Inferences on Flow at the Base of Earth's Mantle Based on Seismic Anisotropy

Designing 3D Digital Metamaterial for Elastic Waves: From Elastic Wave Polarizer to Vibration Control

Elastic wave polarizers, which can filter out linearly polarized elastic waves from hybrid elastic waves, remain a challenge since elastic waves contain both transverse and longitudinal natures. Here, a tunable, digital, locally resonant metamaterial inspired by abacus is proposed, which consists of 3D-printed octahedral frames and built-in electromagnets. By controlling current in the electromagnets, each unit cell exhibits three digital modes, where the elastic waves have different characteristics of propagation under each mode. A variety of waveguides can be formed by a combination of the three modes and desired polarization can be further filtered out from hybrid elastic waves in a tunable manner. The underlying mechanism of these polarizer-like characteristics is investigated through a combination of theoretical analysis, numerical simulation, and experimental testing. This study provides a means of filtering out the desired wave from hybrid elastic waves, and offers promise for vibration control of particle distribution and flexible structure.

Fat Plumes May Reflect the Complex Rheology of the Lower Mantle

Recent tomographic imaging of the mantle below major hot spots shows slow seismic velocities extending down to the core-mantle boundary, confirming the existence of mantle plumes. However, these plumes are much thicker than previously thought. Using new laboratory experiments and scaling laws, we show that thermal plumes developing in a visco-plastic fluid present much larger diameters than plumes developing in a Newtonian fluid. Such a rheology requiring a yield stress is consistent with a lower mantle predominantly deforming by pure dislocation climb. Yield stress values between 1 and 10 MPa, implying dislocation densities between 108 and 1010 m-2, would be sufficient to reproduce the plumes morphology observed in tomographic images.

Seismic anisotropy of the D″ layer induced by (001) deformation of post-perovskite

Crystallographic preferred orientation (CPO) of post-perovskite (Mg,Fe)SiO₃ (pPv) has been believed to be one potential source of the seismic anisotropic layer at the bottom of the lower mantle (D″ layer). However, the natural CPO of pPv remains ambiguous in the D″ layer. Here we have carried out the deformation experiments of pPv-(Mg_0.75,Fe_0.25)SiO₃ using synchrotron radial X-ray diffraction in a membrane-driven laser-heated diamond anvil cell from 135 GPa and 2,500 K to 154 GPa and 3,000 K. Our results show that the intrinsic texture of pPv-(Mg_0.75,Fe_0.25)SiO₃ should be (001) at realistic P–T conditions of the D″ layer, which can produce a shear wave splitting anisotropy of ∼3.7% with V_SH>V_SV. Considering the combined effect of both pPv and ferropericlase, we suggest that 50% or less of deformation is sufficient to explain the origin of the shear wave anisotropy observed seismically in the D″ layer beneath the circum-Pacific rim.

The source of the anisotropic layer (D'' layer) at the bottom of the lower mantle remains unclear. Here, using high pressure and temperature experiments, the authors find that seismic anisotropy observed at the D'' layer is caused by 50% deformation of the minerals post-perovskite and ferropericlase.

Modeling defects and plasticity in MgSiO3 post-perovskite: Part 3-Screw and edge [001] dislocations

In this study, we investigate the complex structure of [001] screw and edge dislocation cores in MgSiO₃ post-perovskite at the atomic scale. Both [001] screw and edge dislocations exhibit spontaneous dissociation in (010) into two symmetric partials characterized by the presence of <100> component. In case of edge dislocations, dissociation occurs into ½<101> partials, while for the screw dislocations the <100> component reaches only 15%. Under applied stress, both [001](010) screw and edge dislocations behave similarly. Above the Peierls stress, the two partials glide together while keeping their stacking-fault widths (~11 and ~42 Å for the screw and edge dislocations, respectively) constant. The Peierls stress opposed to the glide of [001](010) screw dislocations is 3 GPa, while that of edge dislocations is 33% lower. Relying on the observed characteristics of the dislocation cores, we estimate the efficiency of [001](010) dislocation glide under the P-T conditions relevant to the lowermost mantle and demonstrate that dislocation creep for this slip system would occur in the so-called athermal regime where lattice friction for the considered slip system vanishes when the temperature rises above the critical T _a value of ~2,000 K.

