Nanoscience and technology

Chiral liquid crystals of two-dimensional colloids have not been extensively investigated. Xu and Gao show that graphene oxide can form chiral liquid crystals, and demonstrate that they can be spun into macroscopic fibres, and that subsequent chemical reduction provides graphene fibres with high conductivity.

Among the wide range of potential applications of graphene, photodetection is believed to be among the most promising. By combining graphene with plasmonic nanostructures, Duan and colleagues observe dramatic improvements in the efficiency and spectral sensitivity of graphene-based photodetectors.

Topological insulators are a unique class of materials characterized by exotic metallic states at their surface, while remaining insulated in the bulk. Sacépéet al. show how to manipulate normal and superconducting electronic transport at the surface of the topological insulator Bi₂Se₃, by tuning a gate-voltage to vary the electronic density.

X-ray ptychography has been used to extend the field of view in high-resolution quantitative imaging. Godardet al. develop Bragg-mode ptychography to reconstruct, in three dimensions, a crystalline specimen that is too large to be studied as a single object with a coherence-limited X-ray beam.

The propagation of magnetic domain walls in nanowires offers promise as the basis of future memory storage technologies. Muñoz and Prieto show that the random pinning of domain walls to structural defects in the nanowires can be suppressed at low fields, thus improving the reliability of the transmission of the domain walls substantially.

The controllable modification of graphene by chemical functionalization can modulate its optical and electronic properties. Sunet al. devise a functionalisation-based method to pattern graphane/graphene superlattices within a single sheet of graphene.

Charge density waves in the structure and electron density of layered materials are closely linked to superconductivity. Using scanning tunnelling techniques, Rahnejatet al. demonstrate the occurrence of such waves in the doped graphene sheets of the superconductor CaC₆.

Mechanical annealing is a process through which the dislocation density in submicrometre metal crystals can be removed purely by applying a mechanical stress. This study shows that mechanical annealing occurs in body centred cubic molybdenum, and not only in face centred crystals as previously thought.

Tunnelling transitions triggered by microwave irradiation between coupled quantum dots have generally been assumed to be spin-conserving. This study shows that this condition is violated in the presence of spin–orbit coupling, thus opening new possibilities for manipulating a two–spin qubit system by microwave irradiation.

Magnetoresistive random access memory offers significant promise as a next-generation memory technology. Nan and colleagues present a design concept for a device that simultaneously possesses ultrahigh storage capacity, ultralow power dissipation, and high-speed operation at room temperature.

External electric fields have been used to control the motion of small objects through electrostatic repulsion. Here, electric fields are used to polarize conducting objects, triggering their movement by spatially separated electrochemical reactions leading to directionally controlled bubble evolution.

Photonic alternatives to electrical circuits require low energy demand and fast modulation speed, which has proven difficult for on-chip devices. Using quantum dot photonic crystal nanocavities, Vučkovićet al. demonstrate an electrically-switchable light-emitting diode with such capabilities.

Detecting bacteria in clinical samples usually requires culture processes that are time consuming and impede rapid diagnoses. Now, a surface-enhanced Raman spectroscopic method is reported that allows the label- and culture-free detection and analysis of bacteria.

DNA nanotubes could be used to transport nano-cargo and incorporated into nano-devices. In this study, rolling circle amplification is used to generate DNA subunits, and their thermodynamic growth results in the formation of nanotubes with a controlled diameter.

Metallic and semiconducting carbon nanotubes generally coexist in 'as-grown' materials. In this study, single-walled nanotubes are sorted using regioregular poly(3-alkylthiophene)s; rational selection of polymers, solvent and temperature allows the selective dispersion of semiconducting carbon nanotubes.

The miniaturization of optical devices is crucial for their on-chip integration with a variety of technological applications. Here, Liuet al. present an ultracompact beam splitter to control the direction of light through the generation of surface plasmon polaritons.

