Volume 12 Issue 1, January 2013

Excitation of organic donor–acceptor systems with high-energy light can produce hot charge-transfer states that are delocalized across the heterojunction and readily dissociate. Two studies now reveal the dynamics of this process and pave the way towards unravelling the details of the molecular landscape that favours fast photocarrier generation.

The evolution of microcrack damage in materials under hostile thermal and mechanical conditions has now been imaged in three dimensions by real-time in situ X-ray microtomography.

Measurements of heat transport across polished nanoscale contacts formed between the tip of a scanning thermal microscope and a surface support the notion that their true contact area consists of discrete atomic contact points.

The magnetocaloric effect could form the basis for efficient refrigeration technologies. The finding that large and reversible magnetocaloric effects can be induced through a strain-mediated feedback mechanism may expand the range of available magnetocaloric materials.

Three-dimensional ordering in liquid-crystalline polymers is induced by the photopolymerization of a mixture of mesogens sandwiched between two patterned substrates. By incorporating an infrared-sensitive dye in the mixture, polymer films that undergo reversible shape deformations on heating are formed.

Altering the composition of the spacer layers present in iron-based superconductors is one strategy for increasing the temperature below which they superconduct. Now, intercalating FeSe with molecular spacer layers is also shown to enhance the superconducting transition temperature.

Optical coatings usually consist of many multilayers of thin films to achieve the desired properties. A new approach using interference effects between an absorbing dielectric film and a metallic substrate now enables ultrathin optical coatings that could also find applications as thin solar cells or photodetectors.

Metamaterials offer a unique potential to guide the propagation of light. However, existing designs of devices such as invisibility cloaks require a restrictive range of materials parameters for their realization. A new approach to cloak devices now lifts such restrictions allowing for a greater flexibility in device design.

The standard picture of organic photovoltaics predicts that excitons, which are created under light irradiation, thermalize before dissociation into free electrons and holes. Experimental results and calculations on a low-bandgap polymer–fullerene blend now illustrate the dynamics of hot charge-transfer states and their contribution to charge generation in bulk heterojunctions.

Supported metal nanoparticles play a pivotal role in areas such as nanoelectronics, energy storage and conversion, and catalysis, but their tendency to grow into larger crystallites is an issue for their stable performance. A strategy based on controlling not only size and composition but also the location of the metal nanoparticles, now reveals the impact of their three-dimensional nanospatial distribution on their catalytic stability.

Gathering information on the evolution of small cracks in ceramic matrix composites used in hostile environments such as in gas turbines and hypersonic flights has been a challenge. It is now shown that sequences of microcrack damage in ceramic composites under load at temperatures up to 1,750 °C can be fully resolved with the use of in situ synchrotron X-ray computed microtomography.

The properties of the insulating ground state from which the superconductivity of copper oxide materials emerges with chemical doping are a topic of extensive research. The observation that superconducting fluctuations are quenched by charge order at low temperatures now provides valuable information on the mechanism for the superconducting to insulator transition.

The thermodynamic properties of magnetocaloric materials show significant promise for energy-efficient cooling applications. The demonstration that large and reversible magnetocaloric effects can be created by means of strain suggests a new approach for inducing them in other magnetic materials.

The effect of nanoscale surface roughness on heat transport across solid interfaces has remained contentious. Now, measurements of the pressure dependence of heat transport across polished nanoscale contacts formed between the tip of a scanning thermal microscope and a surface agree with a model that assumes quantum thermal transport across individual contact points.

Photocurrent generation in organic solar cells relies on the dissociation of excitons into free electrons and holes at donor/acceptor heterointerfaces. Femtosecond spectroscopy and non-adiabatic simulations on the phthalocyanine–fullerene model system now reveal the relaxation dynamics of hot charge-transfer excitons in this process.

Layered oxides are important as electrode materials for batteries and because of the strong electronic correlations resulting from their unique structure. Electrochemical investigations of the layered P2-Na_xVO₂ system in sodium batteries together with in situ X-ray diffraction experiments now result in the elucidation of the room-temperature phase diagram of this system.

Enhancing and optimizing the performance and durability of nanocatalysts for the oxygen reduction reaction is crucial for fuel-cell applications. A class of Pt–Co nanocatalysts consisting of ordered Pt₃Co intermetallic cores with a 2–3 atomic-layer-thick platinum shell now exhibit a large increase in mass activity and specific activity when compared with disordered alloy nanoparticles.