Two-dimensional Object Functions and Three-dimensional Illumination Functions: their Validity, Interaction and Utility

Electron Microscopy and Analysis Group Conference 2013

Jones, L.^1 ; Nellist, P.D.^1

Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom^1

关键词: 2D objects;    Focus values;    HAADF-STEM;    High-angle annular dark fields;    Object functions;    Single images;    Two Dimensional (2 D);    Two-dimensional objects;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/522/1/012015/pdf
DOI  :  10.1088/1742-6596/522/1/012015

来源: IOP

【 摘 要 】

In high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) the data is generally interpreted as the convolution of the sample's sharply-peaked object function with the intensity of the real-valued point-spread function (PSF) of the illumination. As a single image is itself necessarily two-dimensional (2D) it is typically assumed that the object function and PSF can also be accurately described as 2D; this is the so-called 2D-object imaging assumption. Here the validity of these two-assumptions is evaluated using experimental HAADF STEM focal-series. It is found that the contrast contained in each image of the focal-series is accurately described by the convolution of a focus-invariant 2D object with a 2D optical-transfer function (OTF) which describes the illumination at the focus value used for imaging.