Title 



Linear versus nonlinear structural information limit in highresolution transmission electron microscopy
 
Author 



 
Abstract 



A widely used performance criterion in highresolution transmission electron microscopy (HRTEM) is the information limit. It corresponds to the inverse of the maximum spatial object frequency that is linearly transmitted with sufficient intensity from the exit plane of the object to the image plane and is limited due to partial temporal coherence. In practice, the information limit is often measured from a diffractogram or from Young's fringes assuming a weak phase object scattering beyond the inverse of the information limit. However, for an aberration corrected electron microscope, with an information limit in the subangstrom range, weak phase objects are no longer applicable since they do not scatter sufficiently in this range. Therefore, one relies on more strongly scattering objects such as crystals of heavy atoms observed along a low index zone axis. In that case, dynamical scattering becomes important such that the nonlinear and linear interaction may be equally important. The nonlinear interaction may then set the experimental cutoff frequency observed in a diffractogram. The goal of this paper is to quantify both the linear and the nonlinear information transfer in terms of closed form analytical expressions. Whereas the cutoff frequency set by the linear transfer can be directly related with the attainable resolution, information from the nonlinear transfer can only be extracted using quantitative, modelbased methods. In contrast to the historic definition of the information limit depending on microscope parameters only, the expressions derived in this paper explicitly incorporate their dependence on the structure parameters as well. In order to emphasize this dependence and to distinguish from the usual information limit, the expressions derived for the inverse cutoff frequencies will be referred to as the linear and nonlinear structural information limit. The present findings confirm the wellknown result that partial temporal coherence has different effects on the transfer of the linear and nonlinear terms, such that the nonlinear imaging contributions are damped less than the linear imaging contributions at high spatial frequencies. This will be important when coherent aberrations such as spherical aberration and defocus are reduced.   
Language 



English
 
Source (journal) 



Ultramicroscopy.  Amsterdam  
Publication 



Amsterdam : 2010
 
ISSN 



03043991
 
Volume/pages 



110:11(2010), p. 14041410
 
ISI 



000282562100008
 
Full text (Publishers DOI) 


  
