Aqueous Solution‐Processable,Flexible Thin‐Film Transistors Based on Crosslinked Chitosan Dielectric Thin Films

The hydrophilic character of chitosan (CS) limits its use as a gate dielectric material in thin‐film transistors (TFTs) based on aqueous solution‐processable semiconductor materials. In this study, this drawback is overcome through controlled crosslinking of CS and report, for the first time, its application to aqueous solution‐processable TFTs. In comparison to natural CS thin films, crosslinked chitosan (Cr‐CS) thin films are hydrophobic. The dielectric properties of Cr‐CS thin films are explored through fabrication of metal–insulator–metal devices on a flexible substrate. Compared to natural CS, the Cr‐CS dielectric thin films show enhanced environmental and water stabilities, with a high breakdown voltage (10 V) and low leakage current (0.02 nA). The compatibility of Cr‐CS dielectric thin films with aqueous solution‐processable semiconductors is demonstrated by growing ZnO nanorods via a hydrothermal method to fabricate flexible TFT devices. The ZnO nanorod‐based TFTs show a high field‐effect mobility (linear regime) of 10.48 cm² V^?1 s^?1. Low temperature processing conditions (below 100 °C) and water as the solvent are utilized to ensure the process is environmental friendly to address the e‐waste problem.     

Development of flame retardancy properties of new halogen‐free phosphorous doped SiO2 thin films on fabrics

In this study, flame retardancy properties of fabrics treated with phosphorous (P) doped and undoped SiO₂ thin films were developed by sol–gel technique. As to this aim, P‐doped and undoped SiO₂ film were coated on cotton fabric from the solutions prepared from P, Si‐based precursors, solvent, and chelating agent at low temperature in air using sol–gel technique. To determine solution characteristics, which affect thin film structure, turbidity, pH values, and rheological properties of the prepared solutions were measured using a turbidimeter, a pH meter, and a rheometer machines before coating process. The thermal, structural, and microstructural characterization of the coating were done using differential thermal analysis/thermograviometry, fourier transform infrared spectroscopy, X‐ray diffractometry, and scanning electron microscopy. In addition, tensile strength, wash fastness, flame retandancy, and lightness properties of the coated fabrics were determined. To compensate the slight loss of tensile strength of samples, which occurred at the treated fabrics with P‐doped Si‐based solutions, the cotton fabrics were coated with polyurethane films during second step. In conclusion, the flame retardant cotton fabric with durability of washing as halogen‐free without requiring after treatment with formaldehyde was fabricated using sol–gel processing for the first time. Moreover the cotton fabrics, which were treated with P‐doped Si‐based solutions and then coated with polyurethane at second step, still has got nonflammable property. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and Characterization of Low-Dielectric Silica Aerogel Films

Thin films of silica aerogel on a silicon wafer have been synthesized via supercritical drying of wet gel films that were obtained by spin coating the polymeric silica sol, followed by aging in an isopropanol (IPA) or tetraethoxysilane/isopropanol (TEOS/IPA) solution. The viscosity of the sol and the spin rate required to form uniform coating layers were optimized. The film thickness and microstructures could be controlled by adjusting the concentration of the sol, the spin rate, and the aging conditions. The porosities and the dielectric constants of the thin films were in the range of 76%–90% (densities of 0.59–0.22 g/cm³) and 2.0–1.5, respectively. The degree of planarization in the aerogel thin film was ∼100%, and the gap-filling capability on a 0.2 μm tungsten patterning wafer was excellent. In particular, aging the wet gel film in the TEOS/IPA solution was very effective in improving the properties of the aerogel films.     

