Investigation of Commercial Graphenes

For graphene to achieve its full scientific and commercial potential, reliable mass production of the material on the multi-tonne scale is essential. We have investigated five samples of graphene obtained from commercial sources that state they can supply the product on the tonne scale per annum. From electron microscopy at the micrometre to the nanometre scale, and neutron vibrational spectroscopy, we find that none of the materials examined were 100 % isolated graphene sheets. In all cases, there was a substantial content of graphite-like material. The samples exhibited varying oxygen contents, this could be present as carboxylic acid (although other oxygenates, quinones, phenols may also be present) or water. We emphasise that INS spectroscopy is particularly useful for the investigation of inorganic materials that will be used commercially: it provides atomic scale information from macroscopic (10’s of g) amounts of sample, thus ensuring that the results are truly representative.     

Microstructural Characteristics of Hydrothermally Synthesized LiFePO_4 and Relevant Impacts on the Electrochemical Performance

Phospho-olivine LiFePO 4 has been prepared using a facile hydrothermal method by optimizing the reaction temperatures.Structural and morphological properties of the as-prepared LiFePO 4 powders are systematically characterized using X-ray diffraction (XRD),scanning electron microscopy (SEM),transmission electron microscopy (TEM),infrared spectra,UV-vis spectra,and M ssbauer spectroscopy.It is demonstrated that the samples prepared in the temperature range from 160 to 200 ℃ crystallize in a single phase of phospho-olivine structure.All particles are rod-like,showing dimensions of approximately 150～200 nm in width and 500～600 nm in length with a preferential growth direction of [001].Within the lattice of LiFePO 4 rods,Fe 2+ ions partially disorderly occupy the Li + sites,which increases the cell volume.The electrochemical performance of LiFePO 4 is investigated by charge/discharge experiments.It is found that LiFePO 4 rods prepared at 200 ℃ deliver a specific discharge capacity of 147 mAh g-1,which is apparently superior to those prepared at lower reaction temperatures like 160 and 180 ℃.This observation is explained in terms of the thinner surface noncrystalline layer and lower level of Fe 2+ disorderly occupying the Li + sites.     

Polyaniline Nanofibrils Array Synthesized within the Anodic Aluminum Oxide Template

Introduction Many methods for the fabrication of nanoparticles have been developed ranging from lithographic techniques to chemical methods. The method termed template synthesis for preparation of a variety of micro- and nano-materials has been explored1-3. The template membranes employed contain cylindrical pores with mono-disperse diameters, that extend through the entire thickness of the membrane. The diameter of this nanocylinder is determined by the diameter of the pores of the template m…     

Nanorods of transition metal oxalates: A versatile route to the oxide nanoparticles

A versatile route has been explored for the synthesis of nanorods of transition metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates using reverse micelles. Transmission electron microscopy shows that the as-prepared nanorods of nickel and copper oxalates have diameter of 250 nm and 130 nm while the length is of the order of 2.5 μm and 480 nm, respectively. The aspect ratio of the nanorods of copper oxalate could be modified by changing the solvent. The average dimensions of manganese, zinc and cobalt oxalate nanorods were 100 μm, 120 μm and 300 nm, respectively, in diameter and 2.5 μm, 600 nm and 6.5 μm, respectively, in length. The aspect ratio of the cobalt oxalate nanorods could be modified by controlling the temperature.The nanorods of metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates were found to be suitable precursors to obtain a variety of transition metal oxide nanoparticles. Our studies show that the grain size of CuO nanoparticles is highly dependent on the nature of non-polar solvent used to initially synthesize the oxalate rods. All the commonly known manganese oxides could be obtained as pure phases from the single manganese oxalate precursor by decomposing in different atmospheres (air, vacuum or nitrogen). The ZnO nanoparticles obtained from zinc oxalate rods are ～55 nm in diameter. Oxides with different morphology, Fe₃O₄ nanoparticles faceted (cuboidal) and Fe₂O₃ nanoparticles (spherical) could be obtained.     

