Imaging mechanism of carbon nanotubes on insulating and conductive substrates using a scanning electron microscope

Carbon nanotubes (CNTs) were deposited on bare glass, Au (10 nm)/glass, and Au (50 nm)/glass substrates, and observed using a scanning electron microscope (SEM) operating at different accelerating voltages. Depending on the substrate and accelerating voltage, the CNTs exhibit different levels of contrast. On the poorly conductive glass and Au (10 nm)/glass substrates, electrons are supplied or dissipated through the networked CNTs. This generates a potential difference between the CNTs and the (insulating or poorly conductive) substrates. CNTs are visualized as a result of potential contrast. At a low accelerating voltage (1 kV), the substrate is of higher potential than that of the networked CNTs (the ground potential), and the CNTs exhibit bright contrast. At a high-accelerating voltage (5–10 kV), the potential of the substrate is lower than the networked CNTs, and the CNTs exhibit dark contrast. On the Au (50 nm)/glass conductive substrates, the electrons are supplied through both the Au film and the CNTs, and topographic morphology of CNTs is observed.