Synthesis of quasi-1D cuprous oxide nanostructure and its structural characterizations

A wealth of superfine polycrystalline cuprous oxide (Cu₂O) nanowires have been synthesized with hydrazine hydrated (N₂H₄·H₂O), act as the reducing agent, and Cu(OH)₂ nanowires, act as a soft template and surfactant, at room temperature. Two methods were employed for the synthesis of these nanowires, i.e. with and without capping agent (polyethylene glycol Mw 8000). Techniques of powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) pattern, electron diffraction X-ray (EDX) spectroscopy, and UV-visible (UV-vis) spectroscopy have been used to characterize the morphology, structure, crystallinity, purity, and composition of nanowires. The average diameters of Cu₂O nanowires, prepared with and without capping agent, were observed to be 8-10 and 12-15 nm and lengths of several microns, respectively. It is found that capping agent (PEG) confines the dimensions of synthesized nanowires. In addition, the observed optical band gap of products show blue-shift effect compared to the bulk Cu₂O (E_g=2.17 eV), which ascribe it as a promising material for the conversion between solar energy and electrical or chemical energy.     

Controlled synthesis of cuprous oxide nanospheres and copper sulfide hollow nanospheres

Uniform Cu₂O nanospheres have been successfully synthesized by reducing CuSO₄ with ascorbic acid in sucrose solution at room temperature. The diameter of the Cu₂O nanospheres can be tuned from 90 to 280 nm by adding different amounts of sucrose in the solution. Furthermore, CuS hollow nanospheres with different diameters have been obtained based on the Kirkendall effect using the as-prepared Cu₂O nanospheres as sacrificial templates. Cu₂O/Cu_7.2S₄ core/shell nanospheres and Cu_7.2S₄ hollow nanospheres are obtained as the intermediate products at different stages of the conversion process. Through the post-treatment of sodium citrate solution, Cu_7.2S₄ hollow nanospheres can be changed into CuS hollow nanospheres. The products are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM). Optical properties of the products have also been studied.     

Shape evolution of gold nanoparticles

The tetraoctylammonium bromide-stabilized gold nanoparticles have been successfully fabricated. The shape evolution of these nanoparticles under different annealing temperatures has been investigated using high-resolution transmission electron microscopy. After an annealing at 100 °C for 30 min, the average diameters of the gold nanoparticles change a little. However, the shapes of gold nanoparticles change drastically, and facets appear in most nanoparticles. After an annealing at 200 °C for 30 min, not only the size but also the shape changes a lot. After an annealing at 300 °C for 30 min, two or more gold nanoparticles coalesce into bigger ones. In addition, because of the presence of Cu grid during the annealing, some gold particles become the nucleation sites of Cu₂O nanocubes, which possess a microstructure of gold-particle core/Cu₂O shell. These Au/Cu₂O heterostructure nanocubes can only be formed at a relatively high temperature (≥300 °C). The results can provide some insights on controlling the shapes of gold nanoparticles.     

Sonochemical synthesis of Cu2O nanocubes for enhanced chemiluminescence applications

A facile one-step sonochemical synthesis of Cu₂O nanocubes has been developed by ultrasound irradiation of copper sulfate in the presence of polyvinylpyrrolidone and ascorbic acid at pH 11. During sonication, the reaction between acoustic cavitation-generated radicals and CuSO₄ produced Cu(OH)₂ intermediate which then reacted with ascorbic acid to generate Cu₂O nanocubes. The products were characterized by FT-IR, XRD, HRTEM, AFM and particle size analyzer. The prepared Cu₂O nanocubes were found to be very effective for enhancing chemiluminescence in the presence of luminol–H₂O₂ system.     

Synthesis and electrocatalytic activities of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocubes

In this article, a hydrothermal method was developed to synthesize Co₃O₄ nanocubes using hydrogen peroxide (H₂O₂) as oxidant, Co(NO₃)₂·6H₂O as a cobalt source. The products are characterized in detail by multiform techniques including X-ray diffraction (XRD), energy dispersive X-ray analysis (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The results show that the obtained products are Co₃O₄ nanocubes with size ranging between 20 and 40 nm. The effects of the hydrogen peroxide concentration on the size of the products have been studied. The electrocatalytic activities of H₂O₂ reduction on Co₃O₄ nanocubes in phosphate buffer were also evaluated.     

