Mechanical characterization of two-photon polymerization submicron features

Two-photon polymerization (TPP) is promising method for additively manufacturing nanoscale structures with complex geometries. For example, TPP has been used to fabricate very high strength-to-weight lattice structures that can be used in a variety of biomedical and aerospace applications. However, one of the major factors limiting TPP as a true manufacturing technique is the uncertainty in how printing parameters affect the mechanical properties of the materials produced at the voxel level. Therefore, the purpose of this thesis is to characterize the scale dependent effects of speed, power, and post curing methods on TPP resists. In order to achieve this purpose, a custom MEMS tensile tester was designed, fabricated, and calibrated for direct integration into the TPP process with resolution and range capable of measuring <200 nm wide voxel lines. Direct integration was accomplished by applying stiction constraints to the suspended elements and fabricating anti-stiction features under the device layer. The load and displacement stages were measured to have a 100 nN and 1.5 nm resolution, respectively, using digital image correlation. The MEMS tensile tester was used to determine the material properties of TPP voxels written at low and high speeds. High speed voxels were fabricated with line widths varying from 196 nm to 444 nm by increasing the laser power. Both speeds were post processed with three different curing methods. The improvement in elastic modulus from high speed to low speed writing was a determined to be factor of ~2.1. However, it was also found that a UV post cure with radical generators could be used to produce matching material properties between the two writing speeds. That trend is critical for being able to increase the throughput of TPP without scarifying the performance of the fabricated materials. Finally, a strong size effect was found in these TPP materials with a non-linear increase in the elastic modulus (from 3.92 – 6.54 GPa) occurring when the TPP line width was decreased from 444 nm to 196 nm for the UV with radicals post cure condition