Structural and optical properties of ZnS thin films deposited by RF magnetron sputtering

Zinc sulfide [ZnS] thin films were deposited on glass substrates using radio frequency magnetron sputtering. The substrate temperature was varied in the range of 100°C to 400°C. The structural and optical properties of ZnS thin films were characterized with X-ray diffraction [XRD], field emission scanning electron microscopy [FESEM], energy dispersive analysis of X-rays and UV-visible transmission spectra. The XRD analyses indicate that ZnS films have zinc blende structures with (111) preferential orientation, whereas the diffraction patterns sharpen with the increase in substrate temperatures. The FESEM data also reveal that the films have nano-size grains with a grain size of approximately 69 nm. The films grown at 350°C exhibit a relatively high transmittance of 80% in the visible region, with an energy band gap of 3.79 eV. These results show that ZnS films are suitable for use as the buffer layer of the Cu(In, Ga)Se₂ solar cells.     

Microstructure and dielectric properties of Dy/Mn doped BaTiO3 ceramics

Dy/Mn doped BaTiO₃ with different Dy₂O₃ contents, ranging from 0.1 to 5.0 at% Dy, were investigated regarding their microstructural and dielectric characteristics. The content of 0.05 at% Mn was constant in all the investigated samples. The samples were prepared by the conventional solid state reaction and sintered at 1290°, and 1350 °C in air atmosphere for 2 h. The low doped samples (0.1 and 0.5 at% Dy) exhibit mainly fairly uniform and homogeneous microstructure with average grain sizes ranged from 0.3 μm to 3.0 μm. At 1350 °C, the appearance of secondary, abnormal, grains in the fine grain matrix and core–shell structure were observed in highly doped Dy/BaTiO₃. Dielectric measurements were carried out as a function of temperature up to 180 °C. The low doped samples sintered at 1350 °C, display the high value of dielectric permittivity at room temperature, 5600 for 0.1Dy/BaTiO₃. A nearly flat permittivity–temperature response was obtained in specimens with 2.0 and 5.0 at% additive content. Using a Curie–Weiss and modified Curie–Weiss low, the Curie constant (C), Curie like constant (C′), Curie temperature (T_C) and a critical exponent (γ) were calculated. The obtained values of γ pointed out the diffuse phase transformation in highly doped BaTiO₃ samples.     

Structural and nanomechanical properties of BiFeO3 thin films deposited by radio frequency magnetron sputtering

The nanomechanical properties of BiFeO₃ (BFO) thin films are subjected to nanoindentation evaluation. BFO thin films are grown on the Pt/Ti/SiO₂/Si substrates by using radio frequency magnetron sputtering with various deposition temperatures. The structure was analyzed by X-ray diffraction, and the results confirmed the presence of BFO phases. Atomic force microscopy revealed that the average film surface roughness increased with increasing of the deposition temperature. A Berkovich nanoindenter operated with the continuous contact stiffness measurement option indicated that the hardness decreases from 10.6 to 6.8 GPa for films deposited at 350°C and 450°C, respectively. In contrast, Young''s modulus for the former is 170.8 GPa as compared to a value of 131.4 GPa for the latter. The relationship between the hardness and film grain size appears to follow closely with the Hall–Petch equation.     

Dielectric properties of Fe-doped Ba0.65Sr0.35TiO3 thin films fabricated by the sol–gel method

Fe-doped Ba_0.65Sr_0.35TiO₃ (BST) thin films have been fabricated on Pt/Ti/SiO₂/Si substrate using the sol–gel method. The structural and surface morphology, dielectric, and leakage current properties of undoped and 1 mol% and 2 mol% Fe-doped BST thin films have been studied in detail. The results demonstrate that the Fe-doped BST films exhibit improved dielectric loss, tunability, and leakage current characteristics as compared to the undoped BST thin films. The improved figure of merit (FOM) of Fe-doped BST thin film suggests a strong potential for utilization in microwave tunable devices.     

