Electron Holography: Applications to Materials Questions

Lichte, Hannes; Formánek, Petr; Lenk, A.; Linck, Martin; Matzeck, Christopher; Lehmann, Michael; Simon, Paul

doi:10.1146/annurev.matsci.37.052506.084232

Cited by 125 publications

(83 citation statements)

References 44 publications

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“…To date, the only method for capturing large phase changes which also have large-scale features over a significant field of view ͑ ϳ1 m͒ is off-axis electron holography. 9,10 This, though, requires demanding experimental stability for the interfering beams and conventionally there must be an area of free space adjacent to the feature of interest in order to create a true reference wave ͑i.e., where the phase of the electron wave does not change as the wave propagates͒. There are also extremely high demands on the coherence of the illuminating beam.…”

Section: ͒mentioning

confidence: 99%

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Wave-front phase retrieval in transmission electron microscopy via ptychography

et al. 2010

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There are many different strategies that allow the solving of the well-known phase problem corresponding to the loss of phase information during a physical measurement. In microscopy, and, in particular, in transmission electron microscopy, most of these strategies focus on the retrieval of high-resolution information with the importance of lower resolution data often overlooked. Ptychography offers a means to investigate such data. Ptychography is a robust diffractive imaging technique with fast convergence for phase retrieval but, until now, has not been applied at the nanoscale. In this paper, we use the ptychographical iterative engine to retrieve the phase change at the exit plane of metallic nanoparticles using a conventional transmission electron microscope. Ptychographical reconstructions yielded images with a phase resolution of / 10 and a spatial resolution of 1 nm. These results stand as a first step toward aberration-free lensless imaging. The technique lends itself to be an alternative to off-axis electron holography or focal series reconstruction. A very long-standing issue in transmission electron microscopy ͑TEM͒ has been how to measure accurately the phase of the electron wave emanating from the exit surface of the specimen. Because the wavelength of an electron is reduced as it passes through a potential well, the atomic potentials within the specimen can induce significant changes in its phase relative to its free-space propagation. Measurement of the induced phase change at the atomic scale or nanoscale has many important applications: for example, the measurement of the mean inner potential in materials ͑which depends upon the local chemical distribution 1 ͒, the measurement of magnetic fields around nanostructures, 2 or the measurement of internal electric fields within the specimen ͑e.g., at semiconductor junctions 3 ͒.Traditional TEM phase contrast is based upon an approximate version of Zernike's method 4 for thin and weakly scattering specimen. In essence, an interference image is created by adding the unscattered and phase-modified scattered terms. The resulting contrast is then a combination of amplitude and phase components. The transfer function of the lens is a serious limitation of this method, especially at low scattering angles ͑low-resolution components in the image͒, meaning that phase contrast works well only for relatively small-scale features, below about 1.0 nm. Furthermore, the weak-scattering approximation breaks down for all but the thinnest ͑few nanometers͒, light-element specimens.One technique that overcomes some of these limitations requires the recording of two or more images at different defoci of the objective lens, thus imaging a number of planes downstream of the object. As a wave propagates, only one phase distribution will be consistent with the measured changes of intensity. There are several methods for retrieving phase using such data. 5-8 However, because the wave intensity relies on local interference between wavelets in the Fresnel propagation integral,...

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Section: ͒mentioning

confidence: 99%

“…near the image plane and an additional objective mini lens for low-resolution observation ͑ϳ1 m field of view͒. 10 In comparison, in ptychography a large field of view can be reached by simply increasing the number of probe positions.…”

Section: ͒mentioning

confidence: 99%

Wave-front phase retrieval in transmission electron microscopy via ptychography

et al. 2010

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“…10), is staggering. The potential of the technique can perhaps only be rivalled by recent advances in electron holography [91]. While Hannes Lichte and coworkers in Dresden have tentatively demonstrated imaging of the electrical potential surface associated with individual dipoles [92] using electron holography, most progress to date has been made in magnetic materials.…”

Section: Characterisation Of Nanoscale Ferroelectricsmentioning

confidence: 99%

Ferroelectrics at the nanoscale

Gregg¹

2009

Physica Status Solidi (a)

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There are several factors which make the investigation and understanding of nanoscale ferroelectrics particularly timely and important. Firstly, there is a market pressure, primarily from the electronics industry, to integrate ferroelectrics into devices with progressive decreases in size and increases in morphological complexity. This is perhaps best illustrated through the roadmaps for product development in FeRAM (Ferroelectric Random Access Memory) where the need for increases in bit density will require a move from 2D planar capacitor structures to 3D trenched capacitors in the next few years. Secondly, there is opportunity for novel exploration, as it is only relatively recently that developments in thin film growth of complex oxides, self‐assembly techniques and high‐resolution ‘top–down’ patterning have converged to allow the fabrication of isolated and well‐defined ferroelectric nanoshapes, the properties of which are not known. Thirdly, there is an expectation that the behaviour of small scale ferroelectrics will be different from bulk, as this group of functional materials is highly sensitive to boundary/surface conditions, which are expected to dominate the overall response when sizes are reduced into the nanoscale regime.This feature article attempts to introduce some of the current areas of discovery and debate surrounding studies on ferroelectrics at the nanoscale. The focus is directed primarily at the search for novel size‐related properties and behaviour which are not necessarily observed in bulk. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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“…Due to the complexity of both, the scattering and the imaging process, the interpretation of HRTEM images also demands image simulations. Another way of structure retrieval is the determination of the scattered wave function at the exit surface of the crystalline specimen by electron holography or focus series reconstruction [2,3]. Furthermore, various methods of quantitative HRTEM (qHRTEM) exist to determine the local strain and chemical composition on atomic scale [4].…”

Section: Introductionmentioning

confidence: 99%

“…Lorentz microscopy and electron holography are very useful techniques for the evaluation of the structure of magnetic materials [2,9,10]. Additionally, electron holography can be used as an alternative and powerful method for the three-dimensional reconstruction of the shape of nanostructures from two-dimensional phase mapping.…”

Section: Introductionmentioning

confidence: 99%

Advanced microstructure diagnostics and interface analysis of modern materials by high-resolution analytical transmission electron microscopy

Neumann¹,

Kirmse²,

Häusler³

et al. 2010

Bulletin of the Polish Academy of Sciences: Technical Sciences

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Abstract. Transmission electron microscopy (TEM) is a powerful diagnostic tool for the determination of structure/property relationships of materials. A comprehensive analysis of materials requires a combined use of a variety of complementary electron microscopical techniques of imaging, diffraction and spectroscopy at an atomic level of magnitude. The possibilities and limitations of quantitative TEM analysis will be demonstrated for interface studies of the following materials and materials systems: Nickel-based superalloy CMSX-10, (Zn,Cd)O/ZnO/Al2O3, (Al,Ga)N/AlN/Al2O3, GaN/LiAlO2 and FeCo-based nanocrystalline alloys.

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Electron Holography: Applications to Materials Questions

Cited by 125 publications

References 44 publications

Wave-front phase retrieval in transmission electron microscopy via ptychography

Wave-front phase retrieval in transmission electron microscopy via ptychography

Ferroelectrics at the nanoscale

Advanced microstructure diagnostics and interface analysis of modern materials by high-resolution analytical transmission electron microscopy

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