Atomic-Scale Chemical Imaging of Composition and Bonding by Aberration-Corrected Microscopy

Muller, DA; Kourkoutis, Lena F.; Murfitt, Matthew F.; Song, J. H.; Hwang, H. Y.; Silcox, J.; Dellby, Niklas; Krivanek, O. L.

doi:10.1017/s1431927608087448

Cited by 87 publications

(118 citation statements)

References 2 publications

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“…9,10 In particular, the EELS spectrum imaging mode provides the unprecedented benefit of quantitatively probing both the chemistry and structure of the nanofeatures at sub-Å resolution. 11,12 With the recent development of monochromators for electron guns, an energy resolution of 10 meV can be achieved for the EELS analysis, which not only enables the study of the electronic structure and atomic bonds with a much higher accuracy but also provides the capability of interrogating vibrational features in solid materials. 1,13 Improvements in ultrahigh spatial and energy resolutions have been accompanied by remarkable advances of in situ TEM techniques, which enable the real-time observation of the dynamic structural and chemical evolution in materials under a variety of external stimuli or battery operating conditions.…”

Section: Recent Advancements In Aem Capabilitiesmentioning

confidence: 99%

Advanced analytical electron microscopy for lithium-ion batteries

Qian

et al. 2015

NPG Asia Mater

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Lithium-ion batteries are a leading candidate for electric vehicle and smart grid applications. However, further optimizations of the energy/power density, coulombic efficiency and cycle life are still needed, and this requires a thorough understanding of the dynamic evolution of each component and their synergistic behaviors during battery operation. With the capability of resolving the structure and chemistry at an atomic resolution, advanced analytical transmission electron microscopy (AEM) is an ideal technique for this task. The present review paper focuses on recent contributions of this important technique to the fundamental understanding of the electrochemical processes of battery materials. A detailed review of both static (ex situ) and real-time (in situ) studies will be given, and issues that still need to be addressed will be discussed. NPG Asia Materials (2015) 7, e193; doi:10.1038/am.2015.50; published online 26 June 2015 INTRODUCTIONTo implement the commercialization of lithium-ion batteries in electric vehicles and smart grid systems, further improvements are required, especially with respect to the energy/power density, coulombic efficiency and cycle life. These parameters primarily depend on the diffusion of lithium-metal ions, electron transport, structure and chemical dynamics of the electrode/electrolyte materials, among others. During electrochemical cycling, significant changes in the material structure and elemental distributions occur, including ion relocation, lattice expansion/contraction, phase transition and structure/surface reconstruction. These changes could substantially influence ion and electron transport and affect the performance of the entire battery system. Understanding the structure-property relationships for each component and their synergistic behaviors during electrochemical processes is, therefore, essential for the design of new battery materials and the optimization of existing systems.Although many analysis techniques (for example, X-ray diffraction, X-ray absorption spectroscopy, neutron diffraction, nuclear magnetic resonance and so on) have been employed for such studies, most of them can acquire only spatially averaged information. Nevertheless, the structural and chemical evolution of battery materials upon electrochemical cycling can often be linked to specific nanofeatures, such as defects, interfaces and surfaces. As a result, techniques based on analytical transmission electron microscopy (AEM) are ideal tools to study these issues. The capability of AEM to precisely probe the structural/chemical evolutions at an ultrahigh spatial resolution frequently provides insight that cannot be obtained directly using macroscopic characterization methods.

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Section: Recent Advancements In Aem Capabilitiesmentioning

confidence: 99%

Advanced analytical electron microscopy for lithium-ion batteries

Qian

et al. 2015

NPG Asia Mater

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“…The presence of such defects in the LSMO layers and of atomic-scale intermixing at the interfaces correlates with the degradation of the magnetic and transport properties of the multilayers. Whereas this effect is small in thick LSMO films (23), it is dramatic in thin films, resulting in insulating layers with strongly suppressed T c . As the microscopic perfection of the structure is improved, however, the LSMO/STO multilayers can remain ferromagnetic and conducting below T c at layer thicknesses below 2 nm, i.e., five unit cells, with the implication that the upper limit for the interfacial dead layer is now reduced to two unit cells or less.…”

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confidence: 98%

“…The influence of the laser fluence on the properties of thick LSMO films grown by PLD has recently been demonstrated, showing an increase in the A-site/B-site cation ratio and a reduction of T c as the fluence increases (23). The question then arises, to what degree these effects limit the physical properties of LSMO on the nanoscale.…”