Modeling defects and plasticity in MgSiO3 post-perovskite: Part 1-generalized stacking faults

In this work, we examine the transferability of a pairwise potential model (derived for MgSiO₃ perovskite) to accurately compute the excess energies of the generalized stacking faults (GSF, also called γ-surfaces) in MgSiO₃ post-perovskite. All calculations have been performed at 120 GPa, a pressure relevant to the D″ layer. Taking into account an important aspect of crystal chemistry for complex materials, we consider in detail all possible locations of slip planes in the post-perovskite structure. The γ-surface calculations emphasize the easiness of glide of slip systems with the smallest shear vector [100] and of the [001](010) slip system. Our results are in agreement with previous ab initio calculations. This validates the use the chosen potential model for further full atomistic modeling of dislocations in MgSiO₃ post-perovskite.

Shear response of Fe-bearing MgSiO(3) post-perovskite at lower mantle pressures

We investigate the shear response of possible slip systems activated in pure and Fe-bearing MgSiO(3) post-perovskite (PPv) through ab initio generalized stacking fault (GSF) energy calculations. Here we show that the [100](001) slip system has the easiest response to plastic shear among ten possible slip systems investigated. Incorporation of Fe(2+) decreases the strength of all slip systems but does not change the plastic anisotropy style. Therefore, pure and Fe-bearing MgSiO(3) PPv should demonstrate similar LPO patterns with a strong signature of the [100](001) slip system. An aggregate with this deformation texture is expected to produce a V(SH) > V(SV) type polarization anisotropy, being consistent with seismological observations.(Communicated by Ikuo KUSHIRO, M.J.A.).

High-pressure experimental geosciences: state of the art and prospects

This paper aims at reviewing the current advancements of high pressure experimental geosciences. The angle chosen is that of in situ measurements at the high pressure (P) and high temperature (T) conditions relevant of the deep Earth and planets, measurements that are often carried out at large facilities (X-ray synchrotrons and neutron sources). Rather than giving an exhaustive catalogue, four main active areas of research are chosen: the latest advancements on deep Earth mineralogy, how to probe the properties of melts, how to probe Earth dynamics, and chemical reactivity induced by increased P-T conditions. For each area, techniques are briefly presented and selected examples illustrate their potentials, and what that tell us about the structure and dynamics of the planet.

New rules for the old game of porous micro- and nanoparticle synthesis

The field of research focused on the synthesis of micro- and nanoparticles has not yet conclusively addressed the challenges presented by the hierarchical control of surface topography. An established approach to hierarchical multicomposite nanostructured particles is based on template-directed synthesis, while spectacular advances have been reached in nanoparticle fabrication based on a variety of physicochemical processes. These results exemplify an additive route to hierarchical control, where multiple layers are stacked onto each other or where discretely identifiable particles are assembled into a larger spherical conglomerate. We present here a new strategy for the synthesis of micro- and nanoparticles, which we refer to as "textured isomorphic synthesis", that uses only the toolbox of inorganic chemistry coupled to the physics of cavitation, viscous fingering, and bubble nucleation. The results illustrate a topological route to hierarchical control of particle topography where dimples or holes are deterministically introduced on a planar substrate later transformed into isomorphic hollow spherical micro- and nanostructures.

Rational design and synthesis of catalytically driven nanorotors

We report the design and synthesis of nanorotors based upon on-wire lithography. Because of their asymmetric structure, the nanorotors exhibit rotation in a H2O2 bath instead of linear motion. By observing the leading edge of rotation and comparing this result to the nanorotor design, we have concluded that the driving force for motion is dynamic catalytic decomposition of H2O2 which propels, rather than pulls, the nanorotor.

Deformation of (Mg,Fe)SiO 3 Post-Perovskite and D'' Anisotropy

Polycrystalline (Mg(0.9),Fe(0.1))SiO3 post-perovskite was plastically deformed in the diamond anvil cell between 145 and 157 gigapascals. The lattice-preferred orientations obtained in the sample suggest that slip on planes near (100) and (110) dominate plastic deformation under these conditions. Assuming similar behavior at lower mantle conditions, we simulated plastic strains and the contribution of post-perovskite to anisotropy in the D'' region at the Earth core-mantle boundary using numerical convection and viscoplastic polycrystal plasticity models. We find a significant depth dependence of the anisotropy that only develops near and beyond the turning point of a downwelling slab. Our calculated anisotropies are strongly dependent on the choice of elastic moduli and remain hard to reconcile with seismic observations.

