1. Crystal α-Si 3 N 4 / Si-SiO x core-shell / Au-SiO x peapod-like axial triple heterostructure Tian-Xiao Nie, †, ‡ Zhi-Gang Chen, ‡ Yue-Qin Wu, † Yanan Guo, ‡ Jiu-Zhan Zhang, † Yong-Liang Fan, † Xin-Ju Yang, † Zui-Min Jiang *, † and Jin Zou *, ‡ † State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China, and ‡ Materials Engineering and Centre for Microscopy and Microanalysis, The University of Queensland, QLD 4072, Australia * Corresponding authors. (Z. M. J.) E-mail: zmjiang@fudan.edu.cn. (J. Z.) E-mail: j.zou@uq.edu.au.zmjiang@fudan.edu.cnj.zou@uq.edu.au Structural schematic illustration of as- grown sample grown by sputtering system Introduction Morphologies of synthesized heterostructure nanowires Microstructure of synthesized heterostructure nanowires Photoluminescence property Conclusions  Novel crystal α-Si 3 N 4 / Si-SiO x core-shell / Au-SiO x peapod-like axial triple heterostructure nanowires were successful synthesized in bulk quantities.  A temperature dependent multi-step vapor-liquid-solid growth mechanism is proposed to explain the growth of the heterostructure nanowires.  The blue and green luminescence was observed, which could be attributed to the defect center emission in the Si 3 N 4 segment of the heterostructure nanowire. Mechanism proposed Comparative experiments to confirm the formation process of different segments (a)-(c) Typical SEM images of the synthesized nanowires, some nanoparticles embedded in the nanowires, indexed by the arrow. PL spectrum taken from the Si 3 N 4 segment of individual heterostructure nanowire. Its optical image is shown in the inset. Schematic illustration of heterostructure nanowire growth mechanism: (a)-(f) the evolution of the heterostructure nanowires, from the beginning formation of Au alloy droplets to the final formation of heterostructure nanowires. (a) Low-resolution TEM image of single nanowire showing three distinct segments. (b)-(c) Magnified TEM images of the distinct segments. (a)-(c) HAADF images of different segments in the heterostructure nanowire. (d)-(f) The corresponding compositional analysis by EDS. (a), (b) HRTEM image and SAED pattern of the straight segment in the heterostructure nanowire, showing it is α-Si 3 N 4 and [101] growth direction. (c), (d) TEM and HRTEM images of a joint connecting the core-shell segment and the crystalline α-Si 3 N 4 segment. (e), (f) TEM and HRTEM images of the Au-SiO x peapod-like segment. (a), (c), (e) XTEM images of the as-grown Au covered SiO 2 thin film Si substrate with different thickness. (b), (d), (f) The XEM images of the corresponding post-annealing samples at 1200 ºC. Oxide-assisted growth (OAG) mechanism (a) XTEM image of the Au covered 100 nm thick SiO 2 film sample after annealing at 1150 ºC. (b) BEI image of a single nanowire. (c) TEM image of an Au silicide cylinder sheathed in SiO x nanowire matrix. (d) TEM image showing periodic Au nanoparticles with a tiny Au cylinder on the tip.. 1. Formation process of α-Si 3 N 4 segment 2. Formation process of core-shell segment 3. Formation process of Au-SiO x peapod-like segment.  The potential ability of the nanowires can be enhanced by introducing heterostructures to fabricate novel multifunctional devices, and significant advances have been made on the synthesis of axial and radial heterostructure nanowires.  Therefore, it is necessary to search for a simple method to synthesize multi-segment heterostructure nanowires in large quantities.  Si 3 N 4 nanowires are used in composites due to their good resistance to thermal shock and oxidation, high fracture toughness and high module.  In this report, we present a simple and fast synthesis method for self- assembly producing novel crystal α-Si 3 N 4 / Si-SiO x core-shell / Au- SiO x peapod-like axial triple heterostructure nanowire in bulk quantities.