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A small world full of opportunities

Nature Materials 9, 181 (2010). doi:10.1038/nmat2720

Light-concentration effects in photonic nanostructures, reviewed in this issue, promise new applications ranging from tumour therapy to catalysis and enhanced solar cells.

Our choice from the recent literature

Nature Materials 9, 182 (2010). doi:10.1038/nmat2719

Photovoltaics: More solar cells for less

Nature Materials 9, 183 (2010). doi:10.1038/nmat2701

Authors: Jia Zhu & Yi Cui

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.

Magnetization dynamics: Ferromagnets stirred up

Nature Materials 9, 184 (2010). doi:10.1038/nmat2706

Author: Markus G. Münzenberg

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.

Oxide surfaces: Surface science goes inorganic

Nature Materials 9, 185 (2010). doi:10.1038/nmat2708

Author: Ulrike Diebold

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

Topological insulators: Oscillations in the ribbons

Nature Materials 9, 187 (2010). doi:10.1038/nmat2705

Author: Thomas Ihn

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

Material witness: Web designers

Nature Materials 9, 190 (2010). doi:10.1038/nmat2707

Author: Philip Ball

Copenhagen no more

Nature Materials 9, 89 (2010). doi:10.1038/nmat2621

The opportunity of reaching a strong agreement on carbon emission cuts must not be missed again.

Biomaterials offer cancer research the third dimension

Nature Materials 9, 90 (2010). doi:10.1038/nmat2619

Author: Dietmar W. Hutmacher

To deepen understanding and hasten the development of treatments, cancer needs to be modelled more accurately in vitro; applying tissue-engineering concepts and approaches in this field could bridge the gap between two-dimensional studies and in vivo animal models.

Our choice from the recent literature

Nature Materials 9, 94 (2010). doi:10.1038/nmat2620

Superconductivity: Interfaces heat up

Nature Materials 9, 96 (2010). doi:10.1038/nmat2616

Author: Kosmas Prassides

By using an ionic liquid as a gate dielectric, superconductivity can be induced in an inorganic band insulator up to a temperature of 15 K by an electric field, opening new directions in superconductivity research.

Material witness: Stealing a lead on lead

Nature Materials 9, 98 (2010). doi:10.1038/nmat2618

Liquid crystals: Defects dictated

Nature Materials 9, 99 (2010). doi:10.1038/nmat2617

Author: Dirk J. Broer

Stable particle-like molecular architectures are written in a frustrated chiral-nematic liquid crystal using a vortex laser beam. This fundamentally new mechanism to form toroidal features with anisotropic optical properties has great potential to create new applications in liquid-crystal photonics.

Plasmonics for extreme light concentration and manipulation

Nature Materials 9, 193 (2010). doi:10.1038/nmat2630

Authors: Jon A. Schuller, Edward S. Barnard, Wenshan Cai, Young Chul Jun, Justin S. White & Mark L. Brongersma

Plasmonics for improved photovoltaic devices

Nature Materials 9, 205 (2010). doi:10.1038/nmat2629

Authors: Harry A. Atwater & Albert Polman

Multiferroics: A whirlwind of opportunities

Nature Materials 9, 188 (2010). doi:10.1038/nmat2700

Author: Maxim Mostovoy

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.

Enhanced absorption and carrier collection in Si wire arrays for photovoltaic applications

Nature Materials 9, 239 (2010). doi:10.1038/nmat2635

Authors: Michael D. Kelzenberg, Shannon W. Boettcher, Jan A. Petykiewicz, Daniel B. Turner-Evans, Morgan C. Putnam, Emily L. Warren, Joshua M. Spurgeon, Ryan M. Briggs, Nathan S. Lewis & Harry A. Atwater

Si wire arrays are a promising architecture for solar-energy-harvesting applications, and may offer a mechanically flexible alternative to Si wafers for photovoltaics. To achieve competitive conversion efficiencies, the wires must absorb sunlight over a broad range of wavelengths and incidence angles, despite occupying only a modest fraction of the array’s volume. Here, we show that arrays having less than 5% areal fraction of wires can achieve up to 96% peak absorption, and that they can absorb up to 85% of day-integrated, above-bandgap direct sunlight. In fact, these arrays show enhanced near-infrared absorption, which allows their overall sunlight absorption to exceed the ray-optics light-trapping absorption limit for an equivalent volume of randomly textured planar Si, over a broad range of incidence angles. We furthermore demonstrate that the light absorbed by Si wire arrays can be collected with a peak external quantum efficiency of 0.89, and that they show broadband, near-unity internal quantum efficiency for carrier collection through a radial semiconductor/liquid junction at the surface of each wire. The observed absorption enhancement and collection efficiency enable a cell geometry that not only uses 1/100th the material of traditional wafer-based devices, but also may offer increased photovoltaic efficiency owing to an effective optical concentration of up to 20 times.

A homologous series of structures on the surface of SrTiO3(110)

Nature Materials 9, 245 (2010). doi:10.1038/nmat2636

Authors: James A. Enterkin, Arun K. Subramanian, Bruce C. Russell, Martin R. Castell, Kenneth R. Poeppelmeier & Laurence D. Marks

Strontium titanate is seeing increasing interest in fields ranging from thin-film growth to water-splitting catalysis and electronic devices. Although the surface structure and chemistry are of vital importance to many of these applications, theories about the driving forces vary widely. We report here a solution to the 3×1  SrTiO3(110) surface structure obtained through transmission electron diffraction and direct methods, and confirmed through density functional theory calculations and scanning tunnelling microscopy images and simulations, consisting of rings of six or eight corner-sharing TiO4 tetrahedra. Further, by changing the number of tetrahedra per ring, a homologous series of n×1 (n≥2) surface reconstructions is formed. Calculations show that the lower members of the series (n≤6) are thermodynamically stable and the structures agree with scanning tunnelling microscopy images. Although the surface energy of a crystal is usually thought to determine the structure and stoichiometry, we demonstrate that the opposite can occur. The n×1 reconstructions are sufficiently close in energy for the stoichiometry in the near-surface region to determine which reconstruction is formed. Our results indicate that the rules of inorganic coordination chemistry apply to oxide surfaces, with concepts such as homologous series and intergrowths as valid at the surface as they are in the bulk.

Insulating interlocked ferroelectric and structural antiphase domain walls in multiferroic YMnO3

Nature Materials 9, 253 (2010). doi:10.1038/nmat2632

Authors: T. Choi, Y. Horibe, H. T. Yi, Y. J. Choi, Weida Wu & S.-W. Cheong

Transition from a strong-yet-brittle to a stronger-and-ductile state by size reduction of metallic glasses

Nature Materials 9, 215 (2010). doi:10.1038/nmat2622

Authors: Dongchan Jang & Julia R. Greer

Amorphous metallic alloys, or metallic glasses, are lucrative engineering materials owing to their superior mechanical properties such as high strength and large elastic strain. However, their main drawback is their propensity for highly catastrophic failure through rapid shear banding, significantly undercutting their structural applications. Here, we show that when reduced to 100 nm, Zr-based metallic glass nanopillars attain ceramic-like strengths (2.25 GPa) and metal-like ductility (25%) simultaneously. We report separate and distinct critical sizes for maximum strength and for the brittle-to-ductile transition, thereby demonstrating that strength and ability to carry plasticity are decoupled at the nanoscale. A phenomenological model for size dependence and brittle-to-homogeneous deformation is provided.