Enhanced dielectric properties and grain boundary potentials in sulfur-doped CaCu3Ti4O12 thin films

CaCu₃Ti₄O₁₂ (CCTO) has been reported to possess a colossal dielectric constant owing to the intrinsic interfacial polarization via charge accumulations across the grain boundary. Herein, we explore the effects of unusual anion-doping on the dielectric properties of sputter-deposited CCTO thin films using an example of sulfur-doping. A post-annealing process of the films was utilized in a flowing H₂S atmosphere for the sulfur-doping. The incorporation of sulfur into the perovskite structure was evidenced with the changes in chemical states, such as the reduced cations of Cu⁺ and Ti³⁺, the increased concentration of oxygen vacancies, and the formation of S-O bonds. The sulfurized CCTO thin films demonstrated an enhanced relative permittivity of ∼620 at 100 Hz, which is substantially better than that of the unsulfurized film. Direct measurement of the grain-boundary potential using Kelvin probe force microscopy suggests that the enhanced relative permittivity is associated with an increased Schottky barrier height.     

Structural,optical and methanol sensing properties of sprayed In2O3 nanoparticle thin films

Indium oxide (In₂O₃) nanoparticle thin films were grown on cleaned glass substrates by the chemical spray pyrolysis technique using the precursor solution of indium nitrate (In (NO₃)₃). The XRD studies confirm that the films are polycrystalline In₂O₃, possessing cubic structure with lattice parameters, a = b = c = 10.17 Å. The optical studies show a direct optical band gap of 3.32 eV and an indirect band gap of 2.6 eV in the prepared films. The films exhibit high optical transparency >80% in the visible region, reaching a maximum of 85% at 684 nm wavelength. Further, the gas sensing properties of the films have been investigated for various concentrations of methanol in air at different operating temperatures. At 300 °C the film exhibits a very high response 99% to methanol vapor at a concentration of 40 ppm in air, which is ideal to be used as a methanol sensor. The film shows fast response and recovery to methanol vapor at higher operating temperatures. A possible methanol sensing mechanism has been proposed.     

Synthesis and thermal expansion behaviors of spin-coated Sc2Mo3O12 thin films

Orthorhombic Sc₂Mo₃O₁₂ films have been successfully prepared via spin coating technique followed by annealing at 500–750 °C. The phase composition, microstructure, morphology and negative thermal behavior of the synthesized Sc₂Mo₃O₁₂ films were investigated. XRD and XPS analysis indicate that as-deposited film is amorphous. Orthorhombic Sc₂Mo₃O₁₂ films can be prepared after post-annealing at 500–750 °C for 1 h. The crystallinity of Sc₂Mo₃O₁₂ films gradually improved with the increase of post-annealing temperature. SEM analysis shows as-deposited film is smooth and compact, and the grain size of Sc₂Mo₃O₁₂ film grows up as the post-annealing temperature increases. Variable temperature XRD analysis demonstrates that the synthesized orthorhombic Sc₂Mo₃O₁₂ films show stable thermo-chemical and anisotropic NTE property in 25–700 °C. The corresponding coefficients of thermal expansion (CTEs) of the orthorhombic Sc₂Mo₃O₁₂ film in a, b and c directions are ?6.68 × 10^?6 °C^?1, 5.08 × 10^?6 °C^?1 and ?4.76 × 10^?6 °C^?1, respectively. The whole unit cell of the orthorhombic Sc₂Mo₃O₁₂ film shrinks and the volumetric CTE of the Sc₂Mo₃O₁₂ thin film is ?6.36 × 10^?6 °C^?1, and the linear CTE is about ?2.12 × 10^?6 °C^?1 (α_v = 3α_l).     

