Metal Organic Decomposition Method Research Articles

Chemical epitaxial growth of nm-thick yttrium iron garnet films with low Gilbert damping

Nanometer-thick Y3Fe5O12 (YIG) films with very low damping constant have been fabricated on gadolinium gallium garnet substrates using chemical metal-organic decomposition method. Both the microstructure and ferromagnetic properties of the YIG thin films have been studied. High resolution X-ray diffraction result displayed an epitaxial structure of the YIG film. Surface morphology was investigated using an atomic force microscopy. The average surface roughness is about 0.8 ± 0.2 nm for a ∼50 nm thick epitaxial growth YIG film, which is comparable to the result of pulse laser deposition grown films. The coercivity field of the YIG film is around 1.5 Oe. Furthermore, magnetization dynamics properties were studied using a coplanar waveguide vector-network-analyzer ferromagnetic resonance spectrometer. The extracted damping constant is as low as 1.4 × 10−3. The results show that high quality nanometer YIG films can be obtained through chemical epitaxial growth method. It would be very useful for the garnet based spintronics applications.

Stable self-polarization in Nd and Ti codoped BiFeO3 films

Nd (3 %) and Ti (2 %) codoped BiFeO3 (BNFTO) films with different layer and film thicknesses were deposited on LaNiO3(100)/Si substrates using a metal organic decomposition method. The BNFTO films show a highly (100)-preferred orientation. The hysteresis loops of both films are asymmetric with negatively imprinted polarizations, suggesting that both samples are self-polarized regardless of the layer and film thicknesses. More importantly, the P–E hysteresis loops for both films can recover to their asymmetric shapes after high-field measurements, indicating the self-polarizations are quite stable. These results are explained based on the stabilization of the defect complexes. The effects of the self-polarization on the leakage, dielectric and piezoelectric properties of the BNFTO films are investigated.

Three-Dimensional ZnO-BiVO4 Core-Shell Nanosturctured Array for Photoelectrochemical Water Oxidation

In this work, three-dimensional (3D) ZnO-BiVO4 core-shell nanostructured arrays were constructed on fluorine-doped tin oxide (FTO) substrates for use in photoelectrochemical (PEC) water splitting. The ZnO nanodendrite (ND) arrays were grown on FTO substrates using a wet chemical route. A photocurrent density of 0.6 mA/cm2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 at 100 mW cm-2 is monitored in the ZnO ND array photoanode with a thickness of 3 mm. To construct the 3D ZnO-BiVO4 core-shell nanostructured arrays, the BiVO4 nanoparticle (NP) layers were subsequently formed on the surface of ND arrays using metal organic decomposition method. The absorption spectrum of the 3D ZnO-BiVO4 core-shell nanostructured array shows an absorption edge at the wavelength of ~510 nm. An optimized photocurrent density of 2.5 mA/cm2 at 1.23 V vs. RHE is obtained in the 3D ZnO-BiVO4 core-shell nanostructured array photoanode. The 3D ZnO ND array provides a large surface area for the deposition of the thin BiVO4 layer. Moreover, due to the formation of type II heterojunction in the ZnO-BiVO4 core-shell nanostructured array, the photocarriers generated in the ZnO ND core and BiVO4 shell can be effectively separated. Therefore, photoholes generated and collected in the thin BiVO4 layer can transport to the surface for water oxidation. On the other hand, the photoelectron generated and collected in the ZnO ND core can transport to the FTO substrate due to the quasi-single crystal structure of the ZnO ND array. To further improve the PEC performance, Co–Pi was further electrodeposited on the surface of the 3D ZnO-BiVO4 core-shell nanostructured array photoanode. With the Co-Pi deposition, the onset potential in the J-V curve of the 3D ZnO-BiVO4 core-shell nanostructured array photoanode shows a cathodic shift from 0.7 V to 0.2 V vs. RHE. Moreover, the photocurrent density of the 3D ZnO-BiVO4 core-shell nanostructured array photoanode is significantly improved. An optimized photocurrent density of 3.5 mAcm-2 are monitored in the Co-Pi deposited photoanode at 1.23 V vs. RHE.

