Browsing by Author "Cheng, Xiaoxing"

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Atomic-scale mechanism of internal structural relaxation screening at polar interfaces
(2018-05-25)
Li, Mingqiang
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Cheng, Xiaoxing
;
Li, Ning
;
Liu, Heng-Jui
;
Huang, Yen-Lin
The effective screening of the polarization bound charge is a prerequisite to stabilize the ferroelectricity in ferroelectric thin films. Here, by combining annular bright field imaging and electron energy-loss spectroscopy (EELS) in an aberration-corrected scanning transmission electron microscope with phase-field simulations, we investigate the screening mechanism by quantitatively measuring the structural relaxation at Pb(Zr0.2Ti0.8)O-3/SrTiO3 interfaces. We find that the thickness of the interfacial layer is similar to 3.5 unit cells (similar to 1.4 nm) in a domain with upward polarization and similar to 5.5 unit cells (similar to 2.2 nm) in a domain with downward polarization. Phase-field simulations, an EELS analysis, and a lattice parameter analysis verify the existence of interfacial oxygen vacancies accounting for the narrower interfacial layer in the domain with upward polarization. Our study indicates the internal structural relaxation at the interface is the dominant mechanism for the polarization charge screening for ferroelectric films grown on insulating substrates and has implications for our understanding of domain switching in ferroelectric devices.
Unexpected Giant Microwave Conductivity in a Nominally Silent BiFeO3 Domain Wall
(1970-01-01)
Huang, Yen-Lin
;
Zheng, Lu
;
Chen, Peng
;
Cheng, Xiaoxing
;
Hsu, Shang-Lin
Nanoelectronic devices based on ferroelectric domain walls (DWs), such as memories, transistors, and rectifiers, have been demonstrated in recent years. Practical high-speed electronics, on the other hand, usually demand operation frequencies in the gigahertz (GHz) regime, where the effect of dipolar oscillation is important. Herein, an unexpected giant GHz conductivity on the order of 10(3) S m(-1) is observed in certain BiFeO3 DWs, which is about 100 000 times greater than the carrier-induced direct current (dc) conductivity of the same walls. Surprisingly, the nominal configuration of the DWs precludes the alternating current (ac) conduction under an excitation electric field perpendicular to the surface. Theoretical analysis shows that the inclined DWs are stressed asymmetrically near the film surface, whereas the vertical walls in a control sample are not. The resultant imbalanced polarization profile can then couple to the out-of-plane microwave fields and induce power dissipation, which is confirmed by the phase-field modeling. Since the contributions from mobile-carrier conduction and bound-charge oscillation to the ac conductivity are equivalent in a microwave circuit, the research on local structural dynamics may open a new avenue to implement DW nano-devices for radio-frequency applications.