Diffusion research between Ni3Al coating and titanium alloy produced by plasma spraying process

A Ni₃Al coating was prepared by plasma spraying technique on the surface of titanium alloy. Ni-Al mixed powders, coatings and reaction products were investigated by scanning electron microscope, EDS, DSC and XRD. A tight bonding between the coating and the substrate was formed. The X-ray diffraction analysis of the patterns showed that the coating not only had Ni₃Al phase, but also had NiO and Al₂O₃ phase microcontent. Comparing Ni coated Al to Ni₃Al at 900 °C, the diffusion was stronger and the diffusion layer was thicker. A minute pore structure was formed at 1200 °C in the front edge of solid-state reaction layer. So Ni₃Al restrained the solid-state reaction of the coating with the substrate, and as a whole weakened the entry of oxygen atoms into the substrate and quenched the out-diffusion of titanium.     

Synthesis and characterization of room-temperature ferromagnetism in Fe- and Ni-co-doped In2O3

Observation of room-temperature ferromagnetism in Fe- and Ni-co-doped In₂O₃ samples (In_0.9Fe_0.1−xNi_x)₂O₃ (0?x?0.1) prepared by citric acid sol-gel auto-igniting method is reported. All of the samples with intermediate x values are ferromagnetic at room-temperature. The highest saturation magnetization (0.453 μ_B/Fe+Ni ions) moment is reached in the sample with x=0.04. The highest solubility of Fe and Ni ions in the In₂O₃ lattice is around 10 and 4 at%, respectively. The 10 at% Fe-doped sample is found to be weakly ferromagnetic, while the 10 at% Ni-doped sample is paramagnetic. Extensive structure including Extended X-ray absorption fine structure (EXAFS), magnetic and magneto-transport including Hall effects studies on the samples indicate the observed ferromagnetism is intrinsic rather than from the secondary impurity phases.     

Spectroscopic characterization of Ni films on sub-10-nm silica layers: Thermal metamorphosis and chemical bonding

The thermal evolution in the chemical and physical characteristics of the Ni film of thickness 1-50 nm deposited on silica of thickness less than 10 nm was studied. The chemical composition of silica affected the thermal behavior of the Ni overlayer substantially. Nickel deposited on native oxide may diffuse downward into native oxide during annealing and was oxidized. It mainly produced Ni₃O₂ and silicides below 150 °C. Increasing the temperature to 300 °C caused further oxidation of Ni to yield NiO. The sub-10-nm silicon dioxide layer, on the other hand, can inhibit the diffusion of Ni atoms downward when the Ni-deposited sample was annealed. Instead, these atoms aggregated into small particles on the surface at elevated temperatures, causing the substrate to be exposed. The size of the particles produced can be controlled, as it increased almost linearly with the thickness of the Ni film deposited in the low thickness regime. The thinner Ni films yielded smaller, round nanoparticles with better dispersity. The particles formed were strongly adhered to the silicon dioxide surface. The bulk of the particles formed was mainly metallic. Exposing to the air of the Ni particles formed on silicon dioxide mainly produces Ni₂O₃ on the particles.     

Preparation and characterization of NiFe2O4/NiO composite film via a single-source precursor route

NiFe₂O₄/NiO nanocomposite thin films have been successfully prepared through a facile route using nickel iron layered double hydroxide (NiFe-LDH) as a single-source precursor. This synthetic approach mainly involves the formation of NiFe-LDH film by casting the slurry of NiFe-LDH precursor on the α-Al₂O₃ substrate, followed by high-temperature calcination. The composition, microstructure and properties of the films were characterized in detail by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and vibrating sample magnetometer (VSM). The results indicate that NiFe₂O₄/NiO composite film was composed of granules with diameter less than 100 nm, and the thickness of the film was in the range 1-2 μm. The magnetization of the film can be tuned by alternating the Ni/Fe molar ratio of LDH precursor. In addition, the method developed should be easily extended to fabricate other MFe₂O₄/MO composite film systems with specific applications just by an appropriate combination of divalent/trivalent composition in the precursor of LDHs.     

