Transparent ceramics such as magnesium aluminate spinel (MAS) are an outstanding class of materials that combine high optical transparency with remarkable mechanical, chemical and thermal strength. They are particularly interesting for micro-optical applications, since MAS offers a high refractive index in combination with a low optical dispersion, which is inaccessible for other materials including glasses and polymers. However transparent polycrystalline MAS is notoriously difficult to microstructure. Methods such as hot pressing or slip casting only allow simple geometries like plates or domes to be manufactured. More complex geometries require time-consuming and cost-intensive post-processing. We have therefore developed a thermoplastic nanocomposite that can be structured with high accuracy by injection molding. The nanocomposite can subsequently be transformed into a transparent polycrystalline MAS ceramic with a transparency close to the theoretical maximum by thermal debinding, sintering and hot isostatic pressing (HIP). This innovative process makes transparent ceramics for optics and photonics available at low cost and with high production rates.
Polymers are still gaining a lot of interest in the field of optics and sensor technology. Structuring of these components is usually done using high-throughput manufacturing processes such as injection molding, allowing excellent shaping quality and high degree of automation. However, tool production for these tool-based manufacturing methods tends to be time consuming and expensive, limiting the flexibility of these processes. We developed a novel process enabling the fabrication of metallic insets with optical surfaces and structures at the micrometer scale. This involves utilizing high-temperature-stable fused silica glass bodies as molds for metal casting. The process enables the processing of metal alloys such as bronze, brass, and cobalt-chromium at temperatures reaching up to 1400 °C. The metal replications achieve resolutions in the single-digit micrometer range and exhibit a surface roughness in the order of a few nanometers. The manufactured mold tools were successfully tested in a polymer injection molding process.
Due to high optical transparency combined with high thermal and chemical stability transparent fused silica glass is of high interest for many applications in microsystems engineering, especially in the field of microfluidics and micro optics. However, structuring of fused silica is inherently difficult and usually includes high temperatures, complicated and toxic etching processes or time consuming grinding protocols with severe limitation to freedom of design and manufacturing speed. Thus, complex structured fused silica glass has been limited especially on the industrial scale. We developed highly filled, thermoplastic fused silica nanocomposites (so-called Glassomers), that can be processed using commonly available high-throughput polymer manufacturing technologies such as injection molding or continuous extrusion. After the shaping process the thermoplastic Glassomer is converted to pure, transparent glass by subsequent debinding and sintering yielding high-quality fused silica glass with high optical transparency (transmission >90 %) and optical surface quality (Rq < 5 nm). We show injection molding of high-resolution microstructures as well as complex shaped macroscopic components that are subsequently converted to pure fused silica glass enabling for the first time mass-market manufacturing of fused silica glass components, enabling a plethora of applications in micro optics and lab-on-a-chip devices.
Microstructured platinum (Pt) is of great importance in a variety of applications from electronics, sensors, microelectromechanical systems, Lab-on-a-Chip devices as well as medical implants such as the cochlear implant. The high electrical conductivity, high melting point, chemical resilience, high catalytic activity, and biocompatibility make Pt the material of choice in these applications. However, microstructuring of Pt and especially 3D microstructuring is challenging and mostly done using vapour-based techniques, which are restricted in the achievable designs or by novel 3D shaping methods, which are limited in terms of processing speed as well as purity and conductivity of the resulting platinum. We developed a platinum containing photoresin, which can be structured via direct lithography and two-photon polymerization. The resulting exposed platinum photoresin objects are subsequently converted to highly conductive and high purity platinum via thermal debinding and reduction. With the direct lithography method, we show that 2.5- dimensional microstructures, such as electrowetting on dielectric devices can be manufactured. By using two-photon polymerization, we show that complex 3D micro and nanoobjects can be fabricated paving the way for novel applications like metamaterials or catalysis as well as biomedical applications, where high surface areas and the physicochemical properties of Pt are highly desirable. By using lithography and two-photon lithography (TPL), we are able to obtain 2.5- dimensional Pt electrode patterns with a layer thickness of 35 nm and an electrical conductivity of 6.32 × 106 S m-1 as well as complex 3D Pt objects with a resolution of 2 μm and nanopillars of 700 nm, respectively.
Microstructured fused silica glass is of high demand for many applications in microsystems engineering, microfluidics and microoptics. However, structuring of fused silica glass is extremely difficult needing either very high temperatures for melt processing, hazardous chemicals for wet etching or time-consuming mechanical post-processing steps. The lack of feasible high-throughput manufacturing techniques prevent the usage of fused silica for many applications so far. Recently, soft replication and 3D printing of fused silica were introduced using silica nanocomposites that are converted into fused silica glass in a subsequent heat treatment. While these processes allow facile structuring of silica glasses on the laboratory scale, it is not suited for high-throughput manufacturing. In this work, we present a process towards rapid manufacturing of microstructured fused silica glass by hot embossing a thermoplastic silica nanocomposite. The structured nanocomposite is converted to high quality fused silica glass by subsequent debinding and sintering at 1320°C. We show hot embossing of microoptical structures as well as microfluidic channels with an aspect ratio of up to 6. Further, we have developed facile solvent and thermal bonding procedures allowing the fabrication of embedded and fully functional microfluidic chips in fused silica.
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