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Multiphoton absorption polymerization (MAP) is a consolidated technique which allows the fabrication of three-dimensional devices, with high resolution, specific functionalities and nanometric features. In general, to fabricate these devices, different methodologies have been employed, frequently based on complex and expensive experiments. However, no formal investigation has been performed to evaluate how the sample composition can influence the final structure size, without compromising the integrity of fabricated device. Therefore, in this work, using a simple approach, we investigate if the relative proportion of the sample constituents used in MAP can affect the final structure features. Here, we used two three-acrylate monomers, tris(2-hydroxyethyl)isocyanurate triacrylate and ethoxylated(6) trimethylolpropane triacrylate, combined in different proportions with an acylphosphine oxide photoinitiator, known as ethyl-2,4,6-trimethylbenzoylphenylphosphinate. The first monomer provides mechanical stability for the structure and the other reduces the degree of shrinkage upon polymerization. Polymeric structures are fabricated using a Ti:sapphire mode-locked laser oscillator, centered at 780 nm. The laser beam is focused into the sample through a microscope objective (NA=0.85). A pair of galvanometric mirrors and a translational stage allow the laser scanning in all the resin volume, producing three-dimensional structures. Using these acrylate monomers in equal proportion and a typical photoinitiator concentration (3 wt%), we produce structures with feature size on the order of 850 nm. When we change these monomer proportions and increase the photoinitiator concentration, we are able to produce structures at least 30% smaller. This simple approach here demonstrated can be combined with other methods, allowing the device fabrication with nanometric features.
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