Quantized nanolaminates (QNL) are a material system that was developed, produced and characterized by the LZH in 2016 as an alternative optical material. The idea behind it is that, like a normal mixed material, QNLs have a refractive index that is determined by the ratio of the two materials used. However, the electron mobility is severely restricted by the very thin high refractive index material. This results in a higher band gap and a lower absorption edge of the system. Their properties have been demonstrated on ALD and IBS systems. But the complex and slow coating processes meant that only a few iterations could be produced. We have now developed a process on a magnetron sputtering system with a rotating substrate table that makes it possible to produce QNL layers of SiO2 and Ta2O5 at a very high rate of up to 0.8nm/s. This makes it possible to use these nanolaminates economically as a stand-alone material, even in thick and high layer count designs. Because of the process we were able to produce a variety of QNL with different layer thickness and ratio combinations and perform a variety of measurements such as atomic force microscopy (AFM), total scattering (TIS), transmission electron microscopy (TEM) and Laser induced damage threshold (fs-LIDT) to determine their properties. We were able to use the knowledge gained to coat more complex multilayer systems in a range that would otherwise not have been possible with normal Ta2O5-SiO2 coating systems.
Quantized nanolaminates (QNL) are a new type of metamaterials proposed only recently. The basic properties of QNL single layers have been investigated for various material combinations and deposition techniques. Based on these results the hypothesis was put forward that, thanks to the blueshift of the absorption edge, multilayer interference filters composed of QNL-SiO2 will lead to an increased laser damage threshold in the femtosecond regime compared to standard coatings of the same material combination. In our work we will show a comparison of mirrors with and without QNL designed for the wavelength of 1030nm. For these coatings both standard Ta2O5 and SiO2-Ta2O5 QNL were used as high and SiO2 as low refractive index material. Mirrors consisting of Ta22O5 and SiO2 without QNL were also deposited for reference. The designs used were either quarter-wave designs or designs aiming at reducing the electric field. A magnetron sputter system with a rotating table was used for depositing the multilayer designs. The design of the tool allows to deposit a Ta2O5/SiO2 layer pair at every rotation of the table, which results in a QNL deposition rate higher than the rate for the individual materials. In order to accurately terminate the layers at the design thicknesses, broadband optical monitoring was used. Subsequently, the coatings were investigated by spectrophotometry and femtosecond laser induced damage threshold (LIDT) measurements at 1030nm. These measurements showed that samples with QNL exhibit an improved damage threshold compared to standard high-low mirrors as well as to a commercial ion beam coated fs-mirror. Furthermore, it is shown that the designs with optimized electric field exhibit higher LIDT values than their standard λ/4 design counterparts.
The concept of quantum nanolaminates (QNL) postulates the decoupling of band gap and refractive index, which in regular dielectric materials is linked. We will show that the quantization effect can be observed in nanolaminate structures of the material combinations Ta2O5-SiO2 and amorphous silicon-SiO2, which were deposited by magnetron sputter deposition. These nanolaminates were characterized by a variety of different methods, which confirmed the layer structure in the nanometer range and the shift of the absorption edge to shorter wavelength. Furthermore, the use of the QNL as the high refractive index material in optical interference coatings was successfully demonstrated in anti-reflection and long pass filter coatings.
Quantization effects in nanolaminate structures of oxide materials were proposed and experimentally demonstrated only recently. In this paper we will investigate the material combinations of Ta2O5-SiO2 and amorphous silicon-SiO2 deposited by magnetron sputtering and show that the quantization effect is observed in both materials. We will describe the deposition process and demonstrate the tunability of the refractive index and the bandgap energy. Quantized nanolaminates (QNL) composed of Ta2O5-SiO2 in combination with SiO2 were used as high and low refractive materials in optical interference coatings forming an antireflection and a mirror coating, whereas QNL with aSi-SiO2 as the high index material were used in a log pass filter with edge at 720nm. All designs could be deposited successfully with close match to the design. The aSi-SiO2 based filter showed a blocking range throughout the visible spectrum whereas a comparable filter based on SiO2-TiO2 only blocked 500-700nm.
