Showing papers on "Amorphous solid published in 2013"

Photochemical Route for Accessing Amorphous Metal Oxide Materials for Water Oxidation Catalysis

Abstract: Large-scale electrolysis of water for hydrogen generation requires better catalysts to lower the kinetic barriers associated with the oxygen evolution reaction (OER). Although most OER catalysts are based on crystalline mixed-metal oxides, high activities can also be achieved with amorphous phases. Methods for producing amorphous materials, however, are not typically amenable to mixed-metal compositions. We demonstrate that a low-temperature process, photochemical metal-organic deposition, can produce amorphous (mixed) metal oxide films for OER catalysis. The films contain a homogeneous distribution of metals with compositions that can be accurately controlled. The catalytic properties of amorphous iron oxide prepared with this technique are superior to those of hematite, whereas the catalytic properties of a-Fe100-y-zCoyNizOx are comparable to those of noble metal oxide catalysts currently used in commercial electrolyzers.

Amorphous nickel hydroxide nanospheres with ultrahigh capacitance and energy density as electrochemical pseudocapacitor materials

Abstract: Nickel hydroxide is a promising material for capacitor electrodes and most research has focussed on the crystalline form. Here, the authors report that amorphous nickel hydroxide nanospheres, which may be synthesized relatively easily, also exhibit excellent integrated electrochemical performance.

An amorphous red phosphorus/carbon composite as a promising anode material for sodium ion batteries.

Abstract: An amorphous red phosphorus/carbon composite is obtained through a facile and simple ball milling process, and its electrochemical performance as an anode material for Na ion batteries is evaluated. The composite shows excellent electrochemical performance including a high specific capacity of 1890 mA h g(-1), negligible capacity fading over 30 cycles, an ideal redox potential (0.4 V vs. Na/Na(+)), and an excellent rate performance, thus making it a promising candidate for Na ion batteries.

Tunable near-infrared and visible-light transmittance in nanocrystal-in-glass composites

Abstract: Amorphous metal oxides are useful in optical, electronic and electrochemical devices. The bonding arrangement within these glasses largely determines their properties, yet it remains a challenge to manipulate their structures in a controlled manner. Recently, we developed synthetic protocols for incorporating nanocrystals that are covalently bonded into amorphous materials. This 'nanocrystal-in-glass' approach not only combines two functional components in one material, but also the covalent link enables us to manipulate the glass structure to change its properties. Here we illustrate the power of this approach by introducing tin-doped indium oxide nanocrystals into niobium oxide glass (NbOx), and realize a new amorphous structure as a consequence of linking it to the nanocrystals. The resulting material demonstrates a previously unrealized optical switching behaviour that will enable the dynamic control of solar radiation transmittance through windows. These transparent films can block near-infrared and visible light selectively and independently by varying the applied electrochemical voltage over a range of 2.5 volts. We also show that the reconstructed NbOx glass has superior properties-its optical contrast is enhanced fivefold and it has excellent electrochemical stability, with 96 per cent of charge capacity retained after 2,000 cycles.

In Situ TEM of Two-Phase Lithiation of Amorphous Silicon Nanospheres

Abstract: To utilize high-capacity Si anodes in next-generation Li-ion batteries, the physical and chemical transformations during the Li–Si reaction must be better understood. Here, in situ transmission electron microscopy is used to observe the lithiation/delithiation of amorphous Si nanospheres; amorphous Si is an important anode material that has been less studied than crystalline Si. Unexpectedly, the experiments reveal that the first lithiation occurs via a two-phase mechanism, which is contrary to previous understanding and has important consequences for mechanical stress evolution during lithiation. On the basis of kinetics measurements, this behavior is suggested to be due to the rate-limiting effect of Si–Si bond breaking. In addition, the results show that amorphous Si has more favorable kinetics and fracture behavior when reacting with Li than does crystalline Si, making it advantageous to use in battery electrodes. Amorphous spheres up to 870 nm in diameter do not fracture upon lithiation; this is much...

High capacity and rate capability of amorphous phosphorus for sodium ion batteries.

Abstract: Turning on your P/C: An amorphous phosphorus/carbon (a-P/C) composite was synthesized using simple mechanical ball milling of red phosphorus and conductive carbon powders. This material gave an extraordinarily high sodium ion storage capacity of 1764 mA h g(-1) (see graph) with a very high rate capability, showing great promise as a high capacity and high rate anode material for sodium ion batteries.

