Electrochemical properties of compacts of nano-and microdisperse diamond powders in aqueous electrolytes

The electrochemical behavior of compacts of micro-and nanodisperse diamond powders were studied by using model redox K₃[Fe(CN)₆]-K₄[Fe(CN)₆] and Ce(SO₄)₂-Ce₂(SO₄)₃ systems in aqueous electrolytes. The current-voltage curves for compacts of microdisperse diamonds and the kinetics of reactions on these compacts in a solution of the [Fe(CN)₆]^3-/4- system are similar to those obtained by using a metal electrode. For nanodisperse diamonds, the same reactions are essentially irreversible.     

Laser-induced trench etching of GaAs in aqueous KOH solution

Maskless etching of n-type GaAs in a KOH aqueous solution by irradiation of an argonion laser has been investigated to obtain high etching rates and aspect-ratios of etched grooves. High etching rates of up to 805 m/s and an aspect ratio of 8 have been achieved by a single scan of a laser beam. Microprobe photoluminescence (PL), Raman scattering, and Auger electron spectroscopy (AES) measurements were carried out on the trench surface to characterize damage induced by laser wet etching.     

Crystal growth and structural properties of the spinel-type Li1 + xMn2 − xO4 (x = 0.10, 0.14)

Single crystals of the lithium-rich lithium manganese oxide spinels Li_1 + xMn_2 − xO₄ with x = 0.10 and 0.14 have been successfully synthesized in high-temperature molten chlorides at 1023 K. The single-crystal X-ray diffraction study confirmed the cubic Fd3¯m space group and the lattice parameters of a = 8.2401(9) Å for x = 0.10 and a = 8.2273(10) Å for x = 0.14 at 300 K, respectively. The crystal structures have been refined to the conventional values R = 3.7% for x = 0.10 and R = 3.1% for x = 0.14, respectively. Low-temperature single-crystal X-ray diffraction experiments revealed that these single crystal samples showed no phase transition between 100 and 300 K. The electron-density distribution images in these compounds by the single-crystal MEM analysis clearly showed strong covalent bonding features between the Mn and O atoms due to the Mn–3d and O–2p interaction.     

Effects of ultrasonic agitation and surfactant additive on surface roughness of Si (1 1 1) crystal plane in alkaline KOH solution

In the silicon wet etching process, the “pseudo-mask” formed by the hydrogen bubbles generated during the etching process is the reason causing high surface roughness and poor surface quality. Based upon the ultrasonic mechanical effect and wettability enhanced by isopropyl alcohol (IPA), ultrasonic agitation and IPA were used to improve surface quality of Si (1 1 1) crystal plane during silicon wet etching process. The surface roughness R_q is smaller than 15 nm when using ultrasonic agitation and R_q is smaller than 7 nm when using IPA. When the range of IPA concentration (mass fraction, wt%) is 5–20%, the ultrasonic frequency is 100 kHz and the ultrasound intensity is 30–50 W/L, the surface roughness R_q is smaller than 2 nm when combining ultrasonic agitation and IPA. The surface roughness R_q is equal to 1 nm when the mass fraction of IPA, ultrasound intensity and the ultrasonic frequency is 20%, 50 W and 100 kHz respectively. The experimental results indicated that the combination of ultrasonic agitation and IPA could obtain a lower surface roughness of Si (1 1 1) crystal plane in silicon wet etching process.     

High sensitive determination of theophylline based on manganese oxide nanoparticles/multiwalled carbon nanotube nanocomposite modified electrode

Ionics - In this study, the preparation of a glassy carbon electrode (GCE) modified with multiwall carbon nanotubes|MnO2 nanoparticles (MWNT|MnO2) was developed for electrocatalytic detection of...     

