Volume 10 Issue 6, June 2011

Efficient energy harvesting from temperature gradients requires thermoelectric materials with low thermal and high electrical conductivities. A conducting polymer can fulfil these conditions if its doping level is controlled precisely.

Maximum yield of self-assembly for a target structure can be attained with simple rules for the interactions between the structure's building blocks.

Collective cell motion in a continuous tissue is found to be guided by cooperative intercellular forces.

Steady-state remodelling in model cytoskeletal networks results from the combination of marginal stability and molecular-motor activity.

Grain boundaries in polycrystalline graphene are an obstacle to electron transport. However, cunning refinements in growth techniques push the limits to obtain super-sized single-crystal domains.

Although magnetic domain walls could one day be used for information storage, the current challenges to their use are the irreproducibility of their displacement and the limits to their maximum speed. It is now shown that the Rashba effect can be used to provide a solution to both these issues.

Chemical vapour deposition is one of the most promising strategies to grow high-quality graphene sheets on a large scale. It is now shown that this deposition technique can be extended to grow three-dimensional graphene networks with high conductivity and flexibility—both promising features for flexible electronics.

Organic materials are rarely considered for thermoelectric applications, because their low electrical conductivity limits the thermoelectric figure of merit (ZT). It is now shown that by optimizing the oxidation level in a polymer, ZT can reach 0.25, which approaches the values desirable for devices.

The production of fuels from sunlight is crucial to the development of a sustainable energy system. Although noble metals are efficient catalysts for photoelectrochemical hydrogen evolution, earth-abundant alternatives are needed for large-scale use. Bioinspired molecular clusters based on molybdenum and sulphur are now shown to produce hydrogen at rates comparable to platinum.

In contrast to the long-range order of crystalline materials, non-crystalline compounds, such as metallic glasses, have a more inhomogeneous distribution of atoms on a local scale. Atomic force acoustic microscopy now demonstrates how these local variations translate into much stronger variations in local elastic properties of a metallic glass compared with its crystalline counterpart.

Chemical vapour deposition is a promising route for large-scale graphene growth. It is now shown that—through the use of seeds—high-quality, large, single-crystal domains can be grown on a patterned arrangement, and can be used to carefully study the transport across grain boundaries.

The energy-level alignment at the heterojunction critically influences the performance of organic photovoltaic devices. It is now shown that the surface dipole moments of individual organic semiconductor films can be tuned with surface-segregated monolayers before forming bilayer solar cells by a simple film-transfer method.

Production of chemical fuels by solar energy is an attractive and sustainable solution to our energy problems. A highly active photocathode, consisting of electrodeposited cuprous oxide with platinum nanoparticles is now activated for hydrogen evolution resulting from photelectrochemical water reduction.

Active gels—such as the cytoskeleton—are out-of-equilibrium networks that self-organize in complex, dynamic patterns. The mechanisms by which dynamic structures form are, however, poorly understood. Now, a generic mechanism of structure formation, analogous to nucleation and growth in passive systems, is found in a minimal active-gel consisting of actin filaments, molecular-motor filaments and crosslinkers.

The mechanical stresses within and between cells inside an advancing cellular monolayer are mapped experimentally. Cellular migration is found to be oriented in the direction of maximum principal stress indicating that cells collectively migrate to maintain minimal local intercellular shear stress.