New Feasible Concepts of Aberration Correction for Realizing High-Resolution Electron Microscopes

1990 ◽  
Vol 48 (1) ◽  
pp. 202-203
Author(s):  
H. Rose
Keyword(s):  
Spherical Aberration ◽  
Wave Length ◽  
Electron Wave ◽  
Optical Lens ◽  
Resolution Electron ◽  
Rotationally Symmetric ◽  
Electron Microscopes ◽  
The Cost ◽  
Imaging Performance ◽  
Acceleration Voltage

The imaging performance of the light optical lens systems has reached such a degree of perfection that nowadays numerical apertures of about 1 can be utilized. Compared to this state of development the objective lenses of electron microscopes are rather poor allowing at most usable apertures somewhat smaller than 10-2 . This severe shortcoming is due to the unavoidable axial chromatic and spherical aberration of rotationally symmetric electron lenses employed so far in all electron microscopes.The resolution of such electron microscopes can only be improved by increasing the accelerating voltage which shortens the electron wave length. Unfortunately, this procedure is rather ineffective because the achievable gain in resolution is only proportional to λ1/4 for a fixed magnetic field strength determined by the magnetic saturation of the pole pieces. Moreover, increasing the acceleration voltage results in deleterious knock-on processes and in extreme difficulties to stabilize the high voltage. Last not least the cost increase exponentially with voltage.

Probe size and 5th-order aberration

1987 ◽  
Vol 45 ◽  
pp. 134-135 ◽  
Author(s):  
Zhifeng Shao
Keyword(s):  
Electron Probe ◽  
Spherical Aberration ◽  
Wave Length ◽  
Cylindrical Symmetry ◽  
Electron Wave ◽  
Third Order ◽  
The Third ◽  
Probe Radius ◽  
Small Probe ◽  
Probe Size

A small electron probe has many applications in many fields and in the case of the STEM, the probe size essentially determines the ultimate resolution. However, there are many difficulties in obtaining a very small probe.Spherical aberration is one of them and all existing probe forming systems have non-zero spherical aberration. The ultimate probe radius is given byδ = 0.43Csl/4ƛ3/4where ƛ is the electron wave length and it is apparent that δ decreases only slowly with decreasing Cs. Scherzer pointed out that the third order aberration coefficient always has the same sign regardless of the field distribution, provided only that the fields have cylindrical symmetry, are independent of time and no space charge is present. To overcome this problem, he proposed a corrector consisting of octupoles and quadrupoles.

Limits for high-resolution electron microscopy of inorganic materials?

1987 ◽  
Vol 45 ◽  
pp. 4-5
Author(s):  
David J. Smith
Keyword(s):  
Electron Microscopy ◽  
Spherical Aberration ◽  
High Resolution Electron Microscopy ◽  
Inorganic Materials ◽  
Atomic Scale ◽  
Resolution Limit ◽  
Contrast Transfer Function ◽  
Existing Problems ◽  
Resolution Electron ◽  
Electron Microscopes

The era of atomic-resolution electron microscopy has finally arrived. In virtually all inorganic materials, including oxides, metals, semiconductors and ceramics, it is possible to image individual atomic columns in low-index zone-axis projections. A whole host of important materials’ problems involving defects and departures from nonstoichiometry on the atomic scale are waiting to be tackled by the new generation of intermediate voltage (300-400keV) electron microscopes. In this review, some existing problems and limitations associated with imaging inorganic materials are briefly discussed. The more immediate problems encountered with organic and biological materials are considered elsewhere.Microscope resolution. It is less than a decade since the state-of-the-art, commercially available TEM was a 200kV instrument with a spherical aberration coefficient of 1.2mm, and an interpretable resolution limit (ie. first zero crossover of the contrast transfer function) of 2.5A.

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.