Two-phase electrochemical lithiation in amorphous silicon

Abstract: Lithium-ion batteries have revolutionized portable electronics and will be a key to electrifying transport vehicles and delivering renewable electricity. Amorphous silicon (a-Si) is being intensively studied as a high-capacity anode material for next-generation lithium-ion batteries. Its lithiation has been widely thought to occur through a single-phase mechanism with gentle Li profiles, thus offering a significant potential for mitigating pulverization and capacity fade. Here, we discover a surprising two-phase process of electrochemical lithiation in a-Si by using in situ transmission electron microscopy. The lithiation occurs by the movement of a sharp phase boundary between the a-Si reactant and an amorphous Li(x)Si (a-Li(x)Si, x ~ 2.5) product. Such a striking amorphous-amorphous interface exists until the remaining a-Si is consumed. Then a second step of lithiation sets in without a visible interface, resulting in the final product of a-Li(x)Si (x ~ 3.75). We show that the two-phase lithiation can be the fundamental mechanism underpinning the anomalous morphological change of microfabricated a-Si electrodes, i.e., from a disk shape to a dome shape. Our results represent a significant step toward the understanding of the electrochemically driven reaction and degradation in amorphous materials, which is critical to the development of microstructurally stable electrodes for high-performance lithium-ion batteries.

Room Temperature Phosphorescence of Metal-Free Organic Materials in Amorphous Polymer Matrices

Abstract: Developing metal-free organic phosphorescent materials is promising but challenging because achieving emissive triplet relaxation that outcompetes the vibrational loss of triplets, a key process to achieving phosphorescence, is difficult without heavy metal atoms. While recent studies reveal that bright room temperature phosphorescence can be realized in purely organic crystalline materials through directed halogen bonding, these organic phosphors still have limitations to practical applications due to the stringent requirement of high quality crystal formation. Here we report bright room temperature phosphorescence by embedding a purely organic phosphor into an amorphous glassy polymer matrix. Our study implies that the reduced beta (β)-relaxation of isotactic PMMA most efficiently suppresses vibrational triplet decay and allows the embedded organic phosphors to achieve a bright 7.5% phosphorescence quantum yield. We also demonstrate a microfluidic device integrated with a novel temperature sensor based on the metal-free purely organic phosphors in the temperature-sensitive polymer matrix. This unique system has many advantages: (i) simple device structures without feeding additional temperature sensing agents, (ii) bright phosphorescence emission, (iii) a reversible thermal response, and (iv) tunable temperature sensing ranges by using different polymers.

On the biodegradability, mechanical behavior, and cytocompatibility of amorphous Mg72Zn23Ca5and crystalline Mg70Zn23Ca5Pd2alloys as temporary implant materials

Abstract: The evolution of microstructure and mechanical properties of almost fully amorphous Mg72Zn23Ca5 and crystalline Mg70Zn23Ca5Pd2 alloys during immersion in Hank's balanced salt solution (HBSS), as well as their cytocompatibility, are investigated in order to assess the feasibility of both materials as biodegradable implants. Though the crystalline Mg70Zn23Ca5Pd2 sample shows lower wettability and more positive corrosion potential, this sample degrades much faster upon incubation in HBSS as a consequence of the formation of micro-galvanic couples between the nobler Pd-rich dendrites and the surrounding phases. After 22-h immersion, the concentration of Mg ions in the HBSS medium containing the Mg70Zn23Ca5Pd2 sample is six times larger than for Mg72Zn23Ca5. Due to the Zn enrichment and the incipient porosity, the mechanical properties of the Mg72Zn23Ca5 sample improve within the first stages of biodegradation (i.e., hardness increases while the Young's modulus decreases, thus rendering an enhanced wear resistance). Cytocompatibility studies reveal that neither Mg72Zn23Ca5 nor Mg70Zn23Ca5Pd2 are cytotoxic, although preosteoblast cell adhesion is to some extent precluded, particularly onto the surface of Mg70Zn23Ca5Pd2, because of the relatively high hydrophobicity. Because of their outstanding properties and their time-evolution, the use of the Pd-free alloy in temporary implants such as screws, stents, and sutures is envisioned.

Amorphous CoSnO3@C nanoboxes with superior lithium storage capability

Abstract: Amorphous CoSnO3@C nanoboxes have been synthesized by thermal annealing of CoSn(OH)6 nanoboxes, followed by carbon nanocoating. Benifiting from the unique structure, they exhibit exceptional long-term cycling stability over 400 cycles for highly reversible lithium storage.

