Focal-series reconstruction in HRTEM: simulation studies on non-periodic objects

Thust, A.; Coene, W.; Beeck, Marc Op De; Dyck, D. Van

doi:10.1016/0304-3991(96)00011-3

Cited by 257 publications

(144 citation statements)

References 13 publications

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“…Holographic data of the exit-plane wave function of the electron wave in TEM were retrieved by focal series reconstruction (FSR) (29,30). For high-resolution TEM, the combination of a sphericalaberration correction in the microscope with the numerical FSR improved the control and correction of residual parasitic lens aberrations (31).…”

Section: Resultsmentioning

confidence: 99%

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Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures

Bar‐Sadan

Houben

Enyashin

et al. 2008

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

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The characterization of nanostructures down to the atomic scale is essential to understand some physical properties. Such a characterization is possible today using direct imaging methods such as aberration-corrected high-resolution transmission electron microscopy (HRTEM), when iteratively backed by advanced modeling produced by theoretical structure calculations and image calculations. Aberration-corrected HRTEM is therefore extremely useful for investigating low-dimensional structures, such as inorganic fullerene-like particles and inorganic nanotubes. The atomic arrangement in these nanostructures can lead to new insights into the growth mechanism or physical properties, where imminent commercial applications are unfolding. This article will focus on two structures that are symmetric and reproducible. The first structure that will be dealt with is the smallest stable symmetric closed-cage structure in the inorganic system, a MoS 2 nanooctahedron. It is investigated by means of aberration-corrected microscopy which allowed validating the suggested DFTB-MD model. It will be shown that structures diverging from the energetically most stable structures are present in the laser ablated soot and that the alignment of the different shells is parallel, unlike the bulk material where the alignment is antiparallel. These findings correspond well with the high-energy synthetic route and they provide more insight into the growth mechanism. The second structure studied is WS2 nanotubes, which have already been shown to have a unique structure with very desirable mechanical properties. The joint HRTEM study combined with modeling reveals new information regarding the chirality of the different shells and provides a better understanding of their growth mechanism.aberration-corrected high-resolution transmission electron microscopy ͉ inorganic closed-cage structures

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Section: Resultsmentioning

confidence: 99%

“…Focal series reconstruction (FSR) was used to retrieve the phase of the electron exit plane wavefunction (29,30). Experimental focal series were taken with an equidistant focal step corresponding to half the defocus spread of the microscope at the respective acceleration voltage.…”

Section: Methodsmentioning

confidence: 99%

Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures

Bar‐Sadan

Houben

Enyashin

et al. 2008

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

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“…It is an interferogram of scattered beams andin general -image simulations are required to relate the recorded intensity pattern to the materials structure. Directly interpretable images with atomic resolution became available more recently by the reconstruction of the electron exit waves from focal series of lattice images [23,24] (Fig. 1, center) or by recording HAADF-STEM images (Fig.…”

Section: Instrumental Improvementsmentioning

confidence: 99%

“…Therefore, sub-Ångstrom resolution can be achieved [27,28] and dislocation cores in <110> oriented semiconductors can be imaged with truly atomic resolution, which was not possible before since their dumbbell spacing in <110> projection is often smaller (< 0.15 nm) than the typical 0.18 nm Scherzer point resolution of traditional phase contrast microscopes [27]. Moreover, residual lens aberration can be corrected by numerical phase plates in the exit wave reconstruction process [24]. This approach complements the successful correction of lens aberrations by hardware correctors [29] and for reasons outlined in References 22 and 30 it is most advantageous to combine both methods.…”

Section: Instrumental Improvementsmentioning

confidence: 99%

Sub-angstrom imaging of dislocation core structures: how well are experiments comparable with theory?

