Highly transparent polyimide/nanocrystalline-titania hybrid optical materials for antireflective applications

This study prepared polyimide/titania hybrid thin films of, poly(3,3′,4,4′-Benzophenone tetra carboxylic dianhydride)–(4,4-Diaminodiphenyl Ether)/nanocrystalline titania (BTDA-ODA/TiO₂), with a high refractive index. FTIR analysis confirmed the formation of a polyimide and titania matrix. TGA and DSC analysis gauged the decomposition temperature in the range of 455–532 °C, indicating that the addition of titania could increase the glass transition temperature of hybrid films. XRD results indicate the formation of nanocrystalline titania domains of approximately 8–11 nm in the hybrid films. AFM, SEM, TEM, and XRD results show the formation of well-dispersed nanocrystalline titania. The refractive index was measured by ellipsometry, demonstrating an increase in the refractive index of the prepared hybrid thin films from 1.657 to 1.958, when the titania content was increased from 0 to 90 wt.%. UV–vis analysis gauged the cutoff wavelength in the range of 288–357 nm. The prepared polyimide/titania hybrid thin films were used to develop a three layer antireflective (AR) coating on a glass substrate. The average reflectance of the AR was 0.5% for the PT20/PT90/F-siloxane layer and 0.6% for the PT20/PT90/porous silica. Transparency at 550 nm exceeded 90% for both AR coatings.     

Structures and properties of titania thin films annealed under different atmosphere

The effects of crystallinity, phase and oxygen vacancies on optical and photocatalytic properties of titania (TiO₂) thin films were systematically studied. The as-deposited amorphous titania films were prepared by reactive sputtering titanium metal targets in argon–oxygen plasma at 100 °C and subsequently annealed at various temperatures of 400–800 °C in air, vacuum and H₂ atmosphere. The results indicate that in general the crystallinity of the annealed films is enhanced with the increasing annealing temperature. At the same temperature, the H₂ annealed films achieve better crystallinity but containing more oxygen vacancies than the films annealed in air and in vacuum. In H₂ or in vacuum, the concentration of oxygen vacancies in the annealed films increases with increasing temperature, while in air it remains constant. Oxygen vacancies in titania film not only facilitate phase transformation but also lower the band gap of titania, and make the film visible-light responsive. Photocatalytic properties of the TiO₂ films were characterized in UV and visible light irradiation by following the Ag reduction and degradation of methylene blue. The films annealed at 600–700 °C in H₂ possess the best film crystallinity and the proper concentration of oxygen vacancies and exhibit the best photocatalytic performance under both UV and visible light.     

Roughness and fractality of nanostructured TiO2 films prepared via sol-gel technique

Titanium dioxide nanocrystalline thin films were prepared by applying the sol-gel dipping technique using two different titanium (IV) alkoxides: titanium isopropoxide and titanium butoxide. Morphological, structural characterization and examination of the fractal properties were performed by atomic force microscopy (AFM). The effect of the nature of the precursor on the hydrolysis rate and the resulting particle size distribution, roughness, and surface complexity of the TiO₂ films was investigated. Titanium isopropoxide presents higher hydrolysis rates leading to more rough and complex characteristics whereas titanium butoxide films show a relatively smoother surface. Higher fractal dimension values and lower roughness were observed for titania films derived from titanium butoxide. In both cases the obtained films present a complex granular surface network of interconnected particles, suitable for practical applications.     

Synthesis,properties, and anti-reflective applications of new colorless polyimide-inorganic hybrid optical materials

We report the synthesis, properties and anti-reflective applications of new colorless polyimide-inorganic hybrid thin films prepared from 1,4-bis(3,4-dicarboxyphenoxy)-2,5-di-tert-butylbenzene dianhydride (DDBBDA)/oxydianiline (ODA) with silica or titania precursors. The experimental results suggest that the prepared hybrid films have good thermomechanical properties, excellent transparence, tunable refractive indices of 1.550–1.847, and low optical birefringence. The nanocrystalline titania domain size analyzed form TEM and XRD is in the range of 10–20 nm in the hybrid materials. Three-layer anti-reflective films on glass or polymer substrates processed from the hybrid precursors have a relatively low reflection of less than 0.5% in the visible range. These results indicate that the newly prepared colorless polyimide-inorganic hybrid materials have potential applications for optical devices.     

TiO2 pure phase brookite with preferred orientation,synthesized as a spin-coated film

An oriented titania (brookite) film containing neither anatase nor rutile was synthesized by a new modified sol–gel method. The precursor was TiCl₄ with cellulose and oxalic acid as complexing agent. The XRD results show oriented pure brookite titania thin film. The SEM micrograph shows square particles on the crack free continuous film. A diffusion of sodium from the substrate was detected by XPS. It was found that the nature of complexation, the concentration of the precursors, the polymer additive, solution media (low pH, solvent-EG) and the substrate were significant of the oriented brookite TiO₂ films obtained.     

