LPD silica coating of individual single walled carbon nanotubes

Abstract

Single walled carbon nanotubes (SWNTs) have been coated with fluorine-doped silica by liquid phase deposition (LPD) using a silica-H 2 SiF 6 solution and a surfactant stabilized solution of SWNTs. The coating of individual SWNTs versus small ropes is controlled by the choice of surfactant. Since the LPD reaction is performed close to the isoelectric point of the silica, some of the SiO 2 -SWNTs are fused together but the SWNTs remain individual in these composite structures. The SiO 2 -SWNTs have been characterized by SEM, TEM, Raman and IR spectroscopy, and XPS. Raman fluoresence is maintained even with coatings .50 nm. Using the relative intensity of the Raman G peak and the 8,3 SWNT fluorescence as a convenient measure of bundling, it may be shown that any decrease of fluoresence during growth is not due to changes in ionic strength or pH, as a consequence of addition of the LPD solution or the presence of HF as a side product in the deposition. The Raman D and G modes show no change in intensity, while the Fano line increases, both suggesting that no sidewall functionalization or proton adsorption of the SWNTs occurs during coating. The UV-visible-near infrared spectra shows a red shift in the first Van Hove transitions of the coated SWNTs inferring that the SWNTs in SiO 2 -SWNTs are in a more polarizable and inhomogeneous environment than that of surfactant solutions. Mats of SiO 2 -SWNT may be deposited onto silicon and gold substrates and through lithography may be patterned by etching off selected areas of the silica coating.

Coating single-walled carbon nanotubes with cadmium chalcogenides

“…This comparison suggests that the presence of surfactant under high coating concentrations facilitates formation of CdSe colloids in a similar manner to that observed for the LPD of silica onto SWNTs in the presence of excess surfactant. 7,14 However, we note that unlike the silica system where spherical particles are formed when there is an excess of surfactant, the CdSe particles are formed irrespective of the surfactant : SWNT ratio but as a function of excess cadmium and selenium reagents. Furthermore, whereas the silica spheres show highly uniform size and shape, the CdSe particles are clearly agglomerates of smaller particles.…”

“…Our initial studies in this area concerned the formation of non-covalently attached silica coatings around individual SWNTs (SiO 2 -SWNTs). [5][6][7] Based upon these results we were interested in expanding the range of coating materials, in particular, the investigation of an analogous process for semiconductor materials such as cadmium chalcogenides (CdE where E 5 S, Se). We note there has been a recent report of coating multi-walled carbon nanotubes (MWNTs) with ZnS using a LPD process.…”

Fabrication of silica nanotubes using silica coated multi-walled carbon nanotubes as the template

“…In addition, (3) surfactants were employed to give negative or positive charges on CNTs and followed by the synthesis of silica onto surface of CNTs [12][13][14]. In most cases, a uniform silica layer on CNTs was not achieved, whereas dangling silica particles were adsorbed on CNTs, resulting in the incomplete coverage of the surface of CNTs by the silica layer.…”

New Route to Fluorescent Single-Walled Carbon Nanotube/Silica Nanocomposites: Balancing Fluorescence Intensity and Environmental Sensitivity

“…But, traditional sol-gel procedures 20 are performed in alcohol solvents at very acidic or basic pH conditions, which are conditions that can disrupt the SWNT/surfactant assembly resulting in bundling of nanotubes and loss of emission. Recently, our group 21 and others 22,23 have developed methods to make new SWNT/silica nanocomposites in which some of the intrinsic fluorescence from semiconducting SWNTs is maintained. Our work in particular has focused on making composites under biologically friendly conditions.…”