Forming extremely smooth ZnO thin film on silicon substrates for growth of large and well-aligned ZnO rods with the hydrothermal method

Sol–gel zinc oxide (ZnO) thin films generally have non-uniform stripes. After annealing at high temperatures, these thin films are rough and granular. When ZnO rods are grown on such rough and non-uniform surface with the hydrothermal method, collimation, crystalline structure, and defect density are very poor. Here we explore a method to solve this problem. The ZnO thin film is first coated with an Au layer to prohibit the vertical extension of crystallization during the annealing period. As a result, the surface morphology of ZnO thin film is very flat and uniform after annealing. Afterwards, the ZnO rods are grown on the flat and uniform thin film, which gives rise to ZnO rods with very good collimation and crystalline structure. The extremely flat ZnO thin film even enables the fabrication of patterned ZnO rod arrays with regular shapes through lithography.     

紫外光照射对掺铝氧化锌薄膜导电和透光性质的影响

本文采用光助溶胶—凝胶法制备了掺铝氧化锌(AZO)透明导电薄膜.研究了紫外光照射对薄膜导电性和透光性质的影响.结果表明:光照使薄膜的导电性显著提高,且光照后薄膜方阻的降低幅度随薄膜晶粒尺寸的减小而逐渐增加;而随着紫外光照射时间延长,薄膜的紫外吸收边蓝移,近红外区透光率降低.以上实验现象可能与表面吸附氧解吸引起的载流子浓度增加、迁移率升高以及分层退火处理形成的薄膜结构有关.     

(Ni-Mo)/TiO2纳米薄膜光催化降解刚果红的性能与机理

用恒电流复合电沉积方法制备(Ni-Mo)/TiO2薄膜,以扫描电子显微镜(SEM)、X射线衍射(XRD)、拉曼(Raman)光谱和紫外-可见漫反射光谱(UV-VisDRS)对薄膜的表面形貌、晶相结构和光谱特性进行了表征,以刚果红为模拟污染物对薄膜的光催化性能进行了测定,并讨论了刚果红溶液的pH值对薄膜光催化活性的影响.采用循环伏安技术和向溶液中加入活性物种捕获剂的方法对薄膜光催化降解机理进行了探索.结果表明:(Ni-Mo)/TiO2薄膜是由粒径为50-100nmTiO2纳米粒子相和纳米晶Ni-Mo固溶体相构成的复合薄膜.薄膜具有较高的光催化活性,卤钨灯照射80min后,复合薄膜光催化刚果红的降解率是多孔TiO2(DegussaP25)/ITO(氧化铟锡)纳米薄膜的2.43倍.(Ni-Mo)/TiO2薄膜光催化活性的提高主要归因于薄膜层中有效形成的(Ni-Mo)/TiO2异质结和良好的电子通道,以及Ni-Mo纳米晶合金对溶解氧和激发电子还原反应的催化作用.分别给出了在紫外和可见光下薄膜光催化降解刚果红的反应机理.     

Thick transparent rutile TiO2 films crystallized in solution

We report a novel process for the preparation of dense, transparent TiO2 films of 2.5 mum thickness on a F-doped SnO2-covered glass substrate. The starting solution contained peroxotitanate complex ions, which are relatively stable under the experimental conditions, permitting the deposition of highly textured rutile nanocrystalline films. The nanocrystals exhibit specific orientations along the (101) and (002) crystalline planes. Kinetic studies suggest that the precipitation started from the formation of amorphous solids, followed by crystallization through a dissolution-recrystallization process. Although a minor phase of anatase was detected only for powders collected from solutions after film preparation, not for films, the transformation from amorphous to anatase was believed to occur before further transformation of anatase to rutile. The present method enables film synthesis on a surface with a large area, and therefore could be integrated into the processing of electroluminescent devices.     

