Browsing by Author "Morozovska, Anna N."

Now showing 1 - 9 of 9

Atomically Resolved Mapping of Polarization and Electric Fields Across Ferroelectric/Oxide Interfaces by Z-contrast Imaging
(2011-06-03)
Chang, Hye Jung
;
Kalinin, Sergei V.
;
Morozovska, Anna N.
;
Huijben, Mark
;
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.
Enhanced electric conductivity at ferroelectric vortex cores in BiFeO(3)
(2012-01-01)
Balke, Nina
;
Winchester, Benjamin
;
Ren, Wei
;
Chu, Ying Hao
;
Morozovska, Anna N.
Topological defects in ferroic materials are attracting much attention both as a playground of unique physical phenomena and for potential applications in reconfigurable electronic devices. Here, we explore electronic transport at artificially created ferroelectric vortices in BiFeO(3) thin films. The creation of one-dimensional conductive channels activated at voltages as low as 1V is demonstrated. We study the electronic as well as the static and dynamic polarization structure of several topological defects using a combination of first-principles and phase-field modelling. The modelling predicts that the core structure can undergo a reversible transformation into a metastable twist structure, extending charged domain walls segments through the film thickness. The vortex core is therefore a dynamic conductor controlled by the coupled response of polarization and electron-mobile-vacancy subsystems with external bias. This controlled creation of conductive one-dimensional channels suggests a pathway for the design and implementation of integrated oxide electronic devices based on domain patterning.
Enhanced electric conductivity at ferroelectric vortex cores in BiFeO3
(2012-01-01)
Balke, Nina
;
Winchester, Benjamin
;
Ren, Wei
;
Chu, Ying Hao
;
Morozovska, Anna N.
Topological defects in ferroic materials are attracting much attention both as a playground of unique physical phenomena and for potential applications in reconfigurable electronic devices. Here, we explore electronic transport at artificially created ferroelectric vortices in BiFeO3 thin films. The creation of one-dimensional conductive channels activated at voltages as low as 1V is demonstrated. We study the electronic as well as the static and dynamic polarization structure of several topological defects using a combination of first-principles and phase-field modelling. The modelling predicts that the core structure can undergo a reversible transformation into a metastable twist structure, extending charged domain walls segments through the film thickness. The vortex core is therefore a dynamic conductor controlled by the coupled response of polarization and electron-mobile-vacancy subsystems with external bias. This controlled creation of conductive one-dimensional channels suggests a pathway for the design and implementation of integrated oxide electronic devices based on domain patterning.
Ferroelectric Control of the Conduction at the LaAlO3/SrTiO3 Heterointerface
(2013-06-25)
Vu Thanh Tra
;
Chen, Jhih-Wei
;
Huang, Po-Cheng
;
Huang, Bo-Chao
;
Cao, Ye
Ferroelectric domain triggers the charge modulation in semiconductors (invited)
(2014-08-14)
Morozovska, Anna N.
;
Eliseev, Eugene A.
;
Ievlev, Anton V.
;
Varenyk, Olexander V.
;
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.
Ferroelectric domain triggers the charge modulation in semiconductors (invited)
(2014-08-14)
Morozovska, Anna N.
;
Eliseev, Eugene A.
;
Ievlev, Anton V.
;
Varenyk, Olexander V.
;
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.
Interface dipole between two metallic oxides caused by localized oxygen vacancies
(2012-10-11)
Borisevich, Albina Y.
;
Lupini, Andrew R.
;
He, Jun
;
Eliseev, Eugene A.
;
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.
Misfit strain driven cation inter-diffusion across an epitaxial multiferroic thin film interface
(2014-02-07)
Krishnan, P. S. Sankara Rama
;
Morozovska, Anna N.
;
Eliseev, Eugene A.
;
Ramasse, Quentin M.
;
Kepaptsoglou, Demie
Cation intermixing at functional oxide interfaces remains a highly controversial area directly relevant to interface-driven nanoelectronic device properties. Here, we systematically explore the cation intermixing in epitaxial (001) oriented multiferroic bismuth ferrite (BFO) grown on a (001) lanthanum aluminate (LAO) substrate. Aberration corrected dedicated scanning transmission electron microscopy and electron energy loss spectroscopy reveal that the interface is not chemically sharp, but with an intermixing of similar to 2 nm. The driving force for this process is identified as misfit-driven elastic strain. Landau-Ginzburg-Devonshire-based phenomenological theory was combined with the Sheldon and Shenoy formula in order to understand the influence of boundary conditions and depolarizing fields arising from misfit strain between the LAO substrate and BFO film. The theory predicts the presence of a strong potential gradient at the interface, which decays on moving into the bulk of the film. This potential gradient is significant enough to drive the cation migration across the interface, thereby mitigating the misfit strain. Our results offer new insights on how chemical roughening at oxide interfaces can be effective in stabilizing the structural integrity of the interface without the need for misfit dislocations. These findings offer a general formalism for understanding cation intermixing at highly strained oxide interfaces that are used in nanoelectronic devices. (C) 2014 AIP Publishing LLC.
Tunable Metallic Conductance in Ferroelectric Nanodomains
(2012-01-01)
Maksymovych, Peter
;
Morozovska, Anna N.
;
Yu, Pu
;
Eliseev, Eugene A.
;
Chu, Ying-Hao
Metallic conductance in charged ferroelectric domain walls was predicted more than 40 years ago as the first example of an electronically active homointerface in a nonconductive material. Despite decades of research on oxide interfaces and ferroic systems, the metal-insulator transition induced solely by polarization charges without any additional chemical modification has consistently eluded the experimental realm. Here we show that a localized insulator-metal transition can be repeatedly induced within an insulating ferroelectric lead-zirconate titanate, merely by switching its polarization at the nanoscale. This surprising effect is traced to tilted boundaries of ferroelectric nanodomains, that act as localized homointerfaces within the perovskite lattice, with inherently tunable carrier density. Metallic conductance is unique to nanodomains, while the conductivity of extended domain walls and domain surfaces is thermally activated. Foreseeing future applications, we demonstrate that a continuum of nonvolatile metallic states across decades of conductance can be encoded in the size of ferroelectric nanodomains using electric field.