Research articles

Classically, friction is known to increase with increasing normal load. Scanning probe experiments now show that reversible local delamination of chemically modified graphite can lead to an enhancement in friction as the applied load decreases, resulting in an effectively negative friction coefficient.

Phase-change materials show an unusual metal–insulator transition that is induced by disorder in the crystalline state. Numerical computations now show how the transition to the metallic state proceeds from the dissolution of electronic states situated at vacancy clusters to the formation of ordered vacancy layers.

Nickel-rich layered lithium transition metal oxides have been investigated as high-energy cathode materials for rechargeable lithium batteries because of their high specific capacity and relatively low cost. Such an oxide with high capacity (215 mA h g^-1), where the nickel concentration decreases linearly whereas the manganese concentration increases linearly from the centre to the outer layer of each particle, is now proposed.

On application of a focused magnetic field, zinc-doped iron oxide nanoparticles with targeting antibodies attached are shown to activate cell death signalling in a spatially controlled manner. This triggering of apoptosis signalling, via the magnetically activated aggregation of receptors, is observed in both in vitro and in vivo systems.

Quasicrystals are known for their lack of long-range periodic order. The observation in quasicrystals of quantum critical phenomena that are not seen in their crystalline approximants now demonstrates that the quasicrystals also have unique electronic states.

There are a number of approaches to coupling light with thin-film devices such as solar cells. The demonstration now that multiple scattering processes in two-dimensional random media enable efficient light trapping suggests new possibilities for photon management with the benefit of broad spectral and angular operation.

Controlling surface structure at the atomic scale is paramount to developing effective catalysts. The surface structure of MoS₂ is now engineered to preferentially expose edge sites by successfully synthesizing contiguous large-area thin films of a highly ordered double-gyroid MoS₂ bicontinuous network with nanoscale pores.

Understanding the consequences of the interplay of defects and local curvature in crystals is far from complete despite the considerable influence that a defect has on the crystal’s local properties. It is now found that interstitials inserted in curved crystals at oil/glycerol interfaces can fractionate into two dislocations, which glide through the lattice in opposite directions until they get absorbed into existing dislocations, scars or pleats.

The properties of graphene have been widely studied for applications in electronics. Expanding its use in photonics as well, it is now demonstrated that the propagation of terahertz waves can be electronically switched by such a single atomic layer of carbon.

Topological crystalline insulators are a novel state of matter in which the topological features of the electronic structure have been predicted to originate from crystal symmetries. Now an experimental realization of a topological crystalline insulator is reported, in the form of Pb_1−xSn_xSe.

Mechanistic details on how a molecular crystal nucleates on a surface remain limited because it is difficult to probe rare events at the molecular scale. Now, single-molecule real-time transmission electron microscopy shows that a single-molecule template on the surface of carbon nanohorns can nucleate the crystallization of two organic compounds, and that the mechanism is reminiscent of a two-step nucleation process in solution.

Memristors are devices whose dynamic properties are of interest because they can mimic the operation of biological synapses. The demonstration that ferroelectric domains in tunnel junctions behave like memristors suggests new approaches for designing neuromorphic circuits.

Its high carrier mobility is one of the factors that makes graphene interesting for electronic and photonic applications at terahertz frequencies. Such possibilities are now further supported by the demonstration of an efficient room-temperature graphene detector for terahertz radiation that promises to be considerably faster than competing techniques.

Solid-state sensors for the detection of heavy-metal cations require for the most part sophisticated chemistry and equipment. It is now shown that toxic cations in environmental samples can be detected with ultrahigh sensitivity and over a broad range of cation concentrations by measuring the tunnelling current across films of nanoparticles decorated with striped monolayers of organic ligands.

Whether a liquid forms a crystal or a glass on solidification depends on many factors. The finding now that a disordered structure is favoured in B₂O₃ because the system cannot choose between several crystalline polymorphs of similar energy highlights a link between glass formation and crystallization.

The dynamics of spins in single atomic layers of cuprates and other compounds are important for understanding their properties, such as magnetism and high-temperature superconductivity. Now, spin excitations in isolated single layers of a cuprate have been measured, providing valuable feedback on their magnetic properties.

Three-dimensional bioactive scaffolds can support tissue growth for studies in cellular biophysics and regenerative medicine. Such scaffolds have now been integrated with semiconductor nanowires to probe their porous interior, allowing for real-time monitoring of signals such as the response of neural and cardiac tissue models to drugs.

Knowledge of the density of optical states is crucial for understanding the function of photonic devices. A method that can map optical states with subwavelength precision, and therefore allow the study and design of optical properties on the nanoscale, is now reported.

The electronic interactions at the interface of oxide materials promise properties that can be very different from those of the parent compounds. The finding that many-body interactions in oxide superlattices can be used to engineer electronic properties offers a new strategy for designing oxide heterostructures.

Although oxygen vacancy distributions and dynamics control the operation of solid-oxide fuel cells, understanding the atomistic mechanisms involved during operation of the cell has proved difficult. An approach for the direct mapping of oxygen vacancy concentrations based on local lattice parameter measurements by scanning transmission electron microscopy is now proposed.