Nature Materials 8, 535 (2009). doi:10.1038/nmat2485

2009 is turning out to be an interesting year for research funding in the UK. Everyone wants the best science to be funded, but it's not clear that the proposed policy changes will achieve this.

Nature Materials 8, 537 (2009). doi:10.1038/nmat2472

Author: Ulf Leonhardt

Ever since invisibility cloaking has left the realm of fiction and been demonstrated for microwave radiation, cloaking in the visible has been the aim. Having reached the near-infrared, we might be there soon.

Nature Materials 8, 538 (2009). doi:10.1038/nmat2482

Author: Alessandro Troisi

Bulk polycrystalline organic conductors do not behave like two- or three-dimensional materials but as one-dimensional metals.

Nature Materials 8, 539 (2009). doi:10.1038/nmat2483

Author: Vincent M. Rotello

DNA provides more than lock-and-key control of assembly. Careful engineering of hairpins and loops provides the means to control the kinetics of particle assembly, allowing structures to be 'glued' together by heating.

Nature Materials 8, 541 (2009). doi:10.1038/nmat2481

Author: Gerardo Ortiz

A renormalization group study of electric transport in nanocontacts reveals the importance of quantum correlations for achieving a startling ferromagnetic Kondo effect.

Nature Materials 8, 558 (2009). doi:10.1038/nmat2469

Authors: Yusuke Tokunaga, Nobuo Furukawa, Hideaki Sakai, Yasujiro Taguchi, Taka-hisa Arima & Yoshinori Tokura

Controlling ferromagnetism by an external electric field has been a great challenge in materials physics, for example towards the development of low-power-consumption spintronics devices. To achieve an efficient mutual control of electricity and magnetism, the use of multiferroics—materials that show both ferroelectric and ferromagnetic/antiferromagnetic order—is one of the most promising approaches. Here, we show that GdFeO3, one of the most orthodox perovskite oxides, is not only a weak ferromagnet but also possesses a ferroelectric ground state, in which the ferroelectric polarization is generated by the striction through the exchange interaction between the Gd and Fe spins. Furthermore, in this compound, ferroelectric polarization and magnetization are successfully controlled by magnetic and electric fields, respectively. This unprecedented mutual controllability of electricity and magnetism is attributed to the unique feature of composite domain wall clamping of the respective domain walls for electric and magnetic orders. This domain wall feature generally determines the efficiency of the mutual controllability and thus could have an important role towards the application of multiferroics to practical devices.

Nature Materials 8, 563 (2009). doi:10.1038/nmat2476

Authors: Procolo Lucignano, Riccardo Mazzarello, Alexander Smogunov, Michele Fabrizio & Erio Tosatti

The electrical conductance of atomic metal contacts represents a powerful tool for detecting nanomagnetism. Conductance reflects magnetism through anomalies at zero bias—generally with Fano line shapes—owing to the Kondo screening of the magnetic impurity bridging the contact. A full atomic-level understanding of this nutshell many-body system is of the greatest importance, especially in view of our increasing need to control nanocurrents by means of magnetism. Disappointingly, at present, zero-bias conductance anomalies are not calculable from atomistic scratch. Here, we demonstrate a working route connecting approximately but quantitatively density functional theory (DFT) and numerical renormalization group (NRG) approaches and leading to a first-principles conductance calculation for a nanocontact, exemplified by a Ni impurity in a Au nanowire. A Fano-like conductance line shape is obtained microscopically, and shown to be controlled by the impurity s-level position. We also find a relationship between conductance anomaly and geometry, and uncover the possibility of opposite antiferromagnetic and ferromagnetic Kondo screening—the latter exhibiting a totally different and unexplored zero-bias anomaly. The present matching method between DFT and NRG should permit the quantitative understanding and exploration of this larger variety of Kondo phenomena at more general magnetic nanocontacts.

