Fig. 2

TEM images of Au-Ni (a), Au (b), pure HNTs (c), HNTs@Fe₃O₄ (d), HNTs@Fe₃O₄@Au (e), HNTs@Fe₃O₄@Au-Ni (f), and the EDX spectrum of pure HNTs (g), HNTs@Fe₃O₄@Au (h) and HNTs@Fe₃O₄@Au-Ni (i); inset pictures of a and e are the HRTEM images of the Au-Ni and Au NPs