Sol-gel Deposition Method Research Articles

Ce-doping at Mn site to enhance resistive switching performance of spinel MnCo2O4 resistive random access memory devices

The spinel Ce-doping MnCo2O4 (MCO) thin films were fabricated on Pt/Ti/SiO2/Si substrates for resistive switching (RS) layer using sol-gel spin-coating deposition method. The Pt/Mn0.925Ce0.075Co2O4/Pt (Pt/7.5MCC/Pt) device exhibits stabler and superior bipolar RS performance, the concentrated distribution of Reset/Set voltage as low as – 0.62/1.175 V, good cycle endurance and excellent time retention capability. The improvement in the RS performance of the Pt/7.5MCC/Pt devices can be attributable to the effective limitation of the random formation and rupture of conductive filaments by appropriate Ce doping. The carrier transport mechanism of the device at high resistance state can be dominated by the Schottky emission, whereas the carrier transport mechanism at low resistance state consistent with the Ohmic conduction. This work provides a potential performance improvement approach to design the resistive memory devices for data storage applications.

Cu- and Ce-doped MnCo2O4 spinel coatings on ferrite interconnects by electrophoretic deposition

MnCo2O4 spinel coating is considered as one of the most promising protective coatings on the surface of ferritic stainless steel interconnects in solid oxide fuel cells (SOFCs). And the doping of metallic elements and active rare earth elements may further improve the electrical conductivity and antioxidant properties of spinel coatings. In this work we firstly prepare the Cu-doped and Ce-doped MnCo2O4 spinel coatings (abbreviated as MCCu, MCCe) on the surface of SUS430 substrate by Sol-Gel and electrophoretic deposition methods. The optimal doped ratio of Cu and Ce based on the results of oxidized mass gain and area-specific resistance (ASR) tests are determined respectively. Then we deposit Cu-Ce co-doped MnCo2O4 spinel coatings (abbreviated as MCCuCe) accordingly. The successful deposition of the target modified spinel coating on the substrate surface is confirmed using SEM-EDS, XRD, XPS characterization. The performance test results of the MCCuCe coating on the SUS430 surface show that the mass gain after 500 h oxidation at 800 °C in air is 1.3564 × 10−3 mg cm−2, and the ASR at 800 °C after 500 h oxidation is 9.80mΩ cm2, which is much lower than those of the bare SUS430 substrate and the substrate with deposited MnCo2O4 spinel coating. And the MCCuCe protective coating plays a better role in preventing the diffusion of Cr from the substrate. Further analysis prove that the doping Cu mainly contributes to the electrical conductivity and adhesion to the substrate while the doping Ce mainly improve the anti-oxidation and Cr diffusion resistance. This work determines the optimal doped ratio of Cu and Ce and provides a simple way to prepare the Cu-Ce co-doped MnCo2O4 spinel coatings on the ferritic interconnects, which effectively improve comprehensive performances of MnCo2O4 spinel coatings and helps to accelerate the industrial application of SUS430 ferrite in the SOFCs.

Enhanced resistive switching performance of spinel MnCo2O4 resistive random access memory devices: Effects of annealing temperatures and annealing atmospheres

The spinel MnCo2O4 (MCO) thin films were fabricated on Pt/Ti/SiO2/Si substrates for resistive memories via sol-gel spin-coating deposition method under different annealing temperatures and annealing atmospheres. The 650oC-annealing Pt/MCO/Pt device shows better bipolar resistance switching parameters than the devices annealed at 600 °C and 700 °C. The nitrogen-annealing Pt/MCO/Pt device exhibits optimum resistance switching parameters due to increasing of the oxygen-vacancies proportion, formation of confined and stable conductive filaments, and suppressing of the randomness of oxygen vacancies. The carrier transportation mechanisms of the devices with numerous oxygen-vacancies content in low resistance state (LRS) and high resistance state (HRS) are dominated by Ohmic conduction and Schottky emission, respectively. For the devices with fewer oxygen-vacancies content, the conduction mechanisms at LRS and HRS can be described by nearest-neighboring hopping conduction and space-charge-limited current model, respectively. This work indicates that the spinel MCO films have good potential application in resistive random access memory.

