Showing papers on "Contrast transfer function published in 2006"
TL;DR: In this article, the authors demonstrate that confocal imaging trajectories can be established in a transmission electron microscope fitted with two spherical aberration correctors, which allows three-dimensional imaging and analysis of materials with atomic lateral resolution and with a depth resolution of a few nanometers.
Abstract: The authors demonstrate that confocal imaging trajectories can be established in a transmission electron microscope fitted with two spherical aberration correctors. An atomic-scale electron beam, focused by aberration-corrected illumination optics, is directly imaged by a second aberration-corrected system. The initial experiment described indicates how aberration-corrected scanning confocal electron microscopy will allow three-dimensional imaging and analysis of materials with atomic lateral resolution and with a depth resolution of a few nanometers. The depth resolution in the confocal mode is shown to be robust to the uncorrected chromatic aberration of the lenses, unlike depth sectioning using a single lens.
88 citations
TL;DR: The impact of the Cs-corrector on X-ray analysis is theoretically evaluated, in terms of expected improvements in spatial resolution and analytical sensitivity, and the calculations are compared with initial experimental results.
Abstract: A Nion spherical-aberration (Cs) corrector was recently installed on Lehigh University's 300-keV cold field-emission gun (FEG) Vacuum Generators HB 603 dedicated scanning transmission electron microscope (STEM), optimized for X-ray analysis of thin specimens. In this article, the impact of the Cs-corrector on X-ray analysis is theoretically evaluated, in terms of expected improvements in spatial resolution and analytical sensitivity, and the calculations are compared with initial experimental results. Finally, the possibilities of atomic-column X-ray analysis in a Cs-corrected STEM are discussed.
69 citations
TL;DR: An additional correction to the defocus aberration, dependent on object thickness, is described, which becomes important for the use of image simulation programs in predicting optimum high-resolution contrast from thin objects at the sub-angstrom scale.
Abstract: The optimum imaging of an object structure at the sub-angstrom length scale requires precise adjustment of the lens aberrations of a high-resolution instrument up to the fifth order. A least-squares optimization of defocus aberration C1, third-order spherical aberration C3, and fifth-order spherical aberration C5 yields two sets of aberration coefficients for strong phase contrast up to the information limit: one for variable C1 and C3, at fixed C5, another for variable C1, C3, and C5. An additional correction to the defocus aberration, dependent on object thickness, is described, which becomes important for the use of image simulation programs in predicting optimum high-resolution contrast from thin objects at the sub-angstrom scale. For instruments with a sub-angstrom information limit the ultimate structure resolution, the power to resolve adjacent atom columns in a crystalline object, depends on both the instrumental pointspread and an object pointspread due to finite width of the atomic column potentials. A simulation study on a simple double-column model yields a range for structure resolutions, dependent on the atomic scattering power, from 0.070 nm down to 0.059 nm, for a hypothetical 300-kV instrument with an information limit of 0.050 nm.
67 citations
TL;DR: Analysis of the contrast transfer with the possibility of tunable spherical aberration has revealed new imaging modes: high-resolution amplitude contrast, extension of the point resolution to the information limit, and enhanced image intensity modulation for negative phase contrast.
Abstract: The design and construction of a double-hexapole aberration corrector has made it possible to build the prototype of a spherical-aberration corrected transmission electron microscope dedicated to high-resolution imaging on the atomic scale. The corrected instrument, a Philips CM200 FEG ST, has an information limit of better than 0.13 nm, and the spherical aberration can be varied within wide limits, even to negative values. The aberration measurement and the corrector control provide instrument alignments stable enough for materials science investigations. Analysis of the contrast transfer with the possibility of tunable spherical aberration has revealed new imaging modes: high-resolution amplitude contrast, extension of the point resolution to the information limit, and enhanced image intensity modulation for negative phase contrast. In particular, through the combination of small negative spherical aberration and small overfocus, the latter mode provides the high-resolution imaging of weakly scattering atom columns, such as oxygen, in the vicinity of strongly scattering atom columns. This article reviews further lens aberration theory, the principle of aberration correction through multipole lenses, aspects for practical work, and materials science applications.
