Preparation of silica thin films by novel wet process and study of their optical properties

Silicon dioxide (SiO2) thin films have gained considerable attention because of their various industrial applications. For example, SiO2 thin films are used in superhydrophilic self-cleaning surface glass, UV protection films, anti-reflection coatings, and insulating materials. Recently, many processes such as vacuum evaporation, sputtering, chemical vapor deposition, and spin coating have been widely applied to prepare thin films of functionally graded materials. However, these processes suffer from several engineering problems. For example, a special apparatus is required for the deposition of films, and conventional wet processes are not suitable for coating the surfaces of substrates with a large surface area and complex morphology. In this study, we investigated the film morphology and optical properties of SiO2 films prepared by a novel technique, namely, liquid phase deposition (LPD). Images of the SiO2 films were obtained by scanning electron microscopy (SEM) and atomic force microscopy (AFM) in order to study the surface morphology of these films: these images indicate that films deposited with different reaction times were uniform and dense and were composed of pure silica. Optical properties such as refractive index and transmittance were estimated by UV-vis spectroscopy and ellipsometry. SiO2 films with porous structures at the nanometer scale (100-250 nm) were successfully produced by LPD. The deposited film had excellent transmittance in the visible wavelength region.     

高激光损伤阈值266nm紫外增透膜研究

为了研制高激光性能紫外增透膜,分别使用HfO2/SiO2和Al2O3/MgF2两种高低折射率材料组合,采用物理气相沉积技术,设计制备了266 nm增透膜;分析测试了不同材料所组成的增透膜的剩余反射率、粗糙度、光学损耗、界面电场强度和激光诱导损伤阈值等特性。研究结果表明,两组不同膜料制备的266 nm增透膜都能达到剩余反射率<0.2%的要求,且激光诱导损伤阈值都大于5 J/cm(2266 nm,7 ns)。     

非平衡磁控溅射技术制备用于红外减反射的无氢碳膜

红外减反射保护膜具有特定的厚度要求,如能进一步减小无氢类金刚石膜(DLC)的光学吸收,就能使其在较大厚度时不过分损失光通量而得以广泛应用.从这点来讲,无氢类金刚石膜是一种极具开发潜力的材料.本文采用非平衡磁控溅射技术(UBMS)制备了无氢类金刚石膜,并研究了其厚度均匀性.研究结果表明:该非平衡磁控溅射装置有能力获得大于φ150 mm的均匀性范围.对DLC膜红外透射谱的分析表明,分别在Si和Ge基底表面单面制备的DLC薄膜,其峰值透射率在波数2983/cm时分别为68.83%和63.05%,这一结果接近无吸收碳材料理论上所能达到的值.同时,在5000到800/cm范围内,未发现明显的吸收峰.这些优良的光学特性表明,采用非平衡磁控溅射技术制备的无氢DLC膜可以作为窗口的红外增透保护膜使用.     

Dünne ITO‐Schichten als leitfähige,transparente Elektroden. Thin films of ITO as conductive,transparent electrodes

This article deals with materials science aspects of In₂O₃:Sn (“ITO”) coatings and with the process technology of variants of sputtering used to obtain thin films with properties desired for specific applications. As an example, antistatic and antireflective coatings of monitor tubes are presented. The influence of sputter parameters such as substrate temperature, plasma excitation mode, sputter pressure and oxygen partial pressure on the quality of the films is discussed. It is shown how application‐oriented basic research helps to obtain recipes for materials design. Two basic aspects are discussed in more detail: the influence of an oxygen surplus in the films on microstructure and electrical properties and the correlation of electrical and optical parameters of the films.     

Low temperature remote plasma sputtering of indium tin oxide for flexible display applications

Tin doped indium oxide (ITO) has been directly deposited onto a variety of flexible materials by a reactive sputtering technique that utilises a remotely generated, high density plasma. This technique, known as high target utilisation sputtering (HiTUS), allows for the high rate deposition of good quality ITO films onto polymeric materials with no substrate heating or post deposition annealing. Coatings with a resistivity of 3.8 × 10^− 4 Ωcm and an average visible transmission of greater than 90% have been deposited onto PEN and PET substrate materials at a deposition rate of 70 nm/min. The electrical and optical properties are retained when the coatings are flexed through a 1.0 cm bend radius, making them of interest for flexible display applications.     

Antireflecting surface coatings with continuously varying complex refractive index

Nonreflecting coatings for absorbing materials, based on thin films with an inhomogeneous complex refractive index, are considered. The reflectivity of these coatings is determined as a function of the film thickness (in units of the radiation wave length), optical constants, and the radiation incidence angle. It is shown that properly selected absorbing materials can be used to obtain surfaces with extremely low reflection coefficients.     