Wrapping and inclusion of organic molecules with ultrathin,amorphous metal oxide films

In this review, we overview metal oxide nanostructures in which organic molecules play important roles as templates, as structural units, and, in some cases, as hosts. Their structural precision and diversity are discussed from the viewpoint of the topology of a metal-oxygen network. Supramolecular capsules of metal oxides are prepared by the self-assembly of polyoxometalates. Zeolites and mesoporous materials are synthesized by using organic molecules with their assemblies acting as templates. The topological networking of silsesquioxanes makes it possible to produce novel nanocomposites and microporous materials. In the final section, we demonstrate our recent studies into molecular imprinting, the encapsulation of a fluorescent dye, and the wrapping of individual polymer chains. Ultrathin, amorphous metal oxide films can retain the shape of organic molecules and can be used to create molecular composites by precisely wrapping individual molecules. These films are also effective in insulating molecular functions from external environments. The advantages of amorphous metal oxides are discussed in relation to the properties of the corresponding crystalline metal oxides and their potential prospects in nanotechnology.     

高湿度下紫外光辐射对sol-gelTiO_2薄膜强度、结构和亲水性能的影响

应用sol-gel法制备了TiO_2薄膜，在321 K和高湿度下应用500 W高压汞灯对薄 膜进行辐射处理，应用划痕法测定了薄膜的强度。利用红外光谱（IR）、拉曼光谱 （Raman）和接触角仪研究了光辐射对薄膜和结构和亲水性能的影响，结果表明高 湿度下紫外光辐射可以促使刚制备TiO_2薄膜中的羟基、有机基团脱落和Ti-O-Ti结 构生成，使TiO_2薄膜的强度、晶化程度显著提高和薄膜在可见光区域吸收增加。 刚制备的sol-gel TiO_2薄膜的亲水性能随着光辐射先是下降，然后上升，且各向 亲水同性。通过此方法可以在不耐温的基材上制备致密的高强度的和具有一定光致 亲水性能的初步晶化的TiO_2薄膜。     

Pyrolysis, crystallization, and sintering of mesostructured titania thin films assessed by in situ thermal ellipsometry

In-situ thermal ellipsometric analysis is used to elucidate new and fine-scale details on the thermally driven densification, pyrolysis, crystallization, and sintering of dense and ordered mesoporous titania thin films prepared by evaporation-induced self-assembly. The role of the heating schedule, initial film thickness, nature of the substrate and templating agent, solution aging, and presence of water and other additives in the calcination environment is examined. Each of these parameters is shown to have unique and often substantial effects on the final film structure, while the technique itself provides detailed insight into the chemical origin and evolution of these effects. In-situ monitoring and control over the governing chemical processes, such as high-temperature adsorption phenomena that impact nanocrystal growth, is also demonstrated. The evolution of both the porosity and chemical processes occurring inside these materials are evaluated, including extraction of kinetic parameters for the pyrolysis of the template and crystallization of the matrix walls. The latter is shown to be strongly dependent on the presence of mesoscale ordering with ordered cubic films indicating a 1D diffusion-limited crystallization process and dense films following a 3D diffusion-limited process. Less well-ordered mesoporous films, despite similarities in pore volume and pore size distributions, are kinetically more reminiscent of dense films in terms of crystallization. In-situ thermal ellipsometry, by detailing the evolution of the thermally driven chemistry and ceramization that dictate the final film properties, provides immensely important insight into the synthesis and optimization of advanced functional materials based on titania and other metal oxide thin films.     

Crack‐Free Periodic Porous Thin Films Assisted by Plasma Irradiation at Low Temperature and Their Enhanced Gas‐Sensing Performance

Homogenous thin films are preferable for high‐performance gas sensors because of their remarkable reproducibility and long‐term stability. In this work, a low‐temperature fabrication route is presented to prepare crack‐free and homogenous metal oxide periodic porous thin films by oxygen plasma irradiation instead of high temperature annealing by using a sacrificial colloidal template. Rutile SnO₂ is taken as an example to demonstrate the validity of this route. The crack‐free and homogenous porous thin films are successfully synthesized on the substrates in situ with electrodes. The SnO₂ porous thin film obtained by plasma irradiation is rich in surface OH groups and hence superhydrophilic. It exhibits a more homogenous structure and lower resistance than porous films generated by annealing. More importantly, such thin films display higher sensitivity, a lower detection threshold (100 ppb to acetone) and better durability than those that have been directly annealed, resulting in enhanced gas‐sensing performance. The presented method could be applied to synthesize other metal oxide homogenous thin films and to fabricate gas‐sensing devices with high performances.     

