Vapor-liquid-solid growth and properties of one dimensional PbO and PbO/SnO2 nanowires

PbO nanowires have been obtained via a self-catalysed, vapor-liquid-solid mechanism and the reaction of Pb with O-2 between 200 degrees C and 300 degrees C at 10 Pa. These had the form of tapes with a thickness of similar to 20 nm, a width of similar to 150 nm, and a length of up to similar to 100 mu m with a mixed orthorhombic and tetragonal crystal structure. The intermediate temperatures between 300 degrees C and 500 degrees C resulted in the formation of urchin-like structures but higher temperatures lead to a suppression of one-dimensional growth. We found that the morphology can be tuned in a reproducible way by adjusting the pressure, in which case we obtained two-dimensional plates at 1 kPa and spherical particles with diameters of similar to 1-10 mu m at 1 Pa for all temperatures between 100 degrees C and 500 degrees C. We did not obtain any PbO2 nanowires irrespective of the growth temperature and pressure but PbO nanowires were grown on SnO2 nanowires that were subsequently converted into PbO2/SnO2 branched nanowires, which are attractive for energy storage and the realization of advanced lead acid batteries. We describe in detail the properties of the PbO/SnO2 heterojunction by density functional theory calculations and show that it has a type II band line-up, which is also important for energy conversion, e.g. solar cells and photocatalysis.