Showing papers on "Amorphous solid published in 2012"
TL;DR: Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature, which is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that ofthin- film transistors based on thermally annealed materials.
Abstract: A method for annealing metal-oxide semiconductor films with deep-ultraviolet light yields thin-film transistors with performance comparable to that of thermally annealed devices, and widens the range of substrates on which such devices can be fabricated. Solution-processable metal-oxide semiconductors are attractive materials for low-cost, flexible electronics, but the need to anneal the deposited materials at relatively high temperatures limits the range of substrates on which such devices can be fabricated. Now Yong-Hoon Kim and colleagues demonstrate that irradiating the solution-cast films with deep ultraviolet light can obviate the need for an annealing step. In this system, photochemical activation serves essentially the same purpose as annealing, and the resulting semiconducting materials have device performance levels comparable to those produced using the high-temperature techniques. Amorphous metal-oxide semiconductors have emerged as potential replacements for organic and silicon materials in thin-film electronics. The high carrier mobility in the amorphous state, and excellent large-area uniformity, have extended their applications to active-matrix electronics, including displays, sensor arrays and X-ray detectors1,2,3,4,5,6,7. Moreover, their solution processability and optical transparency have opened new horizons for low-cost printable and transparent electronics on plastic substrates8,9,10,11,12,13. But metal-oxide formation by the sol–gel route requires an annealing step at relatively high temperature2,14,15,16,17,18,19, which has prevented the incorporation of these materials with the polymer substrates used in high-performance flexible electronics. Here we report a general method for forming high-performance and operationally stable metal-oxide semiconductors at room temperature, by deep-ultraviolet photochemical activation of sol–gel films. Deep-ultraviolet irradiation induces efficient condensation and densification of oxide semiconducting films by photochemical activation at low temperature. This photochemical activation is applicable to numerous metal-oxide semiconductors, and the performance (in terms of transistor mobility and operational stability) of thin-film transistors fabricated by this route compares favourably with that of thin-film transistors based on thermally annealed materials. The field-effect mobilities of the photo-activated metal-oxide semiconductors are as high as 14 and 7 cm2 V−1 s−1 (with an Al2O3 gate insulator) on glass and polymer substrates, respectively; and seven-stage ring oscillators fabricated on polymer substrates operate with an oscillation frequency of more than 340 kHz, corresponding to a propagation delay of less than 210 nanoseconds per stage.
956 citations
TL;DR: In this article, a scalable wet chemical synthesis for a catalytically active nanostructured amorphous molybdenum sulfide material was presented, which achieved a current density of 10 mA/cm2 at ∼200 mV overpotential.
Abstract: We present a scalable wet chemical synthesis for a catalytically active nanostructured amorphous molybdenum sulfide material. The catalyst film is one of the most active nonprecious metal materials for electrochemical hydrogen evolution, drawing 10 mA/cm2 at ∼200 mV overpotential. To identify the active phase of the material, we perform X-ray photoelectron spectroscopy after testing under a variety of conditions. As deposited, the catalyst resembles amorphous MoS3, but domains resembling MoS2 in composition and chemical state are created under reaction conditions and may contribute to this material’s high electrochemical activity. The activity scales with electrochemically active surface area, suggesting that the rough, nanostructured catalyst morphology also contributes substantially to the film’s high activity. Electrochemical stability tests indicate that the catalyst remains highly active throughout prolonged operation. The overpotential required to attain a current density of 10 mA/cm2 increases by o...
947 citations
TL;DR: It is evidenced that a competition takes place at the end of the discharge of the Sb/Na cell between the formation of the hexagonal and the cubic polymorphs of Na(3)Sb, the last being described in the literature as unstable at atmospheric pressure.
