New Aspects in the Design of Electron Optical Magnification Systems

1972 ◽  
Vol 30 ◽  
pp. 606-607
Author(s):  
Willem H.J. Andersen
Keyword(s):  
Electron Microscope ◽  
Imaging System ◽  
Chromatic Aberration ◽  
Research Tool ◽  
Energy Losses ◽  
Objective Lens ◽  
Theoretical Limit ◽  
Optical Magnification ◽  
Chromatic Aberrations ◽  
High Degree

Electron microscope design, and particularly the design of the imaging system, has reached a high degree of perfection. Present objective lenses perform up to their theoretical limit, while the whole imaging system, consisting of three or four lenses, provides very wide ranges of magnification and diffraction camera length with virtually no distortion of the image. Evolution of the electron microscope in to a routine research tool in which objects of steadily increasing thickness are investigated, has made it necessary for the designer to pay special attention to the chromatic aberrations of the magnification system (as distinct from the chromatic aberration of the objective lens). These chromatic aberrations cause edge un-sharpness of the image due to electrons which have suffered energy losses in the object.There exist two kinds of chromatic aberration of the magnification system; the chromatic change of magnification, characterized by the coefficient Cm, and the chromatic change of rotation given by Cp.

The Reduction of Chromatic Aberrations Due to Instrumental Instabilities

1971 ◽  
Vol 29 ◽  
pp. 14-15
Author(s):  
J. S. Lally ◽  
R. Evans
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Usual Practice ◽  
Voltage Electron ◽  
Short Focal Length ◽  
Chromatic Aberrations ◽  
Electron Microscopes

One of the instrumental factors often limiting the resolution of the electron microscope is image defocussing due to changes in accelerating voltage or objective lens current. This factor is particularly important in high voltage electron microscopes both because of the higher voltages and lens currents required but also because of the inherently longer focal lengths, i.e. 6 mm in contrast to 1.5-2.2 mm for modern short focal length objectives.The usual practice in commercial electron microscopes is to design separately stabilized accelerating voltage and lens supplies. In this case chromatic aberration in the image is caused by the random and independent fluctuations of both the high voltage and objective lens current.

Observability of Very Thick Specimen by Using Transmission Scanning Electron Microscope

1971 ◽  
Vol 29 ◽  
pp. 26-27
Author(s):  
K. Shibatomi ◽  
T. Yamanoto ◽  
H. Koike
Keyword(s):  
Electron Microscope ◽  
Image Quality ◽  
Scanning Electron Microscope ◽  
Chromatic Aberration ◽  
Image Contrast ◽  
Objective Lens ◽  
Thick Specimen ◽  
Transmission Electron ◽  
Scanning Electron

In the observation of a thick specimen by means of a transmission electron microscope, the intensity of electrons passing through the objective lens aperture is greatly reduced. So that the image is almost invisible. In addition to this fact, it have been reported that a chromatic aberration causes the deterioration of the image contrast rather than that of the resolution. The scanning electron microscope is, however, capable of electrically amplifying the signal of the decreasing intensity, and also free from a chromatic aberration so that the deterioration of the image contrast due to the aberration can be prevented. The electrical improvement of the image quality can be carried out by using the fascionating features of the SEM, that is, the amplification of a weak in-put signal forming the image and the descriminating action of the heigh level signal of the background. This paper reports some of the experimental results about the thickness dependence of the observability and quality of the image in the case of the transmission SEM.

Resolution of a Transmitted Electron Image Formed by A Scanning Electron Microscope

1970 ◽  
Vol 28 ◽  
pp. 386-387
Author(s):  
S. Takashima ◽  
H. Hashimoto ◽  
S. Kimoto
Keyword(s):  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Specimen Thickness ◽  
Probe Diameter ◽  
Transmission Electron ◽  
Electron Image ◽  
Conventional Transmission Electron Microscope ◽  
Scanning Electron

The resolution of a conventional transmission electron microscope (TEM) deteriorates as the specimen thickness increases, because chromatic aberration of the objective lens is caused by the energy loss of electrons). In the case of a scanning electron microscope (SEM), chromatic aberration does not exist as the restrictive factor for the resolution of the transmitted electron image, for the SEM has no imageforming lens. It is not sure, however, that the equal resolution to the probe diameter can be obtained in the case of a thick specimen. To study the relation between the specimen thickness and the resolution of the trans-mitted electron image obtained by the SEM, the following experiment was carried out.

