An investigation of the growth of nickel ferrite films on magnesium oxide substrates

Nickel ferrite films have been prepared by chemical vapour deposition and by the oxidation of sputtered and vacuum deposited films at high temperature. The interaction of magnesium oxide substrates with these films has been investigated using a wide range of electron optical techniques. Considerable interdiffusion is observed, which is likely to alter the magnetic properties of these films.     

Planar Hall effect of indium antimonide thin film on silicon and nickel–zinc ferrite substrates

We have investigated Hall and planar Hall (PH) effect of indium antimonide (InSb) films thermally evaporated on two different substrates including Si and soft magnetic Ni–Zn ferrite. Polycrystalline InSb film with an average grain size of 1.2 μm shows substantial electron mobility of 6,700 cm²/Vs for Si and 5,680 cm²/Vs for Ni–Zn ferrite substrates respectively. Four-point bridge type Hall bar of InSb was fabricated using photolithography followed by chemical wet etch. An abrupt change in PH deviated from a normal PH curve was found on a ferrite substrate within a low field range of −50 to 50 Oe while no change happens on the Si substrate. Sharp PH curve immediately returns to the ordinary PH curve when applied field goes over −50 to 50 Oe without leaving any hysteresis of resistance. This is mainly attributed to the presence of the Bloch wall of Ni–Zn ferrite underneath InSb Hall bar. Intragranular domain wall movement is believed to be a prime source of the anomalous PH behavior in the low field range. The linear field dependence of PH in a resolution of 10 mΩ/Oe is sensitive high enough to be used as low-field magnetic sensors.     

Cavity growth in neutron-irradiated magnesium oxide

The growth of cuboidal cavities in neutron-irradiated magnesium oxide after annealing in the temperature range 1475 to 1775° C has been followed using the techniques of transmission electron microscopy and electron spin resonance. Microscopic examination has shown that, while cavities are nucleated on annealing at about 1500° C, most of their growth does not occur until a temperature approaching 1625° C is exceeded. Electron spin resonance spectra from the same samples annealed in the temperature range 1475 to 1575° C indicate that some of the vacancies, which are released to the lattice when cavities are nucleated, are used in the formation, from iron present at impurity level in the crystals, of Fe³⁺ in octahedral symmetry at magnesium sites. This corresponds to the region of negligible cavity growth. For annealing treatments at and above 1625° C however, the fractional volume of crystal occupied by cavities increases by a factor of ten and simultaneously the octahedral symmetry Fe³⁺ transitions disappear. The role of iron in controlling vacancy movement and cavity growth is discussed.     

Correlation of electrolyte-derived inclusions to crystallization in the early stage of anodic oxide film growth on titanium

Pure titanium has been subjected to anodization in sulfuric and phosphoric acid. For a better understanding of the oxide growth and properties of the final film, with a particular interest focused on the solution anions in the early stage of crystallization, microstructural analyses (Raman, Transmission Electron Microscopy [TEM]) of the oxide films were correlated to chemical depth profiling by glow discharge optical emission spectroscopy (GDOES).Raman spectroscopy shows that crystallization of the oxide films starts at potentials as low as 10-20 V. The onset of crystallization and the ongoing increase in crystallinity with increasing anodization potentials had already earlier been correlated to ac-impedance measurements [Jaeggi et al., Surf. Interface Anal. 38 (2006) 182]. TEM observations show a clear difference in the early phase of crystallization between oxides grown in 1 M sulfuric acid compared to 1 M phosphoric acid. Moreover, independent of electrolyte type, nano-sized pores from oxygen bubbles formation were revealed in the central part of the films. Until now, oxygen bubbles inside an anodically grown oxide have not been observed before without the presence of crystalline regions nearby. A growth model is proposed, in which the different starting locations of crystallization inside the films are correlated to the presence of the acid anions as residues in the film, as found by GDOES chemical depth-profiling.     

Observations on the mechanical properties of nickel oxide scales

The mechanical properties of NiO scales produced by the complete oxidation of high-purity (grade-1) Ni and commercial-purity (grade-A) Ni have been investigated at 700 to 1000 C. The modulus of elasticity of both grades of oxide decreased with increasing temperature, whereas the modulus of rupture for grade-A oxide exhibited a maximum at 850 C and that for grade-1 oxide decreased with increasing temperature. At 700 C, elastic deformation to fracture occurred with both oxides, whereas, at temperatures 850 C, plasticity was also observed. The plasticity of grade-1 oxide was 3 times greater than that of grade-A oxide.Creep behaviour of the oxides was studied at 900 and 1000 C. Primary and secondary creep was observed and, in both oxides, the creep rates increased with increasing temperature and load. The creep rate of grade-1 oxide was 10 to 20 times greater than that for grade-A oxide.     

