Picosecond laser interference patterning of periodical micro-architectures on metallic molds for hot embossing of polymers

RANK, ANDREAS; SOLDERA, MARCOS; LASAGNI, ANDRÉS FABIÁN; FU, YANGXI; VOISIAT, BOGDAN

Dresden

Conferencia; Werkstoffwoche 2019; 2019

Deutsche Gesellschaft für Materialkunde e.V.

Surface textures in the micro- and nanoscale are capable of modifying a wide range of surface properties, such as wetting, friction, anti-bacterial behavior and optical reflectivity. Among the vast developed technologies to produce surface micropatterns, Nanoimprinting Lithography (NIL) is a simple, cost-effective and high throughput technology scalable for industrial application. However, fabrication of large-area microstructured molds at low-cost and high processing speed is still challenging. A manufacturing method that fulfills these requirements is Direct Laser Interference Patterning (DLIP), since it is a one-step process that can be used to pattern periodic micro- and submicro-structures in metals, ceramics and polymers with processing speeds up to 1 m2/min.In this study, microstructures were produced employing four-beam DLIP on three different metals, namely Ni, Cr, and Cu, relevant for the production of molds in NIL systems. A picosecond laser source emitting at a wavelength of 532 nm was used to structure periodic hole-like patterns with a spatial period of 5 µm. The influence of the laser parameters on the quality and topographical characteristics of the produced micropatterns was investigated by optical confocal microscopy, scanning electron microscopy and atomic force microscopy. It was found that different topography shapes were generated depending on the irradiated energy density. It was also observed in the three materials that at a fixed laser energy density, the structure depth increases with the number of laser pulses up to 120 pulses. When applying a larger number of pulses, the structures become less defined due to the re-arrangement of molten material around the holes, and therefore the structure depth does not increase, but instead it tends to saturate to a constant depth as the number of pulses increases. Finally, the three studied structured metals were used as embossing molds to imprint micropatterns on polyethylene terephthalate (PET) foils using an electrohydraulic press. The obtained structures were compared to the masters showing a faithful reproduction of the texture.