Structural and pyroelectric properties of sol–gel derived multiferroic BFO thin films

Multiferroic BFO/PZT multilayer films were fabricated by spin-coating method on the (1 1 1)Pt/Ti/SiO₂/Si substrate alternately using PZT(30/70), PZT(70/30) and BFO alkoxide solutions. The structural and ferroelectric properties were investigated for uncooled infrared detector applications. The coating and heating procedure was repeated six times to form BFO/PZT multilayer films. All films showed the typical XRD patterns of the perovskite polycrystalline structure without presence of the second phase such as Bi₂Fe₄O₃. The thickness of BFO/PZT multilayer film was about 200–220 nm. The ferroelectric properties such as dielectric constant, remnant polarization and pyroelectric coefficient were superior to those of single composition BFO film, and those values for BFO/PZT(70/30) multilayer film were 288, 15.7 μC/cm² and 9.1 × 10^?9 C/cm² K at room temperature, respectively. Leakage current density of the BFO/PZT(30/70) multilayer film was 3.3 × 10^?9 A/cm² at 150 kV/cm. The figures of merit, F_V for the voltage responsivity and F_D for the specific detectivity, of the BFO/PZT(70/30) multilayer film were 6.17 × 10^?11 Ccm/J and 6.45 × 10^?9 Ccm/J, respectively.     

Microstructure and ferroelectric properties of dysprosium-doped bismuth titanate thin films

Bi₄Ti₃O₁₂ (BIT) ferroelectric thin films with Dy³⁺ substitution (Bi_4−xDy_xTi₃O₁₂, x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively) were grown on Pt(111)/Ti/SiO₂/Si(100) substrates using sol–gel method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) revealed that after annealing at 710 °C for 10 min, all Bi_4−xDy_xTi₃O₁₂ films became polycrystallites. Among all the deposited thin films, the Bi_3.4Dy_0.6Ti₃O₁₂ specimen exhibits improved ferroelectric properties with the largest average remanent polarization (2Pr) of 53.06 μC/cm² under applied field of 400 kV/cm and fatigue free characteristics (16% loss of 2Pr after 1.5 × 10¹⁰ switching cycles), indicating that it is suitable for non-volatile ferroelectric random access memories applications.     

Evolution of different structural phases of TiO2 films with oxygen partial pressure and Fe doping and their electrical properties

We have studied the influence of oxygen partial pressure (OPP; 250 mTorr–1 × 10^?5 Torr) and Fe doping (2 and 4 at.%) on structural and electrical properties of TiO₂ thin films on LaAlO₃ substrates. X-ray photoelectron spectroscopy suggests that Fe is not in metal cluster form. It is found that the evolution of the three phases; anatase, rutile and brookite of TiO₂ as well as the magneli phase (Ti_nO_2n?1) strongly depends on the OPP and Fe doping concentration. All the films grown at 250 mTorr show insulating behavior, whereas films grown at 1 × 10^?2 and 1 × 10^?4 Torr reveal high temperature metallic to low temperature semiconducting transition. Interestingly, films deposited at 1 × 10^?5 Torr reveal charge ordering, which is contributed to the magneli phase of TiO₂. The present study suggests that functionality of TiO₂ thin film based devices can be tuned by properly selecting the OPP and dopant concentration.     

Synthesis and characteristics of nature-superlattice-structured Bi3TiNbO9–Bi4Ti3O12 ferroelectric thin films by MOD

Natural-superlattice-structured ferroelectric thin films, Bi₃TiNbO₉–Bi₄Ti₃O₁₂ (BTN–BIT), have been synthesized on Pt/Ti/SiO₂/Si by metal organic decomposition (MOD) using BTN–BIT (1 mol:1 mol) solution. BTN–BIT films show natural-superlattice peaks below 2θ = 20° in X-ray diffraction patterns, which indicate that the BTN–BIT films annealed at 700–800 °C in O₂ ambient are consisted of iteration of two unit cells of Bi₃TiNbO₉ and one unit cell of Bi₄Ti₃O₁₂. As the annealing temperature increases from 600 to 750 °C, uniform and crack-free films, better crystallinity and ferroelectric properties can be obtained, but the pyrochlore phase in BTN–BIT films annealed over 800 °C would impair the ferroelectric properties. With the increase of O₂ flow rate from 0.5 to 1.5 L/min, both remanent polarization P_r and coercive electric field E_C increase, which are mainly attributed to reduction of the vacanvies of Bi and oxide ions in the films. Natural-superlattice-structured BTN–BIT thin films having 2–1 superlattice annealed at 750 °C in O₂ ambient with a flow rate of 1.5 L/min exhibit superior ferroelectric properties of P_r = 23.5 μC/cm² and E_C = 135 kV/cm.     

