Prepolymer film growth by adsorption out of solution on silicon and aluminium

A cyanurate prepolymer has been applied to smooth silicon wafers or to distinctly structured aluminium coatings. The surface composition of the substrates has been investigated by X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES) and ellipsometry. The application methods, spin coating and dip coating represent adsorption by a technical process exerting significant shear stresses or nearly equilibrated conditions, respectively. The mean tickness of the prepolymer film has been adjusted by variation of the concentration of the solution and checked by ellipsometry. Atomic Force Microscopy (AFM) monitored the development of the respective film morphologies of all 4 systems (silicon/aluminium, spin/dip coating) in the mean film thickness range from 1 to 50 nm.     

Glass transition behavior of spin-coated thin films of a hydrophilic polymer on supported substrates

Using ellipsometry, it is found the glass transition temperature of the spin-coated polyacrylamide(PAL) thin films on the supported silicon(Si) substrates with an oxide layer decreases with decreasing the film thickness. But Tgs of the asprepared thin films are much higher than that of the bulk sample. Such observations can be attributed to the combined result of the "surface effect" and increased hydrogen bonding interaction between PAL chains due to spin coating/thin film confinement.     

Active sol–gel thin film on nanostructured plasmonic surface

Sol–gel hybrid films based on alkyl bridged polysilsesquioxanes and doped with phenol red molecules, were synthesized for sensing purposes. Doped films changes colour from yellow to orange to red when exposed to hydrochloric acid (HCl) both in solution and gas phases. The synthesis was optimized in order to produce porous films after spin coating. The porosity increases reacting surface area and chemical reactivity of the sensing thin film. Porosity, optical and structural characterizations of these films were investigated by transmission electron microscopy (TEM), Fourier Transform Infrared Spectroscopy (FT-IR) and Spectroscopic Ellipsometry (SE). Variation of optical characteristics upon immersion of the film in the solution was characterized by UV–visible (UV–vis) spectroscopy. Moreover the same porous sensitive hybrid film was deposited on gold sinusoidal grating in order to detect variations of the dielectric film optical constant after HCl solution dip. This variation was revealed by monitoring surface plasmon polariton excitations.     

Comparative characterisation by atomic force microscopy and ellipsometry of soft and solid thin films

Ellipsometry and atomic force microscopy (AFM) were used to study the film thickness and the surface roughness of both ‘soft’ and solid thin films. ‘Soft’ polymer thin films of polystyrene and poly(styrene–ethylene/butylene–styrene) block copolymer were prepared by spin‐coating onto planar silicon wafers. Ellipsometric parameters were fitted by the Cauchy approach using a two‐layer model with planar boundaries between the layers. The smooth surfaces of the prepared polymer films were confirmed by AFM. There is good agreement between AFM and ellipsometry in the 80–130 nm thickness range. Semiconductor surfaces (Si) obtained by anisotropic chemical etching were investigated as an example of a randomly rough surface. To define roughness parameters by ellipsometry, the top rough layers were treated as thin films according to the Bruggeman effective medium approximation (BEMA). Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased etching time, although AFM results depend on the used window size. The combined use of both methods appears to offer the most comprehensive route to quantitative surface roughness characterisation of solid films. Copyright © 2007 John Wiley & Sons, Ltd.     

Modulating the pattern quality of micropatterned multilayer films prepared by layer-by-layer self-assembly