(De)Lithiation Mechanism of Li/SeSx (x = 0–7) Batteries Determined by in Situ Synchrotron X-ray Diffraction and X-ray Absorption Spectroscopy

Abstract: Electrical energy storage for transportation has gone beyond the limit of converntional lithium ion batteries currently. New material or new battery system development is an alternative approach to achieve the goal of new high-energy storage system with energy densities 5 times or more greater. A series of SeSx–carbon (x = 0–7) composite materials has been prepared and evaluated as the positive electrodes in secondary lithium cells with ether-based electrolyte. In situ synchrotron high-energy X-ray diffraction was utilized to investigate the crystalline phase transition during cell cycling. Complementary, in situ Se K-edge X-ray absorption near edge structure analysis was used to track the evolution of the Se valence state for both crystalline and noncrystalline phases, including amorphous and electrolyte-dissolved phases in the (de)lithiation process. On the basis of these results, a mechanism for the (de)lithiation process is proposed, where Se is reduced to the polyselenides, Li2Sen (n ≥ 4), Li2Se2, an...

Multi-phase semicrystalline microstructures drive exciton dissociation in neat plastic semiconductors

Abstract: The optoelectronic properties of macromolecular semiconductors depend fundamentally on their solid-state microstructure. For example, the molecular-weight distribution influences polymeric- semiconductor properties via diverse microstructures; polymers of low weight-average molecular weight (Mw) form unconnected, extended-chain crystals, usually of a paraffinic structure. Because of the non-entangled nature of the relatively short-chain macromolecules, this leads to a polycrystalline, one-phase morphology. In contrast, with high-Mw materials, where average chain lengths are longer than the length between entanglements, two-phase morphologies, comprised of crystalline moieties embedded in largely unordered (amorphous) regions, are obtained. We investigate charge photogeneration processes in neat regioregular poly(3-hexylthiophene) (P3HT) of varying Mw by means of time-resolved photoluminescence (PL) spectroscopy. At 10 K, PL originating from recombination of long-lived charge pairs decays over microsecond timescales. Both the amplitude and decay rate distribution depend strongly on Mw. In films with dominant one-phase chain-extended microstructures, the delayed PL is suppressed as a result of a diminished yield of photoinduced charges, and its decay is significantly faster than in two-phase microstructures. However, independent of Mw, charge recombination regenerates singlet excitons in torsionally disordered chains forming more strongly coupled photophysical aggregates than those in the steady-state ensemble, with delayed PL lineshape reminiscent of that in paraffinic morphologies at steady state. We conclude that highly delocalized excitons in disordered regions between crystalline and amorphous phases dissociate extrinsically with yield and spatial distribution that depend intimately upon microstructure.

Probing the Failure Mechanism of SnO2 Nanowires for Sodium-Ion Batteries

Abstract: Nonlithium metals such as sodium have attracted wide attention as a potential charge carrying ion for rechargeable batteries. Using in situ transmission electron microscopy in combination with density functional theory calculations, we probed the structural and chemical evolution of SnO2 nanowire anodes in Na-ion batteries and compared them quantitatively with results from Li-ion batteries (Huang, J. Y.; et al. Science 2010, 330, 1515−1520). Upon Na insertion into SnO2, a displacement reaction occurs, leading to the formation of amorphous NaxSn nanoparticles dispersed in Na2O matrix. With further Na insertion, the NaxSn crystallized into Na15Sn4 (x = 3.75). Upon extraction of Na (desodiation), the NaxSn transforms to Sn nanoparticles. Associated with the dealloying, pores are found to form, leading to a structure of Sn particles confined in a hollow matrix of Na2O. These pores greatly increase electrical impedance, therefore accounting for the poor cyclability of SnO2. DFT calculations indicate that Na+ d...

Liquid–Liquid Phase Separation in Highly Supersaturated Aqueous Solutions of Poorly Water-Soluble Drugs: Implications for Solubility Enhancing Formulations

Abstract: Highly supersaturated aqueous drug solutions are often generated during drug testing and upon delivery to the patient. The phase behavior of such solutions appears complex and poorly understood, with the formation of colloidal drug aggregates often being reported. In this study, the phase behavior of eight hydrophobic poorly water-soluble drug molecules in highly supersaturated aqueous solutions was examined, and colloid formation was explained in terms of liquid–liquid phase separation (LLPS). A relationship was found between the concentration at which LLPS was observed and the theoretically predicted amorphous “solubility” value, where the latter was predicted based on the thermodynamic properties of the crystalline solid/supercooled liquid and solution activity coefficients. A phase diagram for the ritonavir–water system as a function of temperature was used to demonstrate that LLPS occurs in the metastable region of the phase diagram, and thus LLPS is a precursor to crystallization. Using an amorphous...

