Preparation of ultra fine copper–nickel bimetallic powders for conductive thick film

In this paper, ultrafine nickel-rich Cu–Ni bimetallic powders were synthesized with hydrothermal-reduction method. When polyethyleneglycol (PEG) was employed as protective agent, flake bimetallic powder particles, which have an excellent dispersibility and uniform size of 1.8–2.0 μm, can be prepared. Polyhedral powder particles, which have a uniform particle size in the range from 0.5 to 0.8 μm, were successfully synthesized using gelatin as protective agent. By thermal analysis, it was found that the oxidation-resistance of Cu–Ni powder particles was strong. Above-mentioned flake/polyhedral bimetallic powders were mixed with inorganic binder and vehicle to make conductive thick film. The low resistivity and high adhesion strength of thick film were attributed to high densification and rough interface from interfacial reaction, respectively.     

Electrosynthesis of polyaniline films on titanium by pulse potentiostatic method

Polyaniline (PANI) was synthesized on titanium electrode from aqueous solution containing 0.3 mol L⁻¹ aniline and 1 mol L⁻¹ HNO₃ by pulse potentiostatic method. The chronoamperogram during polymerization process of aniline was recorded. The effects of the synthesis parameters, such as anodic pulse duration (t_a), cathodic pulse duration (t_c), lower limit potential (E_c) and upper limit potential (E_a), on the morphology and electroactivity of the PANI films were investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM results present that flake, mica-like, quasi-fibrous and nano-fibrous PANI film could be synthesized with various polymerization parameters. Under the following conditions, t_a = 0.8 s, t_c = 0.1 s, E_c = 0 V and E_a = 1.0 V, high quality nano-fibrous PANI film with the best electroactivity was obtained. The CV results show that the PANI films with different morphologies, which were prepared under the same anodic polymerization charge, have obvious different characteristics. This means that the PANI films with different morphologies have different electrochemical activity.     

Photo and gas sensitivity of thin Cu-phthalocyanine films studied by spectroscopy of unoccupied electron states

Thin films of Cu-phthalocyanine were thermally deposited in UHV on pyrolytic graphite, n-Si(1 0 0), SiO₂/n-Si, and SiO₂/p-Si substrates. Atomic composition of the films was tested by Auger electron spectroscopy. Evolution of surface potential and density of electron states located 0–25 eV above vacuum level were monitored during the film deposition by means of total current electron spectroscopy (TCS). The resulting spectra of the 2–3 nm thick CuPc films on the different substrates were however identical. Admission of 10⁻⁵ Pa O₂ and NO₂ resulted in a reversible decrease and increase of the film surface potential, respectively. A new peak in the TCS appeared and the spectrum was attenuated on the admission of the gases. These changes were attributed to the interaction between the film and the gas molecules adsorbed. The changes were reversible on the gas evacuation. White light illumination reduced (increased) surface potential of the Cu-phthalocyanine film on SiO₂/n-Si (SiO₂/p-Si) substrate. The gas sensitivity is attributed to the processes at the gas/CuPc film interface, while the photovoltaic properties are attributed to the processes at the CuPc film/substrate interface.     

High coercivity characteristics of FePtB exchange-coupled nanocomposite thick film spring magnets produced by sputtering

Thick film magnets (∼3.2 μm) deposited on silicon substrate at processing temperatures lower than 400 °C, exhibiting high coercivity (H_c ∼ 604 kA m⁻¹), high maximum energy product [(BH)_max = 95 kJ m⁻³] and good surface properties, were obtained by sputtering technique. The effects of sputtering power, substrate temperature (T_s) and film thickness on the magnetic properties of the films were studied. Films exhibiting very good hard magnetic properties are mainly made up of nanosized hard (L1₀-FePt) and soft (Fe₂B and Fe₃B) magnetic phases, which are exchange coupled. The exchange spring behavior in these films was investigated and a high recoil rate of more than 90% was obtained. The ability to deposit permanent magnet thick films exhibiting good hard magnetic as well as surface properties on silicon, as demonstrated in the present work, is very promising for the fabrication of micromagnets for magnetic MEMS.     

