scholarly journals Phase detection limits in off-axis electron holography from pixelated detectors: gain variations, geometric distortion and failure of reference-hologram correction

Microscopy ◽  
2020 ◽  
Author(s):  
Martin Hÿtch ◽  
Christophe Gatel
Keyword(s):  
Direct Detection ◽  
Geometric Distortion ◽  
Electron Holography ◽  
Phase Detection ◽  
Phase Errors ◽  
Interference Fringes ◽  
Phase Images ◽  
Pixelated Detectors ◽  
Systematic Noise ◽  
Theoretical Developments

Abstract We investigate the effect that recording off-axis electron holograms on pixelated detectors, such as charge-coupled devices (CCD) and direct-detection devices (DDD), can have on measured amplitudes and phases. Theory will be developed for the case of perfectly uniform interference fringes illuminating an imperfect detector with gain variations and pixel displacements. We will show that both these types of defect produce a systematic noise in the phase images that depends on the position of the holographic fringes with respect to the detector. Subtracting a reference hologram from the object hologram will therefore not remove the phase noise if the initial phases of the two holograms do not coincide exactly. Another finding is that pi-shifted holograms are much less affected by gain variations but show no improvement concerning geometric distortions. The resulting phase errors will be estimated and simulations presented that confirm the theoretical developments.

Quantitative Electron Holography - From The Basis of Dynamical Interaction to Holographic Materials Analysis

2001 ◽  
Vol 7 (S2) ◽  
pp. 284-285
Author(s):  
Karin Brand ◽  
Chengshan Guo ◽  
Michael Lehmann ◽  
Hannes Lichte
Keyword(s):  
Detection Limit ◽  
Phase 1 ◽  
Ccd Camera ◽  
Lateral Resolution ◽  
Electron Holography ◽  
Phase Detection ◽  
Dynamical Interaction ◽  
Resolution Electron ◽  
Phase Images

Quantitative analysis of a structure means to determine which atoms are where. The where is restricted by the lateral resolution, and the which is related to the sensitivity against differences of the atomic species. Electron holography is on the move to tackle both questions.• where - Lateral Resolution Electron holography has surmounted conventional electron microscopy in that it has reached atomic resolution both in the amplitude and phase images: with our CM30FEG/UT Special Tuebingen electron microscope, the information limit of 0.09nm and the pixel number of the 2048_ - CCD camera allow to take holograms with image details smaller than 0.095nm; the quality of correction of the aberrations allows an interpretable resolution approaching 0. lnm both in amplitude and phase [1].• which - Phase Detection Limit (PDL) The phase detection limit describes the minimum phase difference detectable well above a given noise level.

Development And Applications Of Highly Precise Phase Measurement Technique Using Phase-Shifting Electron Holography

1999 ◽  
Vol 5 (S2) ◽  
pp. 948-949
Author(s):  
K. Yamamoto ◽  
I. Kawajiri ◽  
T. Tanji ◽  
M. Hibino ◽  
T. Hirayama
Keyword(s):  
Magnetic Fields ◽  
Measurement Technique ◽  
Phase Measurement ◽  
Incident Electron ◽  
Phase Shifting ◽  
Phase Image ◽  
Electron Holography ◽  
Magnetic Recording Media ◽  
Interference Fringes ◽  
Phase Images

Today's information-oriented society requires high-density, high-quality magnetic recording media. For the development of such new recording materials, the quantitative observation of magnetic fine structures by electron holography is eagerly awaited. However, the magnetic fields around particles smaller than 50 nm have not been observed because they are too weak to be observed in the usual way. Here, we report a highly precise phase measurement technique, improved phase-shifting electron holography. Using this method, we observed weak electric and magnetic fields precisely. The precision of the reconstructed phase image was as good as 2π/300 rad.In phase-shifting electron holography, the phase images are reconstructed from a series of electron holograms whose interference fringes are shifted relative to one after another. The shifting of interference fringes is achieved by tilting the incident electron beam, which corresponds to shifting the initial phase of the incident electron waves in a specimen plane.

Quanitative aspects of electron diffraction using electron holography

1995 ◽  
Vol 53 ◽  
pp. 616-617
Author(s):  
E. Völkl ◽  
L.F. Allard ◽  
B. Frost ◽  
T.A. Nolan
Keyword(s):  
Electron Beam ◽  
Electron Diffraction ◽  
Software Package ◽  
Spatial Coherence ◽  
Electron Holography ◽  
Image Intensity ◽  
Interference Fringes ◽  
Complex Image ◽  
The Difference ◽  
Recorded Image

Off-axis electron holography has the well known ability to preserve the complex image wave within the final, recorded image. This final image described by I(x,y) = I(r) contains contributions from the image intensity of the elastically scattered electrons IeI (r) = |A(r) exp (iΦ(r)) |, the contributions from the inelastically scattered electrons IineI (r), and the complex image wave Ψ = A(r) exp(iΦ(r)) as:(1) I(r) = IeI (r) + Iinel (r) + μ A(r) cos(2π Δk r + Φ(r))where the constant μ describes the contrast of the interference fringes which are related to the spatial coherence of the electron beam, and Φk is the resulting vector of the difference of the wavefront vectors of the two overlaping beams. Using a software package like HoloWorks, the complex image wave Ψ can be extracted.

