Showing papers on "Contrast transfer function published in 2005"
TL;DR: Application of the maximum-likelihood approach to multi-reference image refinement to a cryo-electron microscopy dataset revealed two major classes for projections of simian virus 40 large T-antigen in complex with an asymmetric DNA-probe, containing the origin of simIAN virus 40 replication.
273 citations
TL;DR: This work presents an alternative and successful method to eliminate the chromatic blur, which consists of monochromating the TEM beam and shows directly interpretable resolutions well below 1A for the first time, which is significantly better than any TEM operating at 200 KV has reached before.
112 citations
TL;DR: In this article, the effect of spherical aberration on the propagation of a single tightly focused femtosecond laser pulse inside fused silica was studied and it was shown that spherical aberrations induced by the air-sample interface extended the focal region and played an important role in the formation of the long plasma channel.
Abstract: We show the effect of a spherical aberration on the propagation of a single tightly focused femtosecond laser pulse inside fused silica. At high power, a long plasma channel across the geometrical focus can be observed under deep focusing. The total channel length decreases with the decrease of the focusing depth at fixed focal length. We found that the spherical aberration induced by the air–sample interface extends the focal region and plays an important role in the formation of the long plasma channel. In certain conditions this spherical aberration can be compensated by a spherical aberration induced by the objective used to focus the laser.
67 citations
TL;DR: A spherical aberration (Cs)-corrected electron microscope for probe- and image-forming systems using hexapole correctors is developed and evaluated experimentally.
Abstract: We have successfully developed a spherical aberration (Cs)-corrected electron microscope for probe- and image-forming systems using hexapole correctors. The performance of the microscope has been evaluated experimentally. The point resolution attained using the image-forming Cs-corrector is better than 0.12 nm. For scanning transmission electron microscopy, the Ronchigram flat area was >40 mrad in half-angle using the probe-forming Cs-corrector.
49 citations
16 May 2005
TL;DR: In this article, the authors demonstrated the correction of the resolution-limiting aberrations for the hexapole corrector, the quadrupole-octopole (QO) corrector and the tetrode mirror.
Abstract: Spherical and chromatic aberrations limit the resolution of conventional electron microscopes. Both defects are unavoidable in the case of static rotationally symmetric electromagnetic fields (Scherzer’s theorem). To compensate for these aberrations, multipole correctors or electron mirrors are required. The correction of the resolution-limiting aberrations is demonstrated for the hexapole corrector, the quadrupole-octopole corrector and the tetrode mirror. Electron mirrors require a magnetic beam separator, which must be free of second-order aberrations. The multipole correctors are highly symmetric telescopic systems compensating for the defects of the round lenses. The hexapole corrector has the simplest structure yet eliminates only third-order spherical aberration and coma, whereas the mirror and the quadrupole-octopole (QO) corrector are able to correct the chromatic aberration as well. The QO corrector eliminates chromatic aberration by means of crossed electric and magnetic quadrupoles and the third-order spherical aberration by octopoles. At present, aberration-corrected electron microscopes obtain a resolution limit of about 1 Angstroem.
44 citations
TL;DR: Two novel correctors, the ultracorrector and the superaplanator are proposed which will yield a resolution limit of about 0.5A and a large field of view of more than 4 x 10(6) image points.
39 citations
TL;DR: Expansion of the aberration function in Zernike aberrations shows that the exact aberration functions are well described by the lowest-order Zernikes spherical aberration and coma term for all but the very highest NA values.
Abstract: Optical disks are read out by focusing a beam of high numerical aperture (NA) through the substrate. Deviations of the thickness from the nominal value result in spherical aberration; tilting the substrate results in coma. Exact analytical expressions for the rms aberration per micrometer thickness mismatch (for spherical aberration) and per degree tilt (for coma) are derived. The paraxial estimates for these sensitivities proportional to NA4 (spherical aberration) and NA3 (coma) underestimate the exact values by a factor of ~2 for the value NA = 0.85, corresponding to the new Blu-ray disk format. Expansion of the aberration function in Zernike aberrations shows that the exact aberration functions are well described by the lowest-order Zernike spherical aberration (A40) and coma (A31) term for all but the very highest NA values.
31 citations
TL;DR: Sharp diffraction patterns are obtained from well-defined areas on both sides of the interface between a Ti-Si-Ge alloy and Si0.54Ge0.46 using the Cs-correction technique.