石墨烯氧化物薄膜电极的光电化学特性

采用浸渍-提拉法制备了一系列石墨烯氧化物(GO)薄膜,并通过X射线衍射(XRD),扫描电镜(SEM),傅里叶变换红外光谱,紫外-可见吸收光谱和光电化学测量等技术对样品进行了表征.在GO电极上观察到阴极光电流,且光电流密度受薄膜的厚度影响.GO薄膜电极厚度为27nm时,光电流密度为0.25μA·cm-2.此外,GO电极的光电响应还受紫外光照影响,随着紫外光照时间的延长,阴极光电流逐渐减小.该工作提供了简便的通过控制薄膜厚度或紫外光照时间来控制GO薄膜半导体光电化学性能的方法.     

Continuous crystalline carbonate apatite thin films. A biomimetic approach.

In contrast to extensive studies on hydroxyapatite thin films, very little has been reported on the thin films of carbonated apatite (dahllite). In this report, we describe the synthesis and characterization of a highly crystalline dahllite thin film assembled via a biomimetic pathway. A free-standing continuous precursor film of carbonated calcium phosphate in an amorphous phase was first prepared by a solution-inhibited templating method (template-inhibition) at an air-water interface. A stearic acid surface monolayer acted as the template, while a carbonate-phosphate solution composed a binary inhibition system. The precursor film formed at the air/water interface was heated at 900 degrees C and transformed into a dense crystalline film that retained the overall shape of the precursor. The crystalline phase was characterized by XRD and IR to be a single-phase carbonate apatite, with carbonate substitutions in both type A (OH-) and type B (PO4(3-)) lattice positions.     

Optical properties of thermally evaporated 4-(4-nitrobenzalideneamino) antipyrine Schiff base thin films

4-(4-nitrobenzalideneamino) antipyrine (NBAA) have been synthesized by refluxed ethanolic solution of 4-aminoantipyrine and p-nitrobenzaldehyde for 4 h and characterized with various physico-chemical techniques. Thin films of NBAA have been prepared by the thermal deposition technique in a vacuum of 1.5 × 10⁻⁵ mbar onto optical flat glass substrates. X-ray diffraction patterns show amorphous nature for all NBAA thin films except UV irradiated thin film which shows amorphous nature with some crystallinity but with small amount. The optical constants of thermally deposited NBAA thin film were investigated in the wavelength range 200–2500 nm. The type of optical transition near the edge of the band gap is found to be indirect allowed transition. The effect of UV irradiation as well as the effect of annealing on the optical properties of NBAA thin films was investigated. The value of the energy gap for thin films under investigation is calculated and found to be 1.56 eV for as-deposited, 1.45 eV for annealed and 1.82 eV for UV irradiation.     

Micropatterning of Sol-Gel Derived Thin Films Using Hydrophobic-Hydrophilic Patterned Surface

Formation process of convexly shaped oxide micropatterns using hydrophobic-hydrophilic patterned surface has been examined, and this technique was applied to several oxide thin films such as SnO₂, ZrO₂, TiO₂ and Al₂O₃. Hydrophobic-hydrophilic patterned surfaces were prepared on glass substrates by selective UV irradiation through a photomask on double-layered films of a very thin TiO₂ gel film as the underlayer and a hydrolyzed fluoroalkyltrimethoxysilane layer as the top layer. Precursor solutions were then spin-coated on the hydrophobic-hydrophilic patterns, and the coated substrates were dried at room temperature. The micropatterns of oxides were very difficult to be formed on the hydrophobic-hydrophilic patterned surfaces from metal-alkoxides as a precursor solution, but convexly shaped micropatterns were formed on the hydrophilic regions of the pattern when metal chlorides or oxychlorides were used as starting materials. This patterning technique potentially has a wide variety of applications such as fabrication of micro-optical components and finely patterned transparent electrodes.     

