Microfabrication via Two-Photon Cross-Linking: An Investigation of Fabrication Parameters

Two-photon lithography (2PL) is a microfabrication technique that has become a standard method for the generation of miniaturized 3D objects. A promising novel approach to laser direct writing is two-photon cross-linking (2PC), which uses thin solid films of copolymers containing small amounts of chromophores acting as a two-photon cross-linker. Upon activation by two-photon light absorption, they form polymer networks through cross-linking via C–H insertion (CHic) at the focal point of the laser beam. As the focal volume moves, polymer structures are written into the film as a latent image. In all regions outside the focal point where cross-linking has not occurred, the polymer is completely removed by extraction with a suitable solvent. The quality of the fabricated structures is determined by the size and overlap of the voxels that constitute the structure and their arrangement, which can be adjusted through parameters such as beam intensity, scan speed, and a proper choice of slicing and hatching. On the one hand, the yield of the photochemical cross-linking process in the voxel needs to be high enough so that percolation is reached; on the other hand, the input of excessive energy must be avoided to prevent photodegradation of the forming structures. In this work, we present a model of the 2PC process, which describes the conditions under which high-resolution 3D structures can be obtained.