Volume 9 Issue 3, March 2010

A solar-cell design based on silicon microwires achieves efficient absorption of sunlight while using only 1% of the active material used in conventional designs.

Conflicting observations of the speed at which various ferromagnetic materials respond to an external femtosecond laser excitation have generated considerable controversy. It is now shown that ferromagnets can be divided in two categories, according to the values of specific magnetic parameters.

A plethora of chemical tools is necessary for probing the surface reconstruction of a complex metal oxide.

The observation of Aharonov–Bohm oscillations in nanoribbons of Bi₂Se₃ opens the way for electronic transport experiments in nanoscale three-dimensional topological insulators.

The formation of vortices in multiferroic hexagonal manganites, where the sign of electric polarization changes six times around the vortex core, points towards the origin of composite multiferroic domain walls.

Plasmonic structures are ideally suited to manipulate light on a scale that is much smaller than the wavelength of the plasmon resonance. This review discusses the applications arising from such extreme light concentration, which range from photonic devices and photovoltaics to localized thermal effects.

This review article surveys the potential of using plasmonic nanostructures to enhance the absorption of photovoltaic devices. As a result, the physical thickness of solar cells can be reduced, leading to new photovoltaic-device designs.

The mechanical properties of many materials are different on the nanoscale than they are in the bulk. In the case of metallic glasses, nanometre-scale samples show enhanced ductility. This tensile ductility has now been quantified for samples with diameters down to 100 nm, where a new regime of increased ductility during deformation is observed.

In most suspensions viscosity decreases with increasing shear rate. The opposite effect, shear thickening, is a problem for industrial applications. An understanding of how particle interactions in suspensions influence shear thickening may lead to a solution of this problem through the design of smart suspensions.

The existence of topological conducting surfaces on insulators has been demonstrated by angular photoemission spectroscopy, but the number of transport experiments on these systems have so far been scarce. Transport evidence of topological surface states is now shown in Bi₂Se₃ nanoribbons through the observation of Aharonov–Bohm oscillations.

Control of magnetization in ferromagnetic metals can be achieved through the spin torque of currents of spin-polarized electrons, usually injected externally. It is now shown that even without this spin-polarized injection, a current can induce strong spin torques through the Rashba effect. The efficiency of this process makes it a realistic candidate for room-temperature spintronic applications.

Why does the bandgap in semiconducting carbon nanotubes depend on the way it is measured? It is now shown that the results obtained by scanning tunnelling spectroscopy are usually influenced by screening, which creates the discrepancy with optical measurements. The results highlight the importance of many-body effects in the electronic properties of carbon nanotubes.

The use of silicon nanostructures in solar cells offers a number of benefits, such as the fact they can be used on flexible substrates. A silicon wire-array structure, containing reflecting nanoparticles for enhanced absorption, is now shown to achieve 96% peak absorption efficiency, capturing 85% of light with only 1% of the silicon used in comparable commercial cells.

Resolving the surface structure and chemistry of oxides such as strontium titanate has so far proved difficult. Rings of six or eight corner-sharing TiO₄ tetrahedra and a homologous series of surface reconstructions for SrTiO₃(110) are now predicted.

Creating p–n junctions using semiconducting polymers has proved to be challenging because of difficulties in depositing semiconducting polymer films. Now, by using a cationic conjugated-polymer electrolyte and a neutral conjugated-polymer layer, devices with a fixed bilayer organic p–n junction and fast response times have been fabricated.

The ability to exert control over domains in multiferroic materials is important in terms of the potential use of these materials. In the multiferroic YMnO₃, structural considerations lead to an unusual cloverleaf pattern of ferroelectric domains, where the domain walls are electrically insulating.

Demagnetization in metals occurs on very different timescales depending on the material. It is now shown that electron–phonon-mediated spin scattering describes the process of demagnetization well in every case, and the differences in timescale are mainly determined by the ratio between Curie temperature and the atomic magnetic moment.

The ability to control the surface chemistry of silicon is important for microelectronic applications. Chemical species can now be stabilized on Si(111) surfaces using a partially alkoxylated surface as a nanopatterning template.

Small interfering ribonucleic acid (siRNA) is used to silence genes and treat conditions such as human immunodeficiency virus. Safe and efficient delivery, however, is proving problematic. A new class of biologically active siRNA polyelectrolyte complexes based on chemically self-crosslinked siRNA is presented, which shows greatly enhanced gene-silencing efficiencies in vitro and in vivo without significantly eliciting an immune response.

Light-concentration effects in photonic nanostructures promise new applications ranging from tumour therapy to catalysis and enhanced solar cells. In this focus we look at how the design of light matter-interactions, for example via plasmonic effects, can be used as an efficient means to control light on the nanoscale, towards the realisation of these applications.