Abstract: Pure micrometric antimony can be successfully used as negative electrode material in Na-ion batteries, sustaining a capacity close to 600 mAh g–1 at a high rate with a Coulombic efficiency of 99 over 160 cycles, an extremely high capacity compared to any other compound tested against both Li and Na. The reaction mechanism with Na does not simply go through the alloying mechanism observed for Li where the intermediate species are those expected from the phase diagram. In the case of Na, the intermediate phases are mostly amorphous and could not be precisely identified. Surprisingly, we evidenced that a competition takes place at the end of the discharge of the Sb/Na cell between the formation of the hexagonal and the cubic polymorphs of Na3Sb, the last being described in the literature as unstable at atmospheric pressure and only synthesized under high pressure (1–9 GPa). In addition, fluoroethylene carbonate added to the electrolyte combined with an appropriate electrode formulation based on carboxymethyl...
842 citations
TL;DR: In this paper, the authors studied the promotional effects of certain transition metal ions on the activity of amorphous MoS3 films and found that Fe, Co, and Ni ions promote the growth of the MoS-3 films, resulting a high surface area and a higher catalyst loading.
Abstract: Molybdenum sulfide materials have been shown as promising non-precious catalysts for hydrogen evolution. This paper describes the study of the promotional effects of certain transition metal ions on the activity of amorphous MoS3 films. Ternary metal sulfide films, M–MoS3 (M = Mn, Fe, Co, Ni, Cu, Zn), have been prepared by cyclic voltammetry of aqueous solutions containing MCl2 and (NH4)2[MoS4]. Whereas the Mn–, Cu–, and Zn–MoS3 films show similar or only slightly higher catalytic activity as the MoS3 film, the Fe–, Co–, and Ni–MoS3 films are significantly more active. The promotional effects of Fe, Co, and Ni ions exist under both acidic and neutral conditions, but the effects are more pronounced under neutral conditions. Up to a 12-fold increase in exchange current density and a 10-fold increase in the current density at an overpotential of 150 mV are observed at pH = 7. It is shown that Fe, Co, and Ni ions promote the growth of the MoS3 films, resulting a high surface area and a higher catalyst loading. These changes are the main contributors to the enhanced activity at pH = 0. However, at pH = 7, Fe, Co, and Ni ions appear to also increase the intrinsic activity of the MoS3 film.
821 citations
TL;DR: The first use of non-centrosymmetric Janus Au-TiO(2) photocatalysts in efficient, plasmon-enhanced visible-light hydrogen generation and the generation of electron-hole pairs for photocatalysis are demonstrated.
Abstract: The first use of non-centrosymmetric Janus Au-TiO(2) photocatalysts in efficient, plasmon-enhanced visible-light hydrogen generation is demonstrated. The intense localization of plasmonic near-fields close to the Au-TiO(2) interface, coupled with optical transitions involving localized electronic states in amorphous TiO(2) brings about enhanced optical absorption and the generation of electron-hole pairs for photocatalysis.
745 citations
TL;DR: Amorphous MoS3 particles are prepared using a simple chemical method as mentioned in this paper using several deposition techniques to fabricate electrodes loaded with amorphous molybdenum sulfide particles.
Abstract: Amorphous MoS3 particles are prepared using a simple chemical method. Several deposition techniques are developed to fabricate electrodes loaded with MoS3 particles. These electrodes are highly active for hydrogen evolution. The catalytically active species appear to be reduced molybdenum sulfide that contains disulfide ligands. The MoS3 particles are annealed to form polycrystalline and single crystalline MoS3 and MoS2 particles. These particles, as well as commercial MoS2 micro-crystals, show inferior catalytic activity compared to the amorphous MoS3 particles.