Sol–Gel‐Derived High‐Performance Stacked Transparent Conductive Oxide Thin Films

Single‐ and multi‐layer transparent conductive oxide (TCO) thin films exhibiting high performance, good packing density and low surface/interface roughness are deposited on silica glass substrates by the sol–gel method. The crystal and microstructural properties of the TCO thin films are evaluated as an alternate to films prepared by ultra‐high vacuum deposition. Tin‐doped indium oxide (ITO) thin films produced using a two‐step drying process showed low surface roughness because of dense packing structure not only horizontal but also vertical directions. As a result, electrical conductivity, carrier concentration, carrier mobility, and optical transmittance of 2.3 × 10³ S/cm, 8 × 10²⁰ cm^?3, 18 cm²/Vs, and over 98% at 500 nm, respectively, were achieved. A multilayer ZnO/ITO stacked structure was also fabricated using the sol–gel process. Our findings suggest that solution‐based methods show promise as an alternative to existing ultra‐high vacuum methods to fabricate TCO thin films.     

Magnetic and electric properties of wrinkled manganite films derived by sol‐gel method

Flat and wrinkled La_0.7Sr_0.3MnO₃ (LSMO) thin films were prepared by sol‐gel method, respectively, on Si (001) substrates by adjusting heating rate at drying stage. Wrinkled film has larger grains than flat film. Coercive field (about 27 Oe) of wrinkled film is higher than that of flat film, which is much low as around 5 Oe. Compared with flat films, wrinkled films have larger magnetization, higher Curie temperature (334 K) and peak resistivity temperature (243 K), and lower resistivity (0.18 Ohm·cm at 300 K). The introducing of wrinkles is an efficient way to induce compressive stress in sol‐gel derived polycrystalline LSMO films and enhance the magnetic and electric properties.     

Functionalized Hybrid Coatings on ABS Surfaces by PLD and Dip Coatings

It is important to give water-repellent and antibacterial properties to the acrylonitrile butadiene styrene (ABS) surfaces of the hearing aids. In this study, the sol–gel Si and sol–gel Ti solutions were prepared from the reactions of silicon ethoxide, titanium butoxide and methacrylic acid. The catalyst and Dynasylan F8815 were added to the sol–gel solutions to give hydrophobic properties onto the ABS surfaces. Additionally, silver nanoparticles were synthesized by nanosecond laser and added to the coating solutions to give extra antibacterial properties. The surfaces of the ABS targets were coated using the sol–gel dip coating and pulsed laser deposition techniques. The coatings with good adhesion between film and substrate and good water-repellent properties were achieved. The average contact angles for the coated ABS surfaces were measured in the range between 120 and 125 degrees. The obtained sol–gel materials and produced thin films onto the ABS surfaces were also analyzed in terms of the antibacterial properties. The highly antibacterial properties were observed in the sol–gel solutions and the thin films.     

Layer‐by‐layer films based on charge transfer interaction of ϕ‐conjugated poly(dithiafulvene) and incorporation of gold nanoparticles into the films

Layer‐by‐layer (LBL) self‐assembled ultrathin films were prepared via consecutively alternating immersion of substrates into solutions of electron donor, poly(dithiafulvene) (PDF), and electron acceptor, poly(hexanyl viologen) (6‐VP). The charge transfer (CT) interaction formed at solid–liquid interfaces between the backbones of the electron acceptor and donor polymers was the driving force of the alternative deposition. The sandwich heterostructure of the LBL film led to electrical anisotropy in the directions parallel and perpendicular to the film surfaces. Incorporation of gold nanoparticles into the LBL films was investigated by reducing gold ions with the PDF layers already deposited on the film surfaces, or depositing PDF‐protected gold colloidal solution as the electron donor layers directly. The influence of the gold nanoparticles on the electrical anisotropy of the LBL films was also illustrated in this research. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1608–1615, 2007     

All Solution‐Based Fabrication of Copper Oxide Thin Film/Cobalt‐Doped Zinc Oxide Nanowire Heterojunctions

Versatile and intriguing solution‐based processes are utilized to synthesize nanostructured materials for device applications to reduce material production and device fabrication costs. This study presents results on the fabrication and characterization of copper oxide (CuO) coated cobalt‐doped zinc oxide nanowires (Co‐doped ZnO NWs)‐based heterojunction diodes prepared by a two‐step synthesis route through combined hydrothermal growth and sol–gel spin coating. Highly dense, well‐ordered, undoped, and Co‐doped ZnO NWs were successfully grown by hydrothermal method. Complementary CuO thin films were synthesized by sol–gel method and subsequently coated onto both undoped and Co‐doped ZnO NWs through spin‐coating technique. Enhanced diode properties with a rectification ratio of 10³ at ±2 V and an ideality factor of n = 2.4 (in dark) were obtained for Co‐doped ZnO NWs‐based heterojunction diodes. The obtained results demonstrated that the investigated heterojunction diode structure fabricated by facile and cost‐effective solution‐based processes can be a promising candidate for the next generation optoelectronic devices.     

