Articles in 2008

It is now shown that femtosecond optical excitation can be used as a tool to investigate the spin-polarization properties of half-metals, and provide a clear distinction between those and metals. Such knowledge is of fundamental importance for the use of these materials in spintronics applications.

Ferroelectric polymers are of interest for use as memory devices for all-organic electronics applications. A fast and efficient embossing technology is now shown not only to lead to high-density arrays of ferroelectric nanocells but also to significantly improve the ferroelectric properties of these structures.

Electronically active materials made by the self-assembly of alternating layers of zinc oxide and conjugated molecules directly onto an electrode combine the advantages of their inorganic and organic components. They are shown to be stable photoconductors with promising device characteristics.

Colloidal synthesis can help to precisely control the shape and composition of catalytic metal nanoparticles, but it has so far proved difficult to use these particles in high-temperature reactions. Core–shell structures capable of isolating Pt-mesoporous silica nanoparticles have now been shown to be catalytically active for ethylene hydrogenation and CO oxidation at high temperature.

One of the challenges posed by spin manipulation in organic semiconductors is the difficulty of measuring the spin polarization and the spin diffusion length. This is now elegantly achieved by a low-energy muon spin rotation.

One of the challenges posed by spin manipulation in organic semiconductors is the difficulty of measuring the spin injection from a ferromagnetic contact and the subsequent spin diffusion length. This is now elegantly achieved by a two-photon photoemission experiment.

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.

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.

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.

Hydrogen generated from splitting water using a catalyst and solar energy is an ideal energy source. A polymeric carbon nitride photocatalyst that is thermally and chemically stable is now shown to produce hydrogen from water even in the absence of noble metal catalysts.

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.

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.

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.

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.

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.

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.

To enable the development of devices based on the electrical manipulation of magnetic molecules, their magnetic state needs to be conserved when electrical contacts are applied. N@C₆₀ molecules have now been integrated as part of single-molecule transistors, and their spin states retained. This achievement may lead towards their use in high-density information storage and quantum-state control.

Defects can significantly alter the physical properties of materials. A detailed experimental analysis of defects in carbon nanotubes enables the relationship between the atomic response and the broadly available macrosopic behaviour to be captured.

Flexible electronics require that all parts can be printed on plastic substrates, but finding materials that can act as high-capacitance dielectrics is a priority. An emerging class of polymer electrolytes, ion gels, can do the job—with high capacitance and at low voltage.

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.