Structural and electrical properties of chemical solution deposited (Bi0.9Tb0.1)(Fe0.975 TM 0.025)O3±δ (TM = Ni, Mn and Ti) thin films

Effects of Tb and transition metal (TM = Ni, Mn and Ti) ions co-doping on the structural, electrical and ferroelectric properties of the BiFeO₃ thin films prepared by using a chemical solution deposition method were reported. From X-ray diffraction and Raman scattering analyses, distorted rhombohedral perovskite structures were observed for all thin films. Improved electrical and ferroelectric properties were observed for the co-doped thin films. Among the thin films, the lowest leakage current density of 2.67 × 10^?6 A/cm² (at 100 kV/cm), large remnant polarization (2P _r ) of 82.2 μC/cm² and low coercive field (2E_c) of 680 kV/cm (at 1,036 kV/cm) were measured for the (Tb, Mn) co-doped thin film.     

Preparation and properties of rare earth (Eu, Tb, Ho) and transition metal (Co) co-doped BiFeO3 thin films

Ferroelectric (Bi_0.9 RE _0.1)(Fe_0.975Co_0.025)O_3-δ (RE = Eu, Tb and Ho) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates via a chemical solution deposition method. All thin films were crystallized in a distorted rhombohedral perovskite structure confirmed by using an X-ray diffraction and a Raman scattering analyses. Compared to the pure BiFeO₃ thin film, improved electrical and ferroelectric properties were observed for the co-doped thin films. Among the thin films, the lowest leakage current density of 4.28 × 10^?5 A/cm² was measured at an applied electric field of 100 kV/cm for the (Bi_0.9Ho_0.1)(Fe_0.975Co_0.025)O_3-δ thin film. This value is approximately three orders lower than that of the pure BFO thin film. Furthermore, a large remnant polarization (2P _r) of 60.2 μC/cm² and a low coercive field (2E _c ) of 561 kV/cm at 980 kV/cm were observed from the (Bi_0.9Ho_0.1)(Fe_0.975Co_0.025)O_3-δ thin film.     

Frequency dependent ferroelectric and electrical properties of (Ho, Ni) co-doped BiFeO3 thin films

We have evaluated the ferroelectric and electrical properties of pure BiFeO₃ (BFO) and (Bi_0.9Ho_0.1)(Fe_1?xNi_x)O_3?δ (BHFN_xO, x = 0.01, 0.02, and 0.03) thin films as frequency varying from 1 to 50 kHz on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. With the frequency from 1 to 10 kHz, the decrease of remnant polarization (2P _r ) of the BHFN_0.02O thin film was about 27 %, from 26 to 19 μC/cm², which is one half lower than those of the BHFN_xO (x = 0.01 and 0.03) thin films. Otherwise, the variation of the coercive electric field (2E _c ) was relatively small, which were 16, 11 and 3 % for the BHFN_xO (x = 0.01, 0.02, and 0.03) thin films. The remnant polarization (2P _r ) and the coercive electric field (2E _c ) values of the BHFN_0.02O thin film show the dependence of measurement frequency and it has been fairly saturated about 30 kHz. Also, the leakage current density of the co-doped BHFN_0.02O thin film showed three orders lower than that of the pure BFO, 2.14 × 10^?6 Å/cm² at 100 kV/cm.     

Studies on structural and electrical properties of transition metal ions (Mn, Co and Cu) co-doped Bi0.9Dy0.1FeO3 thin films

Effects of rare earth Dy and transition metal (TM = Cu, Co and Mn) ions co-doping on the structural, electrical and ferroelectric properties of the BiFeO₃ thin films prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method were investigated. All thin films formed as randomly oriented polycrystalline, with no detectable impurity or secondary phases. Among the thin films, the (Bi_0.9Dy_0.1)(Fe_0.975Mn_0.025)O₃ thin film exhibited well saturated hysteresis loops with remnant polarization (2P _r ) of 51 μC/cm² and low coercive electric field (2E _c ) of 685 at 935 kV/cm and low leakage current density of 1.4 × 10^?5 A/cm² at 100 kV/cm. The enhanced properties observed in the co-doped thin films could be considered as being the results of the suppression of ionic defects and of the modified microstructure.     

