Syntheses and applications of one-dimensional nanomaterials
Hafner, Jason H.
Doctor of Philosophy
Reduced-temperature synthesis of single-wall carbon nanotubes (SWNTs) is of interest for their growth into device architectures and their efficient bulk production. For SWNT synthesis, a high vacuum reactor chamber is built, in which SWNTs are grown via the chemical vapor deposition (CVD) of low-pressure ethylene over iron particles supported on silicon wafers at temperatures down to 550°C. The grown SWNT structure and quality are confirmed by atomic force microscopy (AFM) and micro-Raman spectroscopy to be good quality. SWNT growth kinetics is briefly studied. The nucleation rate depends on the ethylene pressure, which indicates that the arrival of ethylene on the iron surface is the rate-limiting step. The structural and optical properties of gold nanorods suggest their potential uses for the biomedical sensing, imaging, and therapeutic applications. Gold nanorods have been stabilized, conjugated to antibodies, and characterized for biological applications. The stabilizing surfactant cetyltrimethylammonium bromide (CTAB) bilayer which surrounds gold nanorods is replaced by thiol terminated methoxypoly(ethylene glycol) so that the nanorods are stable in buffer solutions free of surfactant. Nanorod bioconjugation is accomplished with a heterobifunctional cross-linker, with antibody activity confirmed by a strip plate assay. The molar extinction coefficient for nanorod with l = 50 nm and d =15 nm is measured to be 4.4 +/- 0.5 x 109 M-1cm-1. Gold nanorod substrates have been fabricated for Localized Surface Plasmon Resonant (LSPR) biosensors. Nanorod shows Surface Plasmon Resonant sensitivity about 180 run per refractive index unit. With nanorod LSPR sensors, we measure the surface affinity constant for biotin-streptavidin interaction and the limit of detection about 0.2 nM of streptavidin. Nanorod growth kinetics has been investigated at the microscopic level. We have shown a simple spectroscopic method to determine the microscopic length and diameter of gold nanorods during synthesis. The temperature dependent growth rate indicates that the nanorod growth follows reaction-limited growth kinetics. We also study the gold nanorod growth mechanism on surface. There is a critical size for a particle to nucleate a nanorod. This critical size is same for surfactants with different chain length. The chain length does, however, affect the isometric growth rate, which is faster for the shorter chain.