KEYWORDS: Coating, Error analysis, Camera shutters, Optical simulations, Neodymium, Global system for mobile communications, Data processing, Tolerancing, Signal processing, Reflectivity
Various types of optical monitoring systems are established in industry. They range from single wavelength, over monochromatic to broadband monitoring to calculate a monitoring signal, which allows to terminate each layer in a filter at the required thickness. State of the art monitoring systems offer the capability of monochromatic and broadband monitoring in a single device. With these technologies available, the question arises how to combine these monitoring strategies for a specific application in a way, which leads to accurate coating results with the least sensitivity to production errors and thus to the highest yield. To answer this question without the need to perform costly coating runs, we developed a software tool, which mimics all the monitoring features of Evatec’s GSM optical monitoring system. Additionally, the software is able to disturb the simulated ideal monitoring signal with errors such as detector noise, drifts, deviations in shutter delay times, etc. The values of these disturbances are specific to the deposition tool. They were determined based on the broadband spectra of actual coating runs. By starting a virtual coating run with defined disturbances, the thickness deviations expected with a selected strategy can be assessed and the development of thickness deviations during the run, i.e. error compensation and error accumulation can be simulated. Within the software, parameters for the termination of each layer can be varied individually and the effect on the coating result can be observed. In order to demonstrate the capability of this tool, a specific coating design was then selected. For this design various monitoring strategies were tested, broadband strategies with different wavelength ranges, monochromatic strategies varying wavelength assignment per layer but also mixed strategies of broadband and monochromatic monitoring. The most stable monitoring strategy resulting from these simulations was coated as well as some of the less promising candidates and their results were compared.
Manufacturing processes from the private and academic sectors were used to deposit anti-reflective and high-reflective coatings composed of Ta2O5 - SiO2 multilayers. Used deposition techniques included three Ion Assisted Deposition (IAD) systems and an Ion Beam Sputtering (IBS) system. Coatings were performed on fused silica (Corning 7980) substrates polished by two different suppliers. LIDT Measurements were performed using a Q-Switched Nd:YAG laser operating at 1064nm. The paper presents a comparison of the coatings in terms of laser damage threshold values, optical properties and surface quality.
Diamond Like Carbon (DLC) is the preferred material for the termination layer in optical interference coatings using infrared (IR) materials since it enhances the environmental stability of the otherwise typically soft substrate and coating materials used in IR. In the state of the art processes, the coating with the infrared materials is deposited in a box coater, then the substrates are transferred and loaded into a separate deposition machine where the DLC layer is then deposited. In the novel box coater presented in this article, the DLC and IR (or dielectric) processes can be run consecutively in the same machine. We will discuss the implementation of the DLC process, then we show how the DLC process was optimized using in-situ stress and broadband optical measurements as well as ex-situ characterization of the adhesion, hardness and abrasion. The resulting single layer DLC films have perfect adhesion to silicon, germanium, glass and antireflection coatings. Furthermore, they are hard and scratch resistant, pass the wiper test and are virtually absorption-free in the 3-5μm and 8-12μm wavelength ranges. We will show the results for adhesion, abrasion and spectral performance of a wideband antireflection coating for 3-5μm including a DLC termination layer.
In this work we want to demonstrate how the methodology of Design of Experiment (DOE) can be used for the
development of ion-assisted ITO films deposited at low temperatures. The optimization method allows us to identify the
process parameters, which yield films with high transmittance and low resistivity. The article will show the results
obtained for transmittance and resistivity. Furthermore, the dispersion of the refractive index and the extinction
coefficient will be determined as well as the surface roughness. In ITO there is a trade-off between transmittance /
absorbance and sheet resistance. Virtually absorption free films could be obtained with a resistivity of 3.2 μΩm, whereas
the lowest resistivity (2.7 μΩm) yielded a transmittance, which was reduced by a few percent.
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