Volume 7 Issue 12, December 2008

Does the high-temperature superconductivity observed in the newly discovered iron pnictides represent another example of the same essential physics responsible for superconductivity in the cuprates, or does it embody a new mechanism?

Externally applied pressure induces superconductivity in the layer compound 1T-TaS₂. Similarities to, and differences from, other superconducting systems promise exciting future experiments on this old, but suddenly rejuvenated, compound.

The durability of glasses and minerals in water has traditionally been predicted using models that ignore the molecular details. Now the surface structure dynamics are shown to play an integral role in their aqueous corrosion.

Accordion-like honeycomb scaffolds support the formation of anisotropically contracting heart tissue in vitro, opening up possibilities in the area of cardiac tissue repair.

The tube model can explain how mutually entangled polymer chains move and interact, but it relies on the loose ends of chains to generate relaxation. Ring polymers have no ends — so how do they relax?

Nanocrystalline materials usually exhibit high strength and their deformation caused by stress is limited. Nanocrystalline CdS with spherical and hierarchical shell geometry is shown not only to withstand extreme stresses, but also to deform considerably before failure.

According to a neutron-scattering study of the structural and magnetic properties of the pnictide CeFeAsO_1−xF_x, the phase diagram of this material shows considerable similarities with the high-T_c cuprate superconductors. These results are an important addition to the effort to find out where superconductivity in these iron–arsenic alloys arises.

Superconductivity is a complex and fascinating phenomenon, made more so by its coexistence with other collective electronic states. A study of the layered compound 1T-TaS₂ under pressure enables the various states of the material to be investigated and compared with other commonly studied layered superconductors.

Carbon-based structures are being intensively investigated for their use in electronic devices. A pronounced non-volatile switching is now observed in two-terminal devices made from graphitic sheets. The highly reliable switching mechanism is explained by the local breaking and rejoining of atomic bonds in the sheets.

Phase-change materials are widely used as non-volatile memories, for example in optical data storage, but the search for improved phase-change materials has proved difficult. Based on a fundamental understanding of their bonding characteristics, a systematic prediction of phase-change properties has now become possible.

Understanding the corrosion mechanism of aqueous silicate glass is crucial for the long-term durability of nuclear waste glasses. This mechanism is generally thought to be associated with chemical affinity, but it is now demonstrated that morphological transformations also have an important role in the leaching kinetics of these glasses.

Zeolite nanocrystals with three-dimensionally ordered mesoporous structures are important for designing molecularly accessible and selective catalysts. With a single zeolite synthesis procedure, uniform nanocrystals and crystal zeolites with ordered imprinted mesoporosity can now be obtained.

Nanomaterials are effective catalysts for many chemical reactions, however, their catalytic properties are most often determined by ensembles of nanoparticles, and so far only averaged results have been measured. Now, the heterogeneous reactivity and the surface structure dynamics of individual gold nanoparticles are revealed by monitoring single fluorogenic reactions.

How do entangled polymer rings relax? Linear polymers can ease their stress because their chains have ends, but cyclic polymers do not. Even trace amounts of linear chains dominate the mechanical properties if present as impurities. Investigation of carefully purified ring polymers reveals they exhibit self-similar dynamics and a power-law stress relaxation.

Construction of tissue-engineering scaffolds that mimic cardiac anisotropy is a challenge. Now, accordion-like honeycomb scaffolds have been created that can form tissue grafts with preferentially aligned heart cells, and with mechanical properties that closely resemble the anisotropy of native myocardium.