Mechanical treatment of TiO2 and ZrO2 oxide mixtures

The mixed ZrO2-TiO2 system (5-50 wt% of ZrO2) has been studied to investigate the influence of the mechanical treatment on its physicochemical properties depending on the composition, time of milling (5, 10 and 20 min, r.p.m. 82) and temperature (400, 550 and 700 degrees C). Samples were characterized by Raman spectroscopy, X-ray powder diffraction, Scanning Electron Microscopy coupled with Energy Dispersion X-ray analyzer, High Resolution-Transmission Electron Microscopy and nitrogen adsorption porosimetry. Results show that srilankite (TiZrO4) phase has been produced. No influence of the milling time and temperature on the phase composition is observed. The presence of zirconia increases the thermal stability of anatase phase up to 700 degrees C hindering the anatase rutile phase transformation.     

Synthesis and microstructure characterization of tetragonal Zr1–xTixO2 (x = 0–1) solid solutions

Oxide powders of Zr_1–xTi_xO₂ (x = 0–1) solid solutions with micron-sized particles were synthesized via a solution combustion method. The synthesis process and Zr/Ti molar ratio were optimized to produce powders with the tetragonal crystal structure. X-ray diffraction, Raman spectroscopy and transmission electron spectroscopy results confirm that a full crystallization microstructure with the single tetragonal phase is obtained after calcination at 600 °C while maintaining the crystallite size <30 nm. Zr/Ti oxide mixtures with Zr ≥ 67 mol% exhibit a tetragonal crystal structure and the embedding Ti in ZrO₂ improves the structure stability. The nitrogen sorption results indicate that the powders possess mesoporous morphology with medium specific surface areas (∼10–50 m²/g). Chemical stability tests show that these powders are relatively stable with negligible removal of titanium and zirconium after elution by 0.5 mol/L HCl. Density functional theory was used to calculate the most stable structure with low energy for the selected composition.     

Microstructure and mechanical properties of polycrystalline NbN/TaN superlattice films

The polycrystalline NbN/TaN superlattice films have been grown on the substrates of 18-8 stainless steel by reactive magnetron sputtering. The microstructure and microhardness of the superlattice films have been studied with X-ray diffraction (XRD), high resolution transmission electron microscopy (HREM) and microhardness tester. The results showed that the NbN layers are of face cubic and the TaN layers are hexagonal crystal structure in the NbN/TaN superlattice films. The lattice plane (111) of NbN are coherent with the (110) of TaN and the lattice mismatch is 3.18%. The NbN/TaN superlattice film demonstrated superhardness effects. The maximum Knoop hardness value reached 5100 kgf/mm² with a modulation period from 2.3 nm to 17.0 nm. It was proved that even if NbN layers did not take the same crystal structure as TaN layers, hardness anomalous phenomenon still can be produced as long as the coherent strains exist.     

Investigation of Zr-incorporated mesoporous titania materials via nonsurfactant templated sol-gel route: Synthesis, characterization and stability

The synthesis of Zr-incorporated mesoporous titania materials was achieved by a HCl-catalyzed nonsurfactant templated sol-gel process, followed by solvent extraction to remove the urea template. The materials were characterized by FT-IR, X-ray energy dispersive spectroscopy (XEDS), nitrogen adsorption-desorption measurement (BET), powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Zirconia has been successfully incorporated into the skeleton of titania and the observed Zr/Ti compositions are close to the designed Zr/Ti molar ratios in the feeds. The content of zirconia has significant effects on the mesoporosity and the pore parameters as well as the thermal and hydrothermal stabilities of the materials. Anatase crystal structures were formed in the materials with low Zr/Ti molar ratios. As the Zr/Ti ratio is increased, the content of anatase structures decreases and the material becomes essentially amorphous at the Zr/Ti ratio of 1/1. The materials have narrowly distributed average pore diameters in the range of 2.5–5.1 nm and disordered pore or channel structures. The incorporation of Zr increases the thermal stability but decreases the hydrothermal stability of the materials.     

Molten salt route of single crystal barium titanate nanowires

Rather long barium titanate nanowires have been synthesised by molten salt method without any organic surfactants. The crystal structure of barium titanate nanowires is identified by X-ray diffraction to be the tetragonal structure phase, Raman spectroscopy and selected area electron diffraction measurements. Furthermore, scanning electron microscopy and transmission electron microscopy observations show that the barium titanate nanowires have uniform cylindrical structure, with lengths from 20 to 80 μm and diameters from 100 nm to 1 μm. Moreover, high resolution transmission electron microscopy observations and selected area electron diffraction analysis show that the barium titanate nanowires are single crystals with a tetragonal structure in nature.     

