Synthesis and optical characterization of submicrometer gold nanotubes grown on goethite rods

Goethite (FeOOH) rods were used as templates for growing gold nanotubes with it length of a few hundred nanometers and an aspect ratio between 3 and 4. Successful uniform growth required surface modification, followed by the attachment of small Aft seeds and one-step seeded growth using formaldehyde as a reducing agent, as previously reported for the growth of Aft shells on silica spheres and hematite spindles. The thickness and Surface roughness of the obtained shells Could be adjusted by simply varying the concentration ratio between seeds (modified goethite rods) and growth reagents (HAuCl4 and formaldehyde). The morphology of the synthesized gold nanotubes was thoroughly characterized by TEM, SEM, and AFM/MFM. The resulting gold nanotubes display well-defined plasmon resonances, with a strong longitudinal mode centered around ca. 1400 nm and if broad band in the visible resulting from the overlap of a transverse mode and if multipolar mode, its wits found from theoretical modeling' using the boundary element method, which provides reasonable agreement with the experimental results.