Electric-field assisted nucleation processes of croconic acid films*

Growth of organic thin films using physical vapor deposition typically follows a three-dimensional mode, resulting in a rough surface, which undermines their application potentials. To address this issue, we have studied the effect of electric field and temperature on the growth dynamics, especially the heterogeneous nucleation process, of croconic acid (CA) films, taking advantage of the large dipole of the molecules and the ferroelectric polarization of the molecular crystals. We found that the nucleation rate has a maximum at an intermediate temperature, and the electric field shifts the maximum nucleation rate towards the lower temperature. An analysis using classical nucleation theory suggests that the electric field decreases sublimation temperature, increases the wetting angle, and decreases the surface diffusion barrier. These results provide important insight into the growth of molecular crystal films under electric fields and pave a way to fabricate films with better surface characteristics for molecular ferroelectric films.