Effect of substrate temperature on the surface and interface oxidation of NiTi thin films

NiTi shape memory alloy thin films are deposited on pure Cu substrate at substrate ambient temperatures of 300 °C and 450 °C. The surface and interface oxidation of NiTi thin films are characterized by X-ray photoelectron spectroscopy (XPS). After a subsequent annealing treatment the crystallization behavior of the films deposited on substrate at different temperatures is studied by X-ray diffraction (XRD). The effects of substrate temperature on the surface and interface oxidation of NiTi thin films are investigated. In the film surface this is an oxide layer composed of TiO₂. The Ni atom has not been detected on surface. In the film/substrate interface there is an oxide layer with a mixture Ti₂O₃ and NiO in the films deposited at substrate temperatures 300 °C and 450 °C. In the films deposited at ambient temperature, the interface layer contains Ti suboxides (TiO) and metallic Ni.     

Magnetic properties in Fe-doped NiO synthesized by co-precipitation

The magnetic properties of 1.5 at% Fe-doped NiO bulk samples were investigated. The samples were prepared by sintering the corresponding precursor in air at temperatures between 400 and 800 °C for 6 h. The synthesis was by a chemical co-precipitation and post-thermal decomposition method. In order to allow a comparison, a NiO/0.76 at% NiFe₂O₄ mixture was also prepared. The X-ray diffraction pattern shows that the samples that were sintered at 400 and 600 °C remain single phase. As the sintering temperature increased to 800 °C, however, the sample becomes a mixture of NiO and NiFe₂O₄ ferrite phases. The samples were investigated by measuring their magnetization as a function of magnetic field. The samples sintered between 400 and 800 °C and the one mixed directly with NiFe₂O₄ nanoparticles show a coercivity value of H_c≈200, 325, 350 and 110 Oe, respectively. The magnetic properties of the samples depend strongly on the sintering temperature. Simultaneously, the field-cooling hysteresis loop shift also observed after cooling the sample sintered at 600 °C to low temperature suggests the possibility of the existence of a ferromagnetic/antiferromagnetic exchange coupling.     

Growth and characterization of Y2O3 thin films

Y₂O₃ thin films were grown on silicon (1 0 0) substrates by pulsed-laser deposition at different substrate temperatures and O₂ pressures. The structure and composition of films are studied by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Y₂O₃ thin films deposited in vacuum strongly oriented their [1 1 1] axis of the cubic structure and the film quality depended on the substrate temperature. The magnitude of O₂ pressure obviously influences the film structure and quality. Due to the silicon diffusion and interface reaction during the deposition, yttrium silicate and SiO₂ were formed. The strong relationship between composition and growth condition was discussed.     

Synthesis of In-doped Ga2O3 zigzag-shaped nanowires and optical properties

In-doped Ga₂O₃ zigzag-shaped nanowires and undoped Ga₂O₃ nanowires have been synthesized on Si substrate by thermal evaporation of mixed powders of Ga, In₂O₃ and graphite at 1000 °C without using any catalyst via a vapor-solid growth mechanism. The morphologies and microstructures of the products were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and photoluminescence spectroscopy (PL). The nanowires range from 100 nm to several hundreds of nanometers in diameter and several tens of micrometers in length. A broad emission band from 400 to 700 nm is obtained in the PL spectrum of these nanowires at room temperature. There are two blue-emission peaks centering at 450 and 500 nm, which originate from the oxygen vacancies, gallium vacancies and gallium-oxygen vacancy pairs.     

Tailoring the exchange bias of Ni/NiO nanogranular samples by the structure control

The exchange bias (EB) effect has been studied in Ni/NiO nanogranular samples obtained by annealing in H₂, at selected temperatures (200≤T_ann≤300 °C), NiO powder previously milled for 5, 10, 20 and 30 h. Both the as-milled NiO powders and the Ni/NiO samples have been analyzed by X-ray diffraction and the exchange bias properties have been investigated in the 5-200 K temperature range. The structure and the composition of the Ni/NiO samples can be satisfactorily controlled during the synthesis procedure by varying both T_ann and the milling time of the precursor NiO powders. In particular, by increasing this last parameter, the mean grain size of the NiO phase reduces down to the final value of 16 nm and the microstrain increases, which is consistent with an enhancement of the structural disorder. The structure of the milled NiO matrix strongly affects the process of nucleation and growth of the Ni nanocrystallites induced by the H₂ treatments, so that, T_ann being equal, the amount and the mean grain size D_Ni of the Ni phase vary substantially in samples having different milling times. Such features of the Ni phase determine the extent of the Ni/NiO interface and consequently the magnitude of the exchange field H_ex: the highest value (∼940 Oe) has been measured at T=5 K in a sample containing ∼7 wt% Ni and with D_Ni=19 nm. However, in Ni/NiO samples with very different structural characteristics and different values of H_ex at T=5 K, the EB effect vanishes at the same temperature (∼200 K) and the same thermal dependence of H_ex is observed. We consider that the evolution of the EB effect with temperature is ultimately determined by the microstructure of the Ni/NiO interface, which cannot be substantially modified by changing the synthesis parameters, milling time and T_ann.     