61 citations
TL;DR: This paper derives formulae to explore the maximum value of the fifth-order spherical aberration for directly interpretable imaging and discusses the optimum imaging conditions and their applicable range.
56 citations
TL;DR: In this article, a spherical aberration corrected transmission electron microscopy (Cs-corrected TEM) technique was used to obtain clearer images in real space than ever before, where oxygen atoms were observed in rutile TiO2.
Abstract: We have developed a spherical aberration corrected transmission electron microscopy (Cs-corrected TEM) technique that allows us to obtain clearer images in real space than ever before. We applied this technique to titanium oxide, in which light elements such as oxygen are difficult to observe using TEM because of its small cross section and electronic damage. In the present study, we successfully observed oxygen atoms in rutile TiO2. In addition, this direct observation of oxygen atoms enabled us to study the Magn?li structure (TinO2n?1), which is caused by oxygen vacancies. These vacancies caused an atomic relaxation of the titanium and oxygen atoms. The relaxed atoms formed a characteristic shear structure of rutile titanium dioxide phase. This shear structure of the Magn?li structure (TinO2n?1) was visualized with a spatial resolution of 0.119?nm. At the same time, the selected area diffraction (SAD) pattern of the defect structure was obtained. Additional spots were shown inside the rutile [110] spot. We made structural models of the shear structure and simulated the diffraction pattern and images using a multi-slice simulation. Additional spots in the simulated diffraction patterns accurately reconstructed the experimental data. We also considered the possibility of the real-space analysis of local structures using spherical aberration corrected transmission electron microscopy.
40 citations
TL;DR: This work will show that an adequately designed reversed-Gaussian aperture permits the production of a focal spot whose form changes very slowly with the spherical aberration, and refers to the use of purely absorbing beam-shaping elements, which with a minimum modification of optical architecture will allow a significant reduction of the spherical Aberrations.
Abstract: In modern high-numerical-aperture (NA) optical scanning instruments, such as scanning microscopes, optical data storage systems, or laser trapping technology, the beam emerging from the high-NA objective focuses deeply through an interface between two media of different refractive index. Such a refractive index mismatch introduces an important amount of spherical aberration, which increases dynamically when scanning at increasing depths. This effect strongly degrades the instrument performance. Although in the past few years many different techniques have been reported to reduce the spherical aberration effect, no optimum solution has been found. Here we concentrate on a technique whose main feature is its simplicity. We refer to the use of purely absorbing beam-shaping elements, which with a minimum modification of optical architecture will allow a significant reduction of the spherical aberration effect. Specifically, we will show that an adequately designed reversed-Gaussian aperture permits the production of a focal spot whose form changes very slowly with the spherical aberration.
27 citations
TL;DR: In this paper, the authors analyzed diffractograms of elastically filtered images of thin amorphous foils of carbon, silicon and germanium using the weak object approximation.
Abstract: In this study we analyse diffractograms of elastically filtered images of thin amorphous foils of carbon, silicon and germanium using the weak object approximation. The use of this approximation leads to a contrast transfer function containing a phase η(u) depending on the spatial frequency u. Furthermore, the derivative of this phase is included in the envelope function of the contrast transfer function. The phase can be attributed to the breakdown of the first-order Born approximation leading to complex scattering amplitudes characterized by this phase η(u). We analyse contrast transfer characteristics to determine the phase of complex scattering amplitudes of carbon, silicon and germanium as a function of spatial frequency and to measure the two-particle structure factor of the corresponding amorphous specimens. The contrast transfer characteristics were calculated from diffractograms of focal series of elastically filtered images. The phases measured show a decay with increasing spatial frequency and additional oscillations. The results for the two-particle structure factor also decay with increasing spatial frequency and contain low local maxima. Both can be attributed to voids or inhomogeneities within the amorphous structure.
23 citations
TL;DR: The first monochromated and aberration-corrected scanning transmission electron microscope operated at 200 kV is described, which improves the energy resolution for studies of energy loss near edge structures and point out another advantage of the combination of both components.