Preparation of ZnO:Al thin film on transparent TPT substrate at room temperature by RF magnetron sputtering technique

Aluminum doped ZnO thin films (ZnO:Al) deposited on flexible substrates are suitable to be used as transparent conductive oxide (TCO) thin films in solar cells because of the excellent optical and electrical properties. TPT films are a kind of composite materials and are usually used as encapsulation material of solar panels. In this paper, ZnO:Al film was firstly deposited on transparent TPT substrate by RF magnetron sputtering. The structural, optical, and electrical properties of the film were investigated by X-ray diffractometry (XRD), scanning electron microscope (SEM), UV–visible spectrophotometer, as well as Hall Effect Measurement System. Results revealed that the obtained film had a hexagonal structure and a highly preferred orientation with the c-axis perpendicular to the substrate. Also, the film showed a high optical transmittance over 80% in the visible region and a resistivity of about 3.03 × 10^? 1 Ω·cm.     

Spectroscopic ellipsometry study of thin film thermo-optical properties

Spectroscopic ellipsometry (SE) was employed to realize in-situ monitoring and the determination of thermo-optic coefficients (TOC) of thin films by integrating a temperature controlled hot stage to the ellipsometer and applying the empirical relationship of Cauchy between the refractive index and wavelength in the data analysis. Magnetron sputtered titanium oxide thin films of 350 nm thick both as-deposited and post-deposition annealed were prepared on silicon wafers for this investigation. Results of ellipsometric analysis show that as-deposited TiO₂ films have a negative TOC of ? 1.21 × 10^? 4 K^? 1 at 630 nm over the test temperature range 304–378 K. The post-deposition annealing at 923 K for 2 hours leads an increase in film refractive index to 2.29 from 2.17 for as-deposited TiO₂ films, and an enhancement in TOC up to ? 2.14 × 10^? 4 K^? 1. X-ray diffraction (XRD) and scanning electron microscopy (SEM) cross-sectional analysis were performed for film structure characterization.     

Growth and characterization of pulsed-laser-deposited polycrystalline Bi3.33Sm0.67Ti3O12 ferroelectric thin films

Ferroelectric Bi_3.33Sm_0.67Ti₃O₁₂ (BSmT) thin films have been fabricated on Pt/TiO_x/SiO₂/Si substrates by pulsed laser deposition and their structural and ferroelectric properties have been characterized. The structure and morphology of the films were characterized using X-ray diffraction, atomic force microscopy, and scanning electron microscopy. About 520-nm-thick BSmT films grown at 700 °C exhibit excellent ferroelectric properties with a remanent polarization (2P_r) of 41.8 μC/cm² and coercive field (E_c) of 91.0 kV/cm, at an applied electric field of 385 kV/cm. The leakage current density was 2.0 × 10^− 6 A/cm² at a dc electric field of 200 kV/cm. The films also demonstrate fatigue-free behavior up to 10⁹ read/write switching cycles with 1 MHz bipolar pulses at an electric field of 192 kV/cm. As a result, Sm-substituted bismuth titanate films with good ferroelectric properties and excellent fatigue resistance are useful candidates for ferroelectric memory applications.     

Formation of F-doped ZnO transparent conductive films by sputtering of ZnF2

Fluorine-doped ZnO transparent conductive thin films were successfully deposited on glass substrate by radio frequency magnetron sputtering of ZnF₂. The effects of rapid thermal annealing in vacuum on the optical and electrical properties of fluorine-doped ZnO thin films have been investigated. X-ray diffraction spectra indicate that no fluorine compounds, such as ZnF₂, except ZnO were observed. The specimen annealed at 500 °C has the lowest resistivity of 6.65 × 10^? 4 Ω cm, the highest carrier concentration of 1.95 × 10²¹ cm^? 3, and the highest energy band gap of 3.46 eV. The average transmittance in the visible region of the F-doped ZnO thin films as-deposited and annealed is over 90%.     

