Optical properties and surface morphology of near infrared multilayer antireflection coatings

Theoretical and experimental studies on multilayer antireflection (AR) coatings useful in the near infrared region, covering 1200 to 2000 nm are carried out, in which the relative merits and demerits of using a low refractive index magnesium fluoride (MgF₂), along with a high refractive index Substance H2 (Sub2) material of E. Merck, in comparison to silicon dioxide (SiO₂) and Sub2, are specifically investigated. It is seen that MgF₂ together with Sub2 produces wider band antireflection coatings, with lower ripple and integrated reflection loss (IRL), R^*, whereas SiO₂/Sub2 combination produces AR coatings with medium spectral coverage, and the coatings are free of structural defects, which in turn are highly durable against adverse environmental conditions.     

深紫外宽入射角范围增透膜设计与制备

在大数值孔径深紫外光学系统中,需要使用宽入射角范围的增透膜光学元件.选择LaF3和MgF2两种镀膜材料,设计了适用于深紫外宽入射角范围的三层、五层和七层三种增透膜系.实验使用热舟蒸发在熔融石英基底上镀制了设计的薄膜,并用紫外分光光度计对其光谱性能进行了测试,得到了在宽入射角范围内具有较高透过率的深紫外增透膜元件.双面镀五层增透膜系的熔石英基片在0°～55°入射角内的剩余反射率小于2.5％,在0°～20°入射角内的透过率大于98％.     

Realization of High Performance AR‐coatings with Dust‐ and Water‐Repellent Properties

Hydrophobic coatings enable the manufacture of easy‐to‐clean surfaces having dust‐ and water‐repellent properties. In this work, a hydrophobic coating is deposited as a top layer on an antireflective (AR) multilayer system to produce low reflectance optical surfaces at a normal incident angle in the visible spectrum with dust‐ and water‐repellent properties for applications in precision optics. It is shown that the hydrophobic coating can be considered, from an optical point of view, as two adjacent thin layers having specific thicknesses and densities. In fact, the hydrophobic layer is one monolayer comprising molecular chains with anchoring groups responsible for the chemical bond with the substrate material and functional groups responsible for the water‐ and oil‐repellent properties. Their optical constants are determined and included in the final coating design. High performance AR coatings having an average reflectance of 0.14% at 7° incident angle in the 400‐680nm spectral range together with a pleasing purplered reflex color are produced. Coated lenses exhibit an excellent abrasion resistance, environmental stability, resistance to cleaning agents, homogeneity and water repellence with contact angles against water higher than 110°.     

Design, production, and reverse engineering of two-octave antireflection coatings

We deal with design and production of optimal two-component antireflection (AR) coatings for an ultra broadband spectral range from 450 nm to 1800 nm. We demonstrate the whole design-production chain including design selection, choosing monitoring technique, coating production, and reverse engineering of the deposited coatings. At each step of this chain we provide thorough analysis on the basis of theoretical results and adequate computational manufacturing experiments. In order to produce the designed AR coatings we use magnetron sputtering deposition technique and accurate time monitoring.     

电沉积法制备碳纳米管/黑镍复合涂层的光学与结构特性

利用复合电沉积的方法在钛合金基体上成功制备出具有优异光学性能的碳纳米管／黑镍复合涂层, 并研究了复合涂层的微观形貌、光学性能以及镀液中碳纳米管浓度和电镀电流密度对光学性能的影响。实验结果表明: 相较于传统电镀方法获得的单一黑镍涂层, 复合涂层的晶粒尺寸明显减小, 形成多孔结构, 表面粗糙程度明显增加。复合涂层对300~2300 nm范围内的入射光吸收率达到98%左右, 在2.5~20 μm范围内的红外吸收率达到94%, 远远高于传统单一黑镍涂层。复合涂层的太阳吸收比会随着镀液中碳纳米管浓度与电镀电流密度的增加呈先增大后减小的变化规律。     

耐摩擦和高透过SiO2/TiO2/SiO2-TiO2增透膜的设计和制备

通过膜层设计理论设计出以K9玻璃为基底的兼具高透过率和高耐摩擦性的三层宽带增透膜,并通过溶胶凝胶技术成功制备了所设计的增透膜.以正硅酸乙酯(TEOS)和钛酸丁酯(TTIP)为前驱体、以盐酸为催化剂制得SiO2和TiO2溶胶.将两种溶胶按一定比例混合得到SiO2-TiO2复合溶胶.实验结果表明:三层增透膜在可见光区的平均透过率达到98.7%,与未镀膜的K9玻璃基片相比提高了7.1%.增透膜经较强机械摩擦后透过率基本保持不变,表明该增透膜具有优良的耐摩擦性.采用六甲基二硅氮烷(HMDS)对增透膜表面进行进一步的修饰,修饰后增透膜与水的接触角提高至94.3°,增透膜的疏水性及环境稳定性得到较大的提高.     