Toward The Simultaneous Correction of Spherical and Chromatic Aberration in Electron Optics by Means of an Electrostatic Electron Mirror

1990 ◽  
Vol 48 (1) ◽  
pp. 206-207
Author(s):  
Gertrude. F. Rempfer
Keyword(s):  
Chromatic Aberration ◽  
Transverse Magnetic ◽  
Objective Lens ◽  
Ion Imaging ◽  
Corrected Image ◽  
Electric And Magnetic Fields ◽  
Chromatic Aberrations ◽  
Improved Performance ◽  
Electron Microscopes ◽  
Image Planes

Optimum performance in electron and ion imaging instruments, such as electron microscopes and probe-forming instruments, in most cases depends on a compromise either between imaging errors due to spherical and chromatic aberrations and the diffraction error or between the imaging errors and the current in the image. These compromises result in the use of very small angular apertures. Reducing the spherical and chromatic aberration coefficients would permit the use of larger apertures with resulting improved performance, granted that other problems such as incorrect operation of the instrument or spurious disturbances do not interfere. One approach to correcting aberrations which has been investigated extensively is through the use of multipole electric and magnetic fields. Another approach involves the use of foil windows. However, a practical system for correcting spherical and chromatic aberration is not yet available.Our approach to correction of spherical and chromatic aberration makes use of an electrostatic electron mirror. Early studies of the properties of electron mirrors were done by Recknagel. More recently my colleagues and I have studied the properties of the hyperbolic electron mirror as a function of the ratio of accelerating voltage to mirror voltage. The spherical and chromatic aberration coefficients of the mirror are of opposite sign (overcorrected) from those of electron lenses (undercorrected). This important property invites one to find a way to incorporate a correcting mirror in an electron microscope. Unfortunately, the parts of the beam heading toward and away from the mirror must be separated. A transverse magnetic field can separate the beams, but in general the deflection aberrations degrade the image. The key to avoiding the detrimental effects of deflection aberrations is to have deflections take place at image planes. Our separating system is shown in Fig. 1. Deflections take place at the separating magnet and also at two additional magnetic deflectors. The uncorrected magnified image formed by the objective lens is focused in the first deflector, and relay lenses transfer the image to the separating magnet. The interface lens and the hyperbolic mirror acting in zoom fashion return the corrected image to the separating magnet, and the second set of relay lenses transfers the image to the final deflector, where the beam is deflected onto the projection axis.

Electron Holography Improving Transmission Electron Microscopy

1990 ◽  
Vol 48 (1) ◽  
pp. 208-209
Author(s):  
Hannes Lichte
Keyword(s):  
Electron Microscopy ◽  
Transfer Functions ◽  
Imaging System ◽  
Spherical Aberration ◽  
Image Plane ◽  
Chromatic Aberration ◽  
Object Wave ◽  
Objective Lens ◽  
Electron Holography ◽  
Wave Aberration

Generally, the electron object wave o(r) is modulated both in amplitude and phase. In the image plane of an ideal imaging system we would expect to find an image wave b(r) that is modulated in exactly the same way, i. e. b(r) =o(r). If, however, there are aberrations, the image wave instead reads as b(r) =o(r) * FT(WTF) i. e. the convolution of the object wave with the Fourier transform of the wave transfer function WTF . Taking into account chromatic aberration, illumination divergence and the wave aberration of the objective lens, one finds WTF(R) = Echrom(R)Ediv(R).exp(iX(R)) . The envelope functions Echrom(R) and Ediv(R) damp the image wave, whereas the effect of the wave aberration X(R) is to disorder amplitude and phase according to real and imaginary part of exp(iX(R)) , as is schematically sketched in fig. 1.Since in ordinary electron microscopy only the amplitude of the image wave can be recorded by the intensity of the image, the wave aberration has to be chosen such that the object component of interest (phase or amplitude) is directed into the image amplitude. Using an aberration free objective lens, for X=0 one sees the object amplitude, for X= π/2 (“Zernike phase contrast”) the object phase. For a real objective lens, however, the wave aberration is given by X(R) = 2π (.25 Csλ3R4 + 0.5ΔzλR2), Cs meaning the coefficient of spherical aberration and Δz defocusing. Consequently, the transfer functions sin X(R) and cos(X(R)) strongly depend on R such that amplitude and phase of the image wave represent only fragments of the object which, fortunately, supplement each other. However, recording only the amplitude gives rise to the fundamental problems, restricting resolution and interpretability of ordinary electron images:

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.

Analysis of electron-specimen interactions of thick biological specimens in Transmission Electron Microscopy at 200 KEV

1993 ◽  
Vol 51 ◽  
pp. 204-205
Author(s):  
Karen F. Han ◽  
Alexander J. Gubbens ◽  
Abraham J. Koster ◽  
Michael B. Braunfeld ◽  
John W. Sedat ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Mass Density ◽  
Three Dimensional ◽  
Chromatic Aberration ◽  
Background Intensity ◽  
Objective Lens ◽  
Dimensional Electron ◽  
Accurate Representation ◽  
Transmission Electron

The primary project of our laboratory is the investigation of chromatin structure by three dimensional electron microscope tomography. The goal is to understand how 30nm fibers fold into higher order chromatin structures. Three dimensional tomography involves the reconstruction of an object by combining multiple projection views of the object at different tilt angles. Due to the electronspecimen interaction and the characteristics of lens aberration in the electron microscope, however, the image is not always an accurate representation of the projected object mass density. In this abstract, we analyze the various types of electron-specimen interaction for thick biological specimens up to 0.7 microns thickness.Electron-specimen interactions include single elastic and inelastic, and multiple elastic and inelastic scattering. Of the imaging electrons, the single elastic and the plasmon electrons give rise to image intensities that can be linearly related to the projected object mass density. Multiply scattered elastic electrons contribute to an increase in background intensity. In addition, due to the chromatic aberration of the TEM’s objective lens, multiply scattered inelastic electrons cause a blurring of the image because of an effective broadening of the focus spread.

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.

An Electron Microscope with Highly Coherent Illumination

1973 ◽  
Vol 31 ◽  
pp. 260-261
Author(s):  
R. E. Worsham ◽  
J. E. Mann ◽  
E. G. Richardson ◽  
N. F. Ziegler
Keyword(s):  
Electron Microscope ◽  
Coherence Length ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Objective Lens ◽  
Coherent Illumination ◽  
Illuminating Beam ◽  
Transmission Microscope

It has been shown theoretically that it is possible to correct for the defocus and the primary spherical aberration of the objective lens in a conventional transmission microscope column if the chromatic aberration can be made negligible and the transverse coherence length of the illuminating beam is about 1000A, or higher. The techniques were demonstrated with simulated micrographs. The microscope shown in the accompanying drawing and photograph was designed to test this procedure experimentally.

An objective lens for an electron microscope with compensated axial chromatic aberration

1978 ◽  
Vol 36 (1) ◽  
pp. 36-37
Author(s):  
H. Koops ◽  
W. Bernhard
Keyword(s):  
Test Specimen ◽  
Focal Length ◽  
Chromatic Aberration ◽  
Electric Quadrupole ◽  
Resolving Power ◽  
Objective Lens ◽  
Virtual Image ◽  
Object Plane ◽  
Magnetic Quadrupole ◽  
Chromatic Aberrations

The resolving power of transmission microscopes is limited by diffraction and by spherical and chromatic aberrations of the objective lens.To compensate the axial chromatic aberration, electric quadrupole fields may be used (1,2). We therefore combined a condenser-objective lens of 2 mm focal length with an electron-optical aplanator (3). Earlier experiments showed that the axial chromatic aberration of the aplanator can be compensated by counteracting electric and magnetic quadrupole fields (4,5). High values of these correcting fields yield a negative chromatic error of the aplanator. It compensates the positive chromatic aberration coefficient of 1.5 mm of the objective lens.The specimen is situated near the middle plane of the condenser-objective lens. This lens produces a 60-fold magnified virtual image in a plane 122 mm above the specimen. The aplanator transfers this image 1:1 into the object plane of the intermediate lens and compensates the aberrations (6).Figure 1 shows a micrograph of a resolution test specimen.

Sign in / Sign up

Export Citation Format

Share Document