Quantitative analysis by reconstruction of HREM focal series

1994 ◽  
Vol 52 ◽  
pp. 740-741
Author(s):  
W. Coene ◽  
A. Thust ◽  
M. Op de Beeck ◽  
D. Van Dyck
Keyword(s):  
Phase Retrieval ◽  
Image Plane ◽  
Initial Guess ◽  
Recursive Least Squares ◽  
Objective Lens ◽  
Electron Wave ◽  
Electron Sources ◽  
Original Algorithm ◽  
Coherent Field ◽  
Direct Interpretation

Compared to conventional electron sources, the use of a highly coherent field-emission gun (FEG) in TEM improves the information resolution considerably. A direct interpretation of this extra information, however, is hampered since amplitude and phase of the electron wave are scrambled in a complicated way upon transfer from the specimen exit plane through the objective lens towards the image plane. In order to make the additional high-resolution information interpretable, a phase retrieval procedure is applied, which yields the aberration-corrected electron wave from a focal series of HRTEM images (Coene et al, 1992).Kirkland (1984) tackled non-linear image reconstruction using a recursive least-squares formalism in which the electron wave is modified stepwise towards the solution which optimally matches the contrast features in the experimental through-focus series. The original algorithm suffers from two major drawbacks : first, the result depends strongly on the quality of the initial guess of the first step, second, the processing time is impractically high.

Electron holography of p-n junctions

1996 ◽  
Vol 54 ◽  
pp. 974-975
Author(s):  
B.G. Frost ◽  
D.C. Joy ◽  
L.F. Allard ◽  
E. Voelkl
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Field Emission ◽  
Ccd Camera ◽  
Image Plane ◽  
Reference Wave ◽  
Field Of View ◽  
Control Mode ◽  
Objective Lens ◽  
Electron Holography

A wide holographic field of view (up to 15 μm in the Hitachi-HF2000) is achieved in a TEM by switching off the objective lens and imaging the sample by the first intermediate lens. Fig.1 shows the corresponding ray diagram for low magnification image plane off-axis holography. A coherent electron beam modulated by the sample in its amplitude and its phase is superimposed on a plane reference wave by a negatively biased Möllenstedt-type biprism.Our holograms are acquired utilizing a Hitachi HF-2000 field emission electron microscope at 200 kV. Essential for holography are a field emission gun and an electron biprism. At low magnification, the excitation of each lens must be appropriately adjusted by the free lens control mode of the microscope. The holograms are acquired by a 1024 by 1024 slow-scan CCD-camera and processed by the “Holoworks” software. The hologram fringes indicate positively and negatively charged areas in a sample by the direction of the fringe bending (Fig.2).

Tandem scanning confocal light microscopy as compared with x-ray diffraction for characterizing the behavior of clays in fluid-saturated petroleum reservoir rock

1989 ◽  
Vol 47 ◽  
pp. 148-149
Author(s):  
C.J. Stuart ◽  
B.E. Viani ◽  
J. Walker ◽  
T.H. Levesque
Keyword(s):  
Light Microscopy ◽  
Image Plane ◽  
Reservoir Rock ◽  
Depth Of Field ◽  
Objective Lens ◽  
Scanning System ◽  
Light Sources ◽  
Petroleum Reservoir ◽  
Image Recording ◽  
Scan Speed

Many techniques of imaging used to characterize petroleum reservoir rocks are applied to dehydrated specimens. In order to directly study behavior of fines in reservoir rock at conditions similar to those found in-situ these materials need to be characterized in a fluid saturated state.Standard light microscopy can be used on wet specimens but depth of field and focus cannot be obtained; by using the Tandem Scanning Confocal Microscope (TSM) images can be produced from thin focused layers with high contrast and resolution. Optical sectioning and extended focus images are then produced with the microscope. The TSM uses reflected light, bulk specimens, and wet samples as opposed to thin section analysis used in standard light microscopy. The TSM also has additional advantages: the high scan speed, the ability to use a variety of light sources to produce real color images, and the simple, small size scanning system. The TSM has frame rates in excess of normal TV rates with many more lines of resolution. This is accomplished by incorporating a method of parallel image scanning and detection. The parallel scanning in the TSM is accomplished by means of multiple apertures in a disk which is positioned in the intermediate image plane of the objective lens. Thousands of apertures are distributed in an annulus, so that as the disk is spun, the specimen is illuminated simultaneously by a large number of scanning beams with uniform illumination. The high frame speeds greatly simplify the task of image recording since any of the normally used devices such as photographic cameras, normal or low light TV cameras, VCR or optical disks can be used without modification. Any frame store device compatible with a standard TV camera may be used to digitize TSM images.