648 citations
TL;DR: In this paper, the authors report on the enhanced hardness of nanocomposite coatings, their thermal stability, protection of the substrate against oxidation at temperatures above 1000°C, X-ray amorphous coatings thermally stable above 1000 °C and new advanced hard Nanocomposites with enhanced toughness which exhibit (i) low values of the effective Young's modulus E ⁎ satisfying the condition H/E < 0.1, (ii) high elastic recovery W e ǫ ≥ 60%, (iii) strongly improved tribological properties,
Abstract: The article reports on the enhanced hardness of nanocomposite coatings, their thermal stability, protection of the substrate against oxidation at temperatures above 1000 °C, X-ray amorphous coatings thermally stable above 1000 °C and new advanced hard nanocomposite coatings with enhanced toughness which exhibit (i) low values of the effective Young's modulus E ⁎ satisfying the condition H/E ⁎ > 0.1, (ii) high elastic recovery W e ≥ 60%, (iii) strongly improved tribological properties, and (iv) enhanced resistance to cracking; here E ⁎ = E(1−ν 2 ), E is the Young's modulus and ν is the Poison's ratio. At the end trends of next development of hard nanocomposite coatings are briefly outlined.
550 citations
TL;DR: The findings indicate that the increase in catalytic activity of films is accompanied by changes in oxidation state and structure that are reminiscent of those observed for conversion of β-NiOOH to γ-NiooH and consequently challenge the long-held notion that the β- NiOOH phase is a more efficient oxygen-evolving catalyst.
Abstract: An oxygen evolution catalyst that forms as a thin film from Ni(aq)2+ solutions containing borate electrolyte (Ni–Bi) has been studied by in situ X-ray absorption spectroscopy. A dramatic increase in catalytic rate, induced by anodic activation of the electrodeposited films, is accompanied by structure and oxidation state changes. Coulometric measurements correlated with X-ray absorption near-edge structure spectra of the active catalyst show that the nickel centers in activated films possess an average oxidation state of +3.6, indicating that a substantial proportion of nickel centers exist in a formal oxidation state of Ni(IV). In contrast, nickel centers in nonactivated films exist predominantly as Ni(III). Extended X-ray absorption fine structure reveals that activated catalyst films comprise bis-oxo/hydroxo-bridged nickel centers organized into sheets of edge-sharing NiO6 octahedra. Diminished long-range ordering in catalyst films is due to their ostensibly amorphous nature. Nonactivated films display...
550 citations
Sandia National Laboratories1, University of Pittsburgh2, Georgia Institute of Technology3, Pennsylvania State University4, University of Maryland, College Park5, National Institute of Standards and Technology6, Los Alamos National Laboratory7, Zhejiang University8, Massachusetts Institute of Technology9
TL;DR: It is shown that in situ transmission electron microscopy can be used to study the dynamic lithiation process of single-crystal silicon with atomic resolution and observe a sharp interface between the crystalline silicon and an amorphous Li(x)Si alloy.
Abstract: In lithium-ion batteries, the electrochemical reaction between the electrodes and lithium is a critical process that controls the capacity, cyclability and reliability of the battery. Despite intensive study, the atomistic mechanism of the electrochemical reactions occurring in these solid-state electrodes remains unclear. Here, we show that in situ transmission electron microscopy can be used to study the dynamic lithiation process of single-crystal silicon with atomic resolution. We observe a sharp interface (~1 nm thick) between the crystalline silicon and an amorphous Li(x)Si alloy. The lithiation kinetics are controlled by the migration of the interface, which occurs through a ledge mechanism involving the lateral movement of ledges on the close-packed {111} atomic planes. Such ledge flow processes produce the amorphous Li(x)Si alloy through layer-by-layer peeling of the {111} atomic facets, resulting in the orientation-dependent mobility of the interfaces.
529 citations
TL;DR: In this paper, orientational polarization in polar polymers can be utilized for high energy density and low loss dielectrics, which can be used for next-generation dielectric capacitors for pulsed power and power conditioning applications.
