Three-dimensional metal micro- and nanostructures offer opportunities to develop multifunctional materials with unique combinations of material properties. Traditional strategies to improve the mechanical properties of materials consist of altering either the microstructure or the composition. Both strategies, albeit successful, tend to be rather incremental. The third approach is that of controlling not only the microstructure but also the architecture¹. By combining the effect of the architecture with the effect of the microstructure, architectured cellular materials with enhanced mechanical properties are achieved.

Modern templating techniques, including colloidal crystal lithography² and 3D laser lithography³, enable the creation of structures with well-defined sub-micron features. Used in combination with electrochemical routes, the deposition of nickel or copper micro-architectures is achieved with fine control of the microstructure and dimensions. Although electrodeposition is a well-established technique, metal electroforming of cellular micro-materials is demanding. Specific challenges include the electrodeposition onto non-conductive surfaces, adequate surface preparation, appropriate throwing power for electrolyte infiltration into submicron features or proper process optimization.

The present talk will cover our recent research activities on the fabrication of nickel and copper regular foams and micro-lattices synthesized by electrochemical processes aiming at achieving high strength and low density materials. Regular porous metal structures are produced by colloidal crystal templating of polystyrene (PS) microspheres. The PS templates are formed by sedimentation of PS microspheres. Under gravity and drying, the PS microspheres form a self-assembled multilayer with a face-centered cubic structure. The templating step is followed by either metal electrodeposition to obtain a metal inverse opal (Figure 1.a) or by electroless deposition of NiB to form a hollow-shell opal (Figure 1.b). The metallic micro-lattices (Figure 1.c) were fabricated by electroless deposition of NiB onto a surface-modified polymer template produced by 3D laser lithography. In situ micromechanical testing of these micro-architectures showed enhanced mechanical properties despite being low density. Increasing the metal coating in micro-lattices from 10 nm to 100 nm improve the mechanical performances by a factor of 3.5 while the density is only multiplied by 2.3.

References:

¹ M.F. Ashby, Philos. Trans. A. Math. Phys. Eng. Sci. 364, 15 (2006).

² A. Stein and R.C. Schroden, Solid State Mater. Sci. 5, 553 (2002).

³ J. Bauer, S. Hengsbach, I. Tesari, R. Schwaiger, and O. Kraft, Proc. Natl. Acad. Sci. U. S. A. 111, 1 (2014).