Volume 9 Issue 4, April 2010

Two deformation mechanisms, involving the cooperative movement of hundreds of atoms, explain the mechanical properties of complex metallic alloys.

Spin relaxation in organic materials is expected to be slow because of weak spin–orbit coupling. The effects of deuteration and coherent spin excitation show that the spin-relaxation time is actually limited by hyperfine fields.

Opening a gap in graphene is still a considerable challenge on the path towards applications. A clever solution to this problem is to exploit the preferential adsorption of hydrogen in patterns that leave narrow stretches of pure graphene in between.

By using drug-encapsulating nanoparticles as the basis for electrostatic assembly, it is possible to generate highly functional films that do double duty. These adaptable thin films can be used both for releasing the drug in a controlled fashion and for biological imaging.

β-sheet stack structures in protein crystals are held together with some of nature's weakest links: hydrogen bonds. It turns out that the size of the crystal stack makes a difference to its strength — and smaller is better.

For a Ti alloy single crystal, the stress required for deformation twinning increases dramatically as the size of the crystal decreases, until at submicrometre sizes, deformation occurs solely by dislocation motion.

Developments in electron microscopy are generating more realistic views of catalysts, allowing optimization of their structure to improve their performance.

The strong dependence of the magnetic properties on the growth conditions in (Ga, Mn)As has created the view that ferromagnetism is associated with an intrinsic inhomogeneity. Muon-spin-relaxation experiments now show that strong and homogeneous ferromagnetism is instead present in both insulating and metallic films.

The strong coupling of light and matter is responsible for phenomena such as Bose–Einstein condensation. In a study of strong-coupling effects in semiconductor microcavities, the interaction between a two-level electronic system and a light field has now been observed.

Multiferroics are promising for their ability to use an electric polarization to control magnetism and vice versa. However, ferroelastic effects during the switching of multiferroics such as BiFeO₃ destabilize the ferroelectric state. A new approach for the switching of these sorts of compound may now represent a solution to this problem.

Several routes designed to induce a bandgap opening in graphene have been proposed. It is now demonstrated that hydrogen adsorption on the Moiré pattern induced by an iridium substrate can induce a bandgap of 450 meV.

Electron transport through metal–molecule contacts greatly affects the operation of electronic devices based on organic semiconductors and single-molecule junctions, but the nature of the contact barrier remains poorly understood. Scanning tunnelling microscopy experiments reveal a significant variation on the submolecular scale, leading to a scheme to locally manipulate the potential barrier of the molecular nanocontacts with atomic precision.

As a liquid approaches its glass transition its dynamics slow down and simultaneously the material becomes more heterogeneous. A static structural heterogeneity, now shown to be widely present in glass-forming liquids, is suggested to be the origin of this dynamic heterogeneity that links structural parameters to the glass transition.

In comparison with the plastic deformation of regular crystalline materials, the mechanisms that govern complex solids with hundreds of atoms in a single unit cell are much less understood. An unusual defect mechanism in complex solids suggests the coordinated movement of hundreds of atoms, a result that improves the understanding of the deformation mechanisms in these types of material.

Controlling the magnetic properties of a materials system by electric means can lead to efficient electronic and memory devices. Now, for the first time, the control of ferromagnetism by the application of an electric voltage is demonstrated in germanium quantum dots for temperatures up to 100 K.

The origin of the effect that a magnetic field has on various electronic properties of organic semiconductors is still controversial. It is now shown that substituting hydrogen for deuterium in conducting polymers changes the response to a magnetic field substantially, proving the essential part played by hyperfine interaction in this effect.

Silicon-based lithium-ion batteries are attractive because in principle they offer higher specific capacities than conventional graphite. A hierarchical bottom-up approach is now used to prepare lithium-ion anodes with improved reversible capacities and stable electrochemical performance.

Counterintuitively, the exceptional strength of silks comes from β-sheet nanocrystals in which the key molecular interactions are weak hydrogen bonds. Simulations now show that nanoconfinement effects make β-sheet nanocrystals the size of a few nanometres stiffer, stronger and tougher than larger ones. These effects can be exploited to create materials with superior mechanical properties.