Abstract: The state-of-the-art polymer dielectrics have been limited to nonpolar polymers with relatively low energy density but ultralow dielectric losses for the past decades. With the fast development of power electronics in pulsed power and power conditioning applications, there is a need for next-generation dielectric capacitors in areas of high energy density/low loss and/or high temperature/low loss polymer dielectrics. Given limitations in further enhancing atomic and electronic polarizations for polymers, this Perspective focuses on a fundamental question: Can orientational polarization in polar polymers be utilized for high energy density and low loss dielectrics? Existing experimental and theoretical results have suggested the following perspectives. For amorphous polar polymers, high energy density and low loss can be achieved below their glass transition temperatures. For liquid crystalline side-chain polymers, dipole mobility is so high that they saturate at relatively low electric fields, and only li...
506 citations
TL;DR: Excellent cyclability was also observed during the reversible sodiation/desodiation cycles, showing great potential of Sn nanoparticles as a robust electrode material for rechargeable batteries.
Abstract: The microstructural changes and phase transformations of tin nanoparticles during electrochemical sodiation were studied with a nanosized sodium ion battery using in situ transmission electron microscopy. It was found that the first sodiation process occurred in two steps; that is, the crystalline Sn nanoparticles were initially sodiated via a two-phase mechanism with a migrating phase boundary to form a Na-poor, amorphous NaxSn alloy (x ∼ 0.5), which was further sodiated to several Na-rich amorphous phases and finally to the crystallized Na15Sn4 (x = 3.75) via a single-phase mechanism. The volumetric expansion was about 60% in the first step and 420% after the second step. However, despite the huge expansion, cracking or fracture was not observed, which is attributed to the second step of the single-phase sodiation that accommodates large portion of the sodiation-induced stress over the entire particle. Excellent cyclability was also observed during the reversible sodiation/desodiation cycles, showing gr...
TL;DR: The significantly reduced treatment time required to remove the Cr(VI) and the applicability in treating the solutions with low pH make MGNCs promising for the efficient removal of heavy metals from the wastewater.
Abstract: A facile thermodecomposition process to synthesize magnetic graphene nanocomposites (MGNCs) is reported. High-resolution transmission electron microscopy and energy filtered elemental mapping revealed a core@double-shell structure of the nanoparticles with crystalline iron as the core, iron oxide as the inner shell and amorphous Si–S–O compound as the outer shell. The MGNCs demonstrate an extremely fast Cr(VI) removal from the wastewater with a high removal efficiency and with an almost complete removal of Cr(VI) within 5 min. The adsorption kinetics follows the pseudo-second-order model and the novel MGNC adsorbent exhibits better Cr(VI) removal efficiency in solutions with low pH. The large saturation magnetization (96.3 emu/g) of the synthesized nanoparticles allows fast separation of the MGNCs from liquid suspension. By using a permanent magnet, the recycling process of both the MGNC adsorbents and the adsorbed Cr(VI) is more energetically and economically sustainable. The significantly reduced treatm...
TL;DR: In this paper, atomic layer deposition (ALD) is used to deposit SnO 2, containing both amorphous and crystalline phases, onto graphene nanosheets (GNS) as anodes for lithium-ion batteries.
Abstract: As one of the most promising negative electrode materials in lithium-ion batteries (LIBs), SnO 2 experiences intense investigation due to its high specifi c capacity and energy density, relative to conventional graphite anodes. In this study, for the fi rst time, atomic layer deposition (ALD) is used to deposit SnO 2 , containing both amorphous and crystalline phases, onto graphene nanosheets (GNS) as anodes for LIBs. The resultant SnO 2 -graphene nanocomposites exhibit a sandwich structure, and, when cycled against a lithium counter electrode, demonstrate a promising electrochemical performance. It is demonstrated that the introduction of GNS into the nanocomposites is benefi cial for the anodes by increasing their electrical conductivity and releasing strain energy: thus, the nanocomposite electrode materials maintain a high electrical conductivity and fl exibility. It is found that the amorphous SnO 2 -GNS is more effective than the crystalline SnO 2 -GNS in overcoming electrochemical and mechanical degradation; this observation is consistent with the intrinsically isotropic nature of the amorphous SnO 2 , which can mitigate the large volume changes associated with charge/discharge processes. It is observed that after 150 charge/discharge cycles, 793 mA h g − 1 is achieved. Moreover, a higher coulombic effi ciency is obtained for the amorphous SnO 2 GNS composite anode. This study provides an approach to fabricate novel anode materials and clarifi es the infl uence of SnO 2 phases on the electrochemical performance of LIBs.
