Showing papers on "Contrast transfer function published in 2003"
TL;DR: Two computer programs are presented, CTFFIND3 and CTFTILT, which determine defocus parameters from images of untilted specimens, as well as defocus and tilt parameters from image of tilted specimens, respectively, using a simple algorithm.
1,480 citations
TL;DR: It is demonstrated in a nonlocal model for electron energy loss spectroscopy (EELS) that delocalization of scanning transmission electron microscopy (STEM) images for single, isolated atoms is primarily determined by the width of the probe, even for light atoms.
Abstract: The ``delocalization'' of inelastic scattering is an important issue for the ultimate spatial resolution of innershell spectroscopy in the electron microscope. It is demonstrated in a nonlocal model for electron energy loss spectroscopy (EELS) that delocalization of scanning transmission electron microscopy (STEM) images for single, isolated atoms is primarily determined by the width of the probe, even for light atoms. We present experimental data and theoretical simulations for Ti $L$-shell EELS in a [100] ${\mathrm{S}\mathrm{r}\mathrm{T}\mathrm{i}\mathrm{O}}_{3}$ crystal showing that, in this case, delocalization is not significantly increased by dynamical propagation. Issues relating to the use of aberration correctors in the STEM geometry are discussed.
102 citations
TL;DR: A method is presented for determining the defocus gradient in thin specimens such as sections and 2D crystals, and for restoration of the images subsequently used for 3D reconstruction, which includes area matching and tilt geometry refinement.
69 citations
TL;DR: A detailed analysis of contrast and signal/noise for both imaging modes is presented and it is conceivable that dark field imaging would be superior to bright field phase contrast microscopy.
47 citations
TL;DR: SiO2/Si(100) interfaces were for the first time observed by a spherical aberration-corrected high-resolution transmission electron microscope in a cross-sectional mode with potential use for semiconductor science and technology, even for the analysis of oxygen atoms at interfaces.
Abstract: siO 2 /Si(100) interfaces were for the first time observed by a spherical aberration-corrected high-resolution transmission electron microscope in a cross-sectional mode. As the Fresnel fringes were not contrasted at the interfaces, the interfacial structures were clearly observed without the need for artificial image contrast. Atomic steps and defects on the Si( 100) surfaces were accurately identified. Also, image simulations with the target imaging performance revealed oxygen atomic columns between silicon-silicon bonds. The present instrument is of potential use for semiconductor science and technology, even for the analysis of oxygen atoms at interfaces.
35 citations
TL;DR: In this article, a three-dimensional reconstruction of nano-scale objects (such as biological macromolecules) can be accomplished using data recorded with a transmission electron microscope using Chahine's method.
Abstract: Three-dimensional reconstruction of nano-scale objects (such as biological macromolecules) can be accomplished using data recorded with a transmission electron microscope An image obtained by a transmission electron microscope can be conceived of as an 'ideal' projection subjected to a contrast transfer function, which attenuates most frequencies, reverses the phase of others and even eliminates some of them Such instrumental aberrations make the problem of reconstruction from such data difficult We reformulate the problem so that Chahine's method becomes applicable to it We demonstrate the performance of our approach with numerical evidence using both simulated and actual electron microscopy data
22 citations
Patent•
20 Feb 2003
TL;DR: In this article, a spherical aberration signal is detected as a differential signal between focus position fluctuation signals respectively in a central section and in a peripheral section of a reproduced flux of light.
Abstract: When reproducing a multilayer optical disk using a high-numerical-aperture objective, the period of time required before the disk is reproduced is reduced by discriminating recording layers. A spherical aberration signal is detected as a differential signal between focus position fluctuation signals respectively in a central section and in a peripheral section of a reproduced flux of light. A recording layer is discriminated using a quantity of correction of spherical aberration at a zero-crossing point of a level or a spherical aberration signal associated with the differential signal. After adding the spherical aberration for the correction of the discriminated layer, residual spherical aberration is corrected by feedback control using a residual spherical aberration signal.
21 citations
TL;DR: In this article, the sub-Angstrom probe of an aberration-corrected scanning transmission electron microscope was used to enable imaging and analysis of nanostructures and interfaces with unprecedented resolution and sensitivity.
Abstract: The sub-Angstrom probe of an aberration-corrected scanning transmission electron microscope will enable imaging and analysis of nanostructures and interfaces with unprecedented resolution and sensitivity. In conjunction with first-principles theory, new insights are anticipated into the atomistic processes of growth and the subtle link between structure and functionality. We present initial results from the aberration-corrected microscopes at Oak Ridge National Laboratory that indicate the kinds of studies that will become feasible in the near future. Examples include (1) the three-dimensional location and identification of individual dopant and impurity atoms in semiconductor interfaces, and their effect on local electronic structure; (2) the accurate reconstruction of surface atomic and electronic structure on nanocrystals, and the effect on optical properties; and (3) the ability to distinguish which configurations of catalyst atoms are active, and why.
