ABSTRACT
The nanometer-scale visualization of sub-surface voids is investigated using ultrasonic force microscopy. Samples with well-defined cavities below the surface of Si(100) wafers were prepared for this purpose using focused ion-beam milling. Ultrasonic force imaging of the Si(100) surface directly above these cavities reveals a reduced contact stiffness compared to regions of bulk Si if the cavities are within about 200nm of the surface. This result is in agreement with Finite Element Analysis simulations which compare the elastic response under the load of the AFM tip on bulk material with and without cavities.
