Preparation and luminescent properties of Rh6G-doped lamellar,hexagonal, and cubic mesostructured SiO2 waveguides

We successfully fabricated laser dye (Rh6G)-doped lamellar, hexagonal, and cubic mesostructured SiO₂ waveguides with a combined method of inorganic/organic co-assembly and soft-lithography. These mesostructured SiO₂ waveguide arrays were made on low-refractive index mesoporous SiO₂ clad films (the upper cladding is air), and waveguiding was confirmed for all samples. When pumping the waveguides with an excitation light at normal incidence, they exhibited a broad emission peak (yellow in color) below certain pumping intensity (pumping threshold), and above the threshold a sharp emission peak (orange in color) was observed from the end of the waveguides. The gain-narrowing is attributed to amplified spontaneous emission that results from the homogenous distribution of highly doped dye molecules (up to 0.8 mol%) within the organized mesochannels of the arrays. The pumping threshold values for the respective mesostructured waveguides are different from each other, increasing in the order of lamellar < hexagonal < cubic mesostructure.     

Synthesis of lamellar mesostructured calcium phosphates using n-alkylamines as structure-directing agents in alcohol/water mixed solvent systems

Lamellar mesostructured calcium phosphates constructed by ionic bonds were prepared by using n-alkylamines (n-C _n H_2n+1NH₂, n = 8–18) at room temperature in the mixed solvent systems of aliphatic alcohol (C _n H_2n+1OH, n = 1–4) and water, and the synthetic conditions were investigated in detail. The mixed solvent systems suppressed the formation of crystalline calcium phosphates like brushite (CaHPO₄·2H₂O) and monetite (CaHPO₄) at low temperatures, successfully affording pure lamellar mesostructured calcium phosphates. Other crystalline phases such as hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) were not formed under the conditions with the Ca/P molar ratios in the range of 0.7–1.0 in the starting mixtures. The Ca/P molar ratio of the lamellar mesostructured calcium phosphates was ca. 1.0, calculated by ICP and ³¹P MAS NMR data. Interestingly, the kind of alcohols strongly influenced the solubilities of calcium phosphate species and n-alkylamines, and then lamellar mesostructured phases were obtained with some morphological variation.     

Highly textural lamellar mesostructured magnesium hydroxide via a cathodic electrodeposition process

Highly textural lamellar mesostructured Mg(OH)₂ thin films were obtained through one-step cathodic reduction of magnesium nitrate bath without any surfactant template at room temperature. Its microstructure, stability and morphology were investigated using XRD, TEM, FT-IR, thermal analysis and SEM technique respectively. The results indicate that the porous hydroxide/oxide materials have highly textural lamellar structures with layer spacing around 3.4 nm. The possible formation mechanism has been discussed.     

Preparation of Mesostructured Lamellar Zirconia

Mesostructured lamellar zirconia was synthesized in the hydrothermal systems using Cetyltrimethyl Ammonium Bromide (CTAB) as a template and zirconyl chloride as zirconium precursor. The as-prepared composites were characterized by X-ray diffraction (XRD), TG-DTA, and DR-UV techniques. The influences of hydrothermal aging time, total concentration of solution, different mole ratio of zirconyl chloride/surfactant, and post treatment on the structure of mesostructured lamellar zirconia were discussed in this article.     

Preparation and luminescent properties of Rh6G-doped lamellar, hexagonal, and cubic mesostructured SiO2 waveguides

We successfully fabricated laser dye (Rh6G)-doped lamellar, hexagonal, and cubic mesostructured SiO₂ waveguides with a combined method of inorganic/organic co-assembly and soft-lithography. These mesostructured SiO₂ waveguide arrays were made on low-refractive index mesoporous SiO₂ clad films (the upper cladding is air), and waveguiding was confirmed for all samples. When pumping the waveguides with an excitation light at normal incidence, they exhibited a broad emission peak (yellow in color) below certain pumping intensity (pumping threshold), and above the threshold a sharp emission peak (orange in color) was observed from the end of the waveguides. The gain-narrowing is attributed to amplified spontaneous emission that results from the homogenous distribution of highly doped dye molecules (up to 0.8 mol%) within the organized mesochannels of the arrays. The pumping threshold values for the respective mesostructured waveguides are different from each other, increasing in the order of lamellar<hexagonal<cubic mesostructure.     

