Preparation of SrZrO<Subscript>3</Subscript> Thermal Barrier Coating by Solution Precursor Plasma Spray

The solution precursor plasma spray (SPPS) process is capable of depositing highly durable thermal barrier coatings (TBCs). In this study, an aqueous chemical precursor feedstock was injected into the plasma jet to deposit SrZrO₃ thermal barrier coating on metal substrate. Taguchi design of experiments was employed to optimize the SPPS process. The thermal characteristics and phase evolution of the SrZrO₃ precursor, as well as the influence of various spray parameters on the coating deposition rate, microhardness, microstructure, and phase stability, were investigated. The experimental results showed that, at given spray distance, feedstock flow rate, and atomization pressure, the optimized spray parameters were arc current of 600 A, argon flow rate of 40 L/min, and hydrogen flow rate of 10 L/min. The SrZrO₃ coating prepared using the optimized spray parameters had single-pass thickness of 6.0 μm, porosity of ~18%, and microhardness of 6.8 ± 0.1 GPa. Phase stability studies indicated that the as-sprayed SrZrO₃ coating had good phase stability in the temperature range from room temperature to 1400 °C, gradually exhibiting a phase transition from t′-ZrO₂ to m-ZrO₂ in the SrZrO₃ coating at 1450 °C with increasing time, while the SrZrO₃ phase did not change.     

Epitaxial SrRuO3 thin films deposited on SrO buffered-Si(001) substrates for ferroelectric Pb(Zr0.2Ti0.8)O3 thin films

SrRuO₃ thin film electrodes are epitaxially grown on SrO buffered-Si(001) substrates by pulsed laser deposition. The optimum conditions of the SrO buffer layers for epitaxial SrRuO₃ films are a deposition temperature of 700 °C, deposition pressure of 1 × 10^?6 Torr, and thickness of 6 nm. The 100 nm thick-SrRuO₃ bottom electrodes deposited above 650 °C on SrO buffered-Si (001) substrates have a rms (root mean square) roughness of approximately 5.0 Å and a resistivity of 1700 µω-cm, exhibiting an epitaxial relationship. The 100 nm thick-Pb(Zr_0.2Ti_0.8)O₃ thin films deposited at 575 °C have a (00l) preferred orientation and exhibit 2P_r of 40 µC/cm², E_c of 100 kV/cm, and leakage current of about 1 × 10^?7 A/cm² at 1 V. The silicon oxide phase which presents within PZT and SrRuO₃ films, influences the crystallinity of the PZT films and the resistivity of the SrRuO₃ electrodes.     

Microstructure and Thermophysical Properties of SrZrO<Subscript>3</Subscript> Thermal Barrier Coating Prepared by Solution Precursor Plasma Spray

Strontium zirconate (SrZrO₃) thermal barrier coatings were deposited by solution precursor plasma spray (SPPS) using an aqueous precursor solution. The phase transition of the SrZrO₃ coating and the influence of the aging time at 1400 °C on the microstructure, phase stability, thermal expansion coefficient, and thermal conductivity of the coating were investigated. The unique features of SPPS coatings, such as interpass boundary (IPB) structures, nano- and micrometer porosity, and through-thickness vertical cracks, were clearly observed evidently in the coatings. The vertical cracks of the coatings remained substantially unchanged while the IPB structures gradually diminished with prolonged heat treatment time. t-ZrO₂ developed in the coatings transformed completely to m-ZrO₂ phase after heat treatment for 100 h. Meanwhile, the SrZrO₃ phase in the coatings exhibited good phase stability upon heat treatment. Three phase transitions in the SrZrO₃ coatings were revealed by thermal expansion measurements. The thermal conductivity of the as-sprayed SrZrO₃ coating was ~1.25 W m^?1 K^?1 at 1000 °C and remained stable after heat treatment at 1400 °C for 360 h, revealing good sintering resistance.     

Room temperature ferroelectric property of BiMnO<Subscript>3</Subscript> thin film with double SrTiO<Subscript>3</Subscript> buffer layers on Pt/Ti/SiO<Subscript>2</Subscript>/Si substrate

We fabricated high quality BiMnO₃ thin films with double SrTiO₃ buffer layers on Pt/Ti/SiO₂/Si substrates, in which the SrTiO₃ buffer layers were used for the reduction of leakage current in BiMnO₃ thin films. We chose an SrTiO₃ thickness of about 5 nm, which was obtained by the fitting of ellipsometer data. We confirmed a remarkable enhancement in leakage current. BiMnO₃ thin films exhibited a ferromagnetic transition with Curie temperature of about 105 K. The BiMnO₃ thin film also showed a good ferroelectric property with a remnant polarization of about 9 μC/cm².     

