Structural, electrical, and optical studies on rapid thermally processed ferroelectric BaTiO3 thin films prepared by metallo-organic solution deposition technique

Polycrystalline BaTiO₃ thin films having the perovskite structure were successfully produced on platinum coated silicon, bare silicon, and fused quartz substrate by the combination of the metallo-organic solution deposition technique and post-deposition rapid thermal annealing treatment. The films exhibited good structural, electrical, and optical properties. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) and metal-ferroelectric-semiconductor (MFS) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 255 and 0.025, respectively, and the remanent polarization and coercive field were 2.2 μC cm⁻² and 25 kV cm⁻¹, respectively. The resistivity was found to be in the range 10¹⁰–10¹² Ω·cm, up to an applied electric field of 100 kV cm⁻¹, for films annealed in the temperature range 550–700 °C. The films deposited on bare silicon substrates exhibited good film/substrate interface characteristics. The films deposited on fused quartz were highly transparent. An optical band gap of 3.5 eV and a refractive index of 2.05 (measured at 550 nm) was obtained for polycrystalline BaTiO₃ thin film on fused quartz substrate. The optical dispersion behavior of BaTiO₃ thin films was found to fit the Sellmeir dispersion formula well.     

Improved thermoelectric properties by adding Al for Zn in (ZnO)mIn2O3

The grain size and density of the sintered (Zn_1 − xAl_xO)_mIn₂O₃ bodies decreased with the small Al₂O₃ content (≤ 0.012), and then increased gradually by further increasing the Al₂O₃ content. The addition of Al for Zn in the (ZnO)_mIn₂O₃ led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient. This indicates that the power factor was significantly enhanced by adding Al for Zn. The thermoelectric power factor was maximized to 1.67 × 10^− 3 W m^− 1 K^− 2 at 1073 K for the (Zn_0.992Al_0.008O)_mIn₂O₃ sample.     

Structure, magnetic and electrical transport properties of (Fe3O4)100 − xPtx composite films

Structure, magnetic and electrical transport properties of the polycrystalline (Fe₃O₄)_100 − xPt_x composite films fabricated using DC reactive magnetron sputtering at ambient temperature were investigated systematically. It is found that the films are composed of inverse-spinel-structured polycrystalline Fe₃O₄ and Pt. Pt addition proves the growth of Fe₃O₄ grains with the (111) orientation. All the films are ferromagnetic at room temperature. The dominant magnetic reversal mechanism turns from domain wall motion to Stoner-Wohlfarth rotation with the increasing x. The electrical transport mechanism also changes with the increasing x because Pt addition decreases the height of the tunneling barrier at the Fe₃O₄ grain boundaries, and makes the magnetoresistance of the films decrease.     

Influence of Se on the electron mobility in thermal evaporated Bi2(Te1−xSex)3 thin films

Thermoelectric solid solutions of Bi₂ (Te_1−xSe_x)₃ with x = 0, 0.2, 0.4, 0.6, 0.8 and 1 were grown using the Bridgman technique. Thin films of these materials of different compositions were prepared by conventional thermal evaporation of the prepared bulk materials. The temperature dependence of the electrical conductivity σ, free carriers concentration n, mobility μ_H, and seebeck coefficient S, of the as-deposited and films annealed at different temperatures, have been studied at temperature ranging from 300 to 500 K. The temperature dependence of σ revealed an intrinsic conduction mechanism above 400 K, while for temperatures less than 400 K an extrinsic conduction is dominant.The activation energy, ΔE, and the energy gap, E_g, were found to increase with increasing Se content. The variation of S with temperature revealed that the samples with different compositions x are degenerate semiconductors with n-type conduction. Both, the annealing and composition effects on Hall constant, R_H, density of electron carriers, n, Hall mobility, μ_H, and the effective mass, m^∗/m₀ are studied in the above temperature range.     

The investigation of (Bi,La)(Ga,Fe)O3-PbTiO3 thin film prepared by PLD technique

In this report, (Bi,La)(Ga,Fe)O₃-PbTiO₃ (BLGF-PT) thin film was prepared on platinum coated Si wafer by pulsed laser deposition (PLD) method. BLGF-PT ceramic with morphotropic phase boundary (MPB) composition was used as the PLD target. The spot of Bi₂Fe₄O₉ impurity phase in X-ray diffraction profile implies a composition deviation in the BLGF-PT thin film from that of target. However, the MPB feature of co-existence of rhombohedral and tetragonal phases remains remarkable in the film. The characterization results of the leakage current and ferroelectric hysteresis loop indicate a desirable insulation in this BLGF-PT thin film. Polarization response by positive-up-negative-down pulse measurement and retention property are further carried out at room temperature to check the intrinsic ferroelectric performance. Moreover, high Curie temperature of 465 °C has been discovered in this BLGF-PT thin film, which may promote the application scope of the thin film.     

