and power collection efficiency.

Only few magnetoelectric materials, where magnetism and ferroelectricity are coupled, are known to exist at room temperature, and in most cases the magnetoelectric coupling is weak. The discovery of strong room-temperature magnetoelectric coupling in Sr₃Co₂Fe₂₄O₄₁ at low magnetic fields is therefore a significant advance towards the practical application of multiferroics.

The mixing of metals to form alloys with enhanced properties has been known at least since the Bronze Age, although being able to predict their properties remains difficult. An analytical model using computational input is now able to quantitatively predict the mechanical properties of metal yield stress in solute-strengthened alloys.

The amorphous nature of metallic glasses makes them interesting for structural applications. However, the interplay between the nature of atomic structures and mechanical properties remains poorly understood. Dynamic micropillar tests now show the important contribution of the inelastic deformation of atomistic free-volume zones to the deformation behaviour of metallic glasses.

Nanoscale porous materials show unique properties that can be important for catalytic, separation and gas-storage applications. A strategy to yield crystalline porous compounds decorated with reactive nitrenes that can chemically trap and convert guest molecules by light stimulation is now reported.

Synthetic solid-state nanopores are of interest at present for their use as single-molecule sensors for characterization and detection of biomolecules. By using self-assembly evaporation and atomic-layer deposition, kinked silica nanopores are shown to exhibit reduction in DNA-translocation velocity and selectivity.

The detailed mechanism of the pH-dependent quenching of semiconductor quantum-dot/dopamine conjugates, confirming quinone as the electron acceptor in the process, is now reported. This electrochemical knowledge of the bioconjugate system is used for the in vitro detection of drug-induced intracellular pH changes.

The conversion of solar energy into electricity usually occurs either electrically or through thermal conversion. A new mechanism, photon-enhanced thermionic emission, which combines electric as well as thermal conversion mechanisms, is now shown to lead to enhanced conversion efficiencies that potentially could even exceed the theoretical limits of conventional photovoltaic cells.

In magnetoelectric compounds, magnetism and ferroelectricity are coupled. The observation of light-induced size changes in the room-temperature magnetoelectric BiFeO₃ now adds optical functionality to magnetoelectric devices that may lead to new applications arising from the coupling of light, electric and magnetic fields.

The control of magnetization by electric fields is important for applications in data storage and sensing. An efficient control of exchange bias by electric fields has now been achieved in thin-film devices in which a ferroelectric antiferromagnet is coupled to a ferromagnet.

Although density functional theory is widely used in surface science, it has a tendency to predict surfaces to be more stable than they actually are experimentally. Using a many-electron approach such as the random-phase approximation enables accurate surface and adsorption energies for carbon monoxide and benzene on metal surfaces to be determined.

Friction between two surfaces is usually studied at low relative sliding speeds. A molecular dynamics study now explores friction at high speeds, showing the emergence of a ballistic friction regime, qualitatively different from standard drift friction. The findings might have important implications for applications in nanoelectromechanical systems.

Regardless of what the origin of superconductivity is in the recently discovered iron-based superconductor, it would be useful to know how good these materials are for applications. Sophisticated experiments now show that SmFeAs_0.75F_0.25 exhibits a high and nearly isotropic critical current, a potentially important result for their use in applications.