Advances in Atomic Force Microscopy for the Electromechanical Characterization of Piezoelectric and Ferroelectric Nanomaterials

김관래 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.9

Given the social demand for self-powering wearable electronics, it is necessary to develop composite materials that exhibit both good flexibility and excellent piezoelectric performances. Intensive research on synthesis methods and devising characterization techniques for piezoelectric nanomaterials in various forms has been conducted. In particular, characterization techniques for piezoelectric nanomaterials require different approaches from those for conventional bulk materials. Atomic force microscopy (AFM)-based characterization techniques work based on the local physical interactions between the AFM tip and sample surfaces, making them an irreplaceable tool for studying the electromechanical properties of piezoelectric nanomaterials. Piezoresponse force microscopy (PFM), conductive AFM (C-AFM), and lateral force microscopy (LFM) are three representative AFM-based techniques used to characterize the piezoelectric and ferroelectric properties of nanomaterials. Coupled with the appearance of diverse novel nanomaterials such nanowires, free-standing nanorods, and electrospun nanofibers, AFM-based characterization techniques are becoming freer from artifacts and the need for quantitative measurements. PFM was initially developed to image the microstructures of piezoelectric materials, and well-calibrated techniques designed to realize quantitative measurements have been applied to nanomaterials. In contrast, C-AFM and LFM were initially used to measure the conductivity of diverse materials and the nanotribology of material surfaces. Over the last decade, they have proved their versatility and can now be used to evaluate the direct piezoelectric effect and the mechanical properties of piezoelectric nanomaterials. In these cases, systematic understanding with regard to the measurement principles is required for accurate measurements and analyses. In the present review article, we discuss earlier work in which AFM-based electromechanical characterization techniques were applied to nanomaterials to evaluate piezoelectric and ferroelectric properties. Also discussed is the importance of gaining a comprehensive understanding of the resulting signals.

Ferroelastic Domain Wall Motions in Lead Zirconate Titanate Under Compressive Stress Observed by Piezoresponse Force Microscopy

김관래 한국전기전자재료학회 2017 전기전자재료학회논문지 Vol.30 No.9

Ferroelectric properties are governed by domain structures and domain wall motions, so it is of significanceto understand domain evolution processes under mechanical stress. In the present study, in situ piezoresponse forcemicroscopy (PFM) observation under compressive stress was carried out for a near-morphotropic PZT. Both 180° andnon-180° domain structures were observed from PFM images, and their habit planes were identified using electronbackscatter diffraction in conjunction with PFM data. By externally applied mechanical stress, needle-like non-180°domain patterns were broadened via domain wall motions. This was interpreted via phenomenological approach such thatthe total energy minimization can be achieved by domain wall motion rather than domain nucleation mainly due to thelocal gradient energy. Meanwhile, no motion was observed from curvy 180° domain walls under the mechanical stress,validating that 180° domain walls are not directly influenced by mechanical stress.

Domain Wall Motions in a Near-Morphotropic Pb(Zr,Ti)O3 Under Mechanical Stress Observed by In Situ Piezoresponse Force Microscopy

김관래 대한금속·재료학회 2019 대한금속·재료학회지 Vol.57 No.1

Many important material properties of ferroelectric ceramics such as piezoelectric coefficient and hysteresis curve are governed by domain structures and their evolution processes. In the present work, domain wall motions in a near-morphotropic Pb(Zr,Ti)O3 under an external compressive stress were observed using in situ piezoresponse force microscopy (PFM). This specific PZT material was chosen due to its complex microstructure, which originates from the coexistence of tetragonal and rhombohedral phases. A micromechanical test rig was installed on the sample stage controller, enabling precise control of the sample position. For the real-time strain monitoring of the PZT sample, a strain gauge was attached to the sample surface on which the PFM scan was conducted. In addition, analysis of the ferroelectric domain structure was assisted by using the electron backscatter diffraction (EBSD) technique to identify the habit planes of non- 180° domain walls and grain boundaries in the PFM images. From a certain grain, a set of large non-180° needle-like domain patterns in the (101) plane were observed before applying a mechanical stress. With increasing compressive stress levels, another set of non-180° needle-like domain patterns grew in the (011) plane, overwriting the domain patterns in the (101) plane. This indicates that polarization switching processes in ferroelectric ceramics take place via a pattern evolution based on the pre-existing domain patterns.

Piezoresponse Force Microscopy를 이용한 Pb(Zr,Ti)O₃ 세라믹의 단계적 Poling에 의한 강유전체 도메인 진화 과정 관찰

김관래,Kim, Kwanlae 한국전기전자재료학회 2019 전기전자재료학회논문지 Vol.32 No.1

Ferroelectric material properties are strongly governed by domain structures and their evolution processes, but the evolution processes of complex domain patterns during a macroscopic electrical poling process are still elusive. In the present work, domain-evolution processes in a PZT ceramic near the morphotropic phase-boundary composition were studied during a step-wise electrical poling using piezoresponse force microscopy (PFM). Electron backscatter diffraction was used with the PFM data to identify the grain boundaries in the region of interest. In response to an externally the applied electric field, growth and retreat of non-$180^{\circ}$ domain boundaries wasere observed. The results indicate that ferroelectric polarization-switching nucleates and evolves in concordance with the pattern of the pre-existing domains.