Preparation by chemical solution deposition and transparent conducting properties of LaRh1-xNixO3 thin films

Transparent conducting thin films have been widely used in lots of fields. The absence of high-performance hole-type transparent conducting thin films, however, seriously limits the wider applications. LaRhO₃ as a type of perovskite material shows hole-type conduction with semiconductor-like properties and no investigations have been carried out about transparent conducting properties on LaRhO₃ thin films. Here, LaRh_1-xNi_xO₃ (x = 0, 0.05, 0.1) thin films were firstly deposited by chemical solution deposition, showing epitaxial growth on single crystal SrTiO₃ (001) substrates with the epitaxial relationship of LaRhO₃(001)[110]||SrTiO₃(001)[110]. With the doping of Ni element, the surface morphology became denser. Hall measurements confirmed that the hole concentration was enhanced with Ni doping, resulting in the decreased resistivity. Low resistivity of 17.3 mΩ cm at 300K was obtained for the LaRh_0.9Ni_0.1O₃ thin films. The electrical transport mechanisms were investigated, showing thermal activation at high temperatures and variable range hopping model for the doped thin films at low temperatures. The transmittance within the visible range for all thin films was higher than 50%. The results will provide a feasible route to deposit hole-type transparent conducting LaRhO₃-based thin films.     

Characterization of non-stoichiometric Ga2O3-x thin films grown by radio-frequency powder sputtering

We report the synthesis and characterization of non-stoichiometric Ga₂O_3-x thin films deposited on sapphire (0001) substrates by radio-frequency powder sputtering. The chemical and electronic states of the non-stoichiometric Ga₂O_3-x thin films were investigated. By sputtering in an Ar atmosphere, the as-grown thin films become non-stoichiometric Ga₂O_2.7, due to the difference in sputtering yield between Ga and O species of the Ga₂O₃ target. The electronic states of the thin films consist of ~85% Ga³⁺ and ~15% Ga¹⁺, corresponding to Ga₂O₃ and Ga₂O, respectively. The films have the electrical characteristics of a semiconductor, with electrical conductivity of approximately 5.0 × 10^-4 S cm^-1 and a carrier concentration of 4.5 × 10¹⁴ cm^-3 at 300 K.     

Boron and nitrogen co-doped ZnO thin films for opto-electronic applications

The transparent conductive oxides such as ZnO have been widely studied due to their potential applications. As a promising wide band gap semiconductor, ZnO thin films with various dopants are important in fabricating the photonic devices to meet the various needs. In this study, boron and nitrogen co-doped ZnO thin films were fabricated at different temperatures (100–600 °C) on sapphire (0 0 1) substrates using pulsed laser deposition technique. X-ray diffractometer, atomic force microscope, spectrophotometer and spectrometer were used to characterize the structural, morphological and optical properties of the thin films. Hall measurements were also carried out to identify the electrical properties of the thin films.     

Atomic layer deposition of Al2O3 thin films on diamond

Atomic layer deposition (ALD) of aluminum oxide thin films on diamond was demonstrated for the first time, and the film properties as a gate insulator for diamond field effect transistor (FET) were examined. The interface between the aluminum oxide and the diamond was abrupt, and the ratio of aluminum to oxygen in the film was confirmed to be stoichiometric by Rutherford back scattering. Even a bumpy surface of polycrystalline diamond film was conformally covered by the Al₂O₃ films. To evaluate the feasibility of the film for FET gate insulator, the electrical characteristics of the Al₂O₃ films deposited by ALD on diamond were measured using metal–insulator–semiconductor structure. It was found that the Al₂O₃ films deposited by ALD were better than those deposited by conventional methods, which indicates that the ALD-Al₂O₃ films are feasible for gate insulators of diamond FETs.     

Effect of argon-oxygen ratio on dielectric and energy storage properties of Ba(Zr0.35Ti0.65)O3 thin films

Lead-free Ba(Zr_0.35Ti_0.65)O₃(short as BZT35) ferroelectric thin films are prepared by RF magnetron sputtering on Pt/Ti/SiO₂/Si substrates. Effects of argon-to-oxygen (short as Ar/O₂) ratios on phase transition, dielectric and energy storage properties are studied. The research found that all thin films are perovskite structures. With the decrease of Ar/O₂, the oxygen vacancies (OVs) in the film are effectively suppressed, which promotes the film to obtain a larger dielectric constant, smaller dielectric loss, and lower leakage current density. The BZT35 film prepared under Ar/O₂ = 40:10 has excellent energy storage density (48.03 J/cm³) and efficiency (87.7%) because of its elongated hysteresis loop, the largest polarization difference (ΔP = 22.91 μC/cm²), higher breakdown field strength (E_b = 4.50 MV/cm) and lower leakage current density (J = 2.3 × 10^?5 A/cm²) and high power density of 7.94 MW/cm³. In addition, the BZT35 film also has excellent frequency stability (500 Hz-20 kHz). These excellent properties show that BZT35 has very broad application prospects in energy storage.     

