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Author Gao, C.; Hofer, C.; Pennycook, T.J. url  doi
openurl 
  Title On central focusing for contrast optimization in direct electron ptychography of thick samples Type A1 Journal article
  Year (down) 2024 Publication Ultramicroscopy Abbreviated Journal  
  Volume 256 Issue Pages 113879-7  
  Keywords A1 Journal article; Electron microscopy for materials research (EMAT)  
  Abstract Ptychography provides high dose efficiency images that can reveal light elements next to heavy atoms. However, despite ptychography having an otherwise single signed contrast transfer function, contrast reversals can occur when the projected potential becomes strong for both direct and iterative inversion ptychography methods. It has recently been shown that these reversals can often be counteracted in direct ptychography methods by adapting the focus. Here we provide an explanation of why the best contrast is often found with the probe focused to the middle of the sample. The phase contribution due to defocus at each sample slice above and below the central plane in this configuration effectively cancels out, which can prevent contrast reversals when dynamical scattering effects are not overly strong. In addition we show that the convergence angle can be an important consideration for removal of contrast reversals in relatively thin samples.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language Wos 001112166400001 Publication Date 2023-11-03  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0304-3991 ISBN Additional Links UA library record; WoS full record; WoS citing articles  
  Impact Factor Times cited Open Access  
  Notes Approved no  
  Call Number UA @ admin @ c:irua:202029 Serial 9066  
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