Patterned multilayer films composed of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) were prepared using dip and spin self-assembly (SA) methods. A silicon substrate was patterned with a photoresist thin film using conventional photolithography, and PAH/PSS multilayers were then deposited onto the substrate surface using dip or spin SA. For spin SA, the photoresist on the substrate was retained, despite the high centrifugal forces involved in depositing the polyelectrolytes (PEs). The patterned multilayer films were formed by immersing the PE-coated substrates in acetone for 10 min. The effect of ionic strength on the pattern quality in dip and spin multilayer patterns (line-edge definition and surface roughness of the patterned region) was investigated by increasing the salt concentration in the PE solution (range 0-1 M). In dip multilayer patterns, the presence of salt increased the film surface roughness and pattern thickness without any deformation of pattern shape. The spin multilayer patterns formed without salt induced a height profile of about 130 nm at the pattern edge, whereas the patterns formed with high salt content (1 M) were extensively washed off the substrates. Well-defined pattern shapes of spin SA multilayers were obtained at an ionic strength of 0.4 M NaCl. Multilayer patterns prepared using spin SA and lift-off methods at the same ionic strength had a surface roughness of about 2 nm, and those prepared using the dip SA and lift-off method had a surface roughness of about 5 nm. The same process was used to prepare well-defined patterns of organic/metallic multilayer films consisting of PE and gold nanoparticles. The spin SA process yielded patterned multilayer films with various lengths and shapes.     

Strategy for Applying Microanalytical Techniques

A combination of microanalysis techniques is used to reveal with great precision the composition and microstructure of typical features in engineering materials. In this paper small particles, very thin films, interfaces and their contiguous region are considered. Small silicon nitride particles in an iron matrix produced by nitriding are characterized quantitatively with High Resolution Electron Microscopy (HREM) and Electron Probe Micro Analysis (EPMA) using Wavelength Dispersive X-ray Spectrometry (WDS). Thin aluminium-oxide films grown on aluminium substrates by thermal oxidation at low pressure are investigated with HREM and X-ray Photoelectron Spectroscopy (XPS). Their thickness, composition and degree of crystallinity are established as a function of oxidation temperature and time. At and near the oxide-layer/MCrAlY-coating (M=Ni and/or Co) interface the aluminium and chromium depletion behaviour of the coating material due to high-temperature oxidation is studied with high-resolution Scanning Electron Microscopy (SEM), EPMA and Auger electron spectroscopy (AES). The composition-depth profiles obtained for the coating material are used to determine the composition dependent diffusion coefficients. These properties are crucial for the prediction through computational modelling of the coating material oxidation behaviour and enable the development of new coating materials.     

Preparation and Characteristics of Porous Silica Films by a Modified Base-Catalyzed Sol-Gel Process Containing PVA: II. Film Preparation

Porous SiO₂ films were successfully deposited on silicon substrates by a modified base-catalyzed Sol-Gel process (MBCP) containing polyvinyl alcohol (PVA). The process conditions, such as the gelation time, the synthesis temperature, the stabilizing agent of the precursor solution and the spin coating speed, the heat-treatment, the annealing temperature of the film on the microstructure and porosity of porous SiO₂ films were systematically investigated by SEM, XRD and ellipsometry techniques. This study provides a novel preparation technique for the porous SiO₂ film. Using this process, the resultant film can reach a thickness of 3.6 m for one layer, a porosity of 25–50%, a low thermal conductivity of 0.11 W/m·K. This film will be used as a low dielectric layer, an thermal-insulating layer and a low refractive index layer.     

Mechanical characterization of Ormosil films on plastics: Young's modulus determination by three points bending

A protective layer has been deposited to improve the scratching properties of polycarbonate organic glasses. The starting solution consists of a mixture of organosilicon compounds, silicon alkoxides or silica colloidal solutions. The deposition is carried out using the dip coating technique. The thickness is about 2–5 µm for the film and 1 mm for the substrate.Young's moduli of the films are obtained by a new three points bending apparatus. Young's modulus of coating depends both on silica content and on the nature of the silica used as a filler.     

Quantitative chemical composition of thin films with infrared spectroscopic ellipsometry: application to hydrated oxide films on aluminium

A method to quantify the composition of thin films using infrared spectroscopic ellipsometry (IRSE), supplemented by visible spectroscopic ellipsometry (VISSE), is proposed. Because ellipsometry measures the thickness and optical constants of a surface layer simultaneously, the absorption coefficient of the film as a function of wavelength can be obtained. Using values of the absorption coefficients for the pure components of the film, the percentages (mol.% or wt.%) of each component in the film can be calculated. The method is demonstrated in a study of the hydration of oxide films on electropolished aluminium and the anodically formed barrier oxide film. The IRSE technique shows that hydration of the films by immersion in boiling water results in the conversion of aluminium oxide to pseudoboehmite. Copyright © 2003 John Wiley & Sons, Ltd.     

