Nanocrystal arrested precipitation in supercritical carbon dioxide

Fluorocarbon-coated silver, iridium, and platinum nanocrystals ranging in s ize from 20 to 120 Angstrom in diameter are synthesized in supercritical (s c)-CO2 by arrested precipitation from soluble organometallic precursors. Th e synthesis is performed in single CO2 phase by reduction with H-2 at eleva ted temperatures ranging from 60 to 100 degreesC. Precursor degradation and particle nucleation occur in the presence of stabilizing perfluoro-octanet hiol ligands, which bind to the surface of the metal agglomerates and quenc h particle growth. The ligands are sufficiently solvated by CO2 to provide a steric barrier to uncontrollable aggregation during synthesis. The partic les redisperse in acetone and fluorinated solvents. The dominant mechanism to particle growth is through cluster agglomeration followed by ligand pass ivation, leading to self-similar size distributions with a standard deviati on of +/- 47%. Additionally, the nanocrystal size is tunable with precursor concentration, with higher precursor loadings resulting in larger nanocrys tal sizes.