Preparation and Characterization of Molybdenum Oxide Thin Films by Sol-Gel Process

This paper presents a new sol-gel process to prepare molybdenum oxide thin films. A molybdenum acetylacetonate sol was prepared by employing the system CH₃COCH₂COCH₃/MoO₃/C₆H₅CH₃/HOCH₂CH₂OCH₃. A molybdenum acetylacetonate gel was prepared by addition of aqueous NH₃. Thermal gravimetry (TG) and differential thermal analyses (DTA) of the gel suggested that crystallization of MoO₃ occurs in a 140 K temperature range around 508°C. MoO₃ films were prepared on fused silica, Si (111) and Al₂O₃ (012) substrates by annealing spin coating films of the sol in oxygen environment at 508°C. X-ray diffraction (XRD) showed that all films crystallize in -MoO₃ structure, and crystallites on fused silica substrate are arbitrarily oriented while those on Si (111) and Al₂O₃(012) substrates oriented in the (010) direction. SEM investigations showed that MoO₃ grains of all films are randomly distributed, with a longitudinal dimension of about 1–5 m and the film thickness is about 1 m.     

Preparation and Characterization of MgO Thin Films by a Novel Sol-Gel Method

MgO thin films have been prepared on Si substrates by a novel and simple sol-gel method using magnesium nitrate and collodion as starting material. Solutions consisting of magnesium nitrate in a mixture of collodion and ethanol were spin-coated onto silicon substrates. It was found that collodion was a necessary component to form stable sols and the crystallization and structures were clearly dependent on the amount of the collodion and the annealing temperature. The MgO thin films with good crystallization were obtained after annealing at 800°C. Meanwhile, the microstructure of the MgO films was examined by transmission electron microscopy and atomic force microscopy.     

New Sol-Gel Route for Processing of PMN Thin Films

Pyrochlore free Pb(Mg_1/3Nb_2/3)O₃ (PMN) thin films were prepared from mixed-metal precursors solutions using the sol-gel process. Lead acetate [Pb(CH₃COO)₂], magnesium acetate [Mg(CH₃COO)₂] and niobium ethoxide [Nb(C₂H₅O)₅] were used as starting materials, while 2-isopropoxy-ethanol was chosen as solvent. The reactivity of the precursors was investigated in order to understand and control the process and thus to prevent the contamination of the PMN with the pyrochlore phase. The solution was spin-coated on TiO₂/Pt/TiO₂/SiO₂/Si substrate. The thin films were characterized by SEM and XRD while dielectric measurements were performed on the bulk ceramic.     

Sol-Gel Processing of PbZrO3 Thin Films

PbZrO₃ (PZ) thin films have been prepared by 2-methoxyethanol route from lead oxide or lead acetate and zirconium n-butoxide. The use of lead oxide as lead source and the seeding layer of TiO₂ on Pt/TiO₂/SiO₂/Si substrate facilitate the formation of the perovskite phase.     

Acetic Acid Based Sol-Gel PLZT Thin Films: Processing and Characterization

PLZT 4/65/35 thin films were prepared by the acetic acid based sol-gel route. The choice of lanthanum precursor, i.e., acetate or nitrate, influences the functional group content of formamide modified sols and the microstructure of the thin films. The lanthanum nitrate based PLZT thin film deposited on Si/SiO2/TiO2 /Pt/TiO2 substrate has a columnar perovskite grain structure, while the lanthanum acetate based one is characterized by a lead-silicon containing reaction layer beneath the platinum electrode. Although lead is depleted from the PLZT thin film the perovskite structure is retained by the use of the top layer with a large excess of PbO.     

