NaCl-like crystals (space group F m3m, No. 225) were formed using 300 nm (+) PS and 130 nm (-) PS particles (β = 0.43) at a 1:1 number ratio. A precise size ratio of approximately √ 2 -1 is required to form NaCl crystals; otherwise, K 4 C 60 is typically observed. The Wulff shape of these crystals is a cube, bound by {100} planes (Extended Data Fig. ).