Preparation of α-Fe2O3 nanoparticles by high-energy ball milling

α-Fe₂O₃ nanoparticles were prepared by high-energy ball milling using α-FeOOH as raw materials. The prepared samples were characterized by transmission electron microscopy (TEM), Mössbauer spectroscopy, X-ray diffraction (XRD) and differential thermal analysis–thermogravimetric analysis (DTA–TGA). The results showed that after 90 h milling α-Fe₂O₃ nanoparticles were obtained, and the particle size is about 20 nm. The mechanism of reaction during milling is supposed that the initial α-FeOOH powder turned smaller and smaller by the high-speed collision during ball milling, later these particles turned to be superparamagnetic, at last these superparamagnetic α-FeOOH particles were dehydrated and transformed into α-Fe₂O₃.     

Novel NdCo<Subscript>5</Subscript> nanoflakes and nanoparticles produced by surfactant-assisted high-energy ball milling

High-energy ball milling has been shown to be a promising method for the fabrication of rare earth—transition metal nanopowders. In this work, NdCo₅ nanoflakes and nanoparticles have been produced by a two-stage high-energy ball milling (HEBM), by first using wet HEBM to prepare precursor nanocrystalline powders followed by surfactant-assisted HEBM. NdCo₅ flakes have a thickness below 150 nm and an aspect ratio as high as 10²–10³; the nanoparticles have an average size of 7 nm. Both the nanoparticles and nano-flakes exhibited high coercivities at low temperatures, with values at 50 K of 3 and 3.7 kOe, respectively. The high values of coercivity can be attributed to the large surface anisotropy of nanoparticles that leads to an effective uniaxial-type of behavior in contrast to the planar anisotropy of the bulk samples. Angle-dependent magnetization measurements at different temperatures were used to determine the spin reorientation transitions in the nanopowders and nanoparticles. The nanoparticles showed spin reorientation temperatures, T _SR1 = 276 and T _SR2 = 237 K which are lower when compared with the values of 290 and 245 K, respectively for bulk.     

Preparation and magnetic studies of nickel ferrite nanoparticles substituted by Sn and Cu

The mixed ferrite systems, namely NiFe_2−2xSn_xCu_xO₄ (x=0, 0.1, 0.2, and 0.3) nanoparticles have been studied to understand their structural and magnetic parameters. The NiFe_2−2xSn_xCu_xO₄ nanoparticles were prepared by high energy ball milling (HEBM). The samples were characterized by the X-ray diffraction technique. All samples exhibited spinel structures. The crystalline size and internal strain were evaluated by XRD patterns using Williamson-Hall and Scherrer methods. Magnetic properties of the nanoparticles ferrite were studied by means of alternating gradient force magnetometry (AGFM) and Faraday balance.     

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy,transmission electron microscopy,X‐ray absorption spectroscopy and X‐ray photoelectron spectroscopy

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High‐resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)‐ and (100)‐oriented planes which stabilizes against further oxidation of the particles. X‐ray absorption spectroscopy (XANES) and X‐ray photoelectron spectroscopy (XPS) measurements at the O 1s‐edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milled for different times. XANES results reveal the presence of the +4 (SiO₂) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2p XPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub‐oxide, +1 (Si₂O), +2 (SiO) and +3 (Si₂O₃), states are present. The analysis of the change in the sub‐oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.     

Mössbauer and magnetic study of Co x Fe3--x O4 nanoparticles

Magnetic nanoparticles of cobalt ferrites Co _x Fe_3−x O₄ (x = 1 or 2) have been obtained either by mechanical milling or thermal treatment of pre-prepared layered double hydroxide carbonate x-LDH–CO₃. Mechanical milling of the 1-LDH–CO₃ leads to the large-scale preparation of nearly spherical nanoparticles of CoFe₂O₄, the size of which (5 to 20 nm) is controlled by the treatment time. Core-shell structure with surface spin-canting has been considered for the nanoparticles formed to explain the observed hysteresis loop shift (from ZFC–FC) in the magnetic properties. Annealing treatment of the 2-LDH–CO₃ below 673 K results in the formation of nearly spherical pure Co₂FeO₄ nanoparticles. At 673 K and above, the LDH decomposition leads to the formation of a mixture of both spinels phases Co₂FeO₄ and CoFe₂O₄, the amount of the latter increases with annealing temperature. Unusually high magnetic hardness characterized by a 22 kOe coercive field at 1.8 K has been observed, which reflects the high intrinsic anisotropy for Co₂FeO₄.     

