Articles in 2008

Conversion electrodes for lithium-ion batteries are capable of high capacity but low energy efficiency and low voltages are problematic. The electrochemical reactivity of MgH₂ with Li shows promise in using metal-hydride electrodes for both lithium-ion-battery and hydrogen storage applications.

Characterizing medium-range order in disordered solids and liquids is crucial for elucidating their structure and transport properties, but it has so far proved difficult. Using a combination of X-ray diffraction and Raman scattering, the pressure-dependent and atomic-void structure of amorphous red phosphorous is determined.

A universal feature of disordered glasses is the appearance of the so-called boson peak in neutron-scattering experiments. A universal link between this boson peak and transverse phonons has now been discovered, and linked to locally favoured structures in the glass.

In a device design that brings mechanical flexibility to silicon photovoltaics, Jongseung Yoon, Alfred J. Baca and colleagues demonstrate how transfer-printing of ultrathin silicon films onto flexible substrates leads to semitransparent and large-scale arrays of integrated solar microcells with high solar-energy conversion efficiencies of 6–8%.

The presence of guest atoms—known as rattlers—in the cages of some clathrate structures is considered to be responsible for the low thermal conductivity of the materials. Neutron spectroscopy provides important evidence regarding the actual phonon dispersion in the material, and the precise way in which this is influenced by rattlers.

The low thermal conductivity in filled skutterudites has been ascribed to rattling atoms inducing a phonon glass. Experimental evidence now shows that the phonon glass description is incorrect, and provides essential insight for the development of microscopic models aimed at describing the thermoelectric properties of these materials.

Cell–matrix interactions have critical roles in regeneration, development and disease. Encapsulated human mesenchymal stem cells can now be induced to differentiate down osteogenic and adipogenic pathways by controlling their three-dimensional environment using tethered small-molecule functional groups.

Magneto-chiral dichroism is an effect in which unpolarized light is absorbed differently for parallel and antiparallel propagation with respect to an applied magnetic field. Previous observations have only seen a rather weak demonstration of this effect. Following a challenging synthesis, strong magneto-dichroism has now been observed in enantiopure chiral ferromagnets.

The observation of Rabi-oscillations between single and triplet states in an organic light-emitting diode demonstrates the possibility of manipulating the spin states in organic electronic devices. The data also provide direct evidence of very slow spin-dephasing, which should prove crucial for the development of organic spintronics.

In solid-state lighting, phosphors are typically used to complement the blue light of the original emitter to achieve white-light emission. The capability to deposit certain phosphors at much lower temperatures than previously enables their use on organic substrates and opens the door to fabricate large-area white-light emitters.

The scales of a fish are its first level of defence. Now, the multilayered structure of fish scales has been analysed according to its mechanical properties and penetration resistance. This study of the four different layers provides a mechanistic understanding of evolutionary design as well as inspiring new materials for armour protection.

Electrodes exhibiting single-phase lithium insertion processes can be advantageous for storage applications such as lithium-ion batteries. By modifying the particle size and ion ordering of LiFeFO₄ electrodes an unprecedented single-phase room-temperature process is observed.

Although lithium iron phosphate is a promising electrode material for lithium-ion batteries, its intercalation mechanism remains unclear. Characterization by X-ray diffraction and electron microscopy demonstrates that the lithium deintercalation process occurs as a wave moving through the crystal, and can be described by a domino-cascade model

Typically, metal alloys are protected from corrosion through the formation of an oxide layer. Nevertheless, alloy degradation does occur. It is now shown that metallic nanoparticles in the oxide layer are instrumental to this process. On the basis of this understanding, improvements in alloy degradation by careful choice of composition are demonstrated.

Although phase-change materials are of significant importance for optical and electronic information storage applications, the search for new materials so far has been based on empirical methods. Now, the discovery that their crystalline phase shows resonant bonding opens the way to a deterministic search for new phase-change materials.

Recent work has provided evidence for the existence of a liquid–liquid transition (LLT) in some single-component fluids. It is now shown that the LLT can be used to control the fluidity and miscibility of triphenyl phosphite with another molecular liquid, demonstrating the possibility of the first definite application for exploiting this phenomenon.

The toughness of human bone is difficult to measure, as it is more difficult to break than to split. It is now shown that in the transverse orientation, relevant for breaking, bone is much tougher than previously thought owing to a surprising increase in toughness during the growth of small cracks.

One of the obstacles in using nanocrystals as fluorophores is that they tend to blink. This was thought to be a very general feature. Now, very-high-quality core–shell CdSe–CdS nanocrystals showing highly reduced blinking have been grown. The reduced blinking seems to be related to the thickness of the CdS shell and the high quality of the core–shell interfaces.

Cooled liquids that fail to reach their thermodynamic ground state either form gels or glasses. Their formation is thought to be promoted by stable local atomic structures. The role of these local structures has now been verified in experiments that also show that their structural variety is much larger than expected.

Fabrication of complex two-dimensional patterns is now possible using ‘rails’ as a guiding mechanism for the self-assembly of microstructures within fluidic channels. The method is efficient, and heterogeneous systems, for example patterns of different living cells for tissue engineering, can be made with high precision.