@article {252426,
	title = { Tetrahedral colloidal clusters from random parking of bidisperse spheres },
	journal = {Physical Review Letters},
	volume = {110},
	number = {14},
	year = {2013},
	note = {See also the commentary by Mike Cates in the Journal Club for Condensed Matter Physics
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	pages = {148303},
	abstract = {Using experiments and simulations, we investigate the clusters that form when colloidal spheres stick irreversibly to{\textemdash}or {\textquotedblleft}park{\textquotedblright} on{\textemdash}smaller spheres. We use either oppositely charged particles or particles labeled with complementary DNA sequences, and we vary the ratio α of large to small sphere radii. Once bound, the large spheres cannot rearrange, and thus the clusters do not form dense or symmetric packings. Nevertheless, this stochastic aggregation process yields a remarkably narrow distribution of clusters with nearly 90\% tetrahedra at α=2.45. The high yield of tetrahedra, which reaches 100\% in simulations at α=2.41, arises not simply because of packing constraints, but also because of the existence of a long-time lower bound that we call the {\textquotedblleft}minimum parking{\textquotedblright} number. We derive this lower bound from solutions to the classic mathematical problem of spherical covering, and we show that there is a critical size ratio αc=(1+√2)≈2.41, close to the observed point of maximum yield, where the lower bound equals the upper bound set by packing constraints. The emergence of a critical value in a random aggregation process offers a robust method to assemble uniform clusters for a variety of applications, including metamaterials.},
	url = {http://dx.doi.org/10.1103/PhysRevLett.110.148303},
	author = {Schade, Nicholas B. and Holmes-Cerfon, Miranda C. and Elizabeth R. Chen and Aronzon, Dina and Jesse W. Collins and Fan, Jonathan A. and Capasso, Federico and Vinothan N. Manoharan}
}
