Yuan Guangtong, Zou Zhihan, Wu Dirui, Xu Shiyao, Lyu Longji, Zhang Yuan, Huang Boyuan, Li Changjian, Li Jiangyu
Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China.
Guangdong Provincial Key Laboratory of Functional Oxide Materials and Devices, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China.
Nano Lett. 2025 Jul 16;25(28):11042-11050. doi: 10.1021/acs.nanolett.5c01925. Epub 2025 Jul 2.
Applications of ferroelectric films critically depend on their polar ordering, which is highly sensitive to the film size and substrate constraint. Previous studies have revealed a much enhanced piezoresponse in ferroelectric nanoislands relaxed from substrate clamping, yet the proposed mechanisms were completely opposite. We revisit this problem utilizing clamped epitaxial and freestanding PbTiO (PTO) films as our model system for systematic investigation via scanning transmission electron microscopy, piezoresponse force microscopy, and second harmonic generation. It is found that freestanding PTO exhibits 97% higher atomic-scale polar displacement compared to the one clamped on the SrAlO/SrTiO (SAO/STO) substrate, with ferroelectric -domains coarsened significantly accompanied by notable polarization rotation and vanishing -domains. These structural changes yield 141% enhancement in the effective piezoelectric coefficient and 404% increase in second harmonic generation intensity for freestanding PTO compared to its epitaxial counterpart clamped by SAO/STO substrate, highlighting the important influence of substrate constraint on ferroelectric films.
铁电薄膜的应用严重依赖于其极化有序性，而极化有序性对薄膜尺寸和衬底约束非常敏感。先前的研究表明，从衬底夹持中释放出来的铁电纳米岛中的压电力响应有显著增强，但所提出的机制却完全相反。我们利用夹持外延和自支撑的PbTiO（PTO）薄膜作为模型系统，通过扫描透射电子显微镜、压电力显微镜和二次谐波产生进行系统研究，重新审视了这个问题。研究发现，与夹持在SrAlO/SrTiO（SAO/STO）衬底上的PTO相比，自支撑PTO的原子尺度极位移高97%，铁电畴显著粗化，同时伴随着明显的极化旋转和畴消失。这些结构变化使自支撑PTO的有效压电系数提高了141%，二次谐波产生强度比被SAO/STO衬底夹持的外延PTO增加了404%，突出了衬底约束对铁电薄膜的重要影响。
