High-resolution environmental transmission electron microscopy: modeling and experimental verification

Quantitative modeling for high-resolution (phase contrast) gas cell environmental transmission electron microscopy (ETEM) imaging is presented in this paper. Concepts of pre-specimen scattering object (PreSO) and post-specimen scattering object (PoSO) are introduced to explain electron scattering caused by gas and window membranes associated with the gas environmental cell (E-cell). PreSO preserves the structural phase information and the effect can be evaluated by averaging the contrast transfer functions (CTFs) over random electron scattering. PoSO is treated as information loss and the unscattered electrons play a major role in determining the ETEM image quality. The theoretical model is compared and matched well with our systematic gas ETEM experimental results under various gas pressures. Extension of our approach to the aberration-corrected ETEM is discussed.