Change of the properties of nanostructured MoO3 thin films using gamma-ray irradiation

Thin films of Molybdenum trioxide (MoO₃) were deposited on glass substrates by the spray pyrolysis at 500?°C and the samples were then exposed to gamma γ radiation doses by ⁶⁰Co radioisotope at different doses (0.1, 10 and 50 kGy). The effects of gamma irradiation on the properties of MoO3 thin films were investigated. The XRD pattern and Raman spectroscopy of as-deposited MoO₃ samples show an orthorhombic structure related to α-MoO₃ with (0k0) preferred orientations. Uv‐vis spectra were studied to investigate the transmission measurements of MoO₃ films. The optical energy band gap and Urbach energy were found to be gamma-dose dependent. Photoluminescence measurements at room temperature using 300?nm wavelength excitation were investigated. SEM images indicate the formation of α-MoO₃ nanorods.     

Electrodeposition and characterization of Cu2O thin films using sodium thiosulfate as an additive for photovoltaic solar cells

Cuprous oxide(Cu_2 O) thin films have been grown by electrodeposition technique onto ITO-coated glass substrates from aqueous copper acetate solutions with addition of sodium thiosulfate at 60 ℃. The effects of sodium thiosulfate on the electrochemical deposition of Cu20 films were investigated by cyclic voltammetry and chronoamperometry techniques. Deposited films were obtained at-0.58 V vs. SCE and characterized by X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), and optical, photoelectrochemical and electrical measurements. X-ray diffraction results indicated that the synthesized Cu20 films had a pure cubic phase with a marked preferential orientation peak along(200) plane and with lattice constants a = b = c = 0.425 nm. FTIR results confirmed the presence of Cu_2 O films at peak 634 cm~(-1) SEM images of Cu_2 O films showed a better compactness and spherical-shaped composition. Optical properties of Cu20 films reveal a high optical transmission(80%) and high absorption coefficient(α 10~4 cm~(-1)) in visiblelight region. The optical energy band gap was found to be 2.103 eV. Photoelectrochemical measurements indicated that Cu20 films had n-type semiconductor conduction, which confirmed by Hall Effect measurements.Electrical properties of Cu20 films showed a low electrical resistivity of 61.30 Ω·cm~(-1), carrier concentration of-4.94 × 10~(15)cm~(-3) and mobility of 20.61 cm~2· V~(-1)·s~(-1).The obtained Cu_2 O thin films with suitable properties are promising semiconductor material for fabrication of photovoltaic solar cells.     

Luminescence properties of terbium-doped SiCN thin films by rf magnetron reactive sputtering

Terbium-doped SiCN (SiCN:Tb) thin films were deposited by rf magnetron reactive sputtering at 800 °C. The as-prepared samples were characterized by XRD, FTIR, and XPS. The results showed that SiCN:Tb films mainly contained both SiC and Si₃N₄ nano-compositions with complicated chemical bond networks. Photoluminescence measurements indicated that the undoped SiCN films exhibited a blue-green light emission, while SiCN:Tb films emitted a strong green one. The SiC nanocrystallites formed in the undoped SiCN films might be responsible for the blue-green light emission, while the formed quaternary Si-C-Tb-O compositions in the doped samples could account for the strong green PL behaviors.     