Tb-doped β-(AlxGa1-x)2O3 epitaxial films on c-sapphire substrates fabricated via a spin-coating method

β-(AlxGa1-x)2O3 epitaxial films are wide-bandgap semiconductors that may be used to fabricate next-generation optoelectronic and high-power devices. In this study, we demonstrate the dual effects of rare-earth doping and bandgap engineering on the structural, chemical, and optical properties of terbium (Tb)-doped β-(AlxGa1-x)2O3 epitaxial films prepared on c-sapphire substrates using an inexpensive sol-gel spin-coating deposition method. The (2¯01)-oriented epitaxial films prepared with Al at concentrations (x) of 0.3, 0.5, and 0.7 exhibit bandgap energies of 4.92, 5.31, and 5.84 eV, respectively. Photoluminescence spectroscopy analysis revealed two types of emission bands with each originating from a different luminescence center. The emission bands captured in the 300–500 nm wavelength range (UV, blue, and green) resulted from intrinsic defects in the recombination processes in the host material, whereas the emissions in the 500–800 nm range could be assigned to radiative emissions from the Tb dopant. Collectively, the results of this study demonstrate the effectiveness of a simple solution deposition approach that can be used to fabricate novel materials and compositions with tunable properties for a broad range of potential applications.

Magnetic properties of Ni/BiFeO3 hybrid nanostructures

Next-generation spintronic applications, including magnetic nanosensors, energy-efficient data storage devices and magnetic memory devices, have obtained scientific and technological interest. One-dimensional (1D) core/shell nanomaterials are particularly interesting due to their promising anisotropic magnetic properties and exchange bias. Here, we investigate a versatile sol-gel and electrochemical deposition method and achieve Ni/BiFeO3 (Ni/BFO)'s controlled growth with tunable structure geometry. Significantly, BFO nanoshells on the pore walls and Ni nanowires inside the nanoshell are successfully deposited. Experimental and analytical observations show that the prepared Ni/BFO nanostructures have the ability to improve magnetic properties. This work presents a pathway for the controlled growth of hybrid nanostructures and provides a platform to study the tunable magnetic properties, suggesting their promise for practical applications.

Carbon tungsten oxide composite cathode materials for aluminum-ion batteries

Aluminum-ion batteries use more abundant materials and suffer from fewer safety risks than lithium-ion batteries. In this work, new cathode materials for Al-ion batteries were synthesized and tested. WO3, carbon materials, and WO3-carbon composite were prepared by sol-gel and chemical vapor deposition methods. These materials differ in microstructure and other physicochemical properties and the possibility of using them as cathode materials was tested. The correlation between the phase composition, structure, microstructure, electrical properties, and electrochemical performance was described based on X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic discharge results. WO3, Norit, and WO3/carbon core-shell composite materials exhibit the smallest average grain size in the range of tens of nanometers while materials based on potato starch carbons contain grains in the range of tens of micrometres. The highest values of the open cell voltage and capacitance of Al-ion cells were found for single-phase WO3 and Norit materials, whereas in the case of single-phase Carbon PS these parameters acquire much lower values.

Surface Treatment of Flexible Barrier Film for Improved Stability of Organic Photovoltaic Mini Modules

The lifetime and stability of organic photovoltaics (OPVs) are the key factors that influence the technology used to scale up and commercialize OPVs. High-performing and reliable devices are used to fabricate the devices of choice. Materials and methods that can be used to prevent the degradation of organic materials, enabling better OPV applications, are being increasingly researched in recent years. Herein, we present the surface modification process of a commercial, flexible barrier film based on polyethylene terephthalate (PET). A sol-gel deposition method was used to modify the surface. Two scalable coating techniques, spray- and bar-coating, were investigated as the processing methods. Treated films were optically, morphologically, and topologically characterized. The modification of the barrier film surface increased the surface hydrophobicity of the bar-coated and spray-coated treated films. This was validated by the contact angle measurements. OPV roll-to-roll (R2R) mini-modules with 4.2% power conversion efficiency were fabricated and encapsulated with the treated films. The lifetime and stability were assessed by conducting accelerated aging tests based on the ISOS-D-3 protocol. The spray-coating technique provided a more stable layer than the bar-coating technique, and the lifetime of the OPV modules encapsulated in spray-coated treated barrier films was increased. Surface modification has been demonstrated to be a promising approach for not only improving the barrier film properties (resulting in the improved lifetimes of the modules) but also reducing the extents of reflectance losses in the OPV modules post encapsulation.