High-resolution electron holography of MgO

1991 ◽  
Vol 49 ◽  
pp. 672-673
Author(s):  
T. Tanji ◽  
K. Urata ◽  
K. Ishizuka
Keyword(s):  
Image Processing ◽  
Wave Function ◽  
Spherical Aberration ◽  
Objective Lens ◽  
Electron Holography ◽  
Electron Wave Function ◽  
Resolution Limit ◽  
Electron Wave ◽  
Transmission Electron ◽  
Resolution Electron

Electron holography is a useful application of a transmission electron microscope instrument equipped with a field emission gun (FE-TEM). The peculiarity of holography is ability to record and reconstruct the complex amplitude of an electron wave function. This characteristic makes many kinds of image processing applicable, for instance, image restoration and interferometry. Especially the correction of aberrations is expected to overcome the resolution limit owing to the spherical aberration of an electron objective lens. A few preliminary works have been reported, where a laser optical system or a digital computer system was used to reconstruct image waves and to correct the aberrations. The image qualities, however, were not enough to improve the point resolution.

First Application of a Spherical-Aberration Corrected Microscope Material Science

1998 ◽  
Vol 4 (S2) ◽  
pp. 384-385
Author(s):  
B. Kabius ◽  
K. Urban ◽  
M. Haider ◽  
S. Uhlemann ◽  
E. Schwan ◽  
...  
Keyword(s):  
Spherical Aberration ◽  
Wave Length ◽  
High Resolution Electron Microscopy ◽  
Objective Lens ◽  
Medium Voltage ◽  
Resolution Electron ◽  
Challenging Tasks ◽  
Commercial Medium ◽  
Atomic Spacing ◽  
Atomistic Structure

One of the most challenging tasks for high-resolution electron microscopy (HREM) is the atomistic investigation of defects and interfaces in thin films of semiconductors and ceramics. In particular, the application of these materials in electronic devices requires the understanding of the atomistic structure responsible for electronic and optical properties. The imaging of these structures requires a point resolution down to 0.1 nm. For example the smallest atomic spacing of GaAs in the (110) projection is 0.14 nm. According to Scherzer the point resolution of the TEM is proportional to spherical-aberration coefficient Cs1/4 and to the wave length λ3/4. Commercial medium-voltage microscopes up to 400 kV offer only a point resolution of 0.16 nm due to the high spherical-aberration constant Cs of the electromagnetic objective lens. Decreasing the wave length λ by increasing the electron energy improves the point resolution, but has the drawback of severe radiation damage and high costs.

An Automated Procedure for On-Line Measurement of Spherical-Aberration Coefficient of High-Resolution Electron Microscopes

1996 ◽  
Vol 54 ◽  
pp. 420-421 ◽  
Author(s):  
M. Pan ◽  
O.L. Krivanek
Keyword(s):  
High Resolution ◽  
Structural Information ◽  
Spherical Aberration ◽  
Amorphous Material ◽  
Ccd Camera ◽  
Objective Lens ◽  
Resolution Electron ◽  
Line Measurement ◽  
On Line ◽  
Electron Microscopes

Spherical aberration coefficient (Cs) of the objective lens and electron wavelength ultimately determine the point-resolution of a high resolution electron microscope (HREM). Accurate measurement of Cs has become increasingly critical for reconstruction of structural information well beyond the point-resolution by means of either electron holography or focal series methods with a field emission gun (FEG) microscope. There are two main existing procedures for Cs measurement, i.e. (1) using diffractograms from a thin amorphous material, and (2) using beam-tilt-induced image displacement (BID). Since these procedures generally involve intensive data measurement, it is highly desirable to have an automated procedure. With an image pickup system such as CCD camera and appropriate software, we have developed an automated procedure for on-line Cs measurement. The procedure is based on analyzing diffractograms from a thin amorphous material such as amorphous carbon or germanium. The use of CCD camera allows for on-line measurement, and also for magnification to be calibrated with high precision, which is critical in Cs measurement.

Informational Analysis of Performance for a High Resolution Electron Microscore

1969 ◽  
Vol 27 ◽  
pp. 182-183 ◽  
Author(s):  
T. A. Welton
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Focal Plane ◽  
Spherical Aberration ◽  
Performance Criteria ◽  
Contrast Level ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Electron Microscopes ◽  
Analysis Of Performance

Conventional performance criteria for transmission electron microscopes generally involve statements of the spatial resolution permitted by the aberrations of the system and the contrast level permitted by the nature of the object under study. An attempt has been made to formulate a more meaningful set of criteria, which take into account all the essential phenomena encountered in the study by transmission electron microscopy of biologically important macromoleeules. These phenomena include beam coherence and energy spread, interaction of beam with sample, defocus and primary and secondary spherical aberration, diffraction by the objective aperture and retardation by a possible phase shift film in the back focal plane, multiple scattering of electrons in the detecting emulsion, and noise arising from electron and silver grain statistics.