Controlling the magnetic properties of nanoparticles is important to enable their widespread use in applications. Antoniaket al. combine X-ray absorption spectroscopy and density functional theory calculations to uncover the origin of these properties in order to appropriately tailor nanoparticle design.

Plasmonic nanostructures and metamaterials can augment the performance of photovoltaic and thermophotovoltaic cells by enhancing their absorption properties. Aydinet al. demonstrate a broadband, ultrathin plasmonic super absorber using crossed trapezoids as part of a metal–insulator–metal stack.

Graphene may be used in nanoscale electronics and devices, but the ability to synthesise uniform graphene with well-controlled layer numbers is necessary for these applications. Using a Ni–Mo alloy, this study demonstrates single-layer graphene growth with 100% surface coverage and tolerance to variations in growth conditions.

Nanofluidic diodes are utilized for the rectification of ionic transport, but their rectifying properties cannot be altered after the devices are made. Here, a field-effect reconfigurable nanofluidic diode is reported in which the forward direction and the degree of rectification can be modulated by a gate voltage.

The interfaces between complex oxides can play host to a range of interesting electronic phenomena. Xieet al. demonstrate that the electronic properties at the LaAlO₃/SrTiO₃interface can be tuned upon application of common polar solvents such as acetone, ethanol and water.

The ability to control the charge and spin of single molecules at metal interfaces underpins the concept of molecular electronics. Mugarzaet al. examine these properties using scanning tunnelling microscopy, and uncover their influence on the magnetism and transport properties of the molecule/metal systems.

Simple routes to self-assembling magnetic materials are elusive. Tew and colleagues produce copolymers containing cobalt complexes, which phase separate to give ferromagnetic properties at room temperature following heat treatment.

Nanocrystals are used in light-emitting diodes and solar cells, but their charge transport in films is unclear. Here, the study of PbS nanocrystal films reveals the role of mid-gap states in their charge transport, suggesting different design needs for devices operated in dark (transistors) versus light (solar cells) conditions.

Plasmon resonances occur as collective excitations of surface electrons in noble metal nanoparticles. This study presents a new way of manipulating their behaviour by creating bimetallic dimers which, as a result of their asymmetric composition, give rise to unusual optical properties.

Quasi-three-dimensional plasmonic crystals have potential uses in miniaturized photonics. In this study, a method is described to enhance plasmonic resonance in the crystals by coupling them to optical modes of Fabry–Perot type cavities, with possible applications in photonic and sensor components.

The manipulation of electrons forms the basis of modern technology, whereas electrical signalling processes in nature are based on ions and protons. Rolandi and colleagues present a proton transistor based on polysaccharide nanofibres, which can control the flow of protonic currents.

Plasmonic nanostructures can be used to manipulate objects larger than the wavelength of light but create thermal heating. In this work, the trapping and controlled rotation of nanoparticles is demonstrated using a plasmonic nanotweezer with a heat sink, predicting a reduction in heating compared with previous designs.

Protein microarrays are useful both in basic research and also in disease monitoring and diagnosis, but their dynamic range is limited. By using plasmonic gold substrates with near-infrared fluorescent enhancement, Tabakman et al. demonstrate a multiplexed protein array with improved detection limits and dynamic range.

Hydrogels have a variety of applications including tissue engineering and controlled drug delivery. Here, liquid-crystal hydrogels are developed which transform into a fluid solution upon cooling; cells can be encapsulated in the gel at room temperature, then released at physiological temperatures.

Property coupling by heteroepitaxy is severely limited in material combinations with highly dissimilar bonding. This report presents a chemical boundary condition methodology to actively engineer two-dimensional film growth in such systems that otherwise collapse into island formation and rough morphologies.

Photodetection is believed to be among the most promising potential applications for graphene. Here, by combining graphene with plasmonic nanostructures, the efficiency of graphene-based photodetectors is increased by up to two orders of magnitude.

DNA origami involves the folding of long single-stranded DNA into designed structures that may aid the development of useful nanomechanical DNA devices. In this study, DNA origami pliers and forceps are shown to undergo conformational changes on single-molecule binding.