Effect of boron doped fullerene C60 film coating on the electrochemical characteristics of silicon thin film anodes for lithium secondary batteries

In this work, boron doped fullerene (B:C₆₀) films were prepared by the radio frequency plasma assisted thermal evaporation technique for use as a coating material for the silicon thin film anode in lithium secondary batteries. Raman and XPS analyses revealed that the boron atoms were well inserted into the fullerene film lattices. The effect of the B:C₆₀ film on the electrochemical characteristics of the silicon thin film was studied by charge–discharge tests, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The B:C₆₀ coated silicon film exhibited a high reversible capacity of more than 1200 mAh g^?1 when cycled 50 times between 0 and 2 V at a current density of 1200 μA cm^?2 (1.5 C). The film also showed good rate capacity at different current densities and a more improved coulombic efficiency of 87.7% in the first cycle in comparison with that of the C₆₀ coated film electrode.     

Variation of atomic spacing and thermomechanical properties in Ni–Mn–Ga/alumina film composites

Ni_51.4Mn_28.3Ga_20.3 thin films deposited on alumina ceramics have been studied by X-ray powder diffraction and dynamic mechanical analysis. Substantial temperature vs. film thickness dependencies of interatomic spacing measured in the direction of the film normal are observed in the range of 25–200 °C and 0.1–5 μm, respectively. The coefficient of thermal expansion (CTE) of the film in the paramagnetic cubic phase has been determined to be equal to (15 ± 1) × 10⁻⁶ K⁻¹ for all the films, in agreement with the CTE of bulk material. The thickness dependent shrinkage of the pseudo-cubic lattice along the film normal direction is attributed to the thermally induced tensile stress in the film plane. The thickness dependence of the elastic modulus of submicron films is obtained. It is shown that the internal stresses result in both the thickness dependence of martensitic transformation temperature and the reversible, thermally induced change in shape of the Ni–Mn–Ga/alumina cantilever actuator.     

Epitaxial growth of γ-Fe2O3 thin films on MgO substrates by pulsed laser deposition and their properties

Epitaxial γ-Fe₂O₃ films were fabricated by pulsed laser deposition at 350 °C in an oxygen-rich atmosphere onto a (0 0 1) or (1 1 0) MgO substrate utilizing the substrate template effect, while the corundum structure α-Fe₂O₃ was obtained when the same experiment was conducted using sapphire or quartz substrate. X-ray photoelectron spectroscopy analysis and low-temperature SQUID measurements confirmed the formation of γ-Fe₂O₃. After annealing at 500 °C for 1 h under oxygen atmosphere, the γ-Fe₂O₃ phase was still maintained. The saturation magnetization (M_s) of the γ-Fe₂O₃ film was around 400 emu cm^?3 for films 10–50 nm thick, which is in agreement with the bulk value. The ultrathin films showed an enhanced Ms value (489 emu cm^?3). In particular, the M_s of the 5 nm thin film did not diminish even if it was subjected to high-temperature annealing due to the stabilizing effect of the epitaxial growth. The thin films obtained had a flat surface, which is desired for spin filter and other applications.     

Ceramic processing strategies for thick films on copper foils

Functional oxides on Cu have multiple applications. For thick films the required high sintering temperatures present a challenge for processing on base metal substrates. In this study it is shown that it is possible to adapt well-known ceramic processing strategies to the fabrication of thick lead zirconate titanate (PZT) films on Cu with useful ferroelectric properties. PZT powders with optimized particle sizes are used to fabricate thick films by electrophoretic deposition in combination with a post-deposition isostatic pressing step. This approach to maximize green packing is sufficient to dramatically lower the required sintering temperatures. 25 μm thick PZT films on Cu sintered at 900 °C have a dielectric permittivity of 585, a loss tangent at 10 kHz of 0.03, a remanent polarization of 19 μC cm^?2 and a coercive field of 22 kV cm^?1. This significant improvement in the dielectric response opens the possibility of using thick PZT films on Cu for a wide range of devices where cost, yield and reliability are concerns.     

