Growth of CdS nanowire crystals: Vapor-liquid-solid versus vapor-solid mechanisms

The difference in the growth conditions, crystalline structure and morphology of CdS nanowire crystals synthesized via the vapor-solid (VS) mechanism on bare substrates and via the vapor-liquid-solid (VLS) mechanism using gold catalyst, respectively, has been studied. It has been found that the growth of CdS nanowire crystals by the VS mechanism depends on the substrate material used and that the roughness of the substrate surface is also an important parameter influencing nucleation of CdS nanowires. The crystals obtained by VLS demonstrated perfect crystal plane orientation and the wurtzite crystallographic symmetry, whereas the crystals obtained by VS mechanism showed transition regions with more rich morphology resulting in changes of the crystalline plane orientation of the growing nanowire, as well as inhomogeneous stoichiometry along the crystal. The rich morphology was attributed to the competition of nucleation rates and growth rates among different crystallographic planes which may be affected by changes in temperature regimes of the growing zone.