Effect of Annealing Temperature on Bi3.25La0.75Ti3O12 Powders for Humidity Sensing Properties

Bi3.25La0.75Ti3O12 (BLT) powders have been synthesized via the metal–organic decomposition method with annealing of the BLT precursor solution at 350°C, 450°C, 550°C, 650°C or 750°C. The crystalline structure and morphology of the BLT powders were characterized by x-ray diffraction analysis, field-emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, and specific surface and pore size analyses. The humidity sensing properties of the BLT powders annealed at the five temperatures were investigated to determine the effect of annealing temperature. The annealing temperature strongly influenced the grain size, pore size distribution, and specific surface area of the BLT powders, being largely correlated to their humidity sensing properties. The specific surface area of the BLT powder annealed at 550°C was 68.2 m2/g, much larger than for the other annealing temperatures, and the majority of the pores in the BLT powder annealed at 550°C were mesoporous, significantly increasing the adsorption efficiency of water vapor onto the surface of the material. The impedance of the BLT powder annealed at 550°C varied by more than five orders of magnitude over the whole humidity range at working frequency of 100 Hz, being approximately five times greater than for BLT powders annealed at other temperatures. The response time was about 8 s, with maximum hysteresis of around 3% relative humidity. The BLT powder annealed at 550°C exhibited the best humidity sensing properties compared with the other annealing temperatures. We expect that these results will offer useful guidelines for preparation of humidity sensing materials.

Improving the photoactivity of bismuth vanadate thin film photoanodes through doping and surface modification strategies

Currently, one of the most attractive and desirable ways to solve the energy challenge is harvesting energy directly from the sunlight through the so-called artificial photosynthesis. Among the ternary oxides based on earth–abundant metals, bismuth vanadate has recently emerged as a promising photoanode. Herein, BiVO4 thin film photoanodes have been successfully synthesized by a modified metal-organic precursor decomposition method, followed by an annealing treatment. In an attempt to improve the photocatalytic properties of this semiconductor material for photoelectrochemical water oxidation, the electrodes have been modified (i) by doping with La and Ce (by modifying the composition of the BiVO4 precursor solution with the desired concentration of the doping element), and (ii) by surface modification with Au nanoparticles potentiostatically electrodeposited. La and Ce doping at concentrations of 1 and 2 at% in the BiVO4 precursor solution, respectively, enhances significantly the photoelectrocatalytic performance of BiVO4 without introducing important changes in either the material structure or the electrode morphology, according to XRD and SEM characterization. In addition, surface modification of the electrodes with Au nanoparticles further enhances the photocurrent as such metallic nanoparticles act as co-catalysts, promoting charge transfer at the semiconductor/solution interface. The combination of these two complementary ways of modifying the electrodes has resulted in a significant increase in the photoresponse, facilitating their potential application in artificial photosynthesis devices.

Significant reduction in spin pumping efficiency in a platinum/yttrium iron garnet bilayer at low temperature

The temperature evolution of a direct-current electromotive force (EMF) generated by spin pumping and the inverse-spin Hall effect in a platinum (Pt)/yttrium iron garnet (YIG) bilayer was investigated down to 80 K. The magnitude of the EMF decreased significantly with decreasing temperature and disappeared at approximately 80 K. 40-nm-thick YIG films fabricated by a metal organic decomposition method exhibited single-peak ferrimagnetic resonance (FMR) spectra without any spin wave resonance, which allowed us to precisely analyze the FMR spectra. We determined that the temperature evolution of the Gilbert damping constant is the dominant factor in the temperature dependence of the EMF. The comparison of the FMR linewidth between the X- and Q-bands revealed that an increase in Gilbert damping constant at low temperatures is not due to the enhancement of the spin pumping efficiency but due to an additional spin relaxation in the YIG film itself, which reduces the precession angle of the magnetization under the FMR conditions.

Solubility limit and luminescence properties of Eu3+ ions in Al2O3 powder

Al–Eu–O compounds are synthesized from Al2O3:Eu2O3=(1–x):x mixtures (x=0–0.15) by the metal organic decomposition method and subsequently calcined at various temperatures from Tc=750 to 1200°C in dry O2 atmosphere. The structural and luminescence properties of these compounds are investigated using X-ray diffraction analysis, photoluminescence (PL) analysis, PL excitation spectroscopy, and luminescence lifetime measurements. The present study focuses on the effects of the Eu2O3 addition (x) on the material and phosphor properties of Al2O3:Eu3+. The stable phase of α-Al2O3 is synthesized at Tc>1100°C and cubic γ-Al2O3 phase at Tc≤1100°C. The calcination temperature dependence of the PL intensity yields an activation of Ea~0.8eV for Eu3+ ions in the Al2O3 host. The luminescence decay time is determined to be ~0.8ms, independent of x. Temperature dependence of the PL intensity at T=20–450K exhibits thermal quenching behavior with energies of 17meV and 0.28eV at low (<200K) and high temperatures (>200K), respectively. The solubility limit of Eu3+ ions in α-Al2O3 is determined to be ~1%. The schematic energy-level diagram of Eu3+ in α-Al2O3 is also proposed for the sake of a better understanding of the luminescence process of this phosphor system.