Characterization of interface between CuInSe2 and In2O3

CuInSe₂/In₂O₃ structures were formed by depositing CuInSe₂ films by stepwise flash evaporation onto In₂O₃ films, which were grown by DC reactive sputtering of In target in presence of (Ar+O₂) gas mixture. Phase purity of the CuInSe₂ and In₂O₃ films was confirmed by Transmission Electron Microscopy (TEM) studies. X-ray diffraction (XRD) results on CuInSe₂/In₂O₃/glass structures showed sharp peaks corresponding to (112) plane of CuInSe₂ and (222) plane of In₂O_3. Rutherford Backscattering Spectrometry (RBS) investigations were carried out on CuInSe₂/In₂O₃/Si structures in order to characterize the interface between In₂O₃ and CuInSe₂. The results show that the CuInSe₂ films were near stoichoimetric and In₂O₃ films had oxygen deficient composition. CuInSe₂/In₂O₃ interface was found to include a ∼20 nm thick region consisting of copper, indium and oxygen. Also, the In₂O₃/Si interface showed the formation of ∼20 nm thick region consisting of silicon, indium and oxygen. The results are explained on the basis of diffusion/reaction taking place at the respective interfaces.     

An extreme change in structural and optical properties of indium oxynitride deposited by reactive gas-timing RF magnetron sputtering

The indium oxynitride (InON) films were achieved by reactive RF magnetron sputtering indium target which has the purity of 99.999% with a novel reactive gas-timing technique. The structural, optical and electrical properties in a series of polycrystalline InON films affected by gas-timing of reactive N₂ and O₂ gases introduced to the chamber were observed. The X-ray photoelectron spectroscopy revealed that the oxygen content in thin films that compounded to indium and nitrogen, which increased from 10% in indium nitride (InN) to 66% in indium oxide (In₂O₃) films. The X-ray diffraction peaks show that the phase of deposited films changes from InN to InON and to In₂O₃ with an increasing oxygen timing. The hexagonal structure of InN films with predominant (0 0 2) and (0 0 4) orientation was observed when pure nitrogen is only used as sputtering gas, while InON and In₂O₃ seem to demonstrate body-center cubic polycrystalline structures depending on gas-timing. The surface morphologies investigated from atomic force microscope of deposited films with varying gas-timing of O₂:N₂ show indifferent. The numerical algorithm method was used to define the optical bandgap of films from transmittance results. The increasing oxygen gas-timing affects extremely to the change of crystallinity phase from InN to InON and to In₂O₃, the increase of optical bandgap from 1.4 to 3.4 eV and the rise of sheet resistance from 15 Ω/□ to insulator.     

Structural relation and epitaxial properties of hexagonal InN and oxidized cubic In2O3

The epitaxial properties and structural relation between hexagonal InN and cubic In₂O₃ phases were studied by synchrotron X-ray scattering and X-ray photoelectron spectroscopy. The cubic bixbyite In₂O₃ phase on the sapphire(0001) substrate was formed after an annealing time of 10 min at 10⁻⁵ Torr after the hexagonal InN film was grown at 550 °C, above the dissociation temperature of InN, by RF-magnetron sputtering. The crystal orientation was cubic In₂O₃(222), parallel to Al₂O₃(0001) and parallel to hexagonal InN(0002) before the oxidation process. The cubic In₂O₃ phase was believed to be formed layer by layer by the oxidation of the hexagonal InN phase.     