Synthesis of PbTe nanowire arrays using lithographically patterned nanowire electrodeposition

We describe the preparation by electrodeposition of arrays of lead telluride (PbTe) nanowires using the lithographically patterned nanowire electrodeposition (LPNE) method. PbTe nanowires had a rectangular cross-section with adjustable width and height ranging between 60-400 nm (w) and 20-100 nm (h). The characterization of these nanowire arrays using X-ray diffraction, transmission electron microscopy and electron diffraction, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy (XPS) is reported. PbTe nanowires were electrodeposited using a cyclic electrodeposition-stripping technique that produced polycrystalline, stoichiometric, face-centered cubic PbTe with a mean grain diameter of 10-20 nm. These nanowires were more than 1 mm in length and two additional processing steps permitted their suspension across 25 microm air gaps microfabricated on these surfaces. The LPNE synthesis of lithographically patterned PbTe nanowires was carried out in unfiltered laboratory air. Nanowires with lengths of 70-100 microm showed an electrical resistivity comparable to bulk PbTe. XPS reveals that exposure of PbTe nanowires to air causes the formation on the nanowire surface of approximately one monolayer of a mixed lead oxide and tellurium oxide within a few minutes.     

合成和表征NiFe2O4纳米线阵列

采用真空灌注结合溶胶-凝胶和氧化铝模板法,在多孔氧化铝模板中制备了平均直径为50 nm的NiFe2O4纳米线阵列.X射线衍射结果显示所制备的纳米线是纯相的NiFe2O4纳米线,透射电镜和电子衍射的结果显示已制备的纳米线是多晶的且表面光滑,场发射扫描电镜图片显示纳米线是大面积且平行有序的、纳米线的长度和所用的氧化铝模板的厚度相当.磁测量的结果显示此纳米线阵列有形状各向异性,同块状材料相比矫顽力有所增强.对纳米线的生长机理做了简单的讨论.     

氧化锡纳米线的制备及其乙醇气体敏感性能

采用热蒸发法成功制备氧化锡纳米线。用X射线衍射、扫描电子显微镜和透射电子显微镜对所制备纳米线的晶格结构和表面形貌进行表征。所制材料为金红石氧化锡单晶结构,纳米线直径为50~200nm,长度为5~15μm,符合气-液-固生长机制。以氧化锡为气敏材料,制备了旁热式结构气敏元件,测试该元件对浓度范围为25×10^-6 ~500×10^-6 的乙醇气体环境的敏感性能。结果表明,该元件的最佳工作温度约为260℃;在25×10^-6 和500×10^-6 的乙醇气体中,灵敏度分别为7.54和111.01,响应时间为2~20s,恢复时间为5~33s;在测试范围内灵敏度与气体浓度具有良好的线性关系;7天内重复测量误差在5%以内,稳定性较好。     

Large-scale synthesis of mullite nanowires by molten salt method

Single-crystalline mullite (3Al2O3 2SiO2) nanowires have been produced in large quantities by a low cost and environmentally benign molten salt synthesis (MSS) method. The raw materials, Al2(SO4)3 and SiO2 powders, react in molten Na2SO4 at 1000 degrees C to produce mullite nanowires without the use of surfactants or templates. After the synthesis, the remaining salts can be easily separated from the products by washing with water. The final products are characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, selected-area electron diffraction, and inductively coupled plasma-atomic emission spectrometry. The thermal and chemical behavior of the raw materials is investigated by heating at a rate of 10 degrees C/min up to 1200 degrees C in air followed by thermogravimetric and differential scanning calorimetry analyses. The single-crystalline mullite nanowires have diameters of 30-80 nm and lengths from several hundreds of nanometers to micrometers and the growth mechanism is discussed.     