Characterization of JEOL 3000f TEM Equipped for Electron Holography

2000 ◽  
Vol 6 (S2) ◽  
pp. 228-229
Author(s):  
M. A. Schofield ◽  
Y. Zhu
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Design Of Experiment ◽  
Electron Holography ◽  
Fringe Spacing ◽  
Interference Fringes ◽  
Transmission Electron ◽  
Careful Design

Quantitative off-axis electron holography in a transmission electron microscope (TEM) requires careful design of experiment specific to instrumental characteristics. For example, the spatial resolution desired for a particular holography experiment imposes requirements on the spacing of the interference fringes to be recorded. This fringe spacing depends upon the geometric configuration of the TEM/electron biprism system, which is experimentally fixed, but also upon the voltage applied to the biprism wire of the holography unit, which is experimentally adjustable. Hence, knowledge of the holographic interference fringe spacing as a function of applied voltage to the electron biprism is essential to the design of a specific holography experiment. Furthermore, additional instrumental parameters, such as the coherence and virtual size of the electron source, for example, affect the quality of recorded holograms through their effect on the contrast of the holographic fringes.

Phase Detection for Nanometer Scale Metal Film’s Thickness Based on SPR Effect

2011 ◽  
Vol 320 ◽  
pp. 377-381 ◽  
Author(s):  
Jin Dong Xin ◽  
Qing Gang Liu ◽  
Chao Liu ◽  
Ting Ting Li ◽  
Shi Yi Liu
Keyword(s):  
Film Thickness ◽  
Resonance Effect ◽  
Polarized Light ◽  
Nanometer Scale ◽  
Phase Detection ◽  
Surface Plasmon Resonance Effect ◽  
Interference Fringes ◽  
Reflected Light ◽  
Phase Data ◽  
Spr Effect

It is found that the phase position of p-component of reflected light changes with the metal film thickness, while the phase position of s-component almost doesn’t change in the Surface Plasmon Resonance effect. S-polarized light is taken as reference and interferometry is adopted to turn the change of the phase position into the change of interference fringes position in the paper, and the film thickness can be derived from it. The simulation results indicated that, through making use of piecewise quadratic fitting on the phase data, the inaccuracy with the range of film thickness is between 30 and 80 nanometers is not more than 0.33 nm.

Electron Holography and Digital Imaging for Analysis of Nanostructured Materials

1998 ◽  
Vol 4 (S2) ◽  
pp. 750-751
Author(s):  
L. F. Allard ◽  
E. Voelkl ◽  
A. K. Datye ◽  
A. H. Carim
Keyword(s):  
Nanostructured Materials ◽  
Digital Camera ◽  
Digital Processing ◽  
Quantitative Information ◽  
Electron Holography ◽  
Additional Information ◽  
Camera Systems ◽  
Phase Images ◽  
Ultra Fine Particle ◽  
Rapid Processing

Many nanostructured materials are formed from powder precursors having ultra-fine particle sizes. Techniques of electron microscopy have proven invaluable for characterizing the structure of the precursor materials in order to better understand the fundamental processes that govern consolidation of the materials into the final nanophase structures. In recent years, the rapidly developing technique of electron holography has increasingly been applied for characterizing particle morphologies. The advent of the modern field emission microscope, which offers beam coherency sufficient to produce high contrast interference fringes for optimum hologram formation, and especially the availability of digital camera systems for hologram acquisition and rapid processing have both combined to bring electron holography to the forefront of techniques for characterization of nanostructured materials.Electron holograms typically yield phase images that can give quantitative information on crystal morphologies, but much additional information can result from digital processing of holograms.

Least Squares Phase Unwrapping Algorithm Based on Topographic Factors

2011 ◽  
Vol 105-107 ◽  
pp. 1876-1879
Author(s):  
Wei Ke Liu ◽  
Gou Lin Liu ◽  
Xiao Qing Zhang
Keyword(s):  
Least Squares ◽  
Weighted Least Squares ◽  
Phase Unwrapping ◽  
Local Phase ◽  
Complex Signals ◽  
Topographic Factors ◽  
Interference Fringes ◽  
Phase Images ◽  
New Phase ◽  
Accuracy And Stability

The phase of complex signals is wrapped since it can only be measured modulo-2; unwrapping searches for the 2-combinations that minimize the discontinuity of the unwrapped phase, as only the unwrapped phase can be analyzed and interpreted by further processing. Weighted least squares phase unwrapping algorithm could avoid errors transmission in the whole phase images, but it could not avoid defect and overlay of interference fringes caused by topographic factors. Therefore, a new phase unwrapping and weights choosing method based on local phase frequency estimate of topographic factors was presented. Experiments show it is an efficient phase unwrapping method which well overcome the defect of under-estimate slopes by least squares algorithm, and has higher accuracy and stability than other methods.

