Feasibility of Nano-Acoustic Subsurface Imaging for Atomic Force Microscopy

The feasibility of a new imaging regime for sub-surface Atomic Force Microscopy (AFM) is investigated using synthetic aperture focusing technique. This technique uses two Atomic Force Microscopy (AFM) probes to emit acoustic pulses and sense echoes. Unlike other existing subsurface AFM methods, Nano-Acoustic Subsurface AFM (NASAFM) provides cross-sectional images of a sample below the surface with depth information in the nanometre scale. In order to determine the best resolution, two ideal wideband AFM probes are considered in simulation. The results show that a 20 ps pulse with a bandwidth of 330 GHz was able to resolve two 50 nm discs, 500 nm below the surface, separated by 340 nm. Future work is needed to understand the relation between resolution and bandwidth, the optimal imaging parameters, and the sensing technique.