Volume 11 Issue 2, February 2012

Interfaces formed by transition-metal oxide materials offer a tremendous opportunity for fundamental as well as applied research. Yet, as exciting as these opportunities are, several challenges remain.

The application of inhomogeneous strain to silicon photonic structures may lead to new optically active devices based on second-order nonlinear processes.

The ability of laser interference potentials to trap and control colloidal particles opens up a new potential area of 'toy systems' displaying real physics. A beautiful example is the study of friction between colloidal crystals and a variety of artificially created surface potentials.

For colloidal particles adsorbed at liquid/liquid interfaces, it is now found that the height of a particle above the interface equilibrates much more slowly than expected. Such a slow relaxation has major implications for the understanding of effective interactions between colloids at fluid interfaces.

Limiting reliance on non-renewable fossil fuels inevitably depends on a more efficient utilization of solar energy. Materials scientists discuss the most viable approaches to produce high-energy-density fuels from sunlight that can be implemented in existing infrastructures.

From magnetism, ferroelectricity and superconductivity to electrical and thermal properties, oxides show a broad range of phenomena of fundamental as well as practical relevance. Reviewed here are the emergent phenomena arising at the interface between oxide materials, which have attracted considerable interest based on advances in thin-film deposition techniques.

A local atom probe has been used to study the transport properties of graphene, revealing the different effects of surface steps and changes in layer thickness on substrates. Understanding the details of the defect-induced degradation of transport properties is essential for improving the efficiency of devices.

One of the interesting features of graphene is that its properties change with the number of layers. A procedure to create monolithic devices with elements made out of different numbers of graphene layers is now shown, and a practical demonstration of this method is given by realizing transistor arrays with chemical-sensing functionalities.

The frictional properties of a two-dimensional colloidal crystal reveal that excitations known as kinks and antikinks form when the crystal is dragged along a solid surface. This phenomenon, which was predicted previously but never observed, demonstrates the potential of using colloidal crystals to study frictional properties that are otherwise difficult to characterize.

Highly monodisperse silver polyhedral nanocrystals passivated with polymers are shown to behave as quasi-hard particles that self-assemble by sedimentation into millimetre-sized supercrystals, which correspond to the particles' three-dimensional densest packings. Monte Carlo simulations confirm the observed self-assembled structures, including an exotic structure for octahedra that is stabilized by depletion forces induced by an excess of polymer in solution.

Colloidal particles adsorbed at liquid interfaces are commonly assumed to be at equilibrium, but holographic microscopy experiments now reveal that microspheres bound to a water/oil interface may take months to equilibrate. The observed ageing dynamics agree with a model of thermally activated hopping of the particle/interface contact line over nanoscale surface defects, and have implications for understanding the interactions between adsorbed colloidal particles.

The coherence lifetime of a material system to be used in quantum information protocols has to be long enough for several quantum operations to occur before the system loses its quantum coherence. The spins of impurities in silicon have been shown to have coherence lifetimes up to tens of milliseconds, but now all records are beaten with those in high-purity silicon reaching a few seconds.

Photonic devices on silicon offer the benefit of combining advanced electronic functionality with the high bandwidth of silicon photonics. Now, efficient second-order nonlinear activity in silicon waveguides strained by a silicon nitride top layer considerably advances the potential of all-optical data management on a silicon platform.

A key step in fuel-cell energy-conversion processes is electro-oxidation of the fuel at the anode, but ways to improve electrocatalytic activity remain unclear. Using ceria–metal structures, H₂-oxidation reactions are shown to be dominated by electrocatalysis at the oxide/gas interface with minimal contributions from the oxide/metal/gas triple-phase boundaries.

Electrochemical oxidation of metals produces anodic oxides with highly regular arrangements of pores; however, the mechanisms of pore initiation and self-ordering are not well understood. Now, a quantitative analysis method is proposed that examines the roles of oxide dissolution and ionic conduction in the morphological stability of anodic oxide films.

The relay mechanism in which hydrogen atom transfer occurs along hydrogen bonds plays a crucial role in many functional compounds. Using a scanning tunnelling microscope, the transfer of hydrogen atoms along hydrogen-bonded chains assembled on a Cu(110) surface is shown to be controllable and reversible.

Oxide materials show an amazing variety of electronic and ionic phenomena. In this focus issue we review the progress in oxide thin film technology and highlight the outstanding challenges for the fundamental understanding and practical implementation of complex oxides in devices.