Piezoresponse Force Microscopy를 이용한 Pb(Zr,Ti)O3 세라믹의 단계적 Poling에 의한 강유전체 도메인 진화 과정 관찰

김관래 한국전기전자재료학회 2019 전기전자재료학회논문지 Vol.32 No.1

Ferroelectric material properties are strongly governed by domain structures and their evolution processes, butthe evolution processes of complex domain patterns during a macroscopic electrical poling process are still elusive. Inthe present work, domain-evolution processes in a PZT ceramic near the morphotropic phase-boundary composition werestudied during a step-wise electrical poling using piezoresponse force microscopy (PFM). Electron backscatter diffractionwas used with the PFM data to identify the grain boundaries in the region of interest. In response to an externally theapplied electric field, growth and retreat of non-180° domain boundaries wasere observed. The results indicate thatferroelectric polarization-switching nucleates and evolves in concordance with the pattern of the pre-existing domains. 강유전체의 물성들은 도메인 구조와 도메인 진화과정에 의해 결정되지만, 거시적인 폴링 과정에 의해 발생하는 복잡한 도메인 패턴의 진화과정들에 대한 이해는 아직 명확하지 않다. 본 연구에서는, 단계적인 전기적 폴링과정 중, Morphotropic Phase Boundary 근처의 PZT 세라믹에서 발생하는 도메인 진화과정들을 Piezorespnose Force Microscopy (PFM)을 이용하여 관찰하였다. 관찰하고자 하는 그레인 경계를 이미징하기 위해 PFM과 함께 EBSD를 사용하였다. 얻게 된 PFM 이미지들로부터, 외부 전기장에 의해 성장하고 물러서는 non-180° 도메인 구조들이 관찰되었다. 결과들로부터, 강유전체 분극 스위칭은 기존에 존재하던 도메인 패턴들의 진화에 의하여 진행됨을 알 수 있다.

시장조사에서 실험계획에 의한 최적상품 결정에 관한 사례연구

김관래 한국품질경영학회 1987 품질경영학회지 Vol.15 No.2

[세션초청논문] Piezoresponse Force Microscopy를 이용한 강유전체 도메인구조 이미징

김관래(Kwanlae Kim),박동혁(Dong Hyuck Park) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11

원자현미경을 활용한 압전 기반 센서에 관한 연구

김관래(K. L. Kim),양이준(Y. J. Yang) Korean Society for Precision Engineering 2019 한국정밀공학회 학술발표대회 논문집 Vol.2019 No.5월

미래 사회 초등학교장의 역할 변화 전망

김관래(Kwan Rae Kim),김도기(Do Ki Kim) 한국지방교육경영학회 2022 지방교육경영 Vol.25 No.3

이 연구의 목적은 제4차 산업혁명시대를 맞이하여 미래 사회로의 전환이 빠르게 일어나고 있는 이 때, 미래 사회 변화에 따른 초등학교장의 역할을 새롭게 전망해 보는 데 있다. 이를 위해 기존의 미래 교육 및 미래 학교 교육의 변화에 관한 선행연구를 분석하였고, 이에 기반하여 미래 초등학교의 역할 변화 및 초등학교장의 역할 변화를 전망하였다. 연구 결과, 미래 사회는 과학 기술의 비약적 발전을 토대로 혁신이 가속되고 사회변동이 크며, 국가 간 더욱 긴밀히 연결되는 지구촌이 되고, 인간성과 가치가 지금보다 더 중시되는 사회로 변화될 것으로 전망되었다. 또한, 미래 사회에는 학교 체제, 학교 기능, 교육 내용과 방법, 학교 구성원이 크게 변화될 것으로 전망되며, 초등학교도 역시 복합 플랫폼, 지역 커뮤니티 활성화, 개인별 맞춤형 교육과정과 방법 적용, 학교 구성원의 다변화 측면에서 변화가 예상되었다. 이러한 미래 변화에 따라 초등학교장의 역할도 기존의 역할에 더해 공동체 빌더, 네트워크 크리에이터, 교육 디자이너, 학교 컨설턴트, 지원적 리더로서의 역할이 더욱 강조될 것으로 전망하였다. 연구 결과를 바탕으로 미래 초등학교장의 역할을 수행하는 데 필요한 역량을 구체적으로 연구할 것을 제언하였다. The purpose of this study is to take a new perspective on the role of elementary school principals according to future social changes at a time when the transition to the future society is rapidly taking place in the era of the 4th industrial revolution. To this end, previous studies on changes in the existing future education and future school education were analyzed, and based on this, the role change of the future elementary school and the role change of the elementary school principal were predicted. As a result of the study, it is predicted that the future society will be transformed into a society where innovation is accelerated, social fluctuations are large, and countries are more closely connected, and humanity and values are more important than now, based on the rapid development of science and technology. In addition, the school system, school functions, educational contents and methods, and school members are expected to change significantly in the future society, and elementary schools also have a complex platform, vitalization of local communities, application of individually customized curriculum and methods, and diversification of school members. change was expected. According to these future changes, the role of the elementary school principal as a community builder, network creator, educational designer, school consultant, and supportive leader will be more emphasized in addition to the existing role. Based on the research results, it was suggested to study in detail the competencies needed to fulfill the role of future elementary school principals.

각도분해 압전 현미경을 이용한 강유전체 도메인 구조 매핑

김관래(K. Kim) Korean Society for Precision Engineering 2018 한국정밀공학회 학술발표대회 논문집 Vol.2018 No.10월