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.
The process of computed axial lithography (CAL) has been established as one of the fastest available photopolymer 3D printing methods, offering smooth surfaces (r.m.s. surface roughness as low as 6 nm) and the ability to process high-viscosity precursor materials (100,000 cP demonstrated). Recently we showed successful printing of microscale geometries into dispersions of silica nanoparticles in a refractive-index-matched photopolymer. After exposing the 3D geometry via patterned tomographic illumination the material is debinded and sintered. In this way, external features of 50 µm and internal channels of 150 µm diameter have been achieved. This processing technique offers a promising route to production of 3D glass microfluidic devices and complex monolithic micro-optical devices. We will describe the status of optics fabrication via CAL. We will also consider the influence of light scattering on spatial resolution and possible ways of addressing this effect.
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.
Structuring polymeric materials is important for almost all applications in microsystems engineering, microfluidics and microoptics. Especially rapid prototyping using direct optical printing methods has gained great importance, also for facilitating product development for microfluidic applications. However, the choice of materials is still limited. Polystyrene (PS) is the material of choice for medical, biological and biochemical applications due to its biocompatibility, optical transparency, surface properties and low costs. However, PS is usually structured using industrial polymer replication techniques like injection molding or hot embossing. So far, only little work has been done on rapid prototyping and direct printing of microfluidic chips in PS. In this work, we present a novel liquid polystyrene prepolymer, which can be photocured and structured on the microscale using direct lithography printing. Using this method microchannels with a minimum channel width of 500 µm have been fabricated. The cured PS shows material properties comparable to those of commercially available polystyrene.
Poly(dimethylsiloxane) (PDMS) is one of the widely-used materials to fabricate microfluidic devices because of its facile handling, optical transparency and elastic mechanical properties. However, this polymer has its limitations if chemical, thermal and mechanical stability are needed for novel devices such as flow through “chemistry-on-chip” synthesis. Fused silica glass or borosilicate glass are indubitably the materials of choice for chemical synthesis due to its extraordinary chemical and thermal stability as well as its optical transparency. Microfluidic glass devices are however notoriously difficult to fabricate and usually require wet chemistry or dry etching using hazardous chemicals like hydrofluoric acid (HF). To overcome these fabrication issues, we have developed the Glassomer process that renders the structuration of fused silica glass like a polymer possible including technologies like softlithographic replication or stereolithography printing. In order to take the concept of “chemistry-on-chip” to the next level, electronics need to be integrated into the Glassomer process for the detection and localization of droplets inside microfluidic devices, for electrochemical analysis and electrochemical synthesis. In this work, we show that platinum electrodes can be integrated into the process using wires and sputtering of platinum in the polymeric state. The samples are subsequently converted into transparent fused silica glass via thermal debinding and sintering. We demonstrate that with our process the fabrication of glass microfluidic devices containing electronic conductors is feasible and facile to obtain and that they can be used to detect changes of conductivity
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