The ORNL Aberration-Corrected STEM/TEM Project

2001 ◽  
Vol 7 (S2) ◽  
pp. 906-907
Author(s):  
L. F. Allard ◽  
E. Voelkl ◽  
D. A. Blom ◽  
T. A. Nolan ◽  
F. Kahl ◽  
...  
Keyword(s):  
Spherical Aberration ◽  
National Laboratory ◽  
Dark Field ◽  
Electron Gun ◽  
Objective Lens ◽  
Resolution Limit ◽  
Oak Ridge ◽  
Transfer Characteristics ◽  
Dark Field Imaging ◽  
Electron Microscopes

Field emission electron microscopes operating at 200kV or 300kV and incorporating aberration correctors for either the incident electron probe or for the primary aberrations of the objective lens (OL) are currently under development for several laboratories in the world. OL-corrected instruments require monochromators for the electron beam, built into the electron gun prior to the accelerating stages, in order to optimize the contrast transfer characteristics of the objective lens to push the instrumental resolution limit to well beyond 0.1nm. This will allow the point resolution limit as controlled by the correction of spherical aberration Cs to potentially extend to the instrumental limit of better than 0.1nm. Figure 1 shows the contrast transfer characteristics of a Cs-corrected 200kV TEM, both without and with a beam monochromator.Dedicated STEM instruments such as the 300kV VG-603 and lOOkV VG-501 at Oak Ridge National Laboratory, and other VG instruments at Cornell University and IBM Co. are also being adapted (by Nion Co., Kirkland, WA) to incorporate aberration correctors for the incident probe. The aim is to improve the resolution of the VG-603 instrument in dark-field imaging mode, for example, from 0.13nm to 0.05nm. in another ORNL project, the High Temperature Materials Laboratory has contracted JEOL Ltd. to construct a STEM-TEM instrument with a probe corrector designed and built by CEOS GmbH (Heidelberg, Germany).

Stem Without Spherical Aberration

1999 ◽  
Vol 5 (S2) ◽  
pp. 670-671 ◽  
Author(s):  
O.L. Krivanek ◽  
N. Dellby ◽  
A.R. Lupini
Keyword(s):  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Operating Voltage ◽  
Resolution Limit ◽  
New Paradigm ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Two Generations

Even though two generations of electron microscopists have come to accept that the resolution of their instruments is limited by spherical aberration, three different aberration correctors showing that the aberration can be overcome have recently been built [1-3]. One of these correctors was developed by us specifically for forming small electron probes in a dedicated scanning transmission electron microscope (STEM) [3, 4]. It promises to revolutionize the way STEM instruments are built and the types of problems that they are applied to.As was the case with the Berlin Wall, when a barrier that was once thought immovable finally crumbles, many of the consequences can be quite unexpected. For STEM, the removal of spherical aberration (Cs) as the main resolution limit is likely to lead to a new paradigm in which:1) The resolution at a given operating voltage will improve by about 3x relative to today's best. When Cs can be adjusted arbitrarily in a STEM being used for microanalysis or dark field imaging, defocus and Cs are set to values that optimally oppose the effect of the 5th-order spherical aberration C5.

Plenary Special Lectures

2013 ◽  
Vol 19 (S3) ◽  
pp. 11-14
Author(s):  
Harald Rose ◽  
Joris Dik
Keyword(s):  
Spherical Aberration ◽  
Rotational Symmetry ◽  
Objective Lens ◽  
Aberration Correction ◽  
Time Varying ◽  
Resolution Limit ◽  
Space Charges ◽  
Rotationally Symmetric ◽  
Electron Microscopes

The correction of the aberrations of electron lenses is the long story of many seemingly fruitless efforts to improve the resolution of electron microscopes by compensating for aberrations of round electron lenses over a period of 50 years. The problem started in 1936 when Scherzer demonstrated that the chromatic and spherical aberrations of rotationally symmetric electron lenses are unavoidable. Moreover, the coefficients of these aberrations cannot be made sufficiently small. As a result, the resolution limit of standard electron microscopes equals about one hundred times the wavelength of the electrons, whereas modern light microscopes have reached a resolution limit somewhat smaller than the wavelength. In 1947, Scherzer found an ingenious way for enabling aberration correction. He demonstrated in a famous article that it is in theory possible to eliminate chromatic and spherical aberrations by lifting any one of the constraints of his theorem, either by abandoning rotational symmetry or by introducing time-varying fields, or space charges. Moreover, he proposed a multipole corrector compensating for the spherical aberration of the objective lens.

