Zhang et al. Nanoscale Research Letters 2012, 7:312 http://www.nanoscalereslett.com/content/7/1/312 Page 4 of 6 Figure 3 Synthetic procedure and TEM images and size distribution of Pd NPs. (a) Schematic illustration of the synthetic procedure used for the preparation of monodisperse Pd NPs with different sizes by stepwise seed-mediated solvothermal growth. TEM images of Pd NPs prepared after the first (b), second (c) and third growths (d). as ‘artificial atoms’ as they can exhibit atomic-like beha- viors [25,26]. Just as commonly observed in the fcc metal nanocrystals, {111} surface was often exposed to minimize the total surface energy. In the present case, the {111} surfaces were also exposed in this concept; thus, the predominate morphologies were octahedron or distorted octahedron. The fcc structure was further proved in the TEM ana- lysis. Figure 5a shows the TEM image of one typical superlattice crystals. Figure 5b is an enlarged TEM Figure 4 Typical SEM image of the 3-D superlattice of Pd NPs. (a) SEM image of superlattice crystals formed by as-prepared Pd NPs with the size of about 8 nm, (b) single superlattice crystal with octahedron shape, (c) exposed surfaces arranged by close-packed nanocrystals, (d) magnified step surface.