New nanocomposites containing metal nanoparticles, carbon nanotube and polymer

Metal-carbon nanotube-graft-polymer (MCNT-g-P) nanocomposites were synthesized and characterized successfully. In this work, multiwall carbon nanotubes (MWCNT) were opened using HNO₃/H₂SO₄ mixture and filled by metal nanoparticles such as silver nanoparticles through wet chemistry method. Then MWCNT containing metal nanoparticles were used as macroinitiator for ring opening polymerization of ε-caprolactone and MCNT-g-P nanocomposites were obtained. Length of grafted polymer arms onto the MWCNT was controlled using MWCNT/ε-caprolactone ratio. Structure and properties of nanocomposites were evaluated by TEM, DSC, TGA, and spectroscopy methods.     

Amorphization of the intermetallic compounds Co2Zr and Fe2Zr under mechanical grinding

The crystalline intermetallic compounds Co₂Zr and Fe₂Zr were produced in the stoichiometric composition and milled in a planetary ball mill for different milling periods. The samples were investigated in respect to the question if a crystal-to-glass transition occurs due to the milling process. Three different experimental methods were used for this study: X-ray diffraction, Mößbauer spectroscopy, and measurements of the specific heat capacityc _p . The intermetallic compound Fe₂Zr is very suitable for this study since it is ferromagnetic at room temperature. Thus it shows characteristic features in the Mößbauer spectrum and in the measurement of the specific heat capacityc _p . The investigation shows that the intermetallic compounds Co₂Zr and Fe₂Zr undergo a crystal-to-glass transition under mechanical grinding but the X-ray diffraction patterns show that the transformation is not complete. Even after long milling periods always an amount of a crystalline phase is present in the milled samples. In comparison the mechanically ground samples show the same properties as mechanically alloyed powder mixtures of the two elements of the same chemical composition. A probable explanation for the development of an amorphous phase by mechanical grinding of the crystalline compounds Co₂Zr and Fe₂Zr is the accumulation of internal strain in the crystalline grains. Another possible explanation, the addition of iron impurities to the crystalline compounds due to the wear debris of the milling equipment, seems to be improbable since the intermetallic phases Co₂Zr and Fe₂Zr show extended existance ranges in the equilibrium phase diagrams and hence are stable in respect to a variation in the composition.     

Near-edge X-ray absorption fine structure spectroscopy and structural properties of Ni-doped CeO2 nanoparticles

Ni-doped CeO₂ nanoparticles were prepared by using the co-precipitation method. The prepared nanoparticles were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, field emission scanning electron microscopy (FE-SEM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The XRD results infer that Ni-doped CeO₂ nanoparticles have single phase nature similar to that of pure CeO₂ nanoparticles. We have calculated lattice parameters using Powder-X software, particle size using Scherer’s formula and strain using the Williamson-Hall method for all the synthesized samples. We have observed a systematic decrease in the lattice parameters, particle size and strain with an increase in Ni doping in CeO₂. The FE-SEM micrographs also confirm that Ni-doped CeO₂ have nanocrystalline behavior and particles are spherical shaped. From the Raman spectra, it is observed that the intensity of classical CeO₂ vibration modes first increases then decreases with Ni doping. The NEXAFS spectra measured at Ce M_4,5 and Ni L_3,2 edges clearly indicate that Ce ions are in the +4 valence state and Ni ions are in the +2 valence state.     