Multiscale dynamic Monte Carlo/continuum model of drying and nonideal polycondensation in sol‐gel silica films

The process of forming sol‐gel silica thin films involves multiple length and time scales ranging from molecular to macroscopic, and it is challenging to fully model because the polymerization is nonideal. A multiscale model is described to link macroscopic flow and drying (controlled by process parameters) to film microstructure (which dictates the properties of the films). In this modeling strategy, dynamic Monte Carlo (DMC) polymerization simulations are coupled to a continuum model of drying. The entire DMC simulation is treated as a particle of sol whose position and composition are tracked using a diffusion/evaporation finite difference method. By simulating swarms of particles starting from different positions in the film, the multiscale model predicts different drying/gelation phenomena, and predicts the occurrence of gradients of concentration and gelation in the films which can lead to the formation of a gel skin near the top surface of the film. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Preparation,optimization, and voltammetric characteristics of poly(o‐phenylenediamine) film as a dopamine‐selective polymeric membrane

Poly(o‐phenylenediamine) films were electrochemically prepared on gold electrodes from the corresponding monomer in an aqueous solution at a constant potential. The polymeric films prepared in this one‐step procedure were found to be thin and insoluble in the aqueous solution. Cyclic and differential pulse voltammetric techniques were used to examine the permeation properties of ascorbic acid and dopamine at the resultant polymeric film electrode. Then, the effects of the chemical and electrochemical variables (e.g., film thickness, polymerization potential, concentrations of monomer and electrolyte) on the permselectivity characteristics of the polymeric film were systematically investigated and the optimal values for each parameter were determined. Furthermore, it was found that the optimized polymer electrode was found to be stable for the successive runs. As a result, it is claimed that poly(o‐phenylenediamine) film can be used as a dopamine‐selective polymeric membrane. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 327–332, 2001     

Fabrication of superhydrophobic silica‐based surfaces with high transmittance by using polypropylene and tetraeyhoxysilane precursors

Preparation of superhydrophobic silica‐based surfaces via sol–gel process by adding polyethylene glycol (PEG) polymer into the precursor solution has been developed. Surface roughness of the films was obtained by removing the organic polymer at 500°C and then the hydrophobic groups bonded onto the films were obtained by self‐assembly modification with a monolayer. Characteristic properties of the as‐prepared films were analyzed by contact angle measurements, scanning electron microscopy, atomic force microscopy, UV–vis scanning spectrophotometer, and X‐ray photoelectron spectrophotometer. The experimental parameters were varied by the type of silane species, the R ratio, the hydrolysis time of the precursor solution, the molecular weight of PEG, the pH value of mixing solution, and the different reagents for modification. The results showed that optimum ratio of TEOS/H₂O/ethanol in the sol–gel process for precursor solution was set to 1/10/4. The better contact angles of the films can be obtained by the acid catalyst reaction, especially the pH value of mixing solution was adjusted to 0. When the as‐prepared rough films were modified with (tridecafluoro‐1,1,2,2‐tetrahydrooctyl) dimethylchlorosilane (TFCS), the contact angle of the film can be promoted to 150.4°, and the transmittance of the films in the visible light region was greater than 94.5%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Optimization of Effective Sol‐Gel Parameters for the Synthesis of Mesoporous γ‐Al2O3 Using Experimental Design

Mesoporous nanocrystalline γ‐alumina was prepared by a template‐free sol‐gel method using aluminum ethoxide as precursor. Significant parameters, such as the water/aluminum ethoxide molar ratio, the pH of the solution, and the time and temperature of aging, were optimized by the Taguchi method to obtain γ‐alumina with a high surface area and pore volume. The influences of the main parameters on the catalytic performance of the prepared catalysts were investigated via dehydration of methanol to dimethyl ether in a fixed‐bed reactor. The catalysts were characterized by X‐ray diffraction, N₂ adsorption‐desorption, ammonia temperature‐programmed desorption, and scanning electron microscopy techniques. The results show that the aging temperature had a significant influence on the catalyst performance.     