Room temperature multiferroic properties of (Bi0.95La0.05)(Fe0.97Mn0.03)O3/NiFe2O4 double layered thin film

(Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film was prepared on a Pt(111)/Ti/SiO₂/Si(100) substrate by a chemical solution deposition method. X-ray diffraction and Raman scattering spectroscopy studies confirmed the formation of the distorted rhombohedral perovskite and the inverse spinel cubic structures for the (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film. The (Bi_0.95La_0.05)(Fe_0.97Mn_0.03)O₃/NiFe₂O₄ double layered thin film exhibited well saturated ferromagnetic (2 M_r of 18.1 emu/cm³ and 2H_c of 0.32 kOe at 20 kOe) and ferroelectric (2P_r of 60 μC/cm² and 2E_c of 813 kV/cm at 866 kV/cm) hysteresis loops with low order of leakage current density (4.5 × 10⁻⁶ A/cm² at an applied electric field of 100 kV/cm), which suggest the ferroelectric and ferromagnetic multi-layers applications in real devices.     

Structural and optical studies on dc reactive magnetron sputtered Cu2O films

Cuprous oxide (Cu₂O) thin films were deposited by dc reactive magnetron sputtering technique onto glass substrates by sputtering of pure copper target in a mixture of argon and oxygen gases under various oxygen partial pressures in the range 8 × 10^− 3–1 × 10^− 1 Pa at a constant substrate temperature of 473 K and a sputtering pressure of 4 Pa. The dependence of cathode potential on the oxygen partial pressure was explained in terms of cathode poisoning effect. The influence of oxygen partial pressure on the structural and optical properties of Cu₂O films was systematically studied. Single phase films of Cu₂O were obtained at an oxygen partial pressure of 2 × 10^− 2 Pa. The films formed at an oxygen partial pressure of 2 × 10^− 2 Pa were polycrystalline with cubic structure and exhibited an optical band gap of 2.04 eV.     

Study on adhesion and wear resistance of multi-element (AlCrTaTiZr)N coatings

Multi-element (AlCrTaTiZr)N films were deposited on cemented carbide and M2 steel substrates by reactive RF magnetron sputtering. Prior to nitride film deposition, an interlayer between the film and the substrate was introduced to improve adhesion property. The influence of interlayer materials (Ti, Cr, and AlCrTaTiZr alloy) and interlayer thickness (0–400 nm) on the adhesion and tribological properties of films was investigated. In this study, the nitride film deposited at R_N = 20% exhibited the highest hardness (35.2 GPa) and the lowest residual compressive stress (? 1.52 GPa), and was prepared as the top layer for further testing. The interlayer materials can effectively improved the film adhesion onto the cemented carbide substrates, and the adhesive failure was not observed even under the normal load of 100 N. For M2 steel substrates, only the Cr interlayer can slightly improve the film adhesion, and the cohesive and adhesive failure can be found at relatively lower applied load. The optimal interlayer thickness was 100–200 nm for the 1 µm-thick (AlCrTaTiZr)N film and can be related to the stress evolution. The friction coefficient and wear rate for the (AlCrTaTiZr)N film were 0.82 and 4.9 × 10^? 6 mm³/Nm, respectively, and almost kept constant under different interlayer materials and thickness. The worn-through event of the nitride film during tribological test occurred easily owing to its poor adhesion behavior, and can be improved by interlayer additions.     

Influence of Ar/O2 ratio on the properties of transparent conductive ZnO:Ga films prepared by DC reactive magnetron sputtering

Ga-doped zinc oxide (ZnO:Ga) transparent conductive films with highly (002)-preferred orientation were deposited on glass substrates by DC reactive magnetron sputtering method in Ar + O₂ ambience with different Ar/O₂ ratios. The structural, electrical, and optical properties were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The resistivity and optical transmittance of the ZnO:Ga thin films are of the order of 10^− 4 Ω cm and over 85%, respectively. The lowest electrical resistivity of the film is found to be about 3.58 × 10^− 4 Ω cm. The influences of Ar/O₂ gas ratios on the resistivity, Hall mobility, and carrier concentration were analyzed.     

Biopolymer-manganese oxide nanoflake nanocomposite films fabricated by electrostatic layer-by-layer assembly

Bio-nanocomposite films based on chitosan and manganese oxide nanoflake have been fabricated via the layer-by-layer (LBL) self-assembly technique. UV–vis absorption spectra showed that the subsequent growth of the nanocomposite film was regular and highly reproducible from layer to layer. X-ray photoelectron spectroscopy (XPS) spectra confirmed the incorporation of chitosan and manganese oxide nanoflake into the films. Scanning electron microscopy (SEM) images revealed that the nanocomposite film had a continuous surface and a layered structure. A sensitive hydrogen peroxide (H₂O₂) amperometric sensor was fabricated with the chitosan–manganese oxide nanoflake nanocompoite film. The sensor showed a rapid and linear response to H₂O₂ over the range from 2.5 × 10^? 6 to 1.05 × 10^? 3 M, with a sensitivity of 0.038 A M^? 1 cm^? 2.     

