Chromatic imaging effects in hvem: an avenue to partial energy filtering

1988 ◽  
Vol 46 ◽  
pp. 828-829
Author(s):  
Mircea Fotino
Keyword(s):  
Image Quality ◽  
Spherical Aberration ◽  
Objective Lens ◽  
Acceptance Angle ◽  
Energy Filtering ◽  
Lens Aperture ◽  
Transmission Electron ◽  
Angular Acceptance ◽  
Partial Energy ◽  
Imaging Beam

In transmission electron microscopy the normal image is formed by elastic and inelastic electrons that have interacted with the specimen. Their relative contributions to image formation depend on beam accelerating voltage and on angular acceptance determined by the objective-lens aperture.Inelastic scattering occurs primarily within small scattering angles while elastic scattering extends to wider angles. Consequently, the beam accepted by small objective-lens apertures contains a higher proportion of inelastic electrons than the beam accepted by larger apertures. By varying the size of the objective-lens aperture it is thus possible to modify the composition of the imaging beam and thereby the image quality: better resolution and higher image quality are obtained with larger apertures. It is necessary, however, to make sure that the acceptance angle is both larger than the lower limit imposed by diffraction and smaller that the upper limit imposed by spherical aberration.

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.

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

Resolution in the Scanning Transmission Electron Microscope

1972 ◽  
Vol 30 ◽  
pp. 454-455
Author(s):  
M. G. R. Thomson
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Spherical Aberration ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission

The variation of contrast and signal to noise ratio with change in detector solid angle in the high resolution scanning transmission electron microscope was discussed in an earlier paper. In that paper the conclusions were that the most favourable conditions for the imaging of isolated single heavy atoms were, using the notation in figure 1, either bright field phase contrast with β0⋍0.5 α0, or dark field with an annular detector subtending an angle between ao and effectively π/2.The microscope is represented simply by the model illustrated in figure 1, and the objective lens is characterised by its coefficient of spherical aberration Cs. All the results for the Scanning Transmission Electron Microscope (STEM) may with care be applied to the Conventional Electron Microscope (CEM). The object atom is represented as detailed in reference 2, except that ϕ(θ) is taken to be the constant ϕ(0) to simplify the integration. This is reasonable for θ ≤ 0.1 θ0, where 60 is the screening angle.

Design of a new objective lens for an HB-501A STEM

1991 ◽  
Vol 49 ◽  
pp. 416-417
Author(s):  
Earl J. Kirkland ◽  
Robert J. Keyse
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
Specimen Holder ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
High Resolution Microscopy

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.

A Quantitative Nanodiffraction System for Ultrahigh Vacuum Scanning Transmission Electron Microscopy

2003 ◽  
Vol 9 (5) ◽  
pp. 468-474 ◽  
Author(s):  
Gary G. Hembree ◽  
Christoph Koch ◽  
John C.H. Spence
Keyword(s):  
Electron Microscope ◽  
Dynamic Range ◽  
Spherical Aberration ◽  
Ultrahigh Vacuum ◽  
Objective Lens ◽  
Specimen Preparation ◽  
Modulation Transfer ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission

Of all the long-lived particles available as probes of condensed matter, and of all the signals available on a modern electron microscope, electron nanodiffraction patterns provide the strongest signal from the smallest volume. The technique is therefore perfectly suited to nanostructural investigations in inorganic chemistry and materials science. The Vacuum Generators HB501S, an ultrahigh vacuum (UHV) variant of the HB501 scanning transmission electron microscope (STEM), with side-entry double-tilt stage, specimen preparation and analysis chamber, three postspecimen lenses, and cold field-emission tip with integral magnetic gun lens, has therefore been modified to optimize nanodiffraction and quantitative convergent beam electron diffraction (QCBED) performance. A one-micrometer grain-size phosphor screen lying on a fiber-optic faceplate atop the instrument is fiber-optically coupled to a 2048 × 2048 charge-coupled device (CCD), 16-bit camera. This arrangement promises to provide much greater sensitivity, larger dynamic range, and a better modulation transfer function (MTF) than conventional single crystal scintillator (YAG) CCD systems, with noticeable absence of cross talk between pixels. The design of the nanodiffraction detector system is discussed, the gain of the detector is measured, the spherical aberration constant of the objective lens is measured by the Ronchigram method, and preliminary results from the modified instrument are shown.

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.

Aberration-Corrected STEM: the Present and the Future

2001 ◽  
Vol 7 (S2) ◽  
pp. 896-897
Author(s):  
O.L. Krivanek ◽  
N. Dellby ◽  
P.D. Nellist ◽  
P.E. Batson ◽  
A.R. Lupini
Keyword(s):  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
High Angle ◽  
Successful Operation ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Full Speed ◽  
Aberration Corrected

Surprising as it may seem, aberration correction for the scanning transmission electron microscope (STEM) is now a practical proposition. The first-ever commercial spherical aberration corrector for a STEM was delivered by Nion to IBM Research Center in June 2000, and other deliveries have taken place since or are imminent. At the same time, the development of corrector hardware and software is still proceeding at full speed, and our understanding of what are the most important factors for the successful operation of a corrector is deepening continuously.Fig. 1 shows two high-angle dark field (HADF) images of [110] Si obtained with the IBM VG HB501 STEM operating at 120 kV, about 2 weeks after we fitted a quadrupole-octupole corrector into it. Fig. 1(a) shows the best HADF image that could be obtained with the corrector's quadrupoles on but its octupoles off. Sample structures were captured down to about 2.5 Å detail, easily possible in a STEM with a high resolution objective lens with a spherical aberration coefficient (Cs) of 1.3 mm. Fig. 1(b) shows a HADF image obtained after the Cs-correcting octupoles were turned on and the corrector tuned up. The resolution has now improved to 1.36 Å. This is sufficient to resolve the correct separation of the closely-spaced Si columns.

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.

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