Simulation studies of the self-assembly of cone-shaped particles

We investigate the self-assembly of anisotropic cone-shaped particles decorated by ringlike attractive "patches". In a recent paper, we demonstrated that the self-assembled clusters, which arise due to the conical particle's anisotropic shape combined with directional attractive interactions, are precise for certain cluster sizes, resulting in a precise packing sequence of clusters of increasing sizes with decreasing cone angles (Chen et al. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 717-722). Here we explore the dependence of cluster packing on the cone angle and cooling rate and discuss the "stability" and "metastability" of the resulting structures as well as polymorphism of non-"magic-number" clusters. We investigate large clusters of cones and discuss the implication of our simulation results in the context of the Israelachvili packing rule for surfactants and a recent geometrical packing analysis on hard cones in the limit of large numbers of cones.

Multicomponent nanoparticles via self-assembly with cross-linked block copolymer surfactants

We describe a simple and versatile protocol to prepare water-soluble multifunctional nanostructures by encapsulation of different nanoparticles in shell cross-linked, block copolymer micelles. This method permits simultaneous incorporation of different nanoparticle properties within a nanoscale micellar container. We have demonstrated the co-encapsulation of magnetic (gamma-Fe2O3 and Fe3O4), semiconductor (CdSe/ZnS), and metal (Au) nanoparticles in different combinations to form multicomponent micelles that retain the precursor particles' distinct properties. Because these multifunctional hybrid nanostructures spontaneously assemble from solution by simultaneous desolvation of nanoparticles and amphiphilic block copolymer components, we anticipate that this can be used as a general protocol for preparing multifunctional nanostructures without explicit multimaterial synthesis or surface functionalization of nanoparticles.

Formation of Fractal-Like Structures Driven by Carbon Nanotubes-Based Collapsed Hollow Capsules

Carbon nanotubes (CNTs) based hollow capsules were obtained by degradation under acidic conditions of core-shell nanocomposites build up upon adsorption of multilayers of CNTs (shell) onto melamine-formaldehyde (MF) spheres (core). By evaporation of the dispersions obtained, polymeric fractal patterns from the degradation products of the MF core were formed onto silicon wafers. The proposed mechanism for the formation of these structures is based on the role of the capsules as arrangements of heterogeneities that facilitate the dewetting of the liquid polymeric films.

Electrochemical template synthesis of multisegment nanowires: fabrication and protein functionalization

Multisegment nanowires represent a unique platform for engineering multifunctional nanoparticles for a wide range of applications. For example, the optical and magnetic properties of nanowires can be tailored by modifying the size, shape, and composition of each segment. Similarly, surface modification can be used to tailor chemical and biological properties. In this article, we report on recent work on electrochemical template synthesis of nanogap electrodes, the fabrication of multisegment nanowires with embedded catalysts, and the selective functionalization of multisegment nanowires with proteins.

Self-assembly of laterally-tethered nanorods

We report results from a computational study of laterally tethered nanorod "shape amphiphiles". Our simulations predict that the model nanorods self-assemble into stepped-ribbon-like micelles, a centered rectangular stepped-ribbon phase, and two structurally different liquid crystalline bilayer phases: one in which the bilayers have C(mm) symmetry and another in which they have P(2) symmetry. We provide a possible explanation for the transition between the two C(mm) and P(2) liquid crystalline phases.

Core-shell and segmented polymer-metal composite nanostructures

Composite nanostructures (approximately 200 nm wide and several micrometers long) of metal and polyaniline (PANI) in two new variations of core-shell (PANI-Au) and segmented (Au-PANI and Ni-Au-PANI) architectures were fabricated electrochemically within anodized aluminum oxide (AAO) membranes. Control over the structure of these composites (including the length of the gold shells in the core-shell structures) was accomplished by adjusting the time and rate of electrodeposition and the pH of the solution from which the materials were grown. Exposure of the core-shell structures to oxygen plasma removed the PANI and yielded aligned gold nanotubes. In the segmented structures, a self-assembled monolayer (SAM) of thioaniline nucleated the growth of PANI on top of metal nanorods and acted as an adhesion layer between the metal and PANI components.