Phase transformation of ZrO2 nanoparticles produced from zircon

This article focuses on the phase transformation of zirconia (ZrO₂) nanoparticles produced from zircon using a bottom-up approach. The influence of mechanical milling and thermal annealing on crystalline phase transformation of ZrO₂ nanoparticles was explored. It was found that the iron oxide, as an inherent impurity present in ZrO₂ nanoparticles, produced from zircon stabilises the cubic phase after calcination at 600°C. The stabilised cubic phase of ZrO₂ nanoparticles was disappeared and transformed into partial tetragonal and monoclinic phases after mechanical milling. The phase transformation occurred on account of the crystal defect induced by high-energy mechanical milling. The destabilisation of cubic phase into monoclinic phase was observed after the thermal annealing of ZrO₂ nanoparticles at 1000°C. The phase transitions observed are correlated to the exclusion of iron oxide from the zirconia crystal structure.     

Further studies of the sensitivities attainable in using three optical functions to calculate n, k and thickness for thin films

All 56 combinations of three optical functions chosen from R_s, R_p, T_s, T_p, Φ_rs, Φ_rp, Φ_ts and Φ_tp have been investigated to discover their regions of sensitivity in n, k and d/λ coordinate space. When the arrays of error parallelepipeds were plotted, single quadrant patterns of high sensitivity were generated by 21 of these combinations, these being the ones containing one photometric and two polarimetric functions; the best combination was R_pΦ_rpΦ_tp which was viable at all angles of incidence and all thicknesses up to d/λ = 0.08. The remaining 35 combinations produced two-lobe patterns which were insensitive at small angles of incidence but improved as the angle of incidence increased and were best at 60°.     

不同生长环境下砷化镓纳米颗粒的应变场模拟

对于埋嵌在薄膜材料中的纳米颗粒,在其生长过程中总是不可避免地伴随着应变场的产生,而这种应变场的分布能反映纳米颗粒的结构变化,纳米颗粒结构与它的物理性能有重要的关系.研究埋嵌在不同薄膜材料中的纳米颗粒生长过程中的应变场分布对于调控纳米颗粒的物理性能有着重要的意义.本文利用有限元算法分别计算了埋嵌在非晶氧化铝薄膜和非晶二氧化硅薄膜材料中的砷化镓纳米颗粒生长过程中的应变场分布.砷化镓纳米颗粒在以上两薄膜材料生长过程中都受到非均匀偏应变作用.对于埋嵌在氧化铝薄膜中的砷化镓纳米颗粒,其生长过程中,纳米颗粒内部受到的应变大于纳米颗粒表面受到的应变;而对于埋嵌在二氧化硅薄膜中的砷化镓纳米颗粒,纳米颗粒内部受到的应变小于纳米颗粒表面受到的应变.选择砷化镓纳米颗粒生长的薄膜材料可以调控纳米颗粒生长过程中的应变场分布,从而进一步调控纳米颗粒的晶格结构和形貌及其物理性能.     

Rapid synthesis and size control of CuInS2 semi-conductor nanoparticles using microwave irradiation

The properties of CuInS₂ semi-conductor nanoparticles make them attractive materials for use in next-generation photovoltaics. We have prepared CuInS₂ nanoparticles from single source precursors via microwave irradiation. Microwave irradiation methods have allowed us to increase the efficiency of preparation of these materials by providing uniform heating and rapid reaction times. The synergistic effect of varying thiol capping ligand concentrations as well as reaction temperatures and times resulted in fine control of nanoparticle growth in the 3–5 nm size range. Investigation of the photophysical properties of the colloidal nanoparticles were performed using electronic absorption and luminescence emission spectroscopy. Qualitative nanoparticles sizes were determined from the photoluminescence (PLE) data and compared to HRTEM images.