Yttrium-doped TiO2 films prepared by means of DC reactive magnetron sputtering

Y₂O₃-doped TiO₂ films were prepared on glass substrates by means of pulsed DC reactive magnetron sputtering method using titanium and yttrium mixed target. XPS results showed that the films were composed of fully oxidation states of the two elements, Y₂O₃–TiO₂ composite oxides. The existence of yttrium inhibited the crystal growth of TiO₂ in the films and Y₂O₃ mainly presented in its amorphous state in the films. UV–vis transmittance of the films decreased whereas their reflectance increased slightly. Yttrium doping had detrimental effect on photocatalytic activity of the TiO₂ films. Photocatalytic degradation efficiency of methyl orange solution declined along with increasing yttrium concentration.     

Effect of Ar:N2 flow rate on morphology,optical and electrical properties of CCTO thin films deposited by RF magnetron sputtering

Calcium copper titanate (CCTO) thin films were deposited on indium tin oxide (ITO) substrates using radio frequency (RF) magnetron sputtering, at selected Ar:N₂ flow rates (1:1, 1:2, 1:4, and 1:6 sccm) at ambient temperature. The effect of Ar:N₂ flow rate on the morphology, optical and electrical properties of the CCTO thin films were investigated using FESEM, XRD, AFM, Hall effect measurement, and UV–Vis spectroscopy. It was confirmed by XRD analysis that the thin films were produced is CCTO with cubic crystal structure. As the flow rate of Ar:N₂ increased up to 1:6 sccm, the thin film thickness reduced from 87 nm to 35 nm while the crystallite size of CCTO thin film decreased from 27 nm to 20 nm. Consequently, the surface roughness of thin film was halved from 8.74 nm to 4.02 nm. In addition, the CCTO thin films deposited at the highest Ar:N₂ flow rate studied, at 1:6 sccm; are having the highest sheet resistivity (13.27 Ω/sq) and the largest optical energy bandgap (3.68 eV). The results articulate that Ar:N₂ flow rate was one of the important process parameters in RF magnetron sputtering that could affect the morphology, electrical properties and optical properties of CCTO thin films.     

As-deposited LiCoO2 thin film cathodes prepared by rf magnetron sputtering

LiCoO₂ thin films were deposited using radio frequency (rf) magnetron sputtering system on stainless steel substrates. Different rf powers, up to 150 W, were applied during deposition. The as-deposited films exhibited (1 0 1) and (1 0 4) preferred orientation and the nanocrystalline film structure was enhanced with increasing rf power. The film crystallinity was examined using X-ray diffraction, Raman scattering spectroscopy and transmission electron microscopy. The compositions of the films were determined by inductively coupled plasma-mass spectroscopy. The average discharge capacity of as-deposited films is about 59 μAh/(cm² μm) for cut-off voltage range of 4.2 and 3.0 V. From the electrochemical cycling data, it is suggested that as-deposited LiCoO₂ films with a nanocrystalline structure and a favorable preferred orientation, e.g. (1 0 1) or (1 0 4) texture, can be used without post-annealing at high temperatures for solid-state thin film batteries.     

Ferroelectric BaTiO3/SrTiO3 multilayered thin films for room-temperature tunable microwave elements

Ferroelectric BaTiO₃/SrTiO₃ with optimized c-axis-oriented multilayered thin films were epitaxially fabricated on (001) MgO substrates. The microstructural studies indicate that the in-plane interface relationships between the films as well as the substrate are determined to be (001)_SrTiO3//(001)_BaTiO3//(001)_MgO and [100]_SrTiO3//[100]_BaTiO3//[100]_MgO. The microwave (5 to 18 GHz) dielectric measurements reveal that the multilayered thin films have excellent dielectric properties with large dielectric constant, low dielectric loss, and high dielectric tunability, which suggests that the as-grown ferroelectric multilayered thin films can be developed for room-temperature tunable microwave elements and related device applications.     

