Articles in 2009

Sodium beta-alumina (SBA) compositions are well known as ionic conductors. Nevertheless, ionic and electron conductivities perpendicular to the lattice planes in the material are very low. It is now shown that by exploiting this property, SBAs can be used as transistor gate dielectrics in solution-processed devices using oxide-based and polymer electrodes.

Bioelastomers generally show elasticity similar to that of rubber, which originates from entropic forces linked to deformation. It is now shown that in the egg capsule of a large marine shell, the elasticity is instead based on a structural transition. The results could have a significant impact on engineering protective encapsulating systems inspired by natural elastomers.

Soft embryonic stem cells respond to small localized forces by increasing cell protrusion and spreading; in contrast, cells that are differentiated from them—which are ten times stiffer—do not spread. The deformation of the cell cytoskeleton is thus shown to be an important determinant of cellular response to force.

By including small molecules with block copolymers in polymer nanocomposites, various types of nanoparticle can be positioned within the composite with unprecedented precision over several length scales. Moreover, the spatial distribution of nanoparticles within the combined material can be varied by exposure to heat or light, creating a new route to stimuli-responsive materials.

The efficiency of solar cells depends not only on the generated current, but also the photovoltage produced. Ground-state charge-transfer complexes are shown to have an important role in influencing the open-circuit voltage of several polymer–fullerene solar-cell blends; future chemical tuning of the polymers could maximize the complexes’ role in affecting the voltage for increased power-conversion efficiency.

Characterizing the internal architecture of zeolites is crucial for understanding their structure–function relationships, and for acid–base heterogeneous catalysis. Using a unique combination of diffraction and microscopy techniques provides a unified picture of the morphology of intergrowth structures and confirmation of surface barriers for molecular diffusion.

The interfacial energy between a macroscopic surface consisting of different materials and a liquid is independent of the surface structure. It is now shown that because of the way in which a multicomponent nanoscale surface affects the solvent–molecule arrangement, it is both the surface structure and composition that dictate the interfacial energy.

The performance of hybrid solar cells depends critically on the morphology of both the polymeric and the inorganic components. Electron tomography is used to resolve the morphology in three dimensions; coupling this information with three-dimensional exciton-diffusion studies enables the differentiation of charge generation and transport as performance-limiting factors.

Anhydrous proton-conducting materials capable of operating at high temperature are required for fuel-cell applications. Encapsulation of a proton-carrier imidazole molecule in aluminium porous coordination polymers in anhydrous conditions results in high proton conductivity above 100 ^∘C.

Controlled domain formation in block copolymer mixtures or lipid bilayers could lead to more highly ordered assemblies and delivery of drugs. It is now shown that mesoscale domain formation within assembled mixtures of neutral and anionic polymer amphiphiles can be induced by the divalent cations calcium and copper.

Controlling the magnetic properties by using an electric field is a promising route towards spintronics or magnetic data storage applications. Using dicobaltocene as a test case, it is now demonstrated theoretically that an electrostatic potential can be used to control the spin states in molecules.

The ability to replace surface hydrogen by multivalent atoms to form semiconductors with tailored properties is critical for microelectronic applications. The mechanistic pathway involved in the nitridation of H-terminated silicon surfaces using ammonia vapour is now explained.

Creating laboratory-grown bone for implantation into injury sites is an aim of regenerative medicine. However, newly grown bone may not have the same structural and compositional properties as native bone. Materials characterization shows that the source of cells for the new bone growth has a significant effect on its properties.

Metal nanoparticles can be prepared with good control of particle size and shape by solution-state chemistry, but controlling their physicochemical properties remains a challenge. A generic protocol for transferring metal ions from water to an organic medium is now used to synthesize a range of metallic and semiconductor nanoparticles having multiple functionalities.

Plasmonic nanostructures enable the concentration of large electric fields into small spaces. The classical analogue of electromagnetically induced transparency has now been achieved in such devices, leading to a narrow resonance in their absorption spectrum. This combination of high electric-field concentration and sharp resonance offers a pathway to ultracompact sensors with extremely high sensitivity.

Although sequential adsorption of dyes in TiO₂ electrodes is ideal for extending the range of light absorption in dye-sensitized solar cells, high-temperature processing has so far limited its application. A method for the selective positioning of organic dye molecules with different absorption ranges is now reported in a mesoporous inorganic oxide film.

The manufacture of polymeric microactuators is complicated when using techniques like lithography, but inkjet printing can be used to deposit self-organizing liquid-crystal networks instead. Printing sub-units with different inks is easily scalable and creates light-driven actuators with sections that can be individually addressed to mimic the flapping movements of cilia.

The light-emitting electrochemical cell (LEC) is one application of organic semiconductors. Scanning kelvin probe microscopy and light-emission data obtained from operational planar LECs provide insight into the devices. The measured electrostatic potential profiles confirm that there is in situ formation of a dynamic p–n junction in the organic semiconductor during operation.

The successful use of shape-memory alloys relies on the microscopic understanding of the associated phase transformations. A recently developed analytical technique of structural data is now applied to nanoprecipitates in Ni–Ti, and clearly reveals a connection between the strain that these precipitates introduce and the phase transformation that is often observed.

The mechanisms underlying the fracture of glasses are poorly understood. It is now shown that intrinsic density fluctuations in glass are enhanced during the deformation process, and may therefore be the origin of fracture in glasses. This understanding may lead to the design of glasses with improved mechanical properties.