Essential Macleod Program (EMP) simulated fabrication of high quality Zn:SnO2/Ag/Zn:SnO2 multilayer transparent conducting electrode on flexible substrates

In the quest of promising Indium free amorphous transparent conducting oxide (TCO), Zn-doped SnO₂/Ag/Zn-doped SnO₂ (OMO) multilayer films were prepared on flexible polyethylene terephthalate (PET) substrates by RF sputtering at room temperature (RT). Growth parameters were optimized by varying sputtering power and working pressure, to have high electrical conductivity and optical transmittance. Optimization of the thickness of each layer was done by Essential Macleod Program (EMP) simulation to get the higher transmission through OMO multilayer. The sheet resistance and transmittance of 3 at% Zn-doped SnO₂ thin film (30 nm) were 2.23 kΩ/□, (ρ ~ 8.92×10⁻³ Ω∙cm) and 81.3% (at λ ~ 550 nm), respectively. By using optimized thicknesses of Zn-doped SnO₂ (30 nm) and Ag (12 nm) and optimized growth condition Zn-doped SnO₂/Ag/Zn-doped SnO₂ multilayer thin films were deposited. The low sheet resistance of 7.2 Ω/□ and high optical transmittance of 85.1% in the 550 nm wavelength region was achieved with 72 nm multilayer film.     

Synthesis of TiO2 porous thin films by polyethylene glycol templating and chemistry of the process

Titanium dioxide porous films have been deposited on glass slides by sol–gel technology. Tetrabutylorthotitanate and polyethylene glycol were used as a precursor and template, respectively. The chemical mechanism is discussed in relation to the sol–gel transition, which provides a possible theoretic explanation to the formation of TiO₂ porous films. The morphology of porous TiO₂ thin films strongly depends on the amount of water, the types of solvents and complexing agents, and the concentration and molecular weight of the template. It was shown that the diameter of pores is tunable in the range of 10–500 nm and the maximum of BET specific area of the films is 72 m²/g.     

Nanostructured SnO2 thin films for NO2 gas sensing applications

We report the synthesis of nanostructured SnO₂ by a simple inexpensive sol–gel spin coating method using m-cresol as a solvent. This method facilitates rapid synthesis at comparatively lower temperature enabling formation of nanostructures suitable for gas-sensing applications. Various physicochemical techniques have been used for the characterization of SnO₂ thin films. X-ray diffraction analysis confirmed the single-phase formation of tetragonal SnO₂ having crystallite size 5–10 nm. SnO₂ showed highest response (19%) with 77.90% stability toward 100 ppm nitrogen dioxide (NO₂) at 200 °C. The response time of 7 s and recovery time of 20 min were also observed with the same operating parameters. The probable mechanism is proposed to explain the selective response toward nitrogen dioxide. Impedance spectroscopy studies showed that the response to nitrogen dioxide is mainly contributed by grain boundaries. The reproducibility and stability study of SnO₂ sensor confirmed its candidature for detection of NO₂ gas at low concentration (10–100 ppm) and lower operating temperature.     

Carbon coated porous tin peroxide/carbon composite electrode for lithium-ion batteries with excellent electrochemical properties

A porous tin peroxide/carbon (SnO₂/C) composite electrode coated with an amorphous carbon layer is prepared using a facile method. In this electrode, spherical graphite particles act as supporter of electrode framework, and the interspace among particles is filled with porous amorphous carbon derived from decomposition of polyvinylidene fluoride and polyacrylonitrile. SnO₂ nanoparticles are uniformly embedded in the porous amorphous carbon matrix. The pores in amorphous carbon matrix are able to buffer the huge volume expansion of SnO₂ during charge/discharge cycling, and the carbon framework can prevent the SnO₂ particles from pulverization and re-aggregation. The carbon coating layer on the outermost surface of electrode can further prevent porous SnO₂/C electrode from contacting with electrolyte directly. As a result, the repeated formation of solid electrolyte interface is avoided and the cycling stability of electrode is improved. The obtained SnO₂/C electrode presents an initial coulombic efficiency of 77.3% and a reversible capacity of 742 mA h g⁻¹ after 130 cycles at a current density of 100 mA g⁻¹. Furthermore, a reversible capacity of 679 mA h g⁻¹ is obtained at 1 A g⁻¹.     

