Figure 1
Phys. Rev. Lett. 93, 015502 (2004)

Shapely silicon. A clump of several hundred silicon atoms can form a not-quite-crystalline icosahedron, at least according to calculations (click image for larger version). Compared to the run-of-the-mill crystalline nanoparticle, the icosahedral particle could be a more useful light source or detector.