Gold tip formation on perpendicularly aligned semiconductor nanorod assemblies

A facile spin cast process is used for the instantaneous asymmetric formation of gold tips on perpendicularly aligned CdS nanorod superlattices. Tip size varies as a function of precursor solution concentration and growth time. A single uniform tip occurs on the end facets of each nanorod in the array when an optimised gold chloride solution is used, with multiple tipping 10 occuring with variations in precursor concentration. HRTEM shows that the gold tip growth does not always occur centro-symmetrically on the nanorods, with growth occuring on the (101) or the (001) facet of the wurtzite nanocrystal depending on the rod shape. X-ray diffraction confirms that the gold tips are crystalline with a 60% lattice mismatch with the wurtzite CdS nanocrystal suggesting strain relief may be a factor in tip formation. The gold tipped nanorods are further 15 characterised by photoluminescence spectroscopy.