Ceramic nanolattices hold up under pressure

Apply a large enough stress to a piece of brittle material, and it will break—most likely at a preexisting flaw or weak spot. 

The larger the piece of material, the more likely it is to contain a large flaw, and the less likely it is to withstand a large stress. In contrast, nanoscale samples of single crystalline materials can be much stronger than their bulk counterparts, even if they do contain flaws. Although the reasons for that size effect are not entirely clear, Julia Greer (Caltech) and colleagues have now taken the first steps toward exploiting it to create strong, lightweight metamaterials. Using two-photon lithography, Greer and colleagues produced polymer scaffolds with various geometries. They then coated the scaffolds with an 80-nm-thick layer of titanium nitride, a brittle ceramic. Etching away the polymer left them with nanolattices, such as the one shown in the figure, made of hollow TiN tubes. When deformed, the lattices exhibited a tensile strength of 1.75 GPa, close to the theoretical limit for TiN (estimated to be 3.27 GPa) and orders of magnitude higher than for typical bulk TiN samples. And unlike bulk TiN, the lattices couldbend without breaking and spring back nearly to their original shape, even after 30 cycles of deformation. But don't look for products made of TiN lattices any time soon: The researchers' two-photon-lithography fabrication technique doesn't lend itself to mass production.