Electromechanical detection in scanning probe microscopy: Tip models and materials contrast

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 tipsurface 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.

Ionic field effect and memristive phenomena in single-point ferroelectric domain switching

“…To analyse the possible mechanisms of the normal and abnormal polarization switching, we note that the application of the bias to the tip leads both to the normal and radial electric field. Both components can be readily estimated in the effective charge approximation 40 , as plotted in Fig. 4 (see Supplementary Note 1 for details).…”

Local probing of ionic diffusion by electrochemical strain microscopy: Spatial resolution and signal formation mechanisms

“…We adopt the method equivalent to the decoupled approximation previously used for ferroelectric materials. 31,32,33,34 In this case, (a) the lithium concentration is found ignoring the diffusion-strain coupling effects, (b) the local stresses are calculated using corresponding constitutive relations (Vegard law), and (c) strain and displacement fields in solid are calculated using appropriate Green's function. We further neglect inhomogeneous thermal expansion in comparison with chemical contribution.…”

Quantification of in-contact probe-sample electrostatic forces with dynamic atomic force microscopy

“…The use of such a technique is crucial here since the model outlined above requires inputs of a contact resonance frequency as well as a Q-factor, which cannot be extracted from single-frequency measurements. During BE, the full contact resonance peak is acquired and fitted with the single harmonic oscillator model to extract response amplitudes and resonance quality factors [46,47]. All experiments were made with a Bruker Icon AFM in a controlled low-humidity environment (Ar-filled glove box) on a 44 nm-thick amorphous HfO2 thin film sputtered on a (120 nm Au)/SiO2/Si substrate.…”