Exit-surface wave reconstruction using a focal series

1992 ◽  
Vol 50 (2) ◽  
pp. 988-989
Author(s):  
W.J. de Ruijter ◽  
M.R. McCartney ◽  
David J. Smith ◽  
J.K. Weiss
Keyword(s):  
Surface Wave ◽  
Spherical Aberration ◽  
Data Extraction ◽  
High Sensitivity ◽  
Geometric Distortion ◽  
Variation Method ◽  
Objective Lens ◽  
Immediate Reconstruction ◽  
Exit Surface ◽  
Electron Microscopes

Further advances in resolution enhancement of transmission electron microscopes can be expected from digital processing of image data recorded with slow-scan CCD cameras. Image recording with these new cameras is essential because of their high sensitivity, extreme linearity and negligible geometric distortion. Furthermore, digital image acquisition allows for on-line processing which yields virtually immediate reconstruction results. At present, the most promising techniques for exit-surface wave reconstruction are electron holography and the recently proposed focal variation method. The latter method is based on image processing applied to a series of images recorded at equally spaced defocus.Exit-surface wave reconstruction using the focal variation method as proposed by Van Dyck and Op de Beeck proceeds in two stages. First, the complex image wave is retrieved by data extraction from a parabola situated in three-dimensional Fourier space. Then the objective lens spherical aberration, astigmatism and defocus are corrected by simply dividing the image wave by the wave aberration function calculated with the appropriate objective lens aberration coefficients which yields the exit-surface wave.

The ORNL Aberration-Corrected STEM/TEM Project

2001 ◽  
Vol 7 (S2) ◽  
pp. 906-907
Author(s):  
L. F. Allard ◽  
E. Voelkl ◽  
D. A. Blom ◽  
T. A. Nolan ◽  
F. Kahl ◽  
...  
Keyword(s):  
Spherical Aberration ◽  
National Laboratory ◽  
Dark Field ◽  
Electron Gun ◽  
Objective Lens ◽  
Resolution Limit ◽  
Oak Ridge ◽  
Transfer Characteristics ◽  
Dark Field Imaging ◽  
Electron Microscopes

Field emission electron microscopes operating at 200kV or 300kV and incorporating aberration correctors for either the incident electron probe or for the primary aberrations of the objective lens (OL) are currently under development for several laboratories in the world. OL-corrected instruments require monochromators for the electron beam, built into the electron gun prior to the accelerating stages, in order to optimize the contrast transfer characteristics of the objective lens to push the instrumental resolution limit to well beyond 0.1nm. This will allow the point resolution limit as controlled by the correction of spherical aberration Cs to potentially extend to the instrumental limit of better than 0.1nm. Figure 1 shows the contrast transfer characteristics of a Cs-corrected 200kV TEM, both without and with a beam monochromator.Dedicated STEM instruments such as the 300kV VG-603 and lOOkV VG-501 at Oak Ridge National Laboratory, and other VG instruments at Cornell University and IBM Co. are also being adapted (by Nion Co., Kirkland, WA) to incorporate aberration correctors for the incident probe. The aim is to improve the resolution of the VG-603 instrument in dark-field imaging mode, for example, from 0.13nm to 0.05nm. in another ORNL project, the High Temperature Materials Laboratory has contracted JEOL Ltd. to construct a STEM-TEM instrument with a probe corrector designed and built by CEOS GmbH (Heidelberg, Germany).

Plenary Special Lectures

2013 ◽  
Vol 19 (S3) ◽  
pp. 11-14
Author(s):  
Harald Rose ◽  
Joris Dik
Keyword(s):  
Spherical Aberration ◽  
Rotational Symmetry ◽  
Objective Lens ◽  
Aberration Correction ◽  
Time Varying ◽  
Resolution Limit ◽  
Space Charges ◽  
Rotationally Symmetric ◽  
Electron Microscopes

The correction of the aberrations of electron lenses is the long story of many seemingly fruitless efforts to improve the resolution of electron microscopes by compensating for aberrations of round electron lenses over a period of 50 years. The problem started in 1936 when Scherzer demonstrated that the chromatic and spherical aberrations of rotationally symmetric electron lenses are unavoidable. Moreover, the coefficients of these aberrations cannot be made sufficiently small. As a result, the resolution limit of standard electron microscopes equals about one hundred times the wavelength of the electrons, whereas modern light microscopes have reached a resolution limit somewhat smaller than the wavelength. In 1947, Scherzer found an ingenious way for enabling aberration correction. He demonstrated in a famous article that it is in theory possible to eliminate chromatic and spherical aberrations by lifting any one of the constraints of his theorem, either by abandoning rotational symmetry or by introducing time-varying fields, or space charges. Moreover, he proposed a multipole corrector compensating for the spherical aberration of the objective lens.