Synthesis of Bi2O3 and Bi4(SiO4)3 Thin Films by the Sol-Gel Method

Bi2O3 thin films were prepared by dipping silica slides in ethanolic solutions of tris(2,2-6,6-tetramethylheptane-3, 5-dionato)bismuth(III) [Bi(dpm)3] [1] and heating in air at temperatures 500°C. Bi4(SiO4)3 homogeneous thin films were obtained from the reaction of the bismuth oxide coating with the silica glass substrate at temperatures higher than 700°C. For heat treatments at temperatures between 600°C and 700°C, Bi2SiO5 coatings were obtained. The composition and microstructure evolution of the films were determined by Secondary Ion-Mass Spectrometry (SIMS), X-Ray Photoelectron Spectroscopy (XPS) and Glancing Angle X-Ray Diffraction (GA-XRD). The synthesis procedure was reproducible and allowed the control of the Bi2O3 phase composition. Moreover, the thin film annealing parameters were correlated with the formation of bismuth silicates, among which Bi4(SiO4)3 (BSO) is very appealing for the production of fast light-output scintillators [2].     

Ferroelectric PZT Thin Films by Sol-Gel Deposition

Sol-gel spin coating has a low thermal budget, is cheap compared to vacuum-based techniques and is now routinely used to produce dense, pore-free ferroelectric films. PbZrx Ti(1 – x)O3 (PZT) is utilized in most applications because it has a large remanent polarization, high piezo- and pyroelectric coefficients and optimized electromechanical coupling factors, depending on precise composition. This paper will review some of the principles and applications of PZT films and highlight using transmission electron microscopy some of the basic problems and solutions involved in producing device-quality material on Si-substrates.     

溶胶凝胶法制备铜铁矿结构p型透明导电氧化物薄膜

铜铁矿结构p型透明导电氧化物(transparent conducting oxide, TCO)薄膜是一类在电子学领域具有广泛应用前景的新材料,因其可与n-TCO薄膜形成真正意义上的“透明器件”而备受关注。本文介绍了铜铁矿结构p-TCO的结构特性以及溶胶凝胶法的基本原理和特点;系统地介绍了溶胶凝胶法制备铜铁矿结构p-TCO薄膜的工艺;分析比较了有机醇盐、无机盐溶胶体系的优缺点;最后讨论了进一步的发展方向,指出溶胶凝胶法是一种高效可行的制备p-TCO薄膜的方法。     

络合剂作用下光催化氧化纳米铁氧化物的生成及机理

进行了空气氧化Fe(OH)₂悬浮液, 络合剂(乙二胺、草酸、柠檬酸)作用下光催化氧化制备FeOOH的研究. 结果表明: 在室光下, 一定量乙二胺、草酸、柠檬酸的加入有利于纯γ-FeOOH的生成; 且随光强的增强, γ-FeOOH的晶化性降低. 机理分析表明: 可见光存在下, 络合剂的加入, 不仅使中间物绿锈GR(II)结晶度变差, 溶解加快; 而且络合剂与Fe^2＋形成的配合物可吸收部分可见光, 生成强氧化型的自由基, 使反应初期Fe^2＋快速氧化为Fe^3＋, 快的氧化速度利于生成低晶化度的γ-FeOOH.     

Stress and Moisture-Sorption in Ozone-Annealed Films of Zirconium Oxide Obtained from Sol-Gel

The stress development in zirconium oxide films prepared by sol-gel and annealed under ozone-enriched oxygen has been investigated. The organic compounds are mostly oxidized at 200°C with ozone and the stress rises up to higher values than the stress in films annealed with pure oxygen between 200 to 400°C. During exposure to humid air of films annealed at 150°C under pure or ozone-enriched oxygen chemical transformations of organic compounds have been observed. The moisture-induced stress change during film exposure to the ambient air also has been investigated. The competition between hydration of ZrO₂, H-bound formation, surface ionization and capillary condensation mechanisms is discussed.     