Synthesis and characterization of wormhole-like mesostructured polyaniline

Wormhole-like mesostructured polyaniline (PANi) has been synthesized by using sodium dodecyl benzene sulfonate (SDBS) as a structure directing agent and iron trichloride (FeCl₃ · 6H₂O) or ammonium persulfatee (APS, (NH₄)₂S₂O₈) as an oxidant in an acidic solution. The formation mechanism and structure of polyaniline was studied by powder X-ray diffraction, transmission electron microscopy and FT-IR spectroscopy. It was indicated that aniline (AN)/SDBS would form lamellar structure in an acidic solution, then after introducing oxidant, the wormhole like mesostructures would be formed. The reaction conditions, such as oxidant, oxidant/AN molar ratio, HCl/AN molar ratio, and the reaction temperature had influence on the formation of mesostructures.     

New templated method to synthesize electrochromic mesoporous tungsten oxides

Mesoporous tungsten oxides were synthesized with a new nonionic gemini surfactant template, which was then removed by calcination. The effect of calcination on the as-synthesized product was studied with TG–DSC and Fourier-transform infrared spectroscopy. The results of X-ray diffractions, high-resolution transmission electron microscopy, and nitrogen sorption analyses show that the mesoporous tungsten oxide calcined at 300 °C preserved accessible vermicular mesoporosity with specific surface area of 145.5 m²/g. Enhanced electrochromic response was found for the mesostructured sample from the simultaneous voltammetric and spectrophotometric studies.     

Mesolamellar phases containing [Fe(CN)6]3? anion

The mesostructured lamellar phases with the general formula [C _n H_2n+1N(CH₃)₃]₃[Fe(CN)₆] (n = 14, 16, 18) were prepared by ion-exchange/precipitation reaction of alkyltrimethylammonium surfactants and K₃[Fe(CN)₆] complex in aqueous medium. The phases were characterized using powder X-ray diffraction, high-resolution transmission electron microscopy, IR spectroscopy, thermogravimetric, and differential scanning calorimetry means. The results obtained all support a proposed model of crystal structure for these materials, in which the layers are constructed by monolayer of the discrete complex molecules, and the surfactants tails of opposite head groups deeply penetrate and arrange with a tilt angle of 63°.     

Synthesis and characterization of multi-lamellar mesostructured hydroxyapatites using a series of fatty acids

A family of lamellar mesostructured hydroxyapatites are synthesized using five terminal linear aliphatic carboxylic acids (capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid with the general formula of C _n−1H_2n−1CO₂H, n = 10, 12, 14, 16, 18). The study of X-ray diffraction shows that the hydroxyapatite samples exhibit similar multi-lamellar mesostructure and their interlamellar spacing is proportional to the carbon numbers of carboxylic acids. The transmission electron microscopic images on the products prove the parallel aligned configuration. Fourier transform infrared spectra displays the characteristic components of hydroxyapatite in as-prepared samples. Thermogravimetric analysis, elemental analysis (C, H), and inductively coupled plasma analysis were further used to confirm the organic and inorganic composition of the products.     

New trends in V–P–O solids

On the basis of the industrial interest of the oxovanadium phosphate catalysts, current research effort in this field is focused mainly on the development of synthetic strategies directed towards obtaining open-framework materials. There is a growing body of work describing preparations using hydrothermal procedures under a diversity of conditions. A great number of new solids, whose nets range from lamellar arrays to micro- and mesostructured organizations, has been prepared in last years. In this context, the applicability of concepts and procedures from the zeolites chemistry to systems involving transition elements is critically analyzed.     

Ion etching of amorphous and semicrystalline fibres

Ion etching of amorphous and semicrystalline fibres produces structures which can be observed in either the transmission electron microscope or the scanning electron microscope. The structures so produced have previously been identified as resulting from the etching process (artifacts), or as representing characteristics of the material, or both. The artifacts can be eliminated or minimized by rotating the sample during irradiation, using a low angle of incidence, and ensuring that the temperature of the sample surface remains low. When such precautions are used, amorphous fibres and semicrystalline fibres which arenot oriented remain featureless after ion etching. Oriented semicrystalline fibres, however, develop a striated structure which is oriented perpendicular to the stretch direction. The spacing between the striations is in the range of 500 to 5000 å, an order of magnitude larger than the characteristic lamellar spacing in the materials. These transverse structural features reflect characteristic features of drawn fibres; but the relation between these features and the lamellar spacing is unclear.     

