Characterization of Fe/Cr multilayers by analytical transmission electron microscopy

Different techniques of analytical TEM were used to investigate Fe/Cr multilayers. These multilayers show a dependence of their electrical resistance as a function of the magnetic field. This effect called giant magnetoresistance can be utilized for example in magnetic recording heads. Typical dimensions of the single layer thickness are in the nanometer region. Therefore the microstructure of this material has been investigated by transmission electron microscopy (TEM). To get additional analytical information energy dispersive X-ray spectroscopy (EDXS) and electron energy loss spectroscopy (EELS) can be used. Received: 15 July 1997 / Revised: 5 February 1998 / Accepted: 6 February 1998     

Electrical properties of the YSZ/STO/YSZ-STO superlattice electrolyte film at low temperatures

This study is focused on characterization of the low temperature properties of the YSZ/STO/YSZ superlattice film deposited onto unilateral polished SrTiO₃ (STO) monocrystalline substrates using pulsed laser deposition (PLD). The phase composition, structure, surface morphology and electrical properties of the oxygen ion conducting electrolyte YSZ/STO/YSZ multilayers were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The minimum conductivity activation energy of YSZ/STO/YSZ is 0.76 eV at 300–500°C. The YSZ/STO/YSZ superlattice film shows an enhancement in conductivity by three orders of magnitude compared to bulk YSZ at a temperature of 300°C.     

In Situ Fabrication of Inorganic/Organic Hybrid Based on Cu/Co‐ZIF and Cu2O

We successfully fabricate a well‐defined inorganic/organic hybrid Cu₂O@Cu/Co‐ZIF (ZIF=zeolitic imidazolate frameworks) by use of growth of dual‐metal Cu/Co‐ZIF on the obtained Cu₂O hollow spheres. The key point of the strategy is coupling the in situ self‐sacrificing template. Cu₂O and the coordination of metal ions (Cu⁺ and Co²⁺) with 2‐methylimidazole. This new hybrid was characterized by powder X‐ray diffraction, (scanning) transmission electron microscopy, energy‐dispersive spectroscopy mapping, in situ FT‐IR spectroscopy, UV/Vis diffuse reflection spectroscopy, N₂ sorption measurements, and electron spin resonance. It was evidenced that Cu/Co‐ZIF nanocrystals have been assembled to continuous shells surrounding the Cu₂O cores as well as in the voids between layers and inner pores. Cu₂O@Cu/Co‐ZIF exhibits visible light responsiveness and holds potential as narrow band gap semiconductor and visible photocatalyst.     

溶剂热方法合成Cu2ZnSnS4空心球

以氯化亚铜,硝酸锌,氯化锡和硫脲作为反应前驱体,聚乙二醇作为模板,利用溶剂热方法合成Cu₂ZnSnS₄中空球。其中,聚乙二醇对于产物的最终形成起到关键作用。文章讨论了Cu₂ZnSnS₄中空球的生长机制,并通过X射线衍射(XRD)、拉曼光谱、场发射电子显微镜(FESEM)、透射电子显微镜(TEM)、X射线能量色散谱(EDX)、X射线光电子谱(XPS)、选区电子衍射谱(SAED)和紫外-可见光分光光度计(UV-Vis)等技术对样品的微结构以及光学性质进行了表征和分析。结果显示Cu₂ZnSnS₄中空球为四方晶体,尺寸为600 nm。其禁带宽度为1.52 eV,适用于制作光伏器件。     

Fabrication and Characterization of Nanocomposite Flexible Membranes of PVA and Fe3O4

Composite polymer membranes of poly(vinyl alcohol) (PVA) and iron oxide (Fe₃O₄) nanoparticles were produced in this work. X-ray diffraction measurements demonstrated the formation of Fe₃O₄ nanoparticles of cubic structures. The nanoparticles were synthesized by a coprecipitation technique and added to PVA solutions with different concentrations. The solutions were then used to generate flexible membranes by a solution casting method. The size and shape of the nanoparticles were investigated using scanning electron microscopy (SEM). The average size of the nanoparticles was 20±9 nm. Raman spectroscopy and Fourier-transform infrared spectroscopy (FTIR) were utilized to investigate the structure of the membranes, as well as their vibration modes. Thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated the thermal stability of the membranes and the crystallinity degree. Electrical characteristics of the thin membranes were examined using impedance spectroscopy as a function of the nanoparticles’ concentrations and temperatures. The resistivity of the fabricated flexible membranes was possible to adjust by controlled doping with suitable concentrations of nanoparticles. The activation energy decreased with the nanoparticles’ concentrations due to the increase in charge carriers’ concentrations. Therefore, the fabricated membranes may be applied for practical applications that involve the recycling of nanoparticles for multiple application cycles.     