High-power mechanical energy harvesting could be an alternative to batteries, but efficient energy conversion technology has been missing. Here, a novel mechanical-to-electrical energy conversion method is described that is based on reverse electrowetting and is uniquely suited for high-power energy harvesting.

Composites of carbon nanotubes and superconductors provide technologically important new, or improved, functionalities. Here, with a chemical solution approach, well-aligned carbon nanotube forests embedded in a superconducting NbC matrix are shown to effectively enhance the superconducting properties of NbC.

Being able to determine the wetting properties of individual nanoparticles would aid the preparation of particles with controlled surface properties. Isaet al. develop an in situ freeze-fracture shadow-casting method and use this to determine structural and thermodynamic properties of various 10 nm particles at fluid interfaces.

Chemical manipulation of fullerenes has allowed the production of heptagon-containing fullerenes, but they have not been synthesised using bottom-up approaches. Here, a heptagon-containing fullerene[68] is obtained as C₆₈Cl₆from a carbon arc plasma.

The use of carbon nanotubes in nanoelectronics requires an understanding of their resistive, or Joule, heating at interconnects. Here, Joule heating dynamics are imaged in real time by following the evolution of resistive hot spots with a transmission electron microscope.

High critical temperature superconductors could be used to produce ideal electric power lines, but the misalignment of crystalline grain boundaries reduces current density. Here, pnictide superconductors are found to be more tolerant to misaligned grain boundaries than cuprates.

Flux-closure patterns are rarely observed in ferroelectric materials and almost exclusively form at the nanoscale. McQuaidet al. report mesoscopic dipole closure patterns formed in free-standing single-crystal lamellae of BaTiO₃, thought to result from an unusual set of experimental conditions.

Single-molecule magnets could be useful for the development of spintronic devices. Here single-molecule magnets are encapsulated in carbon nanotubes without affecting the properties of the guest molecules, which may be useful in the development of spintronic or high-density magnetic storage devices.

Covalent reactions on carbon nanotube surfaces typically occur at random positions on the hexagonal lattice. Denget al. show that Billups–Birch reductive alkylation takes place at, and propagates from, sp³defect sites, leading to confinement of the reaction fronts in the tubular direction.

Optical computing, involving on-chip integrated logic units, could provide improved performance over semiconductor-based computing. Here, a binary NOR gate is developed from cascaded OR and NOT gates in four-terminal plasmonic nanowire networks; the work could lead to new optical computing technologies.

The construction of three-dimensional hierarchical heterostructures can lead to improved electrochemical properties. Maiet al. synthesize a three-dimensional multicomponent oxide, MnMoO₄/CoMoO₄, which is used to produce a supercapacitor with enhanced performance.

Glucose biofuel cells can be used to produce clean energy from renewable sources, but their use is limited by poor stability and low power output. In this study, bioelectrodes are fabricated using carbon nanotubes and the resulting biofuel cells have improved stability and power.

The unoccupied electronic levels of graphene are modified by corrugation, doping and presence of impurities. Here, the authors map discrete electronic domains within a single graphene sheet using scanning transmission X-ray microscopy and provide insight into the modification of unoccupied levels.

Waveplates are used in optoelectronics to alter the polarization of light, but they do not typically perform achromatically, which is important for applications such as three-dimensional displays. Here, biologically inspired periodically multilayered structures are produced, which function as achromatic visible-light waveplates.

Optoelectronic devices such as conventional semiconductor lasers are used to study the chaotic behaviour of nonlinear systems. Here chaos is observed for quantum-dot microlasers operating close to the quantum limit with potential for new directions in the study of chaos in quantum systems.

Single nanoparticles are known to emit light intermittently, or 'blink', but the mechanisms describing this phenomenon are not fully understood. This study demonstrates that, for small clusters of blinking nanoparticles, the number of particles within a cluster dramatically influences blinking time.