Co<SUP>2+</SUP> Distribution and the Related Magnetic Evolution in Ca-substituted Spinel CoFe₂O₄

Magnetic properties of cobalt ferrites with a portion of CoSUP2+/SUP ions being replaced by CaSUP2+/SUP were investigated by vibrating-sample magnetometry (VSM). The CaSUBx/SUBCoSUB1-x/SUBFe₂O₄ (x ≤ 0.2) specimens were prepared as thin films by a sol-gel deposition method. According to the VSM results, the saturation magnetization (MSUBS/SUB) of the Ca-substituted ferrite decreased from that of CoFe₂O₄ proportional to the Ca composition x. Raman spectral analyses revealed that the Ca-substituted ferrites had a lower tetrahedral CoSUP2+/SUP population in the spinel lattice compared to CoFe₂O₄. The decreasing trend of MSUBS/SUB is consistent with the result of theoretical evaluation in which the relative population of CoSUP2+/SUP ions among the tetrahedral and octahedral sites is proportional to the relative Raman scattering intensities of 615 and 470 cmSUP-1/SUP peaks, respectively.

The effect of palladium doping on optical and electrochromic properties of sol-gel ‎deposited tungsten oxide films

In this paper, palladium doped-tungsten oxide thin films have been prepared by sol-gel deposition method. In this way, tungstic ‎acid obtained by Kudo method was doped by different amounts of palladium chloride and were deposited on transparent ‎conductive oxide of ITO/glass by dip-coating method. The effect of Pd doping on morphology and optical properties as well as ‎electrochemical characteristics were investigated using scanning electron microscopic (SEM), UV-Vis spectroscopy, cyclic ‎voltammetry (CV) and optical transmission at 632.8 nm constant wavelength. SEM revealed that the WO3 layers have a thickness ‎of 450-500 nm were obtained with smooth and uniform surfaces. Also, the transparency of layers was above 85%, for which the ‎optical gap was decreased by increasing Pd content. The voltammetry results showed that the doped palladium reduces the ‎catholic potential, increases the chemical stability of tungsten oxide thin films, stabilizing the electrochemical performance of ‎these layers. Finally, we measured the electrochromic response time and the corresponding electrochemical efficiencies

Effects of Scandium Doping on Structural and Magnetic Properties of Cobalt Ferrite Thin Films

Structural and magnetic properties of Sc-substituted cobalt ferrites were studied by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and vibrating-sample magnetometry. The ScSUBx/SUBCoFeSUB2-x/SUBO₄ (x ≤ 0.3) specimens prepared as thin films by a sol-gel deposition method were polycrystalline having cubic spinel structure with a small increase in the lattice constant compared to CoFe₂O₄. The Raman spectral analyses suggested that the Sc-doped specimens have higher tetrahedral CoSUP2+/SUP population than that of pristine CoFe₂O₄. The magnetic hysteresis curves of the ScSUBx/SUBCoFeSUB2-x/SUBO₄ specimens indicated that the saturation and remanent magnetization decrease proportionally with the increase of Sc composition (x). The decrease in the ferrimagnetic parameters is understandable in terms of the octahedral substitution of non-magnetic ScSUP3+/SUP ions. However, the octahedral ScSUP3+/SUP ions caused an increase of the coercivity.