Electron Microscopic Observation of Crystal Lattice Images

1972 ◽  
Vol 30 ◽  
pp. 548-549
Author(s):  
Tsutomu Komoda
Keyword(s):  
Electron Microscope ◽  
Spherical Aberration ◽  
Electron Microscopic Observation ◽  
Chromatic Aberration ◽  
Operating Conditions ◽  
Optimum Operating ◽  
Objective Lens ◽  
Electron Microscopic ◽  
Electron Microscopes ◽  
Lattice Resolution

Electron microscope images of crystal lattices have been observed by many authors since the first achievement by Menter in 1956. During these years, the optimum operating conditions with electron microscopes have been investigated for the high resolution lattice imaging. Finally minute lattice spacings around 1 Å have been resolved by several authors by using contemporary instruments. The major lattice planes with low index in crystals are almost within a range of spacing capable to be resolved by electron microscopy (1-3 Å). Therefore, the observing techniques are now essential for practical studies in the area of crystallography as well as metal physics.Although the point to point resolution of the electron microscope is restricted due to the spherical aberration of the objective lens in addition to the diffraction, the lattice resolution is mainly limited due to the chromatic aberration under the normal illumination.

State of the development of multipole correctors for a probe-forming system and a high-resolution 200kV TEM

1995 ◽  
Vol 53 ◽  
pp. 596-597
Author(s):  
M. Haider ◽  
J. Zach
Keyword(s):  
High Resolution ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Limiting Factors ◽  
Objective Lens ◽  
Probe Diameter ◽  
Physical Limit ◽  
Low Energies ◽  
Routine Basis ◽  
Electron Microscopes

The development of modern high resolution electron microscopes has shown the emergence of new modern microscopes which are easy to operate and, more importantly, with which one can attain high resolution on a routine basis. However, the physical limit set by the inherent aberrations of electron lenses could not be overcome by simply optimising the geometry of the pole pieces. The only direct way to get rid of the aberrations of the round lenses is to use a corrector with which the resolution limiting aberrations can be compensated.For the observation of uncoated biological surfaces we started a project to develop a Low Voltage Scanning Electron Microscope (LVSEM). The main problem with using low energies is to design electron optics with which one can achieve high resolution in the range of 1 nm at energies of 1 keV and below. Hence, the two main axial aberrations of such a probe forming system: the chromatic and the spherical aberration Cc and C3, respectively, have to be considered as the limiting factors of the probe diameter. Therefore, the compensation of these two aberrations is the best choice as one does not want to run into other limitations if, for example, the geometry of the objective lens is scaled down in order to obtain small aberration coefficients.

Mirror-hexapole corrector with compact beam splitter for eliminating the chromatic and spherical aberration of low-voltage EMs

1992 ◽  
Vol 50 (1) ◽  
pp. 94-95
Author(s):  
H. Rose
Keyword(s):  
Beam Splitter ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Deflection System ◽  
Magnetic Deflection ◽  
Electron Microscopes ◽  
Electrostatic Mirror ◽  
Illuminating Beam

To significantly improve the performance of electron microscopes it is necessary to enlarge the usable aperture. At low voltages this requirement can only be met if the chromatic and the spherical aberration are corrected simultaneously. For imaging surfaces with reflected electrons (LEEM) a magnetic deflection system separating the illuminating beam from the image-forming beam must be incorporated in the region above the objective lens. Since the use of an electrostatic mirror for the correction of the chromatic aberration also necessitates such a system, it would be extremely helpful if the beam splitter can be designed in such a way that it also separates the parts of the image-forming beam heading toward and away from the mirror.

Advanced computing for ultra-high-resolution in TEM

1995 ◽  
Vol 53 ◽  
pp. 36-37
Author(s):  
A. Thust ◽  
W. M. J. Coene
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
Objective Lens ◽  
Medium Voltage ◽  
Extra Information ◽  
Electron Microscopes ◽  
Advanced Computing ◽  
Direct Use ◽  
Delocalization Effects ◽  
Conventional Medium

1. Introduction Attempts to push the resolution of electron microscopes towards 1 Å follow presently two different strategies. One approach takes advantage of the short electron wavelength provided by high-voltage instruments (E > 1 MeV) resulting in an "interpretable" point resolution close to the information limit. An alternative strategy is based on the idea to extend the information limit of conventional medium-voltage instruments (E ≈ 200 - 300 keV) by taking advantage of the excellent coherence properties of field-emission guns (FEG). In the latter approach, however, the gain of extra information beyond the "interpretable" point resolution is of no direct use for structure interpretation. Generally, the interpretability of single highresolution images suffers from a loss of phase information and from contrast-delocalization effects, the latter being caused by the spherical aberration and the defocussing of the objective lens. These derealization effects become drastically apparent when aiming at the ultra-high resolution regime (d < 1.5 Å) which is routinely accessible with medium-voltage FEG-TEMs.