Effects of complexing agent on CdS thin films prepared by chemical bath deposition

CdS films have been prepared by chemical bath deposition (CBD) without stirring using weak and strong complexing agents, i.e., ammonia and ethylenediaminetetraacetic acid (EDTA). The optical, structural, and morphological properties of chemical bath deposited CdS films have been investigated. When the complexing agent is ammonia, five peaks in the X-ray diffraction (XRD) patterns from the CdS film, respectively, correspond to the interplanar spacing of 3.5498, 3.3429, 3.1449, 2.0574, and 1.7487 Å, which are definitely ascribed to hexagonal structure; unfortunately, this hexagonal CdS film is with poor morphology and its optical property in the visible region is not desirable for the solar cells. While, when the complexing agent is EDTA, three diffraction peaks in the XRD patterns from the CdS film, respectively, correspond to the interplanar spacing of 3.1164, 2.6716, and 1.8507 Å, indicating that the film is of a cubic structure. Furthermore, the CdS film has good morphology and its optical property in the visible region is compliant to the requirements of solar cells.     

Evaluation of TiO2 coatings obtained using the sol–gel technique on surgical grade type 316L stainless steel in simulated body fluid

Gel titania is the titania which was prepared by hydrolysis of a titanium isopropoxide through a sol–gel process. A film of this titania was coated on surgical grade 316L stainless steel using a sol–gel dipping technique. The densified films at 700 °C in vacuum were characterized by X-ray diffraction and EDXA analysis for its crystallinity and purity. The content of the films were determined by FT–IR spectroscopy. The morphology of the coating was analyzed by SEM. The corrosion behavior of 316L SS samples coated with densified titania films were studied in simulated body fluid Ringer's solution by DC potentiodynamic polarization and AC impedance spectroscopic methods. The corrosion kinetic parameters show a considerable increase in the corrosion resistance for the coated steel samples in comparison to the pristine steel substrates.     

Development of low temperature approaches to device quality CdS: A modified geometry for solution growth of thin films and their characterisation

Cadmium sulphide thin films have been grown using a modified chemical bath deposition method with four innovative features: i) ethylenediamine was used as the complexing agent, enabling the use of low cadmium concentrations, ii) a rectangular bath geometry with heated glass plate walls was employed, iii) a low deposition temperature (30 °C) was used and iv) nitrogen gas was flowed over the substrate surface during growth. The latter two features eliminate the formation and adherence of gas bubbles on the substrate during growth, hence reducing pinhole formation. On inspection, films were found to be specularly reflective and homogeneous with no visible pinholes. Characterisation was performed by atomic force microscopy, grazing incidence X-ray diffraction, optical transmittance and photoluminescence spectroscopy. It was shown that films possessed a low surface roughness value of 5.2 nm, were highly crystalline, textured, had a grain size of 15 nm and a bandgap of 2.42 eV. Preliminary results from CdTe/CdS thin film photovoltaic devices demonstrate a notable efficiency of 9.8%.     

钛溶胶复合有机硅涂层材料的制备与表征

以钛酸丁酯(TBT)和γ-(2,3-环氧丙氧)丙基三甲氧基硅烷(GLYMO)为原料,通过溶胶-凝胶法制备了一类钛溶胶复合有机硅涂层材料,并采用多种手段对复合涂层的微结构和光学性质进行了表征。结果表明,所得复合涂层材料的表面平整光滑,可见光透过率在91%以上。随着钛含量的增加,涂层的折射率在1.49～1.56(633nm)范围内呈上升趋势。     

Ammonia-free chemical bath deposition of nanocrystalline ZnS thin film buffer layer for solar cells

In this work, we prepared zinc sulfide thin films on glass substrates by ammonia-free chemical bath deposition method using thioacetamide as the sulfide source and Ethylene Diamine Tetra Acetic Acid disodium salt as the complexing agent in a solution of pH = 6.0. Thin films of ZnS with different thicknesses of 18–450 nm were prepared. The effect of film thickness and annealing temperature in atmospheric air, on optical properties, band gap energy and grain size of nanocrystals were studied. The X-ray diffraction analysis showed a cubic zinc blend structure and a diameter of about 2–5 nm for ZnS nanocrystals. The Fourier Transform Infrared spectrum of films revealed no peaks due to impurities. The as-deposited ZnS films had more than 70% transmittance in the visible region. The direct band gap of as-deposited films ranged from 3.68 to 3.78 eV and those of annealed films varied from 3.60 to 3.70 eV.     

