On the validity of the weak-phase and other approximations in the analysis of electron microscope images

Misell, D L

doi:10.1088/0022-3727/9/13/006

Cited by 25 publications

(19 citation statements)

References 10 publications

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“…The two opposite SPP filtered images will be identical and the magnitude of the two-dimensional gradient squared can be seen directly from a single SPP filtered image. The same holds for a weak phase/weak amplitude object [51], where both the phase and the amplitude are assumed to be proportional to the thickness of the sample. As a consequence their gradients are parallel and, again, no difference in the opposite SPP filtered images will be observed.…”

Section: Average and Difference Of = ±1 Spp Filtered Imagesmentioning

confidence: 92%

Spiral phase plate contrast in optical and electron microscopy

et al. 2016

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The use of phase plates in the back focal plane of a microscope is a well established technique in optical microscopy to increase the contrast of weakly interacting samples and is gaining interest in electron microscopy as well. In this paper we study the spiral phase plate (SPP), also called helical, vortex, or two-dimensional Hilbert phase plate, that adds an angularly dependent phase of the form e i φ k to the exit wave in Fourier space. In the limit of large collection angles, we analytically calculate that the average of a pair of = ±1 SPP filtered images is directly proportional to the gradient squared of the exit wave, explaining the edge contrast previously seen in optical SPP work. We discuss the difference between a clockwise-anticlockwise pair of SPP filtered images and derive conditions under which the modulus of the wave's gradient can be seen directly from one SPP filtered image. This work provides the theoretical background to interpret images obtained with a SPP, thereby opening new perspectives for new experiments to study for example magnetic materials in an electron microscope.

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Section: Average and Difference Of = ±1 Spp Filtered Imagesmentioning

confidence: 92%

Spiral phase plate contrast in optical and electron microscopy

et al. 2016

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“…A weak phase (linear) approximation at each slice may also be assumed [31][32][33][34]. Scattering through a single slice is calculated by integration with the function,…”

Section: Accounting For Propagation Through the Specimen-the M-plamentioning

confidence: 99%

Structure retrieval with fast electrons using segmented detectors

et al. 2016

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We introduce an algorithm for the reconstruction of the complex transmission function of a specimen using segmented detectors in scanning transmission electron microscopy geometry. The phase of the transmission function can be related to magnetic and electric fields within the specimen and is sensitive to lighter elements. The technique is demonstrated for simulated data and also using experimental datasets taken from a MoS 2 monolayer and a SrTiO 3 crystal. We present an extension to the algorithm to account for uncertainties in the illuminating probe. The algorithm can be implemented using fast Fourier transforms, and this provides the possibility of reconstructing specimen transmission functions in real time.

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“…Nonetheless, for a thick object, the focal defocus is displaced by the expression of

|Δ f| = t

(Misell, ). The sign of the focal defocus relies on the adjusted parameters and the measured object.…”

Section: Analysis Of the Factors Affecting The Measured Size Of The Omentioning

confidence: 99%

Dependence of the measured size of the objects on the parameters of the transmitted light source in video measurement microscopy

Liu

2013

Journal of Microscopy

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SummaryParameter adjustment of the transmitted light source yields a good-quality image for video measurement microscopy. However, a disadvantage is that the measured size of the objects changes simultaneously while the parameters of the transmitted light source are adjusted, which directly affects the measurement accuracy adversely. Furthermore, the variation of the objects' measured size leads to the magnification variation as well. In order to analyse how the measured size of the objects varies with the parameters, we apply a photometric method and an operator algebra method to derive a unified mathematical model that correlates the parameters of the transmitted light source with the measured size of the objects. Theoretical results show that factors including the illumination intensity, the diameter of the aperture stop and the field stop and the object thickness are important to the measured size of the objects. The simulation results have been verified thoroughly using a wide variety of internal and external diameter measurement experiments. The proposed method has proved to be suitable to determine how these parameters affect measured size of the objects.

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On the validity of the weak-phase and other approximations in the analysis of electron microscope images

Cited by 25 publications

References 10 publications

Spiral phase plate contrast in optical and electron microscopy

Spiral phase plate contrast in optical and electron microscopy

Structure retrieval with fast electrons using segmented detectors

Dependence of the measured size of the objects on the parameters of the transmitted light source in video measurement microscopy

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