Thin film nonstoichiometric chromium oxide-based cathode material for rechargeable and primary lithium batteries

The application of nonstoichiometric chromium oxide-based thin film cathodes in lithium rechargeable and primary batteries operating at high rates has been demonstrated. Films of varying composition have been obtained by anionic Cr (VI) species electrodeposition on a 1X18N10Т grade stainless steel cathode from fluoride-containing electrolytes. The effect of film doping by Li⁺ ions during its electrosynthesis has been сonsidered. As-prepared films were studied by scanning and transmission electron microscopies, 3D optical profiler, thermogravimetric analysis, chemical analysis, and X-ray diffraction (XRD). The main phase components of the electrodeposited films regardless of Li⁺ in an electrolyte are Cr₂O₃, α-CrOOH, β-CrOOH, and metallic chromium as shown by XRD pattern refinement. The electrochemical reduction rate in a non-aqueous electrolyte (1 M LiClO₄ in PC/DME) correlates with the chromium oxide-hydroxide component content of film. Primary CrO _x -Li CR2325 mock-up cathode coating can be discharged in a pulsed mode at 10 Ω external resistance with 80–84 mA cm^?2 current densities for 10–100 ms. Thin film cathodes electrodeposited in the presence of lithium ions become rechargeable when the lithium content of the film reaches 0.02 wt.%. Mock-ups of CR2325 coin battery with a thin film cathode doped with lithium ions can be discharged more than 40 times with 136 mAh g^?1 specific capacity, 461 Wh kg^?1 specific energy and 154 W kg^?1 power density at 30 kΩ external resistance. The simplicity of thin film preparation makes this technology promising for thin film lithium batteries.     

Determination of optical constants and thickness of passivating films on nickel from multiple-angle-of-incidence reflectivity measurements

A method is proposed which allows to determine without non-optical assumptions the complex refractive index and the thickness of thin surface films from measurements of the relative changes of reflectivity due to the formation or removal of the film at different angles of incidence with monochromatic light polarized perpendicular or parallel to the plane of incidence. The exact equations for the reflectivity change are used, since the linear approximation introduces systematic errors which are too large in view of the experimental accuracy. The method is applied to the passivating film formed on nickel in 1 M sulphuric acid after 1 h at U_HSS=0.85 V. A complex refractive index n₂=2.10 (±0.05)–0.46 (±0.02) i and a film thickness d=2.1 (±0.1) nm were found. In the spectrum of the optical constants in the range 1.4≤hv/e V≤4.8 a characteristic peak of the absorption coefficient was observed at 3.1 e V. Both the values at γ=500 nm and the spectra of the optical constants are explained by a partly hydrated nickel oxide film.     

Optical,electrical, and electrochemical behavior of p-type nanostructured SnO<Subscript>2</Subscript>:Ni (NTO) thin films

The physical and electrochemical properties of sol-gel synthesized nickel-doped tin oxide (NTO) thin films were investigated. The X-ray diffraction results showed that NTO samples exhibited a tetragonal structure. The average crystallite size and the unit cell volume of the films were reduced by Ni increment, while the stacking fault probability was increased. Furthermore, the field-emission scanning electron microscopy images clearly displayed that the worm-like surface morphology of the SnO₂ thin films was altered to the spherical feature in 3 and 10 mol% NTO samples. Moreover, by virtue of Ni incorporation, the average transparency of the SnO₂ thin films rose up from 67 to 85% in the visible region; also, the optical band gap of the SnO₂ sample (3.97 eV) increased and the thin film with 3 mol% dopant concentration showed a maximum value of 4.22 eV. The blue/green emission intensities of photoluminescence spectra of SnO₂ thin film changed via Ni doping. The Hall effect measurements revealed that by Ni addition, the electrical conductivity of tin oxide thin films altered from n- to p-type and the carrier concentration of the films decreased due to the role of Ni²⁺ ions which act as electron acceptors in NTO films. In contrast, 20 mol% Ni-doped sample had the highest mobility about 9.65 cm² (V s)^?1. In addition, the cyclic voltammogram of NTO thin films in KOH electrolyte indicated the charge storage capacity and the surface total charge density of SnO₂ thin films enhanced via Ni doping. Moreover, the diffusion constant of the samples increased from 2?×?10^?15 to 6.5?×?10^?15 cm² s^?1 for undoped and 5 mol% dopant concentration. The electrochemical impedance spectroscopy of the NTO thin films in two different potentials showed the different electrochemical behaviors of n- and p-type thin films. It revealed that the 20 mol% NTO thin film had maximum charge transfer at lower applied potential.     

