Letters in 2008

Elucidation of the framework structure of zeolites can sometimes prove difficult. The combination of powder diffraction and electron microscopy using a charge-flipping algorithm enables ordered silicon vacancies in a zeolite catalyst to be revealed.

The presence of organic solvents in solar cells has hindered the application of devices, especially in flexible cells. Now, by mixing three solid salts, a solvent-free liquid electrolyte for dye-sensitized solar cells has been discovered that shows both excellent efficiency and stability.

The interfaces between some perovskite oxide insulators show spectacular electronic properties, originating from the formation of an electron gas. The spatial extent of the electron gas is still under debate. Conducting tip atomic force microscopy is now used to show that, depending on the growth conditions, the high-mobility electron gas can extend to hundreds of micrometres or to just a few nanometres from the interface.

The occupation of specific crystallographic sites by tetrahedrally coordinated aluminium atoms in zeolites has a strong influence on their catalytic and separation performance. X-ray standing waves are now used to directly and unambiguously determine the distribution and ordering of aluminium on active sites in a microporous scolecite system.

Although ferroelectric polarization is of interest for the development of non-volatile memories, the read-out of the polarization state is destructive. The blending of semiconducting and ferroelectric polymers in a phase-separated network achieves non-volatile memory arrays that can be read out non-destructively.

One-dimensional metals are predicted to exhibit charge-order fluctuations and become insulators at low temperature. Experiments on silicide nanowires grown on silicon reveal that fluctuations in the narrowest wires determine the electronic properties, and can be exploited in nanoelectronic devices.

The contractile forces of cells can cause extracellular matrices to detach from their surroundings, which is problematic for biological studies and tissue engineering. Now, multiple phases of cell-seeded hydrogels can be integrated using a collagen-fibre-mediated method, resulting in the construction of well-defined and stable patterns of three-dimensional matrices.

Cluster expansion has been a particularly successful computational method that has allowed the identification of the relationship between lattice configurations and scalar properties in crystals. A tensorial version of the method that will enable prediction of tensor-valued properties is now introduced. It is validated by predicting anisotropic properties relevant to semiconductor optoelectronic devices.

Metamaterials enable a number of intriguing photonic functionalities from superlensing to cloaking. The demonstration of truly three-dimensional metamaterials by a direct laser writing process offers the possibility of complex photonic functionalities at optical frequencies.

The electric polarization of dipoles on the surface of a ferroelectric material can influence the energetics of materials adsorption. The demonstration of this effect on the physisorption kinetics of gases such as carbon dioxide may be used to control adsorption and surface chemistry on the nanoscale.

Diluted magnetic semiconductor devices where magnetism can be controlled by an electric field are of significant interest for applications, as they combine the appealing properties of multiferroics with existing semiconductor technology. By using a ferroelectric polymer as the gate of a transistor device, non-volatile electric control over the magnetism of (Ga,Mn)As has now been achieved.

X-ray diffraction computed tomography can provide high-resolution phase mapping of nanocrystalline and powdered crystalline materials. Moreover, a reverse analysis offers the possibility to extract, a posteriori, the scattering/diffraction pattern from a selected area of the tomography image.

Composites with added carbon nanotubes are known for their improved mechanical strength. Laminates of thin films of aluminium and carbon nanotubes are now used for the fabrication of micromechanical resonators with significantly enhanced mechanical properties.

C₆₀-based solids are the archetypal molecular superconductors, reaching transition temperatures as high as 33 K. Now, Cs₃C₆₀ solids, having a transition temperature of 38 K, have been isolated. Both face-centred-cubic and body-centred-cubic phases were synthesized, and, uniquely among C₆₀ solids, the superconducting phase was found to be body-centred cubic.

Efficient light emission combined with high charge-carrier mobility has proven elusive for polymer semiconductors, because high mobility is typically achieved using approaches that quench luminescence. A new strategy, introducing a limited number of more-effective hopping sites between otherwise relatively isolated polymer chains, achieves this aim.

Microporous materials such as zeolites are widely used in separation and catalytic applications. A thermally stable family of zeolites with chiral and achiral structures built from the same layer is now reported.

Despite the demonstration that nanowires can grow below the eutectic point, a clear understanding of how this happens has not been reached. Video-rate transmission electron microscopy brings new insight into the issue, showing in real time the growth of silicon nanowires with palladium catalysts.

A highly conductive channel, a few nanometres wide, can be reversibly created by an AFM tip operating at room temperature at the interface between two oxide insulators. This discovery could provide a powerful method for the design and realization of electronic circuits at the nanoscale.

Induced multiferroics, where ferroelectricity arises through the magnetic order, have attracted significant interest, despite maximum Curie temperatures of only 40 K. The discovery of multiferroic coupling up to 230 K in CuO therefore represents a major advance towards high-T_C multiferroics.

Modulated proton transport has a significant role in biological processes such as ATP synthesis and in electrochemical energy conversion. Electrostatic gating of proton conduction that can be actively modulated is now shown in aligned mesoporous silica thin-films.