Nanolamellar structure obtained by simple crystallization of an amorphous cobalt-based magnetic alloy

A novel modulated nanolamellar structure with a lamellar spacing of about 5 nm was obtained by simple heat treatment of an initially amorphous Co/sub 65/Si/sub 15/B/sub 14/Fe/sub 4/Ni/sub 2/ magnetic alloy. The crystallographic characteristics of this nanolamellar structure were investigated using selected area diffraction pattern, Kikuchi maps, convergent beam electron diffraction, and X-ray diffraction techniques. The crystal structure of the lamellae was found to be a novel phase with a C-base centered orthorhombic crystal structure of a=0.74 nm, b=1.07 nm, and c=0.77 nm, the nanolamellar structure was modulated along the (0 0 1) plane. High-resolution transmission electron microscopy observations showed negligible lattice mismatch between neighboring lamellae. Electron energy loss spectroscopy mapping showed a periodic variation of boron composition corresponding to the nanolamellar periodicity. The formation of the nanolamellar structure was found to be due to spinodal decomposition within the grains formed by crystallization of the alloy.     

Fabrication and characterization of Zr and Co co-doped LiMn2O4 nanowires using sol–gel–AAO template process

The Zr and Co co-doped LiMn₂O₄ nanowires are fabricated successfully by using sol–gel process with porous anodic aluminum oxide (AAO) as the template. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization show that the synthesized LiZr _x Co _y Mn_(2-x-y)O₄ nanowires are uniformly distributed, high-ordered, and parallel to each other, and few microscopic defects are found. Selected area electron diffraction (SAED) pattern, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) investigations jointly demonstrate that the synthesized nanowires have a similar single spinel structure of LiMn₂O₄ crystal though Zr and Co are doped. Since the LiZr _x Co _y Mn_(2-x-y)O₄ nanowires can be mass-produced by using this method, it is expected to find promising application as a new cathode material in lithium ion battery.     

Syntheses of titania and poly(3,4-ethylenedioxythiophene) bilayer nanotubes

Synthesis of bilayer tubes of poly(3,4-ethylenedioxythiophene) (PEDT) and titania by electrochemical polymerization of PEDT and chemical deposition of titania in the pores of anodic alumina was reported. Electron diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and fourier transformed infrared spectroscopy (FTIR) were used to characterize these bilayer tubes. SEM photographs show the tubes of uniform diameters around 200 nm. TEM photographs confirm the formation of titania and PEDT bilayer tubes of 230 nm and 100 nm diameter, the thickness of outside TiO2 layer and inner PEDT layer are around 20 nm under the experimental condition. The XPS spectra of the bilayer tubes show that the Ti2p peak shifts to a lower binding energy and S2p peak shifts to a higher binding energy. Electron diffraction patterns show that TiO2 nanotubes formed was single crystals of anatase phase. I-V characteristic curves were measured for samples prepared under various conditions.     

A HRTEM and XRD Study of the Potassium Hexatitanate Nanowires

The structure of potassium hexatitanate (K_2Ti_6O_13) nanowires has been investigated using both the Rietveld powder diffraction profile fitting technique and high resolution transmission electron microscopy (HRTEM) image simulations. From the Rietveld analysis it was shown that the nanowires had a monoclinic structure of the space group C2/M and the lattice parameters were a=1.5582 nm, 6=0.382 nm, c=0.9112 nm. HRTEM conclusions agree with refinement results obtained from experimental XRD data. The good agreement between the experimental and simulated images confirms that the nanowires is indeed K2Ti6O13 nanowire.The growth axes of nanowires were mainly along the [010] direction.     

纳米颗粒自组装合成氧化锆奇异纳米结构的研究

通过微乳液方法制备了Zr(OH)4前驱体,在添加KCl的条件下对其进行热处理,获得了ZrO2的奇异纳米结构,包括规则的六边形纳米颗粒、纳米晶须和纳米管.试验表明,氯离子在纳米颗粒自组装过程中起着重要作用.采用透射电镜(TEM)、选取电子衍射(SAED)和X射线衍射(XRD)对试样进行了分析表征.     

合金化热镀锌镀层组织Γ相的结构分析

为了研究合金化热镀锌镀层组织Γ相的结构,采用聚焦离子束(FIB)方法制备了合金化热镀锌无间隙原子(IF)钢板镀层横截面透射电镜(TEM)试样,应用TEM对其显微结构进行了观察和选区电子衍射分析,应用X射线能谱仪(EDX)测定了Γ相的化学成分,并介绍了FIB方法制备TEM试样的过程.结果表明,Γ相选区衍射花样中存在明显的超点阵衍射.证明Γ相是一种有序金属间化合物;计算机模拟电子衍射花样的结果给出了Γ相的原子占位.     

