Letters in 2010

Plasmon lasers can operate at dimensions well below the diffraction limit. Their small size promises uses in nanophotonic circuits and for other size-critical applications. The demonstration of a sub-diffraction-limited plasmon laser with low losses, which enables its room-temperature operation, takes a significant step towards realizing the potential of these lasers.

Theoretical models of colloids with directional and anisotropic interactions have predicted the existence of both liquids with vanishing density, and arrested networks at equilibrium — that is, not undergoing phase separation. Experimental evidence of empty liquids and equilibrium gels is now provided for Laponite, a synthetic clay. These observations further our understanding of anisotropic interactions in colloidal suspensions.

A one-step preparation method of electrospun, synthetic scaffolds with controlled surface chemistry and functionality is reported. On addition of amphiphilic macromolecules, non-specific protein adsorption on the fibres’ surfaces is reduced, and by the further covalent attachment of certain peptide sequences to the fibres, specific bioactivation of the scaffold is achieved.

A low-temperature, solution-based preparation of amorphous, metal oxide semiconducting thin-films is reported. This ‘sol–gel on chip’ hydrolysis approach yields thin-film transistors with high field-effect mobilities, reproducible and stable turn-on voltages and high operational stability.

Ratchet systems can extract work from non-equilibrium processes. Yet present electronic ratchets only operate at cryogenic temperatures and generate low currents, which are clear limitations for their practical use. Now, organic electronic ratchets providing enough power to drive simple logic circuits at room temperature have been realized.

The chemical versatility of organic semiconductors promises to be of great use to electronics and spintronics. As an example, it is now demonstrated that the spin polarization of extracted carriers from an organic semiconductor device can be controlled by the insertion of a thin layer of polar material. This approach opens up ideas for future spintronic device concepts.

Skyrmions are vortex-like arrangements of spin magnetic moments, which so far have been observed in only a few compounds, and only at low temperatures. The discovery that skyrmions can be stabilized by thin magnetic films close to room temperature promises their use in spintronic devices.

Blood platelets aggregate to form clots that prevent haemorrhage. Knowledge of single-platelet mechanics is scarce, however. Atomic force microscopy experiments now show that platelets contract rapidly on contact with fibrinogen, and adhere strongly to multiple fibrin polymers, enhancing the elasticity of clots. These findings are relevant to disorders of platelet function, such as thrombosis.

The only way diamond can be polished is by pressing it against small diamond crystals, but this works well only for certain crystallographic orientations. The details of this wear mechanism have now been uncovered in simulations that suggest wear occurs via a thin amorphous layer on the diamond surface.

The atomic configuration of metallic glasses is a long-standing issue important to the understanding of their properties. Nanobeam electron diffraction experiments now enable a direct determination of the local atomic order in a metallic glass.

Although crumpled sheets have large resistance to compression, little is known about the dynamical evolution of their three-dimensional spatial configurations. The formation of a network of ridges and vertices into which the energy is localized is now observed during dynamic crumpling under isotropic confinement.

The surface-directed mineralization of calcium phosphate from simulated body fluid is studied by cryogenic transmission electron microscopy. Prenucleation clusters aggregate close to the surface, then amorphous calcium phosphate forms in this region, leading to the nucleation of oriented apatite crystals at the surface.

Magnons are collective excitations of spins in a material, and just like individual electron spins, they could form the basis for novel computing concepts. Now, determination of the almost loss-less electrical switching of magnons at room temperature takes us a step closer to such ‘magnonic’ devices.

Cathode degradation and methods for improving the selectivity of anode catalysts remain crucial challenges for the design of polymer electrolyte membrane fuel cells. A chemically modified Pt electrode with a self-assembled monolayer of calix[4]arene molecules is now shown to selectively block the undesired oxygen reduction reaction.

The role of collagen in bone apatite mineralization has so far remained unclear. Now, on combining cryogenic electron microscopy and in vitro systems, it is shown that collagen works alongside inhibitors of hydroxyapatite nucleation to control infiltration of amorphous calcium phosphate into collagen fibrils and convert the amorphous phase into apatite crystals.

The detection of acoustic signals is of relevance for a range of practical applications, for example in medical diagnostics. However, in contrast to the rectification of electric current in diodes, acoustic rectification has not yet been achieved. The first experimental demonstration of an acoustic rectifier therefore promises significant impact for practical applications.

A spin-polarized current induces a spin torque on the magnetization of a ferromagnetic film, which according to theory leads to spin-wave emissions. These spin waves have now been observed with a mapping technique that shows a highly directional emission. The results are of key importance to understanding the physics of spin waves and their possible use in spintronic devices.

The formation of a NaTl lattice structure by DNA-mediated assembly of gold nanoparticles and virus-like protein nanoparticles is reported. The inorganic and organic components each form diamond-like frameworks that interpenetrate to give the NaTl lattice. These diamond-like structures are of interest for potential applications as photonic materials.

The fabrication of oxide thin-film heterostructures has improved considerably over the past few years. The first demonstration of the fractional quantum Hall effect in an oxide now attests to the potential of these compounds to rival conventional semiconductors.

The improvement of catalysts for the oxygen-reduction reaction is an important challenge for fuel cells and other electrochemical-energy technologies. A composite nanoporous Ni–Pt alloy with a tailored geometric architecture is now shown to exhibit high mass activity for oxygen reduction.