In situ AFM study of the growth of banded hedritic structures in thin films of isotactic polystyrene

The growth of banded hedrites of isotactic polystyrene (iPS) is followed in situ, using atomic force microscopy (AFM). The melt layer surrounding the growing hedritic front is much thinner than both the hedrite front and the far-field melt. Growth occurs simultaneously in three dimensions: radially, circumferentially and height. The height of the hedrite growth front being so much higher than the adjacent molten pool, the observed propagation of the front requires that it be covered by a thin film of molten material, likely drawn up the face of the front by capillarity. As the hedritic front grows in height, it demands material at a higher rate than can be delivered from the far-field melt and the stacked lamellae stop growing, layer by layer, from the top downward, until only the basal lamella continues to grow (at a constant velocity). The kinetics of the position of the lowest point ahead of the growth front slows with time during this process. Supplying only the basal layer, the adjacent molten pool is replenished and now begins to feed new layers of growing lamellae as the process repeats itself. The creation of the new lamellar layers appears to be coupled to morphological instability of the basal layer, in the form of growth front serrations, likely causal of the giant screw dislocations.     

Synthesis of NiMn2O4 thin films via a simple solid-state reaction route

Herein, NiMn₂O₄ (MNO) spinel oxide thermistor films were synthesized on a SiO₂/Si substrate via annealing the electron beam evaporated Mn–Ni–Mn metal trilayers in air at different temperatures. The X-ray diffraction (XRD) results indicate that polycrystalline spinel-structured MNO thermistor films were formed. The surface particle size of the series MNO films quickly reduced from ~300 to ~120 nm with a temperature increase from 650 to 750 °C, and then, slowly reduced to 80 nm or even smaller with a temperature increase from 750 to 950 °C. Specifically, 750 °C anneal formed the spinel MNO film with largest B value of 5067 and Ea value of 0.4366. The proposed synthesis route for MNO spinel oxide film has been proven to be feasible.     

Solution-processed BiFeO3 thin films with low leakage current

Bismuth ferrite (BiFeO₃) is an attractive multiferroic material that shows strong ferroelectric and antiferromagnetic properties. Nevertheless, producing high-quality oriented BiFeO₃ on technology-important platinized silicon substrates by low-cost solution deposition methods is still challenging. In this work, polycrystalline Mn and Ti co-doped BiFeO₃ (BFO) thin films were fabricated on platinized silicon substrates by a solution deposition method. PbTiO₃ nanocrystals were used as a seed layer between the electrode and the BFO thin films to induce a preferential (100) pseudocubic orientation. We show that the introduction of a PbTiO₃ seed layer strongly reduces the leakage current. The films show excellent room-temperature ferroelectric properties at low frequencies (300 Hz), with epitaxial-like remanent polarization as high as 51 μC/cm² and coercive field of 500 kV/cm.     

Effects of annealing atmospheres on the structure and ferromagnetic properties of Fe0.12Cu0.02Zn0.86O thin films

Fe_0.12Cu_0.02Zn_0.86O thin film was deposited on a Si substrate using r. f. sputtering with no heating and an Ar/O₂ ratio of 10%. After deposition, the specimens were annealed at 400 °C for 1 h, in nitrogen and hydrogen atmospheres. The X-ray diffractometry (XRD) analysis results show that the crystallinity of Fe_0.12Cu_0.02Zn_0.86O thin film annealed in a nitrogen atmosphere is better than that of the film annealed in a hydrogen atmosphere. The X-ray photoelectron spectroscope (XPS) results show that there are more oxygen vacancies in the Fe_0.12Cu_0.02Zn_0.86O thin film annealed in a hydrogen atmosphere. The magnetic force microscope (MFM) analysis results also demonstrate that some magnetism particles are precipitated for the Fe_0.12Cu_0.02Zn_0.86O thin film annealed in a hydrogen atmosphere. This results in an improvement in the ferromagnetic properties, and the saturation magnetization is 70.2 emu/cm³, which is about 25% larger than that for the as-grown Fe_0.12Cu_0.02Zn_0.86O thin film.     

