Copper Nanoparticles Prepared fromOxalic Precursors

The synthesis of nanoparticles of copper metal via a soft chemistry route is presented in this paper. The method is based on the thermal decomposition under nitrogen or hydrogen of oxalic precursors with a well-controlled morphology and particle size. The precipitation of the copper oxalates in a water-alcohol medium allows the submicron size of the precursor grains to be controlled and, consequently, the nanometric size of the metallic copper particles to be determined, as required, between 3.5 and 40 nm. The majority of the final particles are made of pure copper metal although some present a superficial layer of cuprous oxide (Cu2O)

Nanocomposite Fe1xO=Fe3O4, Fe=Fe1xO thin films prepared by RF sputtering and revealed by magnetic coupling effects

Magnetic and semi-conducting nanocomposite iron oxide thin films have been prepared under bias polarization, by radio-frequency sputtering of a magnetite target. The nature of the phases obtained in the thin films depends on the bias power density. The increase in power density, from 0 to 110mW=cm2, allows the preparation of magnetite, magnetite/wustite and wustite/a-iron nanocomposites successively. Magnetic measurements at low temperature show exchange bias for two-phases films even though the minor phase is not detected by grazing angle X-ray diffraction. The exchange bias can reach very high values of about 4300 Oe. Electrical properties at room temperature are interpreted taking into account both the modifications of the film compactness, and the nature of the phases from which they are made

Thin films preparation by rf-sputtering of copper/iron ceramic targets with Cu/Fe=1: From nanocomposites to delafossite compounds

In the Cu–Fe–O phase diagram, delafossite CuFeO2 is obtained for the CuI oxidation state and for the Cu/Fe=1 ratio. By decreasing the oxygen content, copper/spinel oxide composite can be obtained because of the reduction and the disproponation of cuprous ions. Many physical properties as for instance, electrical, optical, catalytic properties can then be affected by the control of the oxygen stoichiometry. In rf-sputtering technique, the bombardment energies on the substrate can be controlled by the deposition conditions leading to different oxygen stoichiometry in the growing layers. By this technique, thin films have been prepared from two ceramic targets: CuFeO2 and CuO+CuFe2O4. We thus synthesized either Cu0/ CuxFe1−xO4 nanocomposites thin films with various Cu0 quantities or CuFeO2-based thin films. Two-probes conductivity measurements were permitted to comparatively evaluate the Cu0 content, while optical microscopy evidenced a selfassembly phenomenon during thermal annealing

Nanostructured cobalt manganese ferrite thin films for gas sensor application

Ferrite compounds are very important because of their optical, electrical or magnetic properties. Moreover, many papers relate to their development as possible gas sensor. In this study, we were interested in using cobalt-manganese-ferrite as sensitive layer for CO2 sensor devices. Such an application required a high surface activity, and consequently a small crystallite size and a large surface area. The physical vapor deposition (RF-sputtering) is widely used for thin film synthesis. In this work, porous thin films were obtained from a Co1Mn0.65Fe1 3504 target sputtered under pure argon plasma, by optimizing the deposition parameters (gas pressure, power). The deposition time was adjusted in order to obtain an average thickness of 300 nm. Structural (G-XRD) and microstructural (SEM-FEG, gas adsorption, electron microprobe) analyses were carried out on these thin films. The chemical composition was found to be homogeneous on the whole surface of the samples. The grain size ranged from 10 to 25 nm. The surface enhancement factor (SEF) was about 100 m2/m2, which is equivalent to a specific surface area of 76 m2/g for the ferrite layer. In conclusion, these nanostructured cobalt-manganese-ferrite films appear to be quite suitable for an application as gas sensors

Patterned ferrimagnetic thin films of spinel ferrites obtained directly by laser irradiation

Some spinel ferrites can be oxidized or transformed at moderate temperatures. Such modifications werecarried out on thin films of mixed cobalt copper ferrites and maghemite, by heating small regions with alow-power laser spot applied for about 100 ns. The very simple laser heating process, which can be donedirectly with a conventional photolithographic machine, made it possible to generate two-dimensionalmagnetization heterogeneities in ferrimagnetic films. Such periodic structures could display the specificproperties of magneto-photonic or magnonic crystals