溶剂热方法合成Cu2ZnSnS4空心球

以氯化亚铜,硝酸锌,氯化锡和硫脲作为反应前驱体,聚乙二醇作为模板,利用溶剂热方法合成Cu₂ZnSnS₄中空球。其中,聚乙二醇对于产物的最终形成起到关键作用。文章讨论了Cu₂ZnSnS₄中空球的生长机制,并通过X射线衍射(XRD)、拉曼光谱、场发射电子显微镜(FESEM)、透射电子显微镜(TEM)、X射线能量色散谱(EDX)、X射线光电子谱(XPS)、选区电子衍射谱(SAED)和紫外-可见光分光光度计(UV-Vis)等技术对样品的微结构以及光学性质进行了表征和分析。结果显示Cu₂ZnSnS₄中空球为四方晶体,尺寸为600 nm。其禁带宽度为1.52 eV,适用于制作光伏器件。     

Point-defect associated thermionic hole emissions from p-type Si/Si 1 − x Ge x /Si quantum well structures

The thermionic hole emissions from a p-type Si_0.67Ge_0.33 quantum well with a width of 7 nm and a point defect were investigated using deep level transient spectroscopy. An activation energy of 0.22 eV from the quantum well is consistent with the heavy hole level from the bottom of the well. The defect-related band with an energy of 0.30 eV originated from the space charge related to the point defect in the vicinity of the quantum well heterostructure. The origin of the point-defect-related band was confirmed by photoluminescence and the deep level was further clarified by using capacitance-voltage measurements and simulation by introducing a simple model of an interfacial hole trap center. The deep hole trap center apparently disappeared by an annealing effect, indicating that point defects are subject to thermal annealing. The microscopic measurement provides evidence on point defects in the quantum well structure and the thermal annealing also enhances the thermionic hole emission from the quantum well structure. Received: 22 August 1998 /Accepted: 15 February 1999     

Characterization of thin metastable vanadium oxide films by Raman spectroscopy

Thin films are potentiodynamically generated on vanadium in Ba²⁺/acetate electrolyte systems at high voltages. The influence of the anodic potential up to 400 V on the composition and structure of the about 500 nm thin anodic conversion films are investigated. Raman spectroscopy indicates that different film types depend on the electrochemical process parameters. The relationship between the Raman laser excitation power and the amorphous or microcrystalline film structure is also discussed. Beside metastable disordered structures the films contain crystalline phases of V₂O₅, V₄O₉ and barium vanadate, respectively. Received: 15 July 1997 / Revised: 16 February 1998 / Accepted: 21 February 1998     

Iron oxide on carbon‐based supports as efficient catalysts for organic compounds oxidation

For the first time, iron oxide on carbon aerogel, amine functionalized carbon nanotube, black carbon and carboxylic acid functionalized carbon nanotube in the presence of H₂O₂ was reported as an efficient and stable catalyst for the selective oxidation of sulfides and alcohols. The catalysts were characterized by scanning electron microscopy, energy‐dispersive spectroscopy, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction, Fourier transform infrared spectroscopy and atomic absorption spectroscopy. In the next step, catalytic reactivity toward sulfide to sulfoxide and alcohol to aldehyde/ketone oxidation in the presence of H₂O₂ was studied and discussed.     

Template induced sol-gel synthesis of highly ordered LaNiO3 nanowires

The highly ordered LaNiO₃ nanowires of the rare-earth perovskite-type composite oxide were controlled synthesized within a porous anodic aluminum oxide (AAO) template by means of sol-gel method using nitrate as raw materials and citric acid as chelating agent. The results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the obtained LaNiO₃ nanowires had a uniform length and diameter, which were determined by the thickness and the pore diameter of the applied AAO template. The results of X-ray diffraction (XRD) and the selected-area electron diffraction (SAED) indicated that the LaNiO₃ nanowires were perovskite-type crystalline structures. Furthermore, X-ray photoelectron spectroscopy (XPS) and the energy dispersive X-ray (EDX) spectroscopy demonstrated that the stoichiometric LaNiO₃ was formed.     