Study of novel biodegradable thermo‐sensitive hydrogels of methoxy‐poly(ethylene glycol)‐block‐polyester diblock copolymers

A series of biodegradable thermo‐sensitive hydrogels were synthesized by ring‐opening polymerization of methoxy‐poly(ethylene glycol) (mPEG) and various ester monomers, i.e. D ,L ‐lactide, glycolide, β‐propiolactone, δ‐valerolactone and ε‐caprolactone. The copolymers were characterized using ¹H NMR spectroscopy and gel permeation chromatography. The micelle properties were also measured. The results indicated that the diblock copolymers formed nano‐micelles at low concentrations in aqueous phase. The lower critical solution temperatures of the diblock copolymers were above 35 °C at 1 wt%. As the temperature increased above room temperature, the diblock copolymer solutions underwent a sol‐to‐gel phase transition, which was manifested in viscosity increases, indicative of the formation of a gel. The mPEG–polyester diblock copolymer solutions exhibited sol‐gel transition behavior as a function of temperature and polymer concentration. Copyright © 2010 Society of Chemical Industry     

ZrO2-SiO2二元系统平面光波导薄膜的制备与性能表征

应用溶胶-凝胶技术,以TEOS与ZrOCl2·8H2O为先驱体,研制了用于有源光波导基质材料的ZrO2-SiO2二元系统薄膜,探明了ZrO2-SiO2二元系统薄膜折射率、厚度与薄膜组分、匀胶速度、陈化时间、热处理温度的内在关系,实现薄膜厚度和薄膜折射率在一定范围内的连续可调,为研制一类新型的光通信窗口有源光波导材料提供了基质材料.     

Preparation of superhydrophobic silica‐based films by using polyethylene glycol and tetraethoxysilane

Preparation of superhydrophobic silica‐based films via sol‐gel process by adding polyethylene glycol (PEG4000) in the silica sol precursor solution has been developed. The casting films were prepared by casting the above solution on the glass and adding poor solvent on it or not. Surface roughness of the films was obtained by removing polymer from the films at high temperature. Then, the hydrophobic group on the surfaces was obtained by reaction with hexamethyldisilazane (HMDS). Characteristic properties of the as‐prepared surface of the films were analyzed by contact angle measurement, scanning electron microscopy (SEM), atomic force microscope (AFM), Fourier transform infrared (FT‐IR) spectrophotometer, and X‐ray photoelectron spectrometer (XPS). The results showed that the contact angles of the films were varied with the PEG weight fraction of the films, the solvent for the PEG solution, the reaction temperature and time, and adding poor solvent (n‐hexane) or not. However, the surface roughness has been controlled by adjusting the experimental parameters during the early period. The contact angle of the film that prepared by spraying the poor solvent (n‐hexane) onto each coating layer for four times after casting process was greater than 150°. It was difficult to obtain superhydrophobic surface without adding n‐hexane onto any coating layer in this system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Solution-processed semiconducting aluminum-zinc-tin-oxide thin films and their thin-film transistor applications

We prepared aluminum-zinc-tin-oxide (AZTO) thin films by the solution spin-coating method and investigated their physical and electrical properties according to different incorporated amounts of Al. AZTO films annealed at 400 °C were amorphous. Though SnO₂ crystallites were detected in films annealed at temperatures higher than 500 °C, the number of crystallites decreased as the Al content increased. Thin films had a smooth and uniform surface morphology with an optical transmittance value higher than 92% in the visible range. Electrical conductivity and its temperature dependence varied markedly according to the amount of Al incorporated in the film. We therefore systematically investigated activation energies for carrier transport for each film composition. Thin-film transistors (TFTs) were fabricated using solution-processed AZTO as an active channel layer. The effects of the amount of Al incorporated in the thin film on TFT characteristics were also evaluated. The best device performance was observed for a TFT with a 5 mol%-Al-incorporated AZTO channel. Field effect mobility, subthreshold swing, and on/off ratio were approximately 0.24 cm² V⁻¹ s⁻¹, 0.69 V/dec, and 1.03×10⁶, respectively.     