Aberration Correction in Electron Microscopy

1978 ◽  
Vol 36 (3) ◽  
pp. 185-196 ◽  
Author(s):  
H. Koops
Keyword(s):  
Phase Contrast ◽  
Collection Efficiency ◽  
Spherical Aberration ◽  
Objective Lens ◽  
Resolution Limit ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Beam Transmission ◽  
Contrast Image ◽  
Fixed Beam

Most presently available fixed-beam transmission electron microscopes (FBEM) yield a resolution limit close to the theoretically predicted value which is determined by diffraction and by the spherical aberration of the objective lens. The larger the aperture the better is the collection efficiency of the elastically scattered electrons forming the image. To increase the useful objective aperture it is necessary to overcome the spherical aberration. In the case of a phase contrast image it is possible, at least in principle, to compensate the effect of the spherical aberration by subsequent holographic processing of the electron micrograph.

Computer Simulation of the Imaging of Atomic Defects in Metals

1977 ◽  
Vol 35 ◽  
pp. 14-16 ◽  
Author(s):  
P. M. Fields ◽  
J. M. Cowley
Keyword(s):  
Local Strain ◽  
Dark Field ◽  
Objective Lens ◽  
Heavy Atoms ◽  
Dark Field Imaging ◽  
Resolution Electron ◽  
Localized Defects ◽  
Computer Calculations ◽  
Electron Microscopes ◽  
Diffraction Patterns

Localized defects in metals, such as vacancies and interstitials, should have scattering powers for electrons comparable with those of the single heavy atoms which have been imaged in recent years by use of high resolution electron microscopes. It should therefore be possible to obtain appreciable contrast from such defects with current lOOkV electron microscopes. However in order to distinguish the intensity variations due to these defects from those due to specimen surface structure, contamination or other causes, it may be necessary to use the improved resolution of high voltage microscopes so that the characteristic shapes of the defects and their local strain fields can be recognized.In order to test these speculations, we have made computer calculations of the images and diffraction patterns to be expected from split interstitials in thin crystals of gold and aluminum for bright-field and dark-field imaging with a lOOkV microscope with an objective lens having Cs = 1.8mm and for a l000kV microscope, Cs = 1.8mm.

Development Program for a 500-kV High Resolution Microscope

1969 ◽  
Vol 27 ◽  
pp. 184-185
Author(s):  
R. E. Worsham ◽  
J. E. Mann ◽  
E. G. Richardson ◽  
G. G. Slaughter ◽  
N. F. Ziegler
Keyword(s):  
High Resolution ◽  
Liquid Helium ◽  
Spherical Aberration ◽  
National Laboratory ◽  
Development Program ◽  
Objective Lens ◽  
Helium Temperature ◽  
Oak Ridge ◽  
Point To Point ◽  
High Resolution Microscopy

The goal of the development program for high resolution microscopy at Oak Ridge National Laboratory is a 100-500 kV instrument with a point-to-point resolution of at least 1Å. As reported previously, this microscope is intended for biological specimens to be observed at liquid helium temperature. This resolution is to be achieved principally by reduction of the primary spherical aberration for the objective lens with a quadrupole-octupole system of lenses.

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.

Limits for high-resolution electron microscopy of inorganic materials?

