Articles in 2008

The electronic properties of interfaces between two different solids can differ strikingly from those of the constituent materials, as demonstrated by the high conductivity at the interface between insulating perovskite oxide layers. Metallic conductivity is now observed at the interface between organic insulators, which promises new scientific developments for organic electronics.

Nanomagnets are very promising structures for magnetic data storage. However, it is found that during exposure to ambient oxygen for processing, a nanomagnet develops a sidewall oxide layer that is detrimental for its magnetic properties. The problem can be solved by deposition of a metal layer (aluminium) that reduces and almost eliminates the problem.

The structural organization of surface groups on nanoparticles is proven to be important for cell membrane penetration. Nanoparticles coated with alternating ribbon-like arrangements of hydrophobic and anionic ligands penetrate membranes without causing disruption. These design rules may have implications for toxicity issues and drug delivery applications of nanomaterials.

Fast-ion conductors are needed to reduce the operating temperature of solid-oxide fuel cells. The identification of the conduction mechanism in electrolytes where conduction is based on mobile oxygen interstitials rather than the usual anion vacancies offers a generic design principle for novel solid electrolytes.

Relaxor ferroelectrics, which show a strong dependence of electric polarization on the applied electric field, are promising for applications such as sensors and actuators. Neutron-scattering experiments now establish a direct link between the unique piezoelectric properties of relaxors and local clusters of randomly oriented polarization specific to these materials.

Organic holographic materials are pursued as versatile and cheap data-storage materials. However, previously such materials either needed the application of an external electric field or had mostly poor efficiencies. Now, a novel recording process based on a photoisomerization process demonstrates significantly improved writing properties of holograms.

Understanding how excited states behave at heterojunctions between polymers in blends is fundamental to designing better organic solar cells and light-emitting diodes. A quantum-mechanical molecular-scale model of how excitations behave at heterojunctions has been developed, showing an unexpectedly wide but specific range of excitonic states.

Multiferroic materials are of interest because they allow control of their magnetic properties through electric fields. However, room-temperature magnetoelectrics often show antiferromagnetic order, reducing the effects of such coupling. A novel approach demonstrates switchable electric field control over a local magnetic field through the indirect route of exchange bias.

Chiral detection using organic sensors has been limited to concentration levels of parts-per-thousand. The use of a thin-film transistor and of semiconducting oligomers with chiral side arms improves differential detection of enantiomers to parts per million.

The large-scale production of high-quality graphene layers is one of the main challenges to be overcome for successful application of this material. Epitaxial growth on ruthenium substrate produces homogeneous domains of single- and double-layer graphene on the scale of several tens of micrometres. The electronic properties of the second layer show great potential for applications.

Inducing and understanding insulator–metal transitions in binary oxide can be challenging. A transition driven chemically by an internal redox reaction is now observed in a non-stoichiometric, amorphous gallium oxide.

We’re all familiar with the annoying problem of trying to peel sticky tape from a surface, only for the detached piece to narrow into a point and break off. Surprisingly, this phenomenon can be put to good use in deriving the mechanical parameters of a wide variety of thin, adhesive films.

The nature of electrostatic charges produced at the surface of insulators by rubbing is the subject of a long-standing discussion. The charges created on polytetrafluoroethylene by rubbing with polymethylmethacrylate are identified here to be electrons rather than ions.

Phase-change materials are of commercial interest for their use in rewritable optical disks and as non-volatile memories, although little is known about the dynamics of the phase transition. The numerical simulation of the entire write-erase cycle therefore provides important clues towards the development of new phase-change materials.

To produce hydrogen by reforming hydrocarbons, efficient catalysts capable of removing carbon monoxide are needed. This can now be achieved via a preferential oxidation mechanism using nanoparticle catalysts consisting of a ruthenium core covered with platinum.

Coherent diffraction experiments and molecular dynamics enable the study of atomic contraction in gold nanocrystals. They reveal a surface-orientation dependence of the atomic bond contraction—remarkably different from the situation in bulk.

Two-phase materials hold great promise for multifunctional applications. To realize practical devices, it is first necessary to obtain a high degree of control of the phase composition. By taking into account the properties of each phase, it is now possible to control the strain at the interfaces between them in two-component materials, and obtain phase ordering at large scales.

The nature of the charge transport in organic semiconductors is subject to intense research. A study on the thermal and charge transport of single-crystal thin-film polymers now shows close similarities between the transport properties of organic and inorganic semiconductors.

Controlling and monitoring individual spins is desirable for building spin-based devices. The optical manipulation of the spin of manganese ions in gallium arsenide is now possible. The spins of a small number of ions can be oriented by selecting the polarization of a laser beam. Reduction of the ion concentration enables control of single manganese spins.

A three-step synthetic method that involves silica coating, heat treatment and removal of the silica layer is reported for the preparation of hollow iron oxide nanocapsules. The magnetite nanocapsules made by this simple wrap-bake-peel process show potential as drug-delivery vehicles and MRI contrast agents.