Electric-Double-Layer Oriented Field-Screening Effect on High-Resolution Electromechanical Imaging in Conductive Solutions

Complex electrical behavior, including the field-screening distribution and possible electrochemical effects, makes electromechanical imaging by piezoresponse force microscopy in conductive liquids a critical challenging issue in studying the functionalities and performance of piezoelectric materials. Here, we propose a theoretical model to directly quantify the electric-field-screening effect inside the tip-sample junction in a variety of electrolytes of varying ionic strength. The field-screening effect resulting from an electric double layer in the tip-surface system offers the benefit of better understanding of the central physical mechanism in electrical probing by scanning probe microscopy (SPM) in a polar liquid medium. Experimentally, an intrinsic piezoresponse in ferroelectric antiparallel-polarization regions is observed in electrolytes with various assemblies of valences and with various molarities through updating the design of a nanoelectrode probe. Accompanied by the unveiling of the underlying physical mechanism, these experimental results pave the way to the broad application of in vivo or in operando electrical analysis on the nanoscale by the SPM technique in conductive-liquid environments.