Superconducting Thin Films Made by Chemical Solution Deposition

$\text{Dy}_{1-x}(\text{Gd} \text{or} \text{Yb})_{x}\text{Ba}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ samples were prepared using chemical solution deposition, based on trifluoroacetate metal–organic decomposition methods. X-ray diffraction results demonstrated the formation of the RE123 superconducting phase with strong in-plane and out-of-plane texture. For all samples doped with Gd or Yb, c-lattice constants were observed to decrease. Measurements of the onset critical transition temperature $(\text{T}_{c}^{\mathrm{onset}})$ were found to decrease with increasing Yb content, whereas only minor changes were observed for samples with Gd. Critical current density $(\text{J}_{c})$ analysis demonstrated that doping with Yb significantly increased the self-field $\text{J}_{c}$ value from 3.8 MA/cm2 to 6.0 MA/cm2 for the pure sample and the 10% Yb-doped sample, respectively. In contrast, samples doped with Gd were characterized by the lowest self-field $\text{J}_{c}$ values. Investigation of pinning force mechanisms revealed that the samples in this study were dominated by normal surface pinning.

Magneto-optical switching devices based on Si resonators

The magneto-optical switching devices based on Si ring and Si photonic crystal resonators have been fabricated using a Bi3Fe5O12 (BIG) film deposited by the metal organic decomposition (MOD) method. The quality of the obtained BIG film was evaluated by X-ray diffraction and the magneto-optical Kerr effect and relatively good results were obtained. The light modulations of both devices were ≦20% at a wavelength of ∼1.5 µm. The operation mechanisms of both devices are explained by the Cotton–Mouton effect where the magnetic field direction is perpendicular to the light propagation direction.

Effect of mesoporous structure on Bi3.25La0.75Ti3O12 powder for humidity sensing properties

Bi3.25La0.75Ti3O12 (BLT) powder is synthesized via a metal-organic decomposition (MOD) method, and mesoporous structure is formed in the BLT powder via nanocasting method. The humidity sensing properties of BLT and mesoporous BLT (M-BLT) humidity sensors are investigated at room temperature within the relative humidity (RH) range of 11–95%. The BET surface area of M-BLT powder (10.8m2/g) is remarkably bigger than it of BLT powder (0.4m2/g). The optimum working frequency of BLT and M-BLT humidity sensors are 100Hz, and the impedance variation of M-BLT humidity sensor is about six orders of magnitude within the whole humidity range from 11% to 95% RH, which is six times more than it of BLT humidity sensor (only about one order of magnitude). Linearity of the M-BLT humidity sensor is obviously better than it of the BLT humidity sensor, and its maximum linear error is only 2% at 75% RH. The response time and recovery time of M-BLT humidity sensor are about 32s and 68s at 100Hz. The results indicate that mesoporous structure is beneficial for enhancing the humidity sensing properties of materials, and nanocasting method would be one of important and effective approach for preparing high-performance humidity-sensing material.

Direct current imaging using a magneto-optical sensor

Magneto-optical (MO) imaging was implemented for the visualization of direct currents (DC) of patterned current wires using bismuth substituted yttrium iron garnet (Bi:YIG) sensor films prepared by the metal organic decomposition (MOD) method. The minimum detectable magnetic field range of the MO sensor was calculated to be about 0.2G. To enhance the contrast of DC images, in the image processing we have inverted the DC without changing the optical orientation between the analyzer and polarizer of the MO system. The measured magnetic field distributions of patterned current wires induced by a DC were in good agreement with results of COMSOL Multiphysics simulations.

