Optimizing Two-Photon Initiators and Exposure Conditions for Three-Dimensional Lithographic Microfabrication.

Abstract

The radical photoinitiation characteristics of a range of D-it-D chromophores (where D is an electron-donor and 1t is a biphenyl, stilbene, or bis(styryl)benzene conjugated bridge) under two-photon excitation are reported. Photo-crosslinkable resins were formulated with these initiators and were used to fabricate a variety of complex three-dimensional structures by two-photon induced polymerization (TPIP). These structures illustrate that TPIP can be a highly versatile technique for the rapid single-step fabrication of complex microstructures and devices. The new two-photon resins were found to be as much as 50 times more sensitive than resins containing conventional UV initiators. The increased two-photon sensitivity is attributed to the large two-photon absorption cross-sections and the efficient electron-transfer mediated initiation of the polymerization by the D-it-D chromophores. A three-dimensional test-structure was used to evaluate how varying the intensity and the exposure times affects the shape and dimensions of the polymerization volume element (voxel). Conditions were found for which the voxel could be as small as -200 nm in width and -700 nm in length, even though the wavelength of the two-photon excitation radiation was 775 nm.

Fabrication and Characterization of Two‐Photon Polymerized Features in Colloidal Crystals

“…1b) can be used to map the TPP response; [16,24,47,49,50,54,56,57] however, this is not suitable for operation in modulated beam rastering. Here, the subsequent lines and possibly scans overlap the same volume within a radical lifetime, (typical value range from~0.1 to 10 s).…”

Multiphoton Fabrication

“…As an example, equal parts of the alkoxylated trifunctional acrylates (SR9008) and tris(2-hydroxyethyl)isocyanurate triacrylate (SR368) can be mixed with approximately 1 % w/w photoinitiator and then combined with a poly(styrene-co-acrylonitrile) polymer binder in a 3:1 ratio. [54,57,64,83] The binder is dissolved in dioxane and mixed with the monomers, after which the sample is cast. After the solvent evaporates, the resulting film is rigid, allowing structures such as links on a chain to be made without fear of the resin reflowing (Figure 3 d).…”

Fabrication and Characterization of Three-Dimensional Silver-Coated Polymeric Microstructures

“…The semisolid formulation used in this work is similar to one described by Cumpston et al [14] and Kuebler et al [15] but differs in two regards. First, bis(dimethylamino)benzophenone was used as the free-radical polymerization photoinitiator.…”

“…MPM based on photoinitiated crosslinking has been described in detail elsewhere. [4,14,15] Ultrashort laser pulses are tightly focused into the volume of the resin. Multiphoton excitation occurring at the focal point initiates polymerization and crosslinking.…”