Chemical bonding and optoelectrical properties of ruthenium doped yttrium oxide thin films

Highly infrared transparent conductive ruthenium doped yttrium oxide (RYO) films were deposited on zinc sulfide and glass substrates by reactive magnetron sputtering. The structural, optical, and electrical properties of the films as a function of growth temperature were studied. It is shown that the sputtered RYO thin films are amorphous and smooth surface is obtained. The infrared transmittance of the films increases with increasing the growth temperature. RYO films maintain greater than ∼65% transmittance over a wide wavelength range from 2.5 μm to 12 μm and the highest transmittance value reaches 73.3% at ∼10 μm. With increasing growth temperature, the resistivity changed in a wide range and lowest resistivity of about 3.36 × 10⁻³ Ω cm is obtained at room temperature. The RYO thin films with high conductivity and transparency in IR spectral range would be suitable for infrared optical and electromagnetic shielding devices.     

Effects of the sulfidation temperature on the structure,composition and optical properties of ZnS films prepared by sulfurizing ZnO films

Nanocrystalline ZnS films have been prepared by sulfidation of the reactive magnetron sputtered ZnO films. The structure, composition and optical properties of the sulfurized ZnO films as a function of the sulfidation temperature (T_S) have been systematically studied. It is found that at T_S ⩾ 400 °C ZnO is completely converted to ZnS with the hexagonal structure. The ZnS films have a strongly (0 0 2) preferred orientation and an optical transparency of about 80% in the visible region. In addition, at T_S < 444.6 °C (boiling point of sulfur), some residual sulfur decomposed from H₂S gas can adhere to the sulfurized film surface while at T_S = 580 °C a S/Zn ratio much higher than the ideal stoichiometric proportion of ZnS is obtained for the ZnS films. ZnS films with a minimum XRD FWHM value of 0.165° and a good S/Zn ratio of 0.99 are obtained at a temperature of 500 °C indicating the ZnS films to be suitable for use in the thin film solar cells.     

Enhanced dielectric properties of Mn doped Ba0.6Sr0.4TiO3 thin films fabricated by pulsed laser deposition

Pure and 2 mol% Mn doped Ba_0.6Sr_0.4TiO₃ (BST) thin films have been deposited on La_0.67Sr_0.33MnO₃ (LSMO) coated single-crystal (001) oriented LaAlO₃ substrates using pulsed-laser deposition technique. The bilayer films of BST and LSMO were epitaxially grown in pure single-oriented perovskite phases for both samples, and an enhanced crystallization effect in the BST film was obtained by the addition of Mn, which were confirmed by X-ray diffraction (XRD) and in situ reflective high energy electron diffraction (RHEED) analyses. The dielectric properties of the BST thin films were measured at 100 kHz and 300 K with a parallel-plate capacitor configuration. The results have revealed that an appropriate concentration acceptor doping is very effective to increase dielectric tunability, and to reduce loss tangent and leakage current of BST thin films. The figure-of-merit (FOM) factor value increases from 11 (undoped) to 40 (Mn doped) under an applied electric field of 200 kV/cm. The leakage current density of the BST thin films at a negative bias field of 200 kV/cm decreases from 2.5 × 10^− 4 A/cm² to 1.1 × 10^− 6 A/cm² by Mn doping. Furthermore, a scanning-tip microwave near-field microscope has been employed to study the local microwave dielectric properties of the BST thin films at 2.48 GHz. The Mn doped BST film is more homogeneous, demonstrating its more potential applications in tunable microwave devices.     

Biomimetic mineralisation of apatites on Ca2+ activated cellulose templates

We investigated the activation of regenerated cellulose 2D model thin films and 3D fabric templates with calcium dihydroxide. The Langmuir–Blodgett (LB) film technique was applied for manufacturing of the model thin films using a trimethylsilyl derivative of cellulose (TMS-cellulose). Regenerated cellulose films were obtained by treating the TMS-cellulose LB-films with hydrochloric acid vapours. For 3D templates, regenerated cellulose fabrics (Lyocell®) were used. The regenerated cellulose templates were activated with a Ca(OH)₂-suspension and subsequently exposed to 1.5 × SBF to induce the in situ formation of biomimetic calcium phosphate phases. FTIR and Raman spectroscopy showed that the Ca(OH)₂ and calcite present from reaction with HCO₃⁻ on the template surface were dissolved in the initial stage of exposure to the 1.5 × SBF. After 1 day, the formation of apatitic phases in 1.5 × SBF was observed. According to detailed calculations, high supersaturation levels S in close vicinity to the template surface (S > 16) resulting from the Ca²⁺ diffusion induced the formation of biomimetic calcium phosphate. The biomimetic calcium phosphates were identified by FTIR and Raman spectroscopy as highly carbonated apatites (HCA) lacking hydroxyl ions. 3D fabric templates of regenerated cellulose covered with a biomimetic coating of apatite might be of particular interest for novel scaffold architectures in bone repair and tissue engineering.     