Catechin mediated green synthesis of Au nanoparticles: Experimental and theoretical approaches to the determination HOMO-LUMO energy gap and reactivity indexes for the (+)-epicatechin (2S, 3S)

This work suggests a green method for synthesizing Au nanoparticles (AuNPs) using the aqueous extract of Salix aegyptiaca extract. The mechanism of green synthesized AuNPs was examined by molecular electrostatic potential (MEP) calculations. AuNPs were characterized with different techniques such as Ultraviolet–visible spectroscopy (UV–vis), Fourier-transform infrared spectroscopy (FT-IR) spectroscopy, X-ray diffraction (XRD), and Transmission electron microscopy (TEM). Electrochemical investigation of modified glassy carbon electrode using AuNPs (AuNPs/GCE) shows that the electronic transmission rate between the modified electrode and [Fe (CN)₆]^3?/4? increased. Process of oxidation, energy gap, and chemical reactivity indexes of the (+)-epicatechin (2S,3S) were investigated using electrochemical techniques (cyclic voltammetry (CV) and differential pulse voltammetry (DPV) as well as UV–Visible spectroscopy and compared with quantum mechanical calculations. DPV and CV were used to obtain HOMO energies of the (+)-epicatechin (2S,3S), an optical energy gap was obtained from the UV–Vis spectroscopy. Frontier molecular orbitals analysis (FMO) and reactivity indexes such as chemical hardness (?), electrophilicity (?), electronic chemical potential (μ), electron acceptor power (?⁺), electron donor power (?^?) were determined with functional theory (DFT) calculations. In summary, the HOMO energy obtained from the experimental analyses (E_HOMO (from DPV) = -5.24 eV, and E_HOMO (from CV) = -5.28 eV) has a relative agreement with the HOMO energy calculated by B3LYP/6–31 g (d, p) including the solvent effect (water) (E_HOMO (from B3LYP) = -5.75 eV). Also, UV–Vis spectroscopy gives the bandgap energy equal to 4.31 eV, while the 4.13 eV is calculated by TD-DFT-b3lyp/6–31 + g(d).     

Trigonal pyramidal CuInSe2 nanocryastals derived by a new method for photovoltaic applications

Copper indium selenide (CuInSe₂) nanocrystals with trigonal pyramidal shape are synthesized by a two-step process for photovoltaic applications. Structural, morphological and optical properties of the as-synthesized CuInSe₂ nanocrystals are characterized by using powder X-ray diffraction analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy. Results indicate that the monodispersed nanocrystals show a single phase polycrystalline and the size of the trigonal pyramid is in the range of 10-12 nm, and the average composition ratio of the Cu/In/Se is measured to be 1.0:1.2:2.0. It is also investigated that the size and morphology of the CuInSe₂ nanocrystals can be tuned through a manipulation of the reaction time. Under an illumination of the simulated AM 1.5, the as-fabricated hybrid solar cell based on the P3HT/CuInSe₂ nanocrystals blends exhibits a promising open circuit voltage (V_oc) of 0.42 V and its energy conversion efficiency is as 3 times as that of the solar cell fabricated by only the naked P3HT polymer.     

Morphology‐controlled Electrodeposition of Copper Nanospheres onto FTO for Enhanced Photocatalytic Hydrogen Production

Using CuSO₄ as the copper source, nanostructured copper with four different morphologies was obtained by electrodeposition method on FTO substrates. The as‐synthesized Cu/FTO samples were characterized by X‐ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Raman, X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDS), and transmission electron microscopy (TEM). The effects of electrodeposition potential and electrodeposition time on the Cu/FTO samples and the photocatalytic performance were investigated systematically. The results showed that the Cu/FTO samples were well‐crystallized and the morphologies could be changed from nanoslices to nanodendrites structure with the negative shift of the depositing potential. The electrodeposition potential and time have a significant effect on the amount of H₂ evolution. The obtained Cu nanospheres which were prepared at the potential of −0.65 V for 600 s showed the best photocatalytic behavior. The mechanisms for the photocatalytic activities were also discussed.     

Iron Oxide Nanoparticles: Biosynthesis,Magnetic Behavior,Cytotoxic Effect

Iron oxide nanoparticles have attracted much attention because of their superparamagnetic properties and their potential applications in many fields such as magnetic storage devices, catalysis, sensors, superparamagnetic relaxometry (SPMR), and high-sensitivity biomolecule magnetic resonance imaging (MRI) for medical diagnosis and therapeutics. In this study, iron oxide nanoparticles (Fe₂O₃ NPs) have been synthesized using a taranjabin (camelthorn or persian manna) aqueous solution. The synthesized Fe₂O₃ NPs were identified through powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), field energy scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX), vibrating-sample magnetometer (VSM) and Raman technics. The results show that the nanoparticles have a hexagonal structure with 20 to 60 nm in size. The cytotoxic effect of the synthesized nanoparticles has been tested upon application against lung cancer cell (A549) lines. It was found that there is no cytotoxic activity at lower concentrations of 200 μg/mL. The ability of the synthesized nanoparticles for lead removal in wastewaters was tested. Results show that highest concentration of adsorbent (50 mg/L) has maximum removal efficiency (96.73 %). So, synthesized Fe₂O₃ NPs can be a good candidate to use as heavy metals cleaner from contaminated waters.     

