Microstructure and ferroelectric properties of compositionally graded Nd-doped Bi4Ti3O12 thin films prepared by sol–gel method

The compositionally graded Bi_4?xNd_xTi₃O₁₂ (BNT) thin films were prepared on Pt/Ti/SiO₂/Si substrates by sol–gel method. Their microstructure, ferroelectric and dielectric properties were investigated. The single-phase upgraded and downgraded BNT films were obtained with (117) preferred orientation. Compared to the homogeneous BNT films prepared by the same conditions, the remanent polarization (P _r) and permittivity (ε _r) of compositionally graded BNT films were significantly enhanced. The upgraded BNT film showed larger 2P _r (34.9?μC/cm²) and ε _r (509), and those of downgraded BNT film were 29.4?μC/cm² and 505. Bi element in the downgraded BNT film accumulated near the interface of film/Pt bottom electrode, which deteriorated the compositional gradient and resulted in decreasing 2P _r and ε _r compared to the upgraded BNT film.     

Effects of Bi doping on dielectric and ferroelectric properties of PLBZT ferroelectric thin films synthesized by sol–gel processing

[Pb _0·95(La_1???y Bi _y ) _0·05][Zr_0·53Ti_0·47]O₃ (PLBZT) ferroelectric thin films have been synthesized on indium tin oxide (ITO)-coated glass by sol–gel processing. PLBZT thin films were annealed at a relatively low temperature of 550 °C in oxygen ambient. Effects of Bi doping on structure, dielectric and ferroelectric properties of PLBZT were investigated. Bi doping is useful in crystallization of PLBZT films and promoting grain growth. When the Bi-doping content ${\mathit{y}}$ is not more than 0·4, an obvious improvement in dielectric properties and leakage current of PLBZT was confirmed. However, when the Bi-doping content is more than 0·6, the pyrochlore phase appears and the remnant polarization P _r of PLBZT thin films is smaller than that of $\left({Pb}_{{1-x}} {\bf La}_{x}\right)\!\!\left({Zr}_{{1-y}} {Ti}_{y}\right){O}_{3}$ (PLZT) thin films without Bi doping. PLBZT thin films with excessive Bi-doping content are easier to fatigue than PLZT thin films.     

Thermal stability and electrical properties of Ag–Ti films and Ti/Ag/Ti films prepared by sputtering

Ag–Ti (100 nm) alloy film, and Ti/Ag (100 nm) double-layer and Ti/Ag (100 nm)/Ti triple-layer films were prepared by rf sputtering to investigate the effect of Ti on suppression of agglomeration of the Ag thin film caused by thermal treatment. Scanning electron microscopy revealed that the Ag–Ti and Ti/Ag/Ti films had high thermal stability. X-ray photoelectron spectroscopy analysis showed that the surfaces of both kinds of films were covered with a TiO₂ layer after annealing, which was considered to be the key factor for improvement of the thermal stability of the films. In addition, scratch tests indicated improvement of the adhesive strength of the Ti/Ag/Ti film to the SiO₂ substrate due to the underlying Ti film layer, which effectively promoted suppression of Ag agglomeration. However, the resistivity of the Ag–Ti films increased abruptly with increasing Ti content due to the impurity scattering effect, and minimum usage of the alloying element was required to achieve low resistivity. In contrast, the Ti/Ag/Ti film exhibited both low resistivity and high thermal stability.     

Shape memory behavior of Fe–Pd alloy thin films prepared by dc magnetron sputtering

Fe–Pd films have been deposited onto fused quartz and silicon substrates by dc magnetron sputtering. When an arc-melted and homogenized Fe–30at.% Pd alloy disk was used as a sputtering target, Fe–Pd films fabricated was shown to contain about 24 at.% Pd under the deposition condition used. The target configuration was then modified by placing Pd wires on the target so as to control the Pd content of films with an accuracy of 1 at.% Pd. Fe–Pd films containing 28.5 at.% Pd underwent a thermoelastic fcc-to-fct martensite transformation after annealing at 900 °C followed by quenching into iced water. Apparently, the reverse transformation was also thermoelastic and the thermoelastic transformations occurred repeatedly upon thermal cycling. Some of the Fe–28.5at.% Pd films were peeled off from the quartz substrate and they showed SM effects upon heating after deformation. A diaphragm-shaped free-standing film was also fabricated on a thin Si substrate. This film showed attractive transformation characteristics, including a narrow transformation hysteresis loop of about 4 °C and a small temperature difference between M_f and A_f (about 10 °C) in addition to M_s (43 °C) close to room temperature. This diaphragm-shaped film showed a reversible ballooning behavior with a maximum strain of about 0.05% upon thermal cycling.     

