In Situ Atomic Force Microscopy Tip-Induced Deformations and Raman Spectroscopy Characterization of Single-Wall Carbon Nanotubes

Abstract

In this work, an atomic force microscope (AFM) is combined with a confocal Raman spectroscopy setup to follow in situ the evolution of the G-band feature of isolated single-wall carbon nanotubes (SWNTs) under transverse deformation. The SWNTs are pressed by a gold AFM tip against the substrate where they are sitting. From eight deformed SWNTs, five exhibit an overall decrease in the Raman signal intensity, while three exhibit vibrational changes related to the circumferential symmetry breaking. Our results reveal chirality dependent effects, which are averaged out in SWNT bundle measurements, including a previously elusive mode symmetry breaking that is here explored using molecular dynamics calculations.

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“…This result is expected for chiral SWNTs, where the C-C bonds exhibit a helical structure, and the LO versus TO nature for the two G band peaks is indeed not expected. These results showed the richness of transversal deformation at the isolated SWNT level [81], which are averaged out on SWNT bundle measurements.…”

“…In achiral SWNTs, the G band splits into LO and TO modes, where longitudinal and transversal here stand for parallel and perpendicular to the tube axis. The experiments performed on isolated SWNTs [81] evidenced a previously elusive and fundamental symmetry-breaking effect for the totally symmetric TO G-band mode, which exhibited two distinct Raman-active features with increasing applied pressure. One of the features is related to atomic motion localized at the flattened regions, while the other feature is related to atomic motion localized at the curved regions of the ovalized SWNT.…”

“…Combination of AFM with confocal Raman spectroscopy was made to follow, in situ, the evolution of the SWNT structure with transversal pressure applied to the tube. The G band feature in isolated SWNTs deposited on a substrate was monitored while pressing the tube with the AFM tip [81].…”

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“…Araujo et al 54 used a home built system that combines AFM with confocal Raman spectroscopy to follow, in situ, the evolution with applied transversal pressure of the G-band feature in isolated SWNTs deposited on a substrate (see Fig. 3).…”

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“…3(d)]. The G (þ) mode is confined to the direction of the tube axis which makes it more insensitive to tube diameters' changes and less susceptible to bond hardenings due to hydrostatic pressures (provided that such pressures are much smaller than 1 GPa, which are the cases of small loads applied by AFM tips [54,55] and pressure naturally applied by the nanotubes environment [42e44], which explains the low frequency upshifts observed to this mode (see Fig. 3(c)).…”