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12/2012;
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P Yu,
W Luo,
D Yi,
J X Zhang,
M D Rossell,
C-H Yang,
L You,
G Singh-Bhalla,
S Y Yang,
Q He,
Q M Ramasse, R Erni,
L W Martin,
Y H Chu,
S T Pantelides,
S J Pennycook,
R Ramesh
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ABSTRACT: The control of material interfaces at the atomic level has led to novel interfacial properties and functionalities. In particular, the study of polar discontinuities at interfaces between complex oxides lies at the frontier of modern condensed matter research. Here we employ a combination of experimental measurements and theoretical calculations to demonstrate the control of a bulk property, namely ferroelectric polarization, of a heteroepitaxial bilayer by precise atomic-scale interface engineering. More specifically, the control is achieved by exploiting the interfacial valence mismatch to influence the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state. A broad study of diverse systems comprising different ferroelectrics and conducting perovskite underlayers extends the generality of this phenomenon.
Proceedings of the National Academy of Sciences 05/2012; 109(25):9710-5. · 9.68 Impact Factor
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ABSTRACT: We determine the atomic structure of the pseudotetragonal T phase and the pseudorhombohedral R phase in highly strained multiferroic BiFeO(3) thin films by using a combination of atomic-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy. The coordination of the Fe atoms and their displacement relative to the O and Bi positions are assessed by direct imaging. These observations allow us to interpret the electronic structure data derived from electron energy-loss spectroscopy and provide evidence for the giant spontaneous polarization in strained BiFeO(3) thin films.
Physical Review Letters 01/2012; 108(4):047601. · 7.37 Impact Factor
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P Yu,
J-S Lee,
S Okamoto,
M D Rossell,
M Huijben,
C-H Yang,
Q He,
J X Zhang,
S Y Yang,
M J Lee,
Q M Ramasse, R Erni,
Y-H Chu,
D A Arena,
C-C Kao,
L W Martin,
R Ramesh
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ABSTRACT: We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO3 at the interface with ferromagnet La(0.7)Sr(0.3)MnO3. Using x-ray magnetic circular dichroism at Mn and Fe L(2,3) edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related to an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at the oxygen K edge.
Physical Review Letters 07/2010; 105(2):027201. · 7.37 Impact Factor
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ABSTRACT: Instrumentation and Techniques SymposiaUltra-High-Resolution Transmission Electron Microscopy of Atomically Thin Hexagonal Boron Nitride (h-BN)Article author queryalem n [PubMed]
[Google Scholar]erni r [PubMed]
[Google Scholar]kisielowski c [PubMed]
[Google Scholar]rossell m [PubMed]
[Google Scholar]gannett w [PubMed]
[Google Scholar]zettl a [PubMed]
[Google Scholar]N Alema1, R Ernia2, C Kisielowskia2, MD Rossella2, W Gannetta1 and A Zettla1a1 University of California, Berkeley
Microscopy and Microanalysis 06/2010; 16:120 - 121. · 3.01 Impact Factor
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P Yu,
J S Lee,
S Okamoto,
M D Rossell,
M. Huijben,
C H Yang,
Q He,
J X Zhang,
S Y Yang,
M J Lee,
Q M Ramasse, R Erni,
Y H Chu,
D. A. Arena,
C. -C. Kao,
L W Martin,
R. Ramesh
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ABSTRACT: We report the formation of a novel ferromagnetic state in the antiferromagnet BiFeO3 at the interface with La0.7Sr0.3MnO3. Using x-ray magnetic circular dichroism at Mn and Fe L2,3-edges, we discovered that the development of this ferromagnetic spin structure is strongly associated with the onset of a significant exchange bias. Our results demonstrate that the magnetic state is directly related with an electronic orbital reconstruction at the interface, which is supported by the linearly polarized x-ray absorption measurement at oxygen K-edge. Comment: 17 pages, 4 figures, PRL in press
06/2010;
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R J Zeches,
M D Rossell,
J X Zhang,
A J Hatt,
Q He,
C-H Yang,
A Kumar,
C H Wang,
A Melville,
C Adamo, [......],
Y-H Chu,
J F Ihlefeld, R Erni,
C Ederer,
V Gopalan,
L Q Chen,
D G Schlom,
N A Spaldin,
L W Martin,
R Ramesh
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ABSTRACT: Piezoelectric materials, which convert mechanical to electrical energy and vice versa, are typically characterized by the intimate coexistence of two phases across a morphotropic phase boundary. Electrically switching one to the other yields large electromechanical coupling coefficients. Driven by global environmental concerns, there is currently a strong push to discover practical lead-free piezoelectrics for device engineering. Using a combination of epitaxial growth techniques in conjunction with theoretical approaches, we show the formation of a morphotropic phase boundary through epitaxial constraint in lead-free piezoelectric bismuth ferrite (BiFeO3) films. Electric field-dependent studies show that a tetragonal-like phase can be reversibly converted into a rhombohedral-like phase, accompanied by measurable displacements of the surface, making this new lead-free system of interest for probe-based data storage and actuator applications.