TL;DR: Although differential scanning calorimetry is the most widely used thermal analytical technique applied to the characterization of amorphous solid dispersions, there are many established and emerging techniques which have been shown to provide useful information.
TL;DR: It is shown that fracture locations are highly anisotropic for lithiation of crystalline Si nanopillars and that fracture is strongly correlated with previously discovered anisotrop expansion, and that the critical fracture size depends on the electrochemical reaction rate.
Abstract: From surface hardening of steels to doping of semiconductors, atom insertion in solids plays an important role in modifying chemical, physical, and electronic properties of materials for a variety of applications. High densities of atomic insertion in a solid can result in dramatic structural transformations and associated changes in mechanical behavior: This is particularly evident during electrochemical cycling of novel battery electrodes, such as alloying anodes, conversion oxides, and sulfur and oxygen cathodes. Silicon, which undergoes 400% volume expansion when alloying with lithium, is an extreme case and represents an excellent model system for study. Here, we show that fracture locations are highly anisotropic for lithiation of crystalline Si nanopillars and that fracture is strongly correlated with previously discovered anisotropic expansion. Contrary to earlier theoretical models based on diffusion-induced stresses where fracture is predicted to occur in the core of the pillars during lithiation, the observed cracks are present only in the amorphous lithiated shell. We also show that the critical fracture size is between about 240 and 360 nm and that it depends on the electrochemical reaction rate.
TL;DR: In this paper, the authors compared the catalytic activity of Co3O4 for the oxygen evolution reaction (OER) of the crystalline and amorphous films of a tartrate complex of Co2+ in an aqueous, alkaline solution at elevated temperatures.
Abstract: Crystalline films of Co3O4 are deposited by electrochemically oxidizing a tartrate complex of Co2+ in an aqueous, alkaline solution at elevated temperatures. The crystallinity and stability of the films are a strong function of the deposition temperature. Films deposited at temperatures from 50 to 90 °C are amorphous, but films deposited from refluxing solution at 103 °C are crystalline. The crystalline films adhere strongly to the substrate, whereas the amorphous films peel off of the substrate when dried due to drying stresses. The crystalline films deposit with the normal spinel structure, with a lattice parameter of 0.8097 nm and crystallite size of 26 nm. The catalytic activity of Co3O4 for the oxygen evolution reaction (OER) of the crystalline and amorphous films is compared by Tafel analysis in alkaline solution at pH 14. The crystalline Co3O4 film has a Tafel slope of 49 mV/decade and an exchange current density of 2.0 × 10–10 A cm–2, whereas an amorphous film deposited at 50 °C has a Tafel slope ...
TL;DR: In this paper, a unique amorphous MnOx-C nanocomposite particles with interdispersed carbon are synthesized using aerosol spray pyrolysis, which blocks the penetration of liquid electrolyte to the inside of MnOx, thus reducing the formation of a solid electrolyte interphase and lowering the irreversible capacity.
Abstract: The realization of manganese oxide anode materials for lithium-ion batteries is hindered by inferior cycle stability, rate capability, and high overpotential induced by the agglomeration of manganese metal grains, low conductivity of manganese oxide, and the high stress/strain in the crystalline manganese oxide structure during the repeated lithiation/delithiation process. To overcome these challenges, unique amorphous MnOx–C nanocomposite particles with interdispersed carbon are synthesized using aerosol spray pyrolysis. The carbon filled in the pores of amorphous MnO x blocks the penetration of liquid electrolyte to the inside of MnOx, thus reducing the formation of a solid electrolyte interphase and lowering the irreversible capacity. The high electronic and lithium-ion conductivity of carbon also enhances the rate capability. Moreover, the interdispersed carbon functions as a barrier structure to prevent manganese grain agglomeration. The amorphous structure of MnOx brings additional benefits by reducing the stress/strain of the conver sion reaction, thus lowering lithiation/delithiation overpotential. As the result, the amorphous MnOx-C particles demonstrated the best performance as an anode material for lithium-ion batteries to date.