Boron nitride porous microbelts for hydrogen storage

Abstract: Layered boron nitrides (BNs) are usually viewed as excellent protective coatings and reinforcing materials due to their chemical inertness and high mechanical strength. However, the attention paid to their potential applications in gas sorption, especially in case of hydrogen, has obviously been insufficient. Herein, a novel BN material (i.e., porous microbelts), with the highest specific surface area ever reported for any BN system, up to 1488 m2 g–1, is obtained through one-step template-free reaction of a boron acid–melamine precursor with ammonia. Comprehensive high-resolution transmission electron microscopy, X-ray diffraction, and Raman characterizations all confirm that the obtained BN phase is partially disordered, shows an enlarged average spacing between adjacent (0002) layers (d0002 = 0.38 nm, compared to normal 0.33 nm for a bulk layered BN), and belongs to an intermediate state between hexagonal (h-BN) and amorphous (a-BN) phases. By changing the synthesis temperatures, the textures of obtain...

Production of Colored Pigments with Amorphous Arrays of Black and White Colloidal Particles

Abstract: There are many technical and industrial applications for colored pigments with nonfading properties. The development of a low-cost, high-volume production method for nonfading pigments with low toxicity and minimal environmental impact may promote their widespread use. To accomplish this goal, pigments need to be prepared using abundant and environmentally friendly compounds. Here, we report on the variously colored aggregates formed by spraying fine, submicrometer-sized spherical silica particles. The microstructure of the aggregate is isotropic with a shortrange order on a length scale comparable to optical wavelengths, and exhibits an angle-independent structural color as a result of wavelength-specific constructive interference. Interestingly, the color saturation of these aggregates can be controlled by the incorporation of a small amount of conventional black particles, such as carbon black (CB). We demonstrate that a Japanese-style painting can be successfully drawn with this method. Silicon dioxide, which is a major component of silica particles, is chemically stable and used in scientific glassware suitable for chemical experiments. It is also a primary component of soil and found in abundant supply in nature. Furthermore, in vivo toxicity of silica particles that are greater than 300 nm in diameter has not been detected. Therefore, submicrometer-sized silica particles are one of the best candidates for fabricating environmentally friendly materials. Fine submicrometer-sized spherical silica particles usually appear white to the human eye when they are in powdered form. However, assemblies of these particles can appear colored because of wavelength-specific optical interference, 5, 7] despite the absence of light-absorbing pigments and dyes. Such color is generally referred to as structural color, because it is essentially caused by the microstructure through optical phenomena, such as interference, diffraction, and scattering. 9] Crystalline arrays of fine submicrometersized spherical silica particles (colloidal crystals) are well known examples of assembled particles that have structural colors as a result of a very high reflectance at a certain wavelength of light. However, the structural colors produced by colloidal crystals show distinct variations, which depend on viewing and light illumination angles. Such iridescence makes the use of colloidal crystals as pigments difficult, because typical pigments generally require a constant color at different viewing angles. The iridescences of the colloidal crystals originate from Bragg reflection, which is the reflection mechanism that occurs as a result of the long-range order in the particle arrangement. Thus, if the arrangement is changed from the crystalline structure to the amorphous state, which has only a short-range order, iridescence is expected to be suppressed. In fact, amorphous aggregates of colloidal particles have been reported to exhibit angle-independent structural colors. 4, 5,12] However, amorphous colloidal arrays are difficult to fabricate because submicrometer-sized particles have a strong tendency to crystallize. Previously, amorphous colloidal arrays have been prepared by mixing two different kinds of submicrometer-sized silica particles. 4, 5, 13] These mixtures exhibit structural colors, but the colors are very pale. 4,5] Therefore, such amorphous colloidal arrays are unsuitable for use as brightly colored pigments. A simple synthetic method for the preparation of assemblies of submicrometer-sized particles with angle-independent brilliant structural colors for use as pigments has not yet been reported. Herein, we report a simple and reproducible synthetic procedure for the preparation of pigments that exhibit angleindependent, bright structural colors from amorphous colloidal arrays by spraying fine submicrometer-sized spherical silica particles of uniform size. We added a small amount of black particles to the colloidal amorphous array to enhance the saturation of the structural color by reducing incoherentlight scattering across the entire visible spectrum. Variously [*] Prof. Y. Takeoka, Prof. A. Takano, M. Teshima, Y. Ohtsuka, Prof. T. Seki Graduate School of Engineering, Nagoya University Furo-cho, Chikusa-ku, Nagoya, 464-8603 (Japan) E-mail: ytakeoka@apchem.nagoya-u.ac.jp

PbSe quantum dot field-effect transistors with air-stable electron mobilities above 7 cm2 V(-1) s(-1).