20 citations
TL;DR: This work introduces a technique for merging the information from both images, including signal to noise ratio weighting, contrast transfer function correction, and optional Weiner filtration, which produces a composite image with reduced contrastTransfer function artifacts and optimized contrast.
16 citations
TL;DR: In this article, a dynamical image calculation based on the Bloch wave description is proposed for high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images of [011]-oriented Si have been recorded using different incident beam probes.
Abstract: Atomic-resolution incoherent high-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images of [011]-oriented Si have been recorded using different incident beam probes, and analysed by means of dynamical image calculation based on the Bloch wave description. It is shown how atomic-resolution images are influenced by the semiangle of the probe and the spherical aberration and defocus of the probe-forming lens. The resolution of an incoherent HAADF STEM image can be simply perceived by the contrast transfer function of incoherent imaging which is the Fourier transform of the incident probe intensity.
12 citations
TL;DR: In this paper, it was shown that a combination of hyper-Gaussian amplitude transmittance with phase modulation can provide a five-fold reduction in sensitivity to spherical aberration without the introduction of zeros into the modulation transfer function.
Abstract: Analysis of the expression for Strehl ratio for a circularly symmetric pupil allows one to design complex filters that offer reduced sensitivity to spherical aberration. It is shown that filters that combine hyper-Gaussian amplitude transmittance with hyper-Gaussian phase modulation provide five-fold reduction in sensitivity to spherical aberration. Furthermore, this is achieved without the introduction of zeros into the modulation transfer function and deconvolution can restore the transfer function to that of a diffraction-limited imager. The performance of the derived combined amplitude and phase filter is illustrated through the variation of its axial intensity versus spherical aberration. This technique is applicable to imaging in the presence of significant amounts of spherical aberration as is encountered in, for example, microscopy.
TL;DR: A principal scheme of the transmission electron microscope, where an electrostatic electron mirror serves as its objective, is presented and a technique for eliminating the high-order derivatives of the potential axial distribution in mirror systems from the integrands is described.
Abstract: Computational formulae for the coefficients of the third-order spherical aberration and the second-order axial chromatic aberration are presented for an axially symmetric electrostatic electron mirror. A technique for eliminating the high-order derivatives of the potential axial distribution in mirror systems from the integrands is described. Conditions for elimination of spherical and axial chromatic aberrations, either separately or simultaneously, are found for a three-electrode axially symmetric mirror composed of coaxial cylinders of the same diameter. A principal scheme of the transmission electron microscope, where an electrostatic electron mirror serves as its objective, is presented.
TL;DR: In this article, a phase reconstruction technique in transmission electron microscopy (TEM), called the three-dimensional Fourier filtering method (3D-FFM), was extended to simultaneous correction of spherical aberration and twofold astigmatism.
Abstract: A phase reconstruction technique in transmission electron microscopy (TEM), called the three-dimensional Fourier filtering method (3D-FFM), was extended to simultaneous correction of spherical aberration and twofold astigmatism. The effect of the aberration correction was confirmed experimentally for a wide spatial frequency range in the corrected through-focus images of an amorphous thin film. As an application of this method, the surface structure of a gold nanoparticle was observed. The aberration-free phase image clearly reconstructed the atomic missing-row structure at the edge of the particle. Copyright © 2003 John Wiley & Sons, Ltd.
TL;DR: The 2CE microscope is more robust against spherical aberration than its 2PE counterpart, with the pi/2 configuration providing the clearest advantage.
Abstract: We study the effects of primary spherical aberration on the three-dimensional point spread function (PSF) of the two-color (two-photon) excitation (2CE) (2PE) fluorescence microscope with two confocal excitation beams that are separated by an angle θ. The two excitation wavelengths λ1 and λ2 are related to the single-photon excitation wavelength λe by: 1/λe = 1/λ1 + 1/λ2. The general case is considered where both focused beams independently suffer from spherical aberration. For θ = 0, π/2, and π, the resulting deterioration of the PSF structure is evaluated for different values of the spherical aberration coefficients via the Linfoot’s criteria of fidelity, structural content, and correlation quality. The corresponding degradation of the peak 2CE fluorescence intensity is also determined. Our findings are compared with that of the 2PE fluorescence (λ1 = λ2) under the same aberration conditions. We found that the 2CE microscope is more robust against spherical aberration than its 2PE counterpart, with the π/2 configuration providing the clearest advantage. The prospect of aberration correction in the two-beam 2CE microscope is also discussed.