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:

The theory of super-resolution electron microscopy via Wigner-distribution deconvolution

1992 ◽  
Vol 339 (1655) ◽  
pp. 521-553 ◽  
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Phase Retrieval ◽  
Wigner Distribution ◽  
Super Resolution ◽  
Partial Coherence ◽  
Objective Lens ◽  
Specimen Thickness ◽  
Data Set ◽  
Transmission Electron

The theory of deconvolving the microdiffraction data-set available in a scanning transmission electron microscope or, equivalently, the set of all bright- and dark-field images available in a conventional transmission electron microscope to obtain super- resolution micrographs (which are not limited by the transfer function of the objective lens) is developed and described with reference to holography and other phase-retrieval schemes. By the use of a Wigner distribution, influences of the instrument function can be entirely separated from the information pertaining to the specimen. The final solution yields an unambiguous estimate of the complex value of the specimen function at a resolution which in theory is only limited by the electron wavelength. The faithfulness of the image processing is shown to be not seriously affected by specimen thickness or partial coherence in the illuminating beam. The inversion procedure is remarkably noise insensitive, implying that it should result in a robust and practicable experimental technique, though one that will require very large computing facilities.

Recursive Least-Squares Time Domain Identification of Structural Parameters

1977 ◽  
Vol 44 (1) ◽  
pp. 135-140 ◽  
Author(s):  
P. Caravani ◽  
M. L. Watson ◽  
W. T. Thomson
Keyword(s):  
Least Squares ◽  
Structural Parameters ◽  
Gaussian White Noise ◽  
Initial Guess ◽  
Recursive Least Squares ◽  
Rapid Convergence ◽  
Domain Identification ◽  
Response Data ◽  
Dynamic Excitation ◽  
Two Degree Of Freedom

A method of identifying structural parameters such as damping and stiffness of a building from its time response under dynamic excitation is presented. A least-squares recursive computer algorithm which requires no matrix inversion is developed and tested with the response of a two-degree-of-freedom structure including Gaussian white noise. The algorithm provides means to account for both the model uncertainty and the investigators’ confidence in the initial guess of the parameters. These statistical quantities can be updated with passage of time. The study indicates that rapid convergence to the correct values of the parameters takes place even under severe noise in the response data.

Divergent-beam holography with a 200keV FE TEM

1991 ◽  
Vol 49 ◽  
pp. 678-679
Author(s):  
Xiao Zhang ◽  
David Joy
Keyword(s):  
Optical System ◽  
Photographic Film ◽  
Objective Lens ◽  
Electron Wave ◽  
Transmission Electron ◽  
High Resolution Images ◽  
Phase Data ◽  
Electron Microscopes ◽  
Complete Amplitude ◽  
Commercial Field

A hologram, first described and named by Gabor (1949), permits a medium such as photographic film, which responds only to intensity, to store the complete amplitude and phase information which characterizes an electron wavefront. The hologram is formed by allowing some fraction of a coherent electron wave which has interacted with a specimen to interact again with original incident wave so as to generate an interference pattern. If the hologram is then itself illuminated by a coherent light source and optical system which mimic the original electron-optical system then a pair of images -one real and the other virtual -can be reconstructed and viewed. Because the hologram contains both the amplitude and the phase data of the wavefront, errors and distortions in either component due to aberrations in the objective lens can be corrected by optical manipulates before the image is reconstructed. With the advent of commercial field emission transmission electron microscopes capable of generating both high resolution images and highly coherent electron beams, these holographic techniques are now available as practical tools to improve TEM performance as well as to create new modes of images (Tonomura 1987).

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.

Is electron holography at atomic dimensions going to meet the expectations of Dennis Gabor?

