Stable Layered Structure Research Articles

Microstructure and mechanical properties of as-deposited and annealed TiB2/BN superlattice coatings

TiB2/BN multilayers with the modulation ratios (tTiB2:tBN) ranging from 1:1 to 16:1 and a constant modulation period of 24nm were prepared by magnetron sputtering. The TiB2/BN multilayers were subsequently annealed in a vacuum environment at temperatures of 500–700°C for 30min, then characterized by extensive measurements. All multilayers exhibited small grain sizes and stable layer structures with polycrystalline with TiB2(001), TiB2(101), TiB2(002) textures or amorphous BN, resulting in higher hardness and elastic modulus than that of individual monolithic TiB2 or BN coatings. The hardness of as-deposited multilayer can reach as high as 39.34GPa at tTiB2:tBN=13:1, meanwhile the friction coefficient got to 0.028, which was also the lowest. The hardness and friction were almost unchanged after annealing at 500–700°C, which was attributed to good thermal stability in the layer structure and the existence of stable TiBxNy phases.

Highly Efficient, Irreversible and Selective Ion Exchange Property of Layered Titanate Nanostructures

AbstractLayered titanates (Na2Ti3O7·nH2O) with exchangeable sodium cations located in the interlayer have been synthesized by simple hydrothermal treatment of Ti precursor in concentrated NaOH solutions. By proper control of the synthesis conditions, different morphologies of nanofibers and nanosheets are obtained. The metastable layered structure of the titanates collapses during the ion exchange, resulting in irreversible ion exchange. Target cations (eg., Ag+, Cu2+, Pb2+ and Eu3+) are completely concentrated from water and then tightly immobilized in the interlayer which is of great significance for the removal and subsequent safe disposal of hazardous metal cations. The ion exchange of the nanosheets is much more efficient than that of the nanofibers and other inorganic ion exchangers due to the larger surface area, less stable layered structure and larger amount of interlayer water of the nanosheets. The ion exchange of the titanates is also very selective. Valence, hardness, and radius of cations are main factors affecting the selectivity. Cations trapped in the interlayer are released by an acid‐induced phase transformation of the titanate nanosheets to rutile. Then the rutile can be used as a new Ti precursor to synthesize the titanate nanostructures, resulting in a full cycle of material use. The nanosheets may find applications in the decontamination and safe disposal of radioactive and heavy metal cations and also in the collection of valuable cations from water.

Synthesis and photocatalytic property of the ZrO2/TiO2 pillared laponite

The ZrO2/TiO2 pillared laponite (Ti-Zr-lap) photocatalysts were prepared with intercalation reaction by supercritical fluid drying (SCFD), and characterized by XRD,TEM, SEM and BET surface area analysis, and the photocatalytic properties of Ti-Zr-lap were investigated by degradation of azo dye acid red B (ARB). The results showed that the ZrO2/TiO2 pillared structures in laponite could be formed, with the mass fraction of (Zr4++Ti4+)/laponite (Xm) increasing, the basal spacing and the BET surface area of Ti-Zr-lap significantly increased. The Ti-Zr-lap used as photocatalyst had the advantages of stable and porous layered structure, large surface area with the anatase type TiO2. Compared with the Ti-Zr-lap dried by air drying, the Ti-Zr-lap dried by SCFD showed better photocatalytic property which was very close to that of P25 TiO2. Using the Ti-Zr-lap as photocatalyst with the optimum Xm of 0.16 and the calcination temperature of 500 °C, under the conditions of the initial concentration of ARB 20 mg/L, photocatalyst concentration of 1.5 g/L and irradiation time 60 min, the decoloring rate of ARB could achieve 98.3%, indicating that the Ti-Zr-lap had excellent photocatalytic property.

