The imaging mechanism, imaging depth, and parameters influencing the visibility of carbon nanotubes in a polymer matrix using an SEM

Visualization of embedded carbon nanotubes (CNTs) in polymer using a scanning electron microscope (SEM) has been established as a convenient technique to evaluate CNT dispersion. This technique is known as voltage contrast imaging and is different from material contrast and topographic contrast imaging. By investigating CNT/epoxy composites the voltage contrast imaging theory is further understood. Trapping of electrons at the CNT/epoxy interface induces a local potential difference which enhances the image contrast. By coating the composite with a polymer film of different thicknesses the imaging depth (i.e. from how deep the CNTs can be seen) is determined to be up to 250 nm, and is a function of the accelerating voltage of the SEM. Visibility of CNTs is found to be sensitive to the CNT dispersion and concentration, as well as to the accelerating voltage.