Research articles

Solid-state catalysts do not participate efficiently in the reduction of N₂ to NH₃ because they tend not to form strong bonds with nitrogen molecules. It is now shown that, under ultraviolet radiation, hydrogen-terminated diamond can eject electrons directly in a liquid solution, thus allowing nitrogen reduction without requiring its preliminary adsorption on a solid surface.

Materials displaying colossal permittivity are promising for a range of energy-storage and microelectronics applications. A strategy for achieving temperature- and frequency-independent colossal permittivity using defect-generated giant dipoles is now demonstrated in (Nb+In) co-doped TiO₂ rutile.

Making colloidal nanoparticles with controlled composition and shape is challenging because at the nanoscale surface energy favours highly symmetric structures. Now, a fast, wafer-scale fabrication scheme that combines low-temperature shadow deposition with nanoscale patterning has been developed that produces anisotropic hybrid nanocolloids with designed composition and feature sizes down to 20 nm.

Field-effect transistors based on molybdenum disulphide have latterly garnered significant interest. Their electrical transport characteristics are now studied for different dielectric configurations, and as a function of temperature.

Although the collective cellular motion involved in, for example, wound healing and tumour invasion is suspected to be driven by mechanical stresses within the advancing cell monolayer, how motion and stress relate has remained elusive. Now, stress-microscopy observations of an epithelial cell sheet advancing towards a region where cells cannot adhere reveal that the cells located nearby such a region exert forces that pull them towards the unfilled space, regardless of whether the cells approach or recede from it.

Quantum wells based on mercury telluride are an experimental realization of a two-dimensional topological insulator. By using a scanning superconducting quantum interference device (SQUID) technique, the magnetic fields flowing through HgTe/CdTe heterostructures are imaged both in the quantum spin Hall and the trivial regimes, revealing the edge states associated with the quantum spin Hall state.

Controlling the direction of propagation of domain walls in magnetic nanowires is essential for their use in proposed device applications. It is now shown that Dzyaloshinskii–Moriya interactions determine the chirality of domain walls in metallic ferromagnets placed between a heavy metal and an oxide, which in turn means the direction of propagation can be determined by choosing suitable material properties.

Although site-dependent metal surface segregation in bimetallic nanoalloys affects catalytic activity and stability, segregation on shaped nanocatalysts and their atomic-scale evolution is largely unexplored. Pt_xNi_1−x alloy nanoparticle electrocatalysts with unique activity for oxygen reduction reactions exhibit an unexpected compositional segregation structure across the {111} facets.

Although the coarsening of catalytically active metal clusters can be accelerated by the presence of gases, the role played by gas molecules is difficult to ascertain. Carbon monoxide-induced coalescence of Pd adatoms supported on a Fe₃O₄ surface is now investigated at room temperature, and Pd-carbonyl species are shown to be responsible for their mobility.

At present, there are no known examples of binary icosahedral quasicrystals featuring localized magnetic moments. Now, a family of magnetic binary icosahedral quasicrystals is discovered, offering the possibility of studying the behaviour of coupled magnetic interactions in the presence of aperiodic structural order.

Domain walls forming within magnetic nanowires offer a valuable degree of freedom with which to explore possible future information storage and processing architectures. By taking advantage of the piezoelectric characteristics of perpendicularly magnetized GaMnAsP/GaAs nanowires, large variations in the current-induced domain wall mobilities are obtained.

The controlled vapour phase synthesis of molybdenum disulphide atomic layers and a fundamental mechanism for the nucleation, growth and grain boundary formation in its crystalline monolayers are now reported. Using high-resolution electron microscopy imaging, the atomic structure of the grains and their boundaries in the polycrystalline molybdenum disulphide atomic layers are examined, and the primary mechanisms for grain-boundary formation are evaluated.

Results suggesting the onset of magnetism at the interface between LaAlO₃ and SrTiO₃ have been among the more intriguing associated with this system. Using element-specific techniques such as X-ray magnetic circular dichroism, direct signatures of in-plane ferromagnetic order occurring at the interface are now reported.

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.

Solution printing of organic semiconductors could in principle be scaled to industrial needs, yet attaining aligned single-crystals directly with this method has been challenging. By using a micropillar-patterned printing blade designed to enhance the control of crystal nucleation and growth, thin films of macroscopic, highly aligned single crystals of organic semiconductors can now be fabricated.

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.

Iron pnictide superconductors represent a suggestive alternative to cuprate superconductors for achieving high transition temperatures. Using in situ angle-resolved photoemission spectroscopy, the electronic properties of FeSe are examined as a function of film thickness, providing valuable insights into the mechanism driving the superconductivity in this material.

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.