Subsurface imaging using tip generated stress and electric fields in atomic force microscopy*

It is well known that subsurface nano-objects can be detected by Atomic Force Microscopy (AFM) with either stress or electric fields by using resonance-enhanced dynamic AFM methods, such as Contact Resonance AFM (CR-AFM) or 2^nd-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 subsurface 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 an identical area of a polymer composite film. The film contains single-walled carbon nanotube networks embedded in a polyimide matrix. The depth of the buried carbon nanotube bundles is estimated by combining experiments and FEA. The results obtained by CR-AFM (depth 33.7 ± 2.6 nm) and KPFM (depth 29.1 ± 2.8 nm) are in good agreement. Both techniques exhibit similar depth sensitivity while CR-AFM has a higher lateral resolution.