Articles in 2011

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 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.

Many synthetic polymer nanoparticles used for non-viral gene delivery contain excess cations on their surface, which makes the particles cytotoxic and the delivery of genes inefficient. Terpolymers with a low charge density, high molecular weight and increased hydrophobicity are now shown to have minimal toxicity, and to efficiently deliver the apoptosis-inducing TRAIL gene to transplanted tumours in mice.

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.

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.

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.

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.

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.

Nonlinear optical upconversion processes in nanoparticles, which convert long-wavelength light into short-wavelength emission, are promising for applications such as biological imaging, optical data storage and others. The flexible tuning of upconversion properties in core–shell nanoparticles now offers unprecedented control over the nonlinear optical properties of the nanoparticles.

An electrochemical method that uses ion-selective membranes to electrically modulate ion concentrations in situ along a sciatic nerve in vitro allows for on-demand reversible inhibition of signal propagation as well as up to 40% reduction of the electrical threshold for stimulation. The method may be applicable in implantable neuroprosthetic devices.

The close relationship between crystal structure and electric polarization in ferroelectrics means that strain strongly influences their properties. The demonstration of how strain gradients leading to a higher-order effect, flexoelectricity, can be used to rotate electric polarization in thin films indicates new ways of controlling piezoelectricity by purely mechanical means.

Inorganic nanocrystals are attractive materials for solar-cell applications. However, their performance is often limited by an insufficient alignment of internal energy levels. A tuning of these energy levels has now been achieved by attaching two different molecules to a single nanocrystal, which significantly alters its electronic and optoelectronic properties.

It is easy to imagine that carbon nanotubes deform under strain, but the microscopic mechanism of deformation is difficult to relate to the large-scale one. Through aberration-corrected transmission microscopy the atomic displacement under bending is now mapped out, revealing unexpected details.

Activation of molecular hydrogen is an important step for many applications such as fuel cells and ammonia synthesis, but has so far required high temperatures and expensive noble-metal catalysts. Aluminium doped with small amounts of titanium is now shown to activate molecular hydrogen at temperatures as low as 90 K.

Organic ligands enhance the stability and the solution processability of semiconductor quantum dots, but they can impede charge transport in films of such nanoparticles. Passivation with atomic ligands now offers an alternative strategy that enables the fabrication of PbS colloidal-quantum-dot solar cells with power-conversion efficiencies of up to 6%.

Methodologies capable of directly visualizing and detecting gases are important for a wide variety of applications that involve instantaneous decision-making in complex environments and locations. A strategy for the capture and detection of gases by co-operative structural transformations of a flexible porous coordination polymer and fluorescent reporter molecules is now reported.

First-principles calculations show that water molecules at the surface of crystalline ice have high variability in their binding energies. Such an amorphous character of a crystalline surface is unusual, and for ice it is a result of electrostatic frustration and the relaxation of geometric constraints. The findings have consequences for ice catalysis, surface pre-melting and growth.

Biominerals exhibit properties, morphologies and hierarchical ordering that invariably surpass those of their synthetic counterparts. Artificial biominerals consisting of calcite crystals incorporating copolymer micelles have now been produced. The synthetic crystals show analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite.