Chromatic aberration and low-voltage SEM

1987 ◽  
Vol 45 ◽  
pp. 546-547
Author(s):  
Zhifeng Shao ◽  
A.V. Crewe
Keyword(s):  
Electron Energy ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Primary Electron ◽  
Probe Size ◽  
Non Local ◽  
Optical Treatment ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

For scanning electron microscopes, it is plausible that by lowering the primary electron energy, one can decrease the volume of interaction and improve resolution. As shown by Crewe /1/, at V0 =5kV a 10Å resolution (including non-local effects) is possible. To achieve this, we would need a probe size about 5Å. However, at low voltages, the chromatic aberration becomes the major concern even for field emission sources. In this case, δV/V = 0.1 V/5kV = 2x10-5. As a rough estimate, it has been shown that /2/ the chromatic aberration δC should be less than ⅓ of δ0 the probe size determined by diffraction and spherical aberration in order to neglect its effect. But this did not take into account the distribution of electron energy. We will show that by using a wave optical treatment, the tolerance on the chromatic aberration is much larger than we expected.

Toward High-Resolution Low-Voltage SEM

1988 ◽  
Vol 46 ◽  
pp. 218-219
Author(s):  
Zhifeng Shao
Keyword(s):  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Limiting Factor ◽  
Operating Voltage ◽  
Probe Radius ◽  
Non Local ◽  
Electron Microscopes ◽  
Image Position ◽  
Scanning Electron Microscopes

Recently, low voltage (≤5kV) scanning electron microscopes have become popular because of their unprecedented advantages, such as minimized charging effects and smaller specimen damage, etc. Perhaps the most important advantage of LVSEM is that they may be able to provide ultrahigh resolution since the interaction volume decreases when electron energy is reduced. It is obvious that no matter how low the operating voltage is, the resolution is always poorer than the probe radius. To achieve 10Å resolution at 5kV (including non-local effects), we would require a probe radius of 5∽6 Å. At low voltages, we can no longer ignore the effects of chromatic aberration because of the increased ratio δV/V. The 3rd order spherical aberration is another major limiting factor. The optimized aperture should be calculated as

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.

Current State of Biological High-Resolution Scanning Electron Microscopy

1988 ◽  
Vol 46 ◽  
pp. 180-181 ◽  
Author(s):  
Klaus-Ruediger Peters
Keyword(s):  
High Performance ◽  
Low Voltage ◽  
Backscattered Electrons ◽  
Lens Position ◽  
Low Voltage Operation ◽  
Signal Collection ◽  
Probe Size ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

A new generation of high performance field emission scanning electron microscopes (FSEM) is now commercially available (JEOL 890, Hitachi S 900, ISI OS 130-F) characterized by an "in lens" position of the specimen where probe diameters are reduced and signal collection improved. Additionally, low voltage operation is extended to 1 kV. Compared to the first generation of FSEM (JE0L JSM 30, Hitachi S 800), which utilized a specimen position below the final lens, specimen size had to be reduced but useful magnification could be impressively increased in both low (1-4 kV) and high (5-40 kV) voltage operation, i.e. from 50,000 to 200,000 and 250,000 to 1,000,000 x respectively.At high accelerating voltage and magnification, contrasts on biological specimens are well characterized1 and are produced by the entering probe electrons in the outmost surface layer within -vl nm depth. Backscattered electrons produce only a background signal. Under these conditions (FIG. 1) image quality is similar to conventional TEM (FIG. 2) and only limited at magnifications >1,000,000 x by probe size (0.5 nm) or non-localization effects (%0.5 nm).

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.