Effect of annealing pressure on structure and properties of ferroelectric Bi3.25La0.75Ti3O12 thin films prepared by sol�Cgel method

The effect of annealing pressure was investigated for Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films prepared on Pt/TiO₂/SiO₂/p-Si(100) substrates by sol?Cgel method. The amorphous films were annealed at 750 °C for 30 min under different oxygen pressures varying from 10^?4 to 3 atm. The largest P _r of 17.8 ??C/cm² with the E _c of 73.6 kV/cm was obtained for the film annealed under 0.1 atm P_O2. Then the structure, crystallization degree, and morphology were characterized by X-ray diffraction (XRD), Raman spectroscopy, and field-emission scanning electron microscope (FSEM) to clarify the effect of annealing pressure on the ferroelectric properties. The XRD and Raman spectroscopy results indicated a clear decreasing of the crystallization degree of the films annealed under 10^?4 and 3 atm P_O2. FSEM results showed the different growth orientation of grains under different oxygen pressures. This study indicated some important effects of annealing pressure on the physical properties of BLT thin films.     

Effect of Zn doping on structure and ferroelectric properties of PST thin films prepared by sol–gel method

(Pb _y Sr_1−y )Zn _x Ti_1−x O_3−x thin films were prepared on ITO/glass substrate by sol–gel process using dip-coating method. The phase structure, morphology and ferroelectric property of the thin film were studied. All the thin films show the typical perovskite phase structure. Both the crystallinity and c/a ratio of the perovskite phase increases initially and then decreases gradually with doping Zn in the thin film. Ferroelectric properties of the Zn-doped PST thin films, including ferroelectric hysteresis-loop, remnant polarization and coercive force, decrease gradually with increasing Zn. And the effect of Zn on ferroelectric properties is more obvious in PST thin film with high content of Pb than that with low Pb although the high lead thin film exhibits high intrinsic ferroelectric properties.     

Effect of substrates on epitaxy of Bi4Ti3O12 thin films by dipping—pyrolysis process

Bismuth titanate (Bi₄Ti₃O₁₂) thin films have been prepared on various substrates by the dipping—pyrolysis process using metal naphthenates as starting materials. The crystallinity and in-plane alignment of the films are analysed by X-ray diffraction θ-2θ scans and β scans (polar diagrams), respectively. Highly c-axis-oriented Bi₄Ti₃O₁₂ thin films with smooth surfaces are obtained by heat treatment at 750°C on SrTiO₃ (100), LaAlO₃ (100) and MgO (100) substrates, while films grown on Si (100) exhibit polycrystalline characteristics. The fluctuation of in-plane alignment of epitaxially grown films depends on the lattice-misfit values between the films and the substrates used; Bi₄Ti₃O₁₂ films on MgO shows the largest full width at half maximum values in their β scans.     

RBS,XRR and optical reflectivity measurements of Ti–TiO2 thin films deposited by magnetron sputtering

Single-, bi- and tri-layered films of Ti–TiO₂ system were deposited by d.c. pulsed magnetron sputtering from metallic Ti target in an inert Ar or reactive Ar + O₂ atmosphere. The nominal thickness of each layer was 50 nm. The chemical composition and its depth profile were determined by Rutherford backscattering spectroscopy (RBS). Crystallographic structure was analysed by means of X-ray diffraction (XRD) at glancing incidence. X-ray reflectometry (XRR) was used as a complementary method for the film thickness and density evaluation. Modelling of the optical reflectivity spectra of Ti–TiO₂ thin films deposited onto Si(1 1 1) substrates provided an independent estimate of the layer thickness. The combined analysis of RBS, XRR and reflectivity spectra indicated the real thickness of each layer less than 50 nm with TiO₂ film density slightly lower than the corresponding bulk value. Scanning Electron Microscopy (SEM) cross-sectional images revealed the columnar growth of TiO₂ layers. Thickness estimated directly from SEM studies was found to be in a good agreement with the results of RBS, XRR and reflectivity spectra.     

