Nanoscale Ag2S Hollow Spheres and Ag2S Nanodiscs Assembled to Three-Dimensional Nanoparticle Superlattices

Nanoparticle superlattices are built up with Ag2S hollow spheres (outer diameter, 37 nm; wall thickness, 10 nm; inner cavity size, 17 nm) and Ag2S nanodiscs (diameter, 20 nm; thickness, 7 nm) as building blocks. Both types of Ag2S superstructures are formed via microemulsion-based synthesis, followed by a phase-separation reaction. The nanoparticle superlattices exhibit dimensions of 5-20 mu m. Herein, the Ag2S hollow spheres are arranged like a closest packing of hard spheres, whereas the Ag2S nanodiscs are stacked in parallel rows. Both as-prepared building blocks crystallize with the alpha-Ag2S/acanthite type of structure. The here described nanoparticle superlattices with nanoscale Ag2S hollow spheres are some of the first examples employing nanoscale hollow spheres (diameter <50 nm) as building blocks. The individual building blocks-hollow spheres and nanodiscs-and the nanoparticle superlattices are characterized by advanced electron microscopy (scanning electron microscopy, scanning transmission electron microscopy, and high-resolution transmission electron microscopy), dynamic light scattering, energy-dispersive X-rays, and X-ray diffraction.