Letters

Difficulties in controlling the nucleation and growth of thin films of organic semiconductors have impaired progress in organic electronics. Now, efficient control of the crystallite nucleation and microstructure of a broad range of organic semiconductors without detriment to their electronic properties has been achieved through the addition of small quantities of additives—a widely used strategy in bulk polymer crystallization.

Surface-active macromolecules that are chemically different can be mixed at fluid interfaces if the molecules attract each other, or if they have complementary shapes and a net attraction is induced by a depletant. Now, a strategy that eludes the need for complementarity between the molecules, where tethered molecular brushes induce an entropic net repulsion between like species, achieves long-range arrays of perfectly mixed macromolecules.

Iridate materials are at present the focus of interest because the combination of strong spin–orbit effects and many-body electronic correlations makes their physics non-trivial. Now, the density of states of Sr₃Ir₂O₇ is mapped out spatially using scanning tunnelling microscopy and spectroscopy, yielding insights into the influence of nanoscale heterogeneities on the electronic structure.

The unconventional superconductivity associated with iron pnictide materials has been the subject of intense interest. Using an annealing procedure to control the charge-carrier concentration, the behaviour of an FeSe monolayer deposited on SrTiO₃ is now investigated, and indications of superconductivity at temperatures up to 65 K observed.

Progress in DNA-mediated nanoparticle self-assembly has been hampered by the lack of a general method to control the bonding of nanoparticles of different chemical composition into lattices by means of DNA linkers. An approach that makes possible the functionalization of any nanoparticle that has hydrophobic capping ligands with a dense monolayer of DNA, and allows for independent control of composition, particle size and lattice parameters for a variety of lattices, is now demonstrated.

A ferroelectric tunnelling heterostructure is presented in which both the height and the width of the tunnelling barrier can be electrically modulated, leading to a greatly enhanced tunnelling electroresistance. In Pt/BaTiO₃/Nb:SrTiO₃ heterostructures, an ON/OFF conductance ratio that is about an order of magnitude greater than those reported in normal ferroelectric tunnelling junctions, is demonstrated at room temperature.

Coherent twin boundaries, which usually form during the growth, deformation or annealing of crystalline solids, are widely described as perfect interfaces. Experiments and simulations now show that as-grown coherent twin boundaries in nanotwinned copper consist of incoherent segments and partial dislocations, and significantly affect the material’s mechanical behaviour and deformation mechanisms.

A highly selective and efficient approach to covalently bond complementary DNA strands in solution and on surfaces on demand is shown. The approach involves the substitution of a pair of complementary bases by cinnamate-based crosslinks, which can be activated on exposure to ultraviolet light, and allows chemical patterning of flat and curved surfaces down to micrometre and potentially submicrometre resolutions.

The conversion efficiency of heat to electricity in thermoelectric materials depends on both their thermopower and electrical conductivity. It is now reported that, unlike their inorganic counterparts, organic thermoelectric materials show an improvement in both these parameters when the volume of dopant elements is minimized; furthermore, a high conversion efficiency is achieved in PEDOT:PSS blends.

The conversion of a spin current into an electric signal is known as the inverse spin Hall effect, and is expected to enable the full potential of spintronic devices to be realized. Although the effect has been extensively studied in inorganic metals and semiconductors, it is now shown also to occur in a solution-processed organic polymer placed in proximity to a magnetic insulator.

The development of metallic glasses is hindered by the lack of mechanistic understanding of why some alloys crystallize quickly and thus are poorer at forming glasses than those that crystallize slowly. A molecular dynamics study of the growth rate of a planar crystal surface in model metallic glasses now shows that their glass-forming ability is determined by the structure of the crystal/liquid interface.

Spillover of reactants from one active site to another is important in heterogeneous catalysis but is notoriously hard to detect or control, especially for hydrogen. The hydrogen spillover pathway on a Pd–Cu alloy can now be controlled by reversible adsorption of a spectator molecule. This effect observed during a surface catalysed reaction should prove useful for controlling uptake and release of hydrogen in a model storage system.

The silver chalcogenide semimetals are known for their appealing magnetoresistive properties. It is now shown that when copper silver selenide is doped with nickel, these properties are maintained, resulting in high electron mobilities and, in turn, a significant thermoelectric effect.

Pseudocapacitance is commonly associated with surface or near-surface reversible redox reactions. The kinetics of charge storage in T-Nb₂O₅ electrodes is now quantified and the mechanism of lithium intercalation pseudocapacitance should prove to be important in obtaining high-rate charge-storage devices.

Designing synthetic surfaces whose properties dynamically adapt in response to mechanical stimuli is challenging. Now, liquid-infused nanoporous elastic substrates that respond to stretching by continuously changing their transparency and wettability—a consequence of smooth variations in surface roughening as the liquid flows inside the pores—are demonstrated.

The optical and electronic performance of inorganic nanocrystal assemblies stabilized by organic ligands has been extensively investigated, whereas less attention has been paid to their thermal transport properties. It is now shown that the thermal conductivity of these composite systems is determined by the vibrational states of both inorganic and ligand regions, as well as by their relative volumes.

The dynamics of thin magnetic films revealed by ultrafast laser techniques cannot be explained by standard equilibrium descriptions. Diffraction experiments using an X-ray laser now allow the spin dynamics of the separate magnetic constituents of ferromagnetic GdFeCo alloys to be spatially resolved.

Despite recent progress in the production of bendable thin-film transistors, their development is limited by leakage currents and fragile inorganic oxides. Combining graphene and single-walled carbon nanotube electrodes with a geometrically wrinkled inorganic layer, highly stretchable and transparent field-effect transistors have now been demonstrated.

Artificially grown superlattices consisting of iron pnictide materials offer a strategy for tailoring their superconducting properties. The fabrication of compositionally modulated oxygen- and cobalt-doped BaFe₂As₂ heterostructures yields vertically aligned defects that introduce strong vortex pinning sites and enhance the materials’ critical current density.

Measuring and characterizing dynamic charge density waves in cuprate superconductors is a challenging task. By using a method based on ultrafast spectroscopy, the problem is overcome and detecting the presence and lifetimes of these fluctuations is made possible.