Effects of ZnO addition on electrical and structural properties of amorphous SnO2 thin films

Amorphous Zn–Sn–O (ZTO) thin films with relative Zn contents (= [at.% Zn]/([at.% Zn] + [at.% Sn])) of 0, 0.08 and 0.27 were fabricated by co-sputtering of SnO₂ and ZnO targets at room temperature. Changes in structural, electrical and optical properties together with electron transport properties were examined upon post-annealing treatment in the temperature range from 200 to 600 °C in vacuum and in air. Characterization by XRD showed that an amorphous ZTO thin film crystallized at higher temperatures with increasing Zn content. Crystallized ZTO films with a relative Zn content of 0.27 might not contain a single SnO₂ phase which is observed in the films of the other compositions. Amorphous ZTO films showed decreasing electrical resistivities with increasing annealing temperature, having a minimum value of 1 × 10^− 3 Ω cm. Upon crystallization, the resistivities increased drastically, which was attributed to poor crystallinity of the crystallized films. All the ZTO films were found to be degenerate semiconductors with non-parabolic conduction bands having effective masses varying from 0.15 to 0.3 in the carrier concentration range of 6 × 10¹⁸ to 2 × 10²⁰ cm^− 3. As for a ZTO film with a relative Zn content of 0.27, the degree of non-parabolicity was much lower compared with films of the other compositions, leading to a relatively stable mobility over a wide range of carrier concentration.     

Oxygen partial pressure dependence of the structural properties of CdO thin films deposited by a modified reactive vacuum evaporation process

Thin films of cadmium oxide were thermally deposited on glass substrates at partial pressures of oxygen, pO₂ in the range 1.33×10⁻² to 0.133 Pa at a substrate temperature of 160 °C. Energy dispersive analysis of X-ray fluorescence (EDAX) revealed that the CdO films deposited at pO₂ value of 4.00×10⁻² Pa were nearly stoichiometric. X-ray diffractometry (XRD) confirmed the polycrystalline nature of the film structure. All the films showed an fcc structure of the NaCl-type, as the dominant phase. The films exhibited preferred orientation along the (1 1 1) diffraction plane. The texture coefficients calculated for the various planes at different oxygen partial pressures (pO₂) indicated that the maximum preferred orientation of the films occurred along the (1 1 1) plane at an oxygen partial pressure of 4.00×10⁻² Pa. This was interpreted in terms of oxygen chemisorption and desorption processes. The lattice parameters determined from the diffraction peaks were in the range 4.655–4.686 Å. The average lattice parameter a₀ found by extrapolation using the Nelson–Riley function was 4.696 Å. Both the lattice parameter and the crystallite size were found to increase with increased partial pressure of oxygen. On the other hand, the strain and dislocation density were found to decrease as the partial pressure of oxygen was raised. A maximum (80%) in the optical transmittance at λ=600 nm and minimum in the electrical resistivity (9.1×10⁻⁴ Ω cm) of the films occurred at an optimum partial pressure of oxygen of 4.00×10⁻² Pa. The results are discussed.     

The low temperature synthesis of Al doped ZnO films on glass and polymer using pulsed co-magnetron sputtering: H2 effect

It has been reported that a small amount of hydrogen in argon plasma induces an increase in the crystallite size of the as-deposited films. In addition, control of the hydrogen partial pressure is expected to improve the carrier mobility by increasing the crystallinity of the film (larger crystal size and lower grain boundary effects). Al doped ZnO (AZO) films were deposited by co-CFUBM (closed field unbalanced magnetron) sputtering. The ultimate aim was to deposit transparent films on a polymer substrate with a low electrical resistivity. Therefore, the structural, optical and electrical properties of AZO films were investigated as a function of the hydrogen partial pressure. A minimum resistivity and maximum transparency of 8 × 10^− 4 Ω cm and 88.1% were obtained, respectively. A critical P_H2 was expected to improve the carrier mobility by increasing the crystallinity of the film. However, above this value, conductivity reduced due to the formations of oxides such as ZnO and Al₂O₃ in the AZO films.