Li-ion diffusion kinetics in LiFePO4 thin film prepared by radio frequency magnetron sputtering

LiFePO₄ thin films were prepared by radio frequency (RF) magnetron sputtering and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and atomic force microscope (AFM). Li-ion chemical diffusion coefficients, , were measured by potentiostatic intermittent titration technique (PITT), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). The effects of Ag content, film thickness, and film orientation on the electrochemical performance and Li-ion chemical diffusion coefficients of the LiFePO₄ thin films were investigated. values were measured using the liquid electrolyte and the solid electrolyte, and the obtained values were discussed. The values by PITT and EIS were in the range of 10⁻¹⁴ to 10⁻¹² and 10⁻¹⁵ to 10⁻¹² cm² s⁻¹, respectively and that by CV was in the order of 10⁻¹⁴ cm² s⁻¹.     

Effect of Fe-doping on the structural,optical and magnetic properties of ZnO thin films prepared by RF magnetron sputtering

In this paper, we report the fabrication and systematic characterization of Fe Doped ZnO thin Films. Fe_xZn_1−x O (x=0<0.05) films were prepared by RF magnetron sputtering on Si (400) substrate. Influence of Fe doping on structural, optical and magnetic properties has been studied. The X-ray diffraction (XRD) analysis shows that Fe doping has affected the crystalline structure, grain size and strain in the thin films. The best crystalline structure is obtained for 3% Fe Doping as observed from Atomic Force Microscopy (AFM) and X-ray diffraction (XRD). The magnetic properties studied using Vibrating Sample Magnetometer reveals the room temperature ferromagnetic nature of the thin films. However, changing the Fe concentration degrades the magnetic property in turn. The mechanism behind the above results has been discussed minutely in this paper.     

Spark plasma sintering of nanocrystalline BaTiO3-powders: Consolidation behavior and dielectric characteristics

BaTiO₃ nanopowders prepared by two different wet chemical routes, one based on microemulsion-mediated synthesis (M-BT) and the other one on the alkoxide-hydroxide method (A-BT) were consolidated by spark plasma sintering (SPS). The densification process, the linear shrinkage rates and the relative densities achieved were strongly dependant on the synthetic route. The results show that fully densified BaTiO₃ ceramics with a grain size of about 200 nm can be obtained in both cases by controlling the sintering temperature during the SPS process. The study of dielectric properties revealed that M-BT derived ceramics show higher permittivity values compared to those obtained for A-BT. The influence of the barium/titanium ratio on the sintering behavior and the dielectric properties is discussed.     

Relation between electrical properties of aerosol-deposited BaTiO3 thin films and their mechanical hardness measured by nano-indentation

ABSTRACT: To achieve a high capacitance density for embedded decoupling capacitor applications, the aerosol deposition (AD) process was applied as a thin film deposition process. BaTiO3 films were fabricated on Cu substrates by the AD process at room temperature, and the film thickness was reduced to confirm the limit of the critical minimum thickness for dielectric properties. As a result, the BaTiO3 thin films that were less than 1-μm thick showed unstable electric properties owing to their high leakage currents. Therefore, to overcome this problem, the causes of the high leakage currents were investigated. In this study, it was confirmed that by comparing BaTiO3 thin films on Cu substrates with those on stainless steels (SUS) substrates, macroscopic defects and rough interfaces between films and substrates influence the leakage currents. Moreover, based on the deposition mechanism of the AD process, it was considered that the BaTiO3 thin films on Cu substrates with thicknesses of less than 1 μm are formed with chinks and weak particle-to-particle bonding, giving rise to leakage currents. In order to confirm the relation between the above-mentioned surface morphologies and the dielectric behavior, the hardness of BaTiO3 films on Cu and SUS substrates was investigated by nano-indentation. Consequently, we proposed that the chinks and weak particle-to-particle bonding in the BaTiO3 thin films with thicknesses of less than 0.5 μm on Cu substrates could be the main cause of the high leakage currents.     