WO3+掺杂对纳米TiO2薄膜可见光致亲水性的影响

用溶胶-凝胶法和浸渍-提拉工艺在载波片上制备了均匀、透明的WO^3＋掺杂的纳米TiO2薄膜.用XRD、紫外-可见分光光度计分析了样品的晶相和光吸收性能,研究了WO^3＋的掺杂、掺杂量及热处理温度对薄膜可见光致亲水性的影响,并考察了薄膜在停止光照后,其亲水性能的变化.结果表明,与纯TiO2薄膜相比,掺WO^3＋的TiO2薄膜对可见光的吸收有所增强,并有一定的红移现象,且在可见光照射下,亲水性能都有提高,WO^3＋的最佳掺杂量为3%（物质的量比）;薄膜的最佳煅烧温度为773K;停止光照后,掺WO3＋的TiO2薄膜亲水性能持续的更久.     

EDTA辅助水热法制备不同形貌的氟化镁钠

以氟化钠、六水合氯化镁为主要原料, EDTA (乙二胺四乙酸二钠盐)为辅助剂, 通过水热法制备出不同形貌的氟化镁钠。考察了溶液pH、反应温度、时间和络合剂对产物形貌和物相的影响, 并对其形成机理进行了探讨。采用扫描电镜(SEM)、X射线衍射(XRD)和傅里叶变换红外光谱(FT-IR)等手段对产物形貌和物相进行了表征。结果表明: 在该反应体系中, EDTA既作为原料提供钠离子, 又作为络合剂与镁离子形成络合物; 反应温度、pH和络合剂对产物的形貌和物相有较大影响; 所得产物结晶度高, 有表面光滑的微米立方体晶体和纳米粒子聚集的微米空心球颗粒, 粒径均在1~3 μm之间。     

A facile room temperature synthesis of ZnO nanoflower thin films grown at a solid–liquid interface

Hierarchical ZnO films consisting of nanoflower particulates are successfully grown by a solid–liquid interface reaction technique at room temperature without additives like surfactants, capping agent, or complexing agent. The structural, morphological, and photocatalytic properties of these films are studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV–Vis spectroscopy. The nucleation, growth processes and hence the resulting morphology of the end product can be regulated by changing the concentration of LiOH and the time of reaction. SEM throws light on the chronology of the flower formation by studying the intermediate morphology. Electron microscopy results indicated that these ZnO nanostructures self-assembled to produce flower-like nanostructures. The highest photocatalytic efficiency was observed for the films prepared at the concentration of LiOH 0.5 mg/mL in ethanol at 24 h. On the basis of the results, a plausible growth mechanism for the formation of flower-like ZnO nanostructures is discussed.     

RF reactive magnetron sputtering for Fe-doped titania films deposited from ceramic targets

Fe-doped titania films are prepared by RF magnetron sputtering on Si wafers with specifically designed TiO₂ targets containing different amounts of Fe₂O₃ powder as a dopant source. The physical properties of the films are investigated in terms of the preparation conditions, such as Fe₂O₃ content in the target, RF power, substrate temperature and working pressure. The films show the typical crystallographic orientation. The growth rate increases with increasing RF power, but decreases with working pressure. Films with 40 nm and the transmittance over 90% at the visible region are prepared by using Fe-doped titania target.     

Intrinsic selectivity in capillary electrophoresis for chiral separations with dual cyclodextrin systems

Defined as the ratio of the affinity factors of the analytes for a complexing agent, the intrinsic selectivity is representative of the very nature of the complexing agent. When more than one complexing agent are present in the background electrolyte, it is possible to define several intrinsic selectivities according to whether complexing agents are considered separately or all together. A theoretical model with respect to selectivity is presented for separations that involve two complexing agents, using the concept of apparent constant for complex formation. When only independent complexation occurs (absence of mixed complexes), then the intrinsic selectivity of a complexing agent X in the presence of a complexing agent Y can be easily related to the intrinsic selectivity of each complexing agent and to complex formation constants. Dual systems of cyclodextrins (CDs), implementing the cationic mono(6-amino-6-deoxy)-β-cyclodextrin (β-CD-NH(2)) and a neutral CD (trimethyl-β-CD (TM-β-CD) or dimethyl-β-CD (DM-β-CD)), were studied to illustrate this model and to offer an alternative to the separation of neutral enantiomers when β-CD-NH(2) shows no or insufficient stereoselectivity. With a dual β-CD-NH(2)/TM-β-CD system at pH 2.3, arylpropionic acid enantiomers were baseline resolved and benzoin derivatives were partially resolved. For the arylpropionic acids, β-CD-NH(2), which is not stereoselective, confers on them a nonzero mobility, while TM-β-CD allows the chiral recognition. A study of the respective influence of ΤM-β-CD and β-CD-NH(2) concentrations was performed to determine the optimal conditions with respect to resolution. This theoretical approach allowed characterization of the intrinsic selectivity of neutral CDs for pairs of neutral enantiomers and therefore identification of the potential of neutral chiral agents for neutral enantiomers.     

