The rich and complex arrangements of metal atoms in high‐index metal facets afford appealing physical and chemical properties, which attracts extensive research interest in material science for the applications in catalysis and surface chemistry. However, it is still a challenge to prepare large‐area high‐index single crystals in a controllable and cost‐efficient manner. Herein, entire commercially available decimeter‐sized polycrystalline Cu foils are successfully transformed into single crystals with a series of high‐index facets, relying on a strain‐engineered anomalous grain growth technique. The introduction of a moderate thermal‐contact stress upon the Cu foil during the annealing leads to the formation of high‐index grains dominated by the thermal strain of the Cu foils, rather than the (111) surface driven by the surface energy. Besides, the designed static gradient of the temperature enables the as‐formed high‐index grain seed to expand throughout the entire Cu foil. The as‐received high‐index Cu foils can serve as the templates for producing high‐index single‐crystal Cu‐based alloys. This work provides an appealing material basis for the epitaxial growth of 2D materials, and the applications that require the unique surface structures of high‐index metal foils and their alloys.
We study the roles of graphene acting as a buffer layer for growth of an AlN film on a sapphire substrate. Graphene can reduce the density of AlN nuclei but increase the growth rate for an individual nucleus at the initial growth stage. This can lead to the reduction of threading dislocations evolved at the coalescence boundaries. The graphene interlayer also weakens the interaction between AlN and sapphire and accommodates their large mismatch in the lattice and thermal expansion coefficients; thus, the compressive strain in AlN and the tensile strain in sapphire are largely relaxed. The effective relaxation of strain further leads to a low density of defects in the AlN films. These findings reveal the roles of graphene in III-nitride growth and offer valuable insights into the efficient applications of graphene in the light-emitting diode industry.
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