Articles in 2009

The size distribution of polymer vesicles and phospholipids is usually polydisperse as there are no selection rules for the overall size. A method combining photolithography and molecular self-assembly can now produce giant polymer vesicles with controlled and narrow size distributions.

The high capacity and energy densities of lithium sulphur batteries make them promising for applications, but their widespread realization has been hindered by problems at the interface between the cell components. A conductive mesoporous carbon–sulphur cathode framework capable of constraining sulphur growth and generating electrical contact to the insulating sulphur is now reported.

Stretchable electronics enables applications on arbitrary curved surfaces or on movable parts to be made. Based on a new technique for printing with carbon nanotube pastes, stretchable active matrix displays containing integrated electronic circuits are now realized.

Free-standing nanoparticle superlattices offer interesting possibilities for the design of devices free from undesired effects of substrates. DNA can now be used to obtain superlattices with control over interparticle spacing, offering an alternative perspective on the synthesis of nanoparticle solids.

Concerns over safety and the inability to control release have hampered progress towards instilling siRNA into mucosal tissue for protection against and treatment of human disease. Nanoparticles made from FDA-approved polymers have now been loaded with large amounts of siRNA and topically applied to vaginal mucosa leading to sustained gene silencing.

Multiferroics offer intriguing opportunities for sensing and information storage applications, although their integration into electronic devices has been difficult owing to a lack of suitable electronic control. Electric modulation of conduction is now achieved for a doped multiferroic, resulting in complete control over the ferroelectric state itself.

Microstructure evolution in complex nonlinear systems, such as quasiperiodic two-phase chessboard structures, is a fascinating fundamental phenomenon. It is demonstrated that under certain conditions a transformation from tweed to nanowire chessboards develops by spinodal decomposition.

A process based on spray-assisted layer-by-layer deposition produces conformal coatings on individual fibres within the bulk porous substrate. Additional processing creates a sublayer with properties that differ from the substrate. The method is used to fabricate a material that acts as both a toxin barrier and a photocatalyst.

The size reduction of thin-film ferroelectric capacitors has been hampered by effects that arise as ferroelectric films reach only a few unit cells in height. However, rather than inevitably resulting in a ‘dead layer’, an enhancement of ferroelectricity at certain metal–oxide interfaces is now predicted.

Explaining the quantitative relationships between processing conditions and oxide-layer geometry for the growth of porous anodic alumina has so far proved difficult. A model for steady-state growth of these amorphous films, incorporating metal and oxygen ions transported by plastic flow and coupled electrical migration, is now proposed.

Discotic liquid crystals are materials with high charge-carrier mobility, which are promising for molecular electronics. They self-organize into stacks, usually with a twist of 30^∘, but the shape and periphery of the molecules can now be altered to produce materials with a twist of 60^∘. Defect-limited mobilities of these materials reach 0.2 cm² V⁻¹ s⁻¹, but the potential defect-free mobility could be up to 10 cm² V⁻¹ s⁻¹.

Freezing water containing salts is believed to produce pure ice and a salt hydrate. Neutron-diffraction measurements of the ice phase obtained by recrystallizing the glassy state of LiCl salt solution at high pressure suggests something different. The data reveal an ‘alloyed’ ice VII structure incorporating Li and Cl ions.

Applications of high-temperature superconductivity rely on transporting a large current without dissipation. It is now shown how the inclusion of a combination of two types of defect can be used to control and optimize the performance of the high-temperature superconductor YBa₂Cu₃O₇.

Proteins are usually produced in living cells, but hydrogels that incorporate genes demonstrate that cells aren’t always needed. The gels produce a wide variety of proteins without cells, and with higher yields than the equivalent solution method. Materials-related proteins that have been difficult to produce by other methods can now be made in greater quantities.

Anisotropic superstructures produced by the self-assembly of spherical nanoparticles are realized. Uniformly grafting polymer chains onto inorganic spherical nanoparticles produces particles with amphiphile-like behaviour. Mixing these with monodisperse polymer facilitates the self-assembly of numerous anisotropic nanocomposites.

Polymer crystals have a range of melting temperatures, therefore simultaneous melting and crystallization can take place. New crystals are seeded from some of the initial crystalline material, and as the orientation of the second-generation material is correlated with the starting crystal, orientated arrays of polymer crystals are produced.

Although heterogeneous ice nucleation is investigated in a number of fields, a mechanism for the process remains elusive. Ice with a pentagon-based chain structure is now seen to form on a Cu(110) surface, revealing that the structure of ice–water films can adapt to maximize water–metal bonding and achieve strong hydrogen bonding within the layer.

What drives a phase transition in the heavy-fermion compound URu₂Si₂ is one of the major unsolved problems in condensed-matter physics. Numerical calculations now demonstrate how antiferromagnetic ordering leads to a symmetry breaking that alters the material’s band structure and therefore its electronic properties.

Graphene nanostructures—like nanoribbons or quantum dots—hold great potential for applications. An extensive STM study elucidates how the details of the nanostructure edges heavily influence the electronic properties, which can vary between metallic and semiconducting according to the predominancy of zigzag or armchair edges.

Molecular rotors have seen considerable interest as functional molecules on surfaces or for applications as memory devices. However, it is now shown that molecular rotation may also be used to induce ferroelectricity in a molecule.