(105b) Preparation of Monodisperse Silicon Nanocrystals Through Density-Gradient Ultracentrifugation In Organic Solvents

Monodisperse colloidal suspensions of ligand-stabilized silicon nanocrystals, synthesized through a nonthermal low-pressure plasma reaction, are prepared through density-gradient ultracentrifugation in mixed organic solvents. Density-gradient profiles of mixed chloroform and m-xylene are used to control the settling speed of the nanoparticles and hence optimize their transient separation by size along the depth of polyoxymethylene ultracentrifuge tubes. The mean size and polydispersity of the extracted fractions are characterized through photoluminescence spectroscopy and transmission electron microscopy, and the self-assembly of fractions into close-packed crystal lattices is achieved using an immiscible two-fluid evaporation scheme. The photophysical properties of the purified nanocrystal lattices are compared with those of the starting materials, and the influence of atmospheric oxygen and temperature on the stability of nanocrystal ensemble photoluminescence is measured. Supported by the DOE through DE-FG36-08GO88160.