Gold tip formation on perpendicularly aligned semiconductor nanorod assemblies

A facile spin-casting 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 occurring with variations in precursor concentration. HRTEM shows that the gold tip growth does not always occur centrosymmetrically on the nanorods, with growth occurring 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 characterised by photoluminescence spectroscopy.