Research articles

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.

An organic electronic device capable of precisely delivering neurotransmitters in vitro and in vivo is demonstrated. The device mimics the nerve synapse by converting electronic addressing in the delivery of neurotransmitters, thereby enabling exact dosage determination through electrochemical relationships. The system also ensures minimally disruptive delivery by avoiding fluid flow, and provides simple on–off switching.

Quantum confinement effects have an important role in photonic devices. However, rather than seeking perfect confinement of light, leaky-mode resonances are shown to be ideally suited for enhancing and spectrally engineering light absorption in nanoscale photonic structures.

Solar power is an important part of the strategy towards using more renewable energy. The development of low-cost photovoltaic nanopillar structures fabricated on thin aluminium substrates will contribute to this effort, as it promises new applications for flexible, mass-produced solar cells.

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.

Hydrogels are hydrated polymer networks with applications in biotechnology and medicine. When created from alpha-helical peptides with engineered peptide sequences, their formation mechanisms can be controlled, leading to diverse properties. For instance, those with hydrogen-bonded networks melt on heating, but those formed through hydrophobic interactions strengthen when warmed.

The transport and mechanical properties of polymer electrolytes make them important materials for all-solid-state electrochemical devices such as batteries or electrochromic displays. Crystalline polymer electrolytes containing alkali metal salts are now found to exhibit ionic conductivity 1.5 orders of magnitude higher than the best conductor reported so far.

The electric control of magnetism in magnetic devices has remained problematic, particularly as energy losses due to current flow can be large. The demonstration of electric control of magnetization in a non-centrosymmetric insulating magnetic material therefore represents a new strategy for future applications.

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.

Metamaterials allow the design of new functionality through the engineered control of light propagation, although broadband operation with these materials requires singularities in their refractive index. As a first example of a technique that uses a topological defect to achieve such behaviour in a real system, an omnidirectional metamaterial retroreflector is demonstrated.

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.

Aberration-corrected microscopy can provide structural information with atomic precision. It is now shown that even single impurity atoms in a buried interface can be imaged, provided that a particular imaging mode is used. This result can lead to a much clearer understanding of advanced materials and devices that make use of the properties of interfaces.

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.

‘Click’ chemistry has been broadly exploited, but the intrinsic toxicity of the reactions involved makes its translation to biological applications troublesome. Copper-free click chemistry avoids the problems of toxicity, enabling direct encapsulation of cells within click hydrogels. Tailoring of the gels with biological functionalities is also enabled in real time with micrometre-scale resolution.

A route connecting density functional theory and the numerical renormalization group method represents the first approach to studying atomic contacts—including magnetic elements—at an atomic level. When applied to the case of a nickel impurity in a gold nanowire, the strategy provides a clear connection between the geometry and the transport properties.

Designing and building molecular machines at the nanometre scale is a conceptual and synthetic challenge. Rotation of a single molecule has been observed but controlling the direction of the rotation has so far proved difficult. The step-by-step rotation of a molecular gear mounted on an atomic-scale axis is now controlled by a scanning tunnelling microscope.

Functionalizing colloidal particles with DNA is a powerful tool for guiding their assembly, using the complementary ‘sticky ends’ of the molecules. However, other attributes of DNA can be used to engineer interactions between particles more subtly. Temperature- or time-controlled formation of loops or hairpins in DNA provides switchable connections for novel materials from particle assemblies.

Superconductivity was recently observed in the binary iron-based compound, FeSe. It is now shown that under pressure, the transition temperature can rise above 36 K. In addition, no static magnetic ordering is observed for this system, contrary to FeAs superconductors.

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.