Research articles

Local heating and conduction will have a major role in the stability of nanoscale devices based on molecular junctions, so reliable methods are needed to measure the temperature of such junctions. Researchers have now developed a technique to monitor the effective temperature of current-carrying molecular junctions based on surface-enhanced Raman spectroscopy.

Most solids expand when they are heated, but some non-magnetic materials expand when they are cooled. Researchers have now observed evidence for negative thermal expansion (NTE) in nanocrystals of two magnetic materials. Moreover, the NTE effect in nanocrystals of CuO is four times larger than that observed in the celebrated NTE material zirconium tungstate.

Combining discrete molecular junctions to make integrated circuits is a major goal in molecular electronics, but problems with reliability, stability and yield have hindered progress. Researchers have now overcome some of these challenges to simultaneously fabricate 20,000 molecular junctions on a single wafer and connect 200 of them in series.

Maskless nanolithography is a flexible nanofabrication technique but it suffers from low throughput. By developing a new approach that involves 'flying' an array of plasmonic lenses just 20 nm above a rotating surface, it is possible to increase throughput by several orders of magnitude.

The alarming growth of the antibiotic-resistant superbugs has created a demand for sensors that can investigate antibiotics and their modes of action. The label-free detection of the antibiotic vancomycin binding to mucopeptides on cantilever arrays, with 10 nM sensitivity and at clinically relevant concentrations in blood serum, could lead to improved biosensors and a better understanding of antibiotic drug action in bacteria.

Confining light below the diffraction limit is likely to be a feature of future optical data transmission systems, but it will be necessary to integrate such waveguides with diffraction-limited components. The coupling of light from a polymer optical waveguide into multiple silver nanowire plasmonic waveguides shows that this will be possible.

A combination of scanning transmission electron microscopy and electron energy loss spectroscopy has been used to produce and analyse images of free-standing graphene sheets with atomic resolution. The influence of microstructural peculiarities on the stability of the sheets and the evolution and interaction of point defects were also explored.

Polymer–silica nanocomposite gels can be used to culture cells in a three-dimensional environment, offering a way to propagate cells without using enzymes to dissociate them from the surface of conventional cell culture flasks. This approach relies on the dependence of the viscosity of the gel on stress

Nanoparticle superlattices are promising for many applications but the de-wetting processes normally used to produce these systems are not compatible with conventional patterning methods. Researchers have now developed an approach for patterning such superlattices that involves moulding microdroplets containing the nanoparticles and spatially regulating their de-wetting process.

The first observation of saturating transistor characteristics in a graphene field-effect transistor is reported. The saturation velocity is attributed to scattering by interfacial phonons in the silicon dioxide layer supporting the graphene channels. These results demonstrate the feasibility of graphene devices for analogue and radio-frequency circuit applications without the need for bandgap engineering.

A numerical model of a cell from the electric eel shows that artificial cells can be built to have higher power output densities and greater energy conversion efficiencies than natural cells, allowing them to potentially power medical implants and other devices.

Molecular transport through nanoscale pores is important in many areas of science, but it is difficult to obtain information about the molecules as they pass through the pore. Now it has been shown that imaging with a transmission electron microscope can be used to observe the structure and orientation of a hydrocarbon chain as it passes through a defect in the wall of a carbon nanotube, and also to study how the chain interacts with the nanopore.

Single-electron devices offer many advantages over traditional devices, but it is a challenge to fabricate them in large numbers. A novel geometry in which the source and drain electrodes are vertically separated by thin dielectric films, and nanoparticles attached to the sidewall of the dielectric films act as Coulomb islands, can now be used for the CMOS-compatible fabrication of single-electron devices that operate at room temperature.

The development of molecular devices will require functional molecules that can be integrated into larger architectures and addressed selectively. Now it has been shown that molecular switches, adsorbed in a homogeneous two-dimensional layer, can be collectively switched with spatial selectivity. The probability of a molecule switching is controlled by the surrounding molecules and the supporting surface.

Current techniques to determine reaction rates on the nanoscale measure ensemble averages, making it difficult to relate the catalytic activity of nanoparticles to their morphology. Researchers have now used surface plasmon spectroscopy to observe the kinetics of a redox reaction catalysed by a gold nanoparticle and also the atomic deposition of gold onto a nanocrystal.

The challenge in developing electrical biosensors lies in connecting a molecule detector to an electrical switch. Attaching ion channels to certain cell receptors forms a detector–switch pair that converts chemical information into a measurable electrical signal, creating a platform suitable for screening drugs and other molecules.

Nanoscale particles play an important role in the chemical and biological sciences, but efforts to make nanoparticles from borosilicate glass — which exhibits high tolerance to chemicals and solvents — have proved unsuccessful so far. Now it has been shown that upon mixing a silicon–boron binary oxide solution with water, borosilicate nanoparticles are produced as a result of a vigorous exothermic phase separation.

Conjugated polymer fibres offer many advantages over other photonic materials, such as tunable properties and easy processability, making them attractive for optoelectronic applications. The waveguiding performance and emission tunability of fully conjugated, electrospun polymer nanofibres have been assessed and their forward emission shown to improve after periodic structures are imprinted using nanoimprint lithography.

Semiconducting carbon nanotubes have a direct bandgap, which means that they could form the basis of nanoscale light sources. However, nanotubes tend to emit light over a broad range of wavelengths and directions. Placing the nanotube in a microcavity reduces the spectral width of the output and makes the emission highly directional. This microcavity-controlled, current-driven on-chip emitter is thus an important first step in the development of nanotube-based nanophotonic devices.

Photoacoustic imaging offers higher spatial resolution than most optical imaging techniques, but contrast agents are needed because many diseases in their early stages do not display a natural photoacoustic contrast. Using single-walled carbon nanotubes conjugated with a peptide as a contrast agent allows the non-invasive photoacoustic imaging of tumours in animals.