TY - JOUR
T1 - Domain orientation relationship of orthorhombic and coexisting monoclinic phases of YO1.5-doped HfO2 epitaxial thin films
AU - Kiguchi, Takanori
AU - Shiraishi, Takahisa
AU - Shimizu, Takao
AU - Funakubo, Hiroshi
AU - Konno, Toyohiko J.
N1 - Funding Information:
This research was supported by the JSPS KAKENHI Grant Numbers 16K14378 and 17H05327, and by the SUZUKI Foundation, Yashima Environment Technology Foundation, Shorai Foundation for Science and Technology, Hosokawa Powder Technology Foundation, Tokuyama Science Foundation, and the Nippon Sheet Glass Foundation for Material Science and Engineering. The use of electron microscopy for this study was supported by the Tohoku University Nanotechnology Platform Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan, and Dr. Makoto Nagasako, Institute for Materials Research, Tohoku University for the use of electron microscopy.
Publisher Copyright:
© 2018 The Japan Society of Applied Physics.
PY - 2018/11
Y1 - 2018/11
N2 - Domain structures with ferroelectric and ferroelastic characteristics of the epitaxial thin films of the polar orthorhombic phase of 7 mol % YO1.5-doped HfO2 (YHO) were investigated by aberration-corrected scanning transmission electron microscopy (STEM). The high-angle annular dark-field (HAADF)-STEM images of the YHO thin film reveal that the individual domain size is approximately 10 nm. Multislice simulation demonstrated that STEM imaging can detect individual domains on the nanoscale avoiding superposition with other domains in the projection direction. The STEM analysis of the domain structure of the polar orthorhombic phase elucidated that the orientation relationship between neighboring domains was affected by two factors: (i) tilt or twist relationship between the longest b-axis in the domains, and (ii) parallel or perpendicular relationship between the rotation axis and the longest b-axis. Corresponding to the longest b-axis orientation, two types of domain walls (DWs) exist: the strained DWs and the less strained ones. The latter should move more easily with less strain, and are of the tilt type with the longest b-axis parallel to the domain rotation axis. STEM imaging also reveals the coexistence of a nonpolar monoclinic phase, which deforms the orthorhombic phase around the monoclinic phase. This factor should also diminish the DW mobility. We propose that the formation of the monoclinic phase should be inhibited and that the longest b-axis should be oriented in the in-plane direction for improving the ferroelectric properties. The two-dimensional tensile stress is expected to be preferred for preparing a-/c-oriented YHO epitaxial thin films. The elastic constraint plays an important role for these purposes for controlling the ferroelectric properties of HfO2 thin films.
AB - Domain structures with ferroelectric and ferroelastic characteristics of the epitaxial thin films of the polar orthorhombic phase of 7 mol % YO1.5-doped HfO2 (YHO) were investigated by aberration-corrected scanning transmission electron microscopy (STEM). The high-angle annular dark-field (HAADF)-STEM images of the YHO thin film reveal that the individual domain size is approximately 10 nm. Multislice simulation demonstrated that STEM imaging can detect individual domains on the nanoscale avoiding superposition with other domains in the projection direction. The STEM analysis of the domain structure of the polar orthorhombic phase elucidated that the orientation relationship between neighboring domains was affected by two factors: (i) tilt or twist relationship between the longest b-axis in the domains, and (ii) parallel or perpendicular relationship between the rotation axis and the longest b-axis. Corresponding to the longest b-axis orientation, two types of domain walls (DWs) exist: the strained DWs and the less strained ones. The latter should move more easily with less strain, and are of the tilt type with the longest b-axis parallel to the domain rotation axis. STEM imaging also reveals the coexistence of a nonpolar monoclinic phase, which deforms the orthorhombic phase around the monoclinic phase. This factor should also diminish the DW mobility. We propose that the formation of the monoclinic phase should be inhibited and that the longest b-axis should be oriented in the in-plane direction for improving the ferroelectric properties. The two-dimensional tensile stress is expected to be preferred for preparing a-/c-oriented YHO epitaxial thin films. The elastic constraint plays an important role for these purposes for controlling the ferroelectric properties of HfO2 thin films.
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U2 - 10.7567/JJAP.57.11UF16
DO - 10.7567/JJAP.57.11UF16
M3 - Article
AN - SCOPUS:85057175347
VL - 57
JO - Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes
JF - Japanese Journal of Applied Physics, Part 1: Regular Papers & Short Notes
SN - 0021-4922
IS - 11
M1 - 11UF16
ER -