Effect of oxygen vacancy and Mn-doping on electrical properties of Bi4Ti3O12 thin film grown by pulsed laser deposition

An amorphous Bi₄Ti₃O₁₂ phase was formed when films were grown at <400 °C while Bi₂Ti₂O₇ and Bi₂Ti₄O₁₁ transient phases were developed when films were grown at 400–500 and 600 °C, respectively. A homogeneous Bi₄Ti₃O₁₂ crystalline phase was formed in the film grown at 700 °C. The high leakage current density (5 × 10^?7 A cm^?2 at 0.2 MV cm^?1) of the film grown at 300 °C under 100 mTorr oxygen partial pressure (OPP) decreased to 2 × 10^?8 A cm^?2 for the film grown at 200 mTorr OPP, due to the decreased number of intrinsic oxygen vacancies. However, when OPP exceeded 200 mTorr, the electrical properties were deteriorated due to the formation of oxygen interstitial ions. Mn-doping at a suitable level improved the electrical properties of the films by producing extrinsic oxygen vacancies that reduced the number of intrinsic oxygen vacancies. Schottky emission was suggested as the leakage current mechanism of the Bi₄Ti₃O₁₂ film.     

Giant dielectric response in (Li,Ti)-doped NiO ceramics synthesized by the polymerized complex method

This paper reports on the synthesis of nanocrystalline (Li, Ti)-doped NiO powders (i.e., Li_0.3Ti_0.02Ni_0.68O, abbreviated as LTNO) by the polymerized complex (PC) method. The synthesized LTNO powders were characterized by thermogravimetric–differential thermal analysis (TG–DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The powders, with particle sizes of 39, 65 and 72 nm as estimated from XRD, were sintered in air at 1280 °C for 4 h to obtain bulk LTNO ceramics. A giant dielectric constant of 10⁴–10⁵ at low frequency with weak temperature dependence over the measured temperature range (−30 to 160 °C) was observed in the sintered LTNO ceramics. The origin of the high permittivity observed in these LTNO ceramics is attributed to the Maxwell–Wagner polarization mechanism and a thermally activated mechanism.     

Effects of oxygen pressure on electrical properties of (Na0.5K0.5)NbO3 films grown on Pt/Ti/SiO2/Si substrates

(Na_0.5K_0.5)NbO₃ (NKN) films were annealed under various oxygen partial pressures (OPPs), and the effect of the OPP on the electrical properties of the NKN films was investigated. The dielectric and piezoelectric constants of the NKN film were not influenced by the OPP. However, the remnant polarization and coercive field decreased when the OPP exceeded 25.0 torr because of the low breakdown field and high leakage current. The NKN film annealed under air atmosphere exhibited a high leakage current density that decreased with increasing OPP because of the decreased number of oxygen vacancies. The minimum leakage current density of 3.7 × 10^?8 A cm^?2 at 0.3 MV cm^?1 was obtained for the NKN film annealed under an OPP of 25.0 torr. The leakage current increased when the OPP exceeded 25.0 torr because of the formation of oxygen interstitial ions. The leakage current of the Pt/NKN/Pt device was explained by Schottky emission. The obtained Schottky barrier height between the Pt electrode and NKN film was ～1.24 eV.     

Deposition and characterization of superhard biphasic ruthenium boride films

Recently, the superhardness of rhenium diboride films was reported. In this study the first successful preparation and characterization of ruthenium boride films is presented. The morphology, topography, microstructure and hardness of films, prepared by pulsed laser deposition, were investigated. The films, which are 0.7 μm thick, have a dense grain texture, and are composed of two phases Ru₂B₃ (main phase, 65% volume fraction) and RuB₂ (35%). The RuB₂ phase does not show any preferred orientation, while Ru₂B₃ is textured preferentially along the (1 1 4) and (1 0 5) directions, with crystallite growth parallel within 1.9° of average mismatch. The composite Vickers microhardness of the film–substrate systems was measured, and the intrinsic hardness of the films was separated using an area law-of-mixtures approach. The obtained films were found to be superhard, the intrinsic film hardness value (49 GPa) being much higher than that for the RuB₂ bulk used as the target for film deposition and than that for the Ru₂B₃ bulk.     