1989 ◽  
Vol 47 ◽  
pp. 2-3
Author(s):  
Hannes Lichte
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Object Wave ◽  
Objective Lens ◽  
Electron Holography ◽  
High Magnification ◽  
Fourier Space ◽  
Electron Wave ◽  
Object Structure ◽  
Wave Aberration

Electron microscopy faces the following basic situation: The electron wave transmitted through the object is modulated both in amplitude a and phase φ. In order to display the object structure, the object wave a exp(i φ) is transferred by the electron lenses into an image wave A exp(i φ) at sufficiently high magnification, modulated in amplitude and phase as well. However, due to the lens aberrations in the high resolution domain, image and object wave generally do not agree. One has to distinguish between coherent and incoherent aberrations. Coherent aberrations (e.g. spherical) are independent of electron energy andangle of illumination; preferably, their effect is taken into account in Fourier space by means of the wave transfer function WTF(u) = exp(i х (u)) depending on the spatial frequency u; х (u) means the wave aberration of the objective lens.

Introduction to electron holography

1994 ◽  
Vol 52 ◽  
pp. 396-397
Author(s):  
M. R. McCartney
Keyword(s):  
Spherical Aberration ◽  
Phase Changes ◽  
Phase Image ◽  
Objective Lens ◽  
Phase Plate ◽  
Electron Holography ◽  
Imaging Method ◽  
Electron Sources ◽  
Transmission Electron ◽  
Magnetic Potentials

Electron holography is an imaging method in the transmission electron microscope (TEM) whereby the phase and amplitude of the electron wavefront can be obtained separately, unlike the conventional image which represents the intensity of the electron wave without any direct phase information. In particular, the phase image allows for the possibility of directly imaging the electric and magnetic potentials within a sample on the basis of phase changes produced on the incident electron wavefront. There are many advantages to directly imaging the phase structure and specific examples of the unique information available will be shown. For example, once the phase image is obtained it is possible to correct for the phase changes imposed by the transfer function of the objective lens by directly applying an inverse phase plate.Electron holography was originally proposed in 1949 by Gabor as a means of improving the resolution of electron micrography by correction of spherical aberration but was never fully utilized due to inadequate electron sources. In recent years, the availability of reliable field emission guns as coherent electron sources has stimulated renewed interest in the technique.

An improved vision calibration method for coaxial alignment microassembly

2014 ◽  
Vol 34 (3) ◽  
pp. 237-243 ◽  
Author(s):  
Xin Ye ◽  
Jun Gao ◽  
Zhijing Zhang ◽  
Chao Shao ◽  
Guangyuan Shao
Keyword(s):  
Degrees Of Freedom ◽  
Microelectromechanical Systems ◽  
Vision System ◽  
Image Plane ◽  
Calibration Method ◽  
Corner Detection ◽  
Objective Lens ◽  
Content Type ◽  
Assembly Accuracy ◽  
Methodological Guidelines

Purpose – The purpose of this paper is to propose a sub-pixel calibration method for a microassembly system with coaxial alignment function (MSCA) because traditional sub-pixel calibration approaches cannot be used in this system. Design/methodology/approach – The in-house microassembly system comprises a six degrees of freedom (6-DOF) large motion serial robot with microgrippers, a hexapod 6-DOF precision alignment worktable and a vision system whose optical axis of the microscope is parallel with the horizontal plane. A prism with special coating is fixed in front of the objective lens; thus, two parts’ Figures, namely the images of target and base part, can be acquired simultaneously. The relative discrepancy between the two parts can be calculated from image plane coordinate instead of calculating space transformation matrix. Therefore, the traditional calibration method cannot be applied in this microassembly system. An improved calibration method including the check corner detection solves the distortion coefficient conversely. This new way can detect the corner at sub-pixel accuracy. The experiment proves that the assembly accuracy of the coaxial microassembly system which has been calibrated by the new method can reach micrometer level. Findings – The calibration results indicate that solving the distortion conversely could improve the assembly accuracy of MSCA. Originality/value – The paper provides certain calibration methodological guidelines for devices with 2 dimensions or 2.5 dimensions, such as microelectromechanical systems devices, using MSCA.

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