Effect of microstructure morphology on mechanical properties of quenching and partitioning steel

In order to illuminate the relationship between microstructure morphology and final properties of the quenching and partitioning(Q&P) steel, the samples with different microstructure morphology (equiaxed and lamellar) and same volume fraction of each phase are obtained by controlling the initial microstructure and Q&P heat treatment. Because of the feature of microstructure morphology, a large yield ratio and total elongation are obtained in the lamellar sample though yield strength and ultimate tensile strength are relatively lower than that of equiaxed sample. Moreover, the lamellar sample produces a continuous work-hardening rate and better the fracture toughness compared to the equiaxed sample. Thus the lamellar sample is more suitable to be used as automotive structural components.     

Effect of electromigration induced joule heating and strain on microstructural recrystallization in eutectic SnPb flip chip solder joints

A refinement of the lamellar microstructure was observed in eutectic SnPb solder joints in electromigration. Electromigration has both atomic flux and electron flow. The latter generated joule heating and the former caused strain. The formation of nanoscale lamellar microstructure spent a large amount of interfacial energy, and we proposed that the driving force comes from the strain induced by electromigration under a high current density. Kinetically, refinement of the lamellar microstructure required fast atomic diffusion at a high homologous temperature. The joule heating mainly from the on-chip Al interconnect lines tremendously increased the temperature of solder bumps and enabled fast atomic diffusion. The strain induced by electromigration, when combined with a high homologous temperature, could lead to recrystallization in the sample to form the nanoscale lamellae.     

石墨化介孔碳包裹WC纳米粒子的构建及其氧还原性能研究

采用模板复型辅助的化学气相沉积法(CVD)成功制备出一种非贵金属的氧还原反应(ORR)催化剂材料—包裹碳化钨纳米粒子的石墨化介孔碳(WC/MG)复合物。制备的介孔结构WC/MG复合材料不仅具有高氧还原反应电化学催化活性, 还表现出良好的电化学稳定性。在O₂饱和的0.1 mol/L KOH电解质溶液中, 900℃制备的样品WC/ MG-900其半波电势(E_1/2)和极限电流密度仅比商用贵金属催化剂Pt/C分别低50 mV 和 0.2 mA/cm²。Koutecky- Levich曲线和旋转环盘电极实验均表明, 该介孔结构的WC/MG复合材料表现出近似4电子的ORR反应途径, 具有可与Pt/C催化剂相比拟的ORR催化活性, 以及比Pt/C更优越的电化学稳定性和耐甲醇性能, 使得该介孔结构WC/MG复合物在氧还原电极材料中表现出良好的应用前景。     

The structure of high-density polyethylene with a single-crystal texture

The structure of specially prepared high-density polyethylene with a single-crystal texture has been examined by wide-angle and small-angle X-ray diffraction and by electron microscopy. The bulk of the crystallites in the sample are found to be oriented within 8° of a perfect single-crystal texture. The small-angle X-ray diffraction patterns suggest that lamellar crystals are present oriented approximately perpendicular to the chain direction. Replicas taken from fracture surfaces indicate that the structure fractures cleanly parallel to (100) which, taken together with other evidence, suggests that molecules fold by adjacent re-entry in (100) planes. Etching in fuming nitric acid reveals a lamellar crystal structure which is consistent with that deduced from small-angle X-ray diffraction. Replicas which were taken of etched surfaces after deformation showed crystals which were tilted with respect to the chain direction. This is consistent with the deformation having taken place by [001] chain slip within the lamellae [1].     

