Sub-surface AFM imaging using tip generated stress and electric fields

Abstract

It is well known that sub-surface nano-objects can be detected by Atomic Force Microscopy (AFM) with either sub-surface stress or electric fields, by using dynamic AFM methods such as Contact Resonance AFM (CR-AFM) or 2nd-harmonic Kelvin Probe Force Microscopy (KPFM), respectively. However, little is understood regarding the relative differences between the two methods. We present a head-to-head comparison between the sub-surface imaging capabilities of these two methods through experiments and computational models based on finite element analysis (FEA). High resolution subsurface images are obtained using both techniques, from the same area of a polymer composite film containing single-walled carbon nanotube networks embedded in a polyimide matrix. The results are used to interpret quantitatively the observables from CR-AFM and KPFM, with a particular focus on the depth sensitivity and lateral resolution. The depth of the buried carbon nanotube bundles estimated by combining experiments and FEA is found to be in good agreement between the two methods.