三维有序大孔氧化钇稳定氧化锆的制备与表征

以聚苯乙烯(polystyrene, PS)胶体晶体为模板,采用柠檬酸凝胶方法制备氧化钇稳定氧化锆(yttria stabilized zirconia, YSZ)前驱体溶胶,采用浸渍-提拉方法向PS模板的空隙中填充YSZ溶胶,煅烧去除模板后成功地制备了三维有序大孔YSZ材料.研究前驱体溶胶不同浓度、浸渍次数以及煅烧条件等因素对大孔YSZ结构的影响.用扫描电子显微镜对YSZ的微观结构进行表征.结果表明:前驱体溶胶的浓度在0.3～0.4 mol/L的范围内,浸渍次数为1次或2次,煅烧温度为600℃时可以得到高度有序的大孔YSZ.     

Low temperature processed SnO2 films using aqueous precursor solutions

We present a comparison study of the microstructure developments during aqueous solution deposition of SnO₂, particularly, through chemical bath deposition (CBD) and liquid phase deposition (LPD) at very low temperatures (40–75 °C). The effects of solution chemistry on the microstructural details and electrical properties of SnO₂ thin films are presented and discussed. Smooth, nanoparticulate SnO₂ films were obtained from supersaturated precursor solutions with lower precursor concentrations while more aggregated SnO₂ films were generated from higher precursor concentrations. Loosely-packed and porous structures were obtained from low supersaturation solutions with very low pHs. The deposition rates were also evaluated under various deposition conditions. XRD result shows that annealing process helps improve the degree of crystallinity of the as-deposited films that are composed of 3–10 nm nanocrystalline particles. One advantage of LPD of SnO₂ films is in-situ fluorine doping during deposition. The resulting electrical resistivity of F-doped SnO₂ films was about 18.7 Ω cm after the films were annealed at 450 °C.     

Processing of microcellular silicon carbide ceramics with a duplex pore structure

A novel processing route for producing microcellular SiC ceramics with a duplex pore structure has been developed using a polysiloxane, carbon black, SiC, Al₂O₃, Y₂O₃, and two kinds of pore former (expandable microspheres and PMMA spheres). The duplex pore structure consists of large pores derived from the expandable microspheres and small windows in the strut area that were replicated from the PMMA spheres. The presence of these small windows in the strut area improved the permeability of the porous ceramics. The gas permeability coefficients of porous SiC ceramics were 0.13 × 10¹² m² for the porous SiC without PMMA spheres, 0.47 × 10¹² m² for the porous SiC with 10 wt% PMMA spheres, and 0.82 × 10¹² m² for the porous SiC with 20 wt% PMMA.     

New 3D stratified Si-Ca-P porous scaffolds obtained by sol-gel and polymer replica method: Microstructural,mineralogical and chemical characterization

The aim of this research was to develop and characterize a novel stratified porous scaffold for future uses in bone tissue engineering. In this study, a calcium silicophosphate porous scaffold, with nominal composition 29.32 wt% SiO₂ – 67.8 wt% CaO – 2.88 wt% P₂O₅, was produced using the sol-gel and polymer replication methods. Polyurethane sponges were used as templates which were impregnated with a homogeneous sol solution and sintered at 950 °C and 1400 °C during 8 h. The characteristics of the 3D stratified porous scaffolds were investigated by Scanning Electron Microscopy, X-Ray Diffraction, Fourier Transform Infrared Spectrometry, Diametric Compression of Discs Test and Hg porosimetry techniques. The result showed highly porous stratified calcium silicophosphate scaffolds with micro and macropores interconnected. Also, the material has a diametrical strength dependent on the number of layers of the stratified scaffolds and the sintering temperature.     

