Research articles

Experiments to explore electron transport in single molecules generally involve the use of chemical linker groups at both ends of the molecule to firmly anchor it to the source and drain contacts. Here it is shown that oligo-phenylene ethynylene molecules with a single anchor group can form molecular junctions as well. The process is attributed to aromatic stacking between neighbouring molecules in nearby electrodes.

A combination of quantum dots and fluorescence-interference contrast microscopy can be used to monitor the rotation of microtubules with nanometre accuracy as they glide over motor proteins. This approach shows that the microtubules stop rotating when they pick up large cargos, but their velocity does not change.

The mechanical properties of carbon nanotubes rarely match the values predicted by theory owing to a combination of artefacts introduced during sample preparation and inadequate measurements. However, by avoiding chemical treatments and using high-resolution imaging, it is possible to obtain values of the mean fracture strength that exceed previous values by approximately a factor of three.

Fully exploiting the properties of graphene will require a method for the mass production of this remarkable material. The dispersion and exfoliation of graphite in organic solvents can produce graphene monolayers with a yield of about 1% by weight. Moreover, these samples are free from defects and oxides, and can be used to produce semi-transparent conducting films and conducting composites.

The first samples of pristine graphene were obtained by 'peeling off' and epitaxial growth, but chemical approaches are more suited to large-scale production. Exfoliation, reintercalation and expansion of graphite can produce high-quality single-layer graphene sheets suspended in organic solvents, and these sheets can be made into large transparent films by Langmuir–Blodgett assembly.

The performance of state-of-the-art photovoltaic devices based on polymer–nanocrystal composites is still limited by the preparation of the composite films. By blending and annealing cadmium telluride nanocrystals in a polymer–fullerene matrix, high photoconductive gain can be achieved under low applied voltages.

Nanoscale mechanical resonators can make precision measurements of force, position and mass. Atomic resolution in mass sensing at room temperature has now been demonstrated with a carbon nanotube-based resonator that essentially operates as a mass spectrometer. The atomic equivalent of shot noise has also been detected.

The novel electronic properties of graphene can be compromised when it is supported on an insulating substrate. However, suspended graphene samples can display low-temperature mobility values that cannot be attained in semiconductors or non-suspended graphene, and the conductivity approaches ballistic values at liquid-helium temperatures.

Base-pairing drives the assembly of dye-functionalized nanoparticles that have complementary DNA strands attached. This aggregation leads to a massive enhancement of the resonant Raman signal, which may prove useful for sensing applications.

Quantum co-tunnelling through a single-electron transistor limits its performance for many applications. Researchers have now built a nanomechanical single-electron shuttle driven by ultrasound waves in which co-tunnelling is suppressed. This approach could lead to the development of high-performance nanomechanical single-electron devices. (Summary revised 8 July 2008)

Aqueous dispersions of nanoparticles of Triclosan — a commercial antimicrobial agent — display better biocidal activity than organic solutions of the same agent. The nanoparticles are produced by a combination of modified emulsion-templating and freeze-drying.

By carefully controlling the heat capacity and other thermal properties of a superconducting hot-electron nanobolometer, researchers have built a device that is sufficiently sensitive to detect single terahertz photons, making it suitable for use in a future space-based terahertz telescope.

Elastomeric proteins similar to those found in many biological tissues have been engineered so that they can behave as springs or shock absorbers.

Scanning photocurrent microscopy has revealed that metal contacts lead to potential steps that act as transport barriers in graphene devices. The formation of p-type conducting edges surrounding a central n-type channel has also been observed at low carrier densities.

The electrical, optical and mechanical properties of nanowires depend on their morphology. Nanowires that possess both chirality and a branched structure may therefore possess new material properties. Such nanowires can be formed by vapour–liquid–solid branching from a central PbSe nanowire with an axial screw dislocation.

Coating conventional tungsten and stainless steel electrodes with carbon nanotubes improves their performance in research involving the implantation of electrical devices into the nervous system. The results could have an impact on electrophysiology and the development of brain–machine interfaces.

Scanning near-field ultrasonic holography has been used to probe inside cells taken from the lungs of mice that had been exposed to carbon nanohorns, and provides evidence that these particles can enter the cells. The ability to detect nanoparticles below the cell surface could make this technique useful for studying toxicity of nanomaterials.

DNA tiles can be used as a platform to display two different aptamers — short sequences of nucleotides that bind to proteins — with high spatial control, to systematically study the distance dependence of multivalent interactions.

Ferroelectric oxides have emerged as candidate materials for non-volatile data-storage applications, but they can be difficult to process. Researchers have now used a high-temperature deposition process to fabricate arrays of metal–ferroelectric–metal nanocapacitors with a density of 176 gigabits per square inch.

On the basis of first-principles computer simulations, theorists have predicted that zigzag graphene nanoribbons should display magnetoresistance values that are thousands of times higher than previously reported experimental values, and also should be able to generate highly spin-polarized currents.