Volume 3 Issue 12, December 2008

The self-assembly properties of block copolymers are primitive when compared with natural examples such as protein folding but, as Richard Jones reports, promising new approaches and ideas are being explored.

Carbon nanotubes are usually produced in samples that contain a mixture of different diameters and electronic properties; this is a problem for applications in nanoelectronics but is advantageous when generating ultrashort laser pulses.

Producing large quantities of designer DNA nanostructures at low cost has been a long-standing challenge in nanobiotechnology. It is now possible with the aid of bacteria.

Effective catalysts for the oxidative dehydrogenation of alkanes can be created by adding functional groups to carbon nanotubes.

The interplay between angular momentum, electron spin and magnetism at the nanoscale could have applications in spintronics, transducers and actuators, as well as fundamental research.

Most materials expand when they are heated, but some contract instead. A record value of this effect — known as negative thermal expansion — has now been observed in magnetic nanocrystals.

Most experiments on nanoelectromechanical systems (NEMS) have so far been performed in the frequency domain, whereas applications in computation and information storage will require such systems to be operated in the time domain. A time-resolved optical approach to the transduction of ultrahigh-frequency NEMS that works at frequencies from less than 10 MHz to over 1 GHz has now been demonstrated.

When a spin-polarized current passes from a ferromagnet into a non-magnetic material, the spins of the itinerant electrons are ‘flipped’ at the interface between the two materials, producing a mechanical torque. A nanoscale torsion oscillator has now measured this torque in a metallic nanowire in which one half is ferromagnetic and the other non-magnetic. The unprecedented torque sensitivity offered by this device could have applications in spintronics and fundamental physics, chemistry and biology.

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.

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.

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.

Fibre lasers are used as light sources in many fields of science and technology, and the inclusion of a saturable absorber inside the laser cavity enables ultrafast pulses to be generated. It has now been demonstrated that single-wall carbon nonotubes are excellent saturable absorbers, especially in the 1.3–1.5 μm wavelength region used for optical communications, enabling the output of ultrafast fibre lasers to be tuned over wide range of wavelengths.

Carbon nanotubes used as templates for polymerizing lipids into regular ring-shaped water-soluble assemblies that can dissolve various hydrophobic compounds and membrane proteins, could have applications in cosmetics, medicine and materials science.

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.