Porous In(OH)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> hollow nanocubes: low-temperature reaction design,shape evolution,growth mechanism,and photoluminescent property

Porous sulfur-doped In(OH)₃ (In(OH) _x S _y ) hollow nanocubes were fabricated for the first time by taking advantage of a facile solution-phase approach using thioacetamide as the sulfur source at a temperature as low as 80 °C. The phase structures, composition, and morphologies of resulting products were investigated by powder X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The characterization results indicated that the addition of thioacetamide in synthetic solution could not only accelerate the hollowing process and tune the size of nanocubes but also facilitate the doping of sulfur in In(OH)₃. We proposed that the cooperative combination of oriented attachment and Ostwald ripening as well as chemical-etching process governed the crystal growth, resulting in the formation of the porous sulfur-doped In(OH)₃ hollow nanocubes in this study. We also found these novel In(OH)₃-based hollow nanostructures showed evolutional room temperature photolumincence emissions at visible-light region, suggesting their potential application in the optical and photocatalytic fields.     

Fabrication and characterization of Mn-doped Cu2O thin films grown by RF magnetron sputtering

Two series of Mn-doped Cu₂O diluted-magnetic-semiconductor thin films were prepared by radio-frequency (RF) magnetron sputtering. One is prepared at different deposition temperature with the same Mn doping concentration; the other is deposited at the same temperature but with varying Mn concentration. They were used to find out the ferromagnetic-order zone for the Mn-doped Cu₂O systems. Most of the samples show high (1 1 1) orientation, except low doping concentration (<6 at%). No impurities were found by X-ray diffraction and electron diffraction measurement. The doped Mn ions substituted Cu ions in the Cu₂O lattice and there were about 1.5% cation vacancies. The grains shown in the transmission electron microscopy (TEM) images for all the samples were tiny, i.e. just 5 nm in diameter. A rough phase diagram for the ferromagnetic order existing in the Mn-doped Cu₂O thin films was given with varying Mn doping concentration and deposition temperature.     

Preparation and optical properties of Cu2O hollow microsphere film and hollow nanosphere powder via a simple liquid reduction approach

In this work, we report a simple liquid reduction approach to prepare Cu₂O hollow microsphere film and hollow nanosphere powder with Cu(OH)₂ nanorods as precursor and ascorbic acid as the reductant at 60 °C. When Cu(OH)₂ nanorod array film grown on a copper foil is used as the precursor, Cu₂O thin film made up of hollow microspheres with average diameter of 1.2 μm is successfully prepared. When the Cu(OH)₂ nanorods are scraped from the copper foil and then used as the precursor, Cu₂O hollow nanosphere powder with the average diameter of 270 nm is obtained. The samples are characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and ultraviolet-vis light (UV-vis) absorption spectra. A possible formation mechanism of Cu₂O hollow spheres is discussed.     

One-pot synthesis of single-crystalline Cu2O hollow nanocubes

Single-crystalline Cu₂O hollow nanocubes have been successfully synthesized via a simple wet chemical route in the absence of any surfactants or templates. By studying the growth process of the Cu₂O hollow nanocubes, we found that the Cu₂O hollow nanocubes were formed through a reducing and simultaneously etching process. The speed of reducing Cu(OH)₂ into Cu₂O was much faster than the speed of etching Cu₂O. As a result, Cu₂O solid nanocubes were firstly formed, and then the solid nanocubes were gradually etched into hollow nanocubes.     

Optimization of cuprous oxide nanocrystals deposition on multiwalled carbon nanotubes

Cu (I) phenyl acetylide was used as a source of copper to achieve a homogeneous distribution of Cu₂O nanocrystals (10–80 nm) decorated on multiwalled carbon nanotubes (MWCNTs) having an average diameter of 10 nm. Pristine MWCNTs were first oxygen-functionalized by treating them with a mixture of concentrated (H₂SO₄/HNO₃ : 3/1) acids and the products were characterized by X-ray powder diffraction, transmission and scanning electron microscopy, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and thermogravimetric analysis. An easy, efficient and one-step impregnation method was followed to produce copper-containing nanoparticles on the MWCNTs. The copper-treated MWCNTs dried at room temperature were seen to be well decorated by copper-containing nanoparticles on their outer surface. The MWCNTs were then heat-treated at 400 °C in a nitrogen atmosphere to produce a homogeneous distribution of cuprous oxide nanocrystals on their surface. By varying the ratio of copper to oxygen-functionalized MWCNTs, Cu₂O nanocrystals decorated on MWCNTs with different copper content can be obtained.     

