Hybrid hierarchical nanolattices with porous platinum coating

Nanolattices, defined as lattice structures composed of nanometer-sized building blocks, exhibit a wide range of unique properties and represent a new and rapidly growing class of mechanical metamaterials. In this work, we fabricated a core-shell polymer-platinum nanolattice by combining several fabrication techniques. The CAD-designed polymer nanolattices were fabricated by a two-photon lithography technique to achieve the required architecture. The lattices were then coated with a thin film of platinum using the atomic layer deposition (ALD) method. The unique interaction of the gaseous ALD precursor with the polymer surface resulted in a porous nanogranular film, providing a structural hierarchy ranging from the micrometer-size overall dimensions down to the microstructural features of a few nanometers. The nanoporous structure of platinum coating caused its creep-like shrinkage and buckling of the polymer struts during the initial stages of platinum ALD, thus weakening the whole structure. Increasing the thickness of the platinum layer eliminated the porosity and strengthened the lattices, indicating the load-bearing capacity of the architected platinum coating. The yield stress of platinum coating estimated from the results of microcompression tests was comparable to the yield stress of annealed bulk platinum and much lower than the flow stress of solid nanocrystalline platinum nanopillars.