Showing papers on "Contrast transfer function published in 1998"

Subangstrom resolution by underfocused incoherent transmission electron microscopy

Abstract: It is quantitatively explained why incoherent transmission electron microscope imaging is extremely robust to the effects of chromatic aberration, which usually limits the resolution in the conventional coherent mode of imaging. Combining this robustness with using underfocus to counter the effects of spherical aberration, we demonstrate subangstrom lattice resolution and information transfer to 0.078thinspthinspnm. {copyright} {ital 1998} {ital The American Physical Society }

Effects of refractive-index mismatch on three-dimensional optical data-storage density in a two-photon bleaching polymer.

Abstract: Reported is an investigation into the effect of spherical aberration caused by the mismatch of the refractive indices between the recording material and its immersion medium on the three-dimensional optical data-storage density in a two-photon bleaching polymer. It is found both theoretically and experimentally that spherical aberration can be compensated for by a change in the tube length at which a microscope objective is operated in recording and reading processes. After compensation for the spherical aberration it is possible to achieve a three-dimensional recording density of 3.5 Tbits/cm3 for a commercial objective with a numerical aperture of 1.4.

Cryo X-Ray Microscopy Experiments with the X-Ray Microscope at BESSY

Abstract: The transmission X-ray microscope (TXM) at the electron storage ring BESSY was used to image frozen-hydrated objects at cryogenic temperatures and atmospheric pressure. After shock freezing in liquid ethane different initially living biological objects such as cells, chromosomes and algae were investigated at 2.4 nm wavelength in amplitude contrast mode. The high X-ray absorption of cellular structures and the 10-fold lower absorption of frozen water yield natural element contrast. The X-ray images show details inside the biological objects down to 30 nm size, which is about one order of magnitude better than conventional visible light microscopy.

Differential Phase Contrast X-Ray Microscopy

Abstract: The advantages of using a configured detector to obtain differential phase contrast image in a scanning transmission X-ray microscope are described. A prototype system using a CCD detector has been installed on the microscopy beamline at BESSY, and the first images have been acquired.

Analyzing CTF of print by MTF of paper

Abstract: Image quality of print is dependent on the paper characteristics. However, there are relatively few studies on the imaging characteristics of paper. In a previous report, we introduced a new method for measuring the modulation transfer function (MTF) of paper. In this report, a contrast transfer function (CTF) of print is introduced. We find that the CTF of print, CTF print (ω), can be expressed by a simple function of the MTF of paper, MTF paper (ω): CTF print (ω) = [1 + MTF paper (ω)]/2. The CTF of print predicted by the function was approximately same as the measured CTF of print.

Deriving the Coltman correction for transforming the bar transfer function to the optical transfer function (or the contrast transfer function to the modulation transfer function)

Abstract: The Coltman series for obtaining the optical transfer function from measurements of the bar transfer function is mathematically derived. The bar transfer function rather than the contrast transfer function is defined so that the relation remains valid when an image exhibits phase reversal.

Measurement of Spherical Aberration Utilizing an Alternating Phase Shift Mask

Abstract: A spherical aberration function is measured utilizing an alternating phase shift mask (PSM). First, it is theoretically considered that with a highly coherent illumination, the focus of the alternating phase shift lines and spaces (L/S) pattern is equivalent to that of rays in a small annular area of the reference sphere when the aberration function is axially symmetric in the sphere. Then, the focus variation with the pattern pitch is obtained by a printing experiment that employs an alternating PSM. After a primitive mathematical operation, the aberration function is obtained from the experimentally observed focus variation. The aberration function is examined by investigating various anomalous phenomena observed in the printing with the various resolution enhancement techniques (RETs). The comparison between the experimentally observed phenomena and the predictions based on the calculated images with the measured aberration functions shows fair agreement. Consequently, the validity of this measurement method is confirmed.

Preliminary experiments for development of real-time defocus-image modulation processing electron microscope

Abstract: Preliminary experimental results for realizing real-time defocus-image modulation processing in a high-resolution transmission electron microscope are reported in terms of equivalence between objective lens current modulation and accelerating voltage modulation, precise measurement of the voltage centre axis and rapid control of accelerating voltage. The equivalence between the two modulations is clearly demonstrated by showing the similarities of the two respective Thon diagrams. The accelerating voltage change of 1 V leads to 8.75 run focus change in the present electron microscope. A precise method to measure the misalignment of the voltage centre axis is proposed on the basis of three dimensional Fourier analysis using through-focus images. A floating type accelerating voltage generator system was newly designed in order to make the rapid modulation as precisely as possible, which is essentially important for developing a real-time defocus-image modulation processing elearon microscope.

Amplitude Contrast — A Way to Obtain Directly Interpretable High‐Resolution Images in a Spherical Aberration Corrected Transmission Electron Microscope

Abstract: The demonstration of the correction of the spherical aberration in a high-resolution transmission electron microscope makes it feasible to use new contrast mechanisms. To assess the possibilities of amplitude contrast imaging we have performed image simulations for silicon in (110) orientation. The results show that amplitude contrast images are directly interpretable for thicknesses up to almost one extinction distance.