Mechanical spectroscopy of thin polystyrene films

Mechanical spectroscopy is applied to thin polystyrene films of 7.5-730 nm thickness spin coated on a thin silicon reed. Below a thickness of 100 nm, the α-relaxation peak (glass transition) broadens considerably and shifts to lower temperatures by a few degrees. These effects are attributed to a different polymer dynamics at the polymer/vacuum and the polymer/silicon interfaces.     

Tunable multiferroic properties of Mn substituted BiFeO3 thin films

The current study explored the influence of Mn substitution on the electrical and magnetic properties of BiFeO₃ (BFO) thin films synthesized using low cost chemical solution deposition technique. X-ray diffraction analysis revealed that pure rhombohedral phase of BiFeO₃ was transformed to the tetragonal structure with P4mm symmetry on Mn substitution. A leakage current density of 5.7×10⁻⁴ A/cm² which is about two orders of magnitude lower than pure BFO was observed in 3% Mn doped BFO thin film at an external electric field >400 kV/cm. A well saturated (p-E) loops with saturation polarization (P_sat) and remanent polarization (2P_r) as high as 60.34 µC/cm² and 25.06 µC/cm² were observed in 10% Mn substituted BFO thin films. An escalation in dielectric tunability (n_r), figure of merit (K) and quality factor (Q) were observed in suitable Mn doped BFO thin films. The magnetic measurement revealed that Mn substituted BFO thin films showed a large saturation magnetization compared to pure BFO thin film. The highest saturation ~31 emu/cc was observed for 3% Mn substituted BFO thin films.     

Tunable structural transition and multiferroic properties of the composite thin films through the structural transition of magnetic layer

The Bi_0.9Er_0.1Fe_0.96Mn_0.02Co_0.02O₃/Co_1-xMn_xFe₂O₄ (BEFMCO/CM_xFO) thin films have been deposited by sol-gel method. Structural distortion is observed in the BEFMCO with the appearance of trigonal-R-3m: H in the CM_xFO. The enhanced multiferroic properties, well electrically writable and ferroelectric switching properties are obtained in BEFMCO/CM_xFO thin films. The investigation indicates that the structural transformation of the CM_xFO influences the structure and multiferroic properties of BEFMCO and the interfacial effects between BEFMCO and CM_xFO layers. This transformation and Mn-doping cause the change of carriers, which solves the problem that the magnetic layer exacerbates the ferroelectric properties. It promotes to form the weak local electric field, which causes the weak interface effect, and brings out the weak resistive switching in the BEFMCO/CM_xFO thin films. Therefore, it is believed that the BEFMCO/CM_xFO films can offer a potentially tunable structural transformation of composite films for practical applications.     

Magnetoelectricity in CoFe2O4 nanocrystal-P(VDF-HFP) thin films

Transition metal ferrites such as CoFe₂O₄, possessing a large magnetostriction coefficient and high Curie temperature (T_c > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of 0–3 type nanocomposite thin films composed of ferrimagnetic cobalt ferrite nanocrystals (8 to 18 nm) and a ferroelectric/piezoelectric polymer poly(vinylidene fluoride-co-hexafluoropropene), P(VDF-HFP), were prepared by multiple spin coating and cast coating over a thickness range of 200 nm to 1.6 μm. We describe the synthesis and structural characterization of the nanocrystals and composite films by XRD, TEM, HRTEM, STEM, and SEM, as well as dielectric and magnetic properties, in order to identify evidence of cooperative interactions between the two phases. The CoFe₂O₄ polymer nanocomposite thin films exhibit composition-dependent effective permittivity, loss tangent, and specific saturation magnetization (M_s). An enhancement of the effective permittivity and saturation magnetization of the CoFe₂O₄-P(VDF-HFP) films was observed and directly compared with CoFe₂O₄-polyvinylpyrrolidone, a non-ferroelectric polymer-based nanocomposite prepared by the same method. The comparison provided evidence for the observation of a magnetoelectric effect in the case of CoFe₂O₄-P(VDF-HFP), attributed to a magnetostrictive/piezoelectric interaction. An enhancement of M_s up to +20.7% was observed at room temperature in the case of the 10 wt.% CoFe₂O₄-P(VDF-HFP) sample.