Quantitative Control over Electrodeposition of Silica Films onto Single-Walled Carbon Nanotube Surfaces

Control over the thickness of a silica coating on single-walled carbon nanotubes (SWNTs) is highly desirable for applications in optics and in biomedicine. Moreover, a silica coating on SWNTs would also aid in avoiding tube−tube contact and bundle formation as well as tube oxidation, a scenario conducive to the use of appropriately functionalized carbon nanotubes as individualized gate dielectric materials in field effect transistors. In this work, we have developed two feasible and reliable means with which to coat SWNTs with various reproducible thicknesses of silica using an electrochemical sol−gel process. In one procedure, a SWNT mat was used as a working electrode for the direct deposition of silica. In the second, nanotubes were dispersed in solution and silica was deposited onto these solubilized nanotubes in the presence of a platinum working electrode. Applying a negative potential results in the condensation of a silica film onto the SWNT surface. The thickness of the silica coating can be controllably altered by varying the potential of the working electrode as well as the concentration of the sol solution. These methodologies have the advantages of ease of use, environmental friendliness, and utilization of relatively mild reaction conditions.