TL;DR: In this article, the effect of early carbonation on performance of paste at different ages was examined by using XRD, TGA, 29 Si NMR, and SEM to understand the mechanism of concrete carbonation at early age through the microstructure development of its cement paste.
TL;DR: The amorphous Ce-Ti mixed oxides were reported to be catalysts for selective catalytic reduction of NO(x) with NH(3), in which Ce and not Ti acts as their solvent in spite of the fact that Ce is low in content.
Abstract: The amorphous Ce–Ti mixed oxides were reported to be catalysts for selective catalytic reduction of NOx with NH3, in which Ce and not Ti acts as their solvent in spite of the fact that Ce is low in content. The amorphous catalysts were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) equipped with selective area electron diffraction (SAED). The Ce–Ti amorphous oxide shows higher activity than its crystalline counterpart at lower temperatures. Moreover, the presence of small CeO2 crystallites as for the impregnated sample is deleterious to activity. The Ce–O–Ti short-range order species with the interaction between Ce and Ti in atomic scale was confirmed for the first time to be the active site using temperature programmed reduction with H2 (H2–TPR), in situ FTIR spectra of NO adsorption, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine-structure (XAFS). Lastly, the Ce–O–Ti structure was directly observed by field-emission TEM (FETEM).
TL;DR: In this paper, the compositions of grain boundaries (GBs) and other interfaces surrounding Nd 2 Fe 14 B sintered magnets have been investigated by laser-assisted three-dimensional atom probe to understand the mechanism of the coercivity enhancement by post-sinter annealing.
TL;DR: P-SoXS reveals scattering anisotropy in amorphous domains of all-polymer organic solar cells where interfacial interactions pattern orientational alignment in the matrix phase, which probably plays an important role in the photophysics.
Abstract: Molecular orientation critically influences the mechanical, chemical, optical and electronic properties of organic materials. So far, molecular-scale ordering in soft matter could be characterized with X-ray or electron microscopy techniques only if the sample exhibited sufficient crystallinity. Here, we show that the resonant scattering of polarized soft X-rays (P-SoXS) by molecular orbitals is not limited by crystallinity and that it can be used to probe molecular orientation down to size scales of 10 nm. We first apply the technique on highly crystalline small-molecule thin films and subsequently use its high sensitivity to probe the impact of liquid-crystalline ordering on charge mobility in polymeric transistors. P-SoXS also reveals scattering anisotropy in amorphous domains of all-polymer organic solar cells where interfacial interactions pattern orientational alignment in the matrix phase, which probably plays an important role in the photophysics. The energy and q-dependence of the scattering anisotropy allows the identification of the composition and the degree of orientational order in the domains.
TL;DR: Full cell measurement using the TiO( 2)/graphene as the anode material and spinel LiMnO(2) as the cathode material exhibit good high-rate performance and cycling stability, indicating that the Ti O(2)/ graphene nanocomposite has a practical application potential in advanced Li-ion batteries.
Abstract: A simple and scalable method is developed to synthesize TiO2/graphene nanostructured composites as high-performance anode materials for Li-ion batteries using hydroxyl titanium oxalate (HTO) as the intermediate for TiO2. With assistance of a surfactant, amorphous HTO can condense as a flower-like nanostructure on graphene oxide (GO) sheets. By calcination, the HTO/GO nanocomposite can be converted to TiO2/graphene nanocomposite with well preserved flower-like nanostructure. In the composite, TiO2 nanoparticles with an ultrasmall size of several nanometers construct the porous flower-like nanostructure which strongly attached onto conductive graphene nanosheets. The TiO2/graphene nanocomposite is able to deliver a capacity of 230 mA h g–1 at 0.1 C (corresponding to a current density of 17 mA g–1), and demonstrates superior high-rate charge–discharge capability and cycling stability at charge/discharge rates up to 50 C in a half cell configuration. Full cell measurement using the TiO2/graphene as the anode ...
