We present the formation of periodic ripples in ZnO crystal irradiated by a wavelength-tunable femtosecond laser. The results indicate that in the surface thin layer, the periods change from 0.1 lambda to lambda with laser fluences and pulse numbers, and in the subsurface layer the periods are always lambda/2n, where n is the refractive index. The formation processes and mechanisms are also discussed.

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High-performance self-supported Co–N-doped carbon electrocatalyst for ORR with comparable activity to Pt/C in both acidic and alkaline media was prepared.

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