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Self-organization of highly ordered honeycomb buckling patterns in crystalline thin films

Highly ordered honeycomb buckling patterns were self-organized by a simple annealing process. The patterns were formed by thin, layered crystalline films of Al4C3 and carbon synthesized on a sapphire c-plane substrate by chemical vapor deposition. While annealing at 1000 °C, the thin bilayer film wrinkled and began to develop a two-dimensionally periodic pattern. Two patterns, with periodicities of 34 and 20 µm, were observed by two-dimensional fast Fourier transform (2D-FFT) analysis. Both patterns showed clear and sharp peaks at six orientations, corresponding to the vertices of a regular hexagon, similarly to the crystallinity of sapphire. Additionally, a shift of the Raman peak to a lower frequency was observed after annealing. These results reveal that the self-organization of a periodic buckling pattern is possible without complicated conventional lithography through the use of crystalline materials. Thus, the highly periodic hexagonal patterns obtained with thin crystal materials have a high symmetry, as characterized from 2D-FFT, and can be applied as an optical grating.