Comparison of Deterministic and Linear Cosine Spatial Filtering of Transmission Electron Micrographs

1972 ◽  
Vol 30 ◽  
pp. 596-597
Author(s):  
David A. Ansley
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Spatial Filter ◽  
Operating Conditions ◽  
Objective Lens ◽  
List Type ◽  
Spatial Filters ◽  
Transmission Electron ◽  
Wide Range

The coherence of the electron flux of a transmission electron microscope (TEM) limits the direct application of deconvolution techniques which have been used successfully on unmanned spacecraft programs. The theory assumes noncoherent illumination. Deconvolution of a TEM micrograph will, therefore, in general produce spurious detail rather than improved resolution.A primary goal of our research is to study the performance of several types of linear spatial filters as a function of specimen contrast, phase, and coherence. We have, therefore, developed a one-dimensional analysis and plotting program to simulate a wide 'range of operating conditions of the TEM, including adjustment of the:(1) Specimen amplitude, phase, and separation(2) Illumination wavelength, half-angle, and tilt(3) Objective lens focal length and aperture width(4) Spherical aberration, defocus, and chromatic aberration focus shift(5) Detector gamma, additive, and multiplicative noise constants(6) Type of spatial filter: linear cosine, linear sine, or deterministic

Current and future aberration correctors for the improvement of resolution in electron microscopy

2009 ◽  
Vol 367 (1903) ◽  
pp. 3665-3682 ◽  
Author(s):  
M. Haider ◽  
P. Hartel ◽  
H. Müller ◽  
S. Uhlemann ◽  
J. Zach
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Voltage Electron ◽  
System A ◽  
Transmission Electron ◽  
Correction System

The achievable resolution of a modern transmission electron microscope (TEM) is mainly limited by the inherent aberrations of the objective lens. Hence, one major goal over the past decade has been the development of aberration correctors to compensate the spherical aberration. Such a correction system is now available and it is possible to improve the resolution with this corrector. When high resolution in a TEM is required, one important parameter, the field of view, also has to be considered. In addition, especially for the large cameras now available, the compensation of off-axial aberrations is also an important task. A correction system to compensate the spherical aberration and the off-axial coma is under development. The next step to follow towards ultra-high resolution will be a correction system to compensate the chromatic aberration. With such a correction system, a new area will be opened for applications for which the chromatic aberration defines the achievable resolution, even if the spherical aberration is corrected. This is the case, for example, for low-voltage electron microscopy (EM) for the investigation of beam-sensitive materials, for dynamic EM or for in-situ EM.

The direct study by electron microscopy of crystal lattices and their imperfections

1956 ◽  
Vol 236 (1204) ◽  
pp. 119-135 ◽  
Keyword(s):  
Spherical Aberration ◽  
Optical Microscope ◽  
Objective Lens ◽  
Crystal Lattices ◽  
General Validity ◽  
Direct Study ◽  
Transmission Electron ◽  
Wide Range ◽  
Edge Dislocations ◽  
Platinum Phthalocyanine

Thin crystals of copper and platinum phthalocyanine have been studied in the transmission electron microscope. The (20T) planes of the crystal lattice have been resolved and the distance between them (12.0 + 0.2 A) is in close agreement with the X-ray value of 11.94 A. Imperfections in the lattice have been directly observed. Dislocations have been photographed including both complex arrays and unit edge dislocations. Unit steps 12 A high have been observed on the edge of a crystal. In a slightly deformed crystal the deformation of the (20T) planes corresponds geometrically to the deformation of the surface of the crystal as would be expected with elastic deformation. One crystal displaying a feature resembling an incipient cleavage has been observed. The fracture appears to be displaced laterally from one cleavage plane to its neighbour as it traverses the crystal. The mechanism of the formation of the image is discussed in terms of the Abbe theory of image formation in the optical microscope. The image of the planes is formed as a result of interference between the zero-order and first-order spectrum from the (20T) planes. The very high resolution arises from the fact that the diffracted beam from a small crystal traverses a very narrow zone of the objective lens so that the effect of spherical aberration is not severe. Experiment has confirmed the general validity of this approach. It is suggested that this method may be extended to the study of crystals of even smaller lattice dimensions than the phthalocyanines, making possible the direct study of imperfections in a wide range of materials in relation to properties known to be affected by them such as strength, plastic flow and fracture.