Abstract: Selected area diffraction (SAD) from localized areas that are ∼20 nm in diameter has been demonstrated for the first time using a spherical-aberration-corrected transmission electron microscope (C s -corrected TEM). We have succeeded in obtaining sharp diffraction patterns from well-defined areas on both sides of the interface between a Ti-Si-Ge alloy and Si 0 . 5 4 Ge 0 . 4 6 . The errors in the area selection by an SAD aperture are reduced to <2 nm by the C s -correction. The applications of this technique in studies of nanometer-sized materials are discussed.
23 citations
TL;DR: A new algorithm is presented that allows the accurate determination of all non-cylindrically symmetric aberrations up to fourth-order from a crystalline sample using this property of the Ronchigram.
21 citations
Patent•
10 Nov 2005TL;DR: In this article, a diffraction grating is used to focus the inner and outer sides of luminous flux on separate optical detectors before the optical flux is focused on an optical detector and defocusing signals are independently calculated to find the difference there between, thereby providing a spherical aberration signal.
Abstract: In the past there has been a problem that on a detection surface the influence of interference causes a defocusing signal to degrade, narrowing the range in which spherical aberration can be stably detected. Accordingly, a diffraction grating is used to focus the inner and outer sides of luminous flux on separate optical detectors before the optical flux is focused on an optical detector and defocusing signals are independently calculated to find the difference therebetween, thereby providing a spherical aberration signal. This makes it possible to detect spherical aberration signals more stably.
13 citations
TL;DR: The Wasserman-Wolf-Vaskas method is used to design biaspheric objective lenses that satisfy a ray condition that interpolates between the Abbe and the Herschel conditions, making the analytical theory a good approximation for any objective lens used in practice.
Abstract: Spherical aberration arising from deviations of the thickness of an optical disc substrate from a nominal value can be compensated to a great extent by illuminating the scanning objective lens with a slightly convergent or divergent beam. The optimum conjugate change and the amount and type of residual aberration are calculated analytically for an objective lens that satisfies Abbe's sine condition. The aberration sensitivity is decreased by a factor of 25 for numerical aperture values of approximately 0.85, and the residual aberrations consist mainly of the first higher-order Zernike spherical aberration term A60. The Wasserman-Wolf-Vaskas method is used to design biaspheric objective lenses that satisfy a ray condition that interpolates between the Abbe and the Herschel conditions. Requirements for coma by field use allow for only small deviations from the Abbe condition, making the analytical theory a good approximation for any objective lens used in practice.
TL;DR: A simple and practical method for minimizing non-linear image contrast in spherical aberration-corrected (C(S)-corrected) high-resolution transmission electron microscopy is presented and the dynamical diffraction effect is carefully evaluated.
Abstract: A simple and practical method for minimizing non-linear image contrast in spherical aberration-corrected (C(S)-corrected) high-resolution transmission electron microscopy is presented. The effectiveness of the method is considered from the viewpoints of theoretical formulations and image simulations including second-order imaging effects. The method is one of the advantages of C(S)-correction and applied to high-resolution images down to 0.1 nm. The dynamical diffraction effect is carefully evaluated, which shows that the phase deviation of diffracted waves from pi/2 violates the present method in thicker crystals over approximately 10 nm.
TL;DR: The results show that spherical aberration has the greatest effect in degrading an axial point-spread function, and the redistribution of signal strength along the axial direction results in broadening of the FWHM of the plane response function.
Abstract: Pump--probe fluorescence microscopy has been demonstrated to be a powerful tool for obtaining three-dimensional, time-resolved information in bioimaging applications. However, the use of this technique can be complicated by the fact that the different wavelengths used to achieve pump--probe microscopy can result in wavelength-dependent spherical aberration, thus limiting the usefulness of the technique. We address this issue by investigating the effects of refractive-index-mismatch-induced spherical aberration on pump--probe image formation. We model the effects by considering pump--probe imaging performed with an objective with a numerical aperture of 0.75 focusing through an oil-water interface. Our results show that spherical aberration has the greatest effect in degrading an axial point-spread function. In addition to signal loss, the redistribution of signal strength along the axial direction results in broadening of the FWHM of the plane response function. The inclusion of confocal detection tends to improve image resolution but at a significant loss of signal strength.
