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Field enhancement of electronic conductance at ferroelectric domain walls
(2017-11-06)
Vasudevan, Rama K.
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Cao, Ye
;
Laanait, Nouamane
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Ievlev, Anton
;
Li, Linglong
Ferroelectric domain walls have continued to attract widespread attention due to both the novelty of the phenomena observed and the ability to reliably pattern them in nanoscale dimensions. However, the conductivity mechanisms remain in debate, particularly around nominally uncharged walls. Here, we posit a conduction mechanism relying on field-modification effect from polarization re-orientation and the structure of the reverse-domain nucleus. Through conductive atomic force microscopy measurements on an ultra-thin (001) BiFeO3 thin film, in combination with phase-field simulations, we show that the field-induced twisted domain nucleus formed at domain walls results in local-field enhancement around the region of the atomic force microscope tip. In conjunction with slight barrier lowering, these two effects are sufficient to explain the observed emission current distribution. These results suggest that different electronic properties at domain walls are not necessary to observe localized enhancement in domain wall currents.
Interface dipole between two metallic oxides caused by localized oxygen vacancies
(2012-10-11)
Borisevich, Albina Y.
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Lupini, Andrew R.
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He, Jun
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Eliseev, Eugene A.
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Morozovska, Anna N.
Oxygen vacancies are increasingly recognized to play a role in phenomena observed at transition-metal oxide interfaces. Here, we report a study of SrRuO3 and La0.7Sr0.3MnO3 interfaces using a combination of quantitative aberration-corrected scanning transmission electron microscopy, electron energy-loss spectroscopy, and density functional calculations. Cation displacements are observed at the interface, indicative of a dipolelike electric field even though both materials are nominally metallic. The observed displacements are reproduced by theory if O vacancies are present in the near-interface La0.7Sr0.3MnO3 layers. The results suggest that atomic-scale structural mapping can serve as a quantitative indicator of the presence of O vacancies at interfaces.
Ultrathin limit and dead-layer effects in local polarization switching of BiFeO3
(2012-01-31)
Maksymovych, Peter
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Huijben, Mark
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Pan, Minghu
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Jesse, Stephen
;
Balke, Nina
Using piezoresponse force microscopy in an ultrahigh vacuum, polarization switching has been detected and quantified in epitaxial BiFeO3 films from 200 to about 4 unit cells thick. Local remnant piezoresponse was utilized to probe both ferroelectric properties and effects of imperfect electrical contacts. It was found that the shape of electromechanical hysteresis loops is strongly influenced by an extrinsic dielectric gap, primarily through the suppressing effect of the depolarizing field on the spontaneous polarization in the ultrathin films. Furthermore, statistical analysis of the hysteresis loops has revealed lateral variation of the extrinsic dielectric gap with sub-10-nm resolution. Robust and reproducible ferroelectric properties of nanoscale BiFeO3 indicate its potential for nanoscale applications in information storage and spintronics.
Direct Observation of Capacitor Switching Using Planar Electrodes
(2010-10-22)
Balke, Nina
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Gajek, Martin
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Tagantsev, Alexander K.
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Martin, Lane W.
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Chu, Ying-Hao
Ferroelectric polarization switching in epitaxial (110) BiFeO(3) films is studied using piezoresponse force microscopy of a model in-plane capacitor structure. The electrode orientation is chosen such that only two active domain variants exist. Studies of the kinetics of domain evolution allows clear visualization of nucleation sites, as well as forward and lateral growth stages of domain formation. It is found that the location of the reverse-domain nucleation is correlated with the direction of switching in a way that the polarization in the domains nucleated at an electrode is always directed away from it. The role of interface charge injection and surface screening charge on switching mechanisms is explored, and the nucleation is shown to be controllable by the bias history of the sample. Finally, the manipulation of domain nucleation through domain structure engineering is illustrated. These studies pave the way for the engineering and design of the ferroelectric device structures through control of individual steps of the switching process.
Ferroelectric domain triggers the charge modulation in semiconductors (invited)
(2014-08-14)
Morozovska, Anna N.
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Eliseev, Eugene A.
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Ievlev, Anton V.
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Varenyk, Olexander V.
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Pusenkova, Anastasiia S.
We consider a typical heterostructure "domain patterned ferroelectric film-ultra-thin dielectric layer-semiconductor," where the semiconductor can be an electrolyte, paraelectric or multi-layered graphene. Unexpectedly, we have found that the space charge modulation profile and amplitude in the semiconductor, that screens the spontaneous polarization of a 180-deg domain structure of ferroelectric, depends on the domain structure period, dielectric layer thickness and semiconductor screening radius in a rather non-trivial nonlinear way. Multiple size effects appearance and manifestation are defined by the relationship between these three parameters. In addition, we show that the concept of effective gap can be introduced in a simple way only for a single-domain limit. Obtained analytical results open the way for understanding of current-AFM maps of contaminated ferroelectric surfaces in ambient atmosphere as well as explore the possibilities of conductivity control in ultra-thin semiconductor layers. (C) 2014 AIP Publishing LLC.
