Influence of Beam Size, Landing Energy, and Charging Effects on the Apparent Diameter of Substrate-Supported Single-Walled Carbon Nanotubes in Scanning Electron Microscopy Imaging

Due to the apparent width/diameter broadening common for sub-10 nm features, scanning electron microscopy faces many challenges for nanometrology in silicon-based and emerging carbon nanotube (CNT)-based technologies. The influence of beam size (σbeam), landing energy (LE), and charging on the apparent diameter of CNTs (WCNT) is investigated here. Experiments show WCNT increases with increasing σbeam, decreases with increasing LE, and shows little variation between conductive Si and insulating SiO2/Si substrates. Monte Carlo simulations show WCNT remains unchanged with σbeam smaller than ∼1/6 of CNT diameters (dCNT) but begins to increase once σbeam becomes larger, and WCNT varies little with increasing LE if σbeam is fixed. These results suggest (1) σbeam is decisive in the WCNT broadening; (2) the effect of LE is attributed to the change in σbeam instead of the width of interaction volume; and (3) the contribution of charging is minimal with the contrast separation method. We also notice that increasing the LE beyond 3 keV makes CNT almost invisible. This is attributed to the too-small ratio of electron–CNT interaction volume to the electron–substrate interaction volume. Testing LEs ranging from 0.3 to 10 keV, we find optimal balancing of WCNT and visibility in the 0.5–1.0 keV range.