Research articles

A new type of scanning electron microscope with aberration correction allows a resolution of 0.1 nm. The instrument also allows for simultaneous imaging of atoms on the surface and in the bulk of a sample, which represents a real breakthrough in the field.

Although much effort has been directed towards the separation of single-walled carbon nanotube mixtures, chiral-selective growth is required for scalable production and applications. The chiral distribution of carbon nanotubes can now be altered by varying the composition of nickel–iron nanocatalysts.

The interfacial energy between a macroscopic surface consisting of different materials and a liquid is independent of the surface structure. It is now shown that because of the way in which a multicomponent nanoscale surface affects the solvent–molecule arrangement, it is both the surface structure and composition that dictate the interfacial energy.

The magnetic-field-induced strain in magnetic shape-memory alloys can be used in several types of application. However, the strain is high (10%) only in single-crystalline specimens, which are difficult and expensive to obtain. Polycrystalline samples with comparable strain have now been fabricated by introducing pores of similar size to the grains.

When a tip slides on a carbon nanotube, the friction along the transverse direction is much larger than in the parallel direction. It is shown that this behaviour is due to hindered rolling of the tube, and a frictional dissipation that is negligible for a tip sliding along the axis.

The performance of hybrid solar cells depends critically on the morphology of both the polymeric and the inorganic components. Electron tomography is used to resolve the morphology in three dimensions; coupling this information with three-dimensional exciton-diffusion studies enables the differentiation of charge generation and transport as performance-limiting factors.

Anhydrous proton-conducting materials capable of operating at high temperature are required for fuel-cell applications. Encapsulation of a proton-carrier imidazole molecule in aluminium porous coordination polymers in anhydrous conditions results in high proton conductivity above 100 ^∘C.

High pressures have been very useful in stabilizing materials that cannot form at low pressure. However, often high-pressure phases are not stable when recovered in ambient conditions. Bombardment with high-energy heavy ions is now shown to stabilize a high-pressure phase of Gd₂Zr₂O₇ in ambient conditions.

Controlled domain formation in block copolymer mixtures or lipid bilayers could lead to more highly ordered assemblies and delivery of drugs. It is now shown that mesoscale domain formation within assembled mixtures of neutral and anionic polymer amphiphiles can be induced by the divalent cations calcium and copper.

Controlling the magnetic properties by using an electric field is a promising route towards spintronics or magnetic data storage applications. Using dicobaltocene as a test case, it is now demonstrated theoretically that an electrostatic potential can be used to control the spin states in molecules.

The ability to replace surface hydrogen by multivalent atoms to form semiconductors with tailored properties is critical for microelectronic applications. The mechanistic pathway involved in the nitridation of H-terminated silicon surfaces using ammonia vapour is now explained.

Quantum cascade lasers are only one of several applications that could take advantage of the discrete nature of the energy levels in semiconductor quantum dots. It is now shown that the relaxation time between levels is highly sensitive to their energy separation. This knowledge will be essential for the design and optimization of actual devices.

In conventional metals, strong interactions between electrons and the atomic lattice, so-called polarons, often render metals electrically insulating. In the rare case of polaronic metals, however, polaronic properties survive even in the metallic state. Neutron-scattering experiments now reveal that it is through quantum fluctuations that polarons manifest their presence in these enigmatic materials.

Biopatterning, which enables regulation of cell–material interaction, is usually achieved by techniques that rely on physical contact, which can seriously damage cells. A simple and efficient non-contact technique is now demonstrated using an aqueous two-phase polymer system.

Surfaces have an important role in solid–liquid phase transformations, but whereas melting is normally observed at surfaces, freezing usually originates in the bulk. Computational studies now predict surface-induced nucleation in supercooled liquid silicon and germanium, and the proposed nucleation mechanism could prove to be relevant for other tetrahedrally coordinated systems.

Fabricating defect-free three-dimensional photonic crystals over a large area is a challenge that has impeded advances in this field. The development of an etching process for creating such crystals from silicon may therefore allow a broader use of these photonic structures.

Luminescent materials are widely used for imaging and sensing because of their high sensitivity and rapid response. A strategy for modulating dual emission for radiometric sensing in a single component is now shown to enable tumour hypoxia imaging.

Many proteins have buried active sites in their folded states, which are only exposed when the protein is stretched. On mimicking this process with a combination of enzymes buried in polyelectrolyte layers on a silicone sheet, it is shown that enzymatic catalysis is possible only when the substrate is stretched to expose the enzymes, which enables reversible control of reaction progression.

The diffusion of atoms in a solid is essential to many of its properties. However, imaging atomic diffusion has been a difficult task. The development of a technique that allows direct time-resolved imaging of atomic diffusion with coherent X-rays may therefore allow a broader study of this process on the atomic scale.

Creating laboratory-grown bone for implantation into injury sites is an aim of regenerative medicine. However, newly grown bone may not have the same structural and compositional properties as native bone. Materials characterization shows that the source of cells for the new bone growth has a significant effect on its properties.