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confidence: 99%

Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers

Kourkoutis

Song

Hwang

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

142

123

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La 0.7 Sr 0.3 MnO 3 is a conducting ferromagnet at room temperature. Combined with thin SrTiO 3 layers, the resulting heterostructures could be used as highly spin-polarized magnetic-tunnel-junction memories. However, when shrunk to dimensions below an apparent critical thickness, the structures become insulating and ferromagnetic ordering is suppressed. Interface spin and charge modulations are thought to create an interfacial dead layer, thus fundamentally limiting the use of this material in atomic-scale devices. The thickness of this dead layer, and whether it is intrinsic, is still controversial. Here we use atomic-resolution electron spectroscopy to demonstrate that the degradation of the magnetic and transport properties of La 0.7 Sr 0.3 MnO 3 ∕SrTiO 3 multilayers correlates with atomic intermixing at the interfaces, and the presence of extended two-dimensional cation defects in the La 0.7 Sr 0.3 MnO 3 layers (in contrast to three-dimensional precipitates in thick films). When these extrinsic defects are eliminated, metallic ferromagnetism at room temperature can be stabilized in five-unit-cell-thick manganite layers in superlattices, placing the upper limit for any intrinsic dead layer at two unit cells per interface.electron energy loss spectroscopy | manganites | scanning transmission electron microscopy C olossal magnetoresistance, metal-insulator transitions, charge/orbital ordering, and half-metal ferromagnetism are only some of the intriguing phenomena that occur in manganites and have driven interest in the family of perovskite manganese oxides (ABO 3 perovskite structure, B site occupied by Mn) (1). With a Curie temperature (T c ) of ∼370 K, the half-metal La 0.7 Sr 0.3 MnO 3 (LSMO) has been considered a promising candidate for spintronics applications. However, although complete spin polarization in LSMO was inferred from photoemission measurements (2) and a record tunneling magnetoresistance (TMR) ratio of 1,800% was obtained at low temperature in tunnel junctions with manganite electrodes separated by a thin insulating layer of SrTiO 3 (STO) (3), the TMR decreased rapidly as the temperature increased and diminished while still far below T c . One possible origin for the reduced TMR is the reduction of ferromagnetic ordering at the interface between the manganite and the STO. These interfacial effects have been suggested to be dominant as the LSMO layer thickness decreases, causing the magnetization and T c to degrade and the resistivity to increase, ultimately resulting in films that are insulating at all temperatures when the layer thickness decreases below a reported critical value of 7-13 unit cells (4-11). This critical thickness for sustaining conductivity below T c is attributed to an inherent "dead layer" at the interface between . One origin for the reduced T c and saturation magnetization of thin LSMO films compared to the bulk is believed to be a result of spin canting at the LSMO/STO interface (6, 15). Alternatively, magnetic phase separation into ferromagnetic metallic and less-ord...

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“…For transition metal L 2,3 edges of relevance for probing the multivalent titanium and manganese atoms, however, strong core-hole effects produce a significant deviation between the local density of states and the observed energy loss near edge fine structure 26 . Nevertheless, comparison with reference spectra has permitted atomic-resolution twodimensional mapping of oxidation states [27][28][29] .…”

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confidence: 99%

Visualizing the interfacial evolution from charge compensation to metallic screening across the manganite metal–insulator transition

et al. 2014

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Electronic changes at polar interfaces between transition metal oxides offer the tantalizing possibility to stabilize novel ground states yet can also cause unintended reconstructions in devices. The nature of these interfacial reconstructions should be qualitatively different for metallic and insulating films as the electrostatic boundary conditions and compensation mechanisms are distinct. Here we directly quantify with atomic-resolution the charge distribution for manganite-titanate interfaces traversing the metal-insulator transition. By measuring the concentration and valence of the cations, we find an intrinsic interfacial electronic reconstruction in the insulating films. The total charge observed for the insulating manganite films quantitatively agrees with that needed to cancel the polar catastrophe. As the manganite becomes metallic with increased hole doping, the total charge build-up and its spatial range drop substantially. Direct quantification of the intrinsic charge transfer and spatial width should lay the framework for devices harnessing these unique electronic phases.

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Atomic-Scale Chemical Imaging of Composition and Bonding by Aberration-Corrected Microscopy

Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

Cited by 87 publications

References 2 publications

Advanced analytical electron microscopy for lithium-ion batteries

Advanced analytical electron microscopy for lithium-ion batteries

Microscopic origins for stabilizing room-temperature ferromagnetism in ultrathin manganite layers

Visualizing the interfacial evolution from charge compensation to metallic screening across the manganite metal–insulator transition

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