Thin La2Zr2O7 films made from a water-based solution

Thin films of La₂Zr₂O₇ (LZO) are highly regarded as possible buffer layers in the coated conductor configuration. This report describes a new synthesis for thin crystalline LZO films, based on a largely water-based solution, mainly containing metal acetates, acetic acid and an organic amine-base: triethanolamine. Initially, a thin layer of amorphous material is deposited on the textured Ni-5 at%W substrate by means of dip-coating. Only by careful control of the thermal treatment can the layer be transformed into a crystalline layer. Important parameters in this respect are the heating rate and the dwell time. The amorphous gel is analysed by HR-TGA/DTA and HR-TEM. The textured layers are analysed by XRD, pole figures, RHEED, AFM and SEM.     

紫外光下纳米TiO2 薄膜亲水性机理的电化学研究

The nanometer films of TiO2 were prepared by sol-gel method on ITO（Indium-tin oxide,SnO2:In） substrate. The TiO2 film was the anatase phase with a particle size of 100 nm from the measurements of X-ray diffraction and AFM（Atomic-Force-Microscope）. Electrochemical characteristics of ITO/ TiO2 electrode under UV（ultraviolet）irradiation were investigated using the method of cyclic voltammetry. A new oxidative peak was observed at 0.035 V when the TiO2 electrode was irradiated by 253.7 nm UV light for a certain time. The peak current increased with the irradiation time. It was assumed that the new oxidative peak resulted from Ti3+,which was formed during the UV illumination. The changes of hydrophilicity of the TiO2 thin film on ITO under UV light were also observed. It was assumed that the changes of hydrophilicity of the films may be related with the formation of Ti3+ on the surface when the film was irradiated by UV light.     

Preillumination of TiO2 and Ta2O5 photoactive thin films as a tool to tailor the synthesis of composite materials

Illumination of TiO 2 thin films with UV light is known to induce the transformation of the surface of this material from partially hydrophobic into fully hydrophilic. The present work shows that this transformation is accompanied by other effects that may be used to control the synthesis of composite materials. For this purpose, TiO 2 and Ta 2O 5 transparent thin films with a columnar structure and open pores were prepared by electron evaporation at glancing angles. Transparent TiO 2 thin films with micropores (i.e., pores smaller than 2 nm) prepared by plasma enhanced chemical vapor deposition (PECVD) were also used. All these films became hydrophilic upon UV illumination. Rhodamine 6G and Rhodamine 800 dyes were irreversibly adsorbed within the columns of the TiO 2 and Ta 2O 5 thin films by immersion into a water solution of these molecules. Isolated and aggregated molecules of these two dyes were detected by visible absorption spectroscopy. The infiltration adsorption efficiency was directly correlated with the acidity of the medium, increasing at basic pHs as expected from simple considerations based on the concepts of the point of zero charge (PZC) in colloidal oxides. The infiltration experiments were repeated with columnar TiO 2 and Ta 2O 5 thin films that were subjected to preillumination with UV light. It was found that this treatment produced a modification in the type (isolated or aggregated) and amount of dye molecules incorporated into the pores. Moreover, the selective adsorption of a given dye in preilluminated areas of the films permitted the lithographic coloring of the films. Preillumination also controls the UV induced deposition of silver on the surface of the microporous TiO 2 thin films. It was found that the size distribution of the formed silver nanoparticles was dependent on the preillumination treatment and that a well-resolved surface plasmon resonance at around 500 nm was only monitored in the preilluminated films. A model is proposed to account for the effects induced by UV preillumination on the TiO 2 and Ta 2O 5 oxide surfaces. The possibilities of this type of light treatment for the tailored synthesis of nanocomposite thin films (i.e., dye-oxide, metal nanoparticles-oxide) are highlighted.     

Preparation of nano-sized Pt metal particles by photo-assisted deposition (PAD) on transparent Ti-containing mesoporous silica thin film

We have investigated a novel technique for the preparation of nano-sized Pt metals on Ti-containing mesoporous silica (TMS) thin film by photo-assisted deposition (PAD). The transparent TMS thin film was prepared on a quartz plate through sol—gel/spin coating. XRD, UV-Vis and Ti K-edge XAFS measurements revealed the formation of isolated Ti oxide species with a tetrahedral-coordination geometry in the silica framework. Deposition of Pt metal precursor on TMS thin film under UV-light irradiation, followed by reduction with molecular hydrogen, afforded a transparent thin film (Pt/TMS). The formation of highly dispersed nano-sized Pt metals having narrow size distributions was determined by Pd L_III-edge XANES and TEM analysis. The TMS and Pt/TMS thin films have been demonstrated to exhibit a strong hydrophilic property, even before UV irradiation, compared to the common mesoporous silica and TiO₂ thin films. After UV-light irradiation, the contact angle of water droplet on the TMS and Pt/TMS thin films became extremely lower, indicating the appearance of the photo-induced super-hydrophilic property.     

