Sub-ångstro¨m structure characterisation: the Brite-Euram route towards one ångstro¨m

Dyck, D. Van; Lichte, Hannes; Mast, K.D. van der

doi:10.1016/0304-3991(96)00057-5

Cited by 65 publications

(27 citation statements)

References 20 publications

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“…For the first time we report an interpretable resolution of better than 0.085 nm that is close to the 0.080 nm information limit that one expected from such an instrument 25 . A focal series reconstruction package 20 was employed to extend the point resolution of 0.168 nm of the instrument towards its information limit.…”

Section: Introductionsupporting

confidence: 71%

“…Our spherical aberration constant of 0.595 + 0.005 mm is small if the sample is located at the euzentric height and objective lens currents is kept constant. A value of 0.62 + 0.01 mm was reported before 25 .…”

Section: Discussionmentioning

confidence: 87%

“…where ∆ models the 1/e half width of a Gaussian spread of focus due to chromatic aberrations which can be approximated by 15,25,42 : exhibit the same sign. However, misphased information can be transferred far beyond this point resolution to a 1/e 2 limit that is imposed by partial coherence that can be spatial…”

Section: Methodsmentioning

confidence: 99%

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Imaging columns of the light elements carbon, nitrogen and oxygen with sub Ångstrom resolution

et al. 2001

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It is reported that lattice imaging with a 300 kV field emission microscope in combination with numerical reconstruction procedures can be used to reach an interpretable resolution of about 80 pm for the first time. A retrieval of the electron exit wave from focal series allows for the resolution of single atomic columns of the light elements carbon, nitrogen, and oxygen at a projected nearest neighbor spacing down to 85 pm. Lens aberrations are corrected on-line during the experiment and by hardware such that resulting image distortions are below 80 pm. Consequently, the imaging can be aberration-free to this extent. The resolution enhancement results from increased electrical and mechanical stability's of the instrument coupled with a low spherical aberration coefficient of 0.595 + 0.005 mm.

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Section: Introductionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 87%

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Imaging columns of the light elements carbon, nitrogen and oxygen with sub Ångstrom resolution

et al. 2001

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“…With improvements in hardware and special attention to microscope environment, resolving powers close to or exceeding the one Ångstrom (0.1nm) barrier have been achieved by the latest generation of high-voltage HREMs [2][3][4]. Similar performance levels have been reached by dedicated scanning and conventional medium-voltage instruments [5,6], while sub-Ångstrom electron microscopy to resolutions of close to 0.8 nm has since been achieved using exit-wave retrieval [7,8]. Meanwhile, after a relatively dormant period during much of the 1990s, the last several years have witnessed a veritable explosion of further instrumentation hardware, including the successful implementation of aberration correctors for both conventional [9] and scanning [10] TEMs, as well as the design of electron monochromators which provide reduced energy spread and hence improved source coherence [11].…”

mentioning

confidence: 92%

Progress and Perspectives for Atomic-Resolution Electron Microscopy

Smith

2005

MAM

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The atomic-resolution capabilities of the electron microscope, which first became widely accessible in the 1980s, have had a major impact across many disciplines [1]. With carefully prepared samples and correct operating conditions, assisted by quantitative image recording and processing, image characteristics can be interpreted directly in terms of individual atomic columns. With improvements in hardware and special attention to microscope environment, resolving powers close to or exceeding the one Ångstrom (0.1nm) barrier have been achieved by the latest generation of high-voltage HREMs [2][3][4]. Similar performance levels have been reached by dedicated scanning and conventional medium-voltage instruments [5,6], while sub-Ångstrom electron microscopy to resolutions of close to 0.8 nm has since been achieved using exit-wave retrieval [7,8]. Meanwhile, after a relatively dormant period during much of the 1990s, the last several years have witnessed a veritable explosion of further instrumentation hardware, including the successful implementation of aberration correctors for both conventional [9] and scanning [10] TEMs, as well as the design of electron monochromators which provide reduced energy spread and hence improved source coherence [11]. These latest developments have generated great interest and enthusiasm within the microscopy community, as well as attracting much attention from the broader materials community, especially for potential applications related to the rapidly emerging fields of nanoscience and nanotechnology.All electron lenses suffer from performance-limiting aberrations that must be removed in order to attain theoretical resolution limits. Two-fold astigmatism and third-order axial coma can be corrected manually by an experienced operator but for improved reliability and greater accuracy, online computer control or 'autotuning' of the microscope based, for example, on automated diffractogram analysis is recommended [12]. With the advent of aberration correctors, digital acquisition via slowscan CCD cameras has become indispensable. Computer analysis and control of corrector power supplies is essential for determining and then correcting most aberrations up to fourth order, including three-fold objective lens astigmatism and spherical aberration [13,14]. In the case of the probe-forming lens of the STEM, correction of the aberrations is done using multiple quadrupoleoctopole elements following analysis of a Ronchigram or shadow image obtained from a thin amorphous film [10,13]. For conventional TEM imaging, aberration correction is achieved with a double hexapole system and utilizes a tilt series of diffractograms, again relying on the availability of a thin amorphous film [14]. Aberration correction can also be tackled using a posteriori methods, such as exit-wave reconstruction based on through-focal image-series [7,8]. Similar resolution enhancements have been achieved using atomic-resolution electron holography [15]. Chromatic aberration remains as a serious obstacle to achievement of d...

