Volume 5 Issue 11, November 2013

β-MnO₂ nanorods with exposed tunnel structures have been successfully synthesized by a hydrothermal method. The as-prepared β-MnO₂ nanorods have exposed {111} crystal planes with a high density of (1 × 1) tunnels, leading to facile Na-ion insertion and extraction. When applied as cathode materials in Na-ion batteries, the β-MnO₂ nanorods exhibited a superior electrochemical performance with a high initial Na-ion storage capacity of 350 mAh g⁻¹.β-MnO₂ nanorods also demonstrated an excellent high rate capability and a good cyclability.

In this work, transformation optics technique was applied to the thermodynamic area by using the coordinate transformation to the time-dependent heat diffusion equation, which enables the manipulation of the heat flux by predefined diffusion paths. A transient thermal cloaking device engineered with effective thermal materials was experimentally demonstrated by hiding a centimeter-sized vacuum cavity. To facilitate the fabrication a rescaled heat equation taking into account of all the pertinent parameters of various ingredient materials was proposed to guide the practical design of complex transformed thermal devices.

Seven years ago, Wilma Eerenstein, Neil Mathur and Jim Scott published a Venn diagram (above) showing the overlap of piezoelectricity, ferroelectricity (green circle), ferromagnetism (black circle), and magnetoelectricity (blue hatched center circle); and soon thereafter Manuel Bibes put into each sector the crystals which were thought to belong. The overlap region between green and black are multiferroic ferromagnetic-ferroelectrics. Not all were correct; BiMnO₃ is NOT ferroelectric. Of these materials, only Cr₂O₃ and BiFeO₃ function at room temperature (or are magnetoelectric, and the former is neither a ferromagnet nor ferroelectric). Today’s review is an update on the new multiferroic and/or magnetoelectric materials that function at or near ambient temperatures and pressures: Cupric oxide (not actually magnetoelectric), iron magnesium hexaferrites, and perovskite oxides based upon PbTiO₃.

The laser is arguably the most important and versatile optical device. Invented just over 50 years ago,¹ the laser has found immense number of uses from fundamental science and ultra-precision metrology to diverse applications in telecommunications, entertainment, computers, displays, biomedicine, materials processing, defense and homeland security and so on. These are based on fundamental property of the laser to generate coherent light that can be focused to microscopic areas or concentrated in pulses as short as 100 as (1 as =10⁻¹⁸ s). Still, quest for new lasers continues, in particular, to design the smallest and thinnest lasers possible. This is important in many respects, in particular, because such lasers can be directly modulated with a very high frequency. One way to achieve this goal is provided by invention of the spaser (Surface Plasmon Amplification Stimulated Emission of Radiation),² also called plasmonic laser, about 10 years ago. Replacing light quanta—photons—of the laser with electronic excitations at the surface of metals called surface plasmons, which can have atomic-scale dimensions, the spaser itself can be as small or as thin as the dimension of only hundreds of atoms.