Surface of Zn-Mn-O and its role in room temperature ferromagnetism: An XPS analysis

The existence of ferromagnetism in Zn-Mn-O semiconductor samples and dependence on the preparation condition were investigated. We systematically examined the samples with manganese concentration ranging from 0 to 10 at.%, prepared by a solid state reaction route using (ZnC₂O₄·2H₂O)_1−x and (MnC₂O₄·2H₂O)_x as precursors. Thermal treatment was carried out in air at temperatures ranging from 400 to 900 °C. The samples were investigated by X-ray diffraction, transmission electron microscopy, magnetization measurements and XPS spectroscopy. XPS surface composition, chemical analysis and depth profiling were successfully employed on powder revealing the chemical composition at the surface of the grains and underneath. The present investigation suggests that physical properties and observed room temperature ferromagnetism might be due to grain surface effects. It seems that the ferromagnetic phase is correlated with oxygen build up at the surface.     

Thermal stability and reaction properties of passivated Al/CuO nano-thermite

Thermal stability and reaction properties of Al-CuO system, a mixture of 50-200 nm aluminum nanoparticles passivated by nitrocellulose and 12 nm copper (II) oxide, were investigated with microstructure characterization, differential thermal analysis (DTA), and thermogravimetric analysis (TGA). Transmission electron microscopy observation confirmed that the passivation coating successfully hinders the oxidization. TGA revealed that the passivation shell does not influence the ignition temperature of the thermite reaction. Reaction chemistry of the nano-thermite was elucidated by heating the composite both in inert ambient and vacuum. It was found that the thermite reaction composes of three continuing steps: At 570 °C, Al is oxidized into Al₂O₃ by reacting with CuO, which forms Cu₂O and produces a significant amount of heat. Subsequently two endothermic reactions occur. Starting at 800 °C, alumina reacts with Cu₂O and forms CuAlO₂. Above this temperature CuAlO₂ will decompose and eventually produce alumina, Cu, and O₂ at 1000 °C. Since the nano-thermite reaction pathway differs greatly from bulk thermite reactions, these results are important to develop a nano-thermite platform that can be used for a novel low cost, low temperature, and copper based microjoining and advance IC packaging.     

Molten salt synthesis of LaF<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> nanoplates with tunable size and their luminescence properties

A molten salt route to LaF₃:Eu³⁺ nanoplate with tunable size was developed and the products were characterized by the X-ray diffraction (XRD), transmission electron microscopy (TEM), field-emission scanning electron microscopy (FE-SEM) and high-resolution TEM (HR-TEM). It is found that the nanoplates with different sizes (ca. 46, 20, and 12 nm) could be obtained when the molar ratio of the reagents NH₄F and La(NO₃)₃ · 6H₂O was adjusted. The possible formation process of reaction was discussed, and the reasonable mechanism of size controlling was also proposed. Furthermore, the luminescent properties of all the samples with different sizes and doping levels were investigated at room temperature.     

Room temperature chemical synthesis of lead selenide thin films with preferred orientation

Room temperature chemical synthesis of PbSe thin films was carried out from aqueous ammoniacal solution using Pb(CH₃COO)₂ as Pb²⁺ and Na₂SeSO₃ as Se²⁻ ion sources. The films were characterized by a various techniques including, X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HR-TEM), selected area electron diffraction (SAED), Fast Fourier transform (FFT) and UV-vis-NIR techniques. The study revealed that the PbSe thin film consists of preferentially oriented nanocubes with energy band gap of 0.5 eV.     

Synthesis of Fe3O4 nanoparticles without inert gas protection used as precursors of magnetic fluids

Fe₃O₄ nanoparticles were hydrothermally synthesized under continuous microwave irradiation from FeCl₃·6H₂O and FeSO₄·7H₂O aqueous solutions, using NH₄OH as precipitating reagent and N₂H₄·H₂O as oxidation-resistant reagent. The results of X-ray powder diffraction (XRD), FT–IR spectroscopy and scanning electron microscopy (SEM) measurements showed that the synthesized magnetite (Fe₃O₄) nanoparticles had an average diameter of 10 nm. The magnetic properties of the Fe₃O₄ nanoparticles were measured using a vibrating sample magnetometer (VSM), indicating that the nanoparticles possessed high saturation magnetization at room temperature. The Fe₃O₄ nanoparticles were used to prepare magnetic fluids (MFs) based on water, and the properties of the MFs were characterized by a Gouy magnetic balance, a capillary rheometer and a rotating rheometer, respectively.     

