| 초록 |
Raman spectroscopy is a simple, fast, and non-destructive technique to determine characteristics of structurally featuring crystalline and amorphous carbon phases, including the diameters and electronic types of individual SWCNTs. Raman spectra of graphite-like carbon materials show two prominent modes, G peak around 1500~1600 cm-1 and D peak around 1250~1450 cm-1. As suggested in many previous studies, the peak intensity ratio of the D- and G-bands can be dominantly used as a measure to quantify the relative SWCNT fraction and to evaluate the efficiency of purification. SWCNT soot produced by arc discharge contains a significant amount of impurities such as amorphous carbon nanoparticles and metallic catalyst particles mostly encapsulated by carbonaceous nanoparticles (mainly composed of a few graphene inner layers and a thick amorphous carbon outer layer), as well as SWCNTs. Most appropriate is the production of highly pure SWCNTs free of such impurities, but in reality always comes the invaluable together with dirt. In this study, the SWCNT soot produced by arc discharge was analyzed in a powder form by using Raman spectroscopy. Prior to analysis, the SWCNT soot was subject to ultrasonic homogenizing in ethanol to make sure of reliable spectra. The homogenized soot was analyzed in five different positions to obtain its overall property, which was expressed by a mean value and a standard deviation. We conducted temperature-controlled thermal oxidation (TTO) experiments at an incremental temperature interval to monitor the extent of the purification, which was indicated by variation of D-and G-bands. Upon the TTO experiments, the intensity ratio of D- and G-bands exponentially reduced at a higher oxidation temperature. This study also investigated the peak positions, line widths, and relative intensities of D, G-, and G+ peaks for a series of oxidized samples. Conclusively, a ratio of G- and G+ peak intensities seems to offer much information during thermal oxidation, compared to the intensity ratio of D- and G-bands. Other tools such as TGA are necessarily engaged as well, to confirm the validity of the Raman spectroscopy in the material assessment of SWCNT soot upon purification. |