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“…Using exit wave reconstruction, the information limit can be reached by correcting the phase changes due to the spherical aberration (C s ) of the objective lens [1]. A great advantage of this technique is that the amplitude as well as the phase of the exit wave is reconstructed and since the light atom columns are revealed in the phase of the exit wave [2], it is possible to image oxygen atoms in the presence of heavier atoms.…”

mentioning

confidence: 99%

Statistical Estimation of Oxygen Atomic Positions with Sub Ångstrom Precision from Exit Wave Reconstruction

Bals

Aert

Tendeloo

et al. 2005

MAM

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Although high resolution transmission electron microscopy (HRTEM) is considered as the standard technique to study the atomic structure of materials, interpretation of HRTEM images is not always straightforward because of aberrations of the electromagnetic lens system. The information which can be obtained by qualitative HRTEM is therefore limited by the Scherzer point-resolution, but for a coherent electron source (field emission gun) the actual information limit of the microscope is beyond the Scherzer resolution. Using exit wave reconstruction, the information limit can be reached by correcting the phase changes due to the spherical aberration (C s ) of the objective lens [1]. A great advantage of this technique is that the amplitude as well as the phase of the exit wave is reconstructed and since the light atom columns are revealed in the phase of the exit wave [2], it is possible to image oxygen atoms in the presence of heavier atoms.We have applied exit wave reconstruction to determine an atomic model for the new compound Bi 4 Mn 1/3 W 2/3 O 8 Cl of which the space group is determined to be Cm2m [3]. A focal series of 20 images with an equidistant focal decrease is recorded along the [1-10] zone axis and the numerical reconstruction of the exit wave is carried out using the TrueImage software [4]. After reconstruction and correction for the aberrations, the phase is extracted from the complex exit wave. As illustrated in Figure 1, the phase of the exit wave clearly shows the Cl atoms and the projected {WO 6 }/{MnO 6 } octahedra with the oxygen atoms revealed as well. Two types of bismuth atoms can be distinguished in the image, i.e. Bi(1) and Bi(2). Around Bi(2), separate smaller dots corresponding to the oxygen atoms from the basal square plane can be observed, whereas we can observe the Bi(1) blobs with an extension corresponding to the oxygen atoms. Since the projected distance Bi(1)-O is equal to 0.97 Å, which is close to the information limit, it is not possible to observe Bi (1) and O separately.The phase of the exit wave is often considered as the final result, but in this study it is used as a starting point for quantitative refinement of the atom positions. This is done using statistical parameter estimation theory [5,6]. By adapting a parametric model to the experimental phase in the least-squares sense, it is possible to determine the atom positions. Using the Cramér-Rao Lower Bound as a measure of the precision, it can be shown that sub-Ångstrom precision is within reach. The result is presented in Figure 2, where the experimental phase is compared with the model evaluated at the estimated parameters [7].

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Sub-ångstro¨m structure characterisation: the Brite-Euram route towards one ångstro¨m

Cited by 65 publications

References 20 publications

Imaging columns of the light elements carbon, nitrogen and oxygen with sub Ångstrom resolution

Imaging columns of the light elements carbon, nitrogen and oxygen with sub Ångstrom resolution

Progress and Perspectives for Atomic-Resolution Electron Microscopy

Statistical Estimation of Oxygen Atomic Positions with Sub Ångstrom Precision from Exit Wave Reconstruction

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