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

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

The effect of surfactant on the structure and properties of ZnO films prepared by electrodeposition

The effect of surfactant on the formation, structure and properties of ZnO films synthesized by electrodeposition was studied in this work. It was carried out in an aqueous Zn(NO₃)₂ solution containing surfactant op-10 using cathodic galvanostatic method. The results showed that the additive surfactant effectively inhibited hydrogen evolution reaction on cathode surface, maintained stability of the solution pH and improved deposition rate of the films to two times. Grown ZnO films with uniform grain and smooth surface were observed by using atomic force microscopy. Optical characterizations indicated that average optical transmittance of such films was more than 80% in the visible wavelength range, and its optical band gap was near 3.21 eV.     

Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO2 prepared from different nitrogen dopants

Nitrogen-doped TiO₂ was developed to enable photocatalytic reactions using the visible range of the solar spectrum. This work reports on the synthesis, characterisation and kinetic study of interstitial N-doped TiO₂ prepared by the sol–gel method using three different types of nitrogen dopants: diethanolamine, triethylamine and urea. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV–visible spectroscopy were used to analyse the titania. Different interstitial N-doped TiO₂ properties, such as absorption ability in the UV–visible light region, redshift in adsorption edge, good crystallisation and composition ratio of titania structures (anatase and rutile) could be obtained from different nitrogen dopants. Amongst investigated nitrogen precursors, diethanolamine provided the highest visible light absorption ability of interstitial N-doped TiO₂ with the smallest energy bandgap and the smallest anatase crystal size, resulting in the highest efficiency in 2-chlorophenol degradation. The photocatalytic activity of all N-doped TiO₂ can be arranged in the following order: TiO₂/diethanolamine > TiO₂/triethylamine > TiO₂/urea > un-doped TiO₂. The initial rate of 2-chlorophenol degradation using the interstitial N-doped TiO₂ with diethanolamine was 0.59 mg/L-min and the kinetic constant was 2.34 × 10⁻² min⁻¹ with a half-life of 98 min. In all cases, hydroquinone was detected as a major intermediate in the degradation of 2-chlorophenol.     

Sol–gel derived photonic bandgap coatings for solar control

Sol–gel derived photonic bandgap films have been investigated as possible multilayer coatings for solar control glass applications. Multilayer Bragg mirrors, in particular, have been modelled by the Transfer Matrix method, designed to have either near-UV or near-IR reflectivity, but visible transparency, based on alternating aluminosilicate glass/titania quarter-wave stacks. Such composite multilayer structures have been deposited by sol–gel processing on selected glasses and other types of substrates and their optical characteristics have been measured by optical absorption and reflection spectroscopies, as well as spectroscopic ellipsometry to determine the single layer refractive index and thickness. The UV–visible-IR absorption and reflection characteristics of these multilayer coatings revealed solar control properties, due to the presence of peaks near ∼350–400 nm and ∼900–1000 nm, with reflectivities of the order of 70%, which appear promising for solar control application.     

PMMA–SiO2 hybrid films as gate dielectric for ZnO based thin-film transistors

In this paper we report a low temperature sol–gel deposition process of PMMA–SiO₂ hybrid films, with variable dielectric properties depending on the composition of the precursor solution, for applications to gate dielectric layers in field-effect thin film transistors (FE-TFT). The hybrid layers were processed by a modified sol–gel route using as precursors Tetraethyl orthosilicate (TEOS) and Methyl methacrylate (MMA), and 3-(Trimethoxysilyl)propyl methacrylate (TMSPM) as the coupling agent. Three types of hybrid films were processed with molar ratios of the precursors in the initial solution 1.0: 0.25, 0.50, 0.75: 1.0 for TEOS: TMSPM: MMA, respectively. The hybrid films were deposited by spin coating of the hybrid precursor solutions onto p-type Si (100) substrates and heat-treated at 90 °C for 24 h. The chemical bonding in the hybrid films was analyzed by Fourier Transform Infrared Spectroscopy to confirm their hybrid nature. The refractive index of the hybrid films as a function of the TMSPM coupling agent concentration, were determined from a simultaneous analysis of optical reflectance and spectroscopic ellipsometry experimental data. The PMMA–SiO₂ hybrid films were studied as dielectric films using metal-insulator-metal structures. Capacitance–Voltage (C–V) and current–voltage (I–V) electrical methods were used to extract the dielectric properties of the different hybrid layers. The three types of hybrid films were tested as gate dielectric layers in thin film transistors with structure ZnO/PMMA–SiO₂/p-Si with a common bottom gate and patterned Al source/drain contacts, with different channel lengths. We analyzed the output electrical responses of the ZnO-based TFTs to determine their performance parameters as a function of channel length and hybrid gate dielectric layer.