TL;DR: In this article, the authors used high resolution and energy filtered transmission electron microscopy (HRTEM, EFTEM) to study mineral-fluid interfaces using TEM foils cut directly across the reaction boundaries, which allowed measurements to be made directly in cross section at nanometer to sub-nanometer resolution.
TL;DR: By monitoring the kinetics of the formation of amyloid fibrils and glass-like amorphous aggregates, it is shown that solubility and supersaturation will be key factors for further understanding the aberrant aggregation of proteins.
Abstract: Amyloid fibrils and amorphous aggregates are two types of aberrant aggregates associated with protein misfolding diseases. Although they differ in morphology, the two forms are often treated indiscriminately. β2-microglobulin (β2m), a protein responsible for dialysis-related amyloidosis, forms amyloid fibrils or amorphous aggregates depending on the NaCl concentration at pH 2.5. We compared the kinetics of their formation, which was monitored by measuring thioflavin T fluorescence, light scattering, and 8-anilino-1-naphthalenesulfonate fluorescence. Thioflavin T fluorescence specifically monitors amyloid fibrillation, whereas light scattering and 8-anilino-1-naphthalenesulfonate fluorescence monitor both amyloid fibrillation and amorphous aggregation. The amyloid fibrils formed via a nucleation-dependent mechanism in a supersaturated solution, analogous to crystallization. The lag phase of fibrillation was reduced upon agitation with stirring or ultrasonic irradiation, and disappeared by seeding with preformed fibrils. In contrast, the glass-like amorphous aggregates formed rapidly without a lag phase. Neither agitation nor seeding accelerated the amorphous aggregation. Thus, by monitoring the kinetics, we can distinguish between crystal-like amyloid fibrils and glass-like amorphous aggregates. Solubility and supersaturation will be key factors for further understanding the aberrant aggregation of proteins.
TL;DR: The crystallization of Li(15)Si(4) from amorphous Li(x)Si is a spontaneous, congruent phase transition process without phase separation or large-scale atomic motion, which is drastically different from what is expected from a classic nucleation and growth process.
Abstract: It is well-known that upon lithiation, both crystalline and amorphous Si transform to an armorphous LixSi phase, which subsequently crystallizes to a (Li, Si) crystalline compound, either Li15Si4 or Li22Si5. Presently, the detailed atomistic mechanism of this phase transformation and the degradation process in nanostructured Si are not fully understood. Here, we report the phase transformation characteristic and microstructural evolution of a specially designed amorphous silicon (a-Si) coated carbon nanofiber (CNF) composite during the charge/discharge process using in situ transmission electron microscopy and density function theory molecular dynamic calculation. We found the crystallization of Li15Si4 from amorphous LixSi is a spontaneous, congruent phase transition process without phase separation or large-scale atomic motion, which is drastically different from what is expected from a classic nucleation and growth process. The a-Si layer is strongly bonded to the CNF and no spallation or cracking is o...
TL;DR: This work devised an in vitro assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC·H2O in vitro.
Abstract: Crystalline biominerals do not resemble faceted crystals. Current explanations for this property involve formation via amorphous phases. Using X-ray absorption near-edge structure (XANES) spectroscopy and photoelectron emission microscopy (PEEM), here we examine forming spicules in embryos of Strongylocentrotus purpuratus sea urchins, and observe a sequence of three mineral phases: hydrated amorphous calcium carbonate (ACC·H2O) → dehydrated amorphous calcium carbonate (ACC) → calcite. Unexpectedly, we find ACC·H2O-rich nanoparticles that persist after the surrounding mineral has dehydrated and crystallized. Protein matrix components occluded within the mineral must inhibit ACC·H2O dehydration. We devised an in vitro, also using XANES-PEEM, assay to identify spicule proteins that may play a role in stabilizing various mineral phases, and found that the most abundant occluded matrix protein in the sea urchin spicules, SM50, stabilizes ACC·H2O in vitro.