Effects of annealing ambient on ferroelectric properties and surface chemistry of sol–gel derived Bi3.25La0.75Ti3O12 thin films

In this work, Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were prepared by sol–gel coatings followed by rapid thermal annealing in Ar or O₂ ambient. The correlation among annealing ambient, ferroelectric characteristics and surface chemistry of the BLT thin films were investigated. The BLT thin film annealed in Ar showed weaker crystallization, less dense surface and smaller polarization value than that annealed in O₂. After 10⁹ cycles, the remnant polarization of the BLT film annealed in Ar decreased to 83.5 % of the initial value while it remained 89.5 % for the sample annealed in O₂. X-ray photoelectron spectroscopy results indicated the inferior fatigue characteristics of the sample annealed in Ar was the comprehensive result of oxygen vacancies vicinity to Bi and Ti ion in the thin film.     

Effects of RF magnetron sputtering power density on NTC characteristics of Mn–Co–Ni thin films

Thin film NTCR (negative temperature coefficient resistance), based on Mn–Co–Ni oxide, was prepared by reactive RF magnetron sputtering with various sputtering power density (0.95–3.82 W/cm²). The crystalline structure and surface morphology of the NTC thin film were analyzed by XRD and AFM. The NTC characteristics, as a function of sputtering power density, were investigated. The values of B, α ₂₅ and R ₂₅ were in the range of 3,740–3,847 K, ?4.328 to ?4.207 %/K and 8.7–2,082.5 KΩ, respectively. With the increasing power density, the standard resistance (R ₂₅ ) decreased and the consistency of R₂₅ increased. Thin film NTCR with stable B value (3,740 K), low R ₂₅ (10⁴ Ω) and excellent consistency could be fabricated in mass production with about 3.82 W/cm² sputtering power density.     

Power and gas pressure effects on properties of amorphous In–Ga–ZnO films by magnetron sputtering

Amorphous In–Ga–ZnO thin films were deposited on quartz glass substrate at room temperature utilizing radio frequency magnetron sputtering technique. Sputtering power and oxygen flow rate effects on the physical properties of the In–Ga–ZnO films were systematically investigated. It is shown the film deposition rate and the conductivity of the In–Ga–ZnO films increased with the sputtering power. The as-grown In–Ga–ZnO films deposited at 500 W exhibited the Hall mobility of 17.7 cm²/Vs. Average optical transmittance of the In–Ga–ZnO films is greater than 80% in the visible wavelength. The extracted optical band gap of the In–Ga–ZnO films increased from 3.06 to 3.46 eV with increasing the sputtering power. The electrical properties of the In–Ga–ZnO films are greatly dependent on the O₂/Ar gas flow ratio and post-growth annealing process. Increasing oxygen flow rate converted the In–Ga–ZnO films from semiconducting to semi-insulating, but the resistivity of the films was significantly reduced after being annealed in vacuum. Both the as-grown and annealed In–Ga–ZnO films show n-type electrical conductivity.     

Characterization of YBa2Cu3O7−δ thin films deposited by dc magnetron sputtering

It was found from plan-view transmission electron microscopy (TEM) observations that c-oriented YBa₂Cu₃O_7– (YBCO) films on LaAlO₃, prepared by the magnetron sputtering technique had a single crystalline-like YBCO matrix, but always contained some precipitates of impurity phases. A large number of highly defective twin boundaries were also observed in all of these epitaxial films. Such highly defective twin boundaries are thought to be flux pinning centres and also paths for the diffusion of water into YBCO films. Therefore the films need to be passivated against attack from humid air.     

Effect of substrate on microstructure and mechanical properties of sol–gel prepared (K,Na)NbO3 thin films

Lead-free ferroelectric (K, Na)NbO₃ (KNN) thin films (～200 nm thickness) were prepared using a modified sol–gel method by mixing K and Na acetates with the Nb–tartarate complex, deposited by spin-coating method on Pt/Al₂O₃ and Pt/SiO₂/Si substrates and sintered at 650 °C. Pure perovskite phase of K_0.65Na_0.35NbO₃ in film on silicon were revealed, while film on alumina contained also small amount of secondary pyrochlore Na₂Nb₈O₂₁ phase. Homogenous microstructure of film on Si substrate was smoother with the lower roughness (～7.4 nm) and contained spherical (～50 nm) particles. The mechanical properties of films were characterized by nanoindentation. The modulus and hardness of KNN films were calculated from their composite values of film/substrate systems using discontinuous and modified Bhattacharya model, respectively. The KNN film modulus was higher on alumina substrate (91 GPa) in comparison with silicon substrate (71 GPa) and values of film hardness were the same (4.5 GPa) on both substrates.     