Er:YAl3(BO3)4 glassy thin films from polymeric precursor and sol-gel methods: Waveguides for integrated optics

This paper presents the characterization of single-mode waveguides for 980 and 1550 nm wavelengths. High quality planar waveguide structure was fabricated from Y_1 − xEr_xAl₃(BO₃)₄ multilayer thin films with x = 0.02, 0.05, 0.1, 0.3, and 0.5, prepared through the polymeric precursor and sol-gel methods using spin-coating. The propagation losses of the planar waveguides varying from 0.63 to 0.88 dB/cm were measured at 632.8 and 1550 nm. The photoluminescence spectra and radiative lifetimes of the Er^{3+ 4}I_13/2 energy level were measured in waveguiding geometry. For most samples the photoluminescence decay was single exponential with lifetimes in between 640 μs and 200 μs, depending on the erbium concentration and synthesis method. These results indicate that Er doped YAl₃(BO₃)₄ compounds are promising for low loss waveguides.     

Enhancement of saturation magnetization in epitaxial (111) BiFeO3 films by magnetic annealing

We report the enhancement of the saturation magnetization in BiFeO₃ films achieved by magnetic annealing. The saturation magnetization of the film annealed in a magnetic field is found to be 80 emu/cc, which is an increase nearly by a factor of 10 compared to the as-grown one. From the investigation of optical second harmonic generation (SHG), we observe the presence of s_out-polarization under s_in-polarization in the film annealed in a magnetic field, which implies that the spin state is homogeneous antiferromagnetic one rather than cycloidal one. We interpret the observed large enhancement in the saturation magnetization to be due to the magnetic phase transition from cycloidal to homogenous antiferromagnetic one.     

Phase transition behaviors and thermal conductivity measurements of nitrogen-doped Sb2Te3 thin films

Crystallization temperature of nitrogen-doped Sb₂Te₃ (ST) thin films increased with increasing nitrogen doping concentration, which indicates that the long-term stability of the metastable amorphous state can be improved by nitrogen doping. The root-mean-square (rms) roughness values of the films showed a significant decrease with nitrogen doping. Thermal conductivity of nitrogen-doped ST thin films was measured using a transient thermoreflectance (TTR) technique. It was found that the thermal conductivity decreased with increasing nitrogen doping concentration and increased with increasing annealing temperature. Nitrogen-doped ST thin films are suitable phase-change materials for low programming power consumption applications of phase-change random access memory (PCRAM).     

Lead-free piezoelectric thin films of Mn-doped NaNbO3-BaTiO3 fabricated by chemical solution deposition

Lead-free piezoelectric thin films of NaNbO₃-BaTiO₃ were fabricated on Pt/TiO_x/SiO₂/Si substrates by chemical solution deposition. Perovskite NaNbO₃-BaTiO₃ single-phase thin films with improved leakage-current and ferroelectric properties were prepared at 650 °C by doping with a small amount of Mn. The 1.0 and 3.0 mol% Mn-doped 0.95NaNbO₃-0.05BaTiO₃ thin films showed slim ferroelectric P-E hysteresis and field-induced strain loops at room temperature. The 1.0 and 3.0 mol% Mn-doped 0.95NaNbO₃-0.05BaTiO₃ films showed remanent polarization values of 6.3 and 6.2 μC/cm², and coercive field of 41 and 55 kV/cm, respectively. From the slope of the field-induced strain loop, the effective piezoelectric coefficient (d₃₃) was found to be 40-60 pm/V.     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

Electrical and optical properties of (Pb0.9La0.1)TiO3 films prepared by the sol–gel method with ultrasound application

(Pb_0.9La_0.1)TiO₃ thin films were deposited onto indium tin oxide-coated glass and Pt/Ti/SiO₂/Si substrates by spin coating. One set of the solutions was sonication-treated during the sol preparation, while the other remained untreated for comparison. The results were analyzed in terms of perovskite developments, dielectric constants and losses, polarization behavior, and optical properties. Perovskite formation temperatures became lower by application of the sonication process. Furthermore, dielectric/ferroelectric and optical transmittance properties were improved substantially.     