Corrosion behaviour of polycrystalline Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films and its size effects

This study examines the effect of film thickness ranging from 230 to 404 nm on the corrosion resistance of Nb₂O₅ thin films grown by chemical solution deposition. The films were characterized to obtain the relationships between the deposition parameters and the most relevant physical properties (structural, surface morphology and corrosion resistance). From X-ray diffraction and XPS analyses we can conclude that the films were stoichiometric Nb₂O₅ and crystalline. The internal strain and morphology of the film changes as the number of layers increases indicating a thickness dependent grain size. The surface roughness, corrosion resistance were also affected by the film thickness. Electrochemical impedance spectroscopy (EIS) shows that the thicker film have higher passive and charge transfer resistance than the control samples. These results coating layer of Nb₂O₅ improves the corrosion resistance on an API 5L X80 steel alloy due to the formation of a film on the surface.     

Microstructural and electrochemical properties of Ti-doped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> coated LiCoO<Subscript>2</Subscript> films

We studied the microstructural and electrochemical properties of Ti-doped Al₂O₃ (Ti-Al₂O₃) coated LiCoO₂ thin films depending on the Ti composition. The 1.27 at.% Ti-Al₂O₃ coated films had an amorphous structure with better conductivity than that of pure Al₂O₃ films. The Ti-Al₂O₃ coating layer effectively suppressed the dissolution of Co and the formation of lower Li conductivity SEI films at the interface between the LiCoO₂ film and electrolyte. The Ti-Al₂O₃ coating improved the cycling performance and capacity retention at high voltage (4.5 V) of the LiCoO₂ films. The Ti-Al₂O₃ coated LiCoO₂ films showed better electrochemical properties than did the pure Al₂O₃ coated LiCoO₂ films. These results were closely related to the enhanced Li-conductivity and interfacial quality of the Ti-Al₂O₃ film.     

Effects of the FeCl<Subscript>3</Subscript> concentration on the polymerization of conductive poly(3,4-ethylenedioxythiophene) thin films on (3-aminopropyl) trimethoxysilane monolayer-coated SiO<Subscript>2</Subscript> surfaces

This study examined the effects of the FeCl₃ (oxidant) concentration on the vapor phase polymerization (VPP) of conducting poly (3,4-ethylenedioxythiophene) (PEDOT) thin films on (3-aminopropyl)trimethoxysilane (APS)-coated SiO₂ surfaces, in which the interaction between Fe(III) and the -NH₂ groups of APS enabled a uniform distribution of FeCl₃ on the surface. The FeCl₃ concentration has a strong impact on the thickness, surface morphology, and conductivity of the PEDOT films deposited by VPP on an APS monolayer. The thickness of the PEDOT thin films increased linearly as the FeCl₃ concentration increased, as predicted by a model of spun films from a FeCl₃ solution. However, the rate of the increase in PEDOT thin film thickness per unit of FeCl₃ in wt.% was lower than the predicted value. This suggests that the consumption of FeCl₃ not participating in polymerization to produce Fe₂O₃ or FeCl₃ aggregates increased as the FeCl₃ concentration increased. In addition, the surface morphology improved as the FeCl₃ concentration increased from 1 wt.% to 3 wt.% and the conductivity increased to approximately 400 S/cm. However, further increases in the FeCl₃ concentration to 5 wt.% and 7 wt.% significantly degraded the morphology by creating holes in the PEDOT film, which reduced the conductivity.     

Dielectric properties of ZrTiO<Subscript>4</Subscript> thin films synthesized by sol-gel method

ZrTiO₄ thin films were successfully prepared on Pt/Ti/SiO₂/Si(100) substrates by a sol-gel process and gel films were heat-treated at various temperatures. The surface morphology, crystal structure, and dielectric properties of the thin films were investigated. It was possible to obtain ZrTiO₄ phase at temperatures above 650 °C for 2 h, which is much lower than the bulk sintering temperature. The microstructure of well-crystallized ZrTiO₄ thin films was a fine-grained microstructure less than 70 nm in grain size and the surface morphology was smooth with 22.4 rms roughness. The dielectric constant and loss of ZrTiO₄ thin films were 38 and 0.006, respectively, for thin films with 450 nm thickness heat-treated at 900 °C for 2 h.     