Nature Materials 8, 568 (2009). doi:10.1038/nmat2461

Authors: Jason Valentine, Jensen Li, Thomas Zentgraf, Guy Bartal & Xiang Zhang

Invisibility devices have captured the human imagination for many years. Recent theories have proposed schemes for cloaking devices using transformation optics and conformal mapping. Metamaterials, with spatially tailored properties, have provided the necessary medium by enabling precise control over the flow of electromagnetic waves. Using metamaterials, the first microwave cloaking has been achieved but the realization of cloaking at optical frequencies, a key step towards achieving actual invisibility, has remained elusive. Here, we report the first experimental demonstration of optical cloaking. The optical ‘carpet’ cloak is designed using quasi-conformal mapping to conceal an object that is placed under a curved reflecting surface by imitating the reflection of a flat surface. The cloak consists only of isotropic dielectric materials, which enables broadband and low-loss invisibility at a wavelength range of 1,400–1,800 nm.

Nature Materials 8, 572 (2009). doi:10.1038/nmat2470

Authors: Jonathan D. Yuen, Reghu Menon, Nelson E. Coates, Ebinazar B. Namdas, Shinuk Cho, Scott T. Hannahs, Daniel Moses & Alan J. Heeger

Conducting and semiconducting polymers are important materials in the development of printed, flexible, large-area electronics such as flat-panel displays and photovoltaic cells. There has been rapid progress in developing conjugated polymers with high transport mobility required for high-performance field-effect transistors (FETs), beginning with mobilities around 10−4 cm2 V−1 s−1 to a recent report of 1 cm2 V−1 s−1 for poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT). Here, the electrical properties of PBTTT are studied at high charge densities both as the semiconductor layer in FETs and in electrochemically doped films to determine the transport mechanism. We show that data obtained using a wide range of parameters (temperature, gate-induced carrier density, source–drain voltage and doping level) scale onto the universal curve predicted for transport in the Luttinger liquid description of the one-dimensional ‘metal’.

Nature Materials 8, 576 (2009). doi:10.1038/nmat2467

Authors: C. Manzano, W.-H. Soe, H. S. Wong, F. Ample, A. Gourdon, N. Chandrasekhar & C. Joachim

Gears are microfabricated down to diameters of a few micrometres. Natural macromolecular motors, of tens of nanometres in diameter, also show gear effects. At a smaller scale, the random rotation of a single-molecule rotor encaged in a molecular stator has been observed, demonstrating that a single molecule can be rotated with the tip of a scanning tunnelling microscope (STM). A self-assembled rack-and-pinion molecular machine where the STM tip apex is the rotation axis of the pinion was also tested. Here, we present the mechanics of an intentionally constructed molecule-gear on a Au(111) surface, mounting and centring one hexa-t-butyl-pyrimidopentaphenylbenzene molecule on one atom axis. The combination of molecular design, molecular manipulation and surface atomic structure selection leads to the construction of a fundamental component of a planar single-molecule mechanical machine. The rotation of our molecule-gear is step-by-step and totally under control, demonstrating nine stable stations in both directions.

Nature Materials 8, 580 (2009). doi:10.1038/nmat2474

Authors: Chuhong Zhang, Stephen Gamble, David Ainsworth, Alexandra M. Z. Slawin, Yuri G. Andreev & Peter G. Bruce

Polymer electrolytes have been studied extensively because uniquely they combine ionic conductivity with solid yet flexible mechanical properties, rendering them important for all-solid-state devices including batteries, electrochromic displays and smart windows. For some 30 years, ionic conductivity in polymers was considered to occur only in the amorphous state above Tg. Crystalline polymers were believed to be insulators. This changed with the discovery of Li+ conductivity in crystalline poly(ethylene oxide)6:LiAsF6 (refs 4, 5). However, new crystalline polymer electrolytes have proved elusive, questioning whether the 6:1 complex has particular structural features making it a unique exception to the rule that only amorphous polymers conduct. Here, we demonstrate that ionic conductivity in crystalline polymers is not unique to the 6:1 complex by reporting several new crystalline polymer electrolytes containing different alkali metal salts (Na+, K+ and Rb+), including the best conductor poly(ethylene oxide)8:NaAsF6 discovered so far, with a conductivity 1.5 orders of magnitude higher than poly(ethylene oxide)6:LiAsF6. These are the first crystalline polymer electrolytes with a different composition and structures to that of the 6:1 Li+ complex.