The identification of the initial lamellar thickness of polyethylene crystals grown from the melt using synchrotron X-radiation

The lamellar thickness of a sharp fraction of linear polyethylene has been monitored during crystallization at 128.5° C at very short crystallization times (30sec to 30min) using low angle X-ray diffraction (LAXD) by using the powerful synchrotron source at Daresbury. The observed thickness is much lower than expected and does not change with time. The same sample showed two Raman longitudinal accordion modes (LAM), one corresponding to the lamellar thickness observed by LAXD and the other to a much larger thickness. From these, and further parallel experiments using Raman spectroscopy, differential scanning calorimetry and electron microscopy we deduce that the lamellae as initially formed are much thinner than previously expected, that they first thicken by a single, large step-to the usually reported values for melt crystallized polyethylene-and only then do they exhibit a continuous increase in thickness with time corresponding to the isothermal thickening as reported in previous work.     

Super Cold-Drawing Ability and High Tensile Strength of Fe35Ni35Cr20Mn10 High-Entropy-Alloy Wires

Excellent plastic forming ability is a prerequisite for large-scale production of steel wires in engineering application. The process of traditional steel wire production inevitably needs interannealing treatment and corrosion-resistant surface treatment (such as hot-dip galvanizing), consuming a large amount of energy and causing environmental pollution. Herein, a rod of 6.34 mm in diameter, made of Fe₃₅Ni₃₅Cr₂₀Mn₁₀ high-entropy alloy (HEA), is continually cold drawn to 0.08 mm wire without interannealing, reaching an accumulated strain of 8.73 and a section reduction ratio of 99.98%. The mechanical properties are examined by CMT5105 or CMT4503 tensile tester. The microstructure was characterized by scanning electron microscopy (FEI Sirion-400) and transmission electron microscopy (FEI Tecani G2 T20). The wire of 0.08 mm in diameter possesses a high strength of 1868 ± 13 MPa. The formation of nanotwins or twin-groups between the lamellar structures and inside the lamellar structure during cold-drawing can harmonize the deformation between the lamellar structures and between grains in a lamellar structure that guarantee the continual plastic deformation. The high strength of the prepared HEA wires is related to the great increase in dislocation density, the formation of nanotwins, and hard <111> texture and the refinement of lamellar structures.     

On chlorosulphonation and the electron microscopy of polyethylene

It is shown that chlorosulphonation is a major aid to the electron microscopy of polyethylene for various samples which had mostly been crystallized at high pressures and included at least a proportion of the so-called chain-extended form. It is confirmed that sheets of excess electron density are produced at lamellar surfaces, but also including lateral surfaces. This is due primarily to the incorporation of chlorine and sulphur rather than to added uranium. The time to achieve an overall reaction varies sensitively with morphology, decreasing as the number of diffusion channels increases. Crystallinity is gradually lost, but sufficient crystals remain when a sample has become uniform, and in their initial orientations, for diffraction studies to be possible. The technique has been used to demonstrate that, during melt crystallization, the thickness of one lamella changes in response to altered growth conditions. This is direct confirmation that lamellar thickness is determined by secondary nucleation at the growth front. The tapered profile of a growing lamella previously observed in thick crystals of various polymers has been observed for chain-folded polyethylene lamellae, providing further evidence that this is a general feature of melt growth.     

The microstructure of reactively sputtered Ti-N films

Ti-N films with nitrogen concentrations ranging from 0 to 52 at.% prepared by both d.c. magnetron and r.f. reactive sputtering are examined using transmission electron microscopy. The observed microstructures are correlated with physical properties of the films. In particular, the maximum in the microhardness and density and the minimum in the electrical resistivity are found to correspond to a fully dense structure. The sample prepared by magnetron sputtering has a very inhomogeneous and voided microstructure and a lower hardness than the r.f.-sputtered sample with a similar nitrogen content. A theory is proposed for the development of a lamellar microstructure in the films containing two phases.     

Deformation and transformation mechanisms of poly(vinylidene fluoride) (PVF2)

The deformation process and the accompanyingα→β phase transformation of poly(vinylidene fluoride), drawn at 82 to 90 and 130° C, has been characterized by electron microscopy and X-ray and electron diffraction. Micronecking occurs at both draw temperatures, fibrils and mosaic blocks being drawn off the edges of the micronecks. The degree of phase transformation, at the same elongation, is dependent on the draw temperature; at 130° C the majority of the sample remains in theα phase at the natural draw ratio. The phase transformation at both draw temperatures accompanies the transformation from lamellar (block) structure to fibril.