Enhanced mechanical and dielectric behavior of BaTiO3/Cu composites

BaTiO₃/xCu composite ceramics with x = 0-30 wt.% were fabricated by the traditional mixing method in nitrogen gas. The mechanical properties and electric properties of the obtained composites were investigated as a function of the Cu mass fraction using a three bending test and impedance spectroscopy. The results indicated that the relative density of the sintered composites reached above 91%, the Cu-dispersed BaTiO₃ composites enhanced the mechanical properties, particularly the high fracture toughness (∼3.9 MPa m^1/2) and bending strength (∼134 MPa), compared to the monolithic BaTiO₃. Furthermore, the percolation threshold of BaTiO₃/Cu composites was x = 25 wt.%. The permittivity (?_r) markedly increased from ∼2000 for monolithic BaTiO₃ to ∼9000 with increasing Cu up to 30 wt.%. Additionally, the temperature coefficient of this system was less than 5% in the temperature range of 25-115.     

Enhanced photocatalytic activity of Au-buffered TiO2 thin films prepared by radio frequency magnetron sputtering

Au-buffered TiO₂ thin films have been prepared by radio frequency magnetron sputtering method. The structural and morphological properties of the thin films were characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The photocatalytic activity of the samples was evaluated by the photodecomposition of methylene blue. The Au-buffer thin layer placed between the TiO₂ thin films significantly enhanced photocatalytic activity by 50%. Annealing the Au-buffered TiO₂ thin film at 600 °C decreased the film roughness, but it increased the surface area and anatase crystalline size, enhancing the photocatalytic activity.     

Effect of sputtering pressure on structural and dielectric tunable properties of BaSn0.15Ti0.85O3 thin films grown by magnetron sputtering

Lead?free ferroelectric BaSn_0.15Ti_0.85O₃ (BTS) thin films are grown on Pt-coated Si substrates by magnetron sputtering at 650?°C, the effect of sputtering pressure on the microstructural, surface morphological, dielectric properties and leakage characteristic is systematically investigated. XRD analysis shows the crystallinity of BTS thin films with perovskite structure can be improved by appropriate control of the sputtering pressure. The surface morphology analyses reveal that grain size and roughness can be affected by sputtering pressure. The BTS thin films prepared at sputtering pressure of 3.0?Pa exhibit a low dispersion parameter of 0.006, a medium dielectric constant of ~357, a high dielectric tunability of 65.7%@?400?kV/cm and a low loss tangent of 0.0084?@?400?kV/cm. Calculation of figure of merit (FOM) displays a high value of 84.1, and the measurement of leak current shows a very low value of 4.39?×?10^–7 A/cm² at 400?kV/cm. The results indicate that BTS thin film deposited sputtering pressure of 3.0?Pa is an excellent candidate for electrically steerable applications     

Structure,dielectric and piezoelectric properties of Ba0.90Ca0.10Ti1−xSnxO3 lead-free ceramics

Lead-free piezoelectric ceramics Ba_0.90Ca_0.10Ti_1−xSn_xO₃ have been prepared by a conventional ceramic fabrication technique and the effects of Sn⁴⁺ on the structure, dielectric and piezoelectric properties of the ceramics have been investigated. All the ceramics exhibit a pure perovskite structure. After the substitution of Sn⁴⁺, the crystal structure of ceramics is transformed gradually from a tetragonal to an orthorhombic phase, and becomes a pseudo-cubic phase at x≥0.14. The substitution also decreases the Curie temperature greatly from 138 °C at x=0 to 33 °C at x=0.12, and shifts the orthorhombic–tetragonal phase transition to higher temperatures. Coexistence of the orthorhombic and tetragonal phases is formed in the ceramic at x=0.10, leading to significant improvements in the piezoelectric properties: d₃₃=521 pC/N and k_p=45.5%. Our results also reveal that the ceramics sintered at higher temperatures contain larger grains, and thus exhibit more noticeable tetragonal–orthorhombic phase transition and enhanced ferroelectric and piezoelectric properties.     