Optical Switching in VO2 Thin Films

Vanadium dioxide thin films have been deposited from vanadium alkoxides VO(OR)3. An amorphous film is formed that transforms into crystalline VO2 upon heating at 500°C under a reducing atmosphere. Optically transparent VO2 thin films are then obtained that exhibit both electrical and optical switching around 70°C. The switching temperature together with the shape of the hysteresis loop can be modified by doping VO2 films with foreign cations. Doped MxVO2 (M = W6+, Nb5+, Ti4+, Cr3+ or Al3+) thin films have been prepared under the same conditions by mixing the vanadium alkoxide and a metal salt in an alcoholic solution. The switching temperature decreases when the film is doped with high-valent cations (W6+) and increases with low-valent cations (Al3+, Cr3+). The transition temperature first decreases and then increases when TiIV is added to the VO2 film while the width of the hysteresis loop is significantly reduced.     

Enhanced photoinduced super-hydrophilicity in sol–gel TiO2 thin films with co-doped Sn/Nb

In this work, Sn and Nb co-doped TiO₂ were coated on glazed porcelain substrates via sol–gel dip coating method. Field emission-scanning electron microscopy, transmission electron microscopy, and UV–vis spectrophotometer were used to evaluate thickness and optical properties of the thin films. Surface chemical state of thin films was examined by atomic X-ray photoelectron spectroscopy. Water contact angle on the film surfaces was measured by a contact angle analyzer under solar light irradiation. The optical results indicated that Sn/Nb dopant in TiO₂ thin film changed the absorption edge from ultraviolet to visible light and exhibited excellent photo-catalytic ability for degradation of methylene blue solution under solar irradiation. Wettability results indicated that Sn and Nb dopant ions had significant effect on the hydrophilicity property of thin films.     

Effects of UV irradiation on tribological properties of nano‐TiO2 thin films

One‐layer and two‐layer nano‐TiO₂ thin films were prepared on the surface of common glass by sol–gel processing. Water contact angle, surface morphology, tribological properties of the films before and after ultraviolet (UV) irradiation were investigated using DSA100 drop shape analyzer, scanning probe microscopy (SPM), SEM and universal micro‐materials tester (second generation) (UMT‐2MT) friction and wear tester, respectively. The stored films markedly resumed their hydrophilicity after UV irradiation. But UV irradiation worsened tribological properties of the films. After the film was irradiated by UV, the friction coefficient between the film and GCr15 steel ball increased about 10–50% and its wear life shortened about 20–90%. Abrasive wear, brittle break and adherence wear are the failure mechanisms of nano‐TiO₂ thin films. It was believed that UV irradiation increased surface energy of the film and then aggravated adherence wear of the film at initial stage of friction process leading to severe brittle fracture and abrasive wear. Copyright © 2009 John Wiley & Sons, Ltd.     

π‐Conjugated Microporous Polymer Films: Designed Synthesis,Conducting Properties,and Photoenergy Conversions

Conjugated microporous polymers are a unique class of polymers that combine extended π‐conjugation with inherent porosity. However, these polymers are synthesized through solution‐phase reactions to yield insoluble and unprocessable solids, which preclude not only the evaluation of their conducting properties but also the fabrication of thin films for device implementation. Here, we report a strategy for the synthesis of thin films of π‐conjugated microporous polymers by designing thiophene‐based electropolymerization at the solution–electrode interface. High‐quality films are prepared on a large area of various electrodes, the film thickness is controllable, and the films are used for device fabrication. These films are outstanding hole conductors and, upon incorporation of fullerenes into the pores, function as highly efficient photoactive layers for energy conversions. Our film strategy may boost the applications in photocatalysis, energy storage, and optoelectronics.