Abstract: Experimental results from the first monochromated and aberration-corrected scanning transmission electron microscope operated at 200 kV are described. The formation of an electron probe with a diameter of less than 0.2 nm at an energy width significantly under 0.3 eV and its planned application to the chemical analysis of nanometer-scale structures in materials science are described. Both energy and spatial resolution will benefit from this: The monochromator improves the energy resolution for studies of energy loss near edge structures. The Cs corrector allows formation of either a smaller probe for a given beam current or yields, at fixed probe size, an enhanced beam current density using a larger condenser aperture. We also point out another advantage of the combination of both components: Increasing the convergence angle by using larger condenser apertures in an aberration-corrected instrument will enlarge the undesirable chromatic focus spread. This in turn influences spatial resolution. The effect of polychromatic probe tails is proportional to the product of convergence angle, chromatic aberration constant, and energy spread. It can thus be compensated for in our new instrument by decreasing the energy width by the same factor as the beam convergence is increased to form a more intense probe. An alternative in future developments might be hardware correction of the chromatic aberration, which could eliminate the chromatic probe spread completely.
22 citations
Patent•
27 Dec 2006TL;DR: In this article, a method for adjustment of an aberration corrector in a scanning transmission electron microscope is described, where a Ronchigram image is acquired using a spherical standard specimen.
Abstract: In the type of scanning transmission electron microscopes carrying an aberration corrector, a method of assuring more simplified and manipulatable adjustment of the corrector and a scanning transmission electron microscope having that function are provided. A Ronchigram image is acquired using a spherical standard specimen and parameters necessary for the adjustment are acquired from the thus obtained Ronchigram.
19 citations
TL;DR: The traditional defocus phase contrast is compared to two recently developed phase plate techniques, one is the Zernike phase contrast transmission electron microscope, the other is the Hilbert differential contrast thransmission electron microscope.
Abstract: Presented is an evaluation of phase contrast techniques in transmission electron microscopy. The traditional defocus phase contrast is compared to two recently developed phase plate techniques. One is the Zernike phase contrast transmission electron microscope, the other is the Hilbert differential contrast thransmission electron microscope. The imaging characteristics of each technique are discussed. Phase plate techniques provide improved contrast for ice-embedded biological samples which are a challenge for the conventional defocus phase contrast. The flat spectral response of the Zernike and Hilbert modes extends towards the low frequencies which are severely suppressed in the conventional defocus mode. Target applications for each of the phase contrast techniques are discussed based on the specifics of image formation and spectral transfer.
Patent•
26 Dec 2006TL;DR: In this paper, a scanning transmission electron microscope is provided including an electron beam source, convergent lenses, scan coils, a dark field image detector, an A/D converter, and an information processing device.
Abstract: A scanning transmission electron microscope is provided including an electron beam source ( 1 ), convergent lenses ( 3 ), scan coils ( 10 ), a dark field image detector ( 16 ), a bright field image detector ( 17 ), an A/D converter ( 21 ), and an information processing device ( 24 ). In the scanning transmission electron microscope, a spherical aberration corrector ( 7 ) and deflection coils ( 9 a, 9 b ) are disposed before a pre-magnetic field of objective lens ( 11 ). Fourier transform images are produced from scanning transmission images obtained by the dark field image detector ( 16 ) or the bright field image detector ( 17 ) to evaluate deviation in an aberration correction state due to an image shift caused by the deflection coils ( 9 a, 9 b ) at a deflection ratio, so a suitable deflection ratio is fed back. As a result, an electron optics of the scanning transmission electron microscope including the corrector can be easily adjusted.
TL;DR: In this paper, a liquid crystal (LC) lens was designed and fabricated to compensate the spherical aberration caused by a difference in substrate thickness, and the curvature control with a spherical LC lens was optimized to maintain the aberration of a Blu-ray optical pickup even for a thickness variation of ± 25 µm.