直流反应溅射沉积Al2O3薄膜及其在SS-AlN金属陶瓷太阳吸收涂层的应用

在沉积不锈钢-氮化铝(SS-AlN)金属陶瓷太阳吸收集热管的磁控溅射三靶镀膜机上,安装了UPS03反应溅射闭环控制单元,实现反应溅射Al2O3稳定反馈控制。采用国产直流电源在Al靶表面处于过渡态下,成功制备了吸收几乎为零的Al2O3薄膜。溅射功率在14kW时,反应溅射沉积Al2O3的靶电压波动可长时间稳定控制在±3 V范围内,沉积速率为5.4 nm/(min·kW),约为Al靶在无反应气体溅射下沉积Al薄膜速率的74%。采用Al2O3代替AlN作为减反射层,应用到SS-AlN太阳选择性吸收涂层中,进一步提高了复合膜的太阳光学性能,太阳吸收比由AlN作为减反射层的0.956提高到0.965,红外发射比不变,仍为0.044。     

Latest progress on tribological properties of industrial materials

Wear is closely related to friction and lubrication; the study of these three subjects is known as tribology. In science and technology it is concerned with interacting surfaces in relative motion. Soft or hard film coating, alloying and composite structuring have all been developed to control wear and friction. This is achieved by improving materials and surfaces with some characteristics that improve resistance to friction and wear. In recent years, several new solid lubricant and modern lubrication concepts have been developed to achieve better lubricity and longer wear life in demanding tribological applications. Most of the traditional solid lubricants were prepared in the form of metal, ceramic and polymer–matrix composites. They have been used successfully in various engineering applications. Recent progress in thin-film deposition technologies has led to the synthesis of new generations of self-lubricating coatings with composite or multilayered architectures, by using multiplex surface treatments. In this study, typical wear behaviors of representative materials of metallic alloys, ceramics, polymeric materials, and composites are reviewed in relation to their friction behaviors. Additionally, modeling for the wear prediction is outlined.     

Variable refractive index optical coatings

The discrete and restricted values of refractive index of the bulk optical materials at present available are a serious limitation on the usefulness of these materials for optical coatings. This limitation can be overcome by utilizing the atom-by-atom condensation feature of the growth of vapour-deposited thin films, which allows the homogeneous mixing of different materials irrespective of their solubility restrictions. We have used this feature of co-deposition of different materials to form mixed optical materials of variable refractive index, the variation being determined by the composition of the source material. Measurements of the optical constants of these films, prepared by co-evaporation of mixtures of ZnS and MgF₂ of various compositions, have been made. The refractive index of the mixed films is found to be in good agreement with the values predicted on the basis of the Lorentz-Lorentz theory. In addition, the optical equivalence of alternate layers of ZnS and MgF₂ with step thicknesses ranging from 5 to 250 Å has been studied. For step thicknesses less than 100 Å, the optical properties of the composite films are equivalent to those for the homogeneously mixed films. For larger step thicknesses, considerable and complicated interference effects are observed. Thus, variable refractive index composite films can be prepared by (a) co-deposition and (b) deposition of alternate discrete layers of different materials as long as the step thickness does not exceed about 100 Å. Furthermore, these techniques of obtaining optical films of mixed materials can be extended to any combination of materials and therefore they open up a new field in materials technology.     

Schichten über Schichten

Films over films: innovative coatings for complex applications Thin films and coatings have developed as a prerequisite for many technical applications. In this paper, some applications for electrical, electronic, biomedical and optical applications are presented. In this contribution, examples for coatings for conductive and transparent films in photovoltaics, films for biomedical electrodes, for semiconductor contacts and for high‐temperature contacts are presented and discussed. The films are prepared by magnetron‐sputtering and pulsed laser deposition. The influence of the processing parameters on the functional properties of the films is presented.     

Easy‐to‐clean Schichten – spezielle Anwendungen

Easy to clean surfaces – special applications Easy to clean surfaces can be made by wet‐chemical coating with subsequent heat‐treatment. Organically modified metal oxide films form the base reinforced by nano composite structures. The hydro‐ and oleophobic effect is obtained by perfluorinated organic molecule chains in the nano composite sol‐gel coatings. Application specific materials can be synthesized by the proper choice of suitable starting compounds and process parameters. The resulting coatings consist of a three‐dimensional cross‐linked inorganic part (such as a silica network) combined with an organic part. The organic material acts either as a surface modifier (example: alkyl, phenyl) or as crosslinker (example: acrylic, epoxy). The properties of such coating systems can be adjusted to obtain a wide range of glass‐ceramic or polymer‐like properties. The incorporation of nanoparticles into these materials significantly enhances the abrasion and the scratch resistance. Such coatings mainly on metal parts are used in diagnostics, analytical chemistry and medical technology.     