In‐Situ‐Charakterisierung optischer Mehrschichtsysteme in Großflächen‐ Produktionsanlagen

The paper discusses approaches to the insitu analysis of optical multi‐layer coating stacks such as mirror coatings, AR coatings or lowE layer stacks on large‐area substrates in production environments. The stable production of complex layer systems requires in‐situ analysis systems that are able to provide spectral information and optical performance data, but also yield thickness information for individual layers and thus aide the operating staff in detailed analyzing deviations from the production target stack. Solutions incorporating in‐situ optical reflectance, transmittance and ellipsometry measurements wi^th optical data being collected not only for the completed layer stack, but also at intermediate coating stages, are discussed and the accuracy, robustness and stability of different measurement systems and computation strategies are compared.     

Estimation of the average residual reflectance of broadband antireflection coatings

We deal with optimal two-material antireflection (AR) coatings for the visible and adjacent spectral regions. It has been shown before that, for a given set of input parameters (refractive indices of the substrate, ambient medium and high- and low-index coating materials, and for a given spectral width of the AR coating), such designs consist of one or more clusters of layers of approximately constant optical thickness and number of layers. We show that, through the analysis of many different optimal coatings, it is possible to derive two parameters for a simple empirical expression that relates the residual average reflectance in the AR region to the number of clusters. These parameters are given for all possible combinations of relative spectral bandwidth equal to 2, 3, and 4; low-index to ambient-medium index ratio equal to 1.38 and 1.45; and high-to-low index ratio equal to 1.4, 1.5, and 1.7. The agreement between the numerically and the empirically calculated values of residual average reflectance is excellent. From the information presented the optical thin-film designer can quickly calculate the required number of layers and the overall optical thickness of an AR coating having the desired achievable residual average reflectance.     

Theoretical Analysis of Spectral Selective Transmission Coatings for Solar Energy PV System

Spectral selective transmission coatings can adjust the spectrum of incident solar radiation to reduce the waste heat generation in solar cells and to improve solar photovoltaic conversion efficiency. The ideal spectral transmissivity of the coatings should match the spectral response of solar cells, which means the ideal spectral transmissivity should be equal to 1.0 in the range of the spectral response and 0 in the other spectrum. The reflection performance of the three kinds of spectral selective transmission coatings for silicon solar cells are designed and analyzed. The results indicated that the ZnS/Na₃AlF₆ coating systems have a wider reflected infrared (IR) region than the TiO₂/SiO₂ coating systems, but lower transmissivity in the wavelength range of 0.5 μm to 1.1 μm. Furthermore, an Nb₂O₃/SiO₂ coating system is proposed and optimized, which has 31 layers with a smaller total thickness of 2.675 μm. The radiative properties including reflectivity and transmissivity of spectral selective transmission coatings are investigated and theoretically analyzed.     

Temperature-stable bandpass filters deposited with plasma ion-assisted deposition

Plasma ion-assisted deposition with an advanced plasma source was investigated to produce narrow-bandpass filters in the near-infrared spectral range for telecommunication applications. The multilayer coatings were qualified by the optical performance, the vacuum-to-air behavior, the temperature stability, and the film stress. TiO(2)/SiO(2) and Ta(2) O(5)/SiO (2) material combinations were used and compared. The coating system produced low absorbing multilayers with a very low coefficient of expansion and low stress. The coefficient of expansion was in the low 10(-6) °C range, and film stress values in the range between 1 and 2 × 10(8) N/m(2) were obtained. TiO(2)/SiO(2) was the preferred material combination. The optical monitoring system allowed the production of bandpass filters with a performance close to that of the theoretical values.     