Improvement of Depth Resolution of ADF-SCEM by Deconvolution: Effects of Electron Energy Loss and Chromatic Aberration on Depth Resolution

2012 ◽  
Vol 18 (3) ◽  
pp. 603-611 ◽  
Author(s):  
Xiaobin Zhang ◽  
Masaki Takeguchi ◽  
Ayako Hashimoto ◽  
Kazutaka Mitsuishi ◽  
Meguru Tezuka ◽  
...  
Keyword(s):  
Energy Loss ◽  
Electron Energy ◽  
Spherical Aberration ◽  
Depth Resolution ◽  
Chromatic Aberration ◽  
Dark Field ◽  
Probe Size ◽  
Two Factors ◽  
Annular Dark Field ◽  
Electron Energy Loss

AbstractScanning confocal electron microscopy (SCEM) is a new imaging technique that is capable of depth sectioning with nanometer-scale depth resolution. However, the depth resolution in the optical axis direction (Z) is worse than might be expected on the basis of the vertical electron probe size calculated with the existence of spherical aberration. To investigate the origin of the degradation, the effects of electron energy loss and chromatic aberration on the depth resolution of annular dark-field SCEM were studied through both experiments and computational simulations. The simulation results obtained by taking these two factors into consideration coincided well with those obtained by experiments, which proved that electron energy loss and chromatic aberration cause blurs at the overfocus sides of the Z-direction intensity profiles rather than degrade the depth resolution much. In addition, a deconvolution method using a simulated point spread function, which combined two Gaussian functions, was adopted to process the XZ-slice images obtained both from experiments and simulations. As a result, the blurs induced by energy loss and chromatic aberration were successfully removed, and there was also about 30% improvement in the depth resolution in deconvoluting the experimental XZ-slice image.

An Efficient Annular Dark-Field Detector Capable of Single-Electron Counting Adapted to a High-Resolution Field-Emission SEM

1988 ◽  
Vol 46 ◽  
pp. 190-191
Author(s):  
R. Reichelt ◽  
U. Aebi ◽  
A. Engel
Keyword(s):  
High Resolution ◽  
Electron Energy ◽  
Field Emission ◽  
Major Elements ◽  
Dark Field ◽  
Primary Electron ◽  
Transmission Electron ◽  
Annular Dark Field ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

Various high resolution scanning electron microscopes (HRSEM) are now commercially available providing probe sizes in the range of 0.5 to 1.5 nm at 30 keV due to their field emission gun 1.2. Equipped with efficient detector systems (which collect different signals and applied to specifically prepared samples) HRSEM challenge the conventional transmission electron microscope (TEM) with high resolution surface images of biological specimens collecting secondary (SE) or backscattered (BSE) electrons. However, the yield of (SE) carrying high resolution information is rather small, i.e. the SE-I yield at 20 keV primary electron energy amounts to < 1% for the major elements (H; C; N; O; P) constituting biological matter. The yield of BSE is greater than the corresponding total SE yield (electron energy >15 keV), but BSE emerge due to high angle elastic scattering from a surface area with a diameter of typically 30% of the deepest electron penetration R (e.g. R≈10 μm for elements mentioned above at 30 keV).

High resolution at low voltage: A new approach

1989 ◽  
Vol 47 ◽  
pp. 76-77
Author(s):  
Arthur V. Jones
Keyword(s):  
Low Voltage ◽  
Emission Sources ◽  
New Approach ◽  
Design Concepts ◽  
Probe Diameter ◽  
Low Voltage Operation ◽  
Sufficient Intensity ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Immersion Type

With the introduction of field-emission sources and “immersion-type” objective lenses, the resolution obtainable with modern scanning electron microscopes is approaching that obtainable in STEM and TEM-but only with specific types of specimens. Bulk specimens still suffer from the restrictions imposed by internal scattering and the need to be conducting. Advances in coating techniques have largely overcome these problems but for a sizeable body of specimens, the restrictions imposed by coating are unacceptable.For such specimens, low voltage operation, with its low beam penetration and freedom from charging artifacts, is the method of choice.Unfortunately the technical dificulties in producing an electron beam sufficiently small and of sufficient intensity are considerably greater at low beam energies — so much so that a radical reevaluation of convential design concepts is needed.The probe diameter is usually given by

scholarly journals Characterization of a Miniature Electron Energy Analyzer for Scanning Electron Microscopes

2017 ◽  
Vol 902 ◽  
pp. 012017 ◽  
Author(s):  
Ashish Suri ◽  
Andrew Pratt ◽  
Steve Tear ◽  
Christopher Walker ◽  
Mohamed El-Gomati
Keyword(s):  
Electron Energy ◽  
Energy Analyzer ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron
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