4.3 Vacuum evaporated thin films for solar collectors

Selectively absorbing surfaces are important for the efficient use of solarenergy. The main characteristics aimed at for this type of coatings are the highest possible absorptivity for solar radiation and the lowest possible emissivity for thermal radiation. (Temperatures up to 100–200°C). There are several ways to create surfaces with these properties. In the present work evaporated semiconductor films with suitable anti-reflection coatings were used on different metals. For the laboratory tests, the metals were vacuum evaporated on glass substrates. The evaporations were performed with an electron beam gun in a diffusion pumped system. The evaporated thicknesses and the rate of evaporation were controlled by a quartz crystal monitoring system. The selective coatings were studied on flat and rough metal surfaces. Sinusoidal, metal covered gratings with different periods were used as the rough absorber surfaces. This simplified the measurements of absorptivity and emissivity and gave a more thorough understanding of the basic thin film phenomena. It is possible to use gratings because the general rough surface can be looked upon as a superposition of different sinusoidal gratings. A comparison is made between the properties of the layers on flat and rough surfaces. The coatings were subjected to high humidity and high temperature tests. They were also cycled between the intended working temperature and ambient temperature to check possible degradation. Results concerning film adherence and stability during these environmental tests are given.     

平板玻璃表面涂料的研究及应用

透明装饰性涂料在玻璃上的应用使其表面功能多样化,应用范围更加广泛.本文阐述了平板玻璃涂料制备技术中基料树脂的选取、涂膜耐久性以及涂装工艺,并综述了几类玻璃涂料,如普通装饰性涂料、低辐射涂料、防反射涂料以及新型玻璃建材的应用研究进展.     

Dual-band windows (DBW) transparent for fundamental and second harmonic generation frequencies

Using the known “looking glass” transformation property (z → 2π − z, y → 2π − y) of the optical phase thickness z and y of matching layers of two-layer anti-reflection coating, together with the fact that optical characteristics of any film do not change after addition of a half-wavelength layer, we designed dual-band anti-reflection coatings transparent at any preset wavelengths λ₁ and λ₂. On the basis of this result common fractional anti-reflection coatings for second and higher harmonics generation using dispersionless coating materials are developed. Explicit analytical relationships between refractive indices of the layers and substrate are deduced. Since for second harmonic generation the dispersion of materials may be a factor we show how to compensate the known dispersion of the coating materials by special choice of dispersion of a suitable substrate.     

Pre-mineralisation of starch/polycrapolactone bone tissue engineering scaffolds by a calcium-silicate-based process

This work describes a new methodology to produce bioactive coatings on the surface of starch-based biodegradable polymers or other degradable polymeric biomaterials. As an alternative to the more typical bioactive glass precursors, a calcium silicate gel is being employed as a nucleating agent, for inducing the biomimetic formation of a calcium-phosphate (Ca-P) layer. The method has the advantage of being able to coat efficiently both compact materials and porous 3-D architectures aimed at being used on tissue replacement applications and as bone tissue engineering scaffolds. This treatment is also very effective in reducing the incubation periods, being possible to observe the formation of an apatite-like layer, only after 12 h of immersion in a simulated body fluid (SBF). The apatite coatings formed on the compact surfaces or along the fibres of a fibre mesh scaffold structure made from a starch/polycrapolactone blend (SPCL) were analysed and compared in terms of morphology, chemical composition and structure. After the first days of SBF immersion, the apatite-like films exhibit the typical cauliflower like morphology. With increasing immersion times, these films exhibited a partially amorphous nature and the Ca/P ratios became very closer to the value attributed to hydroxyapatite (1.67). It was possible to fully pre-mineralise the SPCL scaffolds and simultaneously to keep the porous morphology of the fibre-bonded scaffold.     

真空管式太阳能集热器研究最新进展

从选择性吸收涂层的材料、结构、热稳定性及真空环境等方面综述了真空管式太阳能集热器的研究进展。不锈钢、Ti、Al、Ni类材料适于制备中低温选择性吸收涂层;而Mo和W类等高熔点材料,适于高温涂层。涂层结构方面,主要有吸收层/介质减反层的光干涉类、金属红外反射层/金属介质吸收层/介质减反层的金属陶瓷类。影响涂层热稳定性的主要因素是高温下涂层的破裂、氧化及元素扩散,涂层厚度与结构也能影响热稳定性。结果表明:①选择性吸收涂层制备,应采用电化学或磁控溅射技术并结合纳米材料对涂层进行多层化、梯度化研究;②应着重发展Mo类金属陶瓷型的热稳定性好的涂层,以实现高温高效集热;③应加快实现太阳能集热器的智能化、自动化与建筑一体化。     