Patent•
26 Dec 2005TL;DR: In this article, a spherical aberration compensator and deflecting coils are mounted on the front step of an objective front magnetic field lens, and an appropriate deflection ratio is given feedback by evaluating deviation of aberration compensation status generated by image shift of deflection ratios 9a, 9b of the deflection coils.
Abstract: PROBLEM TO BE SOLVED: To enable to easily adjust an electro-optical system of a scanning transmission electron microscope equipped with an aberration compensator. SOLUTION: The scanning transmission electron microscope is equipped with an electron beam source 1, a convergent lens 3, a scanning coil 10, a dark field image detector 16, a bright field image detector 17, an A/D converter 21 and an information processing device 24 or the like. A spherical aberration compensator 7 and deflecting coils 9a, 9b are mounted on a front step of an objective front magnetic field lens 11, a Fourier conversion image is formed from a scanning transmission image obtained by the dark field image detector 16 or the bright field image detector 17, and an appropriate deflection ratio is given feedback by evaluating deviation of aberration compensation status generated by image shift of deflection ratios 9a, 9b of the deflection coils. COPYRIGHT: (C)2007,JPO&INPIT
TL;DR: It is demonstrated that the image deconvolution is still successful even when some reflections fall in the vicinity of zero cross of contrast transfer function.
15 Dec 2005-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, low-order aberration properties of magnetic sector deflectors are analyzed by computer simulation and their use in the low-energy electron microscope and the spectroscopic scanning electron microscope is examined.
Abstract: In this paper, low-order aberration properties of magnetic sector deflectors are analysed by computer simulation and their use in the low-energy electron microscope (LEEM) and the spectroscopic scanning electron microscope (SPSSEM) is examined. The simulation method is based upon direct ray tracing through field distributions derived by the finite element method and semi-analytical techniques. A variety of beam conditions and geometries have been investigated in order to operate the sector as a round lens while deflecting the primary beam through 90°. Predicted results from this study are also compared to previous simulation work.
01 Jan 2005
TL;DR: This paper presents a simulation of image formation with variable blur, together with a Fourier-based correction of the blur in a distance-dependent fashion.
Abstract: As electron microscopy advances toward imaging larger specimens at higher resolutions, the effect of variable defocus in image formation becomes more pronounced. This variation in defocus along the direction of electron propagation results in each layer within the specimen (perpendicular to the direction of the electron beam) being blurred by a slightly different contrast transfer function (CTF). Using distance-dependent properties of the 3D Fourier coefficients of the projection data (in the case of 2D projections collected about a single axis of rotation perpendicular to the direction of electron travel), each coefficient can be corrected using a CTF which incorporates the appropriate defocus. This paper presents a simulation of image formation with variable blur, together with a Fourier-based correction of the blur in a distance-dependent fashion.
TL;DR: Radial polarization and spherical aberration Correction together eliminated the main aberrations in uniformly pumped rod-based lasers and predicts further improvements when higher-order aberration correction is applied.
Abstract: Spherical aberration of heavily pumped Nd:YAG rods was corrected by use of spherical relay optics selected to add conjugate amounts of aberration. Wavefront measurements showed elimination of spherical aberration. Correction of spherical aberration allowed 250 W of power to be generated in a radially polarized, birefringence-free oscillator (60% more power than without correction). Scale-up of wavefront maintenance was demonstrated in a two-rod amplifier module (6.3 kW electrical pump power). Radial polarization and spherical aberration correction together eliminated the main aberrations in uniformly pumped rod-based lasers. Rotating adjacent pump chambers substantially reduced the multifold aberrations induced by nonuniformity of the azimuthal pumps. ΔM2 in the radially polarized beam was 0.3 and 1.4 with and without aberration correction, respectively, in each two-pump chamber module. Analysis predicts further improvements when higher-order aberration correction is applied.
TL;DR: The results of practical experiments are presented to verify that with illumination settings typically used in the electron microscopy of biological macromolecules, systematic variations in magnification of 0.5% per microm defocus can easily occur and highlight the need for a magnification-invariant imaging mode to eliminate or to compensate for this effect.
