Fig. 1 Schematic of the furnace system used for the synthesis of SnO2 nanowires

Fig. 2 SEM images of tin dioxides grown under different conditions: a SnO2 heterostructure grown on a substrate with 0.5 mm height and 25-nm gold layer, where inset a1 is for the nanowalls formed in 2 h and inset a2 is for nanowires grown after 2 h; b SnO2 nanowires grown on a substrate with 0.5 mm height and 12.5-nm gold layer, and the inset is the tip of the nanowires; c SnO2 whiskers grown on a substrate with 3 mm height and 12.5-nm gold layer, and the inset is the tip of the whiskers

Fig. 3 EDX patterns of the seed part of nanowires a and the body of nanowires b; the peak of the silicon comes from the substrate

Fig. 4 XRD pattern of tin dioxide nanowires

Fig. 5 Schematic diagrams for the growth of SnO2 nanowalls: a gold dropped on a substrate by sputter coating; b Au-Sn alloy belts formed through shirking at 1000 °C; c nanowalls grown from the “rallying points” and the alloy on the top gradually shirked to points for nanowire growth; d nanowires grown on the top of nanowalls

Fig. 6 High magnification a and low magnification b SEM images of the cross sections of the whiskers

Fig. 7 XRD pattern of a core-shell whiskers specimen

Fig. 8 EDX pattern scanned for full scale of a whisker specimen along its cross section