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Bulk Cu foils have been synthesized via magnetron sputtering with an average twin spacing of 5 nm⁠. Twin interfaces are of {111} type and normal to the growth direction. Growth twins with such high twin density and preferred orientation have never been observed in elemental metals. These Cu foils exhibited tensile strengths of 1.2 GPa⁠, a factor of 3 higher than that reported earlier for nanocrystalline Cu, average uniform elongation of 1%–2%, and ductile dimple fracture surfaces. This work provides a route for the synthesis of ultrahigh-strength, ductile pure metals via control of twin spacing and twin orientation in vapor-deposited materials.

It is well known that the mechanical strength of metallic materials can be enhanced by confinement of dislocation activities with imperfections such as grain boundaries. For example, the strength of single-phase metallic materials with equiaxed grains can be increased by an …