Magnetodielectric composite with ferrite inclusions as substrates for microstrip patch antennas at microwave frequencies

A study has been conducted to estimate the complex permittivity and permeability along with magnetic characterization of different volume fractions of magnetodielectric composites with cobalt ferrite nano inclusions. Using an in touch superstrate technique dielectric properties are estimated. Cavity perturbation technique is used to study the complex permeability of the samples. 4πM_s value and coercivity is measured using vibrating sample magnetometry. Structural and surface morphologies on the composite samples are conducted to determine the size and homogeneous distribution of nano inclusions. The average grain size of cobalt ferrite nanoparticles is found to be ～10 nm. The real part of permittivity and permeability of the samples varies from ～1–2.905 to ～1.01–1.05 with increase in inclusion content from 1% VF to 5% VF, respectively. The tan δ of permittivity and imaginary part of permeability is found to be of the order of ～10^?3 and ～10^?1 respectively. Verification of these composites as potential substrates for microstrip patch antenna is carried out by fabricating simple rectangular patch at 9.5 GHz using transmission line model. Rectangular patch is designed on 5% VF composite system. The return loss for the composite system was found to be ～?19.451 dB which is comparable with that designed on standard glass epoxy substrate (?_r = 4.5).     

Liquid phase epitaxial growth of indium substituted magnesium ferrite films

Single crystal films of Mg(Fe,In)₂O₄ have been grown by means of liquid-phase-epitaxy on (100)/1bMgO substrates using a PbO/1bB₂O₃/1bFe₂O₃ solvent. The final polishing of the substrates appeared to be very important in connection with the necessary large supersaturation of the flux. Electron microprobe analysis revealed Pt and high Pb contents in our films. The easy axis of magnetization is in-plane, probably due to the compressive strain of the films caused by the difference in thermal expansion of MgO and Mg(Fe,In)₂O₄.     

'Spalling' of SAC Pb free solders when used with nickel substrates

Abstract

The term "spalling" refers to the formation in a solder joint of a second layer of intermetallic compound, in addition to and separate from the usual single layer that normally forms on the substrate. It has been observed in Pb-free solders of the SAC type when used in conjunction with a nickel finish. Explanations offered to account for this phenomenon have been based on thermodynamic phase equilibria observed in isothermal sections of the Sn corner of the Cu–Ni–Sn system at temperatures 20°C or more above the solidification temperature of the solder, and without regard to reactions that occur at low temperatures, during freezing. Recent measurement of the liquidus projection of the Sn corner of the Cu–Ni–Sn system as shown the occurrence of a ternary quasiperitectic reaction in the composition range in which "spalling" is observed. Evaluation of the effect of this quasiperitectic reaction shows that its operation during freezing of the solder can account for the "spalling" phenomenon.     

Gas-sensing properties of spin-coated indium oxide film on various substrates

Indium oxide thin films were spin-coated uniformly on alumina and silicon substrates with different roughness for the fabrication of gas-sensing films by a novel method of aqueous acetic acid solution dissolving ln( and ammonium carboxymethyl cellulose. The effects of material properties and surface morphologies of the substrate on film formation and gas-sensing properties of the spin-coated films were studied for various kinds of substrates. Gas-sensing properties including sensitivity, selectivity and the rates of response and recovery were found to be strongly dependent on the kind of substrate and the surface roughness of the substrate as well as film thickness and operating temperature.     

Degradation of the electrochromic nickel oxide film upon redox cycling

The degradation mechanism of electrochromic nickel oxide films by redox cycles was investigated. Films fabricated by sputtering of an oxide target were driven between the colored (oxidized) and bleached (reduced) states in 1 M KOH solution. With the cycles, the transmittance of the colored state decreased. While the peak potential of the redox became larger at first and then became smaller, the response time became rapid at first and slower afterward. The surface of heavily degraded films became uneven and easy to be removed. A higher oxidation voltage caused faster degradation. Heat treatment during deposition or making a film thicker was shown to affect durability.     

Coupled morphological and thin film instabilities generated by inclusions in crystal growth

The interaction of a foreign particle that is suspended in the melt with a planar solidifying interface may induce the onset of morphological instabilities provided that its distance from the interface falls below a critical value. This distance, which is of the order of the particle’s radius, depends on the governing processing and physical parameters. When the particle is in nearcontact with the solid-liquid interface, the disjoining pressure in the melt film that separates the particle from the interface influences the interaction. We derive an expression for the film thickness at which rupture occurs. The critical film thickness, which depicts the competition between the stabilizing influence of surface tension and thermal gradients and the destabilizing influence of the intermolecular forces, varies as (Sh)^1/4, where Sh is the Scheludko number that is modifed by the imposed thermal gradients. We note the existence of a critical value for the particle’s radius below which the stabilizing effects are primarily due to surface tension and above which they are due to the thermal gradients.     

Surface acoustic waves in thin films of barium strontium titanate on magnesium oxide substrates

It is established that, using a thin barium strontium titanate (BST) film as the active element in a surface acoustic wave (SAW) device, it possible to double the working frequency of the converter due to the formation of a periodic domain structure in the BST film. A thin ferroelectric film device with a standard electrode structure is capable of effectively exciting the SAW second harmonic. Variation of the external polarizing voltage applied to the electrodes ensures field-controlled electromechanical feedback in the converter.     

Kinetics of oxide film growth during laser heating

The kinetics of oxidation of the surface of a copper target in air by CO₂ laser radiation are examined with consideration of the thermodiffusion and thermoemf mechanisms.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 58, No. 3, pp. 389–392, March, 1990.