Structural changes during the reaction of Ni thin films with (1 0 0) silicon substrates

Ultrathin films of nickel deposited onto (1 0 0) Si substrates were found to form kinetically constrained multilayered interface structures characterized by structural and compositional gradients. The presence of a native SiO₂ on the substrate surface in tandem with thickness-dependent intrinsic stress of the metal film limits the solid-state reaction between Ni and Si. A roughly 6.5 nm thick Ni film on top of the native oxide was observed regardless of the initial nominal film thickness of either 5 or 15 nm. The thickness of the silicide layer that formed by Ni diffusion into the Si substrate, however, scales with the nominal film thickness. Cross-sectional in situ annealing experiments in the transmission electron microscope elucidate the kinetics of interface transformation towards thermodynamic equilibrium. Two competing mechanisms are active during thermal annealing: thermally activated diffusion of Ni through the native oxide layer and subsequent transformation of the observed compositional gradient into a thick reaction layer of NiSi₂ with an epitaxial orientation relationship to the Si substrate; and, secondly, metal film dispersion and subsequent formation of faceted Ni islands on top of the native oxide layer.     

Preparation of porous nanorod polyaniline film and its high electrochemical capacitance performance

Nano-sized polyaniline (PANI) films were electrochemically deposited onto an ITO substrate by a pulse galvanostatic method (PGM) in an aqueous solution. The morphology of the as-prepared PANI film was characterized using a field emission scanning electron microscope (FESEM). It was observed that the as-prepared PANI films were highly porous, and showed a nano-sized rod-like or coralline-like morphology depending on the charge loading performed in the electropolymerization process. Furthermore, the PANI films were electrochemically measured by the galvanostatic charge–discharge (GCD), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests in 1 mol L^?1 HClO₄ solution. The results showed that such PANI films had a favorable electrochemical activity and an excellent capacitance. The rod-like PANI film prepared with the charge loading of 1000 mC showed the highest discharge capacitance of 569.1 F g^?1 at a low current density of 1 A g^?1. The discharge capacitance retained 97.7% after 1000 cycles at a large current density of 10 A g^?1.     

Structural,electrical and optical properties of p-type transparent conducting SnO2:Al film derived from thermal diffusion of Al/SnO2/Al multilayer thin films

Highly transparent, p-type conducting SnO₂:Al films derived from thermal diffusion of a sandwich structure Al/SnO₂/Al multilayer thin films deposited on quartz substrate have been prepared by direct current and radio-frequency magnetron sputtering using Al and SnO₂ targets. The deposited films were annealed at various temperatures for different durations. The effect of thermal diffusing temperature and time on the structural, electrical and optical performances of SnO₂:Al films has been studied. X-ray diffraction results show that all p-type conducting films possessed polycrystalline SnO₂ with tetragonal rutile structure. Hall-effect results indicate that 450 °C for 4 h were the optimum annealing parameters for p-type SnO₂:Al films, resulting in a relatively high hole concentration of 7.2 × 10¹⁸ cm^?3 and a low resistivity of 0.81 Ω cm. The transmission of the p-type SnO₂:Al films was above 80%.     

BiFeO3 thin films of (1 1 1)-orientation deposited on SrRuO3 buffered Pt/TiO2/SiO2/Si(1 0 0) substrates

BiFeO₃ (BFO) thin films of varying degrees of (1 1 1) orientation were successfully grown on SrRuO₃-buffered Pt/TiO₂/SiO₂/Si(1 0 0) substrates by off-axis radio-frequency magnetron sputtering. They demonstrate much enhanced ferroelectric behavior, including a much enhanced remnant polarization (2P_r ～ 197.1 μC cm^?2 at 1 kHz) measured by positive-up negative-down (PUND), at an optimized deposition temperature of 590 °C. The effects of film deposition temperature on the degree of (1 1 1) orientation, film texture, ferroelectric behavior, leakage current and fatigue endurance of the BFO thin films were systematically investigated. While the degree of (1 1 1) orientation is optimized at 590 °C, the defect concentration in the film increases steadily with increasing deposition temperature, as demonstrated by the dependence of leakage behavior on the deposition temperature. The polarization behavior is shown to strongly depend on the degree of (1 1 1) orientation for the BFO thin film. Oxygen vacancies are shown to involve in the conduction and dielectric relaxation of the BFO thin films deposited at different temperatures, as demonstrated by their dielectric and conduction behavior as a function of both temperature (in the range 294–514 K) and frequency (in the range 10^?1–10⁶ Hz).     