Effect of H2O chemisorption on passivation of Ge(100) surface studied by scanning tunneling microscopy

The electronic passivation of a Ge(100) surface, via the chemisorption of H₂O at room temperature (RT), and the temperature dependence of H₂O coverage were investigated using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). With a saturation H₂O dose at RT, a highly-ordered structure, due to the dissociative chemisorption of H₂O, was observed on a Ge(100) surface with a coverage of 0.85 monolayers (ML). Annealing the room temperature H₂O-dosed Ge surface to 175 °C decreased the coverage of H₂O to 0.6 ML. Further annealing at 250 °C decreased the coverage of H₂O sites to 0.15 ML, and the surface reconstruction of Ge dimers was observed over much of the surface. Annealing above 300 °C induced Ge suboxide structures, similar to the oxygen-dosed Ge surface. STS measurements confirmed that the surface dangling bond states near Fermi energy are removed by the H₂O chemisorption because the dangling bonds of Ge atoms are terminated by ―OH and ―H. The H₂O pre-dose at room temperature provides a template for the ultrathin passivation of Ge(100) surface via atomic layer deposition (ALD) at RT, since near monolayer nucleation can be obtained with a 1/2 hydroxylated and 1/2 hydrogenated Ge surface.     

Catalytic growth and characterization of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

β-Ga₂O₃ nanowires have been synthesized using Ga metal and H₂O vapor at 800 °C in the presence of Ni catalyst on the substrate. Remarkable reduction of the diameter and increase of the length of the Ga₂O₃ nanowires are achieved by separation of Ga metal and H₂O vapor before they reach the substrate. Transmission electron microscopy analyses indicate that the β-Ga₂O₃ nanowires possess a single-crystalline structure. Photoluminescence measurements show two broad emission bands centered at 290 nm and 390 nm at room temperature. Received: 27 June 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +886-6/234-4496, E-mail: wujj@mail.ncku.edu.tw     

Low temperature structural phase transition in hafnium and zirconium tetrafluoride trihydrates

From time-differential perturbed angular correlation (TDPAC) measurements, the monoclinic and triclinic crystal structures in hafnium and zirconium tetrafluoride trihydrates are found to be present simultaneously in both the compounds. From previous TDPAC and XRD investigations, a monoclinic crystal structure for HfF₄·3H₂O but, for its analogues zirconium compound, a triclinic structure was reported. Contrary to earlier reports, the triclinic fraction in HfF₄·3H₂O is found to be maximum (80%) at room temperature. In fact, the triclinic crystal structure of HfF₄·3H₂O is reported here which was not known prior to this report. In ZrF₄·3H₂O, a strong signal (80–90%) for the triclinic structure is found at room temperature while the monoclinic fraction appears as a weak signal (10–15%). Structural phase transitions in these trihydrate compounds have been observed in the temperature range 298–333 K.     

Co-doped magnetite nanowire arrays prepared hydrothermally

Ultrafine cobalt-doped magnetite Co_xFe_3-xO₄ (x=0.1,0.2) nanowire arrays were hydrothermally prepared at 200 °C using ferrous chloride (FeCl₂ · 4H₂O), cobalt chloride (CoCl₂ · 6H₂O) and sodium hydroxide (NaOH) as starting materials. X-ray diffraction (XRD) analysis indicated that these nanowires were face-centered cubic magnetite. Transmission electron microscopy (TEM) images showed that these ultrafine nanowires had self-assembled into ordered two-dimensional nanostructures. Magnetic properties of the nanostructures were measured on a Vibrating Sample Magnetometer at room temperature. PACS 75.50.Tt; 75.60.Ej; 81.07.Bc; 81.10.Dn; 81.16.Rf     

Cu1.5[Cr(CN)6]⋅6.5H2O nanoparticles: synthesis, characterization, and magnetic properties

We have synthesized nanoparticles of Cu_1.5[Cr(CN)₆]⋅6.5H₂O of varying size by using poly(vinylpyrrolidone) (PVP) as a protecting polymer. The particle size variation has been achieved by varying the amount of the PVP surfactant with the reactants. The prepared nanoparticles have been investigated by using X-ray diffraction, transmission electron microscopy, and direct-current magnetization techniques. The nanoparticles crystallize in a face centred cubic structure (space group: Fm3m). The approximate particle sizes for the three samples are 18, 9, and 5 nm, respectively. Non-PVP nanoparticles (18 nm) show a magnetic ordering temperature of 65 K. A decrease in the magnetic ordering temperature was observed with decreasing particle size. These nanoparticles are magnetically very soft, showing negligibly small values of the coercivity and remanent magnetization. The maximum magnetization and spontaneous magnetization values at 5 K are found to decrease with decreasing particle size. The observed magnetization behaviour of the nanoparticles has been attributed to the increasing surface spin disorder with decreasing particle size.