Synthesis,structural, optical,and magnetic properties of Co doped,Sm doped and Co+Sm co-doped ZnS nanoparticles

The compositional, structural, optical and magnetic properties of ZnS, Zn_0.98Co_0.02S, Zn_0.98Sm_0.02S and Zn_0.96Co_0.02Sm_0.02S nanoparticles synthesized by a hydrothermal method are presented and discussed. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies revealed that all the samples exhibited cubic structure without any impurity phases. X-ray photoelectron spectroscopy (XPS) results revealed that the Co and Sm ions existed in +2 and +3 states in these samples. The photoluminescence (PL) spectra of all the samples exhibited a broad emission in the visible region. The room temperature magnetization versus applied magnetic field (M–H) curves demonstrated that the Sm+Co doped nanoparticles exhibited enhanced ferromagnetic behavior compare to Co and Sm individually doped ZnS nanoparticles, which is probably due to the exchange interaction between conductive electrons with local spin polarized electrons on the Co²⁺ or Sm³⁺ ions. This study intensifies the understanding of the novel performances of co-doped ZnS nanoparticles and also provides possibilities to fabricate future spintronic devices.     

Magnetic field orientation dependence of flux pinning in (Gd,Y)Ba2Cu3O7−x coated conductor with tilted lattice and nanostructures

The dependence of the critical current density (J_c) on the orientation of an applied magnetic field was studied for a prototype (Gd,Y)Ba₂Cu₃O_7?x (GdYBCO) coated conductor fabricated by MOCVD on an IBAD-MgO template. Additional rare-earth cations (Y and Gd) and Zr were incorporated into the superconducting film to form (Y,Gd)₂O₃ and BaZrO₃ nanoparticles extended nearly parallel to the a–b planes and to the c-axis, respectively, to enhance the flux pinning. In-field measurement of J_c was carried out with electrical current flowing either along or perpendicular to the longitudinal axis of the tape, while a maximum Lorentz force configuration was always maintained. Details in the angular dependence of J_c were related to the unique structure of the film, specifically the tilt in the GdYBCO lattice and the tilts in the extended (Y,Gd)₂O₃ and BaZrO3 nanoparticles. XRD and TEM were used to study the structure of the coated conductor. The effect of the misalignment between the external field H and the internal field B on the angular dependence of J_c is discussed.     

A simple thermal decomposition synthesis, magnetic properties, and cytotoxicity of La0.7Sr0.3MnO3 nanoparticles

This study reports the new and simple synthesis of magnetic La_0.7Sr_0.3MnO₃ (LSMO) nanoparticles by thermal decomposition method using acetate salts of La, Sr and Mn as starting materials. To obtain the LSMO nanoparticles, thermal decomposition of the precursor is carried out at the temperatures of 600, 700, 800, 900, and 1000°C for 6 hours. The synthesized LSMO nanoparticles were characterized by XRD, FT-IR, TEM and SEM. Structural characterization shows that the prepared particles consisted of two phases of LaMnO₃ (LMO) and LSMO with crystallite sizes ranging from 18 to 55 nm. All the prepared samples have a perovskite structure which changes from cubic to rhombohedral with the increase in the thermal decomposition temperature. Basic magnetic characteristics such as saturation magnetization (M _S) and coercive field (H _C) are evaluated by sample vibrating magnetometry at room temperature (20°C). The samples show soft ferromagnetic behavior with M _S values of ∼9–55 emu/g and H _C values of ∼8–37 Oe, depending on the crystallite size and thermal decomposition temperature. The relationship between the crystallite size and the magnetic properties is presented and discussed. The cytotoxicity of synthesized LSMO nanoparticles was also evaluated with NIH 3T3 cells and the result showed that the synthesized nanoparticles were not toxic to the cells as determined from cell viability in response to the liquid extraction of LSMO nanoparticles.     

