Electromechanical Detection in Scanning Probe Microscopy: Tip Models and Materials Contrast

TL;DR

This paper analyzes electromechanical probing in scanning probe microscopy, focusing on piezoresponse force microscopy (PFM), comparing it with other microscopy techniques, and deriving relationships between signals and material properties for various tip models and material anisotropies.

Contribution

It provides a comprehensive theoretical framework for understanding PFM signals, including analytical relationships for different material anisotropies and tip geometries, enhancing interpretation of nanoscale electromechanical imaging.

Findings

PFM's insensitivity to contact area improves imaging accuracy.

Derived analytical relationships for PFM signals in anisotropic materials.

Analyzed resolution limits and potential for nanoscale orientation imaging.

Abstract

The rapid development of nanoscience and nanotechnology in the last two decades was stimulated by the emergence of scanning probe microscopy (SPM) techniques capable of accessing local material properties, including transport, mechanical, and electromechanical behavior on the nanoscale. Here, we analyze the general principles of electromechanical probing by piezoresponse force microscopy (PFM), a scanning probe technique applicable to a broad range of piezoelectric and ferroelectric materials. The physics of image formation in PFM is compared to Scanning Tunneling Microscopy and Atomic Force Microscopy in terms of the tensorial nature of excitation and the detection signals and signal dependence on the tip-surface contact area. It is shown that its insensitivity to contact area, capability for vector detection, and strong orientational dependence render this technique a distinct class of SPM. The relationship between vertical and lateral PFM signals and material properties are derived analytically for two cases: transversally-isotropic piezoelectric materials in the limit of weak elastic anisotropy, and anisotropic piezoelectric materials in the limit of weak elastic and dielectric anisotropies. The integral representations for PFM response for fully anisotropic material are also obtained. The image formation mechanism for conventional (e.g., sphere and cone) and multipole tips corresponding to emerging shielded and strip-line type probes are analyzed. Resolution limits in PFM and possible applications for orientation imaging on the nanoscale and molecular resolution imaging are discussed.