TL;DR: It is shown that high phase contrast over a broad spatial-frequency range can be achieved by laterally shifting the objective aperture rather than defocusing the specimen, as is normally done.
Abstract: An operator algebra description of Fourier optics is used to examine the imaging properties of transmission electron microscopy when applied to the study of weak specimens. Effects due to the curvature of the incident beam, the finite extent of the source, beam tilt, and objective aperture shift are examined. An expression for the contrast transfer function is derived that can account for either beam tilt in conjunction with a centered aperture or a shifted aperture in conjunction with an aligned beam. It shows that high phase contrast over a broad spatial-frequency range can be achieved by laterally shifting the objective aperture rather than defocusing the specimen, as is normally done.
Patent•
26 May 2003
TL;DR: In this article, a spherical aberration correcting element was proposed to correct the irregular thickness of a disk or irregular thickness in a protective film of the optical disk. But it is not suitable for the case of high NA (numerical aperture) lenses.
Abstract: PROBLEM TO BE SOLVED: To provide a spherical aberration correcting element which can correct the spherical aberration of an objective lens caused by changes in the wavelength of light even when a high NA (numerical aperture) lens having the NA exceeding 0.6 and short wavelength light in a 400 nm band are used, which can correct the spherical aberration of the objective lens caused by irregular thickness of a disk or irregular thickness of a protective film of the optical disk, and which results in high-density recording and reproducing of information of large capacity, and to provide an optical pickup device equipped with the above element. SOLUTION: The spherical aberration correcting element corrects the spherical aberration for light L, and comprises a plano-concave lens 21 and a hologram element 22 disposed on the optical Ax, with the hologram element 22 movable along the optical axis Ax and fixable at any desired position. COPYRIGHT: (C)2005,JPO&NCIPI
TL;DR: A new approach to measuring aberrations of an optical system with coherent illumination is introduced by use of a so-called weak phase object and by digital image recording and processing based on the contrast transfer function theory for coherent systems.
Abstract: A new approach to measuring aberrations of an optical system with coherent illumination is introduced. The optical system is evaluated by use of a so-called weak phase object and by digital image recording and processing. Based on the contrast transfer function theory for coherent systems, the main aberrations of the optical system can be determined. This is a convenient approach to evaluating and measuring complex optical systems with numerous optical elements after assembly and can serve as a simple performance test of an optical instrument in the field.
TL;DR: In this paper, the intensity profile of elastically filtered phase contrast images of thin evaporated amorphous silicon and carbon foils was determined from diffractograms of inelastically filtered images using calculated inelastic transfer functions.
Abstract: We have analysed diffractograms of elastically filtered phase contrast images of thin evaporated amorphous silicon and carbon foils. For this analysis the two-particle structure factor was taken into account. It was determined from diffractograms of inelastically filtered images using calculated inelastic transfer functions. Due to the high accuracy of this new method, we were able to explain and reproduce quantitatively the intensity profile in the low spatial frequency range of the elastically filtered diffractograms. We could show that the weak-phase object approximation, which is normally used for the evaluation of such diffractograms is not adequate in this region. Instead, one has to use the weak-object approximation, which allows for a small imaginary part of the atomic scattering factor. In spite of the latter being only 3–10% of the real part for the analysed materials it is observable, because the two-particle structure factor increases steeply for low spatial frequencies (in the direct...
TL;DR: The Central Dark Line (CDL) as mentioned in this paper is a line of 1 to 1.5 nm wide along the centers of enamel enamel crystallites, which is defined by the contrast of the enamel in underfocus and overfocus.
Abstract: When the enamel crystallites are observed with the transmission electron microscope (TEM), they exhibit a line of 1 to 1.5 nm wide along their centers [1,2]. This line has been named “dark line”, although in reality its contrast is focus dependent: it appears dark in underfocus, disappears when the image goes through focus, and is white in overfocus. Experimental evidences suggested the presence of Octocalcium Phosphate(OCP) and Hydroxyapatite(HA) in Central Dark Line(CDL).
Journal Article•
TL;DR: In this paper, an aberration corrected photoemission electron microscope PEEM3 at the Advanced Light Source (ALS) has been designed and the overall layout and correction scheme are described, which can be used for the study of complex materials at high spatial and spectral resolution.
