Browsing by Author "Wang, Guang-Fu"

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Non-volatile domain nucleation and growth in multiferroic BiFeO(3) films
(2011-06-24)
Chen, Yi-Chun
;
Wang, Guang-Fu
;
Tai, Hsiang-Hua
;
Chen, Jhih-Wei
;
Huang, Yen-Chin
We have presented a systematical study of the domain nucleation and growth behaviors in multiferroic BiFeO(3) (BFO) films. Both the ferroelectric and the ferroelastic switching dynamics were investigated. Several environmental parameters, including the polarization orientations, the monodomain-like matrix, and the ordered domain walls as local boundaries, were well controlled by thin-film strain engineering through changing the vicinal angles of the substrates. The tip-based domain dynamics was studied by subsequent piezoresponse force microscope (PFM) imaging of the domain evolution under external voltage pulses. For the nanodomains written in the monodomain-like environment, the domain wall performed the thermal activated motion. The as-grown 71 degrees domain walls can act as pinning centers for the ferroelectric domain growth driven by low fields; moreover, ferroelastic nucleation near a 71 degrees domain wall will cause the deformation of the domain wall. The ferroelastic domain growth possessed relatively small activation fields, and therefore usually performed non-activated motion. This study revealed the effects of local environments on the dynamics forming nanoscale domains, and opened a pathway for applications in novel non-volatile functional devices.
Non-volatile domain nucleation and growth in multiferroic BiFeO3 films
(2011-06-24)
Chen, Yi-Chun
;
Wang, Guang-Fu
;
Tai, Hsiang-Hua
;
Chen, Jhih-Wei
;
Huang, Yen-Chin
We have presented a systematical study of the domain nucleation and growth behaviors in multiferroic BiFeO3 (BFO) films. Both the ferroelectric and the ferroelastic switching dynamics were investigated. Several environmental parameters, including the polarization orientations, the monodomain-like matrix, and the ordered domain walls as local boundaries, were well controlled by thin-film strain engineering through changing the vicinal angles of the substrates. The tip-based domain dynamics was studied by subsequent piezoresponse force microscope (PFM) imaging of the domain evolution under external voltage pulses. For the nanodomains written in the monodomain-like environment, the domain wall performed the thermal activated motion. The as-grown 71 degrees domain walls can act as pinning centers for the ferroelectric domain growth driven by low fields; moreover, ferroelastic nucleation near a 71 degrees domain wall will cause the deformation of the domain wall. The ferroelastic domain growth possessed relatively small activation fields, and therefore usually performed non-activated motion. This study revealed the effects of local environments on the dynamics forming nanoscale domains, and opened a pathway for applications in novel non-volatile functional devices.
Strain-driven phase boundaries in BiFeO(3) thin films studied by atomic force microscopy and x-ray diffraction
(2012-01-17)
Liu, Heng-Jui
;
Liang, Chen-Wei
;
Liang, Wen-I
;
Chen, Hsiang-Jung
;
Yang, Jan-Chi
We report a detailed study on the strain-driven phase transition between the tetragonal-like and rhombohedral-like phases in epitaxial BiFeO(3) (BFO) thin films which focuses on their structural nature, thermodynamic stability, and ferroelectric/piezoelectric properties. We first show that the tetragonal-like phase, which has a large c/a ratio (similar to 1.2), in the compressively strained BFO is thermodynamically more favorable at high temperature and high strain state (small thickness). We also report a phase transition between two monoclinic phases at 150 degrees C. The two monoclinic phases are differentiated by their c-axis parameters and tilting angles: The low-temperature phase (M(C)) has a c-axis parameter of 4.64 angstrom and a tilting angle (beta = 88.5 degrees) along the a axis, while the high-temperature phase (M(A)) has a c-axis parameter of 4.66 angstrom and a tilting angle (beta = 86.8 degrees) along both of the a and b axes. We further show that samples undergoing the M(C)-M(A) phase transition exhibit ferroelectric polarization rotation and piezoelectric enhancement. Our findings directly unveil the close links between structural changes, polarization rotation, and large piezoelectricity at morphotropic phase boundaries in BiFeO(3).
Strain-driven phase boundaries in BiFeO3 thin films studied by atomic force microscopy and x-ray diffraction
(2012-01-17)
Liu, Heng-Jui
;
Liang, Chen-Wei
;
Liang, Wen-I
;
Chen, Hsiang-Jung
;
Yang, Jan-Chi
We report a detailed study on the strain-driven phase transition between the tetragonal-like and rhombohedral-like phases in epitaxial BiFeO3 (BFO) thin films which focuses on their structural nature, thermodynamic stability, and ferroelectric/piezoelectric properties. We first show that the tetragonal-like phase, which has a large c/a ratio (similar to 1.2), in the compressively strained BFO is thermodynamically more favorable at high temperature and high strain state (small thickness). We also report a phase transition between two monoclinic phases at 150 degrees C. The two monoclinic phases are differentiated by their c-axis parameters and tilting angles: The low-temperature phase (M-C) has a c-axis parameter of 4.64 angstrom and a tilting angle (beta = 88.5 degrees) along the a axis, while the high-temperature phase (M-A) has a c-axis parameter of 4.66 angstrom and a tilting angle (beta = 86.8 degrees) along both of the a and b axes. We further show that samples undergoing the M-C-M-A phase transition exhibit ferroelectric polarization rotation and piezoelectric enhancement. Our findings directly unveil the close links between structural changes, polarization rotation, and large piezoelectricity at morphotropic phase boundaries in BiFeO3.