Improvements in the electron probe forming capabilities and x-ray hole counts in the Philips TEM

1983 ◽  
Vol 41 ◽  
pp. 376-377
Author(s):  
Richard L. McConville
Keyword(s):  
Field Strength ◽  
Electron Probe ◽  
Spherical Aberration ◽  
Focal Length ◽  
Objective Lens ◽  
Parallel Beam ◽  
Tilt Axis ◽  
X Ray ◽  
Small Probe ◽  
Specimen Height

A second generation twin lens has been developed. This symmetrical lens with a wider bore, yet superior values of chromatic and spherical aberration for a given focal length, retains both eucentric ± 60° tilt movement and 20°x ray detector take-off angle at 90° to the tilt axis. Adjust able tilt axis height, as well as specimen height, now ensures almost invariant objective lens strengths for both TEM (parallel beam conditions) and STEM or nano probe (focused small probe) modes.These modes are selected through use of an auxiliary lens situ ated above the objective. When this lens is on the specimen is illuminated with a parallel beam of electrons, and when it is off the specimen is illuminated with a focused probe of dimensions governed by the excitation of the condenser 1 lens. Thus TEM/STEM operation is controlled by a lens which is independent of the objective lens field strength.

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

The CM120 Biotwin: a high-contrast objective lens, optimum cryo-vacuum and improved EDX performance

1995 ◽  
Vol 53 ◽  
pp. 584-585
Author(s):  
Uwe Lücken ◽  
Michael Felsmann ◽  
Wim M. Busing ◽  
Frank de Jong
Keyword(s):  
Life Science ◽  
Focal Length ◽  
Objective Lens ◽  
High Contrast ◽  
Contrast Imaging ◽  
X Ray ◽  
Forming Mechanism ◽  
Similar Image ◽  
High Contrast Imaging ◽  
Low Concentrations

A new microscope for the study of life science specimen has been developed. Special attention has been given to the problems of unstained samples, cryo-specimens and x-ray analysis at low concentrations.A new objective lens with a Cs of 6.2 mm and a focal length of 5.9 mm for high-contrast imaging has been developed. The contrast of a TWIN lens (f = 2.8 mm, Cs = 2 mm) and the BioTWTN are compared at the level of mean and SD of slow scan CCD images. Figure 1a shows 500 +/- 150 and Fig. 1b only 500 +/- 40 counts/pixel. The contrast-forming mechanism for amplitude contrast is dependent on the wavelength, the objective aperture and the focal length. For similar image conditions (same voltage, same objective aperture) the BioTWIN shows more than double the contrast of the TWIN lens. For phasecontrast specimens (like thin frozen-hydrated films) the contrast at Scherzer focus is approximately proportional to the √ Cs.

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.

Defocus ramp correction in spot-scan imaging

1992 ◽  
Vol 50 (1) ◽  
pp. 130-131
Author(s):  
Kenneth H. Downing
Keyword(s):  
Computer Control ◽  
Three Dimensional ◽  
Sufficient Accuracy ◽  
Objective Lens ◽  
Electron Crystallography ◽  
Contrast Transfer Function ◽  
Tilt Axis ◽  
Specimen Height ◽  
The Difference ◽  
Envelope Functions

Three-dimensional structures of a number of samples have been determined by electron crystallography. The procedures used in this work include recording images of fairly large areas of a specimen at high tilt angles. There is then a large defocus ramp across the image, and parts of the image are far out of focus. In the regions where the defocus is large, the contrast transfer function (CTF) varies rapidly across the image, especially at high resolution. Not only is the CTF then difficult to determine with sufficient accuracy to correct properly, but the image contrast is reduced by envelope functions which tend toward a low value at high defocus.We have combined computer control of the electron microscope with spot-scan imaging in order to eliminate most of the defocus ramp and its effects in the images of tilted specimens. In recording the spot-scan image, the beam is scanned along rows that are parallel to the tilt axis, so that along each row of spots the focus is constant. Between scan rows, the objective lens current is changed to correct for the difference in specimen height from one scan to the next.

A 100 KV Transmission Scanning Microscope

1971 ◽  
Vol 29 ◽  
pp. 22-23
Author(s):  
A. V. Crewe
Keyword(s):  
Focal Length ◽  
Electron Gun ◽  
Objective Lens ◽  
Scanning Microscope ◽  
Parallel Beam ◽  
Condenser Lens ◽  
Focal Length Lens ◽  
Short Focal Length ◽  
Pass Through ◽  
Correction System

A 100 kv transmission scanning microscope is now being constructed which should have a point resolution of 2.5 to 3 Å. The design of this microscope is similar to the design of our existing 30 kv 5 Å microscope, but there are several significant changes which are based upon some difficulties and sources of inflexibility of that microscope.A field emission electron gun of our usual design will be used as the source of electrons, the only difference being that the spacing between the anodes has been increased from 2 to 3 cm. The electron beam will then pass through a condenser lens which will produce a parallel beam of electrons. This parallel beam will then be focused onto the specimen by means of a short focal length lens (approximately 1 mm focal length). The reason for using a condenser lens to produce the parallel beam of electrons is that in the future a quadrupole-octupole correction system will be installed in this section of the microscope in order to attempt to correct the spherical aberrations of the objective lens and thereby improve its resolution.