Abstract: An Aberration Corrected Photoemission Electron Microscope at the Advanced Light Source J. Feng 1 , A.A.MacDowell 1 , R.Duarte 1 , A.Doran 1 , E.Forest 2 , N.Kelez 1 , M.Marcus 1 , D.Munson 1 , H.Padmore 1 , K.Petermann 1 , S.Raoux 3 , D.Robin 1 , A.Scholl 1 , R.Schlueter 1 , P.Schmid 1 ,J. Stohr 4 , W.Wan 1 , D.H.Wei 5 and Y.Wu 6 Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA High Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0810, Japan IBM, Almaden Research Center, 650 Harry Road, San Jose, CA 95120 USA Stanford Synchrotron Radiation Laboratory, P.O.Box 20450, Stanford, CA 94309, USA SRRC, No.1 R &D Rd. VI, Hsinchu 300, Taiwan Department of Physics, Duke University, Durham, NC 27708, USA Abstract. Design of a new aberration corrected Photoemission electron microscope PEEM3 at the Advanced Light Source is outlined. PEEM3 will be installed on an elliptically polarized undulator beamline and will be used for the study of complex materials at high spatial and spectral resolution. The critical components of PEEM3 are the electron mirror aberration corrector and aberration-free magnetic beam separator. The models to calculate the optical properties of the electron mirror are discussed. The goal of the PEEM3 project is to achieve the highest possible transmission of the system at resolutions comparable to our present PEEM2 system (50 nm) and to enable significantly higher resolution, albeit at the sacrifice of intensity. We have left open the possibility to add an energy filter at a later date, if it becomes necessary driven by scientific need to improve the resolution further. INTRODUCTION X-ray excited photoemission electron microscope (PEEM) combines the power of modern synchrotron radiation absorption spectroscopy with direct full imaging capability of PEEM. A conventional PEEM system consists of round lenses whose resolution is limited by spherical and chromatic aberration, and the spherical aberration coefficient Cs and the chromatic aberration coefficient Cc always being positive [1]. As a result aberrations can only be minimized by adjusting the geometry of the electrodes but not eliminated. These aberrations limit the ultimate resolution, defined by a 50% value of the Modulation Transfer Function to be typically 50 – 100 nm, for x-ray illumination and a 20 KV extraction field [2]. Aberrations must be compensated in order to remove their deleterious effects on the imaging properties of the microscope. An electron mirror can have aberration coefficients of opposite sign but equal magnitude with respect to those of electron round lens so that in principle, the aberrations can be canceled out and the resolution can be improved ultimately to the diffraction limit. A new X-ray PEEM with an electron mirror aberration corrector at the ALS has been designed (PEEM3) and the overall layout and correction scheme are described. PEEM3 SYSTEM An elliptically polarized undulator (EPU) at the straight sector 11 of the ALS will be used to produce linearly polarized light of arbitrary azimuth and left and right handed circularly polarized radiation with continuous change of ellipticity. A variable line space (VLS) plane grating monochromator beamline will provide soft x-ray in the spectral range from 100eV to 1500eV. A VLS design was chosen as it gives the opportunity to dynamically measure the photon energy, by active monitoring of the position of the zero order beam with respect to that of the monochromatic light defined by the exit slit. This is of crucial importance in minimizing noise in x-ray dichroism
28 May 2003
TL;DR: In this paper, the Wigner distribution of a laser from intensity profiles obtained by moving slit technology was determined experimentally from a plan-convex collimating lens orientated "the wrong way." The magnitude of the aberration can be influenced by the beam diameter at the lens.
Abstract: We determine the Wigner distribution of a laser experimentally from intensity profiles obtained by moving slit technology. In order to find out whether the phase calculated from a measured Wigner distribution can be trusted, we add a known spherical aberration to a Helium Noen laser by a plan-convex collimating lens orientated "the wrong way." The magnitude of the aberration can be influenced by the beam diameter at the lens. The M2-values calculated from the Wigner distribution of the aberrated beam at different levels of aberration is in agreement with theory. The coefficient of spherical aberration obtained from the measurement agrees with the one predicted by aberration theory if the impact of the aberration on the beam profiles is large enough (M2 > 1.2). The Wigner distribution of a tapered semiconductor laser is also examined. The measured phase at the semiconductor facet is aberrated. The aberration however can not be identified to origin from exit of the beam from high index semiconductor to air through a planar interface.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Patent•
27 May 2003
TL;DR: In this paper, a method for minimizing spherical aberration in an optical read/write drive caused by variances in lens thickness and laser wavelength was proposed, where the authors provided an economic solution that pairs objective lenses with laser diodes such that the spherical aberrations caused by the objective lens is offset by the spherical distortions caused by laser wavelength.
Abstract: A method for minimizing spherical aberration in an optical read/write drive caused by variances in lens thickness and laser wavelength. The method provides an economic solution that pairs objective lenses with laser diodes such that the spherical aberration caused by the objective lens is offset by the spherical aberration caused by the laser wavelength, thereby minimizing or completely canceling the overall spherical aberration.