Contrast transfer function

About: Contrast transfer function is a research topic. Over the lifetime, 934 publications have been published within this topic receiving 26533 citations.

Electrostatic mirror objective with eliminated spherical and axial chromatic aberrations

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.

Flexible STEM with Simultaneous Phase and Depth Contrast.

Abstract: Recent advances in scanning transmission electron microscopy (STEM) have rekindled interest in multi-channel detectors and prompted the exploration of unconventional scan patterns. These emerging needs are not yet addressed by standard commercial hardware. The system described here incorporates a flexible scan generator that enables exploration of low-acceleration scan patterns, while data are recorded by a scalable eight-channel array of nonmultiplexed analog-to-digital converters. System integration with SerialEM provides a flexible route for automated acquisition protocols including tomography. Using a solid-state quadrant detector with additional annular rings, we explore the generation and detection of various STEM contrast modes. Through-focus bright-field scans relate to phase contrast, similarly to wide-field TEM. More strikingly, comparing images acquired from different off-axis detector elements reveals lateral shifts dependent on defocus. Compensation of this parallax effect leads to decomposition of integrated differential phase contrast (iDPC) to separable contributions relating to projected electric potential and to defocus. Thus, a single scan provides both a computationally refocused phase contrast image and a second image in which the signed intensity, bright or dark, represents the degree of defocus.

Two-Surface Refracting Systems with Zero Third-Order Spherical Aberration

Abstract: An analysis is made of refracting systems consisting of two spherical surfaces. Solutions are found for those systems having zero third-order spherical aberration. These are in the form of four one-parameter families of functions. Expressions for third-order coma and astigmatism are derived. Parameter domains for useful solutions are indicated. A method for applying these results to optical design is described.

High-order and multipole aberrations by aberration integral and direct ray-tracing methods

Abstract: SUMMARY This paper describes methods for computing high-order aberrations and multipole aberrations in electron optical systems. Two approaches are discussed – the first involves obtaining aberration integrals for the high-order aberration coefficients, in terms of paraxial rays and axial field functions, while the second method uses direct ray-tracing through fields computed accurately by finite element or finite difference methods. The methods are illustrated by several examples, including a wide-angle focusing and deflection system with fifth-order aberrations, a combined magnetic and electrostatic lens, a ‘supertip’ ion source, an electron mirror with negative spherical and chromatic aberration, and a chromatically corrected quadrupole lens.