Versatility of alkyne-modified poly(glycidyl methacrylate) layers for click reactions

Functional soft interfaces are of interest for a variety of technologies. We describe three methods for preparing substrates with alkyne groups, which show versatility for "click" chemistry reactions. Two of the methods have the same root: formation of thin, covalently attached, reactive interfacial layers of poly(glycidyl methacrylate) (PGMA) via spin coating onto silicon wafers followed by reactive modification with either propargylamine or 5-hexynoic acid. The amine or the carboxylic acid moieties react with the epoxy groups of PGMA, creating interfacial polymer layers decorated with alkyne groups. The third method consists of using copolymers comprising glycidyl methacrylate and propargyl methacrylate (pGP). The pGP copolymers are spin coated and covalently attached on silicon wafers. For each method, we investigate the factors that control film thickness and content of alkyne groups using ellipsometry, and study the nanophase structure of the films using neutron reflectometry. Azide-terminated polymers of methacrylic acid and 2-vinyl-4,4-dimethylazlactone synthesized via reversible addition-fragmentation chain transfer polymerization were attached to the alkyne-modified substrates using "click" chemistry, and grafting densities in the range of 0.007-0.95 chains nm(-2) were attained. The maximum density of alkyne groups attained by functionalization of PGMA with propargylamine or 5-hexynoic acid was approximately 2 alkynes nm(-3). The alkyne content obtained by the three decorating approaches was sufficiently high that it was not the limiting factor for the click reaction of azide-capped polymers.     

Comparison of Different High and Low Index Materials in the Manufacture of High Laser Damage Threshold Mirrors at the 351 nm Wavelength

Sol-gel material based mirrors have been produced by forming alternate layers of high refractive index and low refractive index thin films. These mirrors have proven to have a high laser induced damage threshold [LIDT]. Using nitric acid stabilized zirconia derived from zirconium-n-propoxide and base catalyzed silica, a 16 layer mirror with a reflectivity of better than 94% at 351 nm and 45° angle of incidence was fabricated. This had an LIDT of 7.7 J/cm2 at 351 nm with a 0.7 ns pulse width. Crazing prevented further layers being deposited. Both spin and dip coating were attempted with dip coating yielding the best results.The coating structure has been analyzed using XPS depth profiling and AES. The bulk materials have been investigated using transmission electron microscopy (TEM), X-ray diffraction (XRD) and TGA. High refractive index layers using Hafnia with nitric or acetic acid have also been investigated as prospective high LIDT mirrors.Alternative acidic routes to silica have been studied as a possible low index material and a route to preventing crazing.     

磷酸铁纳米薄膜复合光波导氨气传感元件的制备

将硝酸铁和甲醇、磷酸溶液按一定比例混合后,通过旋涂法制备了磷酸铁（FePO₄）纳米薄膜,测定了匀胶机转速对膜厚及烘干温度对膜厚和折射率的影响,并发现薄膜的烘干温度超过150 ℃时,薄膜的厚度（130 nm）和折射率(1.7)变化不大。将该薄膜固定在钾离子交换玻璃光波导表面,研制出FePO₄膜/K⁺交换玻璃复合光波导。酸碱指示剂溴百里酚兰（BTB）作为敏感试剂,固定在复合光波导表面,研制了BTB膜-FePO₄膜/K⁺交换玻璃复合光波导氨气传感元件。采用自装的光波导气体传感检测系统对不同浓度的氨气进行了检测。结果表明,该传感元件能够检测0.35 mg/m³浓度的氨气,并具有响应（10 s）及恢复（90 s）速度快、可逆性好、连续使用等特点。     

Development of Anti-Reflection (AR) Coating on Plastic Panels for Display Applications