Optical and Electrical Properties of Ferroelectric SBN Thin Films Prepared by Sol-Gel Process

Strontium barium niobate thin films were prepared by sol-gel method on various substrates using an improved process, two-step heating process. The two-step heating process applies an additive heat-treatment before crystallization for enhancement of the densification and the nucleation of films. Also, highly c-axis oriented SBN thin films with various compositions were obtained on MgO(100) and Pt(100)/MgO(100) substrates. Their optical and electrical properties such as optical propagation loss, refractive index, P-E hysteresis, and dielectric constant, were characterized as a function of the film composition.     

Evolution of Structure of the Precursor During Sol-Gel Processing of ZnO and Low Temperature Formation of Thin Films

ZnO thin films were prepared on silicon substrate with Pt electrode by the sol-gel processing using Zn alkoxide solution prepared from Zn(NO₃)₂·6H₂O and 2-methoxyethanol. FT-IR spectroscopy showed the presence of Zn species in the alkoxide, with methoxyethoxide and nitrato groups as coordination ligands, indicating formation of Zn(NO₃)(OCH₂CH₂OCH₃). Smooth and homogeneous thin films were obtained by heat treating coating gel films in the temperature range from 250 to 500°C. The ZnO thin films exhibited a preferred growth of crystals with c-axis perpendicular to the Si substrate surface when fired at 250°C. It was discussed that the presence of nitrogen atoms in precursors had affected the phase development of crystals and was the basis of the structural relaxation for crystallization at low temperature.     

Sol-Gel Preparation and Photoelectrochemical Properties of Fe2TiO5 Thin Films

Polycrystalline Fe₂TiO₅ films were prepared on nesa silica glass substrates by the sol-gel method, and their photoanodic properties were measured in a three-electrode wet cell with an aqueous buffer solution of pH = 7. Gel films were crystallized into Fe₂TiO₅ when fired at 500°C. The photoanodic current significantly increased when the films were fired at 700°C, and then decreased with increasing firing temperature. Thicker films obtained by repeating the gel film deposition and firing showed smaller photocurrent, and the 50 nm thick film prepared via non-repetitive deposition exhibited the maximum photocurrent. Although the photoresponse was extended to wavelengths near 500 nm, the maximum quantum yield was as low as 0.12 at a wavelength of 340 nm.     

Ultraviolet-Laser-Induced Crystallization of Sol-Gel Derived Inorganic Oxide Films

Structural changes stimulated by ultraviolet (UV) laser irradiations of sol-gel derived inorganic oxide films were investigated. Dried gel films of TiO₂, Nb₂O₅, Ta₂O₅, SrTiO₃ and Pb(Zr _x Ti_1–x )O₃ (PZT) were found to be crystallized by the laser irradiation. On the other hand, the photo-induced change in gel films of BaTiO₃, LiNbO₃ and LiTaO₃ was not observed although the laser beams were absorbed in the films. These sol-gel films were thermally crystallized at almost the same temperature around 600–700°C except TiO₂. Thus, the UV-laser-induced crystallization is not directly ascribed to a simple thermal effect with the irradiation. Photochemical properties of the cations are assumed to be important for the change in sol-gel films.     

XPS Analysis of Lead Zirconate Titanate Thin Films Prepared Via a Sol-Gel Process

The crystalline phase and composition of sol-gel-derived lead zirconate titanate (PbZr _x Ti_{1 – x} O₃, PZT) thin films were determined by an X-ray photoelectron spectroscopic (XPS) data processing technique. As a result, it was proved that existence of the surface layer with several tens nm in thickness, of which the crystalline phase and composition were different from those of the inside of the thin films, was found. The newly developed XPS analytical technique is much applicable for the characterization of PZT thin film surface.     

