We investigate a novel scheme for brilliant attosecond γ-ray emission and high-yield positron production, which is accomplished with an ultra-intense laser pulse incident upon a Nano-Micro array (NMA) with substrate incorporated. This scheme is able to realize effectively electron acceleration and collid ing geometry. Both the γ-ray flash and positron bunch are then generated with high conversion efficiency. At laser intensity of 8 × 10 23 W/cm 2 , ~27% of the laser energy is transferred successfully into the γ-rays, and ~0.7% of the laser energy into the positrons. As a consequence, ultra-short (~440 as) and ultra-brilliant (~10 24 photons s −1 mm −2 mrad −2 per 0.1%BW @ 15 MeV) γ-ray burst, and high-yield (1.48 × 10 11 ) and overdense (~10 22 cm −3 ) positron bunch are generated. We found a sub-linear scaling of laser-to-photon conversion efficiency (∝ 𝐼 0 0.75 ) and a super-linear scaling of laser-to-positron conversion efficiency ( ∝ 𝐼 0 2.5 ) with the laser intensity.Multi-dimensional particle-in-cell simulat ions show that particle (γ photon and positron) generation can be manipulated by laser-focusing position, and NMA's length and spacing.Optimal conditions for particle generation in NMAs are obtained, indicat ing that micro wire array has the advantage over nanowire array in particle generation in the extreme laser fields. Furthermore, positron annihilat ion effect in high-energy-density (HED) environ ment is discussed. The scheme using NMAs would provide effective avenues toward investigating attosecond nuclear science and HED physics with the coming 10 PW laser facilities.

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