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John O | October 2018

Researchers develop method to produce defect-less metal crystals at unprecedented sizes

By Josh Perry, Editor


Researchers at the Institute for Basic Sciences (IBS) Center for Multidimensional Carbon Materials in Daejeon, South Korea developed a method for converting metal foils into single crystals of up to 32 square centimeters without grain boundaries (GB) that could limit the material properties.


(A) Schematic of the quartz holder that the copper (Cu) foil is suspended from, (B) photograph of the configuration shown schematically in (A). (C) Photograph of the annealed single crystal Cu foil (about 2 cm × 8 cm), next to a ruler. (D) X-ray diffraction (XRD) spectra of the three regions in the annealed single crystal Cu foil indicated by P1-P3 in (C).
(Institute for Basic Science)


According to a report from the institute, the single crystal metals, made from copper, nickel, cobalt, platinum, and palladium, have higher electrical conductivity and other properties that make them superior options for a range of applications.


Researchers, working at the Ulsan (South Korea) National Institute of Science and Technology (UNIST), created contact-free annealing (CFA) to grow the crystals without defects and at larger sizes than previously possible.


“CFA involves heating the polycrystalline metal foils to a temperature slightly below the melting point of each metal,” the report explained. “This new method does not need single crystal seeds or templates, which limit the maximum crystal size, and was tested with five different types of metal foils: copper, nickel, cobalt, platinum, and palladium. It resulted in a 'colossal grain growth', reaching up to 32 square centimeters for copper.”


Each metal had a unique experiment to achieve the crystals. Temperatures were varied and the techniques for creating crystals without grain boundaries varied, but all the metal crystals were larger than previous attempts. Copper was the largest and had the greatest enhancement in electrical properties, with a seven percent increase.


The research was recently published in Science. The abstract read:


“Single-crystal metals have unique properties due to the absence of grain boundaries and strong anisotropy. Commercial single-crystal metals are usually synthesized by bulk crystal growth or by deposition of thin films onto substrates, and they are expensive and small.


“We prepare extremely large single-crystal metal foils by ‘contact-free annealing’ from commercial polycrystalline foils.


“The colossal grain growth (up to 32 cm2) is achieved by minimizing contact stresses, resulting in a preferred in-plane and out-of-plane crystal orientation, and is driven by surface energy minimization during the rotation of the crystal lattice followed by ‘consumption’ of neighboring grains. Industrial scale production of single-crystal metal foils is possible from this discovery.”

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