In situ tempering of melt spun AlGeSi-foils

AlGeSi-alloys of different composition were cast by a melt spin device to ribbons of 40 m thickness. The ribbons melt near 500 °C and should be well suited for brazing of high strength Al-alloys. Because of the existence of metastable phases, these ribbons are brittle in the rapidly solidified state, but increasingly ductile and cuttable after an appropriate annealing between 200 and 400 °C. The thermally induced phase transformations are revealed by the hightemperature X-ray diffractograph as well as, with help of a heating sample holder, by the analytical transmission electron microscope (TEM). The identification of elements and phases is performed by X-ray Bragg reflexes and of electron diffraction (ED) patterns, whereby the latter can be associated to single microstructure details in the sub-m range. Moreover, the distribution of the elements can be seen on distribution maps din the light of characteristic X-ray spectral lines.The observed microstructure of as-quenched AlGe45 with 2 or 4 mass-% Si was of similar appearence but more refined as in the AlGe45 alloy. It consists of -Al primary crystals surrounded by an eutectic mixture of -Al and two metastable intermetallic AlGe(Si) phases. Si was observed exclusively within these metastable phases. During an appropriate tempering the metastable phases transform into the equilibrium phases -Al and -Ge(Si). For this decomposition the temperature is decreased by alloying with Si.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

A simple route to nanocrystalline silicon carbide

Nanocrystalline silicon carbide has been prepared via reacting magnesium silicide (Mg₂Si) with carbon tetrachloride (CCl₄) in an autoclave at 450-600°C. X-ray diffraction patterns of the products can be indexed as the cubic cell of SiC with the lattice constant, a=4.352 Å, in good agreement with a=4.349 Å (JCPDS card No. 75-0254). The transmission electron microscopy images show that the sample mainly consists of nanoparticles with an average size from 30 to 80 nm co-existing with a small fraction of nanorods and nanowires. Typically the nanorods range from 20 to 40 nm in diameter and the nanowires have diameters of 20 nm and lengths up to 10 μm. The Raman spectrum shows a characteristic sharp peak at 790 cm⁻¹. X-ray photoelectron spectra (XPS) gives an atomic ratio of Si to C as 1.08:1.00 from the quantification of the peak intensities. Photoluminescence spectrum reveals that the SiC sample emits ultraviolet light of 328 nm. A possible mechanism and the influence of temperature on the formation of crystalline SiC are proposed.     

Immobilization of Biomolecules on NH3, H2/NH3 Plasma-Treated Nitrocellulose Films

Detectors with covalently immobilized bioactive compounds able to interact with selected analytes are needed for various kinds of biosensors. Protein macromolecules can be immobilized covalently on surfaces with appropriate functional groups such as amine groups. Low pressure plasmas of NH₃ and NH₃/H₂ mixtures were used to incorporate a maximum of 2.4 amine functions per nm² of porous surface under specific conditions. A mechanism of the functionalization process was proposed using on-line emission spectroscopy and mass spectrometry analysis to monitor the reaction process. The physico-chemical modifications created on the plasma-treated material were investigated by surface analytical techniques such as X-ray photoelectron spectroscopy (XPS) and Scanning Electron Microscopy (SEM).     

La6Mo8O33: a new ordered defect scheelite superstructure

The structure of La₆Mo₈O₃₃ has been determined from a triple pattern powder diffraction analysis. Two high-resolution neutron diffraction patterns collected at 1.594 and 2.398 Å and one X-rays were used. This molybdate crystallizes in a non-centrosymmetric monoclinic space group P2₁(N°4), Z=2,a=10.7411(3) Å, b=11.9678(3) Å, c=11.7722(3) Å, β=116.062 (1)°. La₆Mo₈O₃₃ is an unusual ordered defect Scheelite. Hence, it should be described with cation vacancies and an extra oxygen atom following the formula: La₆□₂Mo₈O₃₂₊₁. This extra oxygen atom leads to a pyramidal environment, whereas the other molybdenum atoms present tetrahedral environment. A molybdenum tetrahedral is connecting to the pyramid, forming an [Mo₂O₉] unit.     

Characterization of the Corrosion of Nanostructured 17-4 PH Stainless Steel by Surface Mechanical Attrition Treatment (SMAT)

Abstract

The corrosion properties of nanostructured 17-4PH stainless steel facilitated by a surface mechanical attrition treatment (SMAT) process were studied using electrochemical measurements in 0.6?M NaCl aqueous solution. The microstructure of the surface layer was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results demonstrated the formation of a nanostructured surface layer on the surface of the material. By the combination of SMAT and low-temperature annealing processes, the potentiodynamic polarization measurements and X-ray photoelectron spectroscopy (XPS) spectra demonstrated an improvement in the corrosion resistance of 17-4PH stainless steel with a reduced corrosion current density of 0.241?mA/cm² and a higher chromium content. The improved corrosion resistance may be attributed to the formation of nucleation sites through which chromium may freely move from the matrix to the upper surface and thereby form a protective oxide layer on the surface of the material.     

