Sharahi, Hossein J.Janmaleki, MohsenTetard, LaureneKim, SeonghwanSadeghian, HamedVerbiest, Gerard J.2021-02-182021-02-182021-01http://hdl.handle.net/1880/113104https://doi.org/10.11575/PRISM/46026The development of acoustic subsurface atomic force microscopy, which promises three-dimensional imaging with single-digit nanometer resolution by introduction of ultrasound actuations to a conventional atomic force microscope, has come a long way since its inception in the early 1990s. Recent advances provide a quantitative understanding of the different experimentally observed contrast mechanisms, which paves the way for future applications. In this perspective, we first review the different subsurface atomic force microscope modalities: ultrasonic force microscopy, atomic force acoustic microscopy, heterodyne force microscopy, mode-synthesizing atomic force microscopy, and near-field picosecond ultrasonic microscopy. Then, we highlight and resolve a debate existing in the literature on the importance of the chosen ultrasound excitation frequencies with respect to the resonance frequencies of the cantilever and the observed contrast mechanisms. Finally, we discuss remaining open problems in the field and motivate the importance of new actuators, near-field picosecond ultrasonics, and integration with other techniques to achieve multi-functional non-destructive three dimensional imaging at the nanoscale.engUnless otherwise indicated, this material is protected by copyright and has been made available with authorization from the copyright owner. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.atomic force microscopypicosecond ultrasonicsultrasoundtip-sample interactionfrictionultrasound scattering2D materialslife sciencescompositesnanotechnologythree-dimensional imaging3D imagingjournal articlehttp://dx.doi.org/10.1063/5.0035151