Preparation and Characterization of Organic-Inorganic Hybrid Perovskite (C<sub>6</sub>H<sub>5</sub>CH<sub>2</sub>NH<sub>3</sub>)<sub>2</sub>CuCl<sub>4</sub>

An organic–inorganic hybrid perovskite (C6H5CH2NH3)2CuCl4was synthesized successfully by solution method at room temperature and the thin film of (C6H5CH2NH3)2CuCl4 was also prepared by spin-coating on the quartz substrate. The perovskite and the film were characterized with X-ray diffraction (XRD), Scan electronic microscope (SEM), Atomic force microscope (AFM), Fourier transform infrared spectroscopy and Thermo Gravimetric Analyzer. Results show that the obtained perovskite has unique layer structure and good thermal stability with melting point around 243.3°C. And the prepared film appears very smooth, continuous and uniform with a grain size of 0.1μm, highly oriented with the (0 0 l) planes perpendicular to the substrate surface. Its optical photoluminescence spectrum mainly depends on the inorganic part so the bandgap can be tuned by changing the inorganic composition. The carrier mobility is around 0.26cm2V-1S-1 , which indicates its potential application in field effect transistor with improved film quality.

Characteristics of atmospheric waves in the upper troposphere observed with the Gadanki MST Radar—RASS

Indian MST Radar at Gadanki (13.46ºN, 79.17ºE) working at 53 MHz was operated continuously in Radio Acoustic Sounding System (RASS) mode with six distributed acoustic exciters during 22–25 August 2007 for about 69 h in RASS and turbulence echo modes alternately, with one cycle spanning about 20 min. Temperature and wind velocity were observed in the altitude range 3.6–12 km most of the time and 3.6–20 km, respectively, with a range resolution of 150 m. Presence of an inertia–gravity wave in the lower stratosphere was identified. Perturbations in the wind and temperature fields in the troposphere, however, indicated a mixture of waves with a wide frequency range, within which a dominant periodicity of ∼8 h with a vertical wavelength of ∼4 km was revealed by two-dimensional spectral analysis. Further, signatures of diurnal tide were also observed and the temperature phase profile was found to exhibit a close match with the Global Scale Wave Model (GSWM02). From the RASS virtual temperature profiles, time–height section of Brunt-Väisälä frequency squared was computed to deduce the background atmospheric stability, which showed stable layered structures with slow downward phase progression. Outgoing Longwave Radiation (OLR) over Gadanki and TRMM precipitation data over peninsular India was used as an indicator of convective activity. During the beginning of the observation period, even though lower OLR was seen, corresponding convective activity or precipitation was not seen in the TRMM data. On 24 August, enhanced temperature perturbations could be related to widespread precipitation shown by TRMM.

Stability of monolayers and bilayers in a copolymer-homopolymer blend model

We study the stability of layered structures in a variational model for diblock copolymerhomopolymer blends with respect to perturbations of their interfaces. The main step consists of calculating the first and second derivatives of a sharp-interface Ohta–Kawasaki energy for straight mono- and bilayers and determining the sign of the latter. By developing the interface perturbations in a Fourier series we fully characterise the stability of the structures in terms of the energy parameters. Both for the monolayer and for the bilayer there exist parameter regions where these structures are unstable. For strong repulsive interaction between the monomer types in the diblock copolymer the bilayer is always stable with respect to interface perturbations, irrespective of the domain size. The monolayer is only stable for small domain size. In the course of our computations we also give a Green’s function for the Laplacian on a twodimensional periodic strip.

Layered Titanium Oxide Nanosheet and Ultrathin Nanotubes: A First-Principles Prediction

We propose stable layered structures and ultrathin tubular configurations of titanium oxide (TiO2) nanomaterials on the basis of first-principles calculations within density functional theory. The thinnest TiO2 nanosheet is characterized by a reconstructed (001) bilayer of rutile TiO2, while ultrathin TiO2 nanotubes can be built by rolling up a TiO2NS. These nanotubes are predicted to have high stability, large Young’s modulus, and tunable electronic properties. A possible synthetic route toward these nanostructures is also presented.