Fabrications of hollow nanocubes of Cu(2)O and Cu via reductive self-assembly of CuO nanocrystals

In this work, a template-free synthetic approach for generating single-crystalline hollow nanostructures has been described. Using the small optical band-gap cuprous oxide Cu(2)O as a model case, we demonstrate that, instead of normally known spherical aggregates, primary nanocrystalline particles can first self-aggregate into porous organized solids with a well-defined polyhedral shape according to the oriented attachment mechanism, during which chemical conversion can also be introduced. In contrast to the spherical aggregates, where the nanocrystallites are randomly joined together, the Cu(2)O nanocrystallites in the present case are well organized, maintaining a definite geometric shape and a global crystal symmetry. Due to the presence of intercrystallite space, hollowing and chemical conversion can also be carried out in order to create central space and change the chemical phase of nanostructured polyhedrons. It has been revealed that Ostwald ripening plays a key role in the solid evacuation process. Using this synthetic strategy, we have successfully prepared single-crystal-like Cu(2)O nanocubes and polycrystalline Cu nanocubes with hollow interiors. For the first time, we demonstrate that nanostructured polyhedrons of functional materials with desired interiors can be synthesized in solution via a combination of oriented attachment and Ostwald ripening processes.

Asymmetric ZnO Nanostructures with an Interior Cavity

As a next level of nanofabrication of inorganic materials, free-standing asymmetric nanostructures with an interior space are highly desirable for new applications. In this work, we demonstrate a wet synthesis scheme for bullet-head-like nanostructures of wurtzite zinc oxide (ZnO). The synthesized asymmetric nanostructures are single crystalline, and each has an interior space. In addition to the exterior geometric anisotropy, it is found that the interior space is located at the upper part of the ZnO nanostructures; a new type of structural anisotropy has thus been revealed. On the basis of the present findings, in principle, this synthetic architecture should be applicable to other II-VI compound semiconductors through stabilizing two or more sets of crystallographic planes in solution media. The possibility of dimerization and higher ordered coupling/growth of the ZnO nanostructures has also been addressed.

Olefin Metathesis of the Aligned Assemblies of Conjugated Polymers Constructed through Supramolecular Bundling

The ordered structures constructed from an aligner molecule 1o and conjugated polymers (CPs) were efficiently converted into the poly-pseudo-rotaxane structures by the template-assisted ring-closing olefin metathesis (RCM) of olefinic groups at the peripheral positions of 1o. Moreover, the poly-pseudo-rotaxane structures permitted the separation of the crystalline ordered assemblies of CP by size exclusion chromatography and the preservation of the sheet morphologies after the treatment with trifluoroacetic acid. The morphologies and the periodicities of assemblies were also maintained after the retrieving treatments.

Mesoscale Organization of Nearly Monodisperse Flowerlike Ceria Microspheres

Nearly monodisperse flowerlike CeO2 microspheres were synthesized via a simultaneous polymerization-precipitate reaction, metamorphic reconstruction, and mineralization under hydrothermal condition as well as subsequent calcination. The obtained CeO2 microsphere consists of 20-30 nm thick nanosheets as petals. It has an open three-dimensional (3D) porous and hollow structure and possesses high surface area, large pore volume, and marked hydrothermal stability. It can be doped easily after synthesis, and the initial 3D texture is maintained. The controlling factors and a possible formation mechanism are discussed in detail. This novel material can be used as a support for catalysts with various purposes. With CuO loaded on flowerlike CeO2, the catalytic activities and hydrothermal stability of Cu/CeO2 for ethanol stream reforming were examined. At 300 degrees C, the H2 selectivity reached a maximum value of 74.9 mol %, while CO was not detected within the precision of the gas chromatogram. It produced a hydrogen-rich gas mixture in the wide temperature range (300-500 degrees C) and showed excellent hydrothermal stability at high temperature (550 degrees C), which is a good choice for ethanol processors for hydrogen fuel cell applications.

Plastic Deformation of MgGeO3 Post-Perovskite at Lower Mantle Pressures

Polycrystalline MgGeO3 post-perovskite was plastically deformed in the diamond anvil cell between 104 and 130 gigapascals confining pressure and ambient temperature. In contrast with phenomenological considerations suggesting (010) as a slip plane, lattice planes near (100) became aligned perpendicular to the compression direction, suggesting that slip on (100) or (110) dominated plastic deformation. With the assumption that silicate post-perovskite behaves similarly at lower mantle conditions, a numerical model of seismic anisotropy in the D'' region implies a maximum contribution of post-perovskite to shear wave splitting of 3.7% with an oblique polarization.

Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties

Constraining the chemical, rheological and electromagnetic properties of the lowermost mantle (D'') is important to understand the formation and dynamics of the Earth's mantle and core. To explain the origin of the variety of characteristics of this layer observed with seismology, a number of theories have been proposed, including core-mantle interaction, the presence of remnants of subducted material and that D'' is the site of a mineral phase transformation. This final possibility has been rejuvenated by recent evidence for a phase change in MgSiO3 perovskite (thought to be the most prevalent phase in the lower mantle) at near core-mantle boundary temperature and pressure conditions. Here we explore the efficacy of this 'post-perovskite' phase to explain the seismic properties of the lowermost mantle through coupled ab initio and seismic modelling of perovskite and post-perovskite polymorphs of MgSiO3, performed at lowermost-mantle temperatures and pressures. We show that a post-perovskite model can explain the topography and location of the D'' discontinuity, apparent differences in compressional- and shear-wave models and the observation of a deeper, weaker discontinuity. Furthermore, our calculations show that the regional variations in lower-mantle shear-wave anisotropy are consistent with the proposed phase change in MgSiO3 perovskite.

Ordered Alignment of CdS Nanocrystals on MWCNTs without Surface Modification

This paper describes a facile hydrothermal procedure capable of aligning CdS nanocrystals on multiwalled carbon nanotubes (MWCNTs) without the use of organic bridging molecules such as cysteamine and carboxylates. The direct placement of CdS on MWCNTs allows good mixing and better interfacing between the two nanophases. The synthesis conditions can in principle be tuned to produce modulations in compositions, phases, and crystal orientations to the need of optoelectronic and photonic applications.

Anisotropy of Earth's D″ layer and stacking faults in the MgSiO3 post-perovskite phase

The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the main mineral phase of the Earth's lowermost mantle (the D'' layer). Its properties explain numerous geophysical observations associated with this layer-for example, the D'' discontinuity, its topography and seismic anisotropy within the layer. Here we use a novel simulation technique, first-principles metadynamics, to identify a family of low-energy polytypic stacking-fault structures intermediate between the perovskite and post-perovskite phases. Metadynamics trajectories identify plane sliding involving the formation of stacking faults as the most favourable pathway for the phase transition, and as a likely mechanism for plastic deformation of perovskite and post-perovskite. In particular, the predicted slip planes are {010} for perovskite (consistent with experiment) and {110} for post-perovskite (in contrast to the previously expected {010} slip planes). Dominant slip planes define the lattice preferred orientation and elastic anisotropy of the texture. The {110} slip planes in post-perovskite require a much smaller degree of lattice preferred orientation to explain geophysical observations of shear-wave anisotropy in the D'' layer.

Nanoprobe-Based Affinity Mass Spectrometry for Selected Protein Profiling in Human Plasma

In recent decades, magnetic nanoparticles have emerged as a promising new platform in biomedical applications, particularly bioseparations. We have developed an immunoassay using antibody-conjugated magnetic nanoparticles as an efficient affinity probe to simultaneously preconcentrate and isolate targeted antigens from biological media. We combined this probe with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI MS) to profile proteins in diluted human plasma. The nanoparticles were designed to detect several disease-associated proteins and could be used directly in MALDI MS without an elution step, thereby facilitating multiple antigen screening and the characterization of antigen variants. Plasma antigens bound rapidly (approximately 10 min) to the antibody-conjugated nanoparticles, allowing the assay to be performed within 20 min. With sensitivity of detection in the femtomole range, the nanoscale immunoassay is superior to assays using microscale particles. We applied our method to comparative protein profiling of patients with gastric cancer and healthy individuals and found differential protein expression levels associated with the disease as well as individuals. Given the flexibility of manipulating functional groups on the nanoprobes, their low cost, robustness, and simplicity of the assay, our approach shows promise for targeted proteome profiling in clinical settings.

Mesoscale metallic pyramids with nanoscale tips

We report a simple procedure that can generate free-standing mesoscale metallic pyramids composed of one or more materials and having nanoscale tips (radii of curvature of less than 2 nm). Mesoscale holes (100-300 nm) in a chromium film are used as an etch mask to fabricate pyramidal pits and then as a deposition mask to form the metallic pyramids. We have fabricated two- and three-layered pyramids with control over their materials and chemical functionality.