Electrochemical behaviour of (La1 − xSrx)sCo1 − yNiyO3 − δ as porous SOFC cathodes

This paper shows that storage at room temperature and ambient atmosphere appears to affect the polarisation resistance significantly and R_P decreased initially with storage time. This improvement was more pronounced when stored in moisturised air. The performance was, however, also found to decrease when stored for sufficiently long periods. The absolute values of the electrode response of these materials are very difficult to reproduce and the performance appears to be largely dependent on the manufacturing process of the powder or the electrode itself. In spite of this, the electrode behaviours exhibited similar patterns with respect to the dependence on T and P_O2. An increase in polarisation resistance with time at SOFC operating conditions was observed, which was related exclusively to the electrode reaction kinetics and not to oxygen concentration polarisation. It was also found to be higher when measured in moisturised air.     

Electrochemical and magnetic properties of Li4 / 3Mn2 / 3O2–LiCoO2 solid solution

The compounds Li_(4−x)/3Mn_2(1−x)/3Co_xO₂ (0 < x < 0.5) were prepared by the sol–gel technique. X-ray diffraction patterns of these compounds were identified as α-NaFeO₂ type layered structure, though some super-structure lines, related to the ordered array of Li and transition metal ions in the transition metal layer, were observed. The magnetic susceptibility exhibited an antiferromagnetic transition around 40 K for x < 0.2, however the specimens with x > 0.3 had no magnetic transition. The magnetic percolation may explain these magnetic variations. The electrochemical performances were evaluated for the compound of x = 0.5, and it was seen that the electrochemical properties were sensitive to the potential window. Additionally, it was also found that the discharge capacity strongly depended on the preparation temperature; it took a maximum value at the preparation temperature of 900 °C. The discharge capacity is sensitive not only to the cation mixing degree but also to the particle size.     

Effects of reducing agents on the electrochemical properties of the prepared manganese oxide powders

Manganese oxide powders with high specific capacitance were successfully fabricated via a simple redox reaction at room temperature. The reducing agents used for the redox reaction significantly affected the oxidation states and the electrochemical properties of the prepared manganese oxide powders. As C₂H₅OH was used as the reducing agent, high Mn³⁺ content and high amount of hydroxide were observed in the prepared manganese oxide powders. In addition, the molar ratios of KMnO₄ and C₂H₅OH also influenced the electrochemical properties of the prepared manganese oxide powders. When the molar ratio of KMnO₄ and C₂H₅OH was 1:40, the specific capacitance of the prepared manganese oxide was as high as 402 F/g. These results of the electrochemical analysis showed that, adjusting the molar ratios of KMnO₄ and C₂H₅OH demonstrated to be an effective method for controlling the electrochemical characteristics of manganese oxide powders.     

Laser-induced etching of polycrystalline Al2O3TiC in KOH aqueous solution

Laser-induced etching of polycrystalline Al₂O₃TiC material by a tightly-focused cw Ar ion laser has been investigated in a KOH solution with different concentrations. It is found that the KOH concentration can strongly affect the etching quality where low KOH concentration can result in rough and irregular patterns. Laser-induced etching of polycrystalline Al₂O₃TiC in a KOH solution is found to be a photothermal reaction in which a threshold laser power exists. With an appropriate set of etching parameters, well-defined grooves can be obtained with clean side walls and with an etching rate up to several hundred micrometers per second. The etching behavior is also found to depend on laser scanning direction. It is also found that the grains in the polycrystalline Al₂O₃TiC material play an important role in the etching dynamics and etching quality. This etching process is believed to be applicable to the formation of a slider surface of magnetic heads in the future.     

Sonochemical synthesis of amide-functionalized metal-organic framework/graphene oxide nanocomposite for the adsorption of methylene blue from aqueous solution

Graphene oxide-[Zn₂(oba)₂(bpfb)]·(DMF)₅ metal-organic framework nanocomposite (GO-TMU-23; H₂oba = 4,4′-oxybisbenzoic acid, bpfb = N,N′-bis-(4-pyridylformamide)-1,4-benzenediamine, DMF = N,N-dimethylformamide) is prepared through a simple and large-scale sonochemical preparation method at room temperature. The obtained nanocomposite is characterized by Field Emission Scanning Electron Microscopy (FE-SEM), powder X-ray diffraction (PXRD) and FT-IR spectroscopy. Additionally, the absorption ability of GO-TMU-23 nanocomposite toward cationic dye methylene blue was also performed. Significantly, GO-TMU-23 nanocomposite exhibits remarkably accelerated adsorption kinetics for methylene blue in comparison with the parent materials. The adsorption process shows that 90% of the dye has been removed and the equilibrium status has been reached in 2 min by using the nanocomposites as the adsorbent.     

