Mechanical & Materials Engineering, Department of


First Advisor

Xiaoshan Xu

Date of this Version

Summer 4-18-2021


A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Engineering (Materials Engineering), Under the Supervision of Professor Xiaoshan Xu. Lincoln, Nebraska: May, 2021

Copyright (c) 2021 Yifan Yuan


Compared with inorganic ferroelectrics, organic ferroelectrics have advantages of low cost and low toxicity, are in increasing demand in capacitors, piezoelectric, and memory devices to reduce the environmental load. This work focuses on two types of organic molecular ferroelectric materials, croconic acid (CA) and 2-methylbenzimidazole (MBI). The work here introduces several origins of ferroelectricity in typical organics and their switching mechanism. We then investigated the nucleation, growth, and ferroelectric measurements of CA thin films. We explored the effect of substrate temperature and an external electric field on the nucleation and growth processes. The results can be used to improve the surface characteristics of ferroelectric films fabricated by the physical vapor deposition (PVD) method. Next, we focus on the growth and electric measurements of MBI thin films. We realize the fabrication of MBI thin films by PVD in vacuum. By exploiting the extreme anisotropic growth of MBI crystals, a preferential crystalline orientation along (110) plane and one polarization axis along the out-of-plane direction are acquired. Finally, in situ electrical measurements are performed to gain insights into the amorphous-to-crystalline phase transition in MBI films.

Advisor: Xiaoshan Xu