Two Routes to Vesicle Formation: Metal−Ligand Complexation and Ionic Interactions

Two routes to vesicle formation were designed to prepare uni- and multilamellar vesicles in salt-free aqueous solutions of surfactants. The formation of a surfactant complex between a double-chain anionic surfactant with a divalent-metal ion as the counterion and a single-chain zwitterionic surfactant with the polar group of amine-oxide group is described for the first time as a powerful driving force for vesicle-phases constructed from salt-free mixtures of aqueous surfactant solutions. As a typical example, a Zn(2+)-induced charged complex fluid, vesicle-phase has been studied in aqueous mixtures of tetradecyldimethylamine oxide (C(14)DMAO) and zinc 2,2-dihydroperfluorooctanoate [Zn(OOCCH(2)C(6)F(13))(2)]. This ionically charged vesicle-phase formed due to surfactant complexation has interesting rheological properties and is not shielded by excess salts because there are no counterions in the solution. Such a vesicle-phase of surfactant complex is important for many applications; for example, the vesicle-phase was further used to produce in situ the vesicle-phase of the salt-free cationic/anionic (catanionic) surfactants, C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13). The salt-free catanionic vesicle-phase could be produced through injecting H(2)S gas into the C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) vesicle-phase, because the zwitterionic surfactant C(14)DMAO can be charged by the H(+) released from H(2)S to become a cationic surfactant and Zn(2+) was precipitated as ZnS. After the ZnS precipitates were removed from C(14)DMAO/Zn(OOCCH(2)C(6)F(13))(2) solutions, the final mixed solution does not contain excess salts as do other cationic/anionic surfactant systems. Both the C(14)DMAO-Zn(OOCCH(2)C(6)F(13))(2) complex and the resulting catanionic C(14)DMAOH(+)-(-)OOCCH(2)C(6)F(13) solution are birefringent Lalpha-phase solutions that consist of uni- and multilamellar vesicles. Ring-shaped semiconductor ZnS materials with encapsulated ZnS precipitates and regular spherical ZnS particles were prepared, which resulted in a transition from vesicles composed of metal-ligand complexes to vesicles held together by ionic interactions in the salt-free aqueous systems. This strategy should provide a new method to prepare inorganic materials. The present routes to form vesicles solve a problem: how to prepare nanomaterials using surfactant self-assembly, with structure controlled not by the growing material, but by the phase behavior of the surfactants.

Bundle-like Assemblies of Cadmium Hydroxide Nanostrands and Anionic Dyes

Molecularly flat and extremely long bundle-like assemblies were prepared from cadmium hydroxide nanostrands and polysulfonated dyes. The dye molecules were regularly aligned along with the nanostrands, as confirmed by electron microscopies and UV-vis absorption spectroscopy. Strong electrostatic interaction between the two components was useful to control the fibrous morphologies and optical properties of these organic/inorganic nanocomposites.

Surface tension driven self-assembly of bundles and networks of 200 nm diameter rods using a polymerizable adhesive

This letter demonstrates the first utilization of surface tension based self-assembly on the 200 nm scale to form mechanically stable aggregates comprised of metallic rods. The self-assembly occurs as a result of the minimization of interfacial tension of liquid layers of a hydrophobic polymerizable adhesive that is precipitated on the rods. After the assembly, the adhesive is polymerized to form permanently bonded aggregates. Depending on the patterning of the rods and the chemical functionalization used, either closed 3D bundles or open 2D networks can be formed.

Synthetic Architectures of TiO2/H2Ti5O11·H2O, ZnO/H2Ti5O11·H2O, ZnO/TiO2/H2Ti5O11·H2O, and ZnO/TiO2 Nanocomposites

Although synthetic investigations of inorganic nanomaterials had been carried out extensively over the past decade, few of them have been devoted to fabrication of complex nanostructures that comprise multicomponents/phases (i.e., composite nanobuilding blocks), especially in the area of structural/morphological architecture. In this work, nanobelts of a protonated pentatitanate (H(2)Ti(5)O(11).H(2)O) were synthesized hydrothermally for the first time. Two technologically important transition-metal-oxides TiO(2) and ZnO were then grown respectively or sequentially onto the surface of the as-prepared nanobelts in aqueous mediums. With a main emphasis on organizational manipulation, the present investigation examines general issues of morphological complexity, synthetic interconvertibility, and material combinability related to fabrication of inorganic nanocomposites. Using this model material system, we demonstrate that complex binary and tertiary composite building blocks of TiO(2)/H(2)Ti(5)O(11).H(2)O, ZnO/H(2)Ti(5)O(11).H(2)O, ZnO/TiO(2)/H(2)Ti(5)O(11).H(2)O, and ZnO/TiO(2) can be architected stepwise in solution. Structural features of these nanocomposites have also been addressed.