Microstructure and optical properties of ZnO/porous silicon nanocomposite films

In this study, porous silicon (PS) templates were formed by electrochemical anodization on p-type (100) silicon wafer and ZnO films were deposited on PS substrates using radio frequency (RF) reactive magnetron sputtering technique. The effects of oxygen partial pressures of growth ZnO films and annealing ambience on the microstructure and photoluminescence (PL) of the ZnO/PS nanocomposite films were systematically investigated by X-ray diffraction and fluorescence spectrophotometry. The results indicated that all ZnO/PS nanocomposite films were polycrystalline in nature with a hexagonal wurtzite structure and the (002) oriented ZnO films had the best crystal quality under O₂:Ar ratio of 10:10 sccm and annealing in vacuum. PL measurements at room temperature revealed that ZnO/PS nanocomposite systems formed a broad PL band including the blue and green emissions from ZnO and red-orange emission from the PS. The mechanism and interpretation of broadband PL of the nanocomposites were discussed in detail using an oxygen-bonding model in PS and a native defects model in ZnO.     

LiMn2−xTixO4 spinel-type compounds (x ≤ 1): Structural,electrical and magnetic properties

LiMn_2−xTi_xO₄ compounds with 0 ≤ x ≤ 1 were prepared by solid state reaction and Pechini technique. Powder X-ray diffraction showed that all samples crystallize with the spinel crystal structure (S.G. Fd3¯m). The cubic unit-cell parameter increases with the Ti content. The influence of the Ti content and cationic distribution on the magnetic properties of the compounds was studied by measuring the temperature and magnetic field dependences of the magnetization: substitution by non-magnetic d⁰ Ti⁴⁺ ions appeared to weaken the magnetic interactions between the manganese ions. The electrical properties of LiMnTiO₄ were studied by AC impedance spectroscopy and DC polarisation measurements, which revealed the electronic character of the conduction process.     

Laser-induced etching of polycrystalline Al2O3TiC in KOH aqueous solution

Laser-induced etching of polycrystalline Al₂–O₃TiC material by a tightly-focused cw Ar ion laser has been investigated in a KOH solution with different concentrations. It is found that the KOH concentration can strongly affect the etching quality where low KOH concentration can result in rough and irregular patterns. Laser-induced etching of polycrystalline Al₂O₃TiC in a KOH solution is found to be a photothermal reaction in which a threshold laser power exists. With an appropriate set of etching parameters, well-defined grooves can be obtained with clean side walls and with an etching rate up to several hundred micrometers per second. The etching behavior is also found to depend on laser scanning direction. It is also found that the grains in the polycrystalline Al₂O₃TiC material play an important role in the etching dynamics and etching quality. This etching process is believed to be applicable to the formation of a slider surface of magnetic heads in the future.     

Study of carbon encapsulated iron oxide/iron carbide nanocomposite for hyperthermia

Magnetic nanocomposite has been synthesized successfully using biopolymer route which acts as a source of carbon for carbide formation. The present approach based on thermal decomposition represents a considerable advance over previous reports that often use high-energy procedures or costly and hazardous precursors. X-ray diffraction, high-resolution transmission electron microscopy and vibrating sample magnetometer have been used to characterize the composites. Multi phase formation is evident from X-ray diffraction in the as-prepared samples. Phase confirmation was further done from M (magnetization) versus T (temperature) curve indicating presence of different phases of carbide along with iron oxide. TEM study suggests formation of cuboidal shape nanocomposite using two different quenching conditions. Transmission electron microscopy also confirmed the formation of carbon layer in the vicinity of the Fe₃O₄/Fe₃C nanoparticles. The magnetic measurement shows that the composite nanoparticles exhibit a maximum magnetization of 60 emu g⁻¹ at room temperature. Biocompatibility study with three different cell lines (HeLa, MCF-7 and L929) confirms that these nanocomposites are biocompatible. Temperature versus time measurement in an AC field suggests good heating ability of the samples. These investigations indicate that these nanocomposites may be useful for bioapplications, in particular for hyperthermia.     