Synthesis of KOH/SnO2 solid superbases for catalytic Knoevenagel condensation

KOH/SnO₂ solid superbases of specific morphology and uniform pore structure were synthesized. The SnO₂ support was prepared by reflux digestion using graphene oxide as template and employed for the loading of KOH by means of grinding and thermal treatment. With base strength of 26.5 ≤ H₋ < 33.0 and superbasic sites of 1.362 mmol g^− 1, the 20 wt.%KOH/SnO₂ catalyst exhibits excellent activity in Knoevenagel condensation under mild conditions. The catalytic efficiency is closely related to the base strength and the amount of superbasic sites. The findings disclose a new route for the synthesis of versatile solid superbases using SnO₂ as supports.     

TiO2–SnO2 nanomaterials for gas sensing and photocatalysis

Nanopowders of TiO₂–SnO₂ over a full composition range extending from 100 mol% TiO₂ to 100 mol% SnO₂ are obtained by the sol–gel method from TTIP and SnCl₂·5H₂O precursors of Ti and Sn, respectively followed by calcination at 400 °C. The samples are characterized by means of BET, XRD and TEM. Optical properties of the prepared nanomaterials are studied as well. TEM images indicate that the nanoparticles are regular in shape. The specific surface area, SSA of TiO₂ is 95 m²/g while that of SnO₂ amounts to 129 m²/g. The highest SSA of 156 m²/g is achieved at 20 mol% of TiO₂. Occurrence of rutile, anatase and brookite polymorphic forms depends on the chemical composition of nanopowders. Formation of rutile-type solid solution of TiO₂–SnO₂ over the range of 0–80 mol% TiO₂ is confirmed by Vegard rule applied to lattice constants. Electronic band gap decreases with Ti content from 3.84 eV (100 mol% SnO₂) to 3.18 eV (100 mol% TiO₂).     

Template-assisted synthesis of PbTiO3 nanotubes

Nanotubes of ferroelectric lead titanate (PbTiO₃) have been made by a template-assisted method. An equimolar Pb–Ti sol was dropped onto porous alumina membranes and penetrated into the channels of the template. Single-phase PbTiO₃ perovskite nanotubes were obtained by annealing at 700 °C for 6 h. The nanotubes had diameters of 200–400 nm with a wall thickness of approximately 20 nm. Excess PbO or annealing in a Pb-containing atmosphere was not necessary in order to achieve single-phase PbTiO₃ nanotubes. The influence of the heating procedure and the sol concentration is discussed.     

The effects of solvents on the formation of sol–gel-derived Bi12SiO20 thin films

The sol–gel method was used to synthesize Bi₁₂SiO₂₀ thin films. Two synthesis routes with two different solvents, i.e., 2-ethoxyethanol and acetic acid, were used and compared. Thin films were deposited onto Pt/TiO₂/SiO₂/Si substrates by spin-coating at 3000 rpm and annealed at 700 °C for 1 h. A different coordination of the bismuth ion was observed in the sols prepared with acetic acid (AcOH), and as a result, stable sols were formed with a shorter gelation time t_G = 84 h (c = 0.76 M), when compared with the sols prepared from 2-ethoxyethanol (EtoEtOH) t_G = 580 h (c = 0.76 M). The microstructures of the Bi₁₂SiO₂₀ thin films prepared from sols using EtoEtOH were homogeneous and dense. On the other hand, a porous microstructure was observed for the Bi₁₂SiO₂₀ thin films deposited from the sol in which AcOH was used as the solvent.     

Multilayer porous Pd-doped SnO2 thin film: Preparation and H2 sensing performance

Porous pure and Pd-doped SnO₂ films are prepared using sol-gel synthesis with polystyrene (PS) microspheres as the template. Different characterizations are performed to analyze the microstructure and morphology of the films. The sensing performance of the films at various temperatures and hydrogen concentrations is investigated. Results show that high concentration of PS template significantly influences the continuity of films and the H₂ sensing performance. The porous SnO₂ film with 0.1 wt% PS microspheres exhibits the best performance. At 225 °C, the response magnitude of the porous 1 mol% Pd-doped SnO₂ thin film to 1000 ppm H₂ is 93.18, which is approximately 10.58 times of the pure sample.     

