Figure 5
Schematic of the carrier dynamics leading to the steepening of the strain gradient.
(1) Electrons are excited and (2) cool to form excitons. (3) Excitons then diffuse to the interface and surface where they (4) dissociate due to local band bending. The free carriers screen the depolarization field leading to a structural piezoelectric response. The strain dependence of the piezoelectric coefficient leads to the steepening of the static strain gradient. A BFO unit cell is shown in the inset with Bi, Fe and O atoms represented by purple, brown and red balls. Note that the initial film polarization direction has minimal effect on the lattice change.
