Hyper-Rayleigh Scattering from Gold Nanorods

The first hyperpolarizability of gold nanorods with dimensions 64 × 24 × 24 nm3 is determined by hyper-Rayleigh scattering (HRS) at the fundamental wavelength of 784 nm. For cetyltrimethylammonium bromide (CTAB)-capped nanorods in aqueous solutions, the measured value is βAu–CTAB = (0.88 ± 0.02) × 10–24 esu. For the same nanorods after phase transfer into chloroform with replacement of the CTAB capping layer by a dodecanethiol or an octadecanethiol layer, the measured value is only βAu–C12 = (0.22 ± 0.02) × 10–24 esu and βAu–C18 = (0.20 ± 0.02) × 10–24 esu using the newly determined water hyperpolarizability reference of β = 0.087 × 10–30 esu. In both cases, it is demonstrated through polarization-resolved HRS that the major contribution to the SHG response from these centrosymmetric nanoparticles stems from the surface as a breaking of the centrosymmetry, similarly to what is observed for gold nanospheres. Besides, the reduced hyperpolarizability measured for the gold nanorods with the thioalkane capping...