Germanium Nanowire Synthesis from Fluorothiolate-Capped Gold Nanoparticles in Supercritical Carbon Dioxide

Ge nanowires seeded from Au nanoparticles capped with fluorothiolate ligands were synthesized in supercritical carbon dioxide (sc-CO2) by the thermal decomposition of diphenylgermane (DPG) at a temperature of 380 degrees C and a pressure of 25.7 MPa. Both perfluorinated and semifluorinated capped Au nanoparticles acted as effective catalysts for growing Ge nanowires, with mean diameters of 11 nm (sigma = 2.8) and 14 nm (sigma = 3.5), respectively. The mean diameter of the Ge nanowires grown from the fluorous-capped Au nanoparticles were considerably smaller than those synthesized from dodecanethiol-capped nanoparticles in se-toluene, under the same reaction conditions, i.e., 28 nm and sigma = 10.3. Differences in the ligand conformations on the surface of the Au nanoparticles and phase separation of the fluorocarbon/CO2 and hydrocarbon/toluene systems gave rise to greater steric stabilization of the fluorous-capped Au nanoparticles in CO2, resulting in small diameter nanowires with a relatively narrow size distribution. Electrical analysis of the nanowires showed them to be p-type (hole) semiconductors.