Volume 10 Issue 12, December 2011

Combining the efforts of physicists, materials scientists, economists and resource-strategy researchers opens up an interdisciplinary route enabling the substitution of rare elements by more abundant ones, serving as a guideline for the development of novel materials.

An efficient scheme that realizes broad tunability of photon upconversion in core–shell nanoparticles may lead to applications in biosensing, security labelling and more.

The search for the metallic state of hydrogen at ever higher static pressures has normally required experiments to be performed at temperatures near 100 K. Now, some 30 years after the first attempts at room-temperature compression, the observation of reflective dense hydrogen promises to bring it in from the cold.

The synthesis of a family of plate-like semiconductor nanocrystals yields solutions of small quantum wells with excellent optical properties.

Elastic thin films attached to a foundation under compression develop wrinkles, which in turn can generate invaginated folds. Hierarchical patterns of localized folds have now been observed in thin films under biaxial compression, which show intriguing resemblance to fracture patterns in drying pastes and to venation networks in leaves.

Although heterogeneous photocatalysts for converting solar to chemical energy are mostly semiconductors, metallic plasmonic nanostructures have started to attract interest. Recent progress on plasmon-enhanced, water-splitting composite photocatalysts and photocatalytic reactions on the surface of plasmonic nanostructures of noble metals are now reviewed.

Oxide nanoprecipitates with typical sizes of smaller than five nanometres have been known to considerably enhance the mechanical properties of steel. An atomic-scale characterization is now able to directly verify the crystal structure of these stable oxide nanoclusters.

Molecular hydrogen is expected to display metallic properties under high pressures, but so far experiments performed at low temperatures ( 100 K) have showed that hydrogen remains insulating up to 300 GPa. A transformation of normal molecular hydrogen to a conductive and metallic state at room temperature is now observed above 220 GPa.

Iron-based superconductors all share the same building blocks. So why do local magnetic properties vary from one compound to another? A new theoretical model explains the variation in physical properties and links it to the structural differences, providing a description for a wide range of materials.

Semiconductor nanocrystals have for many years attracted attention for their optical properties and their potential use as superior fluorescence emitters. It is now shown that nanoplatelets can be controllably synthesized and have even more attractive properties.

Conjugated polymers are applied widely in organic optoelectronic devices. The performance of these devices depends critically on polymer morphology, which can be modified by solvent vapour annealing. This process has now been controlled on mesoscopic length scales, bridging the gap between single-molecule and bulk studies, and revealing long-range energy transport in ordered polymer aggregates.

Secondary batteries using organic electrode-active materials promise to surpass present lithium-ion batteries in terms of safety and price. Organic molecules with degenerate molecular orbitals as electrode-active materials are now used in high-capacity organic batteries exceeding 300 A h kg⁻¹.

It is shown that an elastic film on a viscoelastic substrate under biaxial compressive stress forms a hierarchical network of folds generated by repetitive wrinkle-to-fold transitions. The morphology of the hierarchical patterns can be controlled by modifying the geometry and boundary conditions of the membrane.

It is easy to imagine that carbon nanotubes deform under strain, but the microscopic mechanism of deformation is difficult to relate to the large-scale one. Through aberration-corrected transmission microscopy the atomic displacement under bending is now mapped out, revealing unexpected details.

The close relationship between crystal structure and electric polarization in ferroelectrics means that strain strongly influences their properties. The demonstration of how strain gradients leading to a higher-order effect, flexoelectricity, can be used to rotate electric polarization in thin films indicates new ways of controlling piezoelectricity by purely mechanical means.

Nonlinear optical upconversion processes in nanoparticles, which convert long-wavelength light into short-wavelength emission, are promising for applications such as biological imaging, optical data storage and others. The flexible tuning of upconversion properties in core–shell nanoparticles now offers unprecedented control over the nonlinear optical properties of the nanoparticles.

Inorganic nanocrystals are attractive materials for solar-cell applications. However, their performance is often limited by an insufficient alignment of internal energy levels. A tuning of these energy levels has now been achieved by attaching two different molecules to a single nanocrystal, which significantly alters its electronic and optoelectronic properties.

An electrochemical method that uses ion-selective membranes to electrically modulate ion concentrations in situ along a sciatic nerve in vitro allows for on-demand reversible inhibition of signal propagation as well as up to 40% reduction of the electrical threshold for stimulation. The method may be applicable in implantable neuroprosthetic devices.