J.C. Joubert

Characterization of piezoelectric properties of zinc oxide thin films deposited on silicon for sensors applications

Abstract This paper reports the piezoelectric properties of zinc oxide thin films deposited on silicon wafers by a modified CVD technique based on the pyrolysis of an ultrasonic-generated aerosol. The aerosol was obtained from an organic solvent containing dissolved organometallic precursors. Direct measurement of the piezoelectric effect, as well as electromechanical resonance observations, were achieved on small beams. The coupling factor, k , of the layers reached a value of 0.09, which is comparable with the single crystal value.

Preparation of thin films in the system γFe 2 O 3 - Fe 3 O 4 for recording media by spray pyrolysis of organometallic solutions using an ultrasonic pump

Thin films of magnetic spinel iron oxides were prepared by pyrolysis of an ultrasonically generated aerosol of organometallic compounds. The bases of the method and experimental procedure are described. Polycrystalline films of good adherence and homogeneity were obtained. Lattice parameters were observed to be modified by film substrate strain interaction and to depend strongly on the hydrogen content. The oxidation state of iron was discussed in regard to the experimental growing conditions. Corresponding magnetic properties were investigated. Pure magnetite Fe 3 O 4 films with H_{c} = 400 Oe and M_{s} = 400 EMU/cm3and gamma ferric oxides films with H_{c} = 400 Oe and M_{s} = 250 EMU/cm3have been obtained without post deposition heat treatment. Annealing magnetite films in air resulted in a considerable increase of their coercivity (up to 800 Oe).

New mixed oxides as thin film transparent electrodes: Spinel phase CdIn2O4

Abstract New ternary oxides have been studied for use as transparent and conducting films. Thin films of single-phase CdIn2O4 were coated onto glass substrates by the ultrasonic spraying of an aerosol. A resistivity as low as 3.7 × 10 −6 Ω m was achieved for a sample of thickness about 320 nm ( R□ = 11.5 Ω ). The optical properties were investigated and the films have a transmittance of 80% in the visible (taking into account the glass substrate) and a reflectance of 72% at 2.4 microm in the IR. These properties were obtained without post-deposition heat treatment. The change in the electrical and optical properties with the deposition parameters were studied. All the properties are referred to the highly crystalline spinel phase obtained at Ts > 673 K.

Synthesis and magnetic properties of SrZn2-W type hexagonal ferrites using a partial 2Zn2+ → Li+Fe3+ substitution: a new series of permanent magnets materials

Abstract The W-type, SrZn 2 Fe 16 O 27 (SrZn 2 -W), hexagonal ferrite powders using a partial 2Zn 2+ → Li + Fe 3+ substitution for the zinc cations have been prepared, for the first time, by standard ceramic methods. Such a substitution of lithium, according to the Sr[Zn 2(1− x ) (LiFe) x ]Fe 16 O 27 series, gradually increases the saturation magnetization ( M s ), as large as M s ≈ 91 emu/g obtained at room temperature, for a sample with x ≈ 0.5 and sintered at T s ≈ 1100° C for 15 h. Also it favors the formation of W-type ferrite in the reaction by reducing the sintering temperature and the synthesis appears less stringent to atmosphere or calcining times. The product, however, comprises characteristically rather low intrinsic coercivity ( H c ) which can be varied in a wide range from 3530 to 1260 Oe, depending on the amounts of lithium ( x ) used in the series. Grain sizes are utmost under 1 μm. The critical size for the single domain particles was calculated to be 1 μm by using the theory of Kittel. Thus there are several reasons to believe that the decreasing coercivity ( H c H a ) subject to the substitution of lithium in the Sr[Zn 2(1− x ) (LiFe) x ]Fe 16 O 27 ferrites . Moreover, the H c decreases rapidly to about zero in by increasing the grain size over 1 μm (by sintering the samples at reasonably higher T s ≥1200°C for several hours) as solely governed by for the mechanism of multidomain nucleation formation. We also propose a model, for the distribution of the lithium through the probable sublattice sites (octahedral), which satisfactorily accounts for the variation of M s with the substitution of lithium in the ferrite series and the M s we calculated using a collinear Gorters model.