Traditionally, various vacuum-based processes have been used for producing interference-type anti-reflection (AR) coatings on large area substrates for different commercial applications. In this paper, the development of sol-gel derived AR coating on large plastic substrates for display application is presented. The sol-gel dip coating process was used to deposit thin films on large size plastic panels. By developing sols with different refractive indices, multi-layer thin-film AR coating stacks were designed and fabricated. These coatings possess good uniformity and meet stringent automotive specifications. This technology has been commercialized successfully for dashboard instrument panel application in Toyota's new hybrid engine car, named Prius.In this paper, AR coatings prepared by the sol-gel process are reviewed. The basic design concept for an AR coating, the coating preparation procedure, and important parameters of the solution coating process are discussed. Optical constants of the coating materials were characterized by using spectroscopic ellipsometry. Optical, mechanical and environmental tests were performed on the sol-gel derived AR coating stack. The sol-gel derived AR coating possesses equivalent or superior properties when compared to the major commercially available AR coating products.     

Modification of micro-cantilever sensors with sol-gels to enhance performance and immobilize chemically selective phases

A chemical sensor based on the deflection of a surface modified silicon micro-cantilever is presented. A thin film of sol-gel was applied to one side of the micro-cantilever surface using a spin coating procedure. The sensor has been shown to give different responses to vapor phase analytes of varying chemical composition, as well as to varying concentrations of a given analyte. Ethanol, a highly polar molecule, exhibits a strong affinity for the polar sol-gel coating resulting in a large response; pentane, a non-polar hydrocarbon, shows very little response. The sol-gel coating has also been shown to function as a backbone for the immobilization of chemically selective phases on the cantilever surface. Reaction of the sol-gel film with chlorotriethoxysilane and subsequent capping of the remaining reactive surface silanols with hexamethyldisilizane increases the non-polar nature of the film. This results in an increase in the response of the sensor to non-polar analytes. The effects of film thickness and cantilever structure thickness on response were also investigated.     

Microstencils for the patterning of nontraditional materials

A microfabrication technique that uses a photolithographically patterned film as a microstencil has been developed. This microstencil has a bilayer structure comprised of parylene and SU-8 films with thicknesses from 4 to 100 microm. The parylene layer enables the microstencil to be mechanically peeled from hydrophilic substrates. Since no chemicals are required to release the microstencil, this technique can be used to pattern chemically and biologically sensitive materials. The amount of material deposited can be automatically controlled by the height of the SU-8 structures or externally controlled by spin coating or other thin film deposition techniques. This patterning method is very versatile and has been used to pattern features as small as 25 by 25 microm on silicon, glass, and polymer substrates. As an initial demonstration, we have patterned wax, cells, proteins, sol, and CYTOP.     

Modelling the dielectric function of thin films measured by spectroscopic ellipsometry: determination of microstructure and density

The dielectric function of thin-film amorphous hydrogenated silicon (a-Si:H) deposited by the glow discharge and hot wire technique has been investigated by spectroscopic ellipsometry. An improved interpretation of the ellipsometric data taking into account the influence of hydrogen incorporation into the amorphous network enables to determine the film density and the void volume fraction of the material. Thus ellipsometry provides a convenient and contactless means of characterizing the structural properties of thin films. The film density varies considerably with substrate temperature and hydrogen content depending on the individual deposition technique. A reduction of film density is mainly caused by the formation of voids in the amorphous network. The influence of the substrate temperature on the growth of dense a-Si: H films is pointed out.     