Growth and properties of ZnO nanowires synthesized by a simple hydrothermal method

Hexagonal ZnO nanowires were synthesized on pre-seeded silicon (100) substrates by a simple hydrothermal method at a relatively low temperature of 95 °C without any catalyst or template. The pre-seeded layer was produced using the sol–gel spin coating technique with 1 M zinc acetate in ethanol and ethanolamine. The structural properties of the nanowires were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern indicated that the as-grown ZnO nanowires had the single-phase wurtzite structure, formed along the c-axis. SEM revealed that the nanostructure thin film had wire textures and the synthesis processes importantly influence the final size and shape of the ZnO nanowires. High-resolution transmission electron microscopy (HRTEM) provided further insight into the structure of ZnO nanostructures. The obtained HRTEM image was of the tip of an individual nanowire. The ZnO nanowires highly preferentially grew in the (002) crystal plane. The lattice spacing between adjacent (002) lattice planes was calculated to be 0.52 nm. The optical characteristics of the nanowires were determined from cathodoluminescence (CL) spectra. The CL revealed a fairly high surface state density of ZnO nanowires that grew at reaction concentrations of 0.01–0.25 M.     

Magnetic properties of single-crystalline CoSi nanowires

We have observed unusual ferromagnetic properties in single-crystalline CoSi nanowire ensemble, in marked contrast to the diamagnetic CoSi in bulk. High-density freestanding CoSi nanowires with B20 crystal structure are synthesized by a vapor-transport-based method. The reaction of cobalt chloride precursor with a Si substrate produces high-aspect-ratio CoSi nanowires. The high-resolution transmission electron microscopy and electron diffraction studies reveal superlattice structure in CoSi nanowires with twice the lattice parameter of simple cubic CoSi lattice. The zero-field-cooled and field-cooled (ZFC-FC) measurements from the nanowire ensemble show freezing of the disordered surface spins at low temperatures. The magnetoresistance (MR) measurements of single nanowire devices show a negative MR whose magnitude gets larger at lower temperatures.     

Fabrication of large-scale ultra-fine Cd-doped ZnO nanowires

We demonstrate bulk synthesis of highly crystal Cd-doped ZnO nanowires by using (Cd + Zn) powders at 600 °C. These mass ultra-fine ZnO nanowires with about 0%, 1%, 4% and 8% Cd so obtained have been characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED) and high-resolution TEM (HRTEM). They have the uniform diameter of about 20 nm and several hundred microns in length. The growth of the as-synthesized nanowires is suggested for self-catalyzed vapor–liquid–solid.     

Studies on the synthesis of CdCO3 nanowires and porous CdO powder

In the present study, we demonstrate the self transformation of aqueous cadmium acetate into CdCO₃ nanowires through hydrothermal reaction. The reaction temperature and the volume ratio of water to ethanol were found to be crucial for the formation of CdCO₃ nanowires. The nanowires are of single crystal in nature having width ∼ 17-30 nm as observed from selected area electron diffraction (SAED) pattern and transmission electron microscopic (TEM) results. The major weight loss found in thermogravimetric analysis (TGA) corresponds to the formation of CdO and CO₂. The powder X-ray diffraction (PXRD) patterns of CdCO₃ and CdO are respectively indexed to pure rhombohedral and cubic phases. The photoluminescence (PL) spectrum of CdO exhibits an emission peak at 483 nm due to the transition between the valence and conduction bands.     

Structural and optical characterization of strained free-standing InP nanowires

The structural and optical properties of high-quality crystalline strained InP nanowires are reported in this article. The nanowires were produced by the vapor-liquid-solid growth method in a chemical-beam epitaxy reactor, using 20 nm gold nanoparticles as catalysts. Polarization-resolved photoluminescence experiments were carried out to study the optical properties of the InP nanowires. These experiments revealed a large blue shift of 74 meV of the first electron-to-heavy hole optical transition in the nanowires, which cannot be solely explained by quantum size effects. The blue shift is mainly attributed to the presence of biaxial compressive strain in the inward radial direction of the InP nanowires. High-resolution transmission electron microscopy Electron and selected area electron diffraction experiments show that the nanowires have high crystal quality and grow along a [001] axes. These experiments also confirmed the presence of 1.8% compressive radial strain and 2% tensile longitudinal strain in the nanowires. A simple theoretical model including both quantum confinement and strain effects consistently describes the actual energy position of the InP nanowires optical emission.