Quantitative analysis of the correlation between sp3 bonds and functional groups in covalently functionalized single-walled carbon nanotubes

Abstract

The potential of carbon nanotube (CNT)-based applications in diverse scientific fields has been demonstrated by achieving precise control of their surfaces through chemical functionalization. However, the formation of fatal defects like sidewall cleavage is an increasingly important concern as it significantly degrades the performance of CNTs. The presence of these structural disruptions has been ascertained by transmission electron microscopy, but a comprehensive understanding of their surface remains unclear due to its highly localized observation. Here, we demonstrate a framework for quantitative evaluation of the relationship between sp3 bonds and functional groups on CNT surface by combining μ-Raman and energy dispersive X-ray spectroscopy in scanning electron microscope imaging techniques. Nonuniform features of the degree of functionalization in strongly oxidized two types of single-walled CNTs are appropriately visualized in both measurements, allowing a systematic assessment of the surface states. Quantitative analysis reveals that the nm-scale sidewall openness during the chemical process is adequately explained by introducing a variable θ defined as the ratio of the degree of functionalization/defect density. These findings can be widely utilized as a novel evaluation technique to control the reactivity in the surface functionalization of various carbon nanomaterials.