Chemical Solution Growth and Oxygen Diffusion Behavior of Doped CeO2−δ Buffers in Coated Conductors

Ba-, La-, and Zr-doped CeO2−δ films and undoped CeO2−δ film with (00 l) preferred orientation have been prepared on biaxially textured Ni–W substrates by metal organic decomposition (MOD) method. The influences of valences and ionic radii of dopants on the epitaxial growth of CeO2−δ films and oxygen diffusion in the buffer layer were explored by X-ray diffraction (XRD) and atomic force microscopy (AFM). The doping cations with different radii cause the change of the lattice parameter of CeO2−δ film and the mismatch between Ni–W substrate and epitaxial film, which modifies the compressive strain resulted from the elastically lattice deformation in the films. Our results show that the compressive strain is beneficial to the c-axial texture formation of CeO2−δ film. In addition, ionic radius has influence on the surface roughness and the out-of-plane texture of the film. Moreover, the oxygen diffusion results from the inherent variation of the thermodynamic factors, in particular the migration energy of oxygen ions. Meanwhile, larger radius of doping cation would lead to the decrease of the migration energies of oxygen ion due to the steric effect. So compared with the Ba- and La-doped CeO2−δ films, the Zr-doped CeO2−δ film shows slight oxygen diffusion. These results are significant to improving the properties of buffer layer for coated conductors.

Effects of Zn2+ doping content on the structure and dielectric tunability of non-stoichiometric [(Na0.7K0.2Li0.1)0.45Bi0.55]TiO3+δ thin film

The Zn2+ doped non-stoichiometric [(Na0.7K0.2Li0.1)0.45Bi0.55](Ti1−xZnx)O3+δ (NKLBTZnx, x = 0–4 at.%) thin films were deposited on fluorine-doped tin oxide/glass substrates via a metal organic decomposition method. The effect of Zn2+ doping content on microstructure, insulating characteristic and dielectric properties were mainly investigated. All the thin films exhibit similar single perovskite structures without detectable secondary phase and the grain size gradually decreases with the increase of Zn2+ doping content. Compared with other films, NKLBTZn0.01 thin film shows enhanced insulating characteristic with lower leakage current, and improved dielectric properties with a relatively higher dielectric tunability and lower dielectric loss. Moreover, with the increasing of electric field or decreasing of measuring frequency, the dielectric tunability is progressively increased. The tunability and figure of merit for the NKLBTZn0.01 thin film at 300 kV/cm and 1 kHz are 40.1 % and 7.0, respectively. These findings suggest that NKLBTZn thin film has potential applications in microwave dielectric devices.

Electric-Field Tunability of Dielectric in Polycrystalline Sr1-xMnx TiO3 Thin Films**Supported by the National Natural Science Foundation of China under Grant Nos 51225201, 61271078, and 51102133, the National Basic Research Program of China under Grant No 2015CB921201, the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the Fundamental Research Funds for the Central Universities.

The electric-field tunability of dielectric constant (ϵ-E) in Sr1-xMnxTiO3 films (x = 0, 0.005, 0.010, 0.020 and 0.030) prepared by the metal organic decomposition method on Pt/Ti/SiO2/Si substrates is studied in the frequency range from 100 Hz to 1 MHz with different Mn contents at different temperatures. The frequency-independent tunability increases strongly with decreasing the temperature from 300 K to 150 K. The tunability (~31%) in thin films (x = 0.005) at 150 K is obtained and the temperature for the same tunability in ceramics is about 60 K lower than the present one. This tunability is comparable with that in one of ferroelectric Sr1-1.5xBixTiO3 thin films. Similarly, the well-defined P(E) hysteresis loop and 2Pr (1.2μC/cm2) can be obtained at 300K in Sr1-xMnxTiO3 films with x = 0.005. Both the existence of electric dipole or poled micro domain introduced by the doped Mn2+ located in the off-center position at Sr sites and the strain between the thin film and the substrate are the origins of the tunable and polar behavior in Sr1-xMnxTiO3 films.

Influence of bismuth substitution on yttrium orthoferrite thin films preparation by the MOD method

Yttrium orthoferrite thin films with a thickness of about 0.4μm were prepared on glass substrates by using a metal-organic decomposition method. Our studies reveal that it is possible to reduce the crystallization temperature of the yttrium orthoferrite by the substitution of the yttrium ion with bismuth. For the samples BixY1−xFeO3 with x=0.3 and x=0.4, orthorhombic yttrium orthoferrite characteristic peaks in the X-ray diffraction spectra have been detected. The lattice constants of the Bi0.3Y0.7FeO3 film were a=5.905Å, b=7.66Å, c=5.256Å with an average grain size of about 40nm. The magnetization data indicate that the film has in-plane easy axis and weak coercivity which might be explained by a possible secondary garnet phase crystallization. Faraday rotation angle of the sample was measured to be about 0.3°/µm.

