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.

STEM Image Post-processing for Instability and Aberration Correction for Transfer Function Extension

Abstract: Scanning transmission electron microscopy (STEM) images can be limited by either aberrations or, because of the technique's serial acquisition, by the effects of environmental instabilities. MatLab image-processing code was written which performs a two stage process to restore degraded high-resolution high-angle annular dark-field (HAADF) STEM images. Firstly, individual images were analysed to identify and correct for high-frequency scan noise; image resolution and signal-noise ratio (SNR) are used as performance metrics and were improved by up to 11.8% and 49% respectively. Secondly, a focal series was used to identify variations in information transfer as a function of defocus (aberrations) whereafter a single image was reconstructed yielding an increase in resolution and SNR of 9.88% and 205% respectively.

2.7 Å cryo-EM structure of vitrified M. musculus H-chain apoferritin from 200 keV “screening microscope”

Abstract: Here we present the structure of mouse H-chain apoferritin at 2.7 A (FSC=0.143) solved by single particle cryogenic electron microscopy (cryo-EM) using a 200 kV device. Data were collected using a compact, two-lens illumination system with a constant power objective lens, without the use of energy filters or aberration correctors. Coulomb potential maps reveal clear densities for main chain carbonyl oxygens, residue side chains (including alternative conformations) and bound solvent molecules. We argue that the advantages offered by (a) the high electronic and mechanical stability of the microscope, (b) the high emission stability and low beam energy spread of the high brightness Field Emission Gun (x-FEG), (c) direct electron detection technology and (d) particle-based Contrast Transfer Function (CTF) refinement have contributed to achieving resolution close to the Rayleigh limit. Overall, we show that basic electron optical settings for automated cryo-electron microscopy imaging, widely thought of as a "screening cryo-microscope", can be used to determine structures approaching atomic resolution.

Aberration analysis of wide-angle deflectors and lenses by direct ray-tracing and comparison with conventional aberration theories

Abstract: This paper describes numerical techniques for computing aberrations in focusing and deflection systems for charged particle beams, and electron sources and mirrors, by direct ray- tracing of electron or ion trajectories. For such computations to be meaningful and reliable, high accuracy in the computed potential distribution and field components is essential. Suitable methods for potential and field computation in 2D and 3D are outlined, including finite difference and second-order finite element methods, Biot-Savart law and charge density method. A method for direct ray-tracing through these fields is then summarized, using a Runge-Kutta formula. To compare the results of direct ray-tracing with conventional aberration theories, techniques for computing third and fifth-order aberrations using axial field functions and aberration integrals are described. The techniques are illustrated by several examples, including: analysis of spherical and chromatic aberration of an electrostatic lens by direct ray-tracing; analysis of a magnetic probe-forming SEM lens with wide-angle magnetic deflection, with either post-lens or pre-lens deflection; analysis of quadrupole lenses by direct ray-tracing and multipole aberration theory; aberration analysis of an electron mirror by direct ray-tracing; and analysis of the aberration of electron and ion sources.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.