Iron oxide nanotubes of 50−150 nm outer diameter and 2−20 nm wall thickness are prepared in ordered arrays. Atomic layer deposition (ALD) of Fe2O3 from the precursor iron(III) tert-butoxide at 130−180 °C yields very smooth coverage of the pore walls of anodic alumina templates, with thickness growth of 0.26(±0.04) Å per cycle. The reduced Fe3O4 tubes are hard ferromagnets, and variations of the wall thickness d w have marked consequences on the magnetic response of the tube arrays. For 50 nm outer diameter, tubes of d w = 13 nm yield the largest coercive field (H c > 750 Oe), whereas lower coercivities are observed on both the thinner and thicker sides of this optimum.

Thermoelectric materials could play an increasing role for the effi cient use of energy resources and waste heat recovery in the future. The thermoelectric effi ciency of materials is described by the fi gure of merit ZT = ( S 2 σ T )/ κ ( S Seebeck coeffi cient, σ electrical conductivity, κ thermal conductivity, and T absolute temperature). In recent years, several groups worldwide have been able to experimentally prove the enhancement of the thermoelectric effi ciency by reduction of the thermal conductivity due to phonon blocking at nanostructured interfaces. This review addresses recent developments from thermoelectric model systems, e.g. nanowires, nanoscale meshes, and thermionic superlattices, up to nanograined bulk-materials. In particular, the progress of nanostructured silicon and related alloys as an emerging material in thermoelectrics is emphasized. Scalable synthesis approaches of high-performance thermoelectrics for high-temperature applications is discussed at the end. 714 Physical FunctionalityThe direct conversion of heat to electricity in thermoelectric devices is based on the Seebeck effect (named for Thomas J. Seebeck, 1821). In thermoelectric cooling devices use is made of the Peltier effect (named for Jean C. A. Peltier, 1834). [3][4][5] The thermoelectric effects were initially examined in metals. These generate only small thermovoltages of a few tens of microvolts per Kelvin. The electrical potential difference generated per degree of temperature difference is called Seebeck coeffi cient, S , or thermopower.By using semiconductors, substantially higher thermovoltages of some hundreds of μ V/K can be achieved. For thermoelectric applications, low bandgap semiconductors, with typical charge carrier concentrations in the order of 10 19 /cm 3 , are considered most suitable. Apart from a large Seebeck coeffi cient, a good thermoelectric material additionally needs to exhibit a high electrical conductivity and a low thermal conductivity to obtain a large fi gure of merit, ZT , at a certain temperature. The interdependence of these quantities has limited the ZT to values around one for the best conventional thermoelectric materials. For semiconductors and thermoelectric materials, the heat conductivity depends on both free charge carriers (holes or electrons) and phonons: κ tot = κ El + κ Ph . The phonon-based thermal conductivity κ Ph is decoupled from the electric conductivity. Thus, numerous attempts for the optimization of the thermoelectric effi ciency ZT in nanostructures are based on a reduction of the heat transport by phonons.

Molecular self‐attack: According to mythology, a scorpion may sting itself to death; similarly, 3‐aminopropyltriethoxysilane catalyzes its own hydrolysis in the atomic layer deposition (ALD) of SiO2 thin films and nanostructures. Between 120 and 200 °C, the growth rate is constant at 0.06 nm per ALD cycle. The SiO2 films are chemically and optically pure. SiO2 nanotubes of aspect ratio 500 exhibit smooth walls of accurately controlled thickness.

Depleted uranium is a mildly radioactive waste product that is stockpiled worldwide. The chemical reactivity of uranium complexes is well documented, including the stoichiometric activation of small molecules of biological and industrial interest such as H2O, CO2, CO, or N2 (refs 1 - 11), but catalytic transformations with actinides remain underexplored in comparison to transition-metal catalysis. For reduction of water to H2, complexes of low-valent uranium show the highest potential, but are known to react violently and uncontrollably forming stable bridging oxo or uranyl species. As a result, only a few oxidations of uranium with water have been reported so far; all stoichiometric. Catalytic H2 production, however, requires the reductive recovery of the catalyst via a challenging cleavage of the uranium-bound oxygen-containing ligand. Here we report the electrocatalytic water reduction observed with a trisaryloxide U(III) complex [(((Ad,Me)ArO)3mes)U] (refs 18 and 19)--the first homogeneous uranium catalyst for H2 production from H2O. The catalytic cycle involves rare terminal U(IV)-OH and U(V)=O complexes, which have been isolated, characterized, and proven to be integral parts of the catalytic mechanism. The recognition of uranium compounds as potentially useful catalysts suggests new applications for such light actinides. The development of uranium-based catalysts provides new perspectives on nuclear waste management strategies, by suggesting that mildly radioactive depleted uranium--an abundant waste product of the nuclear power industry--could be a valuable resource.

The magnetization reversal in ordered arrays of iron oxide nanotubes of 50 nm outer diameter grown by atomic layer deposition is investigated theoretically as a function of the tube wall thickness, dw. In thin tubes (dw < 13 nm) the reversal of magnetization is achieved by the propagation of a vortex domain boundary, while in thick tubes (dw > 13 nm) the reversal is driven by the propagation of a transverse domain boundary. Magnetostatic interactions between the tubes are responsible for a decrease of the coercive field in the array. Our calculations are in agreement with recently reported experimental results. We predict that the crossover between the vortex and transverse modes of magnetization reversal is a general phenomenon on the length scale considered. PACS numbers: 75.75.+a, 75.10.-b arXiv:1106.2833v1 [cond-mat.mes-hall]