Effect of substrates on magnetization of BiFeO3 films

BiFeO3 (BFO) films were fabricated on Pt/Ti/SiO2/Si and single crystalline LiNbO3 (LN) substrates using metal organic decomposition method and annealed in N2/O2. Magnetizations of these films were systematically characterized. It is found that BFO films prepared on Pt/Ti/SiO2/Si substrates exhibit stronger saturation magnetization (MS) than those prepared on LN substrates, and their magnetizations rely more on annealing atmosphere. We consider that both oxide feature of LN substrates and in-plane compressive stress introduced by LN reduce the Fe2+ content in the top BFO films and further stabilize the films against post-treatment. This work provides a valuable guidance for fabricating high quality magnetic oxide films.

Magneto-optical visualization by Bi:YIG thin films prepared at low temperatures

A device for the imaging of magnetic fields and domain structures based on the Faraday effect has been developed using garnet thin films prepared by the metal-organic decomposition method as indicators. The sensitivity was improved by using high concentration bismuth substituted yttrium iron garnet thin films with in-plane magnetic anisotropy. Low temperature synthesis of the films (BixY3−xFe5O12; x = 2) on glass substrates of thickness about 0.8 μm is described and the Faraday rotation angle is measured to be about −11°/μm.

Mechanical stress effect on leakage current in Bi3.25La0.75Ti3O12 thin films

Bi3.25La0.75Ti3O12 (BLT) ferroelectric thin films were prepared on Pt/Ti/SiO2/Si substrates by metalorganic decomposition method. Mechanical stress effect on leakage current was investigated. The results demonstrate that the leakage current increases with increasing electric field. Under mechanical tensile or compressive stress, the increase trend of the leakage current with electric field shows negligible change in low field region (below 75kV/cm), while that gets weakened in high field region (above 75kV/cm) compared with that at free state (zero stress). At a certain electric field (above 75kV/cm), the leakage current decreases with increasing tensile or compressive stress. The effect of domain reorientation induced by stress combined with the contribution from charge injected into films is found to be reasonable for the explanation of the leakage current in BLT thin films under different stress.

English

One-pot polyol process was combined with metal organic decomposition (MOD) method to fabricate a room-temperature NO2 gas sensor based on tin dioxide and reduced graphene oxide (SO2/RGO) nanocomposite films. X-ray diffractometry (XRD) and scanning electron microscopy (SEM) were used to analyze the structure and morphology of the fabricated films. The electrical and NO2 gas-sensing properties of SnO2 to which various amounts of RGO were added were measured in detail as a function of concentration of NO2 gas at room temperature, to elucidate the contribution of RGO to the NO2 gas-sensing capacity. The sensor that was based on a nanocomposite film of SnO2/RGO exhibited a strong response to low concentrations of NO2 gas at room temperature, satisfactory linearity and favorable long-term stability. Keyword: Tin dioxide (SnO2); reduced graphene oxide (RGO); nanocomposite film; room-temperature NO2 sensor.

Fabrication and characterization of a p-type Cu3Nb2O8 photocathode toward photoelectrochemical reduction of carbon dioxide

We report a new p-type Cu3Nb2O8 as a thin film photocathode, which was fabricated through spin-coating by a metal organic decomposition method. The p-type Cu3Nb2O8 photocathode exhibited a strong cathodic photocurrent, and the incident photon-to-current conversion efficiency plot confirmed that the p-type Cu3Nb2O8 photocathode has the ability to utilize the visible light (λ<ca. 480nm). Furthermore, we demonstrated photoelectrochemical reduction of carbon dioxide with the primary product being carbon monoxide by utilizing the p-type Cu3Nb2O8 photocathode under AM 1.5 G solar light irradiation. From the results of Mott–Schottky analysis, UV–vis measurement and ultraviolet photoemission spectroscopy, the conduction band potential of p-type Cu3Nb2O8 was estimated to be –1.21V versus a normal hydrogen electrode (NHE) at pH 7 with its conduction band edge located at a more negative potential than the reduction potential of carbon dioxide to carbon monoxide. Although the cathodic photocurrent of the p-type Cu3Nb2O8 photocathode gradually decayed with time, it recovered upon thermal annealing in air. This behavior suggests that the photocurrent response of the p-type Cu3Nb2O8 photocathode is intimately related to variation of the valence state of copper ions. In this paper, the photoelectrochemical properties of the p-type Cu3Nb2O8 photocathode are described in conjunction with optical, electrical and structural properties, and characteristics of the p-type Cu3Nb2O8 photocathode for the photoelectrochemical reduction of carbon dioxide are discussed.