Reaction kinetics of α-CuInSe2 formation from an In2Se3/CuSe bilayer precursor film

The reaction pathway and kinetics of α-CuInSe₂ formation from a glass/In₂Se₃/CuSe polycrystalline bilayer precursor film were investigated using time-resolved, in situ high-temperature X-ray diffraction. Bilayer glass/In₂Se₃/CuSe precursor films were deposited on thin glass substrates in a migration enhanced molecular beam epitaxial deposition system. These films were then temperature ramp annealed or isothermally soaked while monitoring the phase evolution. The initial In₂Se₃ and CuSe reactant phases were directly transformed to α-CuInSe₂ without any detectable intermediate phase. Kinetic parameters were estimated using the Avrami and parabolic diffusion controlled reaction models. The parabolic reaction model fitted the experimental data better than the Avrami model over the entire temperature range (230-290 °C) of the set of isothermal experiments, with an estimated activation energy of 162 (±5) kJ/mol.     

Strain relaxation and surface morphology of nickel oxide nanolayers

The surface morphology and the lattice constants of NiO overlayers in the thickness range of 1-20 monolayers (NiO nanolayers) on Pd(1 0 0) have been investigated by high-resolution spot profile low-energy electron diffraction (SPA-LEED) and scanning tunneling microscopy (STM). NiO islands grow epitaxially on Pd(1 0 0) on top of a c(4 × 2) Ni₃O₄ monolayer with a compressed strained lattice, which relaxes gradually attaining the bulk lattice constant at 10-12 monolayers. The strain relaxation is accompanied by the formation of small angle mosaic defect regions at the surface, which have been characterised quantitatively by following the behaviour of the satellites to the main Bragg diffraction rods. The analysis of the diffuse scattering intensity around the (0 0) diffraction spot reveals anisotropic NiO island shapes, whose orientation depends on the growth conditions. An incommensurate superlattice in LEED and STM at intermediate NiO coverages (∼2-6 monolayers) is observed and its origin is discussed.     

Study of Ni/Si(1 0 0) solid-state reaction with Al addition

The characteristics of Ni/Si(1 0 0) solid-state reaction with Al addition (Ni/Al/Si(1 0 0), Ni/Al/Ni/Si(1 0 0) and Al/Ni/Si(1 0 0)) is studied. Ni and Al films were deposited on Si(1 0 0) substrate by ion beam sputtering. The solid-state reaction between metal films and Si was performed by rapid thermal annealing. The sheet resistance of the formed silicide film was measured by four-point probe method. The X-ray diffraction (XRD) was employed to detect the phases in the silicide film. The Auger electron spectroscopy was applied to reveal the element profiles in depth. The influence of Al addition on the Schottky barrier heights of the formed silicide/Si diodes was investigated by current-voltage measurements. The experimental results show that NiSi forms even with the addition of Al, although the formation temperature correspondingly changes. It is revealed that Ni silicidation is accompanied with Al diffusion in Ni film toward the film top surface and Al is the dominant diffusion species in Ni/Al system. However, no Ni_xAl_y phase is detected in the films and no significant Schottky barrier height modulation by the addition of Al is observed.     

The formation model of Ni-Cr oxides on NiCoCrAlY-sprayed coating

The atomic arrangement and distribution of oxides (Cr₂O₃, NiCr₂O₄ and NiO) on the sprayed-NiCoCrAlY coating after oxidation are analyzed. The formation and the growth model of Ni-Cr oxide phases are discussed according to the matching relationship between atoms. The outline character and a scale of spinel NiCr₂O₄ are discussed. The results show that Cr atoms can form two close-packed arrangements in the crystal plane of Cr₂O₃ perpendicular to 〈0 0 1〉 orientation. The atomic spacing in the first arrangement corresponds to double that of Ni/Ni₃Al in {1 1 1} crystal face. This suggests that Ni/Ni₃Al is the substrate for Cr₂O₃ to grow along 〈0 0 1〉 direction. The lattice mismatch between Cr₂O₃ and Ni/Ni₃Al is less than that of Al₂O₃, which indicates that Cr₂O₃ is easier to form than Al₂O₃ during the oxidation process. The atomic spacing in another close-packed arrangement of Cr₂O₃ perpendicular to 〈0 0 1〉 orientation is approximately equal to that of Ni or Cr in the plane of NiCr₂O₄ and NiO perpendicular to 〈1 1 1〉 orientation. So Cr₂O₃ can be the substrate for NiCr₂O₄ and NiO to grow in the 〈0 0 1〉 direction. NiCr₂O₄ and NiO can grow directly along the 〈1 1 1〉 orientation on each other. NiCr₂O₄ can grow outward in the planes of Cr₂O₃ perpendicular to 〈0 0 1〉 and grow inward along 〈1 1 1〉 orientation of NiO.     

