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.