Magnetic and semi-conducting nano-composite films of spinel ferrite and cubic zinc oxide

Magnetic and semi-conducting nano-composite films have been prepared under bias polarization, by radio-frequency sputtering of a pure zinc ferrite target. These composite thin films are made of cubic Zn1 − yFeyO monoxide islands inside a spinel ferrite matrix. The relative proportion of each phase depends on the substrate polarization (i.e. bias power). When no bias is applied the films solely display the diffraction pattern of a spinel phase even if some islands inside the film can be observed by electron microscopy. When the bias power is increased, the spinel phase disappears progressively as enhanced formation of islands takes place in such a manner that the cubic Zn1 − yFeyO monoxide is solely revealed by X-ray diffraction for a bias power higher than 5 W. From bibliographical data and calculated phase diagrams, it can be inferred that these phases would require very low oxygen partial pressure, high temperature and mechanical pressure, to be obtained simultaneously by a conventional ceramic process. This underlines the strong potential of radio-frequency sputtering of oxide targets to prepare original oxides or composite materials

Thermochemistry of iron manganese oxide spinels

Oxide melt solution calorimetry has been performed on iron manganese oxide spinels prepared at high temperature. The enthalpy of formation of (MnxFe1−x)3O4 at 298 K from the oxides, tetragonal Mn3O4 (hausmannite) and cubic Fe3O4 (magnetite), is negative from x=0 to x=0.67 and becomes slightly positive for 0.670.6) spinels of intermediate compositions. The enthalpies of formation are discussed in terms of three factors: oxidation–reduction relative to the end-members, cation distribution, and tetragonality. A combination of measured enthalpies and Gibbs free energies of formation in the literature provides entropies of mixing. ΔSmix, consistent with a cation distribution in which all trivalent manganese is octahedral and all other ions are randomly distributed for x>0.5, but the entropy of mixing appears to be smaller than these predicted values for x<0.4

CO2 sensing properties of semiconducting copper oxide and spinel ferrite nanocomposite thin film

A new active layer for CO2 sensing based on semiconducting CuO–CuxFe3−xO4 (with 0 ≤ x ≤ 1) nanocomposite was prepared by radiofrequency sputtering from a delafossite CuFeO2 target using a specific in situ reduction method followed by post annealing treatment in air. The tenorite–spinel ferrite nanocomposite layer was deposited on a simplified test device and the response in a carbon dioxide atmosphere was measured by varying the concentration up to 5000 ppm, at different working temperatures (130–475 °C) and frequencies (0.5–250 kHz). The results showed a high response of 50% (Rair/RCO2=1.9) at 250 °C and 700 Hz for a CO2 concentration of 5000 ppm

Preparation and electrical properties of dense micro-cermets made of nickel ferrite and metallic copper

Dense micro-cermets made of nickel ferrites and copper micrometric particles were obtained from partial reduction under hydrogenated atmosphere at 350 C of mixed copper nickel ferrites, and sintering in nitrogen at 980 C. The small copper particles are homogeneous in size and well dispersed in the spinel oxide matrix. No exudation of copper metal was observed after sintering. The micro-cermets prepared are semi-conducting materials with electrical conductivity lying from 44 to 130 S/cm at 980 C. Their overall characteristics make them interesting for inert anodes dedicated to aluminium electrolysis in melted cryolite

Nanoenergetic Materials for MEMS: A Review

New energetic materials (EMs) are the key to great advances in microscale energy-demanding systems as actuation part, igniter, propulsion unit, and power. Nanoscale EMs (nEMs)particularly offer the promise of much higher energy densities, faster rate of energy release, greater stability, and more security sensitivity to unwanted initiation). nEMs could therefore give response to microenergetics challenges. This paper provides a comprehensive review of current research activities in nEMs for microenergetics application. While thermodynamic calculations of flame temperature and reaction enthalpies are tools to choose desirable EMs, they are not sufficient for the choice of good material for microscale application where thermal losses are very penalizing. A strategy to select nEM is therefore proposed based on an analysis of the material diffusivity and heat of reaction. Finally, after a description of the different nEMs synthesis approaches, some guidelines for future investigations are provided