Combined analysis methods for investigating titanium and nickel surface contamination after plasma deep etching

Plasma etching techniques can result in damage and contamination of materials, which, if not removed, can interfere with further processing. Therefore, characterisation of the etched surface is necessary to understand the basic mechanisms involved in the etching process and enable process control and cleaning procedures to be developed. A detailed investigation by means of the combined use of scanning electron microscopy coupled with energy-dispersive X-ray spectrometry (SEM/EDS), X-ray photoelectron spectroscopy (XPS) and optical microscopy (OM) has been carried out on deep titanium trenches etched by plasma. This innovative approach has provided a further insight into the microchemical structure of the surface contamination layer on both the titanium and the nickel hard mask surfaces. The described experiments were conducted on 25 to 100-μm wide trenches, first etched in bulk titanium by an optimised Cl₂/SF₆/O₂-based inductively coupled plasma process, through an electroplated nickel hard mask. The results allow to identify chlorine, fluorine and carbon as the main contaminating agents of the nickel mask and to associate three oxidation states around the etched trenches highlighting certain specific aspects related to the passivation mechanism. These observations reinforce the scientific relevance of the combined use of complementary optical and imaging analytical techniques.     

Determination of Arsenic Speciation in Complex Environmental Samples by the Combined Use of TEM and XPS

Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS) have been used to refine the solid-state speciation of As in mine waste materials and stream-bed sediments from the Baccu Locci mine area in Sardinia, Italy. The combined use of TEM and XPS confirmed previous studies and pointed out that: (i) As is contained in plumbojarosite in substitution of S, (ii) As-bearing Fe(III) hydroxides are represented by arsenical 2-line ferrihydrites with most Fe/As molar ratios in the range of 1.6–3.2, (iii) scorodite often lacks long range order. Arsenatian plumbojarosite will tend to dissolve incongruently in ferrihydrite, releasing Pb and As into water. However, Pb is fated to precipitate as Pb(OH)₂ or to be adsorbed onto ferrihydrite, whereas As mobility is favoured since the adsorptive capacity of ferrihydrite for As(V) is notably reduced under the neutral to alkaline pH conditions occurring in the Baccu Locci stream water. Arsenical ferrihydrites will tend to be converted into goethite or hematite with time, releasing As into the water as a consequence of the notably lower density of the adsorption sites of the crystalline Fe(III) phases. Also scorodite is relatively unstable under the Baccu Locci system conditions, and its stability is further decreased owing to the higher solubility of the amorphous form compared to the crystalline one.     

Growth and Characterization of Graphene Layers on Different Kinds of Copper Surfaces

Graphene films were grown by chemical vapor deposition on Cu foil. The obtained samples were characterized by Raman spectroscopy, ellipsometry, X-ray photoelectron spectroscopy and electron back-scatter diffraction. We discuss the time-dependent changes in the samples, estimate the thickness of emerging Cu₂O beneath the graphene and check the orientation-dependent affinity to oxidation of distinct Cu grains, which also governs the manner in which the initial strong Cu-graphene coupling and strain in the graphene lattice is released. Effects of electropolishing on the quality and the Raman response of the grown graphene layers are studied by microtexture polarization analysis. The obtained data are compared with the Raman signal of graphene after transfer on glass substrate revealing the complex interaction of graphene with the Cu substrate.     

Characterization of zero-valent iron nanoparticles

The iron nanoparticle technology has received considerable attention for its potential applications in groundwater treatment and site remediation. Recent studies have demonstrated the efficacy of zero-valent iron nanoparticles for the transformation of halogenated organic contaminants and heavy metals. In this work, we present a systematic characterization of the iron nanoparticles prepared with the method of ferric iron reduction by sodium borohydride. Particle size, size distribution and surface composition were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), high-resolution X-ray photoelectron spectroscopy (HR-XPS), X-ray absorption near edge structure (XANES) and acoustic/electroacoustic spectrometry. BET surface area, zeta (ζ) potential, iso-electric point (IEP), solution Eh and pH were also measured. Methods and results presented may foster better understanding, facilitate information exchange, and contribute to further research and development of iron nanoparticles for environmental and other applications.     