Modeling of Structures Nanocrystalline and Amorphous Alloys

2015 ◽  
Vol 245 ◽  
pp. 60-66
Author(s):  
Aleksandr Dubinets ◽  
Evgeny Pustovalov ◽  
Evgeny B. Modin ◽  
Aleksandr N. Fedorets ◽  
Vladimir Tkachev ◽  
...  
Keyword(s):  
Amorphous Alloys ◽  
Amorphous Matrix ◽  
Nanocrystalline Structure ◽  
Close Packing ◽  
Metal Alloys ◽  
Electron Wave ◽  
Amorphous Metal Alloys ◽  
Nanocrystalline And Amorphous ◽  
Resolution Electron ◽  
Electron Microscopes

In this paper discusses and demonstrates the possibility of modeling materials with amorphous and nanocrystalline structure using random close packing of atoms and nanoclusters models. Concordance structure of the real models alloys was evaluated by the radial distribution function obtained as a result of calculations, and in its modeled structures estimation. Modeling structure of the amorphous matrix and the spatial distribution of nanoclusters in two-component amorphous alloys with composition Fe80B20carried out by Ishikawa method. For modeling structure multicomponent amorphous metal alloys we developed correlation-spectral model of the amorphous matrix and nanoclusters. At modeling passing electron wave through the sample used a layered approach, and for the "visualization" imaging we modeled optical schemes of high-resolution electron microscopes.

scholarly journals Impact of Pupil Aberrations on Wavefront Manipulation

2021 ◽  
Vol 255 ◽  
pp. 03004
Author(s):  
Thomas Nobis
Keyword(s):  
Quantitative Analysis ◽  
Field Dependence ◽  
Spherical Aberration ◽  
Practical Case ◽  
Optical Elements ◽  
Rotationally Symmetric ◽  
Imaging Performance ◽  
The Impact ◽  
Analytical Expressions

A systematic and quantitative analysis is given of the impact of pupil aberrations on the imaging performance in wavefront manipulation applications using adaptive optical elements. For the practical case of rotationally-symmetric types of wavefront corrections, such as defocus or spherical aberration, analytical expressions of the induced aberrations are derived including their pupil and field dependence. Each aberration is thereby related to the specific pupil aberration present at the adaptive element. The results can be used to specify the acceptable amount of pupil correction required for a specific magnitude and type of wavefront manipulation.

Design of objective lens for 200-kV high-resolution electron microscopes

1983 ◽  
Vol 41 ◽  
pp. 314-315
Author(s):  
K. Tsuno ◽  
T. Honda ◽  
Y. Harada ◽  
M. Naruse
Keyword(s):  
Optical Properties ◽  
Computer Technology ◽  
Axial Magnetic Field ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Resolution Electron ◽  
Correction Of Astigmatism ◽  
Three Stages ◽  
Electron Microscopes ◽  
Stage 1

Developement of computer technology provides much improvements on electron microscopy, such as simulation of images, reconstruction of images and automatic controll of microscopes (auto-focussing and auto-correction of astigmatism) and design of electron microscope lenses by using a finite element method (FEM). In this investigation, procedures for simulating the optical properties of objective lenses of HREM and the characteristics of the new lens for HREM at 200 kV are described.The process for designing the objective lens is divided into three stages. Stage 1 is the process for estimating the optical properties of the lens. Firstly, calculation by FEM is made for simulating the axial magnetic field distributions Bzc of the lens. Secondly, electron ray trajectory is numerically calculated by using Bzc. And lastly, using Bzc and ray trajectory, spherical and chromatic aberration coefficients Cs and Cc are numerically calculated. Above calculations are repeated by changing the shape of lens until! to find an optimum aberration coefficients.

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