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The growth of microcrystals can be controlled by various agents such as ions, small charged molecules and polyelectrolytes. However, their use is specific to the crystallizing material. It is now shown that oppositely charged nanoparticles can act as 'universal' surfactants for controlling the growth and stability of microcrystals of inorganic salts and of charged organic molecules.
Progress in photovoltaic technology could soon mean grid parity for solar electricity. In this issue we highlight scientific as well as science-policy strategies aimed towards achieving this goal.
For decades, solar-cell efficiencies have remained below the thermodynamic limits. However, new approaches to light management that systematically minimize thermodynamic losses will enable ultrahigh efficiencies previously considered impossible.
The funding approach taken by the US Department of Energy's SunShot programme, which aims to develop competitive solar technology, has proved very successful. Its director, R. Ramesh, explains why.
Mast cells induce protective immune responses through secretion of stimulatory granules. Microparticles modelled after mast-cell granules are now shown to replicate and enhance the functions of their natural counterparts and to direct the character of the resulting immunity.
The contact angle of water drops on substrates for which the wettability is dominated by van der Waals forces remains unchanged when the substrates are coated with a monolayer of graphene. Such 'wetting transparency' could lead to superior conducting and hydrophobic graphene-coated surfaces with tunable electronic properties.
Understanding oxide dissolution processes on the molecular scale remains a challenge. A study on nanoscale oxides suggests a mechanism for dissolution that proceeds through the formation of oxygen-stuffed metastable structures.
Materials science and technology could offer the opportunity to address vital needs of African people. But improving the infrastructure for science education and dissemination of knowledge is the first step to take.
A quantum critical point occurs when different stable phases of matter are in equilibrium at absolute zero temperature. Describing quantum criticality with a theoretical framework that unifies different types of transitions is highly desirable to understand how phenomena such as superconductivity and magnetism interact in correlated electron systems. A study now provides an indication of an underlying universality of quantum criticality, and highlights the role of dimensionality in such a unified theory.
Interfaces between insulating oxides have revealed exotic electronic and magnetic properties. It is now shown that a complex magnetic structure can emerge in an oxide superlattice, and that specific interfaces can unexpectedly exhibit exchange bias. The observations reveal the induction of antiferromagnetism in a material that is usually paramagnetic.
Magnons are quanta of spin-wave excitations and are likely to play a major role in the physical mechanisms of combining spin and heat transport. Now, a new device that enables the properties of magnons to be measured independently of the thermoelectric contribution of electrons and phonons is shown, providing crucial information for understanding the physics of electron–magnon interactions, magnon dynamics and thermal spin transport.
Among other exotic properties graphene exhibits the highest thermal conductivity observed so far. This is true at least for graphene composed of only 12C atoms. However, it is now shown experimentally that regions of 13C atoms can substantially reduce the thermal conductivity. Aside from their fundamental importance, these results suggest that thermal conductivity can be tailored by varying the relative amounts of carbon isotopes used.
Lumped elements such as resistors, capacitors and inductors play a crucial role in electronic circuits. Now, inspired by metamaterials technology, the experimental realization of lumped circuit elements for optical frequencies provides a standardized platform for applications such as mixing and multiplexing of optical signals.
The large-scale synthesis of single-walled carbon nanotubes (SWCNTs) with controlled chirality—which could find applications in fields such as electronics—remains a great challenge. It is now shown that the growth rates of SWCNTs are directly proportional to their chiral angles, suggesting a route towards selective synthesis based on kinetic control.
It is demonstrated that graphene coatings do not alter the wetting behaviour of copper, gold or silicon surfaces. Such wetting transparency—shown to occur only for surfaces where surface–water interactions are dominated by van der Waals forces—and graphene’s ability to suppress copper oxidation result in a 30–40% increase in condensation heat transfer on copper. The findings have implications for graphene-based coatings with independently tunable electronic and wetting properties.
Dissolution processes affect the performance of oxides in applications ranging from power generation to catalysis. A study on polyoxometalate ions, which are thought to model oxide surfaces, now suggests that dissolution is controlled by the stability of transient oxygen-stuffed structures.
The growth of microcrystals can be controlled by various agents such as ions, small charged molecules and polyelectrolytes. However, their use is specific to the crystallizing material. It is now shown that oppositely charged nanoparticles can act as ‘universal’ surfactants for controlling the growth and stability of microcrystals of inorganic salts and of charged organic molecules.
In the quest for more efficient thermoelectrics, a common strategy has been to introduce nanostructures in bulk crystals, thus reducing the thermal conductivity without affecting the electrical transport properties. A route is now presented in which the aggregation of nanoplatelets creates nanostructured materials that have higher thermoelectric efficiencies than their bulk counterparts.
Flexible electronics and other nanoscale devices require simple yet reliable assembly procedures. An optical welding technique for metal nanowires, based on surface plasmon resonances, is now used to fabricate interconnected nanowire networks with enhanced electrical properties for use as transparent electrodes in solar cells and other electrical devices.
Mast cells act to enhance immune responses through the release of insoluble granules that contain inflammatory mediators. Now, submicrometre polymer particles are shown to replicate and enhance the functions of mast-cell granules in vivo, such as the targeting of draining lymph nodes and the timed release of encapsulated mediators. The particles can also polarize the resulting immune response.
Progress in photovoltaic technology could soon mean grid parity for solar electricity. In this focus issue we highlight scientific as well as science-policy strategies aimed towards achieving this goal.