Fig. 4

SEM images of the assembled structures prepared with spherical IONPs. a SEM image of the homogeneous film. b SEM image of the rod-shaped superstructures, with an inset of microscopic image. c Enlarged SEM image revealing the monolayer and superstructure. d Close-up SEM image and FFT pattern (inset) of the delineated region revealing the hexagonal packing of the nanoparticles