A Spherical-Aberration Corrector Using Electrontransparent Conducting Foils

1973 ◽  
Vol 31 ◽  
pp. 262-263
Author(s):  
M. G. R. Thomson
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Field Of View ◽  
Objective Lens ◽  
Electric Field Gradients ◽  
Field Gradients ◽  
Short Focal Length ◽  
Successful Approach ◽  
Fifth Order

One of the problems associated with building any aberration-corrected electron microscope objective lens lies in the difficulty of obtaining a sufficiently short focal length. A number of systems have focal lengths in the 1cm. range, and these are more suitable for microprobe work. If the focal length can be made short enough, the chromatic aberration probably does not need to be corrected, and the design is much simplified. A corrector device which can be used with a conventional magnetic objective lens of short focal length (Fig. 1) must either have dimensions comparable to the bore and gap of that lens, or have very large magnetic or electric field gradients. A successful approach theoretically has been to use quadrupoleoctopole corrector units, although these suffer from very large fifth order aberrations and a limited field of view.

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.

Observation of Electron Energy Losses in Dark Field Images

1967 ◽  
Vol 25 ◽  
pp. 246-247
Author(s):  
J. S. Lally ◽  
R. M. Fisher ◽  
A. Szirmae ◽  
H. Hashimoto
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Dark Field ◽  
Bragg Angle ◽  
Energy Losses ◽  
Objective Lens ◽  
Characteristic Energy ◽  
Crystalline Materials ◽  
Dark Field Electron

It is commonly assumed that the poor resolution of axially illuminated dark field electron micrographs of crystalline materials is due to the spherical aberration of the objective lens. Actually in many cases the lack of sharpness of the image results from the displacement by chromatic aberration of additional images formed by the electrons which have suffered large energy losses as a result of single or multiple plasmon scattering. In the case of very small diffracting particles, grains or other fine structures in the specimen it is possible to observe multiple images corresponding to these characteristic energy losses. The displacement (Δx) of the image is given by Δx = C f α ΔE/E where C is the chromatic aberration coefficient, f the focal length, α is twice the Bragg angle, E the accelerating potential, and ΔE the energy loss. For a typical plasmon loss of 20 ev the displacement at 100 kv is about 100 Å.

1 Mev Stem: A Progress Report

1980 ◽  
Vol 38 ◽  
pp. 6-7
Author(s):  
P. S. Lin ◽  
J. J. Schuler ◽  
A. V. Crewe
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Spot Size ◽  
Scanning Transmission Electron Microscope ◽  
List Type ◽  
Electron Microscopies ◽  
Wide Range

A high voltage scanning transmission electron microscope(HVSTEM) has a number of unique features: Compared with a high voltage conventional electron microscope, it can provide better resolution and contrast for thick specimens, because of the absence of the chromatic aberration contributed by energy-loss events; Compared with a low voltage STEM, it can collect inelastically scattered electrons more efficiently, since the the characteristic angle of single inelastic scattering varies inversely with energy; The size of the beam can be varied over a wide range for the purpose of selected-area-diffraction. The application of this promising technique in particular to the study of biological molecules which form crystals too thick to be studied with low voltage electron microscopies awaits exploration. In addition, in theory, the spot size of a HVSTEM is better than one Ångstrom – which undoubtly could not be achieved by a low voltage STEM unless the spherical aberration is corrected.

Quadrupole-Octopole and Foil Lens Corrector Systems

1971 ◽  
Vol 29 ◽  
pp. 16-17 ◽  
Author(s):  
M. G. R. Thomson ◽  
E. H. Jacobsen
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Order Effect ◽  
Objective Lens ◽  
Axially Symmetric ◽  
Third Order ◽  
First Order ◽  
Short Focal Length ◽  
Strong Focusing

The theorem due to Scherzer which states, in essence, that a conventional axially symmetric, magnetic or electrostatic lens can never be free from third order spherical aberration is well known. Attempts to circumvent this limitation have been carried out over the past thirty years with little result, but meanwhile the ill effects have been minimized by using magnetic lenses of very short focal length.The most studied alternative is the use of doubly symmetric strong focusing lenses. The first order imaging is performed with three or more quadrupoles, and the third order aberrations corrected with three octopoles. The design by Deltrap for example has no first order effect other than to invert the image, and has a third order spherical aberration coefficient which exactly cancels out that of the magnetic objective lens with which it us used. To avoid chromatic aberration this magnetic objective lens must have a very short focal length (2 mm for 100 kv operation with a resolution of 1 Å), and the overall system then has so much coma that the field of view is limited to 50 Å diameter.

