Phase-Dependent Mechanical Stability of 3D Zirconia Microstructures

In the past decade, significant progress has been made in the three-dimensional (3D) structuring of different classes of materials on the microscale. Direct laser writing (DLW) permits unprecedented shape control and resolution among the additive manufacturing approaches. One of the viable routes focuses on the surface functionalization of the 3D structures, e.g., via electroplating^[1] or atomic layer deposition^[2], which can be combined with other processes for the removal of the polymeric core to obtain hollow architectures. Alternatively, solid-beam structures can be formed via tailor-made solutions enabling the fabrication of solid-beam structures composed of materials other than solely organic polymers have been extensively studied. The recent endeavors resulted in several tailor-made solutions extending the range of materials that can be 3D-printed to metals (e.g., Ni^[3]), ceramics (e.g., ZnO,^[4] TiO₂^[5]), and composites (Au nanoparticle-laden polymer^[6]). From the perspective of mechanical stability, such materials often exhibit excellent chemical, mechanical and physicochemical stability when compared with polymeric materials.<br/><br/>In this study, we investigate the additive manufacturing of microscale 3D zirconia structures and the dependence of their mechanical stability on the crystallographic phase. We are using our previously-established method,^[7] we first pattern pre-ceramic structures, which transform into the self-miniaturized ceramic replicas upon the annealing in the air. We then modify the photoresin composition to improve the material performance under extreme stresses. The <i>in situ</i> nanomechanical material performance is assessed in a nanoindentation study for different 3D architectures and crystallographic phases of zirconia. Focused ion beam tomography is conducted better to understand the inner structure of the 3D materials. Besides, the additional focus is dedicated to precisely determining the crystallographic phase (X-ray powder diffraction, Raman Spectroscopy), chemical composition (X-Ray photoelectron spectroscopy), and defects of the materials (Cathodoluminescence) to better understand the opportunities and current limitations of the presented methodology.<br/><br/>The capability of our additive manufacturing methodology is presented with various 3D lattice structures of micro-to-nano feature sizes. Besides the sole focus on improving the material and structure performance under high strains, our methodology can be utilized to fabricate phosphors,^[7] which can in the future find applications in, e.g., 3D light-emitting devices.<br/><br/><b>Keywords: </b>additive manufacturing, zirconia, direct laser writing, nanoindentation.<br/><br/><b>References:</b><br/>[1] G. Williams, M. Hunt, B. Boehm, A. May, M. Taverne, D. Ho, S. Giblin, D. Read, J. Rarity, R. Allenspach, S. Ladak, <i>Nano Res.</i> <b>2018</b>, <i>11</i>, 845.<br/>[2] D. Jang, L. R. Meza, F. Greer, J. R. Greer, <i>Nat. Mater.</i> <b>2013</b>, <i>12</i>, 893.<br/>[3] A. Vyatskikh, S. Delalande, A. Kudo, X. Zhang, C. M. Portela, J. R. Greer, <i>Nat. Commun.</i> <b>2018</b>, <i>9</i>, 593.<br/>[4] D. W. Yee, M. L. Lifson, B. W. Edwards, J. R. Greer, <i>Adv. Mater.</i> <b>2019</b>, <i>31</i>, 1901345.<br/>[5] A. Vyatskikh, R. C. Ng, B. Edwards, R. M. Briggs, J. R. Greer, <i>Nano Lett.</i> <b>2020</b>, <i>20</i>, 3513.<br/>[6] Q. Hu, X. Z. Sun, C. D. J. Parmenter, M. W. Fay, E. F. Smith, G. A. Rance, Y. He, F. Zhang, Y. Liu, D. Irvine, C. Tuck, R. Hague, R. Wildman, <i>Sci. Rep.</i> <b>2017</b>, <i>7</i>, 17150.<br/>[7] J. Winczewski, M. Herrera, C. Cabriel, I. Izeddin, S. Gabel, B. Merle, A. Susarrey Arce, H. Gardeniers, <i>Adv. Opt. Mater.</i> <b>2022</b>, DOI 10.1002/adom.202102758.