Low voltage STEM imaging of multi-walled carbon nanotubes

We present high magnification STEM images of multi-walled carbon nanotubes recorded with a 5 keV electron beam using a Helios Dual Beam microscope and a dedicated multi-segment transmission (STEM) detector. Images of carbon nanotubes recorded with bright-field (BF), annular dark-field (ADF) and high angle annular dark-field (HAADF) signals all show high contrast features, with internal structures 1–2 nm in width clearly revealed in the STEM images. Thicker regions of the nanotubes appear to show an unusual contrast reversal when comparing ADF and HAADF images. An understanding of the image contrast, and its dependence on thickness, is obtained by computing simulations of the ADF and HAADF images using Monte–Carlo software taking into account electron scattering in the nanotube.

► Low voltage STEM images acquired from multi-walled carbon nanotubes.
► Excellent agreement between experimental low voltage STEM ADF images and simulations based on Monte–Carlo software.
► Monte–Carlo simulations reveal the behaviour of low voltage STEM BF, ADF and HAADF intensities for a range of materials and sample thickness.