Segmental dynamics near the chain end of polystyrene in its ultrathin films: A study by single-molecule fluorescence de-focus microscopy

Rotational motion of fluorophores chemically attached to polystyrene chain-ends in ultra-thin films on solid substrates was studied by single-molecule fluorescence de-focus microscopy. The collective feature of the rotational motion was found and evidenced by the sharp change of the population of fluorophores undergoing rotational motion within a very narrow temperature range (named as the changing temperature, T _c). The T _c value was found to depend on film thickness and interfacial chemistry and the variation of the T _c value is also dependent on the molecular weight of the polymer. The results demonstrate that the spatial confinement effect enhances the segmental mobility near the polymer chain-ends while the interfacial attraction restricts the segmental motion inside the thin film.     

α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films by liquid phase deposition: low-cost option for supercapacitor

In the present study, iron oxide (α-Fe₂O₃) thin films with good adhesion on stainless steel substrates are deposited by liquid phase deposition (LPD) technique, which is additive and binder-free. Iron oxyhydroxide (FeOOH) thin films are formed by means of a ligand-exchange equilibrium reaction of metal-fluoro complex ions and an F^?ions consuming reaction by using boric acid (H₃BO₃) as a scavenging agent. These films are annealed at 500 °C to get α-Fe₂O₃ thin films. The transformation from hydrophobic to hydrophilic nature of the films is observed due to annealing. The films are characterized by different techniques. The α-Fe₂O₃ film is checked for electrochemical supercapacitive performance in Na₂SO₃ solutions of various concentrations. Specific capacitance is calculated from cyclic voltammetry at numerous scan rates (5–200) mV s^?1. The highest obtained value of specific capacitance is 582 F g^?1 at 5 mV s^?1 for 0.5 M Na₂SO₃ electrolyte. The maximum values of specific power and specific energy are 6.9 and 53.4 Wh kg^?1 from the charge-discharge curve at the current density 2 mA cm^?2 in 0.5 M Na₂SO₃ electrolyte.     

Effect of Li- and Ta-doping on the ferroelectric properties of Na0.5K0.5NbO3 thin films prepared by a chelate route

The effects of lithium and tantalum doping on the properties of Na_0.5K_0.5NbO₃ (NKN) thin films were investigated. The films were fabricated by an optimized chelate route which offers the advantage of a simple and rapid solution synthesis. The optimization was achieved by investigating the effects of alkaline volatilization loss on film properties. In this way, undoped NKN thin films fabricated by this conventional method exhibited good ferroelectric properties (P_r ~ 8 μC/cm², and E_c ~ 55 kV/cm for films annealed at 650 °C). The developed chelate route was then used to grow Li (5 %) and Ta (10 %) substituted thin films. Such structures allowed us to compare the effect of these dopant cations on phase formation, microstructure and ferroelectric properties. We show that both modifications produced a remarkable improvement on the ferroelectricity of the films. While the undoped material exhibited large leakage components in films annealed at 600 °C, films modified with Li or Ta presented well saturated ferroelectric hysteresis loops, indicating that those ions have a significant influence on the conducting process. The remnant polarizations of the Ta-doped films are greater than those of the Li-doped samples. This feature is however reversed for films annealed at low temperature (600 °C) due to the presence of a non-ferroelectric secondary phase in the Ta-doped composition.     

Electrical properties of La0.6Ca0.4MnO3–Bi3.4Nd0.6Ti3O12 thin films derived by a sol–gel process

Magnetoelectric (ME) xLa_0.6Ca_0.4MnO₃–(1 ? x)Bi_3.4Nd_0.6Ti₃O₁₂ (LCMO–BNT) composite thin films have been prepared by a sol–gel process and spin-coating technique. The effects of LCMO content on the microstructure, leakage current density, ferroelectric properties, fatigue endurance and ME voltage coefficient of LCMO–BNT thin films derived by sol–gel method were studied. It was found that the composite thin films have better fatigue endurance properties and lower leakage current densities compared with pure BNT thin films, as well as large ME voltage coefficients.     