Abstract: In multilayer recording, it is strongly required to compensate the spherical aberration caused by a difference in substrate thickness. A novel liquid crystal (LC) lens is designed and fabricated to compensate the spherical aberration in this study. The new structure of the LC lens includes both concave and convex surfaces, which can compensate the spherical aberration with a relatively long range. Since a previously developed LC panel showed a very low tolerance to the shift of an objective lens, a new component has been proposed with a special LC lens structure to improve both the tolerance and compensation range. By optimized curvature control with a spherical LC lens, the aberration of a Blu-ray optical pickup can be maintained at 0.018λrms even for a thickness variation of ±25 µm. Finally, the LC lens has been fabricated using a standard one drop filling (ODF) process and evaluated by measuring the variation in focal length as a function of applied voltage.
22 Feb 2006
TL;DR: In this article, a next generation scanning transmission electron microscope (STEM) fitted with a new design of aberration corrector is shown to have improved spatial resolution and beam convergence with a convergence semi-angle of 40 mrad.
Abstract: Through the correction of spherical aberration in the scanning transmission electron microscope (STEM), the resolving of a 78 pm atomic column spacing has been demonstrated along with information transfer to 61 pm. The achievement of this resolution required careful control of microscope instabilities, parasitic aberrations and the compensation of uncorrected, higher order aberrations. Many of these issues are improved in a next generation STEM fitted with a new design of aberration corrector, and an initial result demonstrating aberration correction to a convergence semi-angle of 40 mrad is shown. The improved spatial resolution and beam convergence allowed for by such correction has implications for the way in which experiments are performed and how STEM data should be interpreted.
Patent•
30 Oct 2006
TL;DR: In this paper, an automatic aberration correction using a Ronchigram automatically in a correction method and a device using ronchigrams was proposed. But the method was not suitable for the case where the electron microscope has a function of displaying an image by focusing electron beams (probe) on a test piece, and scanning the electron beams on the test piece.
Abstract: PROBLEM TO BE SOLVED: To carry out aberration correction using a Ronchigram automatically in a aberration correction method and a device using the ronchigram. SOLUTION: The electron microscope has a function of displaying an image by focusing electron beams (probe) on a test piece, scanning the electron beams on the test piece, and interlocking the detected signal of electrons transmitted through the test piece with the electron beam scanning, and comprises a first calculation means to obtain an auto-correlation in micro-regions of a Ronchigram of an amorphous test piece, a detection means to detect aberration of electron beams formed of local angle regions on an open face from the auto-correlation or an Fourier analysis of the auto-correlation, a second calculation means to calculate each aberration based on the detection result, and a control means to control aberration correction operation based on the calculation result of the calculation means. By this structure, aberration correction using Ronchigram can be carried out automatically. COPYRIGHT: (C)2007,JPO&INPIT
TL;DR: A method for the measurement of third-order spherical aberration coefficients (C(s)), using low-order zone-axis Ronchigrams of a crystalline material, and a method for roughly estimating defocus values is presented.
TL;DR: In this paper, a static microfield exposure tool (MET) based on a 0.3 numerical aperture optic and operating at a wavelength of 13.5nm has been developed at the Advanced Light Source, a synchrotron facility at the Lawrence Berkeley National Laboratory.
Abstract: In order to meet the high-resolution printing potential of extreme ultraviolet (EUV) lithography, the projection optics must be of very high quality. The contrast transfer function (CTF), a measure of the aerial-image contrast as a function of pitch, describes one key aspect of projection optic quality. In order to support research into EUV lithography, a static microfield exposure tool (MET) based on a 0.3 numerical aperture optic and operating at a wavelength of 13.5nm has been developed at the Advanced Light Source, a synchrotron facility at the Lawrence Berkeley National Laboratory. This work presents the results of resist-based measurements of the CTF for the MET optic. Although the resist is not an ideal aerial-image detector due to its nonlinear response, it is still possible to study some key characteristics of the optics using such methods. These measurements are based on line/space patterns printed in several different EUV photoresists. The experimental CTF results are compared with the CTF from...
TL;DR: In this article, the authors derived equations for defocus and primary spherical wave aberration coefficients caused by a shift in image plane of a perfect optical system, which is accurate at describing changes in the spherical aberration of an aberrated schematic eye.
Abstract: We derive equations for defocus and primary spherical wave aberration coefficients caused by a shift in image plane of a perfect optical system. The spherical aberration equation is accurate at describing changes in the spherical aberration of an aberrated schematic eye.