Strategies for Spatially Separating Molecules in Mesostructured Sol-Gel Silicate Films

Three strategies for placing molecules in designated regions of mesostructured thin films made by the sol-gel dip-coating technique are demonstrated. These strategies all involve one-step syntheses where all of the components are present in the sol from which the substrate is pulled. Silicate films templated by ionic surfactants contain three spatially-separated regions: a silicate framework, an organic region formed by the hydrocarbon tails of the surfactants, and an intervening ionic interface formed by the charged surfactant head groups. The first method exploits lipophilic interactions between the molecule and the micelle to place it in the organic region. The second method uses chemical bonding of multiple trialkoxysilane groups in a three dimensional array on the molecule to place it in the silica framework. The third method uses multiple functionality at opposite sides of the molecule to enable it to span two regions. Luminescent molecules are used, and spectroscopy monitors the formation.     

溶胶-凝胶工艺制备发光薄膜研究进展

本文综述了通过深胶－凝胶工艺制备发光薄膜的基本过程、薄膜的表征方法、发光薄膜的当前发展及应用情况。依据组成特点,对溶胶－凝胶法制备的发光薄膜乾地了分类阐述,并预言了今后该法制备发光薄膜的发展趋势。     

Ultraviolet-Laser-Induced Crystallization of Sol-Gel Derived Indium Oxide Films

Modification of sol-gel derived indium oxide thin films using ultraviolet lasers was investigated. Irradiation by an ArF excimer (6.4 eV) and the fourth harmonic generation of a Nd : YAG laser (4.7 eV) was found to be effective in crystallization with a loss of hydroxyl groups and a decrease in the sheet resistance of the sol-gel films. Transparent crystalline indium oxide films were successfully obtained by 6.4 eV laser irradiation at fluences below 20 mJ/(cm2·shot), whereas degradation of the films was induced by a relatively high-fluence beam.     

Crystallization Behavior of SiO2-TiO2 Sol-Gel Thin Films

The aim of this work was to investigate the crystallization behavior of thin films of SiO₂−TiO₂ made by the sol-gel process as function of the TiO₂ content and the temperature and time of heat treatment. Precursor solutions were prepared by hydrolysis of TEOS (tetraethoxysilane) and TPOT (titaniums tetraisopropoxide). Multilayer films were spun on single crystal silicon wafers. The compositions studied were (on a molar percentage basis) 20TiO₂−80SiO₂, 30TiO₂−70SiO₂, 40TiO₂−60SiO₂ and pure TiO₂. The films were heat treated at different temperatures between 300°C and 1200°C, for different periods of time (30 s-90 h). The crystallization kinetics were followed by micro-Raman spectrometry. Grazing incidence X-ray diffraction showed that the films crystallized into one or both of two crystalline phase of TiO₂: anatase and rutile (for pure TiO₂ only). The volume fractions of the crystalline phase varied from very low values (<1%), up to 100%, for a TiO₂ sample heat treated at 800°C for 8 hours. The results show that the volume fraction of crystalline phase is strongly influenced by the heat treatment temperature and also, to a smaller extent, by the heat treatment time. The most important parameter, however, is the composition of the films: the higher their TiO₂ concentration, the lower is the crystallization temperature and the larger is the crystallized fraction.     

纳米多孔阳极氧化铁膜的形成及其形貌演变

阳极氧化法制备具有纳米多孔结构的阳极氧化铁膜因其潜在的应用价值而倍受关注。然而,在阳极氧化过程中多孔结构的形成机制至今尚不清楚。本文结合电流密度-电位响应（I-V曲线）及法拉第定律的推导,分析了形成纳米多孔阳极氧化铁膜的过程中阳极电流的组成。结果表明,离子电流（导致离子迁移形成氧化物）和电子电流（导致析出氧气）共同组成阳极电流,并且纳米多孔阳极氧化铁膜的形成与两种电流的占比相关。分段式氧化物之间的空腔以及在阳极氧化初期纳米孔道上覆盖的致密膜,表明氧气泡可能是从氧化膜内部析出。此时,阳离子和阴离子绕过作为模具的氧气泡实现传质,最终导致纳米多孔结构的形成。此外,在阳极氧化铁膜形貌演变过程中,氧气泡不断向外溢出会使表面氧化物被冲破,导致表面孔径不断增大。