Synthesis and characterization of Zn-doped LiCo 0.3Ni 0.4( xMn 0.3Zn xO 2 cathode materials for lithium-ion batteries

Zn-doped LiCo 0.3Ni 0.4− x Mn 0.3Zn x O 2 cathode materials were synthesized via co-precipitation method. The structure, electrochemical performance and thermal stability were characterized by X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammograms (CV), electrochemical impedance spectroscopies (EIS) and differential scanning calorimetry (DSC). LiCo 0.3Ni 0.4− x Mn 0.3Zn x O 2 had stable layered structure with a-NaFeO 2 type with x up to 0.05. The compounds of x = 0.02 showed the best discharge capacity and cycle performance which was related to the most stable structure and Zn-doping prevented structural transformations during the topotactic reactions. Meanwhile, Zn-doping improved the high rate discharge capability and thermal stability.

Numerical modeling of a continuous photochemical pollution episode in Hong Kong using WRF–chem

A continuous and heavy photochemical pollution episode when Typhoon Nari occurred during Sep. 14–19, 2001 in Hong Kong was studied by use of the new generation of regional air quality model WRF–chem V2.1, in which the meteorological model (WRF) and chemical model (chem) are fully coupled on line. In this episode, the regional air quality monitoring stations in Hong Kong recorded high concentrations of O 3, CO and NO x for six days, the maximum concentration of O 3 reached 191 ppb, and the atmospheric visibility dropped to 1.8 km. Investigations showed that WRF–chem can basically simulate this continuous photochemical pollution episode, with the best correlation coefficient of the simulated and the observed O 3 concentrations being 0.84. The production and loss of O 3 were significant in this episode, and the largest rates were 22.7 and −17.6 ppb h −1, respectively. The simulated meteorological conditions showed high temperature, lower relative humidity, strong solar radiation, northerly airstream, and stable boundary layer structure in Hong Kong during the episode, these weather factors were conducive to formation and maintenance of photochemical pollution. It was also clear that the vertical transport played an important role in this episode. As controlled by downdraft at the outside of Typhoon system with more stable atmosphere, air pollutants were limited and accumulated in the low level of boundary layer, leading to high O 3 concentration from photochemical formation.

A hydrogen storage layer on the surface of silicon nitride films

Composition, layer structure, and H-retaining stability of 980°C N2-annealed silicon nitride-oxide (ON) stacks were analyzed using high resolution rutherford backscattering, synchrotron x-ray specular reflectometry, and nuclear reaction analysis. The formation of a Si2N2O layer in the near-surface part of N2-annealed nitride films was discovered. The Si2N2O layer can store hydrogen species that are resistant against energetic electron damage due to their reduced diffusion mobility. Although degrading in air, the Si2N2O layer thus provides reliable hydrogen species, which are desirable in the integrated circuit processing of silicon transistors and silicon ONO trap memories.

Evaluation of Limited-Area Models for the Representation of the Diurnal Cycle and Contrasting Nights in CASES-99

Abstract This study evaluates the ability of three limited-area models [the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5), the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS), and the High-Resolution Limited-Area Model (HIRLAM)] to predict the diurnal cycle of the atmospheric boundary layer (ABL) during the Cooperative Atmosphere–Surface Exchange Study (CASES-99) experimental campaign. Special attention is paid to the stable ABL. Limited-area model results for different ABL parameterizations and different radiation transfer parameterizations are compared with the in situ observations. Model forecasts were found to be sensitive to the choice of the ABL parameterization both during the day and at night. At night, forecasts are particularly sensitive to the radiation scheme. All three models underestimate the amplitude of the diurnal temperature cycle (DTR) and the near-surface wind speed. Furthermore, they overestimate the stable boundary layer height for windy conditions and underestimate the stratification of nighttime surface inversions. Favorable parameterizations for the stable boundary layer enable rapid surface cooling, and they have limited turbulent mixing. It was also found that a relatively large model domain is required to model the Great Plains low-level jet. A new scheme is implemented for the stable boundary layer in the Medium-Range Forecast Model (MRF). This scheme introduces a vegetation layer, a new formulation for the soil heat flux, and turbulent mixing based on the local scaling hypothesis. The new scheme improves the representation of surface temperature (especially for weak winds) and the stable boundary layer structure.