Interface characterization of nickel contacts to bulk bismuth tellurium selenide

Transmission electron microscopy (TEM) characterization of nickel contacts to bulk bismuth tellurium selenide [Bi₂(Te,Se)₃] is reported. Samples were prepared in a dual column focused ion beam/scanning electron microscope (FIB/SEM) system using a lift‐out technique, with ion beam energy and exposure times carefully optimized to minimize sample damage. Diffusion of Ni into Bi₂(Te,Se)₃ was observed and the formation of a nickel telluride (NiTe) interfacial region confirmed after heat treatment at 200 °C. Selected area diffraction patterns provided evidence of a modified bismuth telluride–like structure at the interface, identified by analytical electron microscopy to be composed of Ni and Bi₂(Te,Se)₃. Copyright © 2009 John Wiley & Sons, Ltd.     

ZnO Nanoparticles for Photocatalytic Application in Alkali-Activated Materials

This paper reports an Alkali-Activated Materials (AAM) using two different precursors, metakaolin and a metallurgical slag with photocatalytic zinc oxide nanoparticles, as novel photocatalytic composites. The photodegradation performance of the composites using methylene blue (MB) dye as a wastewater model was investigated by ultraviolet radiations (UV-vis) spectroscopy. Adsorption in dark conditions and photodegradation under UV irradiation are the mechanisms for removing MB dye. The pseudo-first-order kinetic and pseudo-second-order kinetic models were employed, and the experimental data agreed with the pseudo-second-order model in both cases with UV and without UV irradiations. As new photocatalytic materials, these composites offer an alternative for environmental applications.     

Conversion of colloidal aggregates into polymer networks on aging

After long-term aging, surfactant-mediated colloidal aggregates of sulfonated polyaniline (S-PANI) and poly(vinylidene fluoride) (PVF₂) converted into three-dimensional polymer networks, whereas colloidal crystals prepared from pure PVF₂ remained unaltered. A model, where the surfactant tails anchored from the colloidal particles interdigitate with time resulting in coalescence of the particles to form the network morphology, has been proposed. X-ray photoelectron spectroscopy (XPS) revealed higher relative abundances of carbon atoms on the surface of the polymer networks than those of the colloidal aggregates, which adequately supports the proposed model.     

MORE ON THE STRUCTURES OF POLYPHENYLSILSESQUIOXANES

The steric tacticity of polyphenylsilsesquioxanes is discussed based on both structure transformation consideration and the results of calculations, X-ray diffraction patterns, fluorescence emission spectroscopy, and scanning electron microscopy. All of the results show that cis-isotactic conformation is the most probable one for ladderlike polymer polyphenylsilsesquioxane though other conformations such as cissyndiotactic may also be present in the macromolecules depending upon the preparation conditions.     

Chemical Microengineering in Sol-Gel Derived Fluoride and Lanthanide Modified Ceria Materials

The effect of the incorporation of rare earth cations and fluoride anions into the ceria fluorite lattice has been studied. Ternary Ln-Ce-O (Ln = La, Pr, Nd) oxide gels of target Ln : Ce ratios of 1 : 4, 1 : 1.86 and 1 : 1, with and without added fluoride ion, have been prepared, and the oxide materials obtained after calcination at 1223 K examined. Incorporation of Ln results in the formation of Ln/CeO2 solid solutions at low Ln levels, but a microscopic mixture of two cubic phases, pure ceria and a Ln-Ce-O phase of composition Ce0.35La0.65O1.67, is obtained when a 1 : 1 ratio is employed. With fluoride pure CeO2 and LaF3 are the only phases present and no mixed Ln-Ce-O phase is formed. TEM shows that the microstructure of this material is complex. The nature of analogous Pr- and Nd-substituted ceria materials is also described.     

Thermal plasma synthesis of nanotitania and its characterization

Titanium dioxide (TiO₂) nanoparticles were prepared by the thermal plasma synthesis; which give a highly crystalline product. Their morphological studies are carried out by using techniques like SEM, EDAX, TEM and SEAD. Crystal size was calculated by XRD using Scherrer equation; which is observed at two current amperes; at 80 A size ranges between 25 and 30 nm and at 120 A size ranges between 30 and 42 nm. Composition analysis was done by TEM–EDAX, FTIR and Fast Fourier Transform techniques. The FTIR peaks clearly show that synthesized TiO₂ nanoparticles are in anatase phase; this phase is generally preferred because of its high photocatalytic activity, since it has a more negative conduction band edge potential (higher potential energy of photogenerated electrons), high specific area, nontoxic, photochemically stable and relatively in expensive.