辛基三甲氧基硅烷改性SiO2疏水减反膜的制备

以正硅酸乙酯为前驱体, 氨水为催化剂制备标准SiO₂溶胶, 然后在回流前后分别对普通SiO₂溶胶添加适量的辛基三甲氧基硅烷(OTMS)进行修饰, 得到OTMS改性SiO₂溶胶。用未进行OTMS修饰、回流前修饰和回流后修饰的溶胶分别制备减反膜, 并使用傅里叶变换红外光谱仪、核磁共振波谱仪、紫外-可见-近红外分光光度计、原子力显微镜和接触角测试仪对薄膜的结构和性能进行表征。结果表明: 回流前添加OTMS修饰剂制备的改性SiO₂减反膜具有最优异的耐潮湿环境稳定性能, 最高透过率可达99.7%以上; 与水的接触角达到120°, 在潮湿环境中放置4 w后, 透过率只下降0.23%。     

Herstellen von Schraubenmaschinen mit einer keramischen Einlaufbeschichtung

Manufacture of Twin‐Screw Machines with a Ceramic Run‐In Coating It was learned during the material‐research program 316 that, with suitable coating parameters, atmospheric plasma sprayed coatings of ZrO₂ Y₂O₃ may have run‐in properties. This behaviour can be used to protect machine components where there is unlubricated contact with relative motion. Instead of adhesional scoring, which is typical for metallic materials, a controlled abrasion of the run‐in coating can be obtained. Sub‐project I studies the application of such coating systems with an additional corrosion resistant layer of NiCrAl on rotors and casings of twin‐screw machines. This technology provides the possibility of improving the operational behaviour and the reliability as well as the repair of affected casing surfaces. This article describes the research process from model tests through to the application in a twin‐screw machine. Different aspects of the coating process, the corrosion behaviour, machining, expenses and results from practical applications will be evaluated together with industrial partners.     

SiO2 and Al2O3/SiO2 coatings for increasing emissivity of Cu(In, Ga)Se2 thin-film solar cells for space applications

In this study, optical coatings were investigated as substitutes for the coverglass on flexible thin-film space solar cells. The inherent low emissivity of copper-indium-gallium-diselenide (CIGS) thin-film solar cells was increased using optical coatings for thermal balance in space. Evaporated silicon dioxide (SiO₂) and an additional aluminum oxide (Al₂O₃) coating on the CIGS solar cell increased the emissivity from 0.18 to 0.77. Higher emissivity was realized with the Al₂O₃/SiO₂ double-layer coating than with the SiO₂ single-layer coating. The straightforward double-layer coating gives the CIGS solar cells appropriate radiative properties for keeping the cell within a permissible temperature range in space.     

Optical and electrical characterization of r.f. sputtered ITO films developed as art protection coatings

Transparent and conductive tin-doped indium oxide (ITO) films have been prepared by r.f. plasma sputtering technique in Ar and Ar + O₂ gas mixture. The influence of the deposition conditions, film thickness, and substrate heating, as well as the post-annealing treatment on the optical and electrical properties of the ITO films has been investigated.The present study has extended the optical behaviour characterization of the ITO films in a wide UV-VIS-IR spectral region in addition to the comprehensive optical studies of this material at shorter wavelengths.The optical constants: refractive index (n), extinction (k) and absorption (α) coefficient, and the optical band gap (E_go) have been calculated for the ITO films in the spectral range between 350 and 2500 nm. A combination of several well-known theoretical models has been applied to describe precisely the complex optical behaviour of ITO films in separate spectral parts. In this approach, a good overlapping between the experimental and the simulated spectra in the whole investigated spectral region has been achieved.The deposition conditions and the optical and electrical properties of the ITO films have been optimized with respect to the requirements for their applications in art protection coatings.     

Interfacial roughness and related scatter in ultraviolet optical coatings: a systematic experimental approach

For a variety of UV optical coatings, surface roughness was measured by use of an atomic-force microscope (AFM) to study its dependence on the film material and thickness, coating design, and deposition process. After analyzing the corresponding power spectral density functions, we propose a simple classification model for coatings according to the contributions of substrate roughness and intrinsic film roughness to the scattering. Results of scattering measurements on different types of coatings are presented and are found to be in good agreement with predictions based on the AFM data. Consequences for a scatter reduction strategy are discussed.     

Development of optical coatings for 157-nm lithography. II. Reflectance,absorption, and scatter measurement

The total loss that can be suffered by an antireflection (AR) coating consists of reflectance loss, absorption loss, and scatter loss. To separate these losses we developed a calorimetric absorption measurement apparatus and an ellipsoidal Coblentz hemisphere based scatterometer for 157-nm optics. Reflectance, absorption, and scatter of AR coatings were measured with these apparatuses. The AR coating samples were supplied by Japanese vendors. Each AR coating as supplied was coated with the vendor's coating design by that vendor's coating process. Our measurement apparatuses, methods, and results for these AR coatings are presented here.     

