Extended Data Fig. 1: Surface morphology of microstructures assembled from TiO₂ nanoparticles and Fe₃O₄ nanoparticles with different size distribution.

a, SEM image (left) of the zoomed-in surface of the alphabet letter ‘E’ assembled from Fe₃O₄ nanoparticles (NPs) with a uniform size distribution (16.7 ± 2.3 nm) and TEM image (right) of the corresponding NPs. b, SEM image (left) of the zoomed-in surface of a cylinder assembled from TiO₂ NPs with a size distribution of 90.2 ± 15.8 nm and TEM image (right) of the corresponding NPs. c, SEM image (left) of the zoomed-in surface of a microcube assembled from Fe₃O₄ NPs with a broad size distribution (194.9 ± 103.2 nm) and SEM image (right) of the corresponding NPs.