Control of strain relaxation in tensile and compressive oxide thin films

Tensile and compressive solid-solution thin films based on LaAlO₃ and CaZrO₃ compositions were grown on perovskite oxide substrates using pulsed laser deposition to study growth mode transitions and strain relaxation. A buried layer of SrRuO₃ between the thin film and the SrTiO₃ substrate was also introduced to provide an auxiliary embedded strain gauge, which helps identify the critical conditions for the onset of catastrophic strain relaxation events – cracking and dislocation cascades. The results are compared with theoretical predictions to provide guidelines on some general deposition conditions that may be used to obtain smooth, crystalline and defect-free thin films of interest to perovskite-based heterostructures.     

Dielectric properties of Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films deposited onto Ti and TiO<Subscript>2</Subscript> layer

The present study describes the dielectric properties of RF sputtered Ta₂O₅ thin films as a function of the buffer layer and annealing condition. The buffer layers were Ti or TiO₂. And the thin film was annealed in various conditions. The X-ray pattern results showed that the phase of the RF sputtered Ta₂O₅ thin films was amorphous and this state was kept stable to RTA (rapid thermal annealing) even at 700°C. Measurements of the electrical and dielectric properties of the reactive sputtered Ta₂O₅ fabricated in two simple metal insulator semiconductor (MIS) structures, (Cu/Ta₂O₅/Ti/Si/Cu and Cu/Ta₂O₅/TiO₂/Si/Cu) indicated that the amorphous Ta₂O₅ grown on Ti possesses a high dielectric constant (30–70) and high leakage current (10⁻¹–10⁻⁴ A/cm²), whereas a relatively low dielectric constant (−10) and low leakage current (−10⁻¹⁰ A/cm²) were observed in the amorphous Ta₂O₅ deposited on the TiO₂ buffer layer. In addition, the leakage current mechanisms of the two amorphous Ta₂O₅ thin films were investigated by plotting the relation of current density (J) vs. applied electric field (E). The Ta₂O₅/Ti film exhibited three dominant conduction mechanism regimes contributed by the Ohmic emission at low electrical field, by the Schottky emission at intermediate field and by the Poole-Frenkel emission at high field. In the case of Ta₂O₅/TiO₂ film, the two conduction mechanisms, the Ohmic and Schottky emissions, governed the leakage current density behavior. The conduction mechanisms at various electric fields applied were related to the diffusion of Ta, Ti and O, followed by the creation of vacancies, in the rapid thermal treated capacitors.     

VO<Subscript>2</Subscript> thin films: Defect mediation in room temperature ferromagnetic switching characteristics

Vanadium dioxide (VO₂) has tremendous potential in multifunctional device applications related to spintronics, switching, and magnetic recording. We have discovered that the room temperature ferromagnetism (RTFM) in undoped vanadium oxide epitaxial films can be switched on and off by altering the cooling ambient conditions which exhibit a sharp electrical transition at 341 K. By correlating the structural and ferromagnetic properties in VO₂, we envisage the potential for creation of novel multifunctional solid-state devices. High-quality epitaxial VO₂ thin films were grown on c-sapphire (0001) substrates, under different ambient conditions via the domain matching epitaxy paradigm. The observed RTFM has its origin in the valence charge defects with unpaired electrons in V⁺³ in VO₂ thin films, where the concentration of the defects could be varied with oxygen partial pressure. The VO₂ films-with a high ferro- to paramagnetic transition (Curie) temperature around 500 K estimated by fitting the magnetization data to the Bloch’s T^3/2 law, a saturated magnetization of 18 emu/cm³, and with a finite coercivity of 40 Oe at 300 K-can be useful for integrated smart sensors operable at room temperature.     

Experimental and DFT Study of Structural and Optical Properties of Kesterite-Type Cu<Subscript>2</Subscript>ZnSnS<Subscript>4</Subscript> Compound for Solar Cell Applications

In this work, Cu₂ZnSnS₄ (CZTS) thin films were prepared by thermal evaporation from Cu₂SnS₃ and ZnS initially mixed by a mechanical alloying process. Structural and optical properties of CZTS films have been studied. X-ray diffraction results showed that the semiconductor has the Kesterite structure, and the optical absorption coefficient and band gap energy of the thin films were about 10⁴ cm^?1 and 1.46 eV, respectively. The structural and optical properties of Kesterite CZTS, studied by using the full potential linearized augmented plane wave method within the density functional theory, showed good agreement with our experimental results. The surface morphological studies revealed the formation of a smooth, compact and uniform CZTS surface.     

