Change of surface morphology and structure of multi-walled carbon nanotubes film caused by proton irradiation with 170Â keV

The effects of 170 keV proton irradiation for fluences of 5 × 1014 cm−2 and 5 × 1015 cm−2 on surface morphology and structure of multi-walled carbon nanotubes (MWCNTs) film were investigated. The pristine and irradiated MWCNTs films were characterized using scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy. SEM analysis reveals that the proton irradiation for the high fluence of 5 × 1015 cm−2 leads to evident changes in morphology of the MWCNTs film, such as forming uneven film surface, entanglement of nanotubes and the shrinkage of nanotubes. Based on Raman spectroscopic and XPS analyses, it is confirmed that the proton exposure can improve the structural quality of the MWCNTs, and irradiation fluence plays a key role in reducing the disorder of the MWCNTs. This phenomenon could be mainly attributed to restructuring of the defect sites induced by knock-on atom displacements. EPR spectroscopy shows that electrons delocalized over carbon nanotubes increase with increasing irradiation fluence, implying that the MWCNTs film might be sensitive to ionizing radiation to some extent.