Here we describe a method to generate aligned single-walled carbon nanotube (SWNT) films over large-areas and to fabricate SWNT nanoprobes for atomic force microscopy (AFM) using the Langmuir-Blodgett (LB) technique. We synthesized thiophenyl-modified SWNTs through a method based on amidation of oxidized SWNTs. The resulting SWNTs were found to form stable colloidal suspensions in organic solvents such as chloroform, which was a suitable solvent for the LB application. The compression of the thiolphenyl-modified SWNTs spread onto the water surface of an LB trough leaded to a uniform SWNT Langmuir monolayer, where SWNTs were aligned parallel to the trough barrier. We also confirmed optical anisotropy of SWNT LB films transferred onto quartz substrates by polarized UV-vis/NIR spectroscopy studies and electrical property of SWNT LB films by I-V source measurement.
As a application of SWNT LB film, we fabricated SWNT-modified nanoprobes. This simple transfer process included two steps: 1) dipping conventional AFM probes into the Langmuir monolayer and 2) lifting the probes from the water surface. This results in the attachment of SWNTs onto the tips of AFM nanoprobes. We found that the SWNTs assembled on the nanoprobes were well oriented and robust enough to maintain their shape and direction even after successive scans. AFM measurements of a porous alumina substrate using SWNT-modified nanoprobes revealed that the curvature diameter of the nanoprobes was less than 3 nm, which is consistent with those determined directly by high-resolution transmission electron microscopy (HRTEM) measurements. Because of the sharpened tip end, we could obtain more distinct surface profiling with a fine resolution than that obtained from conventional AFM probes. We also demonstrate that the LB method is a scaleable process capable of simultaneously fabricating large-scale SWNT-modified nanoprobes.