TL;DR: Initial results from an ultrahigh-vacuum (UHV) third-order spherical aberration (Cs) corrector for a dedicated scanning transmission electron microscopy, installed at the National Institute for Materials Science, Tsukuba, Japan, are presented here.
Abstract: Initial results from an ultrahigh-vacuum (UHV) third-order spherical aberration (Cs) corrector for a dedicated scanning transmission electron microscopy, installed at the National Institute for Materials Science, Tsukuba, Japan, are presented here. The Cs corrector is of the dual hexapole type. It is UHV compatible and was installed on a UHV column. The Ronchigram obtained showed an extension of the sweet spot area, indicating a successful correction of the third-order spherical aberration Cs. The power spectrum of an image demonstrated that the resolution achieved was 0.1 nm. A first trial of the direct measurement of the fifth-order spherical aberration C5 was also attempted on the basis of a Ronchigram fringe measurement.
01 Jan 2006
TL;DR: An iterative method for the reconstruction of the wave function at an exit surface based on wave-function propagation in free space is described and can be used to correct known coherent aberrations of the system in software and in particular Cs, third-order spherical aberration.
Abstract: An iterative method for the reconstruction of the wave function at an exit surface based on wave-function propagation in free space is described. The method has been tailored to work with a through-focus series of images measured in a high-resolution transmission electron microscope. This approach can be used to correct known coherent aberrations of the system in software and in particular Cs, third-order spherical aberration. The method has been illustrated by application to a through-focus series of twenty high-resolution images of silicon nitride taken at the Lawrence Berkeley National Laboratory, California.
04 Jun 2006
TL;DR: In this paper, a method to compensate the spherical aberration for any optical system and any object position is presented, where the aspheric coefficients are calculated by solving a system of first grade equations.
Abstract: We present a method to compensate the spherical aberration for any optical system and any object position, with this method the spherical aberration could be zero in several pupil positions at the same time. The aspheric coefficients are used to compensate the spherical aberration and they are calculated solving a system of first grade equations.
TL;DR: In this article, single gadolinium atoms in fullerenes encapsulated in a single-wall carbon nanotube were observed by a wave field restoration method based on three-dimensional Fourier filtering in transmission electron microscopy.
Abstract: Single gadolinium atoms in fullerenes encapsulated in a single-wall carbon nanotube were observed by a wave field restoration method based on three-dimensional Fourier filtering in transmission electron microscopy. Single gadolinium atoms were clearly resolved not only in the imaginary part image but also in the real part image of the exit wave field due to an improved signal-to-noise ratio by Fourier filtering and resolution enhancement by correcting spherical aberration and twofold astigmatism. This result indicates that the present method has potential to clarify compositional details of the sample by using their image contrasts.
TL;DR: A substantial increase in the ratio of the object contrast to the substrate contrast can be achieved by utilizing the strong variation of phase contrast with height, which is present when the spherical aberration has been adjusted to a small value.
Abstract: High Resolution Electron Microscopy (HREM) is often used to characterize objects supported by amorphous substrates, usually amorphous carbon. HREM is currently undergoing step change in performance due to aberration correctors. This paper examines the aberration corrected imaging of objects supported by amorphous substrates. In particular, we show that a substantial increase in the ratio of the object contrast to the substrate contrast can be achieved by utilizing the strong variation of phase contrast with height, which is present when the spherical aberration has been adjusted to a small value. This variation is examined using the familiar Weak Phase Object Approximation model from which it is determined that the contrast ratio achieves a maximum at a small nonzero value of the spherical aberration. This result is confirmed by multislice modelling which allows for deviations from the Weak Phase Object Approximation and delocalization effects. One important practical result of this study is the need to place the object of interest on the correct side of the amorphous carbon substrate.
29 Jun 2006
Journal Article•
Journal Article•
TL;DR: In this paper, the authors improved the glass system to reduce the ion diffusion and inter-permeation which may occur to the core-cladding interface, the actual numerical aperture of the fiber image inverters can be improved.