An investigation on structure and texture of silica-magnesia xerogels

Silica-magnesia xerogels were prepared by reacting tetraethoxysilane (TEOS) and magnesium chloride (MgCl₂) under acidic conditions. The TEOS/MgCl₂ molar ratio was varied from 1:0 to 0:1. The xerogels were characterized by a set of complementary techniques, namely, Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). Magnesium contents of silica-magnesia xerogels were between 1.3 and 16.0 wt%. Increasing TEOS/MgCl₂ molar ratio affords higher homogeneity and crystallinity. The presence of low Mg content (<5%) increases specific surface area compared to bare silica. A cubic grain morphology was observed for xerogels with higher Mg content.     

Palladium on magnetic Irish moss: A new nano‐biocatalyst for suzuki type cross‐coupling reactions

A novel heterogeneous magnetic palladium nano‐biocatalyst was designed by utilizing Irish moss, a family of sulfated polysaccharides extracted from algae, as a natural biopolymer. This magnetic Irish moss decorated with palladium (Pd–Fe₃O₄@IM) to form a biomagnetic catalytic system was synthesized and well characterized by FT–IR analysis, X‐ray powder diffraction, field emission scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, atomic absorption spectroscopy and transmission electron microscopy. The catalyst was stable to air and moisture and displayed high catalytic activity in ligand‐free Suzuki–Miyaura cross‐coupling reactions conducted under green chemistry reaction conditions. The aromatic ketones are produced by the cross‐coupling reaction between acid chlorides and aryl boronic acid derivatives in high yields.     

Low temperature synthesis and luminescence investigations of YAG:Ce,Eu nanocomposite powder for warm white light-emitting diode

The preparation of the cerium and europium co-doped YAG materials as well as the study for their synthesis and emitting mechanism of the energy transfer between Ce³⁺ and Eu³⁺ were investigated in the present study. YAG:Ce³⁺, Eu³⁺ powders were synthesized using a high-energy ball milling method in different sintering temperature and atmosphere: air and H₂/N₂. The effects of the synthesis procedure on the crystallinity, morphology, structure, and luminescence spectra were examined by X-ray diffraction, field emission-scanning electron microscopy, and photoluminescence spectroscopy. The europium co-doped YAG:Ce³⁺ phosphors is improved the chromaticity coordinates.     

Na<Subscript>x−y</Subscript>H<Subscript>y</Subscript>Ti<Subscript>2−x</Subscript>Fe<Subscript>x</Subscript>O<Subscript>4</Subscript>·nH<Subscript>2</Subscript>O nanosheets with lepidocrocite-like layered structure synthesized by hydrothermal treatment of ilmenite sand

Na_x−yH_yTi_2−xFe_xO₄·nH₂O nanosheets with lepidocrocite-like layered structure were produced through alkaline hydrothermal treatment at very low temperatures (130°C) from ilmenite sand. The crystal structure, morphology and optical properties were investigated by X-Ray diffraction, transmission electron microscopy, selected area electron diffraction, energy dispersive spectroscopy and UV-Vis spectroscopy. The product shows leaf-like nanosheet morphology with thickness <30 nm and lengths <1 μm. Three lepidocrocite-like titanates (Imm2 space group) with similar a and c lattice parameters but different interlayer distances (b/2) were identified. This appears to be the first preparation of lepidocrocite-like layered nanosheets by a simple, energy efficient (low temperature) and low cost (starting from mineral sand) procedure.     

Nanotubes Made from Deeply Undercooled Cryolite/Alumina Melts

The rapid‐solidification processing (by a cooling rate of 10⁵–10⁶ K/s) was used for the preparation of deeply undercooled cryolite/alumina (Na₃AlF₆/Al₂O₃) melts. We found a mass of nanotubes on the surface of these undercooled melts. The nanotubes were preferentially located on the defect places of the surface with the following approximate dimensions: base≈100×100 nm, length≈1000 nm. The solidified samples with the nanotubes on the surface were analyzed by scanning electron microscopy (SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), and infrared spectroscopy (IR).     

Morphology and Structure of Crystalline Polysaccharides: Some Recent Studies

Summary: In this paper, we review recent studies on the morphology and molecular structure of some polysaccharide crystals from amylose, cellulose, and mannan. The data were recorded using combinations of imaging, diffraction, and spectroscopic techniques: scanning and transmission electron microscopy, electron, neutron, and X-ray diffraction, as well as ¹³C solid-state NMR spectroscopy. Differences were generally found between native crystals, whose features result from in vivo biogenesis and the recrystallized products prepared in vitro.