Towards non-invasive high-resolution 3D nano-tomography by ultrasonic scanning probe microscopy

Nanoscale imaging techniques that can be used to visualize and characterize local aggregations of the embedded nanoparticulates with sufficient resolution have attracted a great deal of interest. Ultrasonic scanning probe microscopy (SPM) and its derivatives are nondestructive techniques that can be used to elucidate subsurface nanoscale features and mechanical properties. Although many different ultrasonic methods have been used for subsurface imaging, the mechanisms and crucial parameters associated with the contrast formation in subsurface imaging are still unclear. Here, the impact of mechanical properties of the nanoparticulates/matrix, size of the nanoparticulates, buried depth of the nanoparticulates, and the ultrasonic excitation frequency on the developed ultrasonic SPM images have been investigated. To verify our theoretical model, experimental measurements of scanning near-field ultrasound holography (SNFUH) have been recreated in our theoretical analysis to reveal comparable variations in phase contrast measured in SNFUH while scanning over the nanoparticulates embedded in bacteria.