Photocatalytic CO2 Reduction and Thermal Properties of Alumina/Silica Coated TiO2 Nanoparticles

In this study, the surface of TiO2 was coated with SiO2 and Al2O3 layers by sol-gel and chemical deposition methods. Firstly, the TiCl4 was magnetically stirred for 1 h in deionized water, and then the NaOH solution was drop wised to the solution and stirred 2h. Finally, the obtained TiO2 was washed, filtered, and dried in a vacuum oven. The surface of TiO2 was coated with SiO2 and Al2O3 layers subsequently by chemical deposition methods. The morphological, thermal, and crystal properties of products were determined via SEM, TGA, and XRD machines. The X-ray diffraction peaks displayed that the TiO2 nanoparticles were synthesized without any extra peaks. Moreover, the SiO2 and Al2O3 coated TiO2 particles contain extra SiO2 and Al2O3 peaks, indicating that the surface of TiO2 was coated via SiO2 and Al2O3. The SEM results displayed that TiO2 and SiO2 and Al2O3 coated TiO2 were spherical in shape, and the size distribution was found to be around 20-50 nm and 200-300 nm, respectively. The photocatalytic and UV–vis analyses were used to determine the CO2 reduction and optical properties of particles. The results showed that the absorption peaks were broad to longer wavelength with a coating of SiO2 and Al2O3. The CO2 reduction performance of TiO2 has been enhanced via coating SiO2 and Al2O3 layer.

Visible-light-driven AgBr–TiO2-Palygorskite photocatalyst with excellent photocatalytic activity for tetracycline hydrochloride

Tetracycline hydrochloride (TC) wastewater has complex components, high concentration of organic matter and certain biological toxicity. Photocatalytic degradation is of great application prospect due to its green, thorough and efficient removal of TC. In this study, heterojunction photocatalyst supported on Palygorskite (Pal) AgBr–TiO2-Pal with visible light response was successfully prepared via sol-gel and liquid deposition method successfully. Taking TC as the target pollutant, the photocatalytic performance of AgBr–TiO2-Pal photocatalys excited by visible light was studied. The spreading/grafting of AgBr–TiO2 on the surface of Pal was improved by a series of structural characterization and composition analysis. The results also demonstrated that the specific surface area of AgBr–TiO2-Pal was about 48.06 m2⋅g−1 with uniform mesoporous slit. The AgBr–TiO2-Pal catalyst was very effective for the degradation of TC, and it still retained its high stability and reusability after five cycles. The results showed that under the best reaction conditions (initial concentration of tetracycline 10 mg⋅L−1, catalyst dosage 0.5 g⋅L−1, pH value 9), with the excitation of visible light, the maximum removal ratio of TC was 90%, and the mineralization ratio was 67%. The removal efficiency and degradation rate of TC by AgBr–TiO2-Pal catalyst were 2.17 and 4.75 times as much as those of TiO2 respectively. The outstanding photocatalytic performance of heterogeneous AgBr–TiO2-Pal catalyst was obtained by fully participate in the reaction by photoinduced charge. This study could be expected to be used in photocatalytic degradation of antibiotic pollutants in wastewater treatment.

Crystallographic and Magnetic Characteristics of Thin-film Ni<SUB>0.5</SUB>Co<SUB>0.5</SUB>Fe₂O₄ Ferrimagnet

Crystallographic and magnetic characteristics of thin-film NiSUB0.5/SUBCoSUB0.5/SUBFe₂O₄ ferrimagnet prepared by a sol-gel deposition method were investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The mixed ferrite NiSUB0.5/SUBCoSUB0.5/SUBFe₂O₄ specimen was found to be polycrystalline having cubic spinel structure with slightly reduced lattice constant compared to CoFe₂O₄. The XPS data indicate that Co and Ni ions in NiSUB0.5/SUBCoSUB0.5/SUBFe₂O₄ have charge valence of +2. The VSM measurements indicate that the NiSUB0.5/SUBCoSUB0.5/SUBFe₂O₄ film have saturation magnetization, remanent magnetization, and coercivity of 257 emu/cm³, 115 emu/cm³, and 0.5 kOe, respectively, which are 62 %, 68 %, and 29 % of those of CoFe₂O₄. The reduction of the magnetic parameters of NiSUB0.5/SUBCoSUB0.5/SUBFe₂O₄ compared to CoFe₂O₄ is primarily attributable to the smaller magnetic moment of high-spin NiSUP2+/SUP ion (2 μSUBB/SUB) than that of CoSUP2+/SUP ion (3 μSUBB/SUB).