Orientation dependence of the dielectric and piezoelectric properties for the Ba0.98Ca0.02Ti0.96Sn0.04O3 thin films

Lead free Ba_0.98Ca_0.02Ti_0.96Sn_0.04O₃ (BCST) thin films with (110), (111) and (001) orientations were processed via chemical solution deposition, and effects of orientation on the dielectric and piezoelectric properties were investigated in some aspects. The (110) orientated BCST thin films exhibit highest Curie temperature (T _c of 85 °C) and lowest dielectric loss (tan δ of 0.02). While, the (111) orientated BCST thin films exhibit highest dielectric tunability (74 %) and largest piezoelectric coefficient (d ₃₃ of 78 pm/V), which indicate that it is a promising lead-free replacement for lead-based applications. The anisotropic dielectric and piezoelectric properties in the three kinds of oriented BCST films has been attributed to the difference of structure, in-plane stress and polarization rotation in orientation engineered BCST films. This work clearly reveals the dielectric and piezoelectric properties of BCST films exhibit a strong sensitivity to orientation.     

Preparation of the visible light responsive TiO2 thin film photocatalysts by the RF magnetron sputtering deposition method

TiO₂ thin film photocatalysts which could induce photoreactions under visible light irradiation were successfully developed in a single process by applying an ion engineering technique, i.e., the radio frequency (RF) magnetron sputtering deposition method. The TiO₂ thin films prepared at temperatures greater than 773 K showed the efficient absorption of visible light; on the other hand, the TiO₂ thin films prepared at around 573 K were highly transparent. This clearly means that the optical properties of TiO₂ thin films, which absorb not only UV but also visible light, can be controlled by the preparation temperatures of the RF magnetron sputtering deposition method. These visible light responsive TiO₂ thin films were found to exhibit effective photocatalytic reactivity under visible light irradiation (λ > 450 nm) at 275 K for the reductive decomposition of NO into N₂ and N₂O. From various characterizations, the orderly aligned columnar TiO₂ crystals could be observed only for the visible light responsive TiO₂ thin films. This unique structural factor is expected to modify the electronic properties of a TiO₂ semiconductor, enabling the efficient absorption of visible light.     

Enhanced ferroelectric,dielectric and leakage properties in Ce and Ti co-doping BiFeO3 thin films

Pure BiFeO₃ (BFO), Ce and Ti individual doping and co-doping BiFeO₃ thin films were fabricated via sol–gel process on Pt/Ti/SiO₂/Si substrates. The microstructure, surface morphology, ferroelectric and dielectric properties of BFO and doped thin films were investigated in detail. X-ray diffraction reveal that all thin films are confirmed the formation of the distorted rhombohedral perovskite structure. No impure phase is identified in all the films. The Ce and Ti co-doping BiFeO₃ (BCFTO) thin films exhibited the enhanced ferroelectricity with a large remnant polarization (2P _r) of 130 μC/cm², and low leakage current density of 9.10 × 10^?6 A/cm² which is more than two orders of magnitude lower than that of pure BFO films at 100 kV/cm. The dielectric constant (364 at 1 kHz) of the BCFTO thin films is much larger than that of pure BFO thin films. These results suggest that the introductions of Ce and Ti provides an effective route for improving the ferroelectric, dielectric and leakage properties of BFO thin films.     

TiO2 nanoparticles synthesized in an aprotic solvent and applied to prepare high-refractive-index TiO2-polyimide hybrid thin films

In this study, very small (2–5 nm) TiO₂ nanoparticles were synthesized in an aprotic solvent, N,N-dimethylacetamide, via hydrolysis and condensation of titanium alkoxide at room temperature. The synthesized TiO₂ sol showed 30 days of storage stability and could be used to prepare high-refractive-index TiO₂-polyimide hybrid thin films by an ex-situ method that involved a spin coating and multistep baking process. The field emission scanning electron microscope image showed a flat and uniform morphology of the hybrid thin film. TiO₂ domains were in the nanometer range, thus avoiding light scattering. The refractive index at 633 nm of the hybrid thin film reached 2.05, which suggested potential applications of the film to anti-reflective coatings and optical waveguides.     

