Articles in 2011

Combining the efforts of physicists, materials scientists, economists and resource-strategy researchers opens up an interdisciplinary route enabling the substitution of rare elements by more abundant ones, serving as a guideline for the development of novel materials.

Although heterogeneous photocatalysts for converting solar to chemical energy are mostly semiconductors, metallic plasmonic nanostructures have started to attract interest. Recent progress on plasmon-enhanced, water-splitting composite photocatalysts and photocatalytic reactions on the surface of plasmonic nanostructures of noble metals are now reviewed.

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.

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.

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.

Persistent phosphors are known from applications such as night-vision goggles where they produce a characteristic green afterglow. The discovery of persistent phosphors that instead operate at near-infrared wavelengths with much longer afterglows may now enable new applications in night-vision surveillance and in bio-imaging.

Molecular hydrogen is expected to display metallic properties under high pressures, but so far experiments performed at low temperatures ( 100 K) have showed that hydrogen remains insulating up to 300 GPa. A transformation of normal molecular hydrogen to a conductive and metallic state at room temperature is now observed above 220 GPa.

Metamaterials are widely studied for their optical properties offering applications such as perfect lenses or cloaking. As is now shown, the interaction between the individual elements of metamaterials can also be used to design magnetoelastic metamaterials, which are able to change their structure in response to light.

The possibility of controlling magnetization by spin-polarized current could lead to devices more energy-efficient than traditional ones using external magnetic fields. Now, an even more efficient method has been demonstrated by using electric-field pulses to switch the magnetization in FeCo magnetic cells.

The possibility of controlling magnetization by spin-polarized current could lead to devices more energy-efficient than traditional ones using external magnetic fields. Now, an even more efficient method has been demonstrated by using electric-field pulses to switch the magnetization in a CoFeB/MgO/CoFeB magnetic tunnelling junction.

Plasmonic nanostructures are known to be an attractive platform for highly sensitive molecular sensors, although they often lack specificity. A plasmonic device with a sharp optical resonance tuned to biomolecules selectively captured on the surface of the device now offers a versatile yet highly specific platform for molecular sensing.

Polymer-based bulk-heterojunction solar cells have shown some of the highest photoconversion efficiencies in organic photovoltaics, but polymer polydispersity impacts their performance. A small-molecule donor is now reported that enables the fabrication of bulk-heterojunction devices with low acceptor content and photoconversion efficiencies of up to 6.7%.

Metal oxides can exchange charges with a wide variety of adsorbed organic molecules, which renders them useful in electronics and catalysis. A study on oxides with a range of electronic properties now shows that energy alignment at metal oxide/organic interfaces is universally governed by electron-chemical-potential equilibration.

Artificial materials that show negative refraction can be used for devices such as perfect lenses. The demonstration of negative refraction in nanostructured metal films, using a nonlinear optical effect—four-wave mixing—therefore opens new possibilities for optical devices.