Science 11/2009; 326(5955):977-80. · 31.20 Impact Factor
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C. Kisielowski,
B. Freitag,
M. Bischoff,
H. van Lin,
S. Lazar,
G. Knippels,
P. Tiemeijer,
M. van der Stam,
S. von Harrach,
M. Stekelenburg, [......],
A.M. Minor,
A.K. Schmid,
T. Duden,
V. Radmilovic,
Q.M. Ramasse,
M. Watanabe, R. Erni,
E.A. Stach,
P. Denes,
U. Dahmen
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ABSTRACT: The ability of electron microscopes to analyze all the atoms in individual nanostructures is limited by lens aberrations. However, recent advances in aberration-correcting electron optics have led to greatly enhanced instrument performance and new techniques of electron microscopy. The development of an ultrastable electron microscope with aberration-correcting optics and a monochromated high-brightness source has significantly improved instrument resolution and contrast. In the present work, we report information transfer beyond 50 pm and show images of single gold atoms with a signal-to-noise ratio as large as 10. The instrument's new capabilities were exploited to detect a buried Σ3 {112} grain boundary and observe the dynamic arrangements of single atoms and atom pairs with sub-angstrom resolution. These results mark an important step toward meeting the challenge of determining the three-dimensional atomic-scale structure of nanomaterials.
Microscopy and Microanalysis 09/2008; 14(05):469 - 477. · 3.01 Impact Factor
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ABSTRACT: We present a transmission electron microscopy investigation of graphene membranes, crystalline foils with a thickness of only 1 atom. By using aberration-correction in combination with a monochromator, 1-A resolution is achieved at an acceleration voltage of only 80 kV. The low voltage is crucial for the stability of these membranes. As a result, every individual carbon atom in the field of view is detected and resolved. We observe a highly crystalline lattice along with occasional point defects. The formation and annealing of Stone-Wales defects is observed in situ. Multiple five- and seven-membered rings appear exclusively in combinations that avoid dislocations and disclinations, in contrast to previous observations on highly curved (tube- or fullerene-like) graphene surfaces.
Nano Letters 07/2008; 8(11):3582-6. · 13.20 Impact Factor
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ABSTRACT: Recent advances in aberration-correcting electron optics have led to increased resolution, sensitivity and signal to noise
in atomic resolution microscopy. Building on these developments, the TEAM project was designed to optimize the electron microscope
around aberration-corrected electron optics and to further advance the limits of the instrument and the technique [1]. The
vision for the TEAM project is the idea of providing a sample space for electron scattering experiments in a tunable electron
optical environment by removing some of the constraints that have limited electron microscopy until now. The resulting improvements
in resolution, the increased space around the sample, and the possibility of exotic electron-optical settings will enable
new types of experiments. The TEAM microscope will feature unique corrector elements for spherical and chromatic aberrations,
a novel AFM-inspired specimen stage, a high-brightness gun and numerous other innovations that will extend resolution down
to the half-Angstrom level.
12/2007: pages 3-4;
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Microscopy and Microanalysis 07/2006; 12:1372 - 1373. · 3.01 Impact Factor
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ABSTRACT: The development of monochromators and aberration correctors for transmission electron microscopes (TEM) has paved the way for a level of imaging and analysis that is unmatched by other methods. While current instrumentation does not permit the optimum spatial resolution of the microscope to be coupled with this high energy resolution, detailed spectroscopic analyses can be performed with ~1nm spatial resolution. Combined with ~0.1 eV energy resolution this is particularly useful for the analysis of the low-loss region of the spectrum, permitting quantum confinement effects and optical responses of individual nanostructures to be measured. Higher spatial resolution can be obtained from aberration corrected STEM, where spectral resolution of ~0.4eV can be coupled with a spatial resolution of <0.1 nm. Such resolution is particularly useful for analyzing core-loss signals at defects and interfaces, where localized structural and compositional modulations are expected to have a large effect on the structure-property relationships. Results from aberration corrected and monochromated systems will be presented to highlight the application of EELS to the study of Si3N4, GaN and extraterrestrial particles.
Journal of Physics Conference Series 02/2006; 26(1):59.
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ABSTRACT: Using an aberration-corrected transmission electron microscope, we report on imaging individual atomic columns of Li in the intermetallic compound Al3Li. The effect of electron energy on the imaging characteristic of Li is investigated by performing measurements at 80 kV employing a monochromated electron beam with an energy spread ΔE of 0.2 eV and at 300 kV with ΔE of 0.8 eV. These settings enable similar information transfer at both microscope operation conditions and allow a direct comparison between the 80 and the 300 kV measurements. Our experimental data show that the phase of the reconstructed exit-plane wave is highly sensitive to light atoms and that the displacement damage of light elements of low threshold recoil energy can be larger at 80 kV than at 300 kV. This behavior can be understood in terms of the relativistic elastic-scattering cross section between electrons and atoms.
Phys. Rev. B. 80(2).