The fabrication of tunable nanoporous oxide surfaces by block copolymer lithography and atomic layer deposition

Patterned nanoscale materials with controllable characteristic feature sizes and periodicity are of considerable interest in a wide range of fields, with various possible applications ranging from biomedical to nanoelectronic devices. Block-copolymer (BC)-based lithography is a powerful tool for the fabrication of uniform, densely spaced nanometer-scale features over large areas. Following this bottom-up approach, nanoporous polymeric films can be deposited on any type of substrate. The nanoporous periodic template can be transferred to the underlying substrate by dry anisotropic etching. Nevertheless the physical sizes of the polymeric mask represent an important limitation in the implementation of suitable lithographic protocols based on BC technology, since the diameter and the center-to-center distance of the pores cannot be varied independently in this class of materials. This problem could be overcome by combining block copolymer technology with atomic layer deposition (ALD): by means of BC-based lithography a nanoporous SiO2 template, with well-reproducible characteristic dimensions, can be fabricated and subsequently used as a backbone for the growth of perfectly conformal thin oxide films by ALD. In this work polystyrene-b-poly(methylmethacrylate) (PS-b-PMMA) BC and reactive ion etching are used to fabricate hexagonally packed 23 nm wide nanopores in a 50 nm thick SiO2 matrix. By ALD deposition of Al2O3 thin films onto the nanoporous SiO2 templates, nanostructured Al2O3 surfaces are obtained. By properly adjusting the thickness of the Al2O3 film the dimension of the pores in the oxide films is progressively reduced, with nanometer precision, from the original size down to complete filling of the pores, thus providing a simple and fast strategy for the fabrication of nanoporous Al2O3 surfaces with well-controllable feature size.     

Chemomechanical effects in optical coating systems

The major in-service failure mechanisms of modern optical coatings for architectural glass can be mechanical (e.g. scratch damage). Many of these coatings are multilayer structures of less than 100 nm thickness and different coating architectures are possible (i.e. different layer materials, thickness and stacking order). These coatings are exposed to different types of climatic conditions. In such circumstances it has been shown that chemomechanical effects can lead to changes in the hardness as well as the fracture resistance of bulk oxides. High performance glass is coated with anti-reflection coatings (e.g. ZnO, SnO₂) and barrier layers (e.g. TiO_xN_y) which are also expected to suffer from such chemomechanical effects. In this study we have demonstrated the chemomechanical behaviour of a range of optical coatings exposed to water. Water exposure tends to reduce the hardness and increase the fracture resistance of the coating making it more vulnerable to plastic deformation during scratching. The susceptibility of different coatings to chemomechanical effects is discussed.     

Lithographically Encrypted Inverse Opals for Anti‐Counterfeiting Applications

Colloidal photonic crystals possess inimitable optical properties of iridescent structural colors and unique spectral shape, which render them useful for security materials. This work reports a novel method to encrypt graphical and spectral codes in polymeric inverse opals to provide advanced security. To accomplish this, this study prepares lithographically featured micropatterns on the top surface of hydrophobic inverse opals, which serve as shadow masks against the surface modification of air cavities to achieve hydrophilicity. The resultant inverse opals allow rapid infiltration of aqueous solution into the hydrophilic cavities while retaining air in the hydrophobic cavities. Therefore, the structural color of inverse opals is regioselectively red‐shifted, disclosing the encrypted graphical codes. The decoded inverse opals also deliver unique reflectance spectral codes originated from two distinct regions. The combinatorial code composed of graphical and optical codes is revealed only when the aqueous solution agreed in advance is used for decoding. In addition, the encrypted inverse opals are chemically stable, providing invariant codes with high reproducibility. In addition, high mechanical stability enables the transfer of the films onto any surfaces. This novel encryption technology will provide a new opportunity in a wide range of security applications.     

Molecular Lubricants and Glues for Micro‐ and Nanodevices

Research advances in molecular coatings from functional polymeric and organic molecules designed as molecular lubricants or molecular glues for micro‐ and nanodevices are presented here, with a focus on organized molecular films from amphiphilic molecules, molecules with reactive ends and functional oligomers. The interfacial properties of molecular coatings critical for their lubrication (see Figure) or adhesive performance at the nanoscale are discussed in conjunction with results on molecular structure and morphology of these coatings. Examples of the latest developments in the field of nanocomposite molecular coatings and applications of molecular lubrication concepts for computer hard drives are presented.