1987 ◽  
Vol 45 ◽  
pp. 4-5
Author(s):  
David J. Smith
Keyword(s):  
Electron Microscopy ◽  
Spherical Aberration ◽  
High Resolution Electron Microscopy ◽  
Inorganic Materials ◽  
Atomic Scale ◽  
Resolution Limit ◽  
Contrast Transfer Function ◽  
Existing Problems ◽  
Resolution Electron ◽  
Electron Microscopes

The era of atomic-resolution electron microscopy has finally arrived. In virtually all inorganic materials, including oxides, metals, semiconductors and ceramics, it is possible to image individual atomic columns in low-index zone-axis projections. A whole host of important materials’ problems involving defects and departures from nonstoichiometry on the atomic scale are waiting to be tackled by the new generation of intermediate voltage (300-400keV) electron microscopes. In this review, some existing problems and limitations associated with imaging inorganic materials are briefly discussed. The more immediate problems encountered with organic and biological materials are considered elsewhere.Microscope resolution. It is less than a decade since the state-of-the-art, commercially available TEM was a 200kV instrument with a spherical aberration coefficient of 1.2mm, and an interpretable resolution limit (ie. first zero crossover of the contrast transfer function) of 2.5A.

Exit-surface wave reconstruction using a focal series

1992 ◽  
Vol 50 (2) ◽  
pp. 988-989
Author(s):  
W.J. de Ruijter ◽  
M.R. McCartney ◽  
David J. Smith ◽  
J.K. Weiss
Keyword(s):  
Surface Wave ◽  
Spherical Aberration ◽  
Data Extraction ◽  
High Sensitivity ◽  
Geometric Distortion ◽  
Variation Method ◽  
Objective Lens ◽  
Immediate Reconstruction ◽  
Exit Surface ◽  
Electron Microscopes

Further advances in resolution enhancement of transmission electron microscopes can be expected from digital processing of image data recorded with slow-scan CCD cameras. Image recording with these new cameras is essential because of their high sensitivity, extreme linearity and negligible geometric distortion. Furthermore, digital image acquisition allows for on-line processing which yields virtually immediate reconstruction results. At present, the most promising techniques for exit-surface wave reconstruction are electron holography and the recently proposed focal variation method. The latter method is based on image processing applied to a series of images recorded at equally spaced defocus.Exit-surface wave reconstruction using the focal variation method as proposed by Van Dyck and Op de Beeck proceeds in two stages. First, the complex image wave is retrieved by data extraction from a parabola situated in three-dimensional Fourier space. Then the objective lens spherical aberration, astigmatism and defocus are corrected by simply dividing the image wave by the wave aberration function calculated with the appropriate objective lens aberration coefficients which yields the exit-surface wave.

Towards 1-Ångstrom-resolution STEM

1993 ◽  
Vol 51 ◽  
pp. 996-997
Author(s):  
H.S. von Harrach ◽  
D.E. Jesson ◽  
S.J. Pennycook
Keyword(s):  
High Resolution ◽  
Field Emission ◽  
Phase Contrast ◽  
Spherical Aberration ◽  
A Priori ◽  
Dark Field ◽  
Image Resolution ◽  
Objective Lens ◽  
Annular Dark Field ◽  
First Results

Phase contrast TEM has been the leading technique for high resolution imaging of materials for many years, whilst STEM has been the principal method for high-resolution microanalysis. However, it was demonstrated many years ago that low angle dark-field STEM imaging is a priori capable of almost 50% higher point resolution than coherent bright-field imaging (i.e. phase contrast TEM or STEM). This advantage was not exploited until Pennycook developed the high-angle annular dark-field (ADF) technique which can provide an incoherent image showing both high image resolution and atomic number contrast.This paper describes the design and first results of a 300kV field-emission STEM (VG Microscopes HB603U) which has improved ADF STEM image resolution towards the 1 angstrom target. The instrument uses a cold field-emission gun, generating a 300 kV beam of up to 1 μA from an 11-stage accelerator. The beam is focussed on to the specimen by two condensers and a condenser-objective lens with a spherical aberration coefficient of 1.0 mm.

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