Effect of complexing agent on growth process and properties of nanostructured Bi2S3 thin films deposited by chemical bath deposition method

Nanostructured Bi₂S₃ thin films have been prepared onto amorphous glass substrates by chemical bath deposition method at room temperature using bismuth nitrate and sodium thiosulphate as cationic and anionic precursors with EDTA as complexing agent in aqueous medium. The X-ray diffraction study reveals that the films deposited without the complexing agent are amorphous in nature and becomes nanocrystalline in the presence of EDTA. The resistivity for the films prepared from EDTA complexed bath is decreased due to the improvement in grain structure. The decrease in optical bandgap and activation energy is observed as the thickness of the film varies from 45 to 211 nm on account of the variation of the volume of complexing agent in reaction bath. Studies reveal that the growth mechanism of Bi₂S₃ gets affected in the presence of complexing agent EDTA and shows impact on structural, electrical and optical properties.     

Preparation of (ZnO)1−x(GaN)x:Mn powder and its photoluminescence properties

(ZnO)_1−x(GaN)_x:Mn²⁺ powder was prepared by a conventional solid-state reaction under an NH₃ gas flow. The sample preparation conditions including the mixing ratio of the raw materials, the annealing temperature, and the annealing time were varied. The crystallinity and the photoluminescence (PL) intensity of this fluorescent material were improved by increasing the amount of ZnO and by increasing the annealing time, and no changes was observed in the PL wavelength. The crystallinity of the samples was enhanced and the PL intensity increased markedly at annealing temperatures of 700 °C and 800 °C, respectively. Moreover, it was clarified that the sample could be synthesized at annealing temperatures of above about 650 °C.     

Varistor properties of ZnO-Pr6O11-CoO-Cr2O3-Y2O3-In2O3 ceramics

The varistor properties of the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃-In₂O₃ ceramics were investigated for different concentrations of In₂O₃. The increase of In₂O₃ concentration slightly increased the sintered density (5.60-5.63 g/cm³) and slightly decreased the average grain size (3.4-2.9 μm). The breakdown field increased from 6023 to 14822 V/cm with increasing concentration of In₂O₃. The nonlinear coefficient increased from 17.6 to 44.6 for up to 0.005 mol%, whereas the further doping caused it to decrease to 36.8. In₂O₃ acted as an acceptor due to the donor concentration, which decreases in the range of 1.02 × 10¹⁷ to 0.24 × 10¹⁷/cm³ with increasing concentration of In₂O₃.     

AC conductivity and dielectric properties of Sb2Te3 thin films

Sb₂Te₃ films of different thicknesses, in the thickness range 300-620 nm, were prepared by thermal evaporation. X-ray analysis showed that the as-deposited Sb₂Te₃ films are amorphous while the source powder and annealed films showed a polycrystalline nature. The AC conductivity and dielectric properties of Sb₂Te₃ films have been investigated in the frequency range 0.4-100 kHz and temperature range 303-373 K. The AC conductivity σ_AC(ω) was found to obey the power law ω^s where s?1 independent of film thickness. The temperature dependence of both AC conductivity and the exponent s can be reasonably well interpreted by the correlated barrier hopping (CBH) model. The experimental results of the dielectric constant ε₁ and the dielectric loss ε₂ are frequency and temperature dependent and thickness independent. The maximum barrier height W_M calculated from dielectric measurements according to the Guintini equation agrees with that proposed by the theory of hopping of charge carriers over a potential barrier as suggested by Elliott for chalcogenide glasses. The effect of annealing at different temperatures on the AC conductivity and dielectric properties was also investigated. Values of σ_AC, ε₁ and ε₂ were found to increase with annealing treatment due to the increase of the degree of ordering of the investigated films. The Cole-Cole plots for the as-deposited and annealed Sb₂Te₃ films have been used to determined the molecular relaxation time τ. The temperature dependence of τ indicates a thermally activated process.     