Effects of annealing temperature on the photocatalytic activity of N-doped TiO2 thin films

The effects of annealing temperature on the photocatalytic activity of nitrogen-doped (N-doped) titanium oxide (TiO₂) thin films deposited on soda-lime-silica slide glass by radio frequency (RF) magnetron sputtering have been studied. Glancing incident X-ray diffraction (GIAXRD), Raman spectrum, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-vis spectra were utilized to characterize the N-doped TiO₂ thin films with and without annealing treatment. GIAXRD and Raman results show as-deposited N-doped TiO₂ thin films to be nearly amorphous and that the rutile and anatase phases coexisted when the N-doped TiO₂ thin films were annealed at 623 and 823 K for 1 h, respectively. SEM microstructure shows uniformly close packed and nearly round particles with a size of about 10 nm which are on the slide glass surface for TiO₂ thin films annealed at 623 K for 1 h. AFM image shows the lowest surface roughness for the N-doped TiO₂ thin films annealed at 623 K for 1 h. The N-doped TiO₂ thin films annealed at 623 K for 1 h exhibit the best photocatalytic activity, with a rate constant (k_a) of about 0.0034 h⁻¹.     

Properties of BaTiO3 synthesized from barium titanyl oxalate

In order to enhance the tetragonality of BaTiO₃ derived from barium titanyl oxalate (BTO), various treatments were carried out by considering the thermal decomposition mechanism of BTO in air. A multi-step heat treatment process and the addition of carbon black, as a particle growth inhibitor, were effective in increasing the tetragonality, whilst maintaining a particle size smaller than 200 nm. The synthesized BaTiO₃ powder with a mean particle size of 177 nm showed a tetragonality and K-factor of 1.0064 and approximately 3, respectively.     

Electrical properties and structure of grain boundaries in n-conducting BaTiO3 ceramics

The electrical properties of positive temperature coefficient (PTC) ceramics are expected to strongly correlate with the potential barrier height at grain boundaries, which in turn may be influenced by the grain boundary structure and chemistry. In this study, n-conducting BaTiO₃ ceramics co-doped by La and Mn were prepared, and the electrical properties were determined by impedance spectroscopy and dc four-point van der Pauw measurements. Detailed analysis of the grain boundary structure was performed by electron microscopy techniques across different length scales. The study revealed that the randomly oriented polycrystalline microstructure was dominated by large angle grain boundaries, which in the present case were dry although a secondary crystalline and glass phase formed at triple junctions. The relationship between the observed grain boundary atomic structures and electrical properties is briefly discussed.     

Low temperature synthesis and dielectric, ferroelectric and piezoelectric study of microwave sintered BaTiO3 ceramics

Barium titanate (BaTiO₃/BT) ferroelectric system was synthesized in single perovskite phase at low temperature by using powders derived from modified solid state reaction (MSSR) and sintered by microwave (MW) processing routes. Conventional calcination temperature was optimized at 900 °C for 4 h. MW sintering of BT samples was carried out at 1100 °C for 30 min to get dense (98% density) ceramics. Room temperature (RT) dielectric constant (?_r) and dielectric loss (tan δ) at 1 kHz frequency of MW sintered BT samples was found to be ∼2500 and 0.03, respectively. Saturated polarization vs. electric field (P-E) loops with remnant polarization (P_r) ∼6 μC/cm² and coercive field (E_c) ∼1.45 kV/cm confirmed the ferroelectric nature of MW sintered BT samples. Piezoelectric coefficient from strain vs. electric field (S-E) loops study was found to be 335 pm/V.