TL;DR: The band gap of the graphene oxide becomes narrower under uniaxial tensile strain, providing an efficient way to tune the electronic properties of graphene oxide-based materials.
Abstract: The mechanical properties, including the Young's modulus and intrinsic strength, of graphene oxides are investigated by first-principles computations. Structural models of both ordered and amorphous graphene oxides are considered and compared. For the ordered graphene oxides, the Young's modulus is found to vary from 380 to 470 GPa as the coverage of oxygen groups changes, respectively. The corresponding variations in the Young's modulus of the amorphous graphene oxides with comparable coverage are smaller at 290–430 GPa. Similarly, the ordered graphene oxides also possess higher intrinsic strength compared with the amorphous ones. As coverage increases, both the Young's modulus and intrinsic strength decrease monotonically due to the breaking of the sp2 carbon network and lowering of the energetic stability for the ordered and amorphous graphene oxides. In addition, the band gap of the graphene oxide becomes narrower under uniaxial tensile strain, providing an efficient way to tune the electronic properties of graphene oxide-based materials.
TL;DR: In this article, the authors investigated the composition, distribution, and ambient stability of the amorphous solid electrolyte interphase (SEI) formed on undoped silicon wafers configured as model electrodes in three different electrochemical conditions using a reduced oxidation interface for transporting air-sensitive samples from a glovebox to an ultra-high-vacuum chamber for X-ray photoelectron spectroscopy (XPS) analysis.
Abstract: Since the potential for alloying lithium with silicon is outside the window of stability of common commercial electrolytes, silicon surfaces form an amorphous solid electrolyte interphase (SEI) under applied potential, which hampers silicon's performance as a lithium-ion battery anode. We have investigated the composition, distribution, and ambient stability of the SEI formed on undoped silicon (001) wafers configured as model electrodes in three different electrochemical conditions using a reduced oxidation interface for transporting air-sensitive samples from a glovebox to an ultra-high-vacuum chamber for X-ray photoelectron spectroscopy (XPS) analysis. Variable potential cycling and step experiments included linear sweep voltammetry (LSV), cyclic voltammetry (CV), and chronoamperometry (CA). CV and LSV experiments on silicon electrodes scanned from open-circuit voltage to lithiation (3–0.01 V vs Li/Li+) showed a suppression of carbonate-containing species relative to CA experiments (potential step for ...
TL;DR: The results show that multiple incidences, lead to the true solution for a filter with a large number of layers, even for a high number of variable parameters.
Abstract: In the present paper we determine the optical constants and thicknesses of multilayer thin film stacks, in the visible and near infrared ranges. These parameters are derived from the transmittance and reflectance spectra measured by a spectrophotometer, for several angles of incidence. Several examples are studied, from a simple single layer structure up to a 22-layer dielectric filter. We show that the use of a large number of incidence angles is an effective means of reducing the number of mathematical solutions and converging on the correct physical solution when the number of layers increases. More specifically, we provide an in-depth discussion of the approach used to extract the index and thickness of each layer, which is achieved by analysing the various mathematical solutions given by a global optimization procedure, based on as little as 6 and as many as 32 variable parameters. The results show that multiple incidences, lead to the true solution for a filter with a large number of layers. In the present study, a Clustering Global Optimization algorithm is used, and is shown to be efficient even for a high number of variable parameters. Our analysis allows the accuracy of the reverse engineering process to be estimated at approximately 1 nm for the thickness, and 2 10−3 for the index of each layer in a 22-layer filter.