Deep Data Analysis of Conductive Phenomena on Complex Oxide Interfaces: Physics from Data Mining
(2014-06-01)
Strelcov, Evgheni
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Belianinov, Alexei
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Hsieh, Ying-Hui
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Jesse, Stephen
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Baddorf, Arthur P.
Spatial variability of electronic transport in BiFeO3-CoFe2O4 (BFO-CFO) self-assembled heterostructures is explored using spatially resolved first-order reversal curve (FOR) current voltage (IV) mapping. Multivariate statistical analysis of FORC-IV data classifies statistically significant behaviors and maps characteristic responses spatially. In particular, regions of grain, matrix, and grain boundary responses are clearly identified, k-Means and Bayesian demixing analysis suggest the characteristic response be separated into four components, with hysteretic-type behavior localized at the BFO-CFO tubular interfaces. The conditions under which Bayesian components allow direct physical interpretation are explored, and transport mechanisms at the grain boundaries and individual phases are analyzed. This approach conjoins multivariate statistical analysis with physics-based interpretation, actualizing a robust, universal, data-driven approach to problem solving, which can be applied to exploration of local transport and other functional phenomena in other spatially inhomogeneous systems.
Electrical Modulation of the Local Conduction at Oxide Tubular Interfaces
(2013-10-01)
Hsieh, Ying-Hui
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Strelcov, Evgheni
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Liou, Jia-Ming
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Shen, Chia-Ying
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Chen, Yi-Chun
Heterointerfaces between complex oxides have sparked considerable interest due to their fascinating physical properties and their offering of new possibilities for next-generation electronic devices. The key to realize practical applications is the control through external stimuli. In this study, we take the self-assembled BiFeO3-CoFe2O4 tubular interface as a model system to demonstrate the nonvolatile electric control of the local conduction at the complex oxide tubular interface. The fundamental mechanism behind this modulation was explored based on static and dynamic conductive atomic force microscopies. We found the movement of oxygen vacancies in the BiFeO3-CoFe2O4 heterostructure is the key to drive this intriguing behavior. This study delivers a possibility in developing next-generation electronic devices.
Atomically Resolved Mapping of Polarization and Electric Fields Across Ferroelectric/Oxide Interfaces by Z-contrast Imaging
(2011-06-03)
Chang, Hye Jung
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Kalinin, Sergei V.
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Morozovska, Anna N.
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Huijben, Mark
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Chu, Ying-Hao
Direct atomic displacement mapping at ferroelectric interfaces by aberration corrected scanning transmission electron microscopy (STEM) (a-STEM image, b-corresponding displacement profile) is combined with the Landau-Ginsburg-Devonshire theory to obtain the complete interface electrostatics in real space, including separate estimates for the polarization and intrinsic interface charge contributions.
Probing Local Ionic Dynamics in Functional Oxides at the Nanoscale
(2013-08-01)
Strelcov, Evgheni
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Kim, Yunseok
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Jesse, Stephen
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Cao, Ye
;
Ivanov, Ilia N.
A scanning probe microscopy technique for probing local ionic dynamics in electrochemically active materials based on the first-order reversal curve current-voltage (FORC-IV) method is presented. FORC-IV imaging mode is applied to a Ca-substituted bismuth ferrite (Ca-BFO) system to separate the electronic and ionic phenomena in this material and visualize the spatial variability of these behaviors. The variable-temperature measurements further demonstrate the interplay between the thermally and electric-field-driven resistance changes in Ca-BFO. The FORC-IV is shown to be a simple, powerful, and flexible method for studying electrochemical activity of materials at the nanoscale and, in conjunction with the electrochemical strain microscopy, it can be used for differentiating ferroelectric and ionic behaviors.
Space- and Time-Resolved Mapping of Ionic Dynamic and Electroresistive Phenomena in Lateral Devices
(2013-08-01)
Strelcov, Evgheni
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Jesse, Stephen
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Huang, Yen-Lin
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Teng, Yung-Chun
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Kravchenko, Ivan I.
A scanning probe microscopy-based technique for probing local ionic and electronic transport and their dynamic behavior on the 10 ms to 10 s scale is presented. The time-resolved Kelvin probe force microscopy (tr-KPFM) allows mapping of surface potential in both space and time domains, visualizing electronic and ionic charge dynamics and separating underlying processes based on their time responses. Here, tr-KPFM is employed to explore the interplay of the adsorbed surface ions and bulk oxygen vacancies and their role in the resistive switching in a Ca-substituted bismuth ferrite thin film.

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