Structural and transport properties of SrRuO3 thin films grown by MOCVD on (0 0 1) SrTiO3 substrates: The role of built-in strain and extra phases

Pure SrRuO₃ (SRO) thin films and SRO thin films containing the extra metallic phases Ru, RuO₂ and Sr₃Ru₂O₇ were deposited by MOCVD on (0 0 1) SrTiO₃ substrates under different conditions (Ru/Sr and Ar/O₂ ratio in the gas phase, substrate temperature, supersaturation). The single-phase compressively-strained SRO film is of high structural quality and shows a ferromagnetic transition at a suppressed Curie temperature (T_c) of about 142 K and low electrical resistivity (230 μΩ cm). Under certain deposition conditions Ru and RuO₂ extra phases form leading to a reduced room temperature resistivity of 100 μΩ cm. On the other hand, the presence of Sr₃Ru₂O₇ increases the resistivity to 385 μΩ cm. We have observed that the existence of the extra phases caused a slight shift of T_c towards the bulk value, while relaxation of the lattice strain resulted in increase of T_c to 160 K. The deviation from the stoichiometric composition in films with extra phases is also confirmed by the residual electrical resistivity ratio. On the other hand, the pure SRO films, the compressively strained and the plastically relaxed exhibit a stoichiometric ratio.     

Influence of Ga2O3 addition on transparent conductive oxide films of In2O3-ZnO

Influence of incorporation of Ga in amorphous In-Zn-O transparent conductive oxide films was investigated as a function of Zn/(Zn + In). For In-Zn-O films with no Ga₂O₃, the range of Zn/(Zn + In) ratio where the amorphous phase appears became narrow at a substrate temperature of 250 °C. With increasing Ga₂O₃ quantity, amorphous films were obtained even at a high substrate temperature of 250 °C in a wider range of Zn/(Zn + In) than that of In-Zn-O films with no Ga₂O₃. This means that the trend of crystallization at higher substrate temperature was disturbed with additional Ga incorporation. For the film deposited from ZnO:Ga (Ga₂O₃: 4.5-7.5 wt%) and In₂O₃ targets, we obtained a resistivity of 2.8 × 10⁻⁴ Ω cm, nearly the same value as that for an In-Zn-O film with no Ga₂O₃. The addition of more than 7.5 wt% Ga₂O₃ induced a widening of the optical band gap.     

Synthesis and characterization of Ca3Co4O9 thin films prepared by sol-gel spin-coating technique on Al2O3(001)

Ca₃Co₄O₉ thin films are deposited on Al₂O₃(001) substrates using a sol-gel spin-coating process. X-ray diffraction shows that the film exhibits a single phase of Ca₃Co₄O₉ with the (00l) planes parallel to the film surface. The temperature dependence of magnetic susceptibility showed as expected the existence of two magnetic transitions similar to those observed in bulk samples: a ferrimagnetic and a spin-state transition around 19 and 375 K, respectively. At 5 K the magnetization curves along the c-axis of the Al₂O₃(001) show that the remanent magnetization and coercive field are close to those obtained for films grown by pulsed laser deposition, which evidences the interest to use such an easy technique to grow complex thin films oxides.     

Synthesis of Tb3Al5O12 (TAG) transparent ceramics for potential magneto-optical applications

Tb₃Al₅O₁₂ transparent ceramics have been prepared by solid state reaction and vacuum sintering. The optical quality and the microstructure of the samples were investigated. The sample sintered at 1650 °C possessed relatively good optical transparency from 400 nm to 1600 nm. The Verdet constant measured at 632.8 nm of the quasi-pore-free Tb₃Al₅O₁₂ transparent ceramic was −172.72 rad T⁻¹ m⁻¹, which was close to the counterpart of Tb₃Al₅O₁₂ single crystal. The thermal conductivity of the sample was also measured. To the best of our knowledge, this is the first time that Tb₃Al₅O₁₂ transparent ceramic with relatively good optical quality and magneto-optical property has been reported.     

FT-IR and UV-Vis-NIR characterisation of pure and mixed MoO3 and WO3 thin films

We report a spectroscopic characterisation of MoO₃, WO₃ and a MoO₃-WO₃ mixed oxide thin films deposited on alumina and silicon substrates. Absorbance FT-IR and diffuse reflectance UV-Vis-NIR spectra were recorded after treatments in vacuum and after interaction with O₂, NO₂/O₂, CO/O₂ or pure CO at increasing temperatures up to 673 K. For all the films, reducing treatments (vacuum, CO or CO/O₂) cause the increase of a variety of broad absorptions both in the Vis-NIR and medium IR regions. These absorptions decrease in intensity after contact with oxidising atmospheres (O₂ or NO₂/O₂), so that they are all assignable to electronic transitions due to the presence of a variety of donor levels related to oxygen defects.