Effects of SiO<Subscript>2</Subscript> and TiO<Subscript>2</Subscript> on resistance stabilities of flexible indium-tin-oxide films prepared by ion assisted deposition

Inorganic buffer layers such as SiO₂ or TiO₂ and transparent conductive indium-tin-oxide (ITO) films were prepared on polyethylene terephthalate (PET) substrates by ion assisted deposition (IAD) at room temperature, and the effects of SiO₂ and TiO₂ on the bending resistance performance of flexible ITO films were investigated. The results show that ITO films with SiO₂ or TiO₂ buffer layer have better resistance stabilities compared to ones without the buffer layer when the ITO films are inwards bent at a bending radius more than 1.2 cm and when the ITO films are outwards bent at a bending radius from 0.8 cm to 1.2 cm. ITO films with SiO₂ buffer layer have better resistance stabilities compared to ones with TiO₂ buffer layer after the ITO films are bent several hundreds of cycles at the same bending radius, for the adhesion of SiO₂ is stronger than that of TiO₂. The compressive stress resulted from inward bending leads to the formation of more defects in the ITO films compared with the tensile stress arising from outward bending. SiO₂ and TiO₂ buffer layers can effectively improve the crystallinity of ITO films in (400), (440) directions.     

A giant polarization value in bismuth ferrite thin films

An approach is used to improve the remanent polarization of BiFeO₃ thin films, where the BiFe_0.96Zn_0.04O₃ thin film with (1 1 1) orientation was grown on the SrRuO₃/SrTiO₃(1 1 1) substrate by rf sputtering. A higher dielectric constant and a lower dielectric loss are demonstrated for the BiFe_0.96Zn_0.04O₃ thin film as compared with those of pure BiFeO₃ thin film. The introduction of Zn deteriorates the magnetic properties of BFO thin films. A giant polarization value of 2P_r ∼ 268.5 μC/cm² is induced for the BiFe_0.96Zn_0.04O₃ thin film as confirmed by PUND, owing to the (1 1 1) orientation, the introduction of Zn, and a low leakage current density.     

Effects of H<Superscript>+</Superscript> Ion Implantation and Annealing on the Properties of CuIn<Subscript>0.75</Subscript>Ga<Subscript>0.25</Subscript>Se<Subscript>2</Subscript> Thin Films

In this paper the effects of post-deposition annealing followed by hydrogen ion-implantation on the properties of CuIn_0.75Ga_0.25Se₂ thin films have been investigated. The samples were grown by flash evaporation onto glass substrates heated at temperature between room temperature and 200 °C. Selected samples were subsequently processed under several sets of conditions, including vacuum, selenium, inert (argon) and forming gas (a 9:1 mixture of N₂:H₂) followed by hydrogen ion-implantation. A high-resolution near-infrared photoacoustic spectrometer (PAS) of the gas-microphone type was used for room temperature analysis of non-radiative defect levels in the as-grown, annealed and hydrogen implanted thin films. The absorption coefficient has been derived from the PA spectra to determine the gap energy and to establish the activation energies for several defect-related energy levels. The changes observed in the PA spectra following annealing and ion-implantation has been directly correlated with the compositional and structural properties of the samples.     

Effect of Ti,Nb, and Ti + Nb Coatings on the Bond Strength-Structure Relationship in Al/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Joints

There is a growing interest in metal-ceramic bonding for wide range of applications in electronic devices and high technology industry for fabrication of metal matrix composites and bonding of ceramic components to metals. The object of the work was to study the effect of Ti, Nb, and Ti + Nb thin films deposited by PVD method on alumina substrates on structure and bond strength properties of Al/Al₂O₃ joints. The joints were fabricated using the results of a wetting experiment and the sessile drop method at a temperature of 1223 K in a vacuum of 0.2 MPa for 30 min of contact. The structure of the metal/ceramic interface was investigated using scanning electron microscopy. The elemental distribution at the metal-ceramic interface was analyzed using energy dispersive x-ray spectroscopy. Transmission electron microscopy was also used to investigate some aspects of the metal/ceramic interface. The bond strength properties of joints were measured using shear test. The shear strength results demonstrated significant improvement of shear strength of Al/Al₂O₃ joints due to the application of Ti + Nb thin film on alumina substrate. Microstructural investigations of the interface indicated that Al/coating/Al₂O₃ couples have diffusion transition interface which influences the strengthening of these joints. A conclusion could be drawn that the presence of thin film layers changes the character of interaction and leads to the formation of new reaction products in the bonding layer.     