PVD‐Schutzschichten für Werkzeuge des Präzisionsblankpressens

PVD protective coatings for precision molding tools Precision glass molding (PGM) is a replicative hot forming process for the production of complex optical components, such as aspherical lenses for digital and mobile phone cameras or optical elements for laser systems. The efficiency and thus also the profitability of the PGM depend on the unit price per pressed component, which correlates primarily with the service lifetime of the pressing tools. To increase tool lifetime, the tool surfaces are coated with protective coatings based on precious metals or carbon using physical vapour deposition (PVD). The PVD coating technology enables the deposition of thin coatings, which also follow more complex surface geometries and achieve a high surface quality. PVD coatings are also commonly used to protect tools from wear and corrosion. This paper presents two chromium‐based nitride hard coatings produced by an industrial PVD unit and investigated for their applicability for PGM. Two different coating architectures were implemented, on the one hand a single coating chromium aluminium nitride (Cr,Al)N coating and on the other hand a nanolaminar CrN/AlN coating with alternating layers of chromium nitride and aluminium nitride. The latter is a coating consisting of hundreds of nano‐layers, only a few nanometers thick. Both coatings, (Cr,Al)N and CrN/AlN, each have a thickness of s ～ 300 nm in order to follow the tool contour as closely as possible. The properties of the coating systems, which are of particular relevance for PGM, are considered. These include on the one hand the adhesion of glass, the roughness and topography of the surface and the adhesion between the coating and the tool material. In addition, the barrier effect of the coatings against diffusion of oxygen was investigated. In order to reproduce the thermal boundary conditions of the PGM, thermocyclic aging tests are performed and their influence on the different properties is described.     

Ion-assisted sputtering deposition of antireflection film coating for flexible liquid-crystal display applications

The optical properties and surface morphologies of sputtering films both without and with use of the ion-assisted deposition (IAD) technique are investigated and compared. Optimal antireflection (AR) coating films with SiO2/Nb2O5 layers, which are grown at 80 degrees C with a 15 cm distance between target and substrate, 55 SCCM oxygen flow (SCCM denotes cubic centimeters per minute at STP), and 1250 W magnetron sputtering power with use of the IAD technique, are used to study the optical performance. By using an atomic force microscope to investigate the surface of the sputtered Nb2O5 films, we find that the films' roughness is 0.185 nm. On a flexible hardness polycarbonate (HPC) substrate with the multilayer AR films, the peak transmittances measured in the visible range are 95.89% and 93.40%, respectively, for coatings with and without use of the IAD sputtering technology. These results are better than those measured with a bare HPC substrate (91.25%) and are well above the commercial liquid-crystal display standard (90%) and flexible application.     

Comparative Study on Optical Properties and Scratch Resistance of Nanocomposite Coatings Incorporated with Flame Spray Pyrolyzed Silica Modified via in-situ Route and ex-situ Route

A new type of transparent scratch resistant coatings including in-situ modified SiO_2(g-SiO_2) in flame spray pyrolysis(FSP) process was prepared. The maximum content of g-SiO_2 in the coating was 15 wt%, which is higher than that of SiO_2 modified by traditional wet chemical route(l-SiO_2, only 10 wt%). The results of transmission electron microscopy have demonstrated that in-situ surface modified g-SiO_2 particles dispersed well with smaller agglomerates in the final coating, which was much better than the particles modified via wet chemical route. Visible light transmittance and haze tests were introduced to characterize the optical quality of the films. All coatings were highly transparent with the visible light transmittance of above 80%, especially for coatings containing g-SiO_2, which exhibited slightly higher visible light transmittance than l-SiO_2 embedded one. The haze value of coatings incorporated with 15wt% g-SiO_2 was 1.85%, even lower than the coating with 5 wt% l-SiO_2(haze value of 2.09%), indicating much better clarity of g-SiO_2. The excellent optical property of g-SiO_2 filled coatings was attributed to the good dispersion and distribution of particles. Nano-indention and nano-scratch tests were conducted to investigate the scratch resistance of coatings on nano-scale. The surface hardness of the coatings rose by 18% and 14%, and the average friction coefficient decreased by 15% and 11%, respectively, compared to the neat coat due to the addition of 10 wt% g-SiO_2 and l-SiO_2. The pencil hardness of the coating with 15 wt% g-SiO_2 increased from 2B for the neat coating to 2H. However, the pencil hardness of coating with 10 wt% l-SiO_2 was only H. The results showed that the g-SiO_2 embedded coatings exhibited higher scratch resistance and better optical properties.