Fabrication of ZnO “Dandelions” via a Modified Kirkendall Process

We report that in addition to the fabrication of hollow nanomaterials, the Kirkendall-type diffusion can also be utilized in synthetic nanoarchitecture, through which low-dimensional nanobuilding blocks can be designed and organized chemically into complex geometrical conformations. Our approach may provide a new chemical alternative to materials self-organization. In principle, a great variety of inorganic "dandelions" and their nanocomposites can be tailored and fabricated through this type of total synthetic architecture.

Variable Azimuthal Anisotropy in Earth's Lowermost Mantle

A persistent reversal in the expected polarity of the initiation of vertically polarized shear waves that graze the D'' layer (the layer at the boundary between the outer core and the lower mantle of Earth) in some regions starts at the arrival time of horizontally polarized shear waves. Full waveform modeling of the split shear waves for paths beneath the Caribbean requires azimuthal anisotropy at the base of the mantle. Models with laterally coherent patterns of transverse isotropy with the hexagonal symmetry axis of the mineral phases tilted from the vertical by as much as 20 degrees are consistent with the data. Small-scale convection cells within the mantle above the D'' layer may cause the observed variations by inducing laterally variable crystallographic or shape-preferred orientation in minerals in the D'' layer.

Hybrid Organic−Inorganic, Rod-Shaped Nanoresistors and Diodes

The electrical properties of template-synthesized three- and four-component rodlike nanostructures consisting of metal and conducting polymer domains have been studied. These structures behave like nanometer-scale resistors and diodes, depending upon their compositions and spatial distribution of the different compositional blocks. In the two-component systems, the conducting polymer block dictates the electrical properties of the nanostructure, and the metal blocks act as leads to facilitate the connection with microscopic circuits. In the three-component systems, the metal blocks provide an additional design flexibility, allowing one to prepare Schottky junctions.

The elasticity of the MgSiO3 post-perovskite phase in the Earth's lowermost mantle

MgSiO3 perovskite has been assumed to be the dominant component of the Earth's lower mantle, although this phase alone cannot explain the discontinuity in seismic velocities observed 200-300 km above the core-mantle boundary (the D" discontinuity) or the polarization anisotropy observed in the lowermost mantle. Experimental and theoretical studies that have attempted to attribute these phenomena to a phase transition in the perovskite phase have tended to simply confirm the stability of the perovskite phase. However, recent in situ X-ray diffraction measurements have revealed a transition to a 'post-perovskite' phase above 125 GPa and 2,500 K--conditions close to those at the D" discontinuity. Here we show the results of first-principles calculations of the structure, stability and elasticity of both phases at zero temperature. We find that the post-perovskite phase becomes the stable phase above 98 GPa, and may be responsible for the observed seismic discontinuity and anisotropy in the lowermost mantle. Although our ground-state calculations of the unit cell do not include the effects of temperature and minor elements, they do provide a consistent explanation for a number of properties of the D" layer.

Theoretical and experimental evidence for a post-perovskite phase of MgSiO3 in Earth's D" layer

The Earth's lower mantle is believed to be composed mainly of (Mg,Fe)SiO3 perovskite, with lesser amounts of (Mg,Fe)O and CaSiO3 (ref. 1). But it has not been possible to explain many unusual properties of the lowermost approximately 150 km of the mantle (the D" layer) with this mineralogy. Here, using ab initio simulations and high-pressure experiments, we show that at pressures and temperatures of the D" layer, MgSiO3 transforms from perovskite into a layered CaIrO3-type post-perovskite phase. The elastic properties of the post-perovskite phase and its stability field explain several observed puzzling properties of the D" layer: its seismic anisotropy, the strongly undulating shear-wave discontinuity at its top and possibly the anticorrelation between shear and bulk sound velocities.