Single-crystal to single-crystal phase transition of cucurbit[5]uril hydrochloride hydrates: large water-filled channels transforming to layers of unusual stability

Cucurbit[5]uril hydrochloride hydrate crystals with large water-filled channels transform to a highly stable layer structure via a single-crystal to single-crystal mechanism; (129)Xe NMR showed that porosity in CB[5] samples depends critically on the method of preparation.

Study of assembly of arachidic acid/LDHs hybrid films containing photoactive dyes

Hybrid monolayers formed with an floating arachidic acid (AA) anions monolayer binding with a densely packed layered double hydroxides (LDHs) monolayer at an air/LDHs suspension interface has been studied by π– A isotherms and TEM images. An ordered multilayer film of AA/LDHs has been fabricated by Langmuir–Blodgett technique on various substrates. The photoactive dyes (methyl orange, MO, and Congo red, CR) can be incorporated into the galleries of LDHs in the AA/LDHs hybrid LB film by an ion intercalation method. The results of FTIR and UV–vis absorption spectra can approve the formation of AA/LDHs/dyes composite films. In addition, UV–vis absorption spectra and LAXRD analyses also provide evidence for the good vertical uniformity and stable layered periodic structure of AA/LDHs/dyes films. More interestingly, it was found that the dye molecules intercalated can be induced by a positively charged LDHs sheet to align in a special orientation and form different aggregates: MO molecules form sandwich H-type aggregates, while CR molecules form head-to-tail J-type aggregates. On the basis of these data, a possible model of the AA/LDHs/dyes composite films was proposed. Also, the dye molecules incorporated into AA/LDHs films exhibit excellent configuration stability under the irradiation of UV light because the LDHs matrix offers a more rigid and constrained environment for them.

Convergences and divergences and thin layer formation and maintenance

The formation and maintenance of thin layers in the presence of turbulent diffusion is considered through the development of a formal framework that evaluates the balance between convergence mechanisms and the diffusive effects of turbulence. Turbulent diffusion acts to broaden layers, thus a convergence is required to produce a persistent and stable layer structure. Convergence mechanisms considered here include straining by a sheared velocity profile, organism motility, and particle buoyancy. The balance between each of these convergences and turbulent diffusion results in a scale estimate for the layer thickness that depends on local conditions. Comparison of these layer thickness scales for each of the three mechanisms enables us to evaluate which mechanism is likely to be dominant in particular situations. An example application of the framework is based on observations of thin layers in East Sound, Washington, for which we conclude that either the buoyancy or straining mechanism could contribute to the maintenance of the layer. Finally, the analytic framework itself provides insights into thin layer dynamics, including the prediction of a finite layer lifetime for shear‐driven layers and the effects of mixing events on the convergence mechanisms acting to maintain the layers.

Effect of fluoroethylene carbonate additive on interfacial properties of silicon thin-film electrode

A silicon thin-film electrode (thickness = 200 nm) is prepared by E-beam evaporation and deposition on copper foil. The electrochemical performance of a lithium/silicon thin-film cell is investigated in ethylene carbonate/diethyl carbonate/1.3 M LiPF 6 with and without 3 wt.% fluoroethylene carbonate (FEC). The addition of FEC remarkably improves discharge capacity retention and coulombic efficiency. The surface morphology and chemical composition of the solid electrolyte interphase (SEI) formed on the surface of the silicon thin-film electrode after cycling are studied through scanning electron microscopy and X-ray photoelectron spectroscopy analysis. A smoother and more stable SEI layer structure is generated by the introduction of the FEC additive to the electrolyte.

High-speed nonchiral-smectic-C liquid-crystal modes for display applications

— Three nonchiral-smectic-C (NSC) liquid-crystal (LC) modes having fast-response and wide-viewing characteristics applicable for next-generation LCDs are described. In the NSC LC modes, fast analog optical modulation is achieved by means of a coupling with an external electric field in a dielectrically driving scheme. The fast response results intrinsically from no interlayer interferences during molecular rotation in the layered structure of the NSC LC. Moreover, the self-formation of two domains and the in-plane variations of the optic axis produce the wide-viewing properties. A step-wise temperature annealing process is employed for a stable and well-aligned smectic layer structure in a time-efficient manner.

