Maji Subrata, Sarkar Piyush Kanti, Aggarwal Leena, Ghosh Sujoy Kumar, Mandal Dipankar, Sheet Goutam, Acharya Somobrata
Centre for Advanced Materials (CAM), Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India.
Phys Chem Chem Phys. 2015 Mar 28;17(12):8159-65. doi: 10.1039/c5cp00218d.
We report on the direct observation of ferroelectric switching and piezoelectric behaviour in ultrathin polyvinylidene fluoride (PVDF) films prepared by horizontal Langmuir-Schaefer (LS) technique. We have prepared pure β-phase by just increasing the number of LS layers without using additional non-ferroelectric assisting agents. Edge-on oriented CH2-CF2 units of PVDF at the air-water interface enable self-orientation of ferroelectric dipoles by means of the hydrogen bonding network. Such restricted conformation of PVDF at the air-water interface results in an increased net dipole moment with the number of LS layers. The film's ferroelectric switching and piezoelectric sensitivity are demonstrated by hysteretic polarization switching loops and butterfly-loops, respectively. Successful circular domain writing on ultrathin LS film, down to 5 monolayers of PVDF, is demonstrated. The achievement of pure β-phase of PVDF at room temperature without using any assisting agents may be promising for non-volatile memory and piezoelectric-based, ultrathin smart sensor devices.
我们报道了通过水平朗缪尔-谢弗（LS）技术制备的超薄聚偏二氟乙烯（PVDF）薄膜中铁电开关和压电行为的直接观察结果。我们仅通过增加LS层数就制备出了纯β相，而无需使用额外的非铁电辅助剂。PVDF在空气-水界面处边缘取向的CH2-CF2单元通过氢键网络实现铁电偶极子的自取向。PVDF在空气-水界面处这种受限的构象导致净偶极矩随LS层数增加。薄膜的铁电开关和压电灵敏度分别通过滞后极化开关回线和蝶形回线得到证明。展示了在低至5个PVDF单分子层的超薄LS薄膜上成功进行圆形畴写入。在不使用任何辅助剂的情况下在室温下实现PVDF的纯β相可能对非易失性存储器和基于压电的超薄智能传感器器件具有前景。