Preparation and characterization of porous,biomorphic SiC ceramic with hybrid pore structure

Bio-carbon template (charcoal) was prepared by carbonizing pine wood at 1200 °C under vacuum, and was impregnated with phenolic resin/SiO₂ sol mixture by vacuum/pressure processing. Porous SiC ceramics with hybrid pore structure, a combination of tubular pores and network SiC struts in the tubular pores, were fabricated via sol–gel conversion, carbonization and carbothermal reduction reaction at elevated temperatures in Ar atmosphere. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) were employed to characterize the phase identification and microstructural changes during the C/SiO₂ composites-to-porous SiC ceramic conversion. Experimental results show that the density of C/SiO₂ composite increases with the number of impregnation procedure, and increases from 0.32 g cm⁻³ of pine-derived charcoal to 1.5 g cm⁻³ of C/SiO₂ composite after the sixth impregnation. The conversion degree of charcoal to porous SiC ceramic increases as reaction time is lengthened. The resulting SiC ceramic consists of β-SiC with a small amount of α-SiC. The conversion from pine charcoal to porous SiC ceramic with hybrid pore structure improves bending strength from 16.4 to 42.2 MPa, and decreases porosity from 76.1% to 48.3%.     

Microstructural and optical properties of SnO2–ZnSnO3 ceramics

This work deals with some physical investigation on SnO₂–ZnSnO₃ ceramics grown on glass substrates at different temperatures (450 °C and 500 °C). Structural and optical properties were investigated using X-Ray diffraction (XRD), Raman, infrared (IR) absorption (FTIR), UV–visible spectroscopy and Photoluminescence (PL) techniques. XRD results revealed the existence of a mixture of SnO₂/ZnSnO₃ phases at different annealing temperatures. Structural analysis showed that both phases are polycrystalline. On the other hand, the optical constants (refractive index, extinction coefficient and the dielectric constants) have been obtained by the transmittance and the reflectance data. The optical band gap energy changed from 3.85 eV to 3.68 eV as substrate temperature increased from 450 °C to 500 °C. Raman, FTIR modes and PL reinforced this finding regarding the existence of biphasic (SnO₂ and ZnSnO₃) which is detected also by X-Ray diffraction analysis. Finally, the Lattice Compatibility Theory was evoked for explaining the unexpected incorporation of zinc ions in a rhombohedral structure within SnO₃ trigonal lattice, rather than the occupation of SnO₂ available free loci. All the results have been discussed in terms of annealing temperature.     

Surfactant-free microwave hydrothermal synthesis of SnO2 nanosheets as an anode material for lithium battery applications

SnO₂ nanosheets were synthesized using microwave hydrothermal method without using a surfactant and organic solvents. Formation of pure nanocrystalline rutile phase of SnO₂ sample was confirmed by X-ray diffraction (XRD) results and the average crystallite size of SnO₂ sample calculated using Scherrer's formula and XRD data is found to be 6 nm. HR-TEM, SAED and EDX results showed the formation of agglomerated nanosize sheets like morphology with high porous structured SnO₂ powder. Further, the formation of high porous structured SnO₂ powder was confirmed from BET surface area results (59.28 m² g^?1). The electrochemical performance of the lithium-ion battery made up of SnO₂ nanosheets, as an anode, was tested through the cyclic voltammetry and galvanostatic charge-discharge measurements. The galvanostatic charge-discharge results of the lithium-ion battery showed good discharge capacity of 257.8 mAh g^?1 after 50 cycles at a current density of 100 mA g^?1. The improved electrochemical properties may be due to the formation of a unique nanosize sheets type morphology with high porous structured SnO₂ powder. High porous structured nanosize sheets type morphology of SnO₂ can help to reduce the diffusion length and sustain the volume changes during the charging-discharging process.Hence, high porous structured nanosize sheets morphology of SnO₂ prepared using the microwave hydrothermal method without using a surfactant and organic solvents can be a better anode material for lithium ion battery applications.     