Abstract: PbSe quantum dot (QD) field effect transistors (FETs) with air-stable electron mobilities above 7 cm2 V–1 s–1 are made by infilling sulfide-capped QD films with amorphous alumina using low-temperature atomic layer deposition (ALD). This high mobility is achieved by combining strong electronic coupling (from the ultrasmall sulfide ligands) with passivation of surface states by the ALD coating. A series of control experiments rule out alternative explanations. Partial infilling tunes the electrical characteristics of the FETs.

Growth and Activation of an Amorphous Molybdenum Sulfide Hydrogen Evolving Catalyst

Abstract: Amorphous molybdenum sulfide films, prepared by electrodeposition, are a class of highly active catalysts for hydrogen evolution. The growth mechanism of the films and the true active species were unclear. Herein, we report a study of the growth and activation of these films using Electrochemical Quartz Crystal Microbalance (EQCM) and X-ray photoelectron spectroscopy (XPS). Three processes, including oxidative deposition, reductive corrosion, and reductive deposition, are occurring during the growth of a molybdenum sulfide film. Deposition method, precursor concentration, and potential window are among the factors influencing the film growth. Regardless of deposition methods, all films exhibit similar catalytic activity on a per mass base. Potentiostatic oxidation (anodic electrolysis) is the method for fastest film growth; it produces a MoS3 film precatalyst which can be electrochemically activated. The activity of the MoS3 precatalyst scales with catalyst loading; at a loading of 0.2 mg/cm2, the current...

Critical Thickness of SiO2 Coating Layer on Core@Shell Bulk@Nanowire Si Anode Materials for Li‐Ion Batteries

Abstract: Amorphous SiO2 coating layers with thicknesses of ca. 2, 7, 10, and 15 nm are introduced into bulk@nanowire core@shell Si particles via direct thermal oxidation at 650-850 °C. Of the coated samples, Si with a coating thickness of ca. 7 nm has the best electrochemical performance. This sample shows an initial discharge capacity of 2279 mA h g(-1) with a Coulombic efficiency of 92% and displays 83% capacity retention after 50 cycles at 0.2C rate.

Imaging Atomic Rearrangements in Two-Dimensional Silica Glass: Watching Silica’s Dance

Abstract: Structural rearrangements control a wide range of behavior in amorphous materials, and visualizing these atomic-scale rearrangements is critical for developing and refining models for how glasses bend, break, and melt. It is difficult, however, to directly image atomic motion in disordered solids. We demonstrate that using aberration-corrected transmission electron microscopy, we can excite and image atomic rearrangements in a two-dimensional silica glass—revealing a complex dance of elastic and plastic deformations, phase transitions, and their interplay. We identified the strain associated with individual ring rearrangements, observed the role of vacancies in shear deformation, and quantified fluctuations at a glass/liquid interface. These examples illustrate the wide-ranging and fundamental materials physics that can now be studied at atomic-resolution via transmission electron microscopy of two-dimensional glasses.

Synthesis of silica nanoparticles from Vietnamese rice husk by sol–gel method

Abstract: Silica powder at nanoscale was obtained by heat treatment of Vietnamese rice husk following the sol–gel method. The rice husk ash (RHA) is synthesized using rice husk which was thermally treated at optimal condition at 600°C for 4 h. The silica from RHA was extracted using sodium hydroxide solution to produce a sodium silicate solution and then precipitated by adding H2SO4 at pH = 4 in the mixture of water/butanol with cationic presence. In order to identify the optimal condition for producing the homogenous silica nanoparticles, the effects of surfactant surface coverage, aging temperature, and aging time were investigated. By analysis of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, the silica product obtained was amorphous and the uniformity of the nanosized sample was observed at an average size of 3 nm, and the BET result showed that the highest specific surface of the sample was about 340 m2/g. The results obtained in the mentioned method prove that the rice husk from agricultural wastes can be used for the production of silica nanoparticles.