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The mechanical properties and the topological structure of cross-sections found in Cybister elytra are presented. SEM images show the similar geometric structure in transverse and longitudinal sections. Elytra consist of several layers: a dense, black epicuticle, an exocuticle that is braided by several parallel chitin fiber layers in a helix structure, and many bridge piers formed by the fiber bundles that connect the exocuticle to the endodermis, forming a composite, light-weight biomaterial. The mechanical properties along the edge of elytra are measured using a nano-indenter. The hardness and modulus of fresh cybister elytra is 0.31 GPa and 6.13 GPa, respectively. The ultimate stresses of fresh elytra, measured by using a tensile test machine, are 169.2 MPa and 194.5 MPa in the transverse and longitudinal directions, respectively, which is twice higher than that of the dried one. The difference in the two directions indicates that this bio-material has been topologically optimized during evolution. The results may provide a biological template to inspire lightweight structure design for aerospace engineering. elytra, morphology, mechanical properties, light-weight structure, tensile test Citation:Yang Z X, Dai Z D, Guo C. Morphology and mechanical properties of Cybister elytra.

Metal halide perovskites have attracted great attention for their superior light energy conversion applications. Herein, we demonstrated a facile synthesis of zero-dimensional Sn2+ perovskite Cs4–x M x SnBr6(M = K+ and Rb+) material through the cation transformation reaction at room temperature. Cs4SnBr6 NCs was mixed with pure metal bromide salts (KBr and RbBr) via the mechanochemical process to successfully synthesize Cs4–x M x SnBr6 perovskite where transformation of Cs to mixed Cs/Rb and mixed Cs/K was achieved. By substituting different cations, the bright fluorescence of the Cs4–x M x SnBr6 was tuned from dim green to greenish-cyan while achieving the photoluminescence (PL) quantum yield of ∼39%. The crystal structure of Sn based perovskite with the substitution of K+ or Rb+ cations was determined by X-ray diffraction (XRD). Moreover, the Cs4–x M x SnBr6 demonstrated superior air stability and exhibited a better photocatalytic activity for CO2 reduction reaction (CO2RR) with high selectivity of CH4 gas with a higher yield rate compared to the pristine Cs4SnBr6 NCs.

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