Kisielowski

Freitag²,

et al. 2006

Philosophical Magazine

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During the past 50 years Transmission Electron Microscopy (TEM) has evolved from an imaging tool to a quantitative method that approaches the ultimate goal of understanding the atomic structure of materials atom by atom in three dimensions both experimentally and theoretically. Today's TEM abilities are tested in the special case of a Ga terminated 30 degree partial dislocation in GaAs:Be where it is shown that a combination of highresolution phase contrast imaging, Scanning TEM, and local Electron Energy Loss Spectroscopy allows for a complete analysis of dislocation cores and associated stacking faults. We find that it is already possible to locate atom column positions with picometer precision in directly interpretable images of the projected crystal structure and that chemically different elements can already be identified together with their local electronic structure. In terms of theory, the experimental results can be quantitatively compared with ab initio electronic structure total energy calculations. By combining elasticity theory methods with atomic theory an equivalent crystal volume can be addressed. Therefore, it is already feasible to merge experiments and theory on a picometer length scale. While current experiments require the utilization of different, specialized instruments it is foreseeable that the rapid improvement of electron optical elements will soon generate a next generation of microscopes with the ability to image and analyze single atoms in one instrument with deep sub Ångstrom spatial resolution and an energy resolution better than 100 meV.

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Atomic Precision Measurement of Individual Atom Positions in Defects by Aberration Corrected HRTEM

Houben

Thust

Urban

2005

MAM

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The combination of imaging in a spherical-aberration corrected transmission electron microscope [1][2] with subsequent numerical focal series reconstruction of the exit-plane wave function (EPW) [3][4] is applied to achieve a reliable quantification of the position of individual atomic columns in defects. An approach for the determination of individual atomic column positions which allows the quantification of the measurement accuracy and is appropriate for non-periodic defects is presented. The approach is based on a regression analysis of peak maxima in the directly interpretable phase image of the EPW retrieved from a focal series of images of a sufficiently thin object. While systematic errors in the positional data are minimized by the compensation of residual aberrations from the EPW, the statistical error due to residual noise in the EPW can be assessed for single, unique atomic columns via the regression analysis.Figs. 1-3 show the application in the case of a 90° [100] tilt grain boundary in YBa 2 Cu 3 O 7-δ (YBCO), where individual positions in the cation and the oxygen sublattice were determined. Fig. 1 displays the EPW retrieved from a focal series taken in a Philips CM200 FEG ST sphericalaberration corrected microscope [2]. The images were acquired at negative spherical aberration to benefit from an enhanced signal of light elements [7]. Residual aberrations are removed from the EPW, resulting in an excellent pattern match with simulated data and a conservation of the symmetry properties of the basic structure in periodic regions. To account for the overlap of neighbouring columns, peak positions for oxygen columns were measured by a multiple Gaussian least-squares fit of phase profiles (Fig. 2a). The regression analysis typically yields a 2σ error radius of 6 pm for oxygen column positions in the periodic parts, increasing to about 20 pm in the grain boundary due to closer spaced columns. For the stronger signal of cation columns 2σ error radii of 2 pm and 4 pm are found respectively. Fig. 3 highlights the individual columns displacements in the reconstructed structure of the grain boundary. Fig. 2b displays the bondlengths between the plane copper Cu2, the chain copper Cu1 and the apical oxygen O1, which are the relevant distances correlated with a charge transfer between the copper planes and the superconducting properties [5]. An excellent match with neutron scattering data from ref. [5] is found in the periodic part, whereas a change of these bondlengths is measured with statistical significance in the grain boundary. Complemented with the sensitivity enhancement for light elements and the possibility of measuring the oxygen occupancy of individual lattice sites offered by the aberration correction [6][7], the atomistic study of the local oxygen coordination at defects in oxide materials can thus provide realistic input data for modelling and understanding electronic-structure relations in these materials.

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Focal-series reconstruction in HRTEM: simulation studies on non-periodic objects

Cited by 257 publications

References 13 publications

Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures

Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures

Sub-angstrom imaging of dislocation core structures: how well are experiments comparable with theory?

Atomic Precision Measurement of Individual Atom Positions in Defects by Aberration Corrected HRTEM

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