Preparation of Cu-Zn/ZnO core-shell nanocomposite by wire electrical explosion and precipitation process in aqueous solution and CO sensing properties

Cu-Zn/ZnO nanocomposites with a novel core-shell structure have been prepared by a surface precipitation process in aqueous solution. X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy are employed to analyze the structure and morphology of the present products. The influence of the annealing temperature on the core-shell structure of the nanocomposites is investigated, and a possible growth model is proposed. Furthermore, the gas sensors based on the Cu-Zn/ZnO nanocomposites are fabricated and tested, which exhibits high sensitivity and fast response to CO. The best results are obtained for the sensor based on the film annealed at 350 °C, which shows that the sensitivity is about 6.3 when the sensor is exposed to 100 ppm CO at the operating temperature of 240 °C. The possible sensing mechanism of the Cu-Zn/ZnO sensing film has also been discussed.     

Structural and electronic properties of the Ti/W(1 1 1) adsorption system

We present theoretical and experimental study of the structural and electronic properties of the Ti/W(1 1 1) adsorption system. Atomic arrangements of the considered surfaces and their electronic structures have been obtained from first-principles pseudopotential calculations based on the density functional theory in a plane-wave-basis implementation. The corresponding experimental data have been provided by photofield emission spectroscopy. Investigations of the clean and Ti-covered W(1 1 1) surfaces indicate substantial structural relaxations deep into the substrate, and a noticeable modification of the surface electronic properties of the system induced already by a thin film of titanium. Configuration with adatoms positioned in substrate-lattice-continuation (i.e., deep-hollow) sites is found to be energetically most favorable. A good agreement between the measured photofield emission spectra and the computed local-density-of-states distributions confirms our theoretical predictions for a clean W(1 1 1) substrate as well as Ti coverages of 0.25 and 1 ML.     

Electrochemical study of the Nd1.95NiO4 + δ/oxide electrolyte interface

Nickelate-based oxides are potential cathodes in Solid Oxide Fuel Cells operating at intermediate temperatures. The chemical compatibility between apatite electrolyte, i.e., La₉Sr₁Si₆O_26.5, and Nd-deficient nickelate, i.e., Nd_1.95NiO_4 + δ, has been characterized. The equilibrium between the nickelate material and the gas phase has been studied as functions of temperature and oxygen partial pressure, using potentiometric measurements with microelectrodes, i.e., metallic or ceramic point electrodes. Two solid electrolytes were used, i.e., apatite and yttria-stabilized zirconia. The response of the nickelate is discussed in terms of oxygen stoichiometry.     

Optoelectronic properties of Cu1−xPtxFeO2 (0 ≤ x ≤ 0.05) delafossite for p-type transparent conducting oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite have been synthesized by solid-state reaction method to investigate their optical and electrical properties. The properties of electrical resistivity and Seebeck coefficient were measured in the high temperature ranging from 300 to 960 K, and the Hall effect and the optical properties were measured at room temperature. The obtained results of Seebeck showed the samples are p-type conductor. The optical properties at room temperature exhibited the samples are transparent visible light material with optical direct gap 3.45 eV. The low electrical resistivity, hole mobility and carrier density at room temperature displayed value ranging from 0.29 to 0.08 Ω cm, 1.8 to 8.6 cm²/V s and 1.56 × 10¹⁸ to 4.04 × 10¹⁹ cm⁻³, respectively. The temperature range for transparent visible light is below 820 K because the direct energy gap contains value above 3.1 eV. Consequently, the Cu_1−xPt_xFeO₂ delafossite enhance performance for materials of p-type transparent conducting oxide (TCO) with low electrical resistivity.