Synthesis and electrochemical properties of Ni doped titanate nanotubes for lithium ion storage

Ni doped titanate nanotubes were synthesized by hydrothermal method using Ni doped rutile TiO₂ nanopowders as a starting material. The electrochemical properties were investigated by cyclic voltammmetric methods. The microstructure and morphology of the synthesized powders were characterized by XRD (X-ray diffraction), and HRTEM (high resolution transmission electron microscopy). Ni doped nanotubes were composed of H₂Ti₂O₅·H₂O with outer and inner diameter of ∼10 nm and 6 nm and showed a initial discharge capacity of 305 mAh/g with poor cycling performance. However, after firing, the Ni doped nanotubes revealed better cycling performance due to lower reaction with hydrate and smaller diameter of the tubes.     

Synthesis and materials properties of transparent conducting In2O3 films prepared by sol-gel-spin coating technique

Transparent conducting indium oxide (In₂O₃) thin films have been prepared on glass substrates by the simple sol-gel-spin coating technique. These films have been characterized by X-ray diffraction, resistivity and Hall effect measurements, optical transmission, scanning electron microscopy and atomic force microscopy for their structural, electrical, optical and morphological properties. The influence of spin parameters, number of coating, process temperature on the quality of In₂O₃ films are studied. In the operating range of deposition, 400-475 °C, all the films showed predominant (2 2 2) orientation. Films deposited at optimum process conditions exhibited a resistivity of 2×10⁻² Ω cm along with the average transmittance of about 80% in the visible spectral range (400-700 nm).     

Fabrication and characterization of Pt intermediate transparent and conducting ITO/Pt/ITO multilayer films

Platinum intermediate transparent and conducting ITO/metal/ITO (IMI) multilayered films were deposited by RF and DC magnetron sputtering on polycarbonate substrates without intentional substrate heating. Changes in the microstructure and optoelectrical properties of the films were investigated with respect to the thickness of the intermediate Pt layer in the IMI films. The thickness of Pt film was varied from 5 to 20 nm.In XRD measurements, neither ITO single-layer films nor IMI multilayer films showed any characteristic diffraction peaks for In₂O₃ or SnO₂. Only a weak diffraction peak for Pt (1 1 1) was obtained in the XRD spectra. Thus, it can be concluded that the Pt-intermediated films in the IMI films did not affect the crystallinity of the ITO films. However, equivalent resistivity was dependent on the presence and thickness of the Pt-intermediated layer. It decreased as low as 3.3×10⁻⁴ Ω cm for ITO 50 nm/Pt 20 nm/ITO 30 nm films. Optical transmittance was also strongly influenced by the Pt-intermediated layer. As Pt thickness in the IMI films increased, optical transmittance decreased to as low as 30% for ITO 50 nm/Pt 20 nm/ITO 30 nm films.     

XRD and XPS characterization of mixed valence Mn3O4 hausmannite thin films prepared by chemical spray pyrolysis technique

Spray pyrolysis technique has been employed successfully for the synthesis of single phase mixed valence spinel hausmannite (Mn₃O₄) thin films using alcoholic start solution of manganese acetate (Mn(CH₃COO)₂·4H₂O) on pyrex glass substrates at atmospheric pressure using air as a carrier gas. Thermal decomposition of the precursor in the temperature range 320-490 °C led to the formation of Mn₃O₄ phase as revealed from the thermogravimetry analysis. Prepared samples are characterized by X-ray diffraction that shows spinel structure with space group I4₁/amd. Pure and well crystallized specimen is subjected to X-ray photoelectron spectroscopy for the surface chemistry investigation of these systems at a molecular level. Surface Mn/O ratio is compared to the bulk composition of the sample. Atomic force micrographs revealed that the morphology and the surface grains of the films largely influenced by the substrate temperature.