Figure 3.

a SEM secondary electron image (SEI) of titanium oxide nanoparticles assembled as nano-chain aggregate (NCA) in sample 2, b magnified from square region in (a) showing equiaxed nanoparticles more or less in coalescence, c histogram about the size distribution of the titanium oxide nanoparticles. d SEI of titanium oxide microtubes in sample 4 which were entangled, bifurcated at triple junction, and formed necks between the adjoined segments as magnified in (e), f histogram about the diameter distribution of the microtubes