New strategies for submicrometric maskless Additive Manufacturing of metallic structures using Nonlinear Photoreduction

Additive manufacturing (AM) and 3D printing are seen as exciting new industrial production methods fully aligned with the industry 4.0 paradigm. The greatest gamble is placed on their potential use in nanotechnology applications. Direct Laser Writing (DLW) is an example of AM with an ever growing relevance.
We analyze the application of a novel technique based on the two-photon reduction of photosensitive metallic precursors [1]. DLW, triggered by two-photon absorption process [2], allows to produce high-quality micro/nanostructures showing features below the laser’s diffraction limit (down to 50nm). A gold precursor, HAuCl₄, a natural polymeric matrix and a femtosecond NIR laser (λ = 780 nm) are used. An interesting comparison is done with another AM technique, stereolithography [3]. We worked on a different scale, using KAuCl₄, an acrylic resin and laser excitations in the UV (405 nm). Photoreduction underlies both methods. The first ensures a fine control on the ionic density and leads to an unpreceded compliance with the geometrical model; the second one permits to create 3D structures of different shapes and thickness with gold nanoparticles inside.
[1] H. B. Sun, S. Kawata, Jour. L. Tech. (2003)
[2] K. Kaneko, H. B. Sun, Appl. Phys. Lett. (2003)
[3] G.Taormina, Polymers (2018)