The imaging mechanism of single-walled carbon nanotubes on Si/SiO₂ wafer in scanning electron microscopy

Abstract

Scanning electron microscopy imaging of both suspended single-walled carbon nanotubes (SWNTs) and contacted SWNTs with Si/SiO₂ substrate has been studied in this paper. The voltage contrast has been investigated by supplying external electric field around the samples. The results show that the image contrast of SWNTs attributes to both voltage contrast from the area surrounding SWNTs (tens of nanometres in both sides of the SWNTs) and electron beam induced emission from SWNTs themselves under low primary beam energy. Under high primary beam energy, however, EBIE dominates the image contrast due to the fact that the voltage contrast caused by implanted charges of the SiO₂ layer is weakened. Imaging under the primary beam energy lower than 1 keV offers widened diameter of SWNTs, which promises that the SWNTs are observable at very low magnification (lower than 100 ×). At a larger magnification, however, imaging under the primary beam energy higher than 10 keV can display more realistic images of the SWNTs. In addition, an appropriate external electric field can improve the images.