The role of the probe is two-fold: it is used both as: (i) an actuator, which allows electric field application through the nanoscale contact with the sample, and (ii) a sensor, which measures the electromechanical response of the sample by monitoring the cantilever mechanical motion (vertical displacement, torsion or bending). In conventional PFM, domain mapping is performed by scanning the sample surface with the probe in the contact regime while monitoring the local piezoelectric strain generated by a small a.c. Based on the recent advances and challenges in the field of nanoferroics and other functional materials, this review offers an outlook for future developments and trends in PFM. Specific attention is paid to challenges in PFM application related to a variety of electromechanical coupling phenomena and the complex image formation mechanisms. After presenting a brief historical overview of the evolution of conventional PFM into a set of advanced modes, it describes the role of PFM in exploration of new emergent phenomena, including DW conductivity, magnetoelectric switching, voltage-free flexoelectric domain control, tunneling electroresistance, domain vertices, and polar vortices. This article, instead of describing the experimental issues of PFM and a variety of accumulated data, focuses on new science and discoveries enabled by PFM. While nanoscale domain imaging has been crucial for the initial advent of nanoferroelectric research, it became also clear that a more careful analysis of the PFM image formation mechanism was necessary, along with comprehensive information on the structure, physics, and chemistry of the materials under investigation, to distinguish real effects from artifacts. However, the wide application of PFM revealed a growing number of challenges and concerns related to the imaging mechanism, data interpretation, and quantification. As the field matured, new advanced PFM modes were developed (Box 2). A number of papers and books provided a comprehensive description of its technical details and gave abundant examples of PFM imaging and modification capabilities 3, 4, 5. Since the publication of the first review book 2, the experimental and physical principles of PFM operation have become common knowledge. With this, PFM has essentially driven the whole field into the realm of the nanoscale 1. ![]() PFM enables non-destructive visualization and control of FE nanodomains, as well as direct measurements of the local physical characteristics of ferroelectrics, such as nucleation bias, piezoelectric coefficients, disorder potential, energy dissipation, and domain wall (DW) dynamics (see Box 1). ![]() ![]() For ferroelectrics and other polar materials, the introduction of one of the voltage-modulated versions of AFM-piezoresponse force microscopy (PFM)-has produced a wealth of new opportunities. The invention of the atomic force microscope (AFM) in 1986 marked a dramatic shift in scientific research by providing a multifunctional toolbox to explore and manipulate functional properties of a wide range of materials at the nanometer scale.
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