Nature Materials 8, 585 (2009). doi:10.1038/nmat2466

Authors: Yunbin He, Antonio Tilocca, Olga Dulub, Annabella Selloni & Ulrike Diebold

The interaction of water with metal oxide surfaces is of fundamental importance to various fields of science, ranging from geophysics to catalysis and biochemistry. In particular, the discovery that TiO2 photocatalyses the dissociation of water has triggered broad interest and intensive studies of water adsorption on TiO2 over decades. So far, these studies have mostly focused on the (110) surface of the most stable polymorph of TiO2, rutile, whereas it is the metastable anatase form that is generally considered photocatalytically more efficient. The present combined experimental (scanning tunnelling microscopy) and theoretical (density functional theory and first-principles molecular dynamics) study gives atomic-scale insights into the adsorption of water on anatase (101), the most frequently exposed surface of this TiO2 polymorph. Water adsorbs as an intact monomer with a computed binding energy of 730 meV. The charge rearrangement at the molecule–anatase interface affects the adsorption of further water molecules, resulting in short-range repulsive and attractive interactions along the [010] and nmat2466-m1gif2726014 directions, respectively, and a locally ordered (2×2) superstructure of molecular water.

Nature Materials 8, 590 (2009). doi:10.1038/nmat2471

Authors: Mirjam E. Leunissen, Rémi Dreyfus, Fook Chiong Cheong, David G. Grier, Roujie Sha, Nadrian C. Seeman & Paul M. Chaikin

Surface functionalization with DNA is a powerful tool for guiding the self-assembly of nanometre- and micrometre-sized particles. Complementary ‘sticky ends’ form specific inter-particle links and reproducibly bind at low temperature and unbind at high temperature. Surprisingly, the ability of single-stranded DNA to form folded secondary structures has not been explored for controlling (nano) colloidal assembly processes, despite its frequent use in DNA nanotechnology. Here, we show how loop and hairpin formation in the DNA coatings of micrometre-sized particles gives us in situ control over the inter-particle binding strength and association kinetics. We can finely tune and even switch off the attractions between particles, rendering them inert unless they are heated or held together—like a nano-contact glue. The novel kinetic control offered by the switchable self-protected attractions is explained with a simple quantitative model that emphasizes the competition between intra- and inter-particle hybridization, and the practical utility is demonstrated by the assembly of designer clusters in concentrated suspensions. With self-protection, both the suspension and assembly product are stable, whereas conventional attractive colloids would quickly aggregate. This remarkable functionality makes our self-protected colloids a novel material that greatly extends the utility of DNA-functionalized systems, enabling more versatile, multi-stage assembly approaches.

Nature Materials 8, 596 (2009). doi:10.1038/nmat2479

Authors: Eleanor F. Banwell, Edgardo S. Abelardo, Dave J. Adams, Martin A. Birchall, Adam Corrigan, Athene M. Donald, Mark Kirkland, Louise C. Serpell, Michael F. Butler & Derek N. Woolfson

Biocompatible hydrogels have a wide variety of potential applications in biotechnology and medicine, such as the controlled delivery and release of cells, cosmetics and drugs, and as supports for cell growth and tissue engineering. Rational peptide design and engineering are emerging as promising new routes to such functional biomaterials. Here, we present the first examples of rationally designed and fully characterized self-assembling hydrogels based on standard linear peptides with purely α-helical structures, which we call hydrogelating self-assembling fibres (hSAFs). These form spanning networks of α-helical fibrils that interact to give self-supporting physical hydrogels of >99% water content. The peptide sequences can be engineered to alter the underlying mechanism of gelation and, consequently, the hydrogel properties. Interestingly, for example, those with hydrogen-bonded networks of fibrils melt on heating, whereas those formed through hydrophobic fibril–fibril interactions strengthen when warmed. The hSAFs are dual-peptide systems that gel only on mixing, which gives tight control over assembly. These properties raise possibilities for using the hSAFs as substrates in cell culture. We have tested this in comparison with the widely used Matrigel substrate, and demonstrate that, like Matrigel, hSAFs support both growth and differentiation of rat adrenal pheochromocytoma cells for sustained periods in culture.