Abstract: It has previously been shown that - in theory - magnification variations can occur in an imaging system as a function of defocus, depending on the field curvature of the illuminating system. We here present the results of practical experiments to verify this effect in the transmission electron microscope. We find that with illumination settings typically used in the electron microscopy of biological macromolecules, systematic variations in magnification of ~ 0.5% per microm defocus can easily occur. This work highlights the need for a magnification-invariant imaging mode to eliminate or to compensate for this effect.
06 May 2005
TL;DR: In this article, resist-based measurements of the contrast transfer function for the 0.3-NA MET optic were performed for both bright-field and dark-field mask patterns, and the orientation dependence of the CTF was measured in order to evaluate the effect of nonrotationally symmetric lens aberrations.
Abstract: Although extreme ultraviolet (EUV) lithography offers the possibility of very high-resolution patterning, the projection optics must be of extremely high quality in order to meet this potential. One key metric of the projection optic quality is the contrast transfer function (CTF), which is a measure of the aerial image contrast as a function of pitch. A static microfield exposure tool based on the 0.3-NA MET optic and operating at a wavelength of 13.5 nm has been installed at the Advanced Light Source, a synchrotron facility at the Lawrence Berkeley National Laboratory. This tool provides a platform for a wide variety of research into EUV lithography. In this work we present resist-based measurements of the contrast transfer function for the MET optic. These measurements are based upon line/space patterns printed in several different EUV photoresists. The experimental results are compared with the CTF in aerial-image simulations using the aberrations measured in the projection optic using interferometry. In addition, the CTF measurements are conducted for both bright-field and dark-field mask patterns. Finally, the orientation dependence of the CTF is measured in order to evaluate the effect of non-rotationally symmetric lens aberrations. These measurements provide valuable information in interpreting the results of other experiments performed using the MET and similar systems.
TL;DR: By using an operator description, the spectrum of a symmetric two-mirror resonator in the presence of spherical aberration is derived.
Abstract: By using an operator description we derive the spectrum of a symmetric two-mirror resonator in the presence of spherical aberration.
TL;DR: In this article, a method of dynamically correcting for chromatic aberration in pulsed gun low energy electron microscope systems is presented based upon the use of a drift tube in combination with electron lenses whose focal strengths can be rapidly modulated.
Abstract: This paper presents a method of dynamically correcting for the chromatic aberration in pulsed gun low energy electron microscope systems. The proposal is based upon the use of a drift tube in combination with electron lenses whose focal strengths can be rapidly modulated. Simulation results that use direct ray tracing of electrons are presented for specific drift tube/correction lens combinations.
01 Jan 2005
TL;DR: A method to quantitatively evaluate the performances of a radiographic detection system consists on measuring the contrast, noise and modulation transfer functions, which have been evaluated for a digital radiographic system based on a single photon counting pixel detector.
Abstract: A method to quantitatively evaluate the performances of a radiographic detection system consists in measuring the contrast, noise and modulation transfer functions. These functions have been evaluated for a digital radiographic system based on a single photon counting pixel detector. The X-ray detector is a Silicon sensor with one side segmented in a matrix of 256 by 256 square contacts with a pitch of 55 mum. The active area is about 2 cm2. The sensor is connected to the Medipix2 read-out chip by bump-bonding. As X-ray source we have used a tube for general radiography. To reproduce the conditions of a radiographic examination, a 4 cm thick lucite block positioned above the detector has been used to simulate a tissue sample. To study the Contrast Transfer Function we have measured the contrast of an 1 mm thick lead slab with respect to the background. To evaluate the scattering contribution from the lucite, the measurements have been performed with and without a collimator placed at the beam exit. To assess the efficiency and noise transfer properties, we have measured the Detective Quantum Efficiency (DQE) of the detector as a function of the tube voltage. The Modulation Transfer Function has been measured applying the slit method for different conditions of tube voltage and energy threshold
TL;DR: A time-of-flight concept that dynamically corrects for chromatic aberration effects in scanning electron microscopes (SEMs) is presented and is predicted to reduce the microscope's chromatic Aberration by an order of magnitude.
28 Feb 2005
TL;DR: In this paper, the development of spherical aberration correction in high-resolution electron microscopy (Cs-corrected HREM) is reviewed by focusing on TEM instruments and recent applications of the method to nano materials and interfaces are described through explaining its characteristic and the future prospects.