Eliminating effects of biprism drift in electron holography

2001 ◽  
Vol 7 (S2) ◽  
pp. 990-991
Author(s):  
F. Kahl ◽  
E. Voelkl
Keyword(s):  
Digital Camera ◽  
Computational Time ◽  
Mixed System ◽  
Electron Holography ◽  
Phase Reconstruction ◽  
Processing Times ◽  
Desktop Computers ◽  
Readout Time ◽  
Phase Images ◽  
Being Moved

Reconstruction of phase images from off-axis electron holograms recorded in a field-emission TEM was for many years a tedious and time-consuming process. The advent of digital imaging systems and ever-faster desktop computers has recently resulted in processing times of a few seconds for a useful phase reconstruction. However, a goal of the “holographer” has been to view the phase images essentially in “live-time”, that is, at least at a few frames per second. This enables effective observation of phase change, through “a window to the phase world,” while the sample is being searched. Chen et al. used a mixture of digital and analog techniques to obtain phase images at nearly TV scan rates. Because optical lens systems provide the fast Fourier processing required for phase reconstructions, their geometry allows phase images to be displayed while the sample is being moved and/or timedependent specimen changes are occurring. Voelkl et al. have described a purely digital system for phase reconstructions from electron holograms that provides several phase images per second, and has several advantages over the mixed system. The refresh rate is presently limited more by the readout time of the slow-scan digital camera than by the computational time of the computer.

Digital imaging for high-resolution electron holography

1992 ◽  
Vol 50 (2) ◽  
pp. 944-945
Author(s):  
L. F. Allard ◽  
T. A. Nolan ◽  
D. C. Joy ◽  
T. Hashimoto
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Digital Imaging ◽  
Electron Holography ◽  
Digital Recording ◽  
Original Image ◽  
Ccd Array ◽  
Resolution Electron ◽  
Phase Images ◽  
High Resolution Images

It is a goal of electron microscopy to eliminate film as the recording medium for electron microscope images in favor of direct digital recording. At present, there are commercially available digital TV systems (e.g. ref. [2]) based on CCD slow scan technology that provide 1M pixel images (i.e. 1k × 1k arrays). Such systems have proven useful for recording standard high resolution images and are sufficient to replace film for most standard electron microscopy. However, the newly developing technique of electron holography requires an advanced digital imaging capability, because the process of reconstruction of amplitude and phase images from a hologram necessarily gives final images that are only one-quarter the size of the original image. For a minimum desired 512 × 512 pixel reconstructed image, the original image should be 2k × 2k, requiring a CCD array with 4M pixels.Electron holograms which are recorded for reconstruction of aberration-corrected images with improved resolution (approaching 0.1 nm) require hologram fringes spaced on the order of 0.3 nm.

Off-axis electron holography of a two-phase polymer

1994 ◽  
Vol 52 ◽  
pp. 444-445
Author(s):  
M. Libera ◽  
M. Gajdardziska-Josifovska ◽  
M. M. Disko
Keyword(s):  
Ccd Camera ◽  
Electron Holography ◽  
State University ◽  
Arizona State University ◽  
Contrast Imaging ◽  
Two Phase ◽  
Phase Images ◽  
Digital Holograms ◽  
Conventional Microscopy ◽  
Styrene Butadiene

Electron holography enables retrieval of phase from an image wave. This phase information is lost in conventional microscopy. As part of an ongoing program to study polymer microstructure via phase-contrast imaging, we report here our first experiences applying off-axis holography to polymers.This study utilized a 48k mw styrene/butadiene diblock copolymer mixed with 30% 25k mw styrene homopolymer. The specimen was cast from toluene, annealed, cryomicrotomed, and osmium stained. Offaxis electron holography experiments were performed at Arizona State University using the Philips 400STFEG microscope operated at 100kV. Digital holograms with =0.25nm fringes, 520kx magnification and Is exposures were recorded using a Gatan slow-scan CCD camera. Numerical hologram reconstruction was performed employing Gatan's Digital Micrograph.Figure 1 shows a diffraction contrast image of the specimen showing alternating styrene-rich (light) and butadiene-rich (dark) lamellae. Absolute phases were obtained from holograms in which vacuum was used as reference (region A in Fig. 1). Typical reconstructed amplitude and phase images from region A are shown in Fig. 2.

Sign in / Sign up

Export Citation Format

Share Document