Sol-gel alumina coating of wire mesh packing

Wire mesh packings have seen increasing applications to multiphase processes in recent years. Despite the high surface area, open structure and thermal and chemical resistance, wire mesh packings have a complex geometry which hinders some chemical applications, including changes of surface properties through application of a uniformly adhesive coating. In this work, the sol-gel deposition method of alumina coating ceramics was investigated for the first time on stainless steel wire mesh by using Dixon rings as example. The kinetics of deposition during the hydrolysis and polycondensation was followed for a range of initial composition of the coating such as the ratios of Al2O3 to water, acid content, polyethyleneimine binder content and the number of deposition cycles. Well-adhered alumina with a thickness up to 20 μm was successfully deposited. The molar ratios of acid to alumina and alumina to water of 0.25 and 0.01, respectively, 48 h of the aging time, 96 h of the mixing time and 2.1 g/L of polyethyleneimine binder formed a free of cracks coating of controlled thickness alumina on the Dixon rings.

Morphological and Structural Properties of Sol-Gel Derived ZnO Thin Films Spin-Coated on Different Substrates

In this work, ZnO thin films were prepared by the low-cost sol-gel deposition method onto six different substrates (glass, ITO coated glass, sapphire (Al2O3), p-Si, p-GaN and polyethylene terephthalate (PET)) to study the effects of these substrates on the morphological and structural properties of the produced films. Precursor solution is Zinc acetate dihydrate based dissolved in ethanol with monoethanolamine (C2H7NO) added to act as a stabilizing agent to the sol. The corresponding ZnO thin films were characterized using field emission scanning electron microscopy (FESEM), high resolution X-ray diffraction (XRD) and atomic force microscopy (AFM). Results revealed distinct morphological and structural properties of ZnO thin films deposited on each substrate. The most uniform morphology was identified on glass, owing to the acquisition of the averagely stable grain sizes (58 nm – 61 nm) and thin film thicknesses (280 nm – 325 nm). High resolution XRD analysis showed that the films deposited on glass, ITO, p-Si, and p-GaN were attributed to hexagonal crystallite structures while the films deposited on sapphire and PET substrates exhibited amorphous phases. Amongst the samples, the ZnO thin film spin coated on p-Si demonstrated preferred orientation in (002) direction.

Improving the performance of dye-sensitized solar cells by incoporating a novel ZnO:Al charge injection layer

In this study, the effect of integrating a ZnO:Al (AZO) charge injection layer into dye-sensitized solar cells (DSSCs) is investigated. The AZO charge injection layer was deposited using a low-cost sol-gel deposition method directly onto fluorine-doped tin oxide (FTO) conducting glass just before TiO2 photoanode coating. The structural and optoelectronic properties of AZO charge injection layer are then investigated as a function of the precursor concentration. The integration of AZO charge injection layer leads to the improvement of power conversion efficiency (PCE) by preventing the electrolyte coming in contact with FTO and improving charge injection from the charge AZO layer. It was found that there is an optimum AZO precursor concentration for charge injection layer deposition and DSSCs fabricated using higher concentration resulted in reduced photovoltaic performance due to reduced light transparency, whilst charge injection layer deposited at lower precursor concentration were found to reduce DSSC performance due to insufficient converage.

Effect of Composition and Dielectric Properties for (YBCO) Superconductor Compound in Different Preparation Methods

The superconductor compound (YBa2Cu2.8Zn0.2O7+δ) is prepared by solid state reaction (SSR), Sol-gel (SG) and laser Pulse deposition (PLD) methods. We used the X-ray diffraction technique, which shows an orthorhombic crystalline system for all the samples, and increase in the high-phase (Y-123) and decrease in low-phase and vary in proportion according to the method of preparation with the emergence of some impurities. The behavior of the samples in terms of electrical resistance and critical temperature was investigated all samples showed superconducting behavior. The properties of the dielectric (real dielectric constant, imaginary dielectric constant, loss tangent, alternating electrical conductivity) were studied as a function of frequency and range (50 Hz-1MHz) at room temperature. The results are demonstrate the apparent change in the dielectric properties by using the method of preparation of laser pulse deposition PLD at the expense of other methods, Microscopic images of the samples were examined at very high magnitudes through the scanning electron microscopy (SEM). In addition to using the titration method to determine the proportion of oxygen.

