Electron Beam at Low Acceleration Voltage does not Damage Carbon Nanotube and Graphene

Abstract

Scanning electron microscope (SEM), offering both convenience and sub-nm lateral resolution, is a principal tool for studying nanomaterials below the Abbe’s diffraction limit. Imaging soft nanomaterials, including single walled carbon nanotubes (SWNTs) and graphene, is usually performed at low acceleration voltage. Imaging carbon nanomaterials in SEM, however, is known to increase the disorder mode (D-mode) in their Raman spectra. Earlier studies attributed the phenomenon to electron beam (e-beam)-induced structural damages to the materials under investigations, which can be recovered by thermal treatment. For more than a decade, researchers have accepted this conclusion without further verification. Here, we perform single-tube measurements and clearly demonstrate that the e-beam-induced D-mode in carbon nanomaterials can be restored chemically even at room temperature, and the e-beam-induced deposition (EBID) of hydrocarbon is not the main cause of the D-mode enhancement. For both SWNTs and graphene, e-beam-induced D-mode can be suppressed by removing amorphous carbon via heat treatment. These results strongly suggest that the e-beam-induced D-mode increase originates solely from the irradiated amorphous carbon, and not from the e-beam-induced structural damage to the carbon nanomaterials. Our study suggests that the notion that has long been accepted by the community needs to be reconsidered, and thus helps to study nanoscale phenomena in nanomaterials minimizing any potential ambiguities.