Abstract: Recent development of spherical aberration correction in high-resolution electron microscopy (Cs-corrected HREM) is reviewed by focusing on TEM instruments. Basis of the the previous HRTEM and new scientific elements for Cs-corrected one are summarized, and recent applications of the method to nano materials and interfaces are described through explaining its characteristic and the future prospects.
TL;DR: Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31-August 4, 2005 as discussed by the authors, presented by as discussed by the authors.
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005
TL;DR: In this article, the use of a deformable lens for dynamic compensation is investigated for spherical aberration during deep multiphoton imaging, where the deformability of the lens is used to compensate for the distortion caused by the incident beam.
Abstract: Spherical aberration degrades optical resolution during deep multiphoton imaging. Wavefront compensation within the objective or of the incident beam restores imaging quality. The use of a deformable lens for dynamic compensation is investigated.
28 Feb 2005
TL;DR: In this paper, the authors describe the performance of aberration-corrected 300kV-STEM, which is the state-of-the-art in the field of scanning transmission electron microscopy.
Abstract: The scanning transmission electron microscope (STEM) with an annular dark-field (ADF) detector provides atomic-resolution incoherent images, whose resolution is dominated, to a good approximation, by the size of convergent electron beams. Improving a spherical aberration of microscope objective lenses has been successful in converging the beam into sub-angstrom scale, promising a remarkably higher resolution for STEM. Here we describe the performance of aberration-corrected 300kV-STEM-the world-best STEM available today. The results clearly demonstrate that a sub-angstrom resolution has been indeed achieved for not only simple structures but also structurally complex systems (quasicrystals).
TL;DR: In this article, a new JEOL 2200FS 200kV field emission STEM/TEM with a hexapole Cs-corrector (CEOS GmbH) for the probe-forming lens and an in-column Omega-type energy filter has been installed at the Advanced Microscopy Laboratory at Oak Ridge National Laboratory (ORNL).
Abstract: A new JEOL 2200FS 200kV field emission STEM/TEM with a hexapole Cs-corrector (CEOS GmbH) for the probe-forming lens and an in-column Omega-type energy filter has recently been installed at the Advanced Microscopy Laboratory (AML) at Oak Ridge National Laboratory (ORNL). The microscope is intended primarily for high-resolution imaging of catalyst systems that are of interest to the U.S. Department of Energy for increased energy efficiency and energy security. In this paper we report on the high-resolution imaging characteristics of our microscope for both conventional high-resolution TEM and STEM imaging. The TEM Scherzer point resolution for our objective lens polepiece (C{sub s} = 0.5 mm) is 0.19 nm, but more significantly the information limit has been demonstrated to be better than 0.09 nm, as shown in Fig. 1. This figure shows a Young's fringe experiment carried out on an amorphous Ge specimen which was estimated to be 10 nm thick. The thickness of the sample damps out the Thon rings to some extent, but the information transfer to sub 0.1 nm resolution is clearly evident. The electron wave at the specimen exit surface with resolution out to the information limit of a microscope may be reconstructed via computational processing of amore » focal or tilt series of images. The extension of the TEM information limit to the sub-0.1 nm range in our microscope can be attributed primarily to the improved objective lens and high tension power supply stabilities provided by JEOL Co. to satisfy our instrument specifications. A contrast transfer function (CTF) calculated using the parameters for our microscope is shown in Fig. 2, computed at the alpha-null defocus condition used for FSR processing. The CTF closely matches the demonstrated Young's fringe pattern, indicating the ability of the microscope to achieve ultimate performance in TEM mode. Characterization of catalyst systems will be a primary focus of the aberration-corrected JEOL 2200FS and therefore high-resolution STEM high-angle annular dark field (HA-ADF) imaging will be applied to understand the atomic-scale arrangement of supported catalyst clusters. By correcting for the primary resolution-limiting aberration of a round electromagnetic lens - the third-order spherical aberration - smaller electron probes with greater probe current can be formed, with resulting improvements in both the point-to-point resolution for HA-ADF imaging and the signal-to-noise ratio. Both benefits are important for the study of the atomic arrangement of catalyst clusters. Figure 3 shows initial HA-ADF imaging images of very small Pt clusters on a 1.1 nm thick amorphous carbon film. Individual Pt atoms are clearly visible with a high signal-to-noise, as is shown in Fig. 4.« less