Collapse of preformed cobalt stearate film on water surface

Preformed cobalt stearate (CoSt) molecules form a film on the water surface, which with barrier compression shows multilayers of different heights that are evidenced from the structures of the films deposited on hydrophilic silicon (0 0 1) substrates by using a horizontal deposition technique at different positions of the surface pressure (π)–specific molecular area (A) isotherm. In-plane morphology and out-of-plane structures are obtained from the atomic force microscopy (AFM) and X-ray reflectivity studies. Electron density profiles (EDPs), extracted from the reflectivity data, show that the monolayer coverage is maximum when π is far before the collapse point (π_c) but with barrier compression domains of multilayers start to form even before π_c. After π_c, two different bilayer repeat distances have been observed from the two different series of the Bragg peaks implying the formation of domains by both the tilted and untilted CoSt molecules. Far after π_c, reflectivity decreases rapidly and morphology of the deposited films changes totally. Structures before and after π_c of the CoSt film have also been obtained by changing the pH of the subphase water. From all the structural information it is clear that the preformed CoSt film collapses in a different way in comparison with the collapse of the standard cobalt stearate monolayer where cobalt stearate molecules were formed at the air–water interface. Reasons for obtaining different structures on the water surface with barrier compression have been proposed.     

Characterization of TiO2 nanotube arrays prepared via anodization of titanium films deposited by DC magnetron sputtering

Highly ordered TiO₂ nanotube arrays were fabricated on a conducting glass substrate in NH₄HF₂/glycol electrolyte via anodization of titanium film which was deposited by direct current magnetron sputtering (DCMS) at different temperatures. The results showed that Ti films with good homogeneity and high denseness could be formed under the conditions Ar pressure 0.35 Pa, direct current 3.5 A, and 2 h at 300 °C. Characterization of the TiO₂ nanotube arrays was investigated comparatively, by altering anodization time. The surface morphology of the samples changed as the anodization time was prolonged from 10 to 150 min at 30 V. The TiO₂ thin film was amorphous and could be transformed into anatase by annealing at 450 °C. On the basis of UV?Cvisible transmission spectra the bandgap of the thin film was calculated to be 3.12 eV, and its tail extended to 2.6 eV.     

Superconducting lead cluster films with particle size dependent reduction ofT c

To investigate films of metal clusters, a neutral lead cluster beam, generated by inert gas aggregation, is characterized via time-of-flight mass spectroscopy and subsequently used for growing a thin film (d=100 Å) on a cold sapphire substrate. In an annealing program the temperature dependence of the electrical resistance of the film is determined by the dc 4-probe technique. Directly after deposition a superconducting transition atT _c =5.6 K is observed which is shifted to higher temperatures with increasing annealing temperature (T _c =6.5 K after annealing at room temperature).     

Efficient electrochromic performance of anatase TiO2 thin films prepared by nebulized spray deposition method

Anatase TiO₂ thin films with high optical modulation, better reversibility, fast switching time, and enhanced coloration efficiency were prepared by nebulized spray pyrolysis technique. X-ray diffraction study confirmed the formation of anatase phase TiO₂ in the present work. This inference was substantiated from the Raman active modes of A_1g, 2 B_1g, and 3 E_g corresponding to O–Ti–O bond in TiO₂. The PL emission peak observed at 400 nm is corresponds to the indirect transition (X_1b?→?Γ₃) from the conduction band to the valence band. The average reflectance of TiO₂ thin films was varied from 31 to 20%. The electrochemical study revealed the excellent performance of TiO₂ films with high optical modulation (ΔT?=?61%), fast switching kinetics (t _b ?=?1.6 s, t _c ?=?2.4 s), good coloration efficiency (100 cm² C^?1), and better reversibility (86%). The efficient electrochromic behavior of films may be due to the smooth microstructure nature, which provides an easy pathway for the diffusion and charge transfer process of Li⁺ ions in TiO₂ film matrix. The fast transfer of Li⁺ ion was realized from the electrochemical impedance spectroscopic measurement.