Influence of aberration on performance during use of resolution enhancement technology

Abstract: We have investigated the influence of a spherical aberration on the printing characteristics with modified illumination. At first, we have developed a simple method for measuring the aberration function with an alternating phase shift mask (PSM), and have measured that in the projection optics of a commercially available KrF stepper. Then the anomalous phenomena observed in the printing with modified illumination are examined with the simulated aerial images with the measured spherical aberration. As a result, we found good coincidence between the simulated images and the anomalies. In conclusion, the origin of the anomalies is ascribed to the spherical aberration in the projection optics.

Correction of aperture aberrations of hybrid lens

Abstract: The possibilities of aberration correction in the case of a single lens are limited. It is well known that, if classic glasses are used, it is impossible to compensate spherical aberration. It can be, however, minimized by proper choice of the ratio between the first and second surface radii of curvature (referred here as (zetz) ). It is possible also, in cost of uncorrected spherical aberration, to compensate III order coma. Additional possibilities of aberration correction occur, however, if a thin diffractive structure is deposited on one of the lens surface. Such lens is usually referred as a hybrid (diffractive-refractive) lens. The diffractive structure typically corresponds to the holographic lens generated by the interference of two spherical waves. The ratio of these waves radii of curvature is treated as a parameter (called here (beta) ) describing fully aberration properties of this structure. A focusing power of the diffractive part typically is only a small fraction ((eta) ) of total focusing power of a hybrid lens, so the diffractive part acts mainly as aberration corrector. Aberration properties of hybrid lens are determined by two parameters: (zetz) and (beta) so it is possible to achieve simultaneous correction of aperture aberrations: spherical aberration and coma. In the paper formulas describing the III-order aberration coefficients were used for calculating the values of parameters (zetz) and (beta) assuring such correction for several values of parameter (eta) and different locations of object plane. The calculations were performed with help of the MATHCAD programme. Basing on the results a number of hybrid lenses (collimating and imaging) were designed. Their imaging quality was then evaluated by numerical calculation of aberration spots. Estimated values of such image characteristics as the aberration spot moment of inertia or third order moment of the spots distribution enable to compare the imaging quality.

Lenses for Electron Microscopy and Microanalysis: Shadowgraph Method of Determining Focal Properties and Aberration Coefficients

Abstract: The performance characteristics of electron microscopes and probe-forming instruments depend ultimately on the focal properties and aberrations of electron lenses. A practical method of experimentally determining the properties of electron lenses is described. The method utilizes shadows cast by two meshes inserted separately in front of the lens and behind the lens to study the properties of the image of a point source. The image properties are then used to calculate the lens properties. The paraxial values of the focal length and focal distance as well as their spherical and chromatic aberrations are determined. Experimental data and the analysis are presented in the form of a tutorial that has been tested in the classroom. Discussions of the relationship between image properties and lens properties, in particular, focal point aberrations and focal length aberrations, and the various ways aberration coefficients can be defined, are included to clarify concepts in optics that are important for microscopists.

Evaluation of scanning electron microscope resolution

Abstract: The evaluation of Scanning Electron Microscopes (SEM) resolution through Two Dimensions Fast Fourier Transform (2D FFT) image analysis is becoming a standard. We propose an improvement of these methods with a patented technique. This new image processing is designed to extract the transfer function of the SEM from the picture and then to realize the analysis of this function. A first algorithm extracts an 'ideal' image of the sample from the 'raw' image obtained on the equipment. Then a second algorithm extracts the SEM transfer function through a comparison between the two images ('ideal' and 'raw'). Finally a third algorithm modelizes the transfer function as a two dimensions Normal function and draws out the result. The representation of the transfer function of the SEM with a Normal function allows to define the shape of an Equivalent of the Electron Beam (EEB). This EEB represents the primary electron beam altered by the interactions with the sample and the losses in the acquisition loop. It is important to outline these alterations as they limit the sharpness of the images obtained from the tool. This way of doing lessens the influence of sample parameters on the final results and thus represent more precisely the SEM Transfer Function.

Effects of spherical aberration on the laser beam of a bar code scanner

Abstract: The modulation transfer function of bar code scanning is a useful tool for evaluating the performance of the scanning laser beam. Understanding the behavior of the scanning laser system near the end of its depth of focus is of particular interest because it may lead to the development of techniques that could effective extend the depth of focus. In the article the MTF at focus and the two extremes of the depth of focus are presented. The presence of spherical aberration in the scanning laser beam generally reduces the depth of focus. The effects of the spherical aberration to the MTF is presented and discussed.

A contribution to the evaluation of scanning electron microscope resolution

Abstract: The evaluation of Scanning Electron Microscopes (SEM) resolution through Two Dimensions Fast Fourier Transform (2D FFT) image analysis is becoming a standard 1,2,3 We propose an improvement of these methods with a patented technique 4 . This new image processing is designed to extract the transfer function of the SEM from the picture and then to realize the analysis of this function. A first algorithm extracts an ideal image of the sample from the raw image obtained on the equipment. Then a second algorithm extracts the SEM transfer function through a comparison between the two images (ideal and raw). Finally a third algorithm modelizes the transfer function as a two dimensions Normal function and draws out the result. The representation of the transfer function of the SEM with a Normal function allows to define the shape of an Equivalent of the Electron Beam (EEB). This EEB represents the primary electron beam altered by the interactions with the sample and the losses in the acquisition loop. It is important to outline these alterations as they limit the sharpness of the images obtained from the tool. This way of doing lessens the influence of sample parameters on the final results and thus represent more precisely the SEM Transfer Function.