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.

Some biological materials observed by a new high-resolution SEM

1987 ◽  
Vol 45 ◽  
pp. 554-555
Author(s):  
K. Tanaka ◽  
A. Mitsushima ◽  
H. Takayama
Keyword(s):  
Endoplasmic Reticulum ◽  
High Resolution ◽  
Electron Probe ◽  
Motor Nerve ◽  
Focal Length ◽  
Biological Materials ◽  
Objective Lens ◽  
Probe Diameter ◽  
Short Focal Length ◽  
Dark Space

Recently we made a high resolution SEM (UHS-T1) with a aid of Hitachi Co. Ltd. It was equipped with a field emission source and the objective lens with short focal length (3.6 mm). The electron probe is estimated to 0.4 nm on calculation, and the probe diameter of 0.5 nm is confirmed by observation in STEM mode. On observation of a biological material (a rat motor nerve cell) which was coated with platinum by an ion sputter coater, the SEM shows 0.5 nm resolution when the width of the dark space criterion was used. In the present study some biological materials are observed with this new SEM. The results are as follows.Specimens were prepared by the aldehyde prefix osmium-DMSO-osmium method. In the specimens, mitochondria, Golgi complex, endoplasmic reticulum and so on, were very clearly observed (Fig.1) in comparison with those observed by ordinary SEM.

scholarly journals A capillary specimen aberration for describing X-ray powder diffraction line profiles for convergent, divergent and parallel beam geometries

2017 ◽  
Vol 50 (5) ◽  
pp. 1331-1340 ◽  
Author(s):  
Alan A. Coelho ◽  
Matthew R. Rowles
Keyword(s):  
Powder Diffraction ◽  
Focal Length ◽  
Numerical Procedure ◽  
Approximation Technique ◽  
Parallel Beam ◽  
X Ray ◽  
Diffraction Angle ◽  
Diffraction Patterns ◽  
Insight Into ◽  
Complex Manner

X-ray powder diffraction patterns of cylindrical capillary specimens have substantially different peak positions, shapes and intensities relative to patterns from flat specimens. These aberrations vary in a complex manner with diffraction angle and instrument geometry. This paper describes a fast numerical procedure that accurately describes the capillary aberration in the equatorial plane for convergent focusing, divergent and parallel beam instrument geometries. Axial divergence effects are ignored and only a cross section of the capillary, a disc, is considered; it is assumed that axial divergence effects can be described using an additional correction that is independent of the disc correction. Significantly, the present implementation uses theTOPAS-Academicaberration approximation technique of averaging nearby aberrations in 2θ space to approximate in-between aberrations, which results in no more than ∼30 disc aberrations calculated over the entire 2θ range, even when the diffraction pattern comprises thousands of peaks. Finally, the disc aberration is convoluted with the emission profile and other instrument and specimen aberrations in a Rietveld refinement sense, allowing for refinement on the specimen's absorption coefficient and capillary diameter, as well as the instrument focal length. Large differences between refined and expected values give insight into instrument alignment.

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.

Use of an Energy Dispersive X-ray Spectrometer on a Transmission Electron Microscope

1971 ◽  
Vol 29 ◽  
pp. 60-61
Author(s):  
Roy H. Geiss ◽  
William A. Jesser
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Focal Length ◽  
Peak Height ◽  
Energy Dispersive ◽  
X Ray ◽  
Specimen Holder ◽  
Transmission Electron ◽  
Specimen Height ◽  
Dispersive System

An Ortec Si(Li) energy dispersive X-ray detector designed for use on a Cambridge scanning electron microscope has been coupled to a Siemens transmission electron microscope by replacing the side tilt control on the Siemens by a brass tube as shown in figure 1. The Siemens specimen holder was modified to tilt the specimen approximately 20° from a horizontal position and to elevate it such that it is just visible to the detector through the side port. This increased specimen height requires an objective focal length of greater than 8 mm and consequently effects a lower resolution of the image, especially at low accelerating voltages. The peak/background in the X-ray spectra is best at 40kV, however, and deteriorates progressively with increasing accelerating voltage.Experiments similar to those of Fuchs, who employed a wavelength dispersive system on a Siemens TEM to measure film thickness, were repeated with the present energy dispersive system by analysing spectra from vacuum deposited gold films of various thicknesses. A linear relation between peak height and thickness was confirmed for several films up to 2000Å thick by comparing spectra from two adjacent grid squares, one covered by a single thickness of gold, the other covered by a double thickness, and noting that the peak heights were in the ratio of 1:2 to within a few percent.

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