title: Synthesis of germanium nanocrystals in high temperature supercritical CO(2).
abstract: Germanium nanocrystals were synthesized in supercritical (sc) CO(2) by thermolysis of diphenylgermane (DPG) or tetraethylgermane (TEG) with octanol as a capping ligand at 500 °C and 27.6 MPa. The Ge nanocrystals were characterized with high resolution transmission electron microscopy (HRTEM), energy-dispersive x-ray spectroscopy (EDS), and x-ray diffraction (XRD). On the basis of TEM, the mean diameters of the nanocrystals made from DPG and TEG were 10.1 and 5.6 nm, respectively. The synthesis in sc-CO(2) produced much less organic contamination compared with similar reactions in organic supercritical fluids. When the same reaction of DPG with octanol was performed in the gas phase without CO(2) present, bulk Ge crystals were formed instead of nanocrystals. Thus, the solvation of the hydrocarbon ligands by CO(2) was sufficient to provide steric stabilization. The presence of steric stabilization in CO(2) at a reduced temperature of 2.5, with a reduced solvent density of only 0.4, may be attributed to a reduction in the differences between ligand-ligand interactions and ligand-CO(2) interactions relative to thermal energy.
authors: Department of Chemical Engineering, Texas Materials Institute, and Center for Nano- and Molecular Science and Technology, The University of Texas at Austin, Austin, TX 78712, USA.
authors: Xianmao
authors: X
authors: Lu
authors: Brian A
authors: BA
authors: Korgel
authors: Keith P
authors: KP
authors: Johnston