Electrospun ZnO–SnO2 composite nanofibers with enhanced electrochemical performance as lithium-ion anodes

ZnO–SnO₂ composite nanofibers with different structures were synthesized by a simple electrospinning approach with subsequent calcination at three different temperatures using polyacrylonitrile as the polymer precursor. The electrochemical performance of the composites for use as anode materials in lithium-ion batteries were investigated. It was found that the ZnO–SnO₂ composite nanofibers calcined at 700 °C showed excellent lithium storage properties in terms of cycling stability and rate capability, compared to those calcined at 800 and 900 °C, respectively. ZnO–SnO₂ composite nanofibers calcined at 700 °C not only delivered high initial discharge and charge capacities of 1450 and 1101 mAh g⁻¹, respectively, with a 75.9% coulombic efficiency, but also maintained a high reversible capacity of 560 mAh g⁻¹ at a current density of 0.1 A g⁻¹ after 100 cycles. Additionally, a high reversible capacity of 591 mAh g⁻¹ was obtained when the current density returned to 0.1 A g⁻¹ after 50 cycling at a high current density of 2 A g⁻¹. The superior electrochemical performance of ZnO–SnO₂ composite nanofibers can be attributed to the unique nanofibrous structure, the smaller particle size and smaller fiber diameter as well as the porous structure and synergistic effect between ZnO and SnO₂.     

Highly conducting and transparent antimony doped tin oxide thin films: the role of sputtering power density

Sb doped SnO₂ thin films were deposited on quartz substrates by magnetron sputtering at 600 °C and the effects of sputtering power density on the preferential orientation, structural, surface morphological, optical and electrical properties had been studied. The XRD analyses confirm the formation of cassiterite tetragonal structure and the presence of preferential orientation in (2 1 1) direction for tin oxygen thin films. The dislocation density analyses reveal that the generated defects can be suppressed by the appropriate sputtering power density in the SnO₂ lattice. The studies of surface morphologies show that grain sizes and surface roughness are remarkably affected by the sputtering power density. The resistivity of Sb doped SnO₂ thin films gradually decreases as increasing the sputtering power density, reaches a minimum value of 8.23×10⁻⁴ Ω cm at 7.65/cm² and starts increasing thereafter. The possible mechanisms for the change in resistivity are proposed. The average transmittances are more than 83% in the visible region (380–780 nm) for all the thin films, the optical band gaps are above 4.1 eV. And the mechanisms of the variation of optical properties at different sputtering power densities are addressed.     

H2 response characteristics for sol–gel-derived WO3-SnO2 dual-layer thin films

This paper describes the deposition of SnO₂ and WO₃ thin films and WO₃-SnO₂ dual-layer thin films using the sol-gel process. The microstructure and morphology of these three thin films were analyzed with FE-SEM and X-ray diffraction. The H₂ response characteristics, including response magnitude, time and transients of the three samples, were investigated at different operation temperatures and H₂ gas concentrations. Although the maximum response magnitude of 29.31 towards 1000 ppm H₂ gas appeared at 225 °C,the WO₃-SnO₂ dual-layer films still had a response magnitude of 24.23 at 175 °C, which is much higher than those of the SnO₂ (4.19) and WO₃ (6.73) thin films. The linear response magnitude profile of the WO₃-SnO₂ dual-layer thin films toward H₂ gas concentration was obtained. The mechanism of the enhanced gas response characteristics was explained by the band bending theory.     

Transparent semiconductor zinc oxide thin films deposited on glass substrates by sol–gel process

Transparent semiconductor ZnO thin films were spin-coated onto alkali-free glass substrates by a sol–gel process. The influence of ZnO sols synthesized via different solvents (2-ME, EtOH or IPA) on the surface morphologies, microstructures, optical properties and resistivities of the obtained films were investigated. The as-coated films were annealed in ambient air at 500 °C for 1 h. X-ray diffraction results showed all polycrystalline ZnO thin films to have preferred orientation along the (0 0 2) plane. The surface morphologies, optical transmittances and resistivity values of the sol–gel derived ZnO thin films depended on the solvent used. The ZnO thin films synthesized with IPA as the solvent exhibited the highest average transmittance 92.2%, an RMS roughness of 4.52 nm and a resistivity of 1.5 × 10⁵ Ω cm.