Back-scattered electron visualization of ferroelectric domains in a BiFeO₃ epitaxial film

Three-dimensional orientation of the ferroelectric (FE) domain structure of a BiFeO₃ epitaxial film was investigated by scanning electron microscopy (SEM) using back-scattered electrons and piezoresponse-force microscopy (PFM). By changing the crystallographic orientation of the sample and the electron collection angle relative to the detector, we establish a link between the orientation of polarization vectors (out-of-plane and in-plane) in the BiFeO₃ film and the back-scattered electron image contrast in agreement with PFM investigations. The different FE polarization states in the domains correspond to altered crystalline environments for the impingent primary beam electrons. We postulate that the resultant back-scattered electron domain contrast arises as a result of either differential absorption (through a channelling effect) or through back-diffraction from the sample, which leads to a projected diffraction pattern super-imposed with the diffuse conventional back-scattered electron intensity. We demonstrate that SEM can be sensitive for both out-of-plane and in-plane polarization directions using the back-scattered electron detection mode and can be used as a non-destructive and fast method to determine 3D FE polarization orientation of domains.