Deposition of thin titanium–copper films with antimicrobial effect by advanced magnetron sputtering methods

The antibacterial effect of thin titanium–copper (Ti–Cu) films combined with sufficient growth of human osteoblastic cells is reported in the paper. Thin Ti–Cu films were prepared by three different plasma-assisted magnetron sputtering methods: direct current magnetron sputtering (dc-MS), dual magnetron sputtering (dual-MS) as well as dual high power impulse magnetron sputtering (dual-HiPIMS). The antimicrobial effect is caused by copper released from the metallic Ti–Cu films, which was measured by atomic absorption spectroscopy (AAS). The copper release is influenced by the chemical and physical properties of the deposited films and was investigated by X-ray diffractometry and X-ray reflectometry (GIXD and XR) techniques. It was found that, within the first 24 h the amount of Cu released from dual-HiPIMS films (about 250 μg) was much higher than from dc-MS and dual-MS films. In vitro planktonic growth tests on Ti–Cu surfaces for Staphylococcus epidermidis and S. aureus demonstrated the killing of both bacteria using the Ti–Cu films prepared using the dual-HiPIMS technique. The killing effects on biofilm bacteria were less obvious. After the total release of copper from the Ti–Cu film the vitality of exposed human osteoblast MG-63 cells increased significantly. An initial cytotoxic effect followed by the growth of osteoblastic cells was demonstrated. The cytotoxic effect combined with growth of osteoblastic cells could be used in joint replacement surgery to reduce the possibility of infection and to increase adoption of the implants.     

Effect of stabilizer on optical and structural properties of MgO thin films prepared by sol–gel method

The effects of monoethanolamine (MEA) and acetylacetone (ACAC) addition as stabilizer on the crystallization behaviour, morphology and optical properties of magnesium oxide were investigated using thermogravimetry (TG/DTG), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Visible, photoluminescence (PL) and Fourier transform infrared (FTIR) spectroscopy. Stabilizer addition reduces transparency of the films. MgO films prepared at 500 °C showed weak orientation of (200). However, the films prepared by addition of stabilizer are amorphous. MgO powders were prepared for exhibiting the structural properties. The patterns of MgO powders showed a preferred orientation of (200). The addition of stabilizer causes a reduction in grain size. SEM micrographs show that a homogenous and crack-free film can be prepared at 500 °C and addition of stabilizer causes an increase in packing density.     

Structural and optical properties of γ-alumina thin films prepared by pulsed laser deposition

Preparation of γ-alumina thin films by pulsed laser deposition from a sintered α-alumina target is investigated. The films were deposited on (100) silicon substrates at 973 K with varying oxygen partial pressures in the range 2.0 × 10⁻⁵-3.5 × 10^− 1 mbar. X-ray diffraction results indicated that the films were polycrystalline γ-Al₂O₃ with cubic structure. The films prepared in the oxygen partial pressure range 2.0 × 10^− 5-3.5 × 10^− 2 mbar contained nanocrystals of sizes in the range 10-16 nm, and became amorphous at pressures > 3.5 × 10^− 1 mbar. Topography of the films was examined by atomic force microscopy using contact mode and it showed the formation of nanostructures. The root-mean square surface roughness of the film prepared at 2.0 × 10^− 5 mbar and 3.5 × 10^− 1 mbar were 1.4 nm and 3.5 nm, respectively. The thickness and optical properties were studied using ellipsometry in the energy range 1.5-5.5 eV for three different angles of incidence. The refractive index was found to decrease from 1.81 to 1.73 with the increase of oxygen partial pressures from 2.0 × 10^− 5 to 3.5 × 10^− 2 mbar. The variation in the refractive index has been found to be influenced by the microstructure of the films obtained as a function of oxygen partial pressure.