Ions transport and self-doping in layer-by-layer conducting polymer films

The self-doping mechanism for charge transport is investigated in layer-by-layer (LBL) films from two conducting polymers, namely poly(o-methoxyaniline) (POMA) and poly(3-thiophene acetic acid) (PTAA). The efficiency of charge intercalation, defined as the ratio between the charge and the mass change, is twice for the POMA/PTAA LBL film in comparison with a cast POMA film. This is attributed to differences in the diffusion-controlled charge and mass transport, where distinct ionic species participate in the LBL films, as demonstrated with experiments using a quartz crystal microbalance. The doping efficiency for LBL film is the same, i.e., 3.93 × 10⁻⁴ and 3.56 × 10⁻⁴ g/C for the Li⁺ and (C₂H₅)₄N⁺ doped films, and is different for the cast POMA film, i.e., 11.3 × 10⁻⁴ for Li⁺ and 6.45 × 10⁻⁴ g/C for (C₂H₅)₄N⁺. Therefore, once no significant differences in the intercalation mechanism are observed when different cations, Li⁺ or (C₂H₅)₄N⁺, are used with the LBL films, this indicates that the self-doping mechanism is controlled by the exchange of anions.     

Effect of various parameters on the conductivity of free standing electrosynthesized polypyrrole films

Electrical characteristics of polypyrrole films electrodeposited in different aqueous electrolyte solutions including p-toluenesulfonate, naphtalenesulfonate, nitrate, tetrafluoroborate, and perchlorate anions were investigated using the Van der Pauw procedure. The polymer films were synthesized by electrochemical oxidation at a fixed potential. Experimental parameters including the pyrrole concentration, electrolyte, applied potential and substrate were shown to affect the electrical conductivity σ of polypyrrole films. Since the substrate contributes significantly to the overall conductivity of polypyrrole-coated electrodes, the results obtained with free standing polymer films appeared more reliable. The results indicated that the p-toluenesulfonate doped PPy film showed the highest average conductivity (σ_293 K = 4.5 × 10⁵ S m^?1) whereas the perchlorate doped one produced the lowest of all the films prepared (σ_293 K = 2 × 10⁴ S m^?1).     

Thermal and mechanical properties of perovskite-type barium hafnate

Polycrystalline samples of the barium perovskite-type oxide, BaHfO₃ were prepared by solid-state reactions from HfO₂ and BaCO₃ powders. The thermal expansion coefficient, heat capacity, thermal diffusivity, thermal conductivity, elastic modulus, Debye temperature, and micro-Vickers hardness were measured. The crystal structure of BaHfO₃ is of the cubic perovskite type with the lattice parameter 0.4171 nm at room temperature. The sample bulk density is 91% of the theoretical density. The average linear thermal expansion coefficient is 6.93 × 10⁻⁶ K⁻¹ in the temperature range between 300 and 1500 K. The Young's modulus equals 194 GPa. The thermal conductivity at room temperature is 10.4 Wm⁻¹K⁻¹.     

Processing and properties of sintered reaction-bonded silicon nitride with Y2O3–MgSiN2: Effects of Si powder and Li2O addition

The effects of Si powder and Li₂O addition on the processing, thermal conductivity and mechanical properties of sintered reaction-bonded silicon nitride (SRBSN) with Y₂O₃–MgSiN₂ sintering aids were studied. Addition of Li₂O provides a less-viscous liquid phase that results in a more uniform and finer pore structure in RBSN with the coarser Si powders, but the pore structure plays a less important role in the densification of RBSN. The thermal conductivity of SRBSN without porosity decreases with increased Al impurity content and also decreases with the Li₂O addition regardless of the Si purity. The impurest coarse Si powder produces the lowest thermal conductivity (93 W m⁻¹ K⁻¹) but the highest four-point bending strength (∼700 MPa) and a higher fracture toughness (∼10 MPa m^1/2). However, the purer fine Si powder produces the highest thermal conductivity (119 W m⁻¹ K⁻¹) and highest toughness (∼11 MPa m^1/2) but the lowest strength (∼500 MPa).