Articles in 2013

The controlled vapour phase synthesis of molybdenum disulphide atomic layers and a fundamental mechanism for the nucleation, growth and grain boundary formation in its crystalline monolayers are now reported. Using high-resolution electron microscopy imaging, the atomic structure of the grains and their boundaries in the polycrystalline molybdenum disulphide atomic layers are examined, and the primary mechanisms for grain-boundary formation are evaluated.

Solution printing of organic semiconductors could in principle be scaled to industrial needs, yet attaining aligned single-crystals directly with this method has been challenging. By using a micropillar-patterned printing blade designed to enhance the control of crystal nucleation and growth, thin films of macroscopic, highly aligned single crystals of organic semiconductors can now be fabricated.

Iron pnictide superconductors represent a suggestive alternative to cuprate superconductors for achieving high transition temperatures. Using in situ angle-resolved photoemission spectroscopy, the electronic properties of FeSe are examined as a function of film thickness, providing valuable insights into the mechanism driving the superconductivity in this material.

Although high proton conductivity and chemical stability in yttrium-doped barium zirconate are of interest for intermediate-temperature solid-oxide fuel cells, there are remaining issues regarding its defect chemistry and macroscopic proton-transport mechanism. Proton transport in this compound is shown to be limited by proton–dopant association, and the presence of two types of proton environment above room temperature are observed, reflecting differences in proton–dopant configurations.

Photoelectrochemical water-splitting is a promising route for the renewable production of hydrogen, but trade-offs between photoelectrode stability and efficiency remain problematic. A metal–oxide–semiconductor photoelectrode architecture demonstrates stable and efficient water splitting using narrow-bandgap semiconductors. Substantial improvement in the performance of Si-based photocathodes is achieved by combining a high-quality SiO₂ layer and bilayer metal catalysts.

A transparent organic field-effect transistor allows the stimulation and recording of the bioelectrical activity of primary neural cells. The cells grow, differentiate and function on the device, which then provides the electrical stimulation, and enables the recording of extracellular current and optical imaging of the modulation of neuronal membrane potential.

Despite recent progress in the synthesis and characterization of molybdenum disulphide, little is yet known about its microstructure. Using refined chemical vapour deposition synthesis, high-quality crystals of monolayer molybdenum disulphide have now been grown. Single-crystal islands and polycrystals containing tilt and mirror twin grain boundaries are characterized, and the influence of the grain boundaries on the material properties of molybdenum disulphide is assessed.

The ferroelectric properties of BiFeO₃ have been the subject of extensive study. Using a range of experimental tools and numerical modelling, it is now shown that its ferroic properties can also be manipulated by strain effects, giving rise to a variety of magnonic phenomena.

The dissipation of heat towards cooler regions of a thermodynamic system is a ubiquitous phenomenon. It is now shown that collective excitations known as spin waves can be used to control the flow of heat in a ferrimagnet consisting of Y₃Fe₅O₁₂.

Analytical techniques reveal that spherical calcium phosphate particles are the first mineralized structures to be formed in the calcification process in cardiovascular tissues. Furthermore, the inner sections of calcified lesions in patients with various cardiovascular diseases are identified as highly crystalline, spherical hydroxyapatite particles that differ in structure from bone mineral.

The range of phenomena associated with the two-dimensional electron gas occurring at oxide interfaces has garnered significant attention. By performing a finite-size scaling analysis, the universality class of the magnetic field-driven quantum phase transition that occurs at the superconducting LaTiO₃/SrTiO₃ interface is now established.

Nickel–cadmium and nickel–metal hydride batteries exhibit memory effects but lithium-ion batteries are widely believed to have none. Now, a memory effect for LiFePO₄ positive electrodes that appears after only one cycle of partial charge and discharge is reported. This observation is important as the slight voltage change that it causes can lead to substantial erroneous estimation of the state of charge of batteries.

The variety of electronic processes occurring within an organic light-emitting diode (OLED) make the prediction of their emission characteristics problematic. It is now shown that all the relevant processes occurring in a stacked OLED can be modelled down to the molecular scale, in turn leading to accurate emission profiles.

Development of the classical lithium-ion technology based on liquid electrolytes has been limited to a certain extent by the intrinsic instability of liquid electrolytes and their mechanical properties. A multifunctional single-ion polymer electrolyte based on polyanionic block copolymers consisting of polystyrene segments is now shown to exhibit enhanced lithium-ion transport, mechanical properties and electrochemical stability window.

Macroscopically long, cell-encapsulating, core–shell hydrogel microfibres that can be assembled into macroscopic cellular constructs by weaving and reeling are shown to reconstitute intrinsic morphologies and functions of living tissues. When transplanted into the subrenal capsular space of diabetic mice, the microfibres normalize blood glucose concentrations for about two weeks and can later be removed.

Josephson plasma solitons are a kind of excitation predicted to occur in cuprate superconductors subject to strong electromagnetic fields. By using intense radiation from a free-electron laser, these modes are now demonstrated experimentally in the copper oxide material La_1.84Sr_0.16CuO₄.

The molecular alignment and order of conjugated polymers within organic electronic devices is an important consideration for the enhancement of device performance. Now, some design rules are revealed that promote the directed alignment of the polymers and result in the fabrication of well-aligned films with highly anisotropic carrier mobilities.

Adhesive interactions between stem cells and the extracellular matrix are known to regulate stem cell differentiation, yet the underlying mechanisms are not well understood. It is now shown that fate decisions of stem cells encapsulated in covalently crosslinked hydrogels are regulated, independently of matrix mechanics and cell morphology, by the cellular tension generated from cell-induced degradation of the hydrogels.

Although poly(vinylidene fluoride) is a well-known organic ferroelectric, its utilization in microelectronics has been hampered by the difficulty in obtaining uniform thin films. By exploiting a high-temperature deposition approach, smooth and thin films of the ferroelectric δ-phase polymorph of this material are now obtained, showing their potential for capacitors and non-volatile memories.

Much less exploited than the spectral and spatial properties of surface plasmons (SPs) are their local density of states (SP-LDOS), which rule a number of important nanoscale phenomena. Using two-photon luminescence microscopy, the SP-LDOS in ultrathin gold nanoprisms is now visualized directly, allowing for the SP modal distribution to be tuned.