Inhibition effect of cerium in hybrid sol–gel films on aluminium alloy AA2024

Aluminium alloys such as AA2024 are susceptible to severe corrosion attack in aggressive solutions (e.g. chlorides). Conversion coatings, like chromate, or rare earth conversion coatings are usually applied in order to improve corrosion behaviour of aluminium alloys. Methacrylate‐based hybrid films deposited with sol–gel technique might be an alternative to conversion coatings. Barrier properties, paint adhesion and possibly self‐healing ability are important aspects for replacement of chromate‐based pre‐treatments. This work evaluates the behaviour of cerium as corrosion inhibitor in methacrylate silane‐based hybrid films containing SiO₂ nano‐particles on AA2024. Hybrid films were deposited on aluminium alloy AA2024 by means of dip‐coating technique. Two different types of coating were applied: a non‐inhibited film consisting of two layers (non‐inhibited system) and a similar film doped with cerium nitrate in an intermediate layer (inhibited system). The film thickness was 5 µm for the non‐inhibited system and 8 µm for the inhibited system. Film morphology and composition were investigated by means of GDOES (glow discharge optical emission spectroscopy). Moreover, GDOES qualitative composition profiles were recorded in order to investigate Ce content in the hybrid films as a function of immersion time in 0.05 M NaCl solution. The electrochemical behaviour of the hybrid films was studied in the same electrolyte by means of EIS technique (electrochemical impedance spectroscopy). Electrochemical measurements provide evidence that the inhibited system containing cerium displays recovery of electrochemical properties. This behaviour is not observed for the non‐inhibited coating. GDOES measurements provide evidence that the behaviour of inhibited system can be related to migration of Ce species to the substrate/coating interface. Copyright © 2010 John Wiley & Sons, Ltd.     

具有金属薄层的p-Si阴极在碱溶液中的光电化学性能

本文用循环伏安曲线和恒电位极化方法考察了具有金属薄层的p型单晶外延硅(p⁺/p-Si)阴极在碱溶液中的光电化学性能。结果表明,镀有钨-镍合金层的p⁺/p-Si阴极和镀有钯的p⁺/p-Si阴极,使氢析出的光电流明显增加。前者的电位比光电流达到相同值的空白p⁺/p-Si电极向正方移动了0.3V以上,后者移动0.25V。同时对p型外延硅(p⁺/p-Si)阴极比p型单晶硅(p-Si)阴极光响应较大的实验结果作了初步解释。扫描电镜结果显示,钨-镍合金沉积层是由许多不连续的“团块”构成的,而不是连续层。     

Low Temperature Bonding of Ceramics by Sol-Gel Processing

Sol-gel bonds were produced between smooth, clean silicon or polycrystalline alumina substrates by spin-coating solutions containing partially hydrolysed silicon alkoxides onto both substrates. The two coated substrates were assembled and the resulting sandwich was fired at temperatures ranging from 300 to 600°C. The influence of the sol-gel chemistry on the film microstructure and interfacial fracture energy was investigated using a wide range of techniques, including ellipsometry, FTIR, TG-DTA, rheology, TEM and micro-indentation. For silicon wafers, an optimum water-alkoxide molar ratio of 10 and hydrolysis water pH of 2 were found. Such conditions led to relatively dense films (>90%), resulting in bonds with significantly higher fracture energy (3.5 J/m²) than those obtained using classical water bonding (typically 1.5 J/m²). Aging of the coating solution was found to decrease the bond strength. Poly-crystalline alumina substrates were similarly bonded at 600°C; the optimised silica sol-gel chemistry yielded interfaces with fracture energy of 4 J/m².     

Photolabile carboxylic acid protected terpolymers for surface patterning. Part 1: Polymer synthesis and film characterization

We present the synthesis and characterization of a series of photolabile phenacyl derivative polymers and their subsequent thin film preparation. These systems are composed of up to three methacrylate units: a photolabile component including a p-methoxyphenacyl moiety which after selective irradiation (UV/laser) can provide free carboxylic groups in specific areas for further modification; an anchoring unit, trimethoxysiloxane or glycidyl methacrylate derivative, which allows the covalent attachment of the polymer to the substrate; and a spacer, methyl methacrylate or styrene, which in the appropriate proportion ensures the formation of films with good quality. Structural and thermal properties of these materials have been analyzed by means of NMR, FTIR, elemental analysis, UV, gel permeation chromatography, differental scanning calorimetry, and thermogravimetric analysis. The polymers have been subsequently processed by spin coating to render ultrathin films (<50 nm). Topographic and structural characterization studies of the films have been carried out with atomic force microscopy, contact angle measurements, and X-ray photoelectron spectroscopy. The extent of the substrate attachment of the polymers depending on the nature of the anchoring groups have been studied by ellipsometry and FTIR.