Analysis of flexochemical effect and its application in scanning probe microscopy

Abstract

Electrochemical processes in solids are affected by the properties of various interfaces, where the flexoelectric effect manifests itself considerably due to the inevitable strong gradient fields. Thus, it is crucial to study the coupling between the electrochemical process and the flexoelectric effect. Based on the continuum theory, we conduct the finite element implementation for the flexochemical effect, being the coupling between flexoelectricity, Vegard effect and chemical reactions. Then the developed method is employed to investigate the flexochemical effect arising in scanning probe microscopy (SPM), including evaluating the contributions from the flexoelectric effect and Vegard effect to the electromechanical response on material SrTiO3 (STO) in piezoresponse force microscopy (PFM) as well as to mechanical redistribution of oxygen vacancy in STO. It is found that at room temperature the nanoscale electromechanical response of the undoped STO in PFM imaging is mainly induced by the converse flexoelectricity while the contribution of direct Vegard effect is negligible. Furthermore, the contact force exerted by SPM tip in manipulating the redistribution of oxygen vacancies is multifunctional, including diminishing vacancies underneath the contact area and enriching the regions around the tip-surface contact edge and inside the sample below the tip, resulting from the synergy of the converse Vegard effect and the direct flexoelectricity. These analyses explain some experimental observations well. This paper provides a continuum framework for the analysis of electrochemomechanical systems with the flexoelectric effect.

Analysis of electromechanical couplings and nonlinear carrier transport in flexoelectric semiconductors

“…In the previous work [32], the finite element implementation for the flexochemical effect was conducted to investigate the electrochemomechanical processes with flexoelectricity considered, which can be utilized to study issues related to flexoelectronics when the Vegard effect is omitted. In order to get weak forms equivalent to partial differential equations (PDEs) and the natural boundary conditions proposed above, the standard Galerkin approach is employed, along with the mixed FEM to avoid difficulties of constructing the C 1 continuous elements when considering flexoelectricity.…”