Stannum doping of layered LiNi 3/8Co 2/8Mn 3/8O 2 cathode materials with high rate capability for Li-ion batteries

Sn doped lithium nickel cobalt manganese composite oxide of LiNi 3/8Co 2/8Mn 3/8− x Sn x O 2 (0 ≤ x ≤ 0.10) was synthesized by stannum substitute of manganese to enhance its rate capability at first time. Its structure and electrochemical properties were characterized by X-ray diffraction (XRD), SEM, cyclic voltammetry (CV), galvanostatic intermittent titration technique (GITT) and charge/discharge tests. LiNi 3/8Co 2/8Mn 3/8− x Sn x O 2 had stable layered structure with α-NaFeO 2 type as x up to 0.05, meanwhile, its chemical diffusion coefficient D Li of Li-ion was enhanced by almost one order of magnitude, leading to notable improvement of the rate capability of LiNi 3/8Co 2/8Mn 3/8O 2. The compound of x = 0.10 showed the best rate capability among Sn doped samples, but its discharge capacity reduced markedly due to secondary phase Li 2SnO 3 and increase of cation-disorder. The compound with x = 0.05 showed high rate capability with initial discharge capacity in excess of 156 mAh g −1. It is a promising alternative cathode material for EV application of Li-ion batteries.

Cluster observations of bounday layer structure and a flux transfer event near the cusp

Abstract. On the 25th January 2002 between 10:00 and 12:00 UT, the four Cluster spacecraft passed through the northern high-latitude cusp, the dayside magnetosphere and into the magnetosheath in a linear formation. In the magnetosphere the PEACE electron spectrometers on the four spacecraft all observed a series of transient bursts of magnetosheath-like plasma, but without bipolar magnetic signatures in the magnetopause normal component as might be expected if the plasma had been injected by transient reconnection (flux transfer events – FTEs). Reordering the data using the magnetopause transition parameter reveals that these plasma observations, the related variations in the magnetic field and the balance of magnetic and thermal gas pressures are consistent with transient entries into a stable high-latitude boundary layer structure. However, once some of the spacecraft entered the magnetosheath, FTE signatures were observed outside the magnetopause at the same time as some of the boundary layer entries occurred at the other spacecraft inside. Thus, (a) the lack of a bipolar BN signature is inconsistent with the traditional picture of a magnetospheric FTE, and (b) the cause of the observed entry of the spacecraft into the boundary layer (pressure pulse or passing magnetosheath FTE) can only be determined by spacecraft observations in the magnetosheath. Keywords. Magnetospheric physics (Magnetopause, cusp and bondary layers; Solar wind- magnetosphere interactions; Magnetosheath)

Design and analysis of triangle phase diagram for preparation of new lithium manganese oxide solid solutions with stable layered crystal structure

A new phase diagram of AB(CD) 1/2 system, where A, B, C, and D represent Li 2MnO 3, LiMO 2 (M = Co, Al, Cr, etc.), LiMnO 2, and LiM′O 2 (M′ = Ni, Cu, Fe, etc.), respectively, was developed to express all compositions of solid solutions with layered manganese oxides. The phase diagram satisfied the theoretical manganese oxidation state of +4 over the whole triangle plane of the diagram and was expressed with a new design equation of Li [ M x ( L i 1 / 3 M n 2 / 3 ) y ( M ′ 1 / 2 M n 1 / 2 ) 1 − x − y ] O 2 . Solid solutions whose compositions were randomly chosen from the phase diagram were experimentally prepared using a direct synthetic method and were subjected to the examination of the structural and electrochemical properties. All the synthesized solid solutions had layered structure with maintaining +4 and showed one-step monotonous discharge curve shape without structural transformation during charge/discharge processes.

Spherical Double Electric Layer Structure and Unprecedented High Stability of the P20O20 Cage and Its Anionic Endohedral Complex Na‐@P20O20

AbstractFor Abstract see ChemInform Abstract in Full Text.