Zeng Qibin, Wang Hongli, Xiong Zhuang, Huang Qicheng, Lu Wanheng, Sun Kuan, Fan Zhen, Zeng Kaiyang
Department of Mechanical Engineering National University of Singapore Singapore 117576 Singapore.
The Key Lab of Guangdong for Modern Surface Engineering Technology National Engineering Laboratory for Modern Materials Surface Engineering Technology Institute of New Materials, Guangdong Academy of Science Guangzhou 510650 China.
Adv Sci (Weinh). 2021 Feb 15;8(8):2003993. doi: 10.1002/advs.202003993. eCollection 2021 Apr.
Piezoresponse force microscopy (PFM), as a powerful nanoscale characterization technique, has been extensively utilized to elucidate diverse underlying physics of ferroelectricity. However, intensive studies of conventional PFM have revealed a growing number of concerns and limitations which are largely challenging its validity and applications. In this study, an advanced PFM technique is reported, namely heterodyne megasonic piezoresponse force microscopy (HM-PFM), which uses 10 to 10 Hz high-frequency excitation and heterodyne method to measure the piezoelectric strain at nanoscale. It is found that HM-PFM can unambiguously provide standard ferroelectric domain and hysteresis loop measurements, and an effective domain characterization with excitation frequency up to ≈110 MHz is demonstrated. Most importantly, owing to the high-frequency and heterodyne scheme, the contributions from both electrostatic force and electrochemical strain can be significantly minimized in HM-PFM. Furthermore, a special measurement of difference-frequency piezoresponse frequency spectrum (DFPFS) is developed on HM-PFM and a distinct DFPFS characteristic is observed on the materials with piezoelectricity. By performing DFPFS measurement, a truly existed but very weak electromechanical coupling in CHNHPbI perovskite is revealed. It is believed that HM-PFM can be an excellent candidate for the ferroelectric or piezoelectric studies where conventional PFM results are highly controversial.
压电力显微镜（PFM）作为一种强大的纳米级表征技术，已被广泛用于阐明铁电性的各种潜在物理机制。然而，对传统PFM的深入研究揭示了越来越多的问题和局限性，这在很大程度上挑战了其有效性和应用。在本研究中，报道了一种先进的PFM技术，即外差兆声波压电力显微镜（HM-PFM），它使用10至10赫兹的高频激励和外差方法来测量纳米级的压电应变。研究发现，HM-PFM能够明确地提供标准的铁电畴和磁滞回线测量结果，并且展示了在高达≈110 MHz的激励频率下的有效畴表征。最重要的是，由于高频和外差方案，在HM-PFM中静电力和电化学应变的贡献都可以显著最小化。此外，在HM-PFM上开发了一种特殊的差频压电响应频谱（DFPFS）测量方法，并且在具有压电性的材料上观察到了独特的DFPFS特性。通过进行DFPFS测量，揭示了CHNHPbI钙钛矿中确实存在但非常微弱的机电耦合。相信HM-PFM可以成为传统PFM结果存在高度争议的铁电或压电研究的优秀候选方法。