The tribological characteristics of phosphorylated 3‐aminopropyltriethoxysilane nanometer film

Thin films deposited on the phosphonate 3‐aminopropyltriethoxysilane (APTES) self‐assembled monolayer (SAM) were prepared on the hydroxylated silicon substrate by a self‐assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X‐ray photoelectron spectrometry. The thickness of the films was determined with an ellipsometer, whereas the morphologies and nanotribological properties of the samples were analyzed by means of atomic force microscopy. As the results, the target film was obtained and reaction may have taken place between the thin films and the silicon substrate. It was also found that the thin films showed the lowest friction and adhesion followed by APTES‐SAM and phosphorylated APTES‐SAM, whereas silicon substrate showed high friction and adhesion. Microscale scratch/wear studies clearly showed that thin films were much more scratch/wear resistant than the other samples. The superior friction reduction and scratch/wear resistance of thin films may be attributed to low work of adhesion of nonpolar terminal groups and the strong bonding strength between the films and the substrate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of super‐hydrophobic film with fluorinated‐copolymer

Organic superhydrophobic films were prepared by utilizing TA‐N fluoroalkylate (TAN) and methyl methacrylate (MMA) copolymer as water‐repellent materials and inorganic silica powder as surface roughness material has been developed. Coating solutions prepared by adding silica powders into copolymer solution directly (one‐step method) and by adding silica powders into monomers and allowing them to react (two‐step method). The results showed that contact angles of the films prepared by one‐step method (37.6 wt % of silica powders in the coating solution) were greater than 150°, but the transmittance of the film at visible light was only 30%. On the other hand, the contact angle of films prepared by two‐step method (20 wt % of silica powders in the coating solution) was greater than 160° and the transmittance of the film was greater than 90%. The contact angle of the film prepared by poly(octyl acrylate), POA, was 32.1°, but while introducing silica powder into the system, the contact angle of the film was reduced to be smaller than 5°. Thus, superhydrophobic and superhydrophilic films can be obtained by introducing a roughening material on the hydrophobic surface and the hydrophilic surface, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1646–1653, 2007     

AUGMENTATION OF PHOTOCATALYTIC ACTIVITY OF TiO2 THIN FILMS PREPARED BY A SOL-GEL TECHNIQUE

In order to increase the photocatalytic activity on TiO₂ thin film per its external surface area, the structure of flat thin film was modified by adding a small amount of polyethylene glycol (PEG) to TiO₂ sol solution. By firing PEG contained in a TiO₂ gel film, a porous structure was developed. The photocatalytic activities of the thin films prepared thus were evaluated by the degradation of 2-propanol in the aqueous solutions under black light illumination. The photocatalytic activity of TiO₂ thin film prepared with added PEG 400 by 2.6 wt% or PEG 2000 by 9.5 wt% was increased by about 30% as compared to that prepared without added PEG.     

Reversible sol–gel transitions in aqueous solutions of N‐isopropylacrylamide ionic copolymers

Ionic copolymers of N‐isopropylacrylamide (NIPA) exhibiting sol–gel transitions in aqueous solutions were investigated. The studies were aimed at understanding of the structure–property relationship in the design of injectable, in situ forming gels for potential biomedical applications in delivery of therapeutics and tissue engineering. Aqueous solutions of NIPA ionic copolymers were found to flow freely at ambient temperatures and formed soft gels with controlled syneresis above 32 °C, the lower critical solution temperature of NIPA. The sol–gel transitions and temperature‐dependent properties of the resulting gels were analyzed using dynamic rheometry and ultraviolet and infrared spectrometry, and were found to be controlled by the molecular weight and composition of copolymers, ionization state of comonomers and composition of aqueous solvent. Copyright © 2008 Society of Chemical Industry