Development of a Computer-Controlled 120kV High-Performance Tem

1996 ◽  
Vol 54 ◽  
pp. 446-447
Author(s):  
H. Kobayashi ◽  
I. Nagaoki ◽  
E. Nakazawa ◽  
T. Kamino
Keyword(s):  
High Resolution ◽  
High Performance ◽  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Wide Field ◽  
High Contrast ◽  
Computer Controlled ◽  
The Magnetic Field

A new computer controlled 120kV high performance TEM has been developed(Fig. 1). The image formation system of the microscope enables us to observe high resolution, wide field,and high contrast without replacing the objective lens pole-piece. The objective lens is designed for high- contrast (HC) and high-resolution(HR) modes, and consists of a double gap and two coils. A schematic drawing of the objective lens and the strength of the magnetic field of the lens is described in Fig.2. When the objective lens is used in HC mode, upper and lower coils are operated at a lens current of same polarity to form the long focal length. The focal length(fo), spherical aberration coefficient(Cs) and chromatic aberration coefficient (Cc) in HC mode at 100kV are 6.5, 3.4 and 3.1mm, respectively. Magnification range at HC mode is × 700 to × 200,000. The viewing area with an objective aperture of a diameter of 10μm is 160mm in diameter. In HR mode, the polarity of lower coil current is reversed to form a shorter focal length for high resolution image observation. The fo, Cs and Cc of the objective lens in HR mode at lOOkV are 3.1, 2.8 and 2.3mm, respectively. The highest magnification in HR mode is × 600,000.

Beyond One Angstrom

1990 ◽  
Vol 48 (1) ◽  
pp. 204-205
Author(s):  
Albert. V. Crewe
Keyword(s):  
Electron Microscopy ◽  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Low Energy ◽  
Objective Lens ◽  
Squeeze Out ◽  
Electron Microscopes

I believe everyone would agree we have just about reached the limit of performance of today's electron microscopes. This is not to say that additional advances will not take place, because there is always one more drop of blood to squeeze out. But it is certainly becoming increasingly apparent that we can not expect more out of the magnetic lenses that we now have. I am sure that everyone who has ever been concerned with this problem has arrived at the same set of conclusions but it may help to set them down one more time.The available resolution in electron microscopy is distressingly poor compared to the wavelength of the electrons. The culprit is always the objective lens. For low energy, say less than 5,000 volts, chromatic aberration is the offending element whereas at high voltages it is the spherical aberration coefficient which we must be concerned with. In both cases, there are some basic restrictions which apply. In the case of chromatic aberration it is always very closely equal with the focal length of the lens and for the spherical aberration coefficient the best we can do is about 1/4 or 1/2 the focal length.

Chromatic Aberration Correction of a Low-Voltage SEM using a Wien Filter: Adjusting the Correction Strength

2001 ◽  
Vol 7 (S2) ◽  
pp. 874-875
Author(s):  
T. Steffen ◽  
P.C. Tiemeijer ◽  
M.P.C.M. Krijn ◽  
S.A.M. Mentink
Keyword(s):  
Low Voltage ◽  
Spherical Aberration ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Aberration Correction ◽  
Wien Filter ◽  
Electron Microscopes ◽  
Working Distance ◽  
Scanning Electron Microscopes

The resolution of state-of-the-art low-voltage scanning electron microscopes (LV SEM), which is currently limited by the chromatic and spherical aberrations of the objective lens, can be improved by incorporating an aberration correcting device. At present four different concepts are discussed in literature: Zach and Haider demonstrated that a quadrupole/octupole corrector can correct both chromatic and spherical aberration. Rose proposed a Wien filter for chromatic aberration correction, which has relaxed stability requirements. Recently, we reported a simplified version of this corrector and showed that a spherical aberration corrector can be integrated in a Wien filter. Henstra and co-workers suggested a purely electrostatic corrector that can correct both chromatic and spherical aberration.For all these concepts problems may arise when the lens-to-sample (working) distance for an aligned corrector is to be changed. in general, the corrector settings depend on the ratio Cc/f2, where Cc and f denote the coefficient of the chromatic aberration and the focal length of the objective lens, respectively. When the working distance is changed, this ratio is no longer perfectly matched to the corrector settings. The tedious realignments and readjustments, which then seem necessary, can be avoided by using a doublet objective lens as illustrated schematically in Figure 1.

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