Plasma-chemical polymerization in CH<Subscript>4</Subscript>-based mixtures containing various amounts of rare gases

For constant-current glow discharge in Ar + Ne + CH₄ mixtures in a pressure range of 13–250 Pa and a discharge current range of 5–100 mA, the following characteristics were determined: gas temperature; longitudinal electric field intensity; radiation line intensities of Ne (3p → 3s) and Ar (4p → 4s) transitions; intensities of H_α, H_β, and H_γ lines of Balmer series; concentrations of Ne, Ar, and H atoms in metastable and resonance states; concentration of atomic hydrogen; and growth rate of polymer films. The composition of the polymer films was analyzed with the use of infrared spectroscopy. Mathematical modeling of discharges under the selected conditions was carried out. The results of calculations were compared to the experimental data. The mechanism of processes that proceed in the glow discharge plasma is shown to depend strongly on the Ne-to-Ar concentration ratio, which results in the qualitative difference between the compositions of films that were grown at the same pressure and discharge current, as well as in the difference between the growth rates of the films.     

High temperature corrosion of hot-dip aluminized steel in Ar/1%SO<Subscript>2</Subscript> gas

Carbon steels were hot-dip aluminized in Al or Al-1at%Si baths, and corroded in Ar/1%SO₂ gas at 700-800 °C for up to 50 h. The aluminized layers consisted of not only an outer Al(Fe) topcoat that had interdispersed needle-like Al₃Fe particles but also an inner Al-Fe alloy layer that consisted of an outer Al₃Fe layer and an inner Al₅Fe₂ layer. The Si addition in the bath made the Al(Fe) topcoat thin and nonuniform, smoothened the tongue-like interface between the Al-Fe alloy layer and the substrate, and increased the microhardness of the aluminized layer. The aluminized steels exhibited good corrosion resistance by forming thin α-Al₂O₃ scales, along with a minor amount of iron oxides on the surface. The interdiffusion that occurred during heating made the aluminized layer thick and diffuse, resulting in the formation of Al₅Fe₂, AlFe and AlFe₃ layers. It also smoothened the tongue-like interface, and decreased the microhardness of the aluminized layer. The non-aluminized steel formed thick, nonadherent, nonprotective (Fe₃O₄, FeS)-mixed scales.     

The role of Ce ions in electrochemical corrosion of 304 SS in Ce(NO<Subscript>3</Subscript>)<Subscript>3</Subscript>.6H<Subscript>2</Subscript>O

Effects of temperature and potential on the electrochemical corrosion behavior of alloy AISI 304 (UNS S30400) Stainless steel were investigated in 3 wt.% cerium nitrate (Ce[NO₃]₃.6H₂O) solution. With an increase in electrolyte temperature from ambient temperature to 90°C, the corrosion potential of the alloy shifted towards the noble direction, and the resistance to polarization increased due to the formation of Ce-oxide on the electrode surface. The oxide films formed at the open circuit potential (OCP) and a passive potential of 0.4 V_SCE were examined by x-ray photoelectron spectroscopy (XPS). The oxide film formed at 50°C and a passive potentialof 0.4 V_SCE consists of mixed oxides of Ce and Cr, whereas that at OCP consists of only Cr oxide. The formation of Cr oxides on the electrode surface was primarily due to the nitrate (NO₃ ⁻) ions in Ce(NO₃)₃.6H₂O electrolyte.     

Magnetoresistance of the La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> single crystal

The dependence of the resistance ρ of the La_0.7Ca_0.3MnO₃ single crystal on the temperature (in a range of 77 < T < 410 K) and magnetic field H is studied. The dependence of the magnetoresistance Δρ/ρ of the ferromagnetic phase on the field is shown to be determined by the competition of two mechanisms. In low magnetic fields, the magnetoresistance is positive Δρ/ρ > 0 and is determined by changes in the resistance with changing magnetization orientation with respect to the crystallographic axes; in high magnetic fields, the magnetoresistance is negative Δρ/ρ < 0, since it is the suppression of spin fluctuations in the magnetic field that plays the principal role. The phase transition from the ferromagnetic to paramagnetic state is a first-order transition close to the second-order one. In the transition range, the magnetoresistance is determined by the resistivity in the zero field ρ(T) and by the shift of the transition temperature T _C(H) in the magnetic field. In the paramagnetic state, the resistivity ρ(T) has an activation character; similarly to the magnetoresistance of other lanthanum manganites, the magnetoresistance of this single crystal is controlled by a change in the activation energy in the magnetic field.