Abstract: Image inverter is a special type of fiber-optic plate,which can directly invert an image by 180° to an image intensifier.The device is making the night vision goggle more compact by integrating the image transfer and image invert function into a phosphor substrate.But due to the image inverter′s special structure,the numerical aperture and luminous flux decrease gradually with the increase of the radial distance from torsion axle centre.Compared with the fiber-optic plate,the image inverter has lower contrast transfer function and lower transmissivity.By improving the glass system to reduce the ion diffusion and inter-permeation which may occur to the core-cladding interface,the actual numerical aperture of the fiber image inverters can be improved.By means of adjusting EMA absorption,not only the needs of image intensifiers can be reached for the transmissivity of fiber image inverter screens,but also the stray light escaping from the optical fiber can be absorbed to the full extent to improve the contrast.With the selection for a reasonable core-cladding ratio,the cladding thickness reduction caused by torsion stretch can be remedied and also the cladding thickness can be increased further more to restrain the light to escape from fibers.The result shows that the innovation mentioned above can improve the contrast transfer characteristics of fiber image inverters.
22 Feb 2006
TL;DR: In this article, a JEOL 2200FS transmission electron microscope equipped with a field emission gun, an objective lens spherical aberration corrector and an in-column energy filter was used to acquire through focal series of high-resolution images of platinum nanocatalyst particles using a small value of the spherical anomaly coefficient.
Abstract: A JEOL 2200FS transmission electron microscope equipped with a field emission gun, an objective lens spherical aberration corrector and an in-column energy filter has been used to acquire through focal series of high-resolution images of platinum nanocatalyst particles using a small value of the spherical aberration coefficient. The degree to which spherical aberration correction provides an improvement to image quality and interpretability for such particles is discussed, both with and without the use of through-focal series restoration.
Journal Article•
TL;DR: In this article, an important diagnosis method of the Kirkpatrick-baez microscope system in ICF experiments was researched. And the model of the KBM was made in computer with 10 µm resolution at 8 keV.
Abstract: An important diagnosis method--Kirkpatrick-Baez microscope system in ICF experiments was researched. The brief aberration of the Kirkpatrick-Baez microscope was calculated. The main aberration, spherical aberration was analyzed, and the spherical aberration is 94% of the total aberration. The configuration was simulated by the ray tracing method. Resolutions in different fields and mirror-lengths were compared. The model of Kirkpatrick-Baez microscope was made in computer with 10 {mu}m resolution at 8 keV. It was studied about the adjusting tolerance method of Kirkpatrick-Baez microscope. When numerical aperture is 0.0037, the angle error range is -0.087 degree-0.067 degree . (authors)
Journal Article•
TL;DR: In this article, the authors reconstructed electron exit waves from focal series of lattice images to obtain near/sub-angstrom values, correcting for dominant aberrations of the objective lens and allowing imaging the atomic structure of crystalline materials directly.
Abstract: With the popularization of field emission gun transmission electron microscopes (FEG-TEM),the information limit and the point resolution become two key important parameters to characterize the resolution ability of the microscopesBecause of the oscillation characteristic of the contrast transfer function,the information between the point resolution and information limit in the high resolution images taken from the FEG-TEM is difficult to interpretReconstruction of electron exit waves from focal series of lattice images extends resolution to near/sub-angstrom values,corrects for dominant aberrations of the objective lens,and allows imaging the atomic structure of crystalline materials directlyThis has enabled us to directly record columns of the light elements carbon,nitrogen and oxygen with sub-angstrom resolutionThis technique establishes the basis of quantitative TEM
TL;DR: In this article, a cross-sectional image of a gold crystal observed along the z-axis was used to study the bending of the interference fringes in the edge region of the crystal.
Abstract: Using a three-dimensional image intensity distribution obtained by spherical aberration-corrected transmission electron microscopy, we studied a cross-sectional image (x-z image) of a gold crystal observed along the z-axis. In this x-z image, the bending of the interference fringes was observed in the edge region. We demonstrated that the bending is caused by a relative phase shift between the electron waves induced by dynamical electron scattering. By comparing with simulated images, the relative phase shift of about π/4 was proved to correspond to a difference in thickness of ∼0.9 nm.