X-ray diffraction,microstructure, Mössbauer and magnetization studies of nanostructured Fe50Ni50 alloy prepared by mechanical alloying

Nanocrystalline Fe₅₀Ni₅₀ alloy samples were prepared by the mechanical alloying process using planetary high-energy ball mill. The alloy formation and different physical properties were investigated as a function of milling time, t, (in the 0–50 h range) by means of the X-ray diffraction (XRD) technique, scanning electron microscopy (SEM), energy dispersive X-ray (EDAX), Mössbauer spectroscopy and the vibrating sample magnetometer (VSM). The complete formation of γ-FeNi is observed after 24 h milling. When milling time increases from 0 to 50 h, the lattice parameter increases towards the Fe₅₀Ni₅₀ bulk value, the grain size decreases from 67 to 13 nm, while the strain increases from 0.09% to 0.41%. Grain morphologies at different formation stages were observed by SEM. Saturation magnetization and coercive fields derived from the hysteresis curves are discussed as a function of milling time.     

Fabrication of water-soluble magnetic nanoparticles by ligand-exchange with thermo-responsive polymers

We report the use of thermo-responsive polymers in the synthesis of Co and γ-Fe₂O₃ nanoparticles using a two-step method involving thermal decomposition of the organometallic complexes in the presence of oleic acid and then followed by ligand-exchange process with thermo-responsive polymer. Among different thermo-responsive polymers investigated, it was found that the polymer based on poly(N-isopropylacrylamide) with a co-monomer component of acrylic acid and acrylamide can be used in the ligand-exchange to coat Co and γ-Fe₂O₃ nanoparticles, respectively. The nanoparticles are found to be water-soluble at temperatures below coil-to-globule phase transition of the coating polymer.     

Green synthesis of silver nanoparticle by <Emphasis Type="Italic">Penicillium purpurogenum</Emphasis> NPMF: the process and optimization

An eco-friendly microbial method for synthesis of silver colloid solution with antimicrobial activity is developed using a fungal strain of Penicillium purpurogenum NPMF. It is observed that increase in concentration of AgNO₃ increases the formation of silver nanoparticle. At 5 mM concentration highly populated polydispersed nanoparticles form. Furthermore, change in pH of the reaction mixture leads to change in shape and size of silver nanoparticles. At lower pH two peaks are observed in the absorption spectra showing polydispersity of nanoparticles. However, highly monodispersed spherical nanoparticles of 8–10 nm size form with 1 mM AgNO₃ concentration at pH 8. Antimicrobial activity of nanoparticles is demonstrated against pathogenic gram negative bacteria like Escherichia coli and Pseudomonas aeruginosa, and gram positive bacteria like Staphylococcus aureus. The antimicrobial activity of silver nanoparticles obtained at different initial pH show strong dependence on the surface area and shape of the nanoparticles.     

Photocatalytic thin films containing TiO2:N nanopowders obtained by the layer-by-layer self-assembling method

In this work, TiO₂-N powders were synthesized by high-energy ball milling, using commercial titanium dioxide (TiO₂) in the anatase phase and urea to introduce nitrogen into TiO₂ in order to enhance their photocatalytic properties in the visible spectral region. Several samples were prepared by milling a mixture of TiO₂-urea during 2, 4, 8, 12 and 24 h and characterized by spectroscopic and analytical techniques. X-ray diffraction (XRD) results showed the coexistence of anatase and high-pressure srilankite TiO₂ crystalline phases in the samples. Scanning electron microscopy (SEM) revealed that the grain size of the powder samples decreases to 200 nm at 24 h milling time. UV-Vis diffuse reflectance spectroscopic data showed a clear red-shift in the onset of light absorption from 387 to 469 nm as consequence of nitrogen doping in the samples. The photocatalytic activity of the TiO₂-N samples was evaluated by methylene blue degradation under visible light irradiation. It was found that TiO₂-N samples had higher photocatalytic activity than undoped TiO₂ samples, which could be assigned to the effect of introducing N atoms and XPS results confirm it. Using polyethylenimine (PEI), transparent thin films of TiO₂-N nanoparticles were prepared by layer-by-layer self assembly method. UV-visible spectrophotometry was employed in a quantitative manner to monitor the adsorbed mass of TiO₂ and PEI after each dip cycle. The adsorption of both TiO₂ and PEI showed a saturation dip time of 15 min.