Preparation of “green” carbon quantum dots coated core-shell type pearl pigment Kieselguhr@TiO2@TiO2-x

In this paper, the green and environmentally friendly pearlescent pigment particles of the core-shell type kieselguhr@TiO2@TiO2-x composite were prepared via sol-gel deposition method, the surface of kieselguhr coated by TiO2, and then the surface of the composites was coated with TiO2-x by the technique of co-precipitation and the route of pyrolysis of the hydrazine salt. Orthogonal design method was employed to study the effects of different operating parameters on properties of the core-shell type kieselguhr@TiO2@TiO2-x composite. Due to characteristics of large specific surface with a lot of hydroxyl groups, the composite pigment were coated with Carbon dots with the assistance of (3-aminopropyl)trimethoxysilane (APS). Thus, the prepared composite pigment was mixed with citric acid and APS followed by hydrothermal reaction at 180 °C to generate carbon quantum dots coated composite pigment (kieselguhr@TiO2@TiO2-x@CDs).The obtained kieselguhr@TiO2@TiO2-x@CDs composite were characterized by X ray powder diffraction (XRD), element analysis, Raman spectra analysis, Hitachi s4800 field emission scanning electron microscopy (FESEM), X ray photoelectron spectroscopy (EDS) and TG-DTA respectively. And the color instrumental measurement was used to determine L*, a* and b* value of a pigment to evaluate the color brightness of the core-shell type kieselguhr@TiO2@TiO2-x composite. In addition, the MTT method, also known as MTT colorimetry, is a way of detecting cell survival and growth, which was employed to study in vitro cytotoxicity of their composite particles against mouse peritoneal macrophages for evaluation of their green application.

A novel “holey-LFP / graphene / holey-LFP” sandwich nanostructure with significantly improved rate capability for lithium storage

The development of high-performance and new-structure electrode materials is vital for the wide application of rechargeable lithium batteries in electric vehicles. In this work, we design a special composite electrode structure with the macroporous three-dimensional graphene areogel framework supporting mesoporous LiFePO4 nanoplate. It is realized using a simple sol-gel deposition method. The highly conductivity graphene nanosheets assemble into an interconnected three-dimensional macroporous areogel framework, while LiFePO4 grows along the graphene nanosheets and generates a mesoporous nanoplate structure. In comparison with LiFePO4, this unique sandwich nanostructure offers a greatly increased electronic conductivity thanks to the framework of graphene nanosheets. Also, the bimodal porous structure of the composite remarkably increases the interface between the electrode/electrolyte and facilitates the transport of Li+ throughout the electrode, enabling the superior specific capacity, rate characteristic and cyclic retention.

Study of the growth time effect on the structural, morphological and electrical characteristics of ZnO/p-Si heterojunction diodes grown by sol-gel assisted chemical bath deposition method

Abstract Well-aligned ZnO nanorods (NRs) have been synthesized by chemical bath deposition (CBD) method on (100) p-type Silicon substrate for various growth times. ZnO seed layers have been pre-coated on Si by sol-gel spin-coating process. The effect of growth time on structural, morphological and electrical properties of ZnO NRs were systematically investigated by X-Ray diffraction, scanning electron microscopy and current-voltage measurements at room temperature. SEM images illustrated that vertical, well-aligned, uniformly distributed, dense ZnO NRs were observed to grow on the Si substrate. Moreover, the growth rate decreases dramatically as the deposition time increased. X-ray diffraction pattern showed that the synthesized ZnO NRs have hexagonal wurtzite structure and exhibit a preferred orientation along the c-axis. The current–voltage analysis provided information about electrical parameters of n-ZnO NRs/p-Si heterojunction diode as a function of the growth time. The results showed an increase in the barrier height ϕb and a decrease in the ideality factor n, as the length of the NRs increased. More details about I–V characteristics measured under illumination and in the dark are also reported.