New spray pyrolysis deposition and magnetic properties of ferrite thin films for microwave applications

Abstract For microwave applications we report a new spray technique based on the pyrolysis of an ultrasonic generated aerosol. Thin films of garnet and spinel ferrites (Y 3 Fe 5 O 12 , LiFe 5 O 8 , Ni 1− x Zn x Fe 2 O 4 ) are grown. The magnetic properties are discussed with respect to the experimental conditions.

High Tc superconducting films prepared by pyrolysis of an ultrasonic-generated aerosol☆

Abstract Thin films of YBa2Cu3O7 − x superconductors have been prepared using a new spray technique based on the pyrolysis of an ultrasonic-generated aerosol containing the YBaCu precursors. This deposition technique leads to a better quality of the film surface compared with the conventional spray techniques and allows accurate control of the film thickness. Films of about 0.2–1 μm in thickness have been annealed in air successively at 500 and 950 °C and then slowly cooled in oxygen to 200 °C. This method leads to well-crystallized YBa2Cu3O7 − x films with good grain size homogeneity and a texture in the 001 direction depending on the heat treatment conditions. SrTiO3, yttrium stabilized ZrO2 or MgO single crystals and ceramics have been used as substrates. In this paper we discuss the influence of experimental conditions and substrates on the microstructure, morphology and superconducting properties of the films.

High Tc superconducting films obtained by pyrolysis of an ultrasonically deposited gel

YBa2Cu3O7−x superconducting thin films have been prepared using a technique based on the pyrolysis of an ultrasonically deposited gel containing the Y-Ba-Cu precursors. This technique allows us to control accurately the film thickness and surface homogeneity. MgO single crystals have been used as substrates. Films about 0.2–10 μm in thickness have been annealed in air at 500°C, heated in oxygen at temperatures ranging from 850 to 1000°C and then slowly cooled in oxygen to room temperature. This method leads to well-crystallized YBa2Cu3O7−x films with a grain size and a texture in the 001 direction depending on the heat treatment conditions. X-ray diffraction, scanning electron microscopy and resistivity measurements are presented in this paper and discussed as a function of the film thickness and experimental conditions.

γFe 2 O 3 films with uniaxial anisotropy obtained by a new assisted CVD technic

Pyrolysis of an ultrasonic generated aerosol has been used for growing thin oxides films (2000 to 8000 A), in the system γFe 2 O 3 - Fe 3 O 4 . Polycrystalline films with good adherence and homogeneity were obtained on glass substrates. The cubic lattice parameter was observed to be sensitive to impurities and to the film-substrate strain interaction. The oxidation state of iron was discussed in regard to the experimental growing conditions and the corresponding magnetic properties were investigated. Partially oxidized Fe 3 O 4 films and pure γ Fe 2 O 3 films both with a magnetization of 400 emu/cc and a coercivity of 400 Oe have been obtained. Controling the oxidation degree of the spinel phase by a post deposition heat treatment allowed us to prepare films with a coercivity ranging from 400 to 1000 Oe. Values as high as 2000 Oe were even obtained by doping the thin films with a few percent of cobalt.

Growth of garnet thin films for magneto-optic memories by pyrosol CVD process

A description is given of the deposition of garnet thin films for magnetooptic memories. The deposition technique (pyrosol process) is based on the pyrolysis of an ultrasonic generated aerosol, which contains the dissolved organometallic precursors. Films have been deposited at temperatures ranging from 520 degrees to 600 degrees C. Y/sub 3/Fe/sub 5/O/sub 12/ polycrystalline thin films with good crystallinity were obtained on glass or fused quartz substrates after annealing the deposited films. Single-crystal thin films were grown by epitaxy on GGG single-crystal wafers as shown by grazing X-ray diffraction and Kikuchi experiments. Magnetic and magnetooptic properties of the films were very close to the bulk material properties. >

Garnet thin film deposited by a new chemical vapour deposition

Abstract For magneto-optical information storage applications we report on the deposition of yttrium-iron-garnet (YIG) thin films by an original deposition process using the pyrolysis of an aerosol produced by ultrasonic spraying (Pyrosol process). The compositions of the films are discussed with regard to the experimental conditions. As-deposited layers were amorphous. After annealing at 700 °C in air, epitaxial YIG layers are obtained on gadolinium-gallium-garnet single crystal and high-quality polycrystalline films on fused quartz. The magnetic and magneto-optical properties of these films are studied.