Letters in 2010

Bilayer membranes encase several biological entities, for example cells and organelles. Their rupture under mechanical stress usually occurs by a pore-formation mechanism. Now, lipid-bilayer membranes spreading on a solid surface are shown to rupture in a series of rapid avalanches causing fractal membrane fragmentation.

The oral delivery of small interfering RNA (siRNA) to diseased intestinal tissue is challenging because of the harsh environment created by gastrointestinal fluids and mucosa. Now, such delivery of siRNA to sites of intestinal inflammation is achieved using polythioketal nanoparticles and gene expression is successfully inhibited in the inflamed tissue.

DNA-functionalized, anisotropic nanostructures, such as triangular nanoprisms and nanorods, are shown to assemble by means of DNA hybridization into colloidal crystal structures. The crystallization parameters of these nanostructures, and hence the dimensionality and symmetry of the resultant superlattice, are strongly influenced by particle shape.

Domain walls in magnetic nanostructures could be used in information storage devices. The speed at which these domain walls can move when a magnetic field is applied has always been found to have a maximum. It is now shown that this can be increased by proper design of the magnetic structures, opening the way to faster and more reliable devices.

By using the spin Seebeck effect, the generation of an electric voltage from a heat gradient is demonstrated for the first time in an insulator. This finding extends the range of potential materials for thermoelectric applications, and provides a crucial piece of information for understanding the physics of the spin Seebeck effect.

The generation of an electric voltage from a heat gradient is demonstrated for the first time in the ferromagnetic semiconductor GaMnAs. This allows flexible design of the magnetization directions, a large spin polarization, and measurements across the magnetic phase transition. The effect is observed even in the absence of longitudinal charge transport.

The typical high-surface-area and voids of nanoscale cage structures make them attractive for catalysis, gas storage and drug delivery. Contrary to other metal–semiconductor particles, a ruthenium cage is now shown to grow selectively on the edges of a faceted copper sulphide nanocrystal.

Polymeric impurities in liquid crystals are known to perturb liquid-crystalline order. It is now shown that spatial gradients in the order, created by illuminating the materials with ultraviolet light, can be used to generate forces that allow the polymers to be concentrated or dispersed in the liquid crystal.

Actin filaments are a principal component of the cell cytoskeleton. Using micropatterning methods, physical influences on the growth of highly ordered actin structures are investigated. The spatial organization of actin nucleation sites is discovered to play an important role in establishing the architecture of actin networks.

Flexible electronic devices should lead to new practical applications. Parallel arrays of inorganic nanowires have now been integrated into a flexible pressure-sensor array on a macroscopic scale. The sensor array operates at low voltage and acts as an artificial electronic skin, sensing pressure profiles with high spatial resolution.

Biochemical assays that use magnetic beads are at present in frequent use. Colour-barcoded magnetic microparticles have now been created without using multiple pigmentations. The coding capacity far exceeds that of alternative spectral encoding systems and is demonstrated in a practical bioassay for DNA detection and identification.

Measuring charge transport on the surface of an organic semiconductor crystal in field-effect transistors is difficult. Now solution-processed thin films have been used in a field-effect transistor allowing spectroscopic characterization of the carrier over a large temperature range. The measurements provide information on the nonlinear transport properties observed at low temperatures.

Graphene films are usually made from domains with different orientations. How does this affect transport? A theory of charge transmission through graphene grain boundaries now predicts two distinct transport behaviours depending on the grain-boundary structure. The results could provide important information for the design of efficient graphene-based electronic devices.

Single phosphorus dopants in silicon are one of the physical systems that could be used for quantum information technology. It is now shown that bismuth dopants have similar properties to their phosphorus counterparts, and could offer even more possibilities for quantum information applications.

Terahertz emitters, such as quantum cascade lasers (QCLs), are of interest for applications in imaging and sensing. Nevertheless, performance problems such as power out-coupling efficiency have limited their technological potential. However, a study now shows that subwavelength surface patterning of terahertz QCLs leads to significantly enhanced beam collimation and power collection efficiency.

Only few magnetoelectric materials, where magnetism and ferroelectricity are coupled, are known to exist at room temperature, and in most cases the magnetoelectric coupling is weak. The discovery of strong room-temperature magnetoelectric coupling in Sr₃Co₂Fe₂₄O₄₁ at low magnetic fields is therefore a significant advance towards the practical application of multiferroics.

The amorphous nature of metallic glasses makes them interesting for structural applications. However, the interplay between the nature of atomic structures and mechanical properties remains poorly understood. Dynamic micropillar tests now show the important contribution of the inelastic deformation of atomistic free-volume zones to the deformation behaviour of metallic glasses.

In magnetoelectric compounds, magnetism and ferroelectricity are coupled. The observation of light-induced size changes in the room-temperature magnetoelectric BiFeO₃ now adds optical functionality to magnetoelectric devices that may lead to new applications arising from the coupling of light, electric and magnetic fields.

Although density functional theory is widely used in surface science, it has a tendency to predict surfaces to be more stable than they actually are experimentally. Using a many-electron approach such as the random-phase approximation enables accurate surface and adsorption energies for carbon monoxide and benzene on metal surfaces to be determined.

Friction between two surfaces is usually studied at low relative sliding speeds. A molecular dynamics study now explores friction at high speeds, showing the emergence of a ballistic friction regime, qualitatively different from standard drift friction. The findings might have important implications for applications in nanoelectromechanical systems.