Calculations and experimental observations of shadow images from multilayers

1990 ◽  
Vol 48 (4) ◽  
pp. 440-441
Author(s):  
Shiyao Wang ◽  
M. Gajdardziska-Josifovska ◽  
J.M. Cowley
Keyword(s):  
Spherical Aberration ◽  
High Sensitivity ◽  
Objective Lens ◽  
Interference Effects ◽  
Probe Position ◽  
Cross Sectional ◽  
Detection Plane ◽  
Resolution Imaging ◽  
Convergent Beam ◽  
Established Technique

The properties of multilayer thin film materials are strongly influenced by the structure of their interfaces. The numerous applications for these materials motivate electron microscopy studies of cross sectional samples in which the interfaces are observed edge on. High resolution imaging is the most established technique, but other techniques, such as Fresnel fringe method and refraction at interfaces, have also been employed to characterize the structure and abruptness of amorphous/polycrystalline multilayers. The aim of this work is to explore the applicability of shadow images from coherent sources to the studies of multilayers.Coherent interference effects are readily observable in the diffraction plane of a VG HB-5 STEM which is equipped with a cold field emission gun. The shadow image of the studied Si/Mo multilayer is obtained on the detection plane when the specimen is illuminated by a stationary convergent beam. This beam is formed with a very large or no objective aperture. Low magnification images are produced at large values of defocus (Fig. 1a), while for lower defocus the magnification increases and the shadow images become more and more distorted because of the objective lens aberration (Fig. 1b and 1c). In addition to the high sensitivity to the defocus. spherical aberration and probe position, the shadow images also appear to be dependent on the interface abruptness.

Quantum noise characteristics in TEM images measured by means of imaging plate

1991 ◽  
Vol 49 ◽  
pp. 546-547
Author(s):  
T. Oikawa ◽  
N. Mori ◽  
F. Hosokawa ◽  
M. Kawasaki
Keyword(s):  
Quantum Noise ◽  
Spherical Aberration ◽  
High Sensitivity ◽  
Amorphous Film ◽  
Original Data ◽  
Objective Lens ◽  
Imaging Plate ◽  
Electron Dose ◽  
Noise Characteristics ◽  
Spatial Frequencies

In the observation of the beam sensitive specimens, it is required to minimize the electron dose. At a very low electron dose, however, the electrons themselves become quantum noise, thus lowering the image quality regardlessly of the performance of the detectors. In the present study, the relationship of quantum noise with the image signal included in TEM images has been measured by means of the Imaging Plate (IP), which is a high sensitivity detector.The instrument used was the TEM-IP system, a PIXsysTEM based on the JEM-2000FXII.Phase contrast images of the amorphous film were taken at a very low dose where quantum noise is dominant. The images were taken using an objective lens with a spherical aberration constant of 2.3 mm and an accelerating voltage of 200 kV. The spatial frequencies included in the images were estimated by Fourier transformation, which was carried out on the IP-processor of the PIXsysTEM, by using the original data from the IP. In this experiment, it was already ascertained that system noise (noise due to the instrument) is negligible.

Multi-dimensional and multi-signal approaches in scanning transmission electron microscopes

2009 ◽  
Vol 367 (1903) ◽  
pp. 3845-3858 ◽  
Author(s):  
C. Colliex ◽  
N. Brun ◽  
A. Gloter ◽  
D. Imhoff ◽  
M. Kociak ◽  
...  
Keyword(s):  
Energy Resolution ◽  
Spherical Aberration ◽  
Objective Lens ◽  
Performance Limits ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Successful Design ◽  
Electron Microscopes ◽  
Data Acquisition And Processing ◽  
Available Information

Developments in instrumentation are essential to open new fields of science. This clearly applies to electron microscopy, where recent progress in all hardware components and in digitally assisted data acquisition and processing has radically extended the domains of application. The demonstrated breakthroughs in electron optics, such as the successful design and practical realization and the use of correctors, filters and monochromators, and the permanent progress in detector efficiency have pushed forward the performance limits, in terms of spatial resolution in imaging, as well as for energy resolution in electron energy-loss spectroscopy (EELS) and for sensitivity to the identification of single atoms. As a consequence, the objects of the nanoworld, of natural or artificial origin, can now be explored at the ultimate atomic level. The improved energy resolution in EELS, which now encompasses the near-IR/visible/UV spectral domain, also broadens the range of available information, thus providing a powerful tool for the development of nanometre-level photonics. Furthermore, spherical aberration correctors offer an enlarged gap in the objective lens to accommodate nanolaboratory-type devices, while maintaining angström-level resolution for general characterization of the nano-object under study.

Aberration Correction in Electron Microscopy

1978 ◽  
Vol 36 (3) ◽  
pp. 185-196 ◽  
Author(s):  
H. Koops
Keyword(s):  
Phase Contrast ◽  
Collection Efficiency ◽  
Spherical Aberration ◽  
Objective Lens ◽  
Resolution Limit ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Beam Transmission ◽  
Contrast Image ◽  
Fixed Beam

Most presently available fixed-beam transmission electron microscopes (FBEM) yield a resolution limit close to the theoretically predicted value which is determined by diffraction and by the spherical aberration of the objective lens. The larger the aperture the better is the collection efficiency of the elastically scattered electrons forming the image. To increase the useful objective aperture it is necessary to overcome the spherical aberration. In the case of a phase contrast image it is possible, at least in principle, to compensate the effect of the spherical aberration by subsequent holographic processing of the electron micrograph.

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