Karlsruher Institut für Technologie (KIT)
The fabrication process defines the 3D structure and composition of a photonic material and thereby, its properties. Macroporous 3D photonic glasses (i-PhGs) can be produced by the infiltration of a template either by sol-gel, colloidal routes, chemical vapor deposition or atomic layer deposition (ALD). Meanwhile, the fabrication of templates is often performed by self-assembly of polymeric or silica monodisperse particles using traditional methods such as vertical convective self-assembly, drop-cast, or spin-coating. However, such techniques present limitations in regard to shape flexibility, often being limited to planar coatings, and the occurrence of defects, such as drying cracks or the “coffee-ring effect” (CRE). Nonetheless, the structural arrangement and template quality, which is defined during the self-assembly process, is crucial for the 3D photonic structure’s properties. Thereby, controlled and tailored particle deposition and assembly is necessary to achieve high-quality photonic structures. Here we will present that the combination of direct writing as an additive manufacturing process with colloidal assembly enables the printing of macroscale crack-free photonic glasses templates. By tailoring the printing parameters for the polystyrene templates, we demonstrate how to avoid CRE and cracks formation, as well as how to print onto non-planar shaped substrates. The printing of additive-free low viscous colloidal suspensions is enabled by an innovative “comb”-strategy. Atomic layer